Journal of Materials in Civil Engineering

In recent years, fiber reinforced concrete has been increasingly used not only for industrial floors but for many other loadbearing structures as well. The different types of synthetic fibers have distinct effects on concrete: micro fibers to reduce plastic shrinkage cracking of concrete, and macro fibers to give higher fracture toughness. This paper investigates whether when using mixed fibers (a blend of micro and macro fibers) the advantages of the two types remain separate or whether a new effect arises. Three-point bending tests are made to examine the effect of the different fiber types on the ductility of concrete. The existing theoretical smeared models’ predictions of expected experimental results are not accurate enough because of the high deviation of the data. In this study a new mechanical model is applied which takes into consideration the real distribution of the fibers in the concrete matrix. Comparing the experimental results with the theoretical model proves that micro fibers help the embedding of macro fibers by reducing micro cracks, and consequently the use of mixed fibers results in an increased fracture toughness.

Permeability testing of concrete is useful to predict moisture transport within the pore network. Conventional permeability tests based on steady-state linear flow-through take too long to get a reliable result and therefore are not frequently used. Development of poromechanical techniques has reduced the permeability testing time significantly. Systematic comparisons of the permeability of cement pastes and mortars obtained by a poromechanical method and a flow-through method were done in this study. The hollow dynamic pressurization (HDP) test was the poromechanical technique used, and the radial flow-through (RFT) test was the flow-through test utilized. Cement paste showed virtually identical results between the HDP and RFT permeability results. However, mortar and concrete, showed a significant difference between the HDP and RFT permeability results. It is hypothesized that the two methods measure effectively different transport properties in the same material. The RFT captures the effect of microstructure on the flux of fluid across or through the cross section of a material, whereas the HDP captures the effect of microstructure on flux of fluid into the smallest pore network of the material. Thus, the RFT is primarily influenced by the largest pores that provide a short-circuit through the cross section (e.g., the pores in the interfacial transition zone), whereas the HDP is primarily influenced by the smaller pores that must be pressurized in order to induce poromechanical coupling. In materials like cement paste that have a large number of rather uniform, well-distributed pores, transport rates through and into the pore network are essentially equivalent because no short-circuits through the cross section exist.

Recently, self-compacting lightweight aggregate concrete (SCLC) has been increasingly used in civil engineering. The bond behavior between plain bars and SCLC is an indispensable factor in the design of members that require high shear capacity. In such members, the anchorage of plain bars might be weakened by lateral tensions, which is experimentally studied in the current paper. A total of 134 pullout specimens considering different compressive strengths of SCLC, bar diameters, and combinations of lateral tension were tested to investigate the local bond stress-slip characteristics between plain round bars and SCLC. The test results show that all specimens failed by pulling out of the bar with no splitting crack. As the average lateral tension increased, the normalized ultimate and residual bond strength ratios of SCLC decreased, whereas the slips at peak bond stress first increased and then remained constant, which were generally parallel to those of normal-weight concrete. An empirical model was finally proposed to describe the local bond stress-slip relationship between plain bars and SCLC under lateral tension.

Soft soils are problematic because of their low strength, low bearing capacity, low permeability, and high compressibility. The addition of lime has a pronounced effect on such soils. In this paper, studies were performed to understand the effect of lime on five different types of soft soil. Similar experiments were conducted on the same soils by using an enzyme as the stabilizer, and also by introducing the enzyme with lime during stabilization. Comparative studies between the sets of experiments using test parameter California bearing ratios (CBRs) revealed that the addition of bio-enzyme with lime accelerated the strength improvement that occurred during lime stabilization and resulted in a stronger soil matrix. Pavement designers can employ the new proposed system of stabilization to possibly reduce pavement subgrade layer thickness.

Biochar is relatively well understood as a soil enhancement. Recently, it has been explored as a construction material. While works had been conducted on deploying biochar for road construction, there is an emerging trend of using biochar as concrete admixture. In comparison, using biochar this way will reduce more greenhouse gas emissions than if carbon is captured and sequestered through mineralization and deployment in construction. The use of biochar-containing construction materials to capture and then lock atmospheric carbon dioxide in buildings and structures can potentially reduce greenhouse gas emissions by an additional 25%. In this review, attention was focused on evaluating biochar’s capability for carbon adsorption, which depends on factors such as pyrolysis conditions (specifically, pyrolysis temperature, heating rate, and pressure) and activation methods (and without surface modification). Gaps in the current literature were identified and important areas for future research proposed.

The effects of nanoalumina (NA) and graphene oxide (GO) on the early-age hydration and mechanical properties of portland cement pastes were investigated in this study. The hydration heat release rate and cumulative heat of cement pastes incorporating different dosages of NA and GO were evaluated using an isothermal calorimeter measurement method. Early-age electrical resistivity development was investigated by a noncontact electrical resistivity technique. The results show that both NA and GO could efficiently accelerate cement hydration. As a physical filler, NA significantly accelerates the hydration of tricalcium aluminate (${\mathrm{C}}_3\mathrm{A}$) in cement. On the other hand, GO is able to obviously reduce the dormant period of cement hydration and shift the heat flow peaks to the left by accelerating the hydration of tricalcium silicate (${\mathrm{C}}_3\mathrm{S}$) in cement. Compared to plain cement pastes, both the compressive and flexural strengths of cement pastes incorporating NA or GO are significantly increased. However, when NA and GO contents exceed the optimal amounts, improvements in flexural strength tend to decline, which is probably due to particle agglomeration. NA-cement paste exhibited slightly higher electrical resistivity than plain cement paste during hydration acceleration and deceleration stages. But GO-cement paste clearly showed lower electrical resistivity, which might be attributed to iron diffusion caused by GO with large surface areas.

Phosphate is usually considered as an excellent retarder in cement-based materials. It is often thought that the mechanism behind this excellent retarding effect is attributed to the precipitation of calcium-based phosphate or the formation of a complex on the surface of the cement particles. However, the generally accepted theory cannot convincingly explain the difference in retarding effect between polyphosphates and monophosphates. In this study, the adsorbing behavior, both adsorption amount and the composition and structure of the adsorption layer of three kinds of phosphates (i.e., trisodium phosphate, sodium tripolyphosphate, and sodium hexametaphosphate), were investigated to illustrate the mechanism behind the different retarding effects. Specifically, the retarding effect of phosphate was evaluated with the analysis of hydration products, hydration heat, and setting time. Inductive coupled plasma (ICP) emission spectrometer was performed to assess the adsorption amount of phosphate, whereas the thickness of the phosphate layer was obtained with X-ray photoelectron spectroscopy (XPS). The adsorption models were then proposed accordingly to illustrate the mechanism behind the different retarding effects. The results show that the retarding effect of phosphates is primarily decided by the thickness of the phosphate layer rather than the adsorption amount. The formation of an adsorption layer of monophosphate is because of the precipitation of calcium-based phosphate in the immediate vicinity of cement particles, whereas that for polyphosphates is attributable to the formation of a Ca-phosphate complex. The better retarding effect of polyphosphate than monophosphate is attributed to a thicker adsorption layer.

This study is an investigation of the rheological properties of bituminous binders and the mechanical properties of hot mix asphalts (HMAs) when a combination of styrene-butadiene-styrene (SBS) and American Gilsonite (AG) is added to bitumen. In this work, HMAs were prepared with two binders containing a single additive (5% SBS and 18% AG) and three binders containing two different additives ($4\%\mathrm{SBS}+6\%\mathrm{AG}$, $3\%\mathrm{SBS}+10\%\mathrm{AG}$, and $2\%\mathrm{SBS}+13\%\mathrm{AG}$), which have the same Superpave performance levels. Tests carried out on the mixes demonstrated that the most effective additives relative to Marshall stability, retained Marshall stability, and indirect tensile strength values were 18% AG and $3\%\mathrm{SBS}+10\%\mathrm{AG}$; the most effective additives relative to stiffness and fatigue life were 18% AG, $2\%\mathrm{SBS}+13\%\mathrm{AG}$, and $3\%\mathrm{SBS}+10\%\mathrm{AG}$; and the most effective additives against moisture-induced damage were 5% SBS, $2\%\mathrm{SBS}+13\%\mathrm{AG}$, and $3\%\mathrm{SBS}+10\%\mathrm{AG}$. A consideration of all of the study’s findings indicate that the utilization of a combination of SBS and AG is provides more benefits than utilizations of SBS or AG alone.

Ammonium hydrolyzed polyacrylonitrile (${\mathrm{NH}}_4\text{-}\mathrm{HPAN}$) is a drilling fluid additive usually used in drilling fluids. However, ${\mathrm{NH}}_4\text{-}\mathrm{HPAN}$ and cement slurry have poor chemical compatibility. When they come into contact with each other, cement slurry can be contaminated, which damages the cementing quality and causes downhole emergency. This paper studies the effects of ${\mathrm{NH}}_4\text{-}\mathrm{HPAN}$ on the properties of cement slurry, such as thickening time, rheological properties, and compressive strength. This paper combines atomic absorption spectrophotometer, zeta probe potentiostat, and environmental scanning electron microscope (ESEM) to explore the ${\mathrm{NH}}_4\text{-}\mathrm{HPAN}$ contamination mechanism in cement slurry. The experimental results show that ${\mathrm{NH}}_4\text{-}\mathrm{HPAN}$ decreases the zeta potential of cement slurry and reduces the electrical property of cement particle surfaces, which causes particles agglomeration. Moreover, ${\mathrm{NH}}_4\text{-}\mathrm{HPAN}$ reacts with cement slurry to generate a netlike cross-linked structure that changes the microstructure of cement slurry and agglomerates cement particles to increase the movement resistance of cement particles. Finally, the rheological properties and thickening time of cement slurry are deteriorated, and the netlike cross-linked structure is adsorbed on the cement particles surfaces, which reduces the rate of hydration reaction and decreases the compressive strength of cement stone. They seriously endanger the safety operation and cementing quality.

In this paper, the results of a study on the influence of sodium hydroxide, calcium hydroxide, aluminum hydroxide, sodium sulfate, calcium sulfate, and calcium sulfate dihydrate as activators on the setting time and mechanical properties of slag–cement mixtures are presented. The results obtained show that the sulfate is more effective in activating the activity of the slag cement than the other chemical activators. Specimens prepared from calcium sulfate, blast-furnace slag, and ordinary portland cement exhibit better mechanical performance compared to admixtures prepared from other mix ratios. The sulfate ions from sulfates would react with ${\mathrm{Ca}}^{2+}$ from slag cement and form the reaction product ettringite. However, the addition of sodium hydroxide seems ineffective in activating the slag cement. Successive addition of sodium hydroxide deteriorates the mechanical strength of the slag cement. The reaction kinetics are also studied by examining the hydration products of slag-blended cement paste through the technologies of X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance spectroscopy (NMR). Those experimental results provide detailed insights into the understanding of how the activators influence the hydration products of slag-blended cement and structural models of calcium silicate hydrates (C-S-H).

Curling of concrete pavements and slabs because of moisture gradients has been documented for many years. Over the past 20 years, significant research has demonstrated the benefits of adding saturated lightweight aggregate fines to concrete to enhance hydration, reduce permeability, and increase strength. This study extends the current research by examining the effect fine lightweight aggregate has on concrete curling behavior. A total of 15 different mix designs were systematically tested following a design of experiments model. The three independent variables were water-to-cementitious ratio, volumetric replacement of fine aggregate with saturated fine lightweight aggregate, and moist curing duration. The addition of saturated fine lightweight aggregates reduced the magnitude of moisture curling in a concrete specimen when compared with an identical mixture without saturated fine lightweight aggregates. In addition, curing duration had an inverse effect on the moisture curling, i.e., the longer curing duration, the higher amount of concrete curling, although a higher concrete strength was achieved. An increase in the water:cement ratio also led to higher curling values within the studied range. Overall, the results indicate that the addition of saturated fine lightweight aggregates has a positive impact on reducing the curling magnitude and drying shrinkage of paving concrete mixtures.

The modification effects of ${\mathrm{nanoSiO}}_2$ on properties of the interface region between cement grain and C─ S─ H gel in cement-based composites are investigated by means of the nanoscratch technique. The nanoscratch test involves driving a Berkovich diamond tip across the interface boundary perpendicularly and recording the lateral force while the normal load applied to the indenter is kept constant. The coefficient of friction (COF), defined as the ratio of lateral force to normal load, indicates an interfacial width close to 200 nm, which is irrelevant to the addition of ${\mathrm{nanoSiO}}_2$. However, the COF value within the interface region decreases significantly if ${\mathrm{nanoSiO}}_2$ is incorporated. The decreased friction between the indenter and the interface is mainly attributed to the reduction of adhesion friction, because the addition of ${\mathrm{nanoSiO}}_2$ has a densification effect on the interface. This study further confirms that ${\mathrm{nanoSiO}}_2$ addition is beneficial for the formation of a denser layer surrounding the unhydrated cement particles in early hydration ages.

Manufacturers reported a loss in fissility in blocks of roofing slates because of air exposure prior to splitting. Samples of three varieties of commercial Spanish roofing slate were subjected to freezing, water saturation, and exposure to air at different temperatures, simulating the conditions that blocks of slate may be subjected to during quarrying. Split samples, thin polished sections, and dust samples were obtained from these blocks and studied via scanning electron microscopy (SEM), thermomechanical analysis (TMA), X-ray diffraction (XRD), and thermogravimetry/differential scanning calorimetry (TG/DSC) under a heating ramp and/or constant temperature conditions. Backscattered electron images show that split surfaces avoided porphyritic quartz elements and propagated primarily in the rock matrix, along the contact zones between phyllosilicate crystallites, but not in their interlayer spaces. The Si-OH groups located on the phyllosilicate surfaces were involved in these processes. Their condensation, which facilitated dewatering from the rock at room temperature, simultaneously led to a shrinkage of the slate perpendicular to schistosity ($S_1$) and a loss in fissility.

In this research, water treatment sludge (WTS) calcium carbide residue (CCR) geopolymers were evaluated as a sustainable masonry nonbearing unit. The WTS was a by-product from a water treatment plant, whereas CCR was a by-product from an acetylene gas factory in Thailand. Sodium hydroxide solution (NaOH) and sodium silicate solution (${\mathrm{Na}}_2{\mathrm{SiO}}_3$) were used for the geopolymerization process. The unconfined compressive strength (UCS), water absorption, and durability of WTS-CCR geopolymer were studied in this research. The test results indicate that the optimal liquid alkaline activator (L)/CCR ratios provided the maximum unit weight decrease with CCR contents for all of the ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ ratios evaluated. The optimal L/CCR ratios were found to be 16, 8, 5.33, 4, 3.2, and 2.67 for CCR contents of 5, 10, 15, 20, 25, and 30%, respectively. The ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ ratio of 70:30 was found to give the highest maximum unit weight and UCS among all of the WTS/CCR ratios tested. Three zones of UCS development with CCR content were evident: the active, inert, and deterioration zones. In the active zone, the UCS increased significantly as the CCR content increased, and the maximum UCS was attained at 10% CCR. In the inert zone, the UCS development was gradual. When the CCR content was more than 20% in the deterioration zone, a subsequent strength decrease was observed. The wet–dry (w–d) cycle strength, ${\mathrm{UCS}}_{(w-d)}$, depends primarily on the initial soaked strength, ${\mathrm{UCS}}_0$. A ${\mathrm{UCS}}_{(w-d)}$ predictive equation was proposed for the assessment of initial strength to attain the required w–d strengths. Based on the UCS and water absorption requirements, an optimum ingredient consisting of 10% CCR and 70:30 ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ at room temperature curing can be recommended for nonbearing masonry units.

A concern with the disposal, use, and general management of coal fly ash (CFA) is the potential for leaching of trace elements. This study provides data and analysis for an innovative method to mitigate leachate generation through engineered water repellency. Engineering water repellency involves modifying the surface of CFA particles with organo-silane (OS). Results indicate that the extent of water repellency can be quantified more accurately with contact angle (CA) measurements determined by increasing a drop size until the three-phase contact line motion becomes approximately constant. For each sample a minimum drop size at which the three-phase contact line motion reaches a stable motion has been identified. This approach allows for CAs to be measured with an accuracy of $\pm 5$ degrees, as opposed to $\pm 20$ degrees or greater with conventional approaches. Five types of CFA were tested using three different OS chemicals at different mix ratios (weight based). This article reports on the pattern that each of the modified CFA exhibits as a function of treatment type and level as well as the unique relationship between steady state motion of the three-phase contact line and drop volume. The extent of water repellency varied considerably as a function of OS treated dosage, which ranged from 1:500 to 1:140 (OS:CFA, by weight). The CAs of all five unmodified CFAs were below 90 degrees whereas the modified CFA resulted in average values of 143°, 135°, 150°, 158°, and 140° for CFA-1, CFA-2, CFA-3, CFA-5, and CFA-6, respectively. This change in CA from hydrophilic ($CA<90°$) to hydrophobic ($CA>90°$) and superhydrophobic ($CA>150°$) clearly indicates the property of highly water repellent material (no infiltration), as a result leachate control is possible.

Engineered cementitious composite (ECC) is an advanced composite material with strain-hardening and multiple-cracking behaviors. The substitution of conventional concrete with ECC can significantly improve the deformation and energy dissipation ability of reinforced concrete (RC) columns. This paper reports on the mechanical behavior of ECC/RC composite columns. An ECC/RC composite column can be obtained by substituting concrete with ECC in the column bottom. The material composition, transverse reinforcement ratio, and axial load level were considered as experimental parameters. Experimental results from reversed cyclic load tests on nine scaled columns are presented. The results indicate that ECC and ECC/RC composite columns have better ductility, better energy dissipation capacity, and slower stiffness degradation than RC columns. The increase in axial load on the ECC/RC composite column negatively affects the ductility but can considerably improve the load capacity and maintain the structural integrity. The results also indicate that the number of stirrups can be properly reduced in ECC and ECC/RC composite columns because of the high-shear strength of ECC.

The Hamburg wheel tracking (HWT) test has been found to be a promising test to evaluate the field rutting performance of asphalt pavements and has been implemented as a material screening test during the mix design process by several state departments of transportation. However, the rutting performance of an asphalt pavement depends not only on the material properties, but also on many other factors such as pavement structure and traffic. To date, there are few performance models that have integrated the Hamburg rutting parameters for pavement rutting prediction. In addition, mechanistic-empirical–based prediction models have been found to have some difficulties in reasonably predicting field rut depth, especially when field variables and confounding factors have to be considered. Therefore, the objective of this paper is to evaluate the relationship between the HWT test results and the field rut depth, then develop a predictive model for field rut depth based on the HWT test results. Field projects consisting of 51 hot mix asphalt (HMA) and warm mix asphalt (WMA) pavements were included in the analysis. These projects were located in different climatic zones with varying traffic levels, pavement structures, and material properties. Through direct correlation, it was found that the field rut depth in general decreased with the increase of the rutting resistance index (RRI). However, HWT test results alone do not have a strong relationship with the field rut depth, and many other factors, such as climate and pavement structure, have to be considered. Further, statistical-based methods in conjunction with engineering interpretation were applied to identify critical influencing factors and develop a prediction model for field rut depth. The developed rutting predictive model indicated that (a) mixture property (rutting resistance index, a parameter developed based on the HWT test), pavement age (month), average annual daily truck traffic (AADTT), and pavement structure (total HMA thickness and overlay thickness) are critical influencing factors for field rut depth; (b) RRI, along with pavement age and traffic data, has the most significant effect on rut depth among the identified five key predictor variables; (c) no significant differences are observed between prediction results of HMA and WMA mixtures, and thus the prediction model can be applied for both; and (d) using the developed predictive model, the effect of the HWT RRI can be considered comprehensively with other factors including climate, traffic, and pavement structure to determine the suitability of a designed asphalt mixture for pavement construction.

Self-healing products such as microcapsules filled with an asphalt rejuvenator present an emerging technology that would allow asphalt mixtures to resist cracking damage caused by vehicular and environmental loading. The objective of this study was to characterize laboratory-prepared microcapsules in order to evaluate thermal stability as well as the self-healing effectiveness of the microcapsules in asphalt mixtures. A three-point bending test was used to evaluate the healing efficiency and stiffness recovery in asphalt mixtures under two healing conditions: room temperature and high temperature. An optical microscope was used to quantify the healing progress of cracked specimens as a function of time. Based on microscopic characterization, it was observed that the produced microcapsules had adequate thermal stability because the microcapsules showed no sign of breakage when exposed to high temperature. An analysis of microscopic images revealed a reduction in the size of the cracks for both healing conditions for a period from 0 to 6 days. A lower healing efficiency was observed for the mixture with microcapsules compared with the control because not all microcapsules have broken during the test and are designed to break over time and not all at once. Results also showed that there was a recovery in the stiffness of the mixtures because the healed stiffness was greater than the damaged stiffness but less than the undamaged stiffness. A greater stiffness recovery was observed at high temperature, which could be explained by binder aging during the 5-day conditioning period.

In this paper, two interface treatments were applied to improve the interface condition, and the shear failure test and repeated shear test were conducted to evaluate the bonding conditions. It is found that the interface shear strength and horizontal shear reaction modulus are largest for the roughening-treated specimen, meaning the improvement on the interface bonding condition of roughening treatment is the best. For all three kinds of specimens, both the horizontal shear reaction modulus and the interface bonding percentage decrease with the loading cycles, meaning the interface bonding condition becomes worse due the repeated loading effects. Compared with the untreated and emulsified asphalt-treated specimen, the roughening-treated specimen has the largest shear reaction modulus, the largest bonding percentage, and the smallest modulus reduction ratio, meaning the antidecay property of roughening treatment is the best. However, even with the best treatment of roughening, the interface is not good enough to ensure the full bonding condition.

Polyurethane materials can be used for nondestructive maintenance of infrastructure, such as slab lifting through injection in a road or railway. Understanding the mechanical behavior and microstructure characteristics of this material is critical to ensure safe service of the infrastructure. This study investigates stress-strain behavior, microstructure characteristics, fatigue behavior, and failure mode of rigid polyurethane grout materials subject to both static and cyclic compressive loads. The densities of the investigated polyurethanes range from 80 to $500\mathrm{kg}/{\mathrm{m}}^3$, which are normally used in grouting. The yielding stress corresponding to 5% strain is measured and predicted based on the microstructure characteristics. The fatigue process of polyurethane can be divided into elastic, incubation, and failure stages. The failure threshold is identified for polyurethanes with different densities and at different stress levels. The failure mode is described based on the microstructure observation.

The interface bonding condition between asphalt concrete layers is unquestioned as one of the significant factors influencing pavement performance. In order to research the interface characteristics of asphalt pavement under traffic loading, this paper presents a procedure to estimate shear strength between the asphalt layers via a direct shear test where both normal and shear stresses are applied to the interface. To do this, first, laboratory testing was conducted under varying conditions of temperature, vertical pressure, and tack coat application rate to analyze the influence of each parameter on interface shear strength. Second, the results from the tests were statistically analyzed for the significance level of each factor on interface shear strength. Finally, prediction models describing interface shear strength under the combined effect of shear and normal stresses at three different temperature levels are proposed and their feasibility is validated. All things considered, findings of this study hope to lead to a greater understanding of the monotonic behavior of interface performance in asphalt pavements.

Compressed stabilized earth blocks (CSEBs) prepared with an enzyme along with a combination of cement and lime have been shown to have a nearly 50% increase in wet compressive strength after two years of aging compared with blocks prepared without enzymes. The influence of enzymes in improving the property of the blocks is confirmed by the changes induced at the microlevel as evidenced by scanning electron microscope (SEM) views. Furthermore, CSEBs prepared with enzymes are also durable and could be beneficial when used as a unit in building construction. The increased strength of the blocks with the use of microdoses of enzymes would lead to a substantial reduction in the quantity of routinely used conventional stabilizers to manufacture blocks of comparable strength and other properties.

The present paper evaluates the technical and environmental feasibility of using iron ore tailings (IOTs) as fine aggregate in the production of interlocking concrete blocks. Initially, environmental, chemical, and physical characterizations of the tailings were carried out. Pavers with IOTs replacing natural aggregate in proportions from 10 to 80% were manufactured and subjected to physical analyses (expansion, porosity, and water absorption), environmental analyses (leaching and dissolution), as well as mechanical tests (compressive strength and surface abrasion). Test results of the IOT pavers were compared to conventional ones and to standard limits. The IOT pavers showed physical and mechanical properties significantly similar, or superior, to the conventional ones, and all within the requirements for regular traffic. Therefore, IOT are technical and environmentally feasible to be used in the production of precast concrete blocks. This reuse also contributes to the reduction of the social and environmental impacts associated to tailings dams.

On the basis of comprehensive analysis of experimental phenomenon and micro/mesomechanism, it is found that concrete failure is controlled by normal stress on failure plane and distortion strain energy (DSE) of the concrete block. These factors are combined to develop a DSE-based Mohr-Coulomb (M-C) criterion for concrete failure, and the DSE-based M-C criterion is extended by considering the effect of normal stress on friction coefficient. The DSE-based M-C criterion can predict the failure of normal-strength concrete (NSC), high-strength concrete (HSC), and air-entrained concrete (AEC) under different loading conditions with high accuracy. The DSE-based M-C criterion is also applied to construct the failure locus of lightweight aggregate concrete (LAC). On the basis of the failure locus and experimental results of LAC, a cutoff is observed from the experimental results of LAC. Although the DSE-based M-C criterion cannot manifest the cutoff, good agreements are observed between the failure locus and experimental results when the experimental values are greater than the cutoff. Through average error (AE) analyses, it can be found that the DSE based M-C criterion has a minimum AE when compared with the Willam-Warnke criterion, He-Song criterion, and Songs criterion.

The use of recycled materials, such as recycled asphalt shingles (RAS), has received considerable attention for its potential to decrease production costs and enhance the sustainability of paving operations. The objective of this study was to characterize the laboratory performance of asphalt mixtures containing RAS with and without re-refined engine oil bottoms (REOB) used as a recycling agent (RA). The RAS type used in this study was postconsumer waste shingles (PCWS). Five 12.5-mm asphalt mixtures were designed to meet Superior Performing Asphalt Pavements (Superpave) design criteria, with two containing no REOB and three containing various amounts. A suite of laboratory tests was used to ascertain the mechanistic behavior of the mixtures against major distresses. Laboratory testing evaluated the high-, intermediate-, and low-temperature properties of laboratory-produced mixtures using the Hamburg loaded-wheel tester (LWT), the semicircular bend (SCB) test, and the thermal stress restrained specimen test (TSRST). For the mixtures evaluated, results indicated that the use of REOB increased the recycled binder ratio, which adversely affected intermediate-temperature fracture resistance. Although the inclusion of 5% RAS and 5% REOB did not adversely affect low-temperature performance; TSRST results showed that as the percentage of REOB increased, low-temperature fracture performance decreased. On the other hand, rutting performance was comparable for the control mixture and the mixtures containing RAS and REOB.

Clay balls can be used as an alternative to natural pebbles in pebble matrix filtration, a method for drinking water treatment. These clay balls are subjected to stresses due to self-weight and overburden in water-saturated conditions. Although there are empirical relationships to evaluate tensile yield strength ($T_s$) of clay balls using Poisson’s ratio ($\mu$), diameter ($d$) of clay balls, and failure polar force ($F_s$), so far for such calculations the value of Poisson’s ratio has been taken from studies based on clay bricks. However, during ball preparation, if clay is mixed with other raw materials from industry wastes, such as saw dust or alum sludge in order to enhance the pollutant removal properties of the filter media, then the Poisson’s ratio of composite balls would be quite different from that of clay bricks. This paper describes a novel method for estimating Poisson’s ratio of composite clay balls by measuring vertical deformation using LVDTs in a uniaxial compressive strength (UCS) apparatus and lateral deformation using particle image velocimetry (PIV).

Load-induced fatigue cracking is one of the primary distress modes in asphalt pavements at intermediate temperatures. The asphalt community is still searching for a reliable methodology to obtain relevant properties of asphalt binder to assess relative cracking performance. This study proposed an enhanced binder fracture energy (BFE) test to determine the fracture tolerance of asphalt binders. The BFE test successfully differentiated unmodified and modified binders based on the characteristics of the true stress–true strain curve. More importantly, binder fracture energy density (FED) quantitatively distinguished rubber-modified, hybrid, and polymer-modified binders. Finally, fracture properties translated well from binder to mixture such that binders with higher FED resulted in higher mixture FED values. Mixture cracking performance was evaluated by using the energy ratio (ER) parameter that is governed by both failure limit (FED) and rate of damage of asphalt mixtures. An excellent correlation was found between binder FED and mixture ER, given binders containing SBS polymer typically lead to a low mixture rate of damage. Therefore, it appears that binder FED obtained from the BFE test can be used to assess relative cracking performance. Future research on binder rate of damage may be necessary to account for new binder modifications.

Sand–foam mixtures have many potential applications in the field of mining and construction. This paper conducts laboratory experiments to investigate rheological characteristics of sand–foam mixtures using free slump flow tests with a cylindrical geometry. It is expected that slump test can provide accurate results to identify the effects of sand concentration, foam:water ratio, and particle size on the rheology of sand–foam mixtures. Three distinct stages are observed in slump of sand foam mixtures. The effect foam:water ratio is more pronounced in variations of slump heights and diameters with time. Yield stress of sand foam mixtures are estimated using the slump model for cylindrical geometries. Estimated yield stress is overall in good agreement with the rheological measurements. Effect of particle size on yield stress of sand foam mixtures is found to be negligible except for dense mixtures ($c_o>0.6$) with higher foam:water ratio ($G_f=0.3$). The averaged bed shear stresses of mixtures are calculated using a simplified one-dimensional momentum equation. A comparison between the averaged bed shear stress and the yield stress of mixtures indicates two distinct behaviours of fluidlike and solidlike during the slump flow spread. Energy dissipation is estimated during the tests. The energy dissipation rates of light sand–foam mixtures are higher than those of dense mixtures. The total energy dissipation of sand–foam mixtures is approximately 95%, which is 10% higher than the energy dissipation of granular flow.

Improvement of poor engineering properties for very high–moisture content fine-grained soils (VHMS) is important for several industries, including dredging. This paper focuses on improving engineering properties of VHMS by way of adding low dosages of portland-limestone cement (PLC) such as ASTM C595 Type IL, which is a more sustainable alternative to ordinary portland cement (OPC) such as ASTM C150 Type I. A key goal was to determine if PLC can satisfactorily enhance the properties of lightly cemented (LC) VHMS (LC-VHMS), defined as having 5% or less cement by total mass. This paper focuses exclusively on the behavior of PLC versus OPC by making use of five matched pairs of OPCs and PLCs from four different cement manufacturing facilities. A series of index property, unconfined compression (UC), and unconsolidated undrained (UU) triaxial tests were performed on LC-VHMS samples collected from a dredged disposal facility near the port of Mobile, Alabama. Overall, the results suggested that using PLC in LC-VHMS can provide a sustainable alternative to OPC while leading to comparable engineering properties (5% stronger to 8% weaker overall depending on the test type).

This paper reports the correlation between existing standards for concrete and the major mechanical properties of geopolymer concrete produced from a range of low-calcium, Class F fly ashes. The data were collected at set points over a 1-year period and include four different sources of fly ash used in the manufacturing of geopolymer concrete. New relationships between mechanical properties and compressive strength were derived using statistical regression analysis. The applicability of current relationships of portland cement (PC) concrete as specified in Australian standards and American Concrete Institute codes for geopolymer concrete have been critically examined. The results indicated that the flexural strength of geopolymer concrete is higher than those predicted using current design equations for PC concrete with a similar compressive strength. However, the splitting tensile strength of geopolymer concrete is comparable to that predicted using the current design equation for PC concrete with similar compressive strength. It was also observed that the ACI 363 R equation significantly overestimates the splitting tensile strength of geopolymer concrete. Similarly, AS 3600 overvalues the elastic modulus of geopolymer concrete. Both of these overestimations may be critical when compressive strength is below 40 MPa.

Discovered in the 1940s, alkali-silica reaction (ASR) causes undesired expansions in concrete. If unmitigated, ASR may cause premature deterioration. Since its discovery, researchers have sought an economical and rapid method for detecting the potential for and presence of ASR. ASR is a global concrete durability problem with a complexity that demands respect. Over the past 15 years, the Wyoming Department of Transportation (WYDOT) has addressed this problem by subjecting aggregates to the accelerated mortar bar test (AMBT) before using them in new concrete. This study combines several classification test methods with an outdoor exposure site (OES) to most accurately classify Wyoming aggregates. Of the aggregate sources studied, 25% are nonreactive, 50% are moderately reactive, one is highly reactive, and the remaining source falls on the border of moderately and highly reactive. The test methods generally agree, and a trend between the aggregate composition and expansion is noted. Recommendations for expansion limits compared to exposure blocks with mixed coarse and fine aggregates are introduced. Wyoming, located in the center of North America, produces subbituminous coal that may not be suitable to mitigate ASR. Because fly ashes are highly dependent on the parent coal, the widespread use of Wyoming coal for power generation in the United States means that fly ashes similar to the ones used in this study are likely to be available for use in concrete in many areas of the country. This emphasizes the need for more detailed chemical studies and predictive tools to determine the suitability of pozzolans and particular aggregate sources. Also, it was found that even the most expansive aggregates can be effectively mitigated using a semilocal fly ash.

An important type of ultra-high-performance concrete uses the hydrated mixture of the American Petroleum Institute (API) Class H cement and silica fume to produce the required binder. In this investigation a computational methodology is formulated to model the shear strength of this matrix, using the results of standard direct shear tests on ambient-hydrated samples. The procedure relies on the National Institute of Standards and Technology (NIST) Virtual Cement and Concrete Testing Laboratory (VCCTL) for the microstructure-based description of the stiffness of the assumed linear-elastic fully-hydrated brittle paste, and on subsequent finite-element analyses of the cylindrical sample. Computational iterations on the material Poisson’s ratio render the adjusted elastic properties. Convergence on the state of stress at the centroid of the critical element at fracture is attained on agreement with experimentally-complemented well-known theories of failure. The predicted inclination of the failure plane was validated by consistent experimental observations on the test samples at the U.S. Army Engineer Research and Development Center (ERDC).

In order to investigate the effect of transverse cracks on chloride penetration and steel corrosion in concrete beams, two series of cracked specimens, Series A, with sustained flexural cracks, and Series B, with precracks, were designed and tested under a cyclic drying-wetting condition of NaCl solution. Profiles of free chloride concentration were obtained from the cracked beams in Series A after 30 and 60 weeks; the corroded rebars were removed from the precracked beams in Series B after nearly 4 years. Experimental and analytical results showed that the depth of the surface convection zone in the cracked concrete varied from 10 to 20 mm, which was greater than that in the sound concrete, and increased with increasing crack width. Around the steel bar located in the inner concrete, beyond the convection zone, chloride content was mainly influenced by concrete type when crack width was less than 0.2 mm, and then by crack width. For precracked concrete, pitting corrosion in the steel was obviously seen where cracks were located, and the scope of localized corrosion expanded when crack width increased. The effect of transverse cracks on steel corrosion depends on the coupled actions of cover depth and crack parameters. For the same specimens, a great difference in the effect of crack width ($\sim 0.2\mathrm{mm}$) on steel corrosion was observed when crack spacing decreased from 250 to 150 mm, especially for the steel bar with a lower cover depth of 20 mm.

This paper examines the effects of reclaimed asphalt pavement (RAP) content and binder grade on the fatigue resistance of Georgia asphalt concrete mixtures. The asphalt concrete mixtures were prepared based on two job mix formulas used in northern and southern Georgia and were composed of 12.5-mm nominal maximum aggregate size aggregate and three asphalt binders (PG 64-22, PG 67-22, and PG 76-22). Dynamic modulus and controlled crosshead cyclic tension fatigue tests were performed using the laboratory-prepared specimens. A simplified viscoelastic continuum damage (S-VECD) model was characterized for each mixture using the dynamic modulus and fatigue test results. The layered viscoelastic pavement analysis for critical distresses (LVECD) program was used to investigate the effects of RAP content and binder grade on the fatigue performance of pavements. The S-VECD model and LVECD program analyses showed that the addition of RAP up to 30% using corrected optimum asphalt content (COAC) method significantly improved the mixtures’ fatigue resistance, especially for the mixtures with PG 64-22 and PG 67-22 binders.

In this paper, binary and ternary blended cements (BC) based on calcined clay (CC, 0–30%) obtained from low-grade kaolinitic clay and limestone filler (LF, 0–10%) were developed and the interaction between the filler effect and pozzolanic effect on the compressive strength, hydration phases, and pore-size distribution were studied. Results show that early compressive strength decreases for high levels of replacement (10LF30CC) because of a dilution effect that cannot be compensated for by the filler and pozzolanic effects. Based on calcium hydroxide (CH) content, the addition of limestone filler in ternary blended cements is favorable to the development of pozzolanic reaction of calcined clay at an early age. This study shows that dilution, filler, and pozzolanic effects are relevant at 2 days, filler and pozzolanic effects are important at 7 days, and the pozzolanic effect is the most important at a later age.

Prediction of chloride ingress is very important for the durability of reinforced concrete structures in chloride-laden environments, especially for concrete with cracks. It is expected that the chloride diffusion coefficient of a crack is much higher than that of the uncracked part in concrete. A single crack in concrete can be a shortcut for chloride ions to pass through. Research on chloride diffusion/migration through cracks in concrete is limited. Therefore, in this paper steady-state chloride diffusion and migration coefficients of cracks in concrete were measured and calculated and the relationship between the two coefficient types was analyzed theoretically and compared with experimental data. The results show that the ratio between the two sets of diffusion/migration coefficients can be related to the ratio between the specimen length and crack length. The measured crack length depends on the resolution of the sampling by microscopy. The optimum unit sampling length for the crack length measurement was found be close to the value of crack width.

Stabilization of poor soils is a technique that can improve engineering properties for road building. Chemical stabilizers such as cement and lime are commonly employed. However, environmental issues and costs involving the production of these materials are making their utilization questionable. Brazil has the fourth largest road network in the world, but only 12% of these roads are paved, which indicates a great need for transport infrastructure at low cost and with good technical and environmental performance. This work proposes the use of basic oxygen furnace steel slag (BOFS) as a chemical soil stabilizer. Sixteen different mixtures of lime, cement, and processed BOFS were tested and compared. The parameters evaluated were unconfined compressive strength, diametrical tensile strength, California bearing ratio, expansibility, and environmental contamination. Results indicate that soils stabilized with BOFS have the same environmental classification as soils stabilized with cement and lime. The BOFS fines successfully stabilized the studied soil, leading to an increase in CBR values of up to 230% along with a decrease in expansibility. The best mechanical performance was observed in the mixture with 15% BOFS and 5% cement by weight, which indicates high performance with high content of BOFS and low cement consumption.

Cracks in concrete accelerate mass transport and shorten the service life of structures. In this study, cracks were physically simulated using a Plexiglas parallel-plate setup with adjustable distance between the plates (to achieve various crack widths) and with two distinct crack wall roughness values. Transport properties of such simulated cracks were measured and linked to crack geometry. Saturated permeability and ion diffusion coefficient of cracks were measured using constant head permeability test, electrical migration test, and electrical impedance spectroscopy. The results showed that the permeability coefficient of a crack is highly dependent on the crack width square, and to a lesser extent, on the crack tortuosity and wall surface roughness. The result of migration and impedance tests showed that crack diffusivity is only slightly affected by crack width and only for cracks tighter than 90 μm. Generally, crack diffusivity was found to be similar to the pore solution diffusivity, multiplied by a crack connectivity coefficient (${\beta }_{\mathrm{cr}}$); the latter can be measured from an electrical conductivity test.

Thermoplastic recycled polystyrene (rPS) and polypropylene (rPP) bounded concretes were formulated by thermal curing. Mechanical properties, thermal crack-healing efficiency, and moisture and temperature susceptibility of the rPS-bounded and rPP-bounded concretes were evaluated with respect to portland cement and asphalt concretes (PCCs and ACs, respectively). The rPS-concrete exhibited a compressive strength slightly higher than that of the ACs. In contrast, rPP-concrete possesses much higher compressive strength, approximately threefold that of the ACs, which is almost equivalent to the strong PCC. However, rPS-concrete demonstrates the highest bending resistance, more than the ACs and twice as rigid as the PCCs, while rPP-bounded concrete was only stiffer than the ACs. The rPS-concrete exhibited flexural strength greater than both the PCCs and the ACs, and the rPP-bounded concrete showed approximately threefold and fivefold bending strength of the PCC and ACs, respectively. A simple crack-healing efficiency assessment test was proposed. Results indicate the high feasibility of utilizing heat treatment to successfully repair cracks at early formation for the thermoplastic recycled plastic concretes (TRPC). The rPP-bounded and rPS-bounded concretes showed better moisture resistance and much lower thermal sensitivity than the ACs.

The primary purpose for sealing joints in rigid pavement—besides limiting incompressible material—is to prevent or reduce the amount of water infiltrating into the pavement structure. The presence of moisture in a pavement structure is a contributor to a variety of governing distress types that eventually deteriorate the integrity of a pavement structure and decreases its service life. The effectiveness of joint sealants to protect any type of concrete pavement against water infiltration has been of interest for many years. More recently, pavement or joint infiltration has been at the heart of both formal and informal studies by state agencies, the Federal Highway Administration (FHWA), and the National Cooperative Highway Research Program (NCHRP) on the effects of joint sealing funded that have pertained to the to seal or not to seal discussion that refers to the utility of sealing joints in concrete pavements. The results of these studies have been limited due to the use of infiltration models more oriented to the permeability of a pavement surface rather than the permeability of the joints. To this end an improved infiltration model is introduced in this paper and the results of a field testing program that was carried out at the Riverside Campus of Texas A&M University to calibrate and validate the model. This paper also addresses sealant effectiveness with respect to different types, degrees of bonding, and joint openings. The model can be used to improve the Ridgeway formula in terms of these factors plus the pressure head and the quality of the sealant installation on the prediction of moisture infiltration through partially sealed joints as part of a pavement design procedure.

Computerized tomography (CT) scanning is one of the most effective techniques used in studying concrete crack initiation and propagation. CT scanning of concrete under uniaxial compression was used to monitor the mesodistribution in concrete. Fractal dimensions and damage variables of CT images corresponding to various crack development stages of concrete were calculated. The CT images’ fractal dimension changes were observed to have the same trend as the concrete damage-loading curves. The fractal dimensions and damage variables of CT images increase rapidly at a certain loading level, indicating a dangerous condition in the concrete. The proposed integration of CT testing and fractal analysis provides a useful and effective tool for monitoring concrete mesodamage and for evaluating concrete performance.

Sliding friction between a pavement and tire is an important concern in traffic safety. The British pendulum test has been used worldwide to evaluate friction characteristics of pavement surfaces. However, because of considerable differences in apparatus, procedures, and operation, significant variability can occur for evaluations of British pendulum number (BPN). In this investigation, a direct shear test (DST) device is modified and proposed to determine the sliding friction coefficient between tire and pavement surface under dry and wet conditions. Dissipated energy values obtained from DST were compared with evaluations of BPN, and a high correlation was obtained. Tests were done using three types of pavement surface: asphalt concrete (AC), cement concrete (CC), and polymer concrete (PC), and two types of tires, namely ribbed and smooth. The proposed method of applying DST has the advantage of considering tire properties such as type, tread depth, and characteristics. Other advantages are consideration of the direct effect of vehicle weight and indirect effect of tire inflation pressure. Therefore, the friction characteristics measured by DST are close to reality. According to results of DST and BPN, the PC under dry and wet conditions had the highest and lowest evaluations for sliding friction coefficients, respectively. In addition, uniaxial compressive strength, abrasion resistance, and impact strength of pavement materials were determined. The PC mixture had the highest evaluations for ductility, compressive strength, abrasion resistance, impact toughness, and energy absorption.

This paper presents the results of research on the electrochemical realkalization (ER) of carbonated concrete with fly ash and slag. The results show that the realkalization depth in concrete increases with an increase in the fly ash content and slag content. The carbonation resistance of realkalized concrete is lower than that of unrealkalized concrete and decreases with an increase in the fly ash and slag content in the concrete. The influence of fly ash on carbonation resistance is similar to that of slag. The maximum shear stress between the carbonated concrete and rebar decreases with an increase in the mineral admixtures regardless of realkalization or unrealkalization, and the influence of the fly ash on the bond behavior is greater than that of the slag.

This paper discusses an experimental investigation of clay brick columns that are externally strengthened by steel wire collars wrapping the horizontal mortar joints. The study aims to prove the effectiveness of the proposed strengthening technique and detect the efficiency of different numbers of steel collars. Additionally, the effect of eccentric loading is investigated. This paper proves that an analytical expression available in the previous literature can be modified to provide the strength of the equivalent homogeneous cross section in simple compression. To this aim, the biaxial strength domain of the bricks is modified to account for the lateral pressure exerted by the steel collars. Moreover, based on the plane cross-section assumption, moment-axial force domains are derived using mechanical parameters that are experimentally determined for the units, the steel collars, and the masonry under centered compression. Finally, the capacity of these domains to give accurate results in relation to the confinement effect produced by the proposed strengthening technique is discussed.

Given the time-dependent microstructural modifications in cement matrix, long-term monitoring of concrete in natural exposures will be necessary. The present research addresses the long-term performance of concrete specimens embedded in coastal soil of a harsh marine environment for 88 months. Chloride ion diffusion, binding capacity, and effects of carbonation and surface coatings were investigated for concrete mixtures with up to 12.5% silica fume (SF) and water-to-cementitious materials ratios ($\mathrm{w}/\mathrm{cm}$) of 0.4 and 0.5. Three types of surface coatings, including bitumen and rubber emulsion, polymer modified cementitious coating, and polyurethane, were also incorporated. It was observed that concentration of bound chloride ion is decreasing as a result of an increase in SF content from 0 to 12.5% and increasing the $\mathrm{w}/\mathrm{cm}$ from 0.4 to 0.5. Slight carbonation was observed at 88 months, with carbonation depths limited to 5.5 mm. Decrease in chloride binding capacity was observed in carbonated areas. Depth of concrete cover to reach 50 and 100 years of service life was calculated. It was observed that a concrete cover of 200 mm can secure 100 years of service life while incorporating a concrete mixture with w/cm of 0.5 and 100% portland cement. The required thickness of cover was reduced to 35 mm in the case of the mixture cast with 12.5% SF and $\mathrm{w}/\mathrm{cm}$ of 0.4. Coating equivalency lines were developed to compare the efficiency of the investigated coatings with corresponding combinations of $\mathrm{w}/\mathrm{cm}$ and SF replacement level.

This paper aims to develop a new material with outstanding energy-absorbing performance regarding its application in protection engineering. The preparation and dynamic performance of basalt fiber–reinforced lightweight concrete confined by a brass strip (FLCB) were experimentally investigated. The FLCB specimens were first prepared based on dense packing theory. Impact compression experiments were then carried out by a $\mathrm{\varphi }100\text{-}\mathrm{mm}$ ($\mathrm{\varphi }$ = diameter) split Hopkinson pressure bar apparatus, which was improved by the pulse-shaping technique. The resulting stress-strain curve, dynamic deformation, and energy-absorbing characteristics were studied. The results show that FLCB, with density of $\mathrm{1,204.2}\mathrm{kg}/{\mathrm{m}}^3$, is a kind of lightweight concrete. The stress-strain curve of FLCB can be divided into three stages: linear elastic, stress platform, and brittle failure. The stress platform stage has a significant effect on the improvement of energy-absorbing performance, and the percentage of the stress platform to the whole curve increases continuously with average strain rate. Both the ultimate strain and the energy-absorbing index are sensitive to strain rate and increase continuously with average strain rate. Furthermore, compared with conventional concrete, the production of FLCB is associated with a higher ultimate strain and energy-absorbing index, and the tendency becomes more obvious with increasing average strain rate. Therefore, FLCB includes a lightweight concrete with excellent energy-absorbing performance and this performance shows clear strain-rate dependence. Due to its features of outstanding energy absorption and low density, FLCB has a promising future to be used as antiexplosive layers in protection engineering.

While significant research has been performed to assess the transport properties of concrete, a vast majority of previous research has focused on behavior in undamaged concrete. This paper describes an investigation to assess the influence of a mechanically induced crack on chloride ingress. Tapered cracks were generated in specimens using a wedge splitting test. The specimens were then used to assess: (1) the chloride ingress, and (2) the physical size of the crack using fluorescent epoxy impregnation. This paper describes the results of concretes that were made with three water-to-cement ratios (w/cs) (0.30, 0.42, and 0.50) and three different maximum aggregate sizes (4, 8, and 16 mm). The results indicate that chloride transport in relatively small cracks can be influenced by the mixture composition (w/c and aggregate size) because this influences the tortuosity of the crack. However, as the width of the crack increases the crack begins to behave as a free surface and the influence of w/c is much less important.

Small voids of varying shapes and sizes are an inherent part of the physical structure of parallel strand lumber (PSL) due to the material’s manufacturing process. To gauge the sensitivity of the material’s mechanical behavior to these voids, this paper proposes and evaluates finite element models that incorporate PSL voids by simulating them as equivalent ellipsoids. It is assumed that the wood phase is a homogeneous and orthotropic continuum, while the void phase is the only source of uncertainty. Two analyses are presented: (1) linear elastic analyses to gauge the effective modulus of elasticity and the distribution of conventional, principal, and effective stresses considering the effect of volume fraction and void shape; (2) nonlinear analyses under uniaxial and biaxial ductile compressive loading scenarios. Linear elastic analyses showed that representing voids as equivalent ellipsoids does not affect the effective elastic moduli and stress distributions in the models under uniaxial loading. Nonlinear analyses confirmed that the overall nonlinear compressive behavior of the models with equivalent ellipsoids are similar to that of their corresponding models with actual voids.

An investigation was conducted to study the behavior of plain concrete and steel fiber reinforced concrete under direct tension fatigue loading. Tests were conducted on dogbone specimens with varying amounts of steel fiber volume content (0, 0.75, and 1.5%). A new concept was introduced in deriving material damage parameters for plain and steel fiber concrete. The parameters developed were implemented into a damage evolution function to enable the prediction of concrete strength and fatigue secant modulus deterioration of steel fiber reinforced concrete. As such, the damage evolution models developed for steel fiber concrete can be implemented into steel fiber reinforced concrete constitutive models for the analysis of fatigue-damaged concrete elements. From the experimental results, the deformation profiles for plain and steel fiber concrete were similar, and the well-known relationship between the fatigue life and secondary strain rate of concrete in compression also exist for plain concrete and steel fiber concrete in tension. In addition, under the same loading parameters, the fatigue life of steel fiber concrete was found to increase as steel fiber content increased from 0 to 1.5%.

Polycarboxylate superplasticizer (PCE) is widely employed in cement-based material to reduce water demand and increase fluidity, and even to improve durability of concrete. Generally, aggregates occupy more than 70% weight of concrete, and those poor-quality aggregates containing clay minerals, especially montmorillonite (Mt), often make PCE ineffective and significantly reduce the workability of concrete; this phenomenon is referred to as poor clay tolerance of PCE. Currently, the poor clay tolerance seriously restrains the practical application of PCE. In this study, the mechanism behind the improvement of the clay tolerance in the presence of polyethylene glycol (PEG) was investigated to explore a valid way to enhance the clay tolerance. Specifically, the clay tolerance in the presence of PEG was assessed with the fluidity of cement-Mt paste. Total organic carbon analyzer was performed to analyze the adsorption behavior of PCE and PEG. The microstructure of the intercalated Mt was characterized with X-ray diffractometer, transmission electron microscopy, Fourier-transform infrared spectrometer and thermogravimetric analysis. An intercalation model was then proposed to explain the mechanism. The results show that in Mt suspension, the interlayer adsorption is mainly responsible for the large adsorption amount of PCE. The improvement in clay tolerance of PCE in the presence of PEG is attributed to the preferential intercalation of PEG, which significantly hinders the intercalation of PCE. The result also suggests that those polymers with positive charge or considerably strong polarity might enhance the clay tolerance of the PCE system through the preferential intercalation. It also provides experience for practical application of PCE.

Achieving greater durability of concrete is desired, particularly in cold climate areas. Accordingly, understanding the internal deterioration of concrete exposed to freeze-thaw cycles is of particular interest. This paper establishes a novel model for predicting the internal deterioration of normal concrete subjected to freeze-thaw cycles. Mathematical formulas and experimental works provide the basis for the model development. Two stages of concrete deterioration are considered and $D\text{-}N$ (damage-number of freeze/thaw cycles) relationships for each stage are developed. Comparisons are made with a sample of 55 experimental tests to validate the paper’s propositions and theoretical results. The paper demonstrates that the proposed model can serve as an effective tool to evaluate concrete deterioration under freeze-thaw cycles. The results add to the literature by providing an understanding of the mechanical deterioration of concrete in cold climate areas greater than currently available. Because the focus of the paper is on normal concrete, the results should be used for other types of concrete with special care.

This work examines the potential use of heterogeneous photocatalysis as an innovative oxidation technology. The aim is to demonstrate that this technology can reduce the damaging effects of vehicle emissions by using nitrogen doped (N-doped) ${\mathrm{TiO}}_2$ as a photocatalyst immobilized above the asphalt road surface. In the study, the photocatalytic effectiveness and durability of N-doped ${\mathrm{TiO}}_2$ photocatalytic asphalt road material were assessed in both the laboratory and the field using direct and indirect measurement. The experimental results show that under visible light irradiation, N-doped ${\mathrm{TiO}}_2$ asphalt road material has a higher activity compared with pure ${\mathrm{TiO}}_2$ asphalt road material. The decontamination rate for ${\mathrm{NO}}_x$ is approximately 27.6, 24.6, 16.3, and 13.8% under irradiation at light wavelengths of 330–420, 430–530, 470–570 and 590–680 nm, respectively. Results of the field test and prediction models suggest that the service life of N-doped ${\mathrm{TiO}}_2$ asphalt road material is approximately 13 months.

Organic paints are applied to galvanized or metalized steel surfaces in a duplex system, which is potentially more sustainable than the zinc-rich primer/steel system. A series of experimental tests were performed to measure and investigate adhesion strengths on three different types of roughened zinc surfaces. The contact angles were also measured for freshly formulated liquid paints on the roughened zinc surfaces to test if there is a correlation between the paint wetting property and the adhesive strengths. By comparing duplex system and zinc-rich primer/steel qualified North East Protective Coating (NEPCOAT) panels, it was found that the paint adhesion of the duplex system is as strong as the zinc primer/steel panels test results. The results also showed that adhesive strengths depend on the match between the paint and type of roughened zinc surfaces. The measurement of liquid paint wetting properties indicates small contact angles correlate with stronger pull-off adhesive strength. The authors of this study suggest that contact angle/strength correlation could be useful as a tool for optimizing the match between the paints and the profiled zinc surface.

Sealants exist under conditions of great strain for extended periods in winter; their viscoelastic characteristics at low temperature can play a critical role in preventing adhesion failure. Two types of hot-poured sealants and two types of silicone sealants are selected for extension tests with reference to a standard bond test. Stress relaxation tests are conducted when a 50% strain is reached. The test data are fitted with extension and stress relaxation with a standard linear solid model to obtain a fitted extension–stress relaxation equation, which is used to obtain viscoelastic characteristic parameters of the model. The fitted result shows that the standard linear solid model can fit the viscoelastic performance at low sealant temperature. Two viscoelastic characteristic parameters of the maximum relaxation ratio and relaxation time can be used to evaluate the stress relaxation ability of different sealants, but the fitting process of the viscoelastic model is more complicated. Therefore a simple stress relaxation index is defined. Results of the evaluation with this index are consistent with results with the maximum relaxation ratio and relaxation time, which indicates that this index is applicable to the evaluation of stress relaxation of sealants and features better practicability and operability. The evaluation of the stress relaxation shows that the relaxation performance of hot-poured sealants at low temperature is better than that of silicon sealants. Therefore hot-poured sealants may be more applicable for use in areas with long-term low temperatures in winter.

A novel aqueous penetrating corrosion inhibitor marked PCI-2016 was prepared by using multicompound and chelate-induced techniques for this paper. Adsorption and inhibition behaviors of PCI-2016 in a chloride solution had been investigated. Test results indicated that the PCI-2016 had an excellent inhibition ability and an identified curative effect on the corrosive steel in the chloride solution. Adsorption of PCI-2016 molecules on the steel surface followed the Temkin adsorption isotherm. The scanning electron microscope (SEM), the energy dispersive spectrometer (EDS), and the atomic force microscope (AFM) images showed many small global or columnar substances had accumulated on the steel surface and the elements of N and Zn in corrosion inhibitors were detected on the steel surface. The X-ray photoelectron spectroscopy (XPS) measurements supported the inhibitor particles that were absorbed on the steel surface by chemisorption and a dense film was formed to inhibit the steel corrosion. Mechanism studies indicated that a stable chelate formed between the iron and N-containing polycarboxylate ligands might be responsible for the high inhibiting efficiency of the inhibitor in the chloride solution.

Despite the availability of reliable stiffness-based quality control evaluation techniques, developing countries still adopt traditional density-based quality control assessment on unbound pavement layers. The objective of this study is to evaluate the effectiveness of lightweight deflectometers (LWD) as a quality control device for modified subgrade under varying drop weights. Experimental investigations were performed on a 240-m long and 9-m wide experimental stretch constructed in Gujarat, India. Mean target stiffness value on the modified subgrade using LWD with 10, 15, and 20-kg drop weights were 40, 51, and 64 MPa, respectively. Percentage variations between target and evaluated stiffness values on the modified subgrade were 2.60, 3.10, and 0.28%, for 10, 15, and 20-kg drop weights, respectively. Subsequently, the influence of in situ moisture content and density on stiffness values of modified subgrade for various drop weights was assessed by correlation analysis, and the results depict a good $R^2$ value from 0.74 to 0.82. The LWD backcalculated moduli (10 kg) and dynamic cone penetrometer estimated resilient moduli values of modified subgrade were compared, and the mean percentage variation was 3.78–4.95%. Thus, there is a substantiate relationship between in situ density and stiffness values that follow similar trends under varying LWD drop weights. Therefore, LWD stiffness-based evaluation on modified subgrade soil contributes to enhancing the effectiveness of quality control measures during construction of low volume roads.

Polyurethane (PU) is a commonly used insulation material for cold storage warehouses. The insulation performance of PU sandwich panels made from blended blowing agents were reassessed by k-factor measurements and insulation thickness calculation based on the cold warehouse design standard, which has proven the significant impact of blowing agent difference on energy saving. The foam poststability was also evaluated by mathematic profiling. The developed three-dimensional paraboloid model based on gridding measurements has provided a scientific method for panel shrinkage evaluation. Cell microstructure characterization and postgrowth angle coefficients calculation were further performed for better understanding the shrinkage problem at the microscopic level. The foaming process model of continuous panel production was developed based on reactivity profiling characterization which has provided a theoretical solution to panel processing.

Conventional hot-asphalt mixtures have an impact on global warming and ${\mathrm{CO}}_2$ emissions, contributing to debates on environmental issues that have been raised in recent years. As an alternative, cold-emulsion asphalt mixtures (CBEMs) provide considerable benefits such as eco-friendliness, energy efficiency, and cost-effectiveness connected with safety. However, their weak early strength along with the need for longer curing times (usually 2–24 months) and higher moisture susceptibility compared to hot-asphalt mixtures have been cited as obstacles to their wider application. That said, the incorporation of waste materials in CBEM mixtures enhances sustainability by decreasing the amount of industrial waste materials needed and conserving natural resources. A new binary blended cement filler (BBCF) material generated from high-calcium fly ash (HCFA) and fluid catalytic cracking catalyst (FC3R) was found to be very effective in providing microstructural integrity with a novel fast-curing cold-asphalt concrete for the binder course (CACB) mixture. Laboratory performance tests included the stiffness modulus test by indirect tension to cylindrical samples, wheel-tracking tests, and water sensitivity. Regarding environmental issues, a toxicity characteristic leaching procedure (TCLP) test was performed to analyze the leachate from various specimens in terms of their concentrations of heavy metals. The findings of these tests have demonstrated that CACB performs extremely well compared to traditional hot mixtures. The stiffness modulus of the BBCF-treated mixture—3,730 MPa after 3 days—is higher than the traditional hot mixture [100/150 penetration (pen)]. In addition, the BBCF-treated mixture offered a superior performance regarding rutting resistance, fatigue resistance, and water susceptibility, as well as revealing a considerably lower thermal sensitivity. More significantly, the BBCF-treated mixture was found comparable to the traditional asphalt concrete binder course after a very short curing time (1 day). Finally, the concentration of heavy metals in the specimens incorporating the BBCF was observed to be less than the regulatory levels determined for hazardous materials and so requirements were satisfied. Consequently, this BBCF-treated mixture has significant potential with reference to its application as a binder course in asphalt pavement.

The primary purpose of this study is to investigate the gamma radiation transmission rate from heavy concrete containing iron oxide and barite aggregates. For this purpose, a number of cubic and cylindrical samples of different sizes and types and various percentages of aggregate participation were made. Compressive strength and gamma radiation tests using a cesium-137 source were carried out on specimens. The results showed that the use of heavy aggregates increases the attenuation coefficient of concrete. Increasing the participation of the iron oxide aggregates caused increasing density and thereby intensification of the attenuation coefficient in samples. Such escalation of the attenuation coefficient in concretes containing barite aggregates is higher than the concretes containing iron oxide. The compressive strength of the samples shows a growing trend with the increase in the presence of heavy aggregates, but this increasing trend only endures until the concrete contains 50% heavy aggregates, and thereafter the downward trend occurs for the compressive strength.

Self-consolidating concrete (SCC) has the potential to increase precast production and quality, especially for production of prestressed concrete (PSC) bridge girders due to its superior workability compared with conventional concrete (CC). To obtain desired fresh and hardened properties for the production of SCC PSC girders, many factors related to material characteristics and mixture proportioning must be considered. An experimental comparison of fresh and hardened properties of SCC mixtures made with different material constituents was conducted in this study. The ultimate objective of this paper is not only to provide an experimental program enabling the investigation of the effect of material constituents on the performance of SCC mixtures but also to gain more knowledge for improved production of SCC PSC girders. The experimental program was established based on technical findings from a literature review and additional input from a survey of several state departments of transportation (DOTs). The mixture constituents used to investigate SCC performance consisted of the type of cement and size and type of coarse aggregate. Testing methods included slump flow, visual stability index (VSI), J-ring, column segregation, and compressive strength. The testing results showed that the type, shape, and size of coarse aggregate have a dominant effect in terms of fresh properties and compressive strength; specifically, mixtures with river gravel had larger spreads than mixtures with crushed limestone. Cement type had the expected effect with mixtures using Type III cement developing higher early strength than those using Type I/II cement. A statistical analysis was performed to determine significant mixture parameters in terms of fresh and hardened properties. It was found that the fine aggregate content was the most significant parameter affecting both fresh and hardened properties’ behavior.

This research discusses the effect of Sasobit on asphalt binder rheology and how different percentages of Sasobit affect its performance. Evaluation is performed according to the Superpave test specifications. Tests include the rotational viscosity (RV), the dynamic shear rheometer (DSR), and the bending beam rheometer (BBR). Several rheological parameters are investigated: the dynamic viscosity ($ή$), the complex modulus ($G^{*}$), the phase angle ($\delta$), the creep stiffness ($S$), and the m-value. The behavior of modified asphalt binder is investigated at a wide range of temperatures ($-6$–160°C). Results show an improvement of the asphalt binder performance at high temperatures, but adverse effects on asphalt binder performance at the low temperatures are observed. The optimum percentage of Sasobit is found to be 2% by mass of the asphalt binder; higher percentages are not recommended.

The paper assessed the rutting and fatigue resistances of binders containing styrene butadiene styrene (SBS) and polyphosphoric acid (PPA). For this purpose, a performance grade (PG) 58-22 base binder was modified in two manners: SBS polymer and reduced SBS polymer plus PPA. The SBS content of the SBS binder and the PPA content of the $\mathrm{SBS}+\mathrm{PPA}$ binders were kept constant. Two $\mathrm{SBS}+\mathrm{PPA}$ binders were investigated, for which the reduced SBS contents were determined differently: one had the same continuous high-temperature PG as the SBS binder, and the other had the same viscosity at 135°C. Multiple stress creep and recovery (MSCR) tests were performed at 40 and 55°C for determining the rutting characteristic, and linear amplitude sweep (LAS) tests were performed at 25°C for determining the fatigue characteristic of the binders. To depict the nonlinearity and predict the rutting resistance more clearly, the high stress levels of 12.8 and 25.6 kPa were added to the MSCR standard procedure. A complex modulus test was also used to evaluate the effectiveness of the new test methods for the SBS and $\mathrm{SBS}+\mathrm{PPA}$ binders and to relate the results to the mixtures’ stiffness parameters. Based on the results, it is found that the nonlinearity caused by the high stress levels (rutting potential) and the fatigue damage of the SBS binder are less than those of the $\mathrm{SBS}+\mathrm{PPA}$ binder with the same continuous PG, but are more than those of the $\mathrm{SBS}+\mathrm{PPA}$ binder with the same viscosity. The results also show good correlations between the binders and mixtures tests data.

Thermomechanical response of coefficient of thermal expansion (CTE) test samples plays an important role in the consistency of CTE test results. Saturated concrete samples while subjected to heating and cooling develop internal pressure due to the dissimilar thermal expansion/contraction of solid and liquid phases. This fundamental property of saturated concrete has not yet been considered as a criterion to improve the CTE test procedure. This paper presents an experimental investigation to reduce the effect of internal water pressure on the measured CTE results. The paper experimentally evaluates three techniques—preconditioning the concrete samples by heating and cooling cycles prior to CTE test, precracking concrete samples, and reducing the rate of temperature change. Preconditioning concrete samples by heating and cooling cycles prior to CTE testing noticeably improves the consistency of CTE test results. Decreasing the rate of temperature change also improves the consistency of the test results but significantly increases the test duration. Precracking shows improvement in a few test parameters, but the results are unreliable for in situ concrete due to the adverse effect of increased porosity.

Foamed warm-mix technology can decrease the construction temperatures of asphalt mixtures, and recycling reclaimed asphalt pavement (RAP) can reduce waste production and resource consumption. Therefore, combining foamed warm-mix asphalt with RAP is an energy saving and resource recycling technology for pavement construction. However, few studies have focused on the interaction of new asphalt and RAP binder to determine the optimum amount of RAP binder in foamed warm-mix recycled asphalt by the rheological characteristics. In this study, foamed warm-mix recycled asphalts with different amounts of RAP binder were prepared in the laboratory. The influences of the amount of RAP binder on the rheological characteristics of foamed warm-mix recycled asphalt were investigated. The high-temperature and low-temperature performance, temperature susceptibility, antifatigue performance, recovery ratio $(R\%)$, and nonrecoverable creep compliance $(J_{nr})$ were evaluated by temperature sweep tests, low-temperature bending tests, and multiple stress creep recovery (MSCR) tests. The results show that foamed warm-mix recycled asphalt exhibited better high-temperature performance, temperature susceptibility, and creep properties but inferior low-temperature performance and fatigue resistance. Furthermore, the optimum amount of RAP binder in foamed warm-mix recycled asphalt is higher than that in hot-mix asphalt.

Shrinkage-reducing admixtures (SRAs) influence moisture and ionic transport in concrete by altering the properties of the pore solution (the surface tension, viscosity, and contact angle). This paper reports measurements of water vapor desorption isotherms in cementitious systems with different SRA contents. In addition, isothermal drying and wicking experiments were performed for concrete with different SRA contents. Similar pore size distributions and pore volumes were measured for plain concrete and concrete containing SRA. Less water was lost during isothermal drying for systems with SRA. Further, there was a reduction in chloride ion penetration for concrete with a higher SRA content during wicking. The transport processes are described quantitatively using a modified moisture-ion transport model. The viscosity of the pore fluid, the capillary pressure, and the ionic diffusion coefficients are considered as a function of SRA concentration. The simulation results are comparable to the experimentally measured data, which sheds light on the feasibility of predicting the moisture loss and chloride migration in concrete containing SRA.

Microencapsulation of rejuvenators was introduced as a new approach to increase the efficiency of rejuvenators toward improving the self-healing rate of asphalt pavement. This study had two primary objectives: (1) to examine the thermal stability of prepared microcapsules containing sunflower oil as core material, and (2) to evaluate the effect of the microcapsule in increasing the self-healing ability of asphalt mixtures. Results showed an acceptable thermal stability of double-walled polyurethane and urea-formaldehyde (PU/UF) microcapsules in the temperature range encountered during mix production. Furthermore, asphalt binder stiffness and m-value measurements demonstrated that microcapsules were successful in decreasing low-temperature stiffness and increasing the m-value of the binder blends. Healing of the cracks defined by reversal of the crack opening was validated in all mixtures through digital image analysis. The mixtures containing sunflower oil as a rejuvenator showed the best performance in self-healing efficiency. However, the healing efficiency of the mix with microcapsules was lower than the mixture with the rejuvenator. This is possibly because of the amount of rejuvenator released from the microcapsules, which was limited to the microcapsules around the crack and not all the rejuvenator available in the mix. The samples healed at room temperature showed higher healing efficiency, compared with the specimens in the oven. The difference in healing efficiency between the two healing conditions (room temperature versus oven temperature) was the largest at Day 1; however, the difference became less pronounced with the progression of healing.

In this study, five different weak soils were mixed with five different sizes of crumb rubber in six different proportions and used to understand the influence of the size and quantity of crumb rubber on the compaction characteristics, unconfined compressive strength, and coefficient of permeability of the soils. The maximum dry unit weight increased with the addition of crumb rubber, with the greatest increase found to occur when 2–4% crumb rubber of any size was added to the soil. An increase in the size of the crumb rubber mixed with kaolinite corresponded to an increase in the maximum dry unit weight. However, the opposite trend was observed when montmorillonite was mixed with crumb rubber. The unconfined compressive strength also increased when crumb rubber was mixed with soil, with the highest strengths also corresponding to the addition of 2–4% of crumb rubber. In all fine-grained soils except those containing montmorillonite, increasing the size of the crumb rubber used resulted in a reduction in the unconfined compressive strength. Moreover, the addition of crumb rubber caused an increase in the permeability of the mixtures. In kaolinite, an increase in the size of the crumb rubber led to a reduction in permeability. The permeability of the mixtures of montmorillonite with crumb rubber dropped as larger-sized crumb rubber was added. However, the coefficient of permeability with the addition of any crumb rubber was always greater than that of the parent soil.

Strain-hardening cementitious composites (SHCCs) exhibiting tensile strain-hardening and multiple cracking are attractive for many structural applications. However, the high cement content makes typical SHCCs less ecofriendly than conventional concrete. One possible approach to improve the sustainability is to substitute cement with industrial wastes such as fly ash. This paper presents an attempt to develop SHCCs with ultrahigh-volume fly ash (HVFA, 80% by weight of binder) for structural applications. From the literature, polyvinyl alcohol (PVA) fiber reinforced HVFA-SHCCs often exhibit low compressive strength, which limits the material to nonstructural applications. The focus of this work was on improving the compressive strength and maintaining the excellent tensile characteristics of PVA fiber reinforced HVFA-SHCCs by a simple and practical method of reducing the water/binder ratio and adding a small amount of silica fume. The selection of fly ash for making such a material is also discussed. With suitable fly ash, HVFA-SHCCs could achieve a compressive strength of 49.4 MPa at 7 days and 69.2 MPa at 28 days, with the corresponding ultimate tensile strain more than 3.5% at 28 days. This kind of HVFA-SHCC is applicable for many structural applications, and the substitution of high percentages of cement with industrial wastes reduces the material cost and the environmental impact significantly.