Journal of Materials in Civil Engineering

Surface resistivity testing has gained popularity as a nondestructive test method to assess the physical and chemical characteristics of concrete. This may be due to the fact that it is sensitive to variations in material parameters, especially cementitious phases. This experimental investigation concentrates on the effects of coarse aggregate type and gradation to determine whether they may be contributing factors in the variability of the resistivity measurements for a given cementitious binder. A total of 21 concrete mixtures designed with various aggregate type (limestone, dolomite, and gabbro), gradation (#67, #57, and #56), and binders (0.40, 0.45, 0.50 water-to-cementitious material ratios with Type I cement and Class C fly ash) were prepared and evaluated using surface resistivity testing. It was found that small changes in gradation may not necessarily influence the outcome of a resistivity test for a given mortar matrix. As for a change in aggregate type, there is minimal impact on the resistivity measurement for mixtures prepared with a Type I cement binder; however, the addition of fly ash seems to have a significant impact. The change in resistivity gain in time varied for all three aggregate types. Here, aggregate–paste interaction had a role in either diminishing or increasing the resistivity value, which may be consequential for concrete mixture classification with respect to ionic penetrability and misinterpretation of binder performance.

The cracking tendency of cast-in-place concrete at early ages under restrained conditions is a concern. In particular, in the building industry, in order to meet the construction speed requirements, external load (due to formwork removal and post-tensioning) is applied while concrete is hydrating, typically 1–4 days after concrete pour. Despite careful design, numerous failures have recently been reported in the industry during construction, prompting this investigation. The paper presents interim findings of a research program investigating the in situ thermal stresses at early ages. The intrinsic thermal stresses including the effects of creep and shrinkage associated with early age concrete were investigated. A degree of reaction–based approach was used to account the evolution of the material properties of concrete. The double power law (DPL) and an American Concrete Institute model were considered to account for the creep and shrinkage effects, respectively. Results show that the tensile strength at early age can be exceeded by the intrinsic thermal stresses.

Utilization of nanomaterials in high-volume fly ash (HVFA) concrete as a means of improving concrete’s properties is feasible. This paper presents experimental data to evaluate the modification effects of $\mathrm{nano}\text{-}{\mathrm{SiO}}_2$ (NS) on early compressive strength and hydration properties of HVFA concrete. To this end, a mixture design method was used to experimentally investigate the early compressive strength development in the NS-incorporated HVFA concrete. For a better understanding of the modification process, several important hydration characteristics of the selected NS-incorporated HVFA cement pastes were analyzed for hydration kinetics, phase composition, and pore structure through isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric/derivative thermogravimetric (TG/DTG), and mercury intrusion porosimetry (MIP) measurements. Experimental results confirmed that NS can partially compensate for the early compressive strength loss of HVFA concrete resulting from high levels of fly ash (FA) replacement. The regression model from mixture design based experiments indicated that the mixture proportion of 58% ordinary Portland cement (OPC), 40% (FA), and 2% (NS) produced the highest early compressive strengths of concrete at 22.9 and 29.0 MPa, for 3 and 7 days, respectively. Hydration characteristics revealed that the addition of NS enhanced early age cement hydration and the formation of calcium silicate hydrate (C-S-H) gels. It also showed a reduction in calcium hydroxide (CH) and porosity in HVFA cement pastes, further contributing to the early compressive strength development of HVFA concrete combined with NS.

The behavior of a composite material, consisting of metakaolin-based alkaline aluminosilicate binder, granules of the same initial composition used as a swelling agent, and calcium carbonate, was studied during firing in the temperature range 25°C–1,000°C. A combination of techniques was used to investigate its microstructure, composition, and properties. The material developed porosity at 200°C, largely contributed by water loss from the swelling agent, resulting in expansion and decrease in thermal conductivity and mechanical strength. Between 400°C and 800°C the thermal insulation characteristics further improved. At 1,000°C, crystallization of new phases with a decrease in the amorphous content produced a small contraction and increased thermal conductivity and mechanical strength. The material exhibited good stability with appropriate characteristics for use as intumescent coating for fire protection of structural elements. Modification of the binder:granules ratio may allow producing composites for specific applications.

This study investigated the rheological, physical, and mechanical properties and injectability of commercially available lime-based grout, and evaluated the performance of the grout injection via cylinder injection and wall tests. Cylinder injection tests were conducted on specimens which were prepared with three different filling materials; the first included only crushed brick particles, the second was a combination of crushed brick particles and hydraulic lime mortar particles, and the third was a combination of crushed brick particles and air lime mortar particles. Traditionally manufactured brick and laboratory-made lime mortars were used in the production of test walls. Historic brick masonries, especially from the Roman and Byzantine periods, were taken into account both in production of the mortars and construction of the test walls. These brick walls were subjected to incremental lateral loading under a uniformly distributed vertical load. Cracks induced by the loading were repaired with grout injection. New cracks formed at different locations, which were close to the previous cracks, during the reloading. The ratio of the increase in the lateral load for a specific crack width was in the range 33%–54% after the grout injection. This revealed that adequate adherence between the wall and the grout was provided.

In geotechnical engineering, geosynthetics are widely used as a reinforcement material for its numerous advantages. Moreover, its strain monitoring is increasingly crucial to ensure the safety of reinforced geotechnical structures. Therefore, a new sensor-enabled geosynthetic material named sensor-enabled geobelts (SEGB) was developed and manufactured. The SEGB has the reinforced function while achieving self-monitoring of strain. Its essence is a kind of conductive polymer, which is made from super conductive carbon black (CB) and high-density polyethylene (HDPE). To study the effects of temperature on the mechanical performance and the tensoresistivity of SEGB, two types of tensile tests were performed between its service temperature ranges ($-20°\mathrm{C}$ to 40°C). The results demonstrate that the tensile strength of SEGB first decreases with temperature and then becomes stable. However, the elongation at break consistently increases with the increase of the temperature. And the measurement results of the electrical resistance indicate the tensoresistivity response of SEGB become more sensitive with the temperature increases. Considering temperature effects, a nonlinear calibration model of the tensoresistivity was proposed to ensure the application of SEGB at different ambient temperatures.

In recent years, due to economic and environmental considerations, the use of waste additives has been highly regarded in pavements. In the case of emulsified cold recycled mixtures (ECRMs), waste additives with pozzolanic properties can accelerate the emulsion setting rate and improve the technical specifications of mixtures. The present study aimed to introduce a new additive in ECRM to achieve a mixture with satisfactory mechanical properties: a combination of cement kiln dust (CKD), a cement production waste, and coal waste ash (CWA), a pozzolanic waste additive. The indirect tensile strength, resilient modulus, and indirect tensile fatigue (ITF) properties of these mixtures were studied at different temperatures and curing periods. The mixtures were also compared with a nonadditive mixture and a mixture containing cement as a conventional ECRM additive. The relationship between mechanical behavior and microstructure of ECRMs was investigated through field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results showed that the mixture containing the new additive had a denser and stiffer structure and better ITF behavior, especially at lower strain levels, than the nonadditive mixture due to effective reaction between CKD and CWA in the presence of water and the formation of calcium silicate hydrate (C-S-H). It had a comparable behavior with cement-containing mixture. According to the experimental results, this ECRM can be recommended for use in the base layer of road pavements.

Incorporating abundant natural resources in highway construction, particularly in pavement manufacturing, is claimed to provide promising benefits. Correspondingly, the experimental study presented in this paper focused on the utilization of sulphur in one pavement layer, namely binder course. To this end, five series of laboratory investigations were undertaken to inspect the physical, rheological, morphological, mechanical, and volumetric impact of sulphur addition to pure bitumen and pavement mixtures. A decrease in both mixing and compaction temperature ranges for sulphur-added mixtures was considered favorable from an economic and environmental point of view, and also a remarkable improvement in their mechanical properties was detected.

An acoustic emission (AE) approach to evaluate the fracture process of porous asphalt mixture (PAM) under compression and splitting testing at different temperatures is presented. Two kinds of PAM, styrene-butadiene-styrene (SBS)-modified porous asphalt mixture (SBSPAM), and crumb rubber and SBS compound-modified porous asphalt mixture (CR/SBSPAM), were investigated and corresponding failure load and AE parameters were obtained. Damage assessments of PAM under compression and splitting testing were carried out using relative AE hits and energy. AE hits and energy had negative correlation with failure load. Damage processes of PAM under compression and splitting testing can be classified into three stages based on variation trends of relative AE hits and energy with load level. The softening effect caused by high temperature can lead to acoustic activity of SBSPAM under compression at a low load level, and the addition of CR can reduce the AE activity caused by the softening effect by improving the temperature susceptibility of binder. Change curves of relative AE hits and energy of CR/SBSPAM are more uniform than those of SBSPAM because of the more stable structure improved by CR modification. The findings of this study can provide references for damage evaluation of PAM using the AE technique.

Environmentally and ecologically friendly biopolymers (xanthan gum, chitosan) and synthetic polymers (polyethylene oxide, polyacrylamide) were employed as novel binders to improve the engineering performance of kaolinite and fly ash–kaolinite mixtures. The floc size, microstructure, physicochemical properties (pH, electrical conductivity, and zeta potential) of polymer-amended kaolinite were investigated, which provided in-depth understanding of the improvement of mechanical properties (Atterberg limits, compaction characteristics, thermal conductivity, and shear strength) from micro to macro. Based on the laboratory observations, it is demonstrated that polyethylene oxide (PEO), chitosan, and polyacrylamide (PAM) induced higher degree of face-to-face (FF) aggregated microfabric through polymer bridging and charge neutralization while xanthan gum led to more edge-to-edge (EE) particle associations. The addition of fly ash was found to reduce the plasticity index, increase the maximum dry unit weight, and decrease the optimum water content of kaolinite, while the organic agents were found to increase the liquid limit and decrease the maximum dry unit weight. The thermal conductivity of fly ash–kaolinite mixtures was found relatively low compared to pure kaolinite, which decreased continuously as the polymer content increased. The unconfined compressive strength (UCS) of organically modified soil increased slightly as the xanthan gum content increased. However, the UCS decreased with the further increase of polymer content ($>0.1\%$ by weight).

At present, most model experiments of tunnel linings use a gypsum-based mixture material as the similar material for static and dynamic research, but the fatigue characteristics of these materials have not been investigated thoroughly and warrant further research. In this work, a fatigue experiment of a gypsum-based mixture material under cyclic loading was carried out, and the fatigue characteristics at different stress levels were investigated and summarized. The experimental results show that the logarithmic number of cycles to failure exhibit linear variation, and the relationship between the resident strain and cyclic time can be approximated by an exponential function. The strain curve shows that there are obvious three-stage characteristics throughout the loading process and that each stage accounts for 10%, 85%, and 5% of the entire loading time, respectively. The dissipation energy varies over a small range, and its average value demonstrates exponential variation at different stress levels. The accumulated residual deformation due to unrecoverable damage pushes the hysteresis curve in the direction of deformation enlargement over the full cycle process. The evolution law of the fatigue damage curve is related to the inherent parameters of the material only, regardless of the stress conditions, exhibiting exponential nonlinear damage accumulation. This investigation provides an informative reference for the fatigue evaluation of similar materials in indoor experiments.

Repeated loading can produce serious hazards to concrete constructions. In this work, hysteresis and dynamic response characteristics of concrete subjected to repeated multilevel compressive loading are investigated through laboratory tests. The influence of maximum and minimum load levels on hysteresis time and dynamic response ratio (DRR) are studied based on the laboratory test results. It is concluded that the maximum load level has a more pronounced effect on DRR and hysteresis time than the minimum load level. During the first repeated loading stage, the hysteresis time linearly increases with the maximum load level, whereas DRR shows the opposite trend. The evolution of DRR and hysteresis time of lateral strain can be subdivided into four phases, which is consistent with the trend of P-wave speed and cumulative acoustic emission (AE) counts. Hysteresis time and DRR can be used as the damage variables during the compressive repeated loading.

Microbiologically induced calcite precipitation (MICP) is a biogeochemical process in which calcite is precipitated within the soil environment due to microorganism activity. Because soil properties are highly influenced by the microorganism population, soil properties can be improved by stimulating microorganisms in the soil with suitable materials. In this research, we investigated the abilities of six different carbon or nitrogen sources (treatments) to stimulate native urease-producing bacteria. Different amounts of yeast extract, sugarcane molasses, sodium acetate, and glucose were used to stimulate indigenous bacterial growth. After 7, 15, and 21 days of treatment, direct shear (DS), unconfined compressive strength (UCS), permeability test results, calcite content, and scanning electron microscopy (SEM) images obtained using an instrument equipped with an energy dispersive X-ray spectroscope (EDX) were used to analyze the samples. The results indicate that yeast extract had the greatest effect on improving soil properties by stimulating indigenous soil bacteria.

This paper discusses the pullout load-displacement behavior of hook end steel fibers having double, triple, and quadruple bends in their ends in geopolymers and cement mortars. Two types of geopolymer are considered, heat cured fly ash geopolymer (HGP) and ambient air cured fly ash/slag blended geopolymer (AGP). All mortars were prepared using the same water/cement and alkali activator/binder ratios in the case of ordinary portland cement (OPC) mortar and both geopolymer mortars, respectively. The embedment length of all three types of hook end steel fibers in all three types of mortar was also the same. The OPC mortar is considered the benchmark of pullout load-displacement behavior of steel fibers in geopolymers. The flexural load-deflection behavior of the three types of hook end steel fiber–reinforced geopolymers and OPC mortars is also studied to evaluate the effect of multiple bends in hook ends on flexural load and deflection capacity. Results show that the maximum pullout load and pullout displacement increases with increases in the number of bends of hook ends of the steel fibers in all three mortars. A similar trend is also observed in the case of energy absorbed (toughness) during the pullout of hook end steel fibers in mortars. The maximum pullout load of all three types of hook end steel fiber was higher in the HGP mortar than in the AGP and OPC mortars. However, the pullout toughness of all three types of hook end steel fiber was higher in the AGP mortar than in the HGP and OPC mortars. The observed pullout load-displacement behavior of the hook end steel fibers correlated well with the flexural load-deflection behavior of the hook end steel fiber–reinforced mortars of the aforementioned three types with higher flexural load of hook end steel fiber–reinforced HGP mortar than that of the AGP and OPC mortars.

Cold bitumen emulsion mixtures (CBEMs) are a promising substitute for hot mix asphalt (HMA) due to their low environmental impact, cost effectiveness, and low energy production costs. Nevertheless, conventional CBEM has some disadvantages, mainly related to the long curing time required to reach its full strength and its higher susceptibility to moisture. This paper reports the experimental test results of research that aimed to investigate and develop a new CBEM containing a waste biomass material, palm leaf ash (PLA), a waste material produced by burning palm leaves. The new CBEM was compared with a conventional cold mix (CCM) as a control. The tests to assess the mixtures’ mechanical properties were the Marshall test, indirect tensile strength, and wheel track test. Durability was evaluated by water sensitivity and aging tests. The results revealed noticeable improvements in the mechanical properties of the CBEMs comprising ordinary portland cement (OPC), and raised the possibility of replacing some of the OPC with PLA without compromising said improvements. Results have shown that the new CBEMs with PLA achieved outstanding results in comparison with traditional CBEM, with and without the addition of OPC. There was also a significant improvement in water sensitivity when using PLA. This paper therefore opens the door for the development of new CBEMs that have outstanding mechanical characteristics when made with biomass ash materials.

Recycled concrete aggregate (RCA) is a high-quality substitute for virgin aggregate as base or subgrade material in pavement construction. However, heavy metal leaching and/or production of high pH leachate are environmental risks commonly associated with the use of RCA. To characterize changes in physical and chemical properties after use, RCA base course and subgrade soil samples were recovered from the Minnesota road research (MnROAD) field site after eight years and compared to the original RCA physical and chemical characteristics. RCA samples were analyzed to determine their mineralogy, carbonate content, acid neutralization capacity (ANC), material pH, and trace element leaching potential. ANC was higher in the recovered RCA and higher for the fine-grained RCA particles than the coarse particles, which was confirmed by extensive carbonation of the fines fractions during field deployment. Material pH of RCA and subgrade soil samples were significantly higher than leachate pH measured in previous and current field investigations of this site, suggesting that conventional laboratory techniques do not represent field conditions and should be modified to better represent field conditions.

Dispersivity and swelling induced by the formation of expansive minerals are deleterious phenomena that can be observed in natural and treated soils. The former is common among sodium-rich soils that are characterized by the deflocculation of the soil’s particles in contact with water. The latter happens due to the growth and hydration of calcium sulfoaluminate minerals as expected in sulfate-rich soils treated with calcium-based stabilizers. The present study assesses the behavior of the Paraguayan sulfate-rich, dispersive as well as expansive, clayey soil after lime stabilization based on an extensive experimental work, which includes unconfined compression, pulse velocity, durability, and free swell tests. This work was designed employing a fractional factorial design in the selection of the experimental runs that enabled statistical evaluation of the influence of the dry unit weight, lime and fly ash content, curing period, mellowing process, and molding moisture content. Results showed that the addition of fly ash, followed by the dry unit weight, were the most influential factors regarding the treated soil’s response in performed tests. In addition, mellowing proved to be essential in reducing the volumetric variation verified in the swelling tests. Also, scanning electron microscopy analysis revealed that ettringite formation was less pronounced when fly ash was added.

The primary goal of this study is to assess the characteristics of coal ash–based controlled low-strength material (CLSM) mixtures made with a cementless binder for the feasible usage as a thermal grout in borehole heat exchangers. In the experimental program, a group of CLSM mixtures made with cement or cementless binder through various ratios of water to binder ($\mathrm{W}:\mathrm{B}$) and water to solid ($\mathrm{W}:\mathrm{S}$). The general properties (e.g., fresh density, flowability, initial setting time, bleeding, unconfined compressive strength, and microstructural analysis), and environmental impacts (e.g., corrosivity and heavy metals) were carried out on CLSM mixtures. Afterward, thermal conductivity was determined following a current specification for verification of the proposed CLSM, which is feasibly used as a thermal grout in geothermal systems (borehole heat exchangers). According to the results, all of the engineering properties and environmental impacts satisfied the specifications of CLSM. In addition, compared with the thermal conductivity values of conventional grouts, those of the proposed CLSM mixtures were higher. In conclusion, owing to good flowability and higher thermal conductivity than conventional grouts, the CLSMs made with cementless binder can be feasibly employed as a thermal grout for borehole heat exchangers.

Durability is a major concern with concrete structures. The ion transport properties of concrete cover can greatly influence the durability of concrete structures since most of the deterioration starts from the surface. The study described here focused on improvement of the durability of conventional concrete (CC) by covering it with nanosilica-modified mortar cover (NMMC). NMMC was designed according to the Dinger-Funk particle-packing model. The results revealed that mortar with low porosity and high strength could be produced by utilizing this particle-packing model, and that the durability of CC could be greatly improved when it was covered with NMMC: the chloride diffusion coefficient decreased by 95.12% and the Coulomb electric flux decreased by 97.02%. The NMMC also increased the freeze-thaw resistance of CC: the mass loss of CC+NMMC was only 1.72% after 300 rapid freeze-thaw cycles. Further, NMMC can significantly improve the carbonation resistance of CC. Almost no carbonation was observed after CC+NMMC was put into a chamber for carbonation for 28 days. The NMMC and CC had comparable drying shrinkage. Through fluidity adjustment and roughing of the NMMC surface, the bonding strength between NMMC and CC reached 5.4 MPa. Scanning electron micrography (SEM) showed a compact bonding between NMMC and CC.

The experimental and theoretical potential of using calcined waste eggshells (CWEs) to remove sulfate from sulfate-laden concrete mixing water was investigated in this work. Waste eggshells were first calcined at 800°C and batch-reacted with sodium sulfate solutions. Laboratory experiments elucidated the effect of initial sulfate concentration, temperature of reaction, and CWE particle size on total sulfate removal. Experimental results indicate a maximum sulfate removal of $29.5\%\pm 2.2\%$ via calcium sulfate mineral precipitation in laboratory batch reactions. To quantify the maximum sulfate removal potential of CWEs, batch reactions were simulated using PHREEQC, a geochemical code. After validating the simulation approach with experimental data obtained herein, PHREEQC was used to investigate the maximum sulfate removed as a function of CWE addition ($\mathrm{g}/\mathrm{L}$). Results indicate that sulfate-laden waters ($\le \mathrm{4,000}\mathrm{ppm}$) can be decreased to $\le \mathrm{3,000}\mathrm{ppm}$ with CWE additions of $\ge 3\mathrm{g}/\mathrm{L}$ in order to comply with the standard specification for maximum allowable sulfates in water intended for use in the production of hydraulic cement concrete.

In this work, the reliability of the vertical vibration testing method (VVTM) is verified using laboratory and field tests. Then, the VVTM, Marshall compaction method (MCM), and modified Marshall compaction method (MMCM) are used to investigate the effects of different compaction methods on the physical and mechanical properties of asphalt mixtures. The results show that the VVTM has the least influence on the aggregate gradation of an asphalt mixture, and the specimens produced using VVTM have the best test accuracy when compared with the field cores. When the density of the asphalt mixture remains fixed, the average mechanical properties, e.g., Marshall stability, compressive strength, splitting strength, and shear strength, of the VVTM specimens are increased by at least 21% compared with those of the MCM specimens. Moreover, the mechanical properties of the mixtures increased by at least 13.2% when the mixture density increases by 1.8%. The results also show that the mechanical strength (Marshall stability, compressive strength, splitting strength, and shear strength) of the asphalt mixture is related to the mixture density and compaction method, whereas the optimal asphalt-aggregate ratio is only related to the mixture density. Moreover, the optimal asphalt-aggregate ratios of the VVTM and MMCM specimens are decreased by approximately 0.3% compared with those of the MCM specimens.

Sulfate heaving often occurs when soils rich with sulfates are treated with calcium-based stabilizers such as lime and cement materials. This heaving has inflicted severe distress on several transportation infrastructure types including highways, runways, tunnel liners, dwellings, and other structures. Soil and environmental factors can influence the sulfate-heaving phenomenon in soils. This paper summarizes lessons learned from sulfate-heaving problems documented in the United States. It includes a summary of the various test methods used to quantify sulfate amounts and different treatment methods applied to sulfate soils to mitigate sulfate-induced heaving distress. In an experimental study documented in this paper, percentage changes in sulfates and reactive alumina before and after treating soils with lime and cement additives are analyzed to explain their contributions to ettringite mineral formation and related soil heaving. A method using reactive alumina and soluble sulfate measurements in effective screening of stabilizer treatments for sulfate rich soils is presented. An unmanned aerial inspection was carried out to inspect the heaving distress on a pavement section built over high-sulfate soils in Texas. This study showed an effective combined lime and fly ash treatment of high-sulfate soils with an extended mellowing period. Updates from ongoing and recently completed investigations of sulfate-heaving mitigation and their salient findings are discussed and presented.

Most of the aggregates in construction material come nowadays from the quarrying of natural resources, and their consumption tends to rise. The aim of this study was to evaluate the total substitution of traditional natural coarse aggregates with alternative, renewable resources, such as mollusk shell waste from the aquaculture industry, to manufacture a recycled porous concrete and its possible use in sound-absorbing barriers for road traffic. Two different shells, separately or as a mix, were used in this research work: Peruvian scallop and Mediterranean mussel. In addition, two different particle size distributions, smaller than 2 mm and between 2 and 7 mm, were used. Acoustic absorption, open porosity, density, mechanical resistance to compression and bending, and resistance to freeze-thaw cycles, along with leaching properties, were studied. The results revealed that specimens formed using any kind of mollusk shell waste with a particle size between 2 and 7 mm exhibited a 40% increase weighted acoustic absorption coefficient over porous concrete specimens made with river gravel. For particles of the same size, the acoustic absorption assessment index showed absorption over 4 dB in 12-cm thickness. In addition, the mechanical properties analyzed showed better values in all specimens made with shell waste than in conventional porous concrete specimens. In the specimens manufactured of mollusk shell waste with a particle size between 2 and 7 mm, compression strength was twice that of conventional porous concrete.

In this study, acoustic emission (AE) analysis was employed to characterize the cracking behavior of various engineered cementitious composites (ECCs) containing different types of fibers. AE monitoring of prism samples cast with these ECCs was conducted in conjunction with four-point flexural tests. An additional conventional concrete (CC) mixture containing coarse aggregates was also examined for the aim of comparison. A number of AE parameters were collected during testing such as signal amplitude, signal strength, and number of hits. Moreover, b-value and intensity analyses were performed on the signal amplitude and signal strength data, respectively. These further analyses yielded three additional parameters including b-value, historic index [$H(t)$], and severity ($S_r$). The analysis of these AE parameters was found to be feasible in detecting the onset of micro and macrocracking stages in all ECCs with any fiber type. No significant variations in terms of the studied AE parameters were found between CC and ECCs at the microcracking stage. However, at the macrocracking and failure stages, the average number of hits, CSS, $H(t)$, and $S_r$ were higher, and the b-value was lower in ECCs compared with CC due to the increased number of cracks in ECCs at these stages. The results of this investigation also presented a developed damage characterization chart for all tested ECCs. This chart can successfully be used to identify the micro and macrocracking stages in ECCs based on the corresponding values of the AE intensity analysis parameters [$H(t)$ and $S_r$].

In the field, the workability and compactability of asphalt mixtures are essential to obtain the desired smoothness and sufficient density of a compacted pavement, especially for the asphalt mixtures prepared at low temperatures. This is mainly because the handling of the asphalt mixture, at a given temperature, is greatly influenced by the viscosity of the asphalt binder. This study evaluated the workability, coatability, and compactability of warm-mix asphalt (WMA) mixtures prepared using foamed asphalt binders incorporating ethanol and sodium bicarbonate (${\mathrm{NaHCO}}_3$) as foaming agents. The service characteristics of foamed asphalt mixtures that were prepared at 80°C and 100°C were compared with those of the control hot-mix asphalt (HMA). PG 58-28 asphalt binder and aggregates from local sources were selected. The control HMA samples were prepared at 155°C and 100°C for the workability and coatability tests and compacted at 145°C and 100°C for the evaluation of the compactability characteristics. It was found that the application of ethanol as a foaming agent has a high potential for improving the mixture coatability, workability, and compactability at low production temperatures. However, the combination of ${\mathrm{NaHCO}}_3$ with 1% ethanol was optimum for these foamed WMA mixtures to maintain the coatability and workability of foamed WMA mixtures. Future work using an antistripping additive (nanohydrated lime) is highly recommended to improve the adhesive and cohesive characteristics and to enhance the moisture-damage resistance of foamed WMA mixtures.

This paper develops a highly efficient numerical method for estimating the chloride diffusivity of mature cement paste. In the method, the two-dimensional microstructure of cement paste is reconstructed through computer simulation. Each unhydrated cement core and the surrounding inner and outer hydration products are incorporated into an equivalent hydration cement particle (EHCP), and the chloride diffusivity is derived analytically. Based on the first-passage-time equation, an efficient two-dimensional random walk simulation is conducted to estimate the chloride diffusivity of cement paste. It is found from the numerical results that the degree of cement hydration, the capillary porosity, and the chloride diffusivity evaluated from two-dimensional simulation are in excellent agreement with those evaluated from a three-dimensional one but at tremendously reduced computational time, which makes it possible for the method to be implemented on a regular computer. It is also found from the numerical results that, with the proposed EHCP model, the computational time for two-dimensional simulation is further reduced by a factor of about 2. Finally, through comparison with the experimental results obtained in this paper and collected from the literature, the validity of the numerical method is verified.

This paper presents a methodology to obtain creep and recovery response of asphalt binders merely by using frequency sweep tests, which are relatively easier to conduct. This proposed methodology would be useful for practitioners and researchers in modeling time-dependent rutting performance of asphalt binders using simple linear viscoelastic measurements obtained from dynamic shear rheometer (DSR). Frequency sweep tests were conducted on four different asphalt binders at temperatures ranging from 10°C to 70°C. Complex modulus master curves were constructed for 40°C, 50°C, and 60°C followed by presmoothing using a power law and modeling using a Prony series. The estimated complex modulus, which is in frequency domain, was translated into the relaxation modulus, a time domain entity. The relaxation modulus was converted to creep compliance using Laplace transform. The resultant creep compliance was modeled using a generalized Burgers model (GBM), which was used for predicting creep and recovery response of asphalt binders for different loading and unloading periods. The predicted creep and recovery profiles were successfully validated with the multiple stress creep and recovery (MSCR) measurements obtained at 40°C, 50°C, and 60°C for all binders.

The use of cement as curing agent to increase the strength of soft ground and reduce the deformation of soft soils has been widely adopted in soft soil engineering. The cemented soil is eventually exposed to the air, and becomes unsaturated in natural environments. This paper presents experimental studies, including suction control using a vapor equilibrium technique, unconfined compression strength tests, scanning electron microscope analysis, and mercury intrusion porosimetry tests, to investigate the influence of suction, cement content, and dry density on the strength and microstructure of unsaturated cemented soils. The experimental results show that unconfined compressive strength increases with increases in suction at the same dry density and the same cement content. The results also indicate that unconfined compressive strength decreases with decreases in dry density at the same cement content and the same suction. The microstructure study shows that, although strength increases with an increase in cement content, the hydration products of cement are seldom observed under high suction. The distribution of internal pores (micropores) in samples with different dry densities is almost the same, but distinct differences in the distribution of pores in aggregates (macropores) are observed.

Applying glass aggregate in asphalt mixtures is an effective approach to addressing environmental pollution. In this research, epoxy asphalt was adopted instead of conventional asphalt. The experiments were performed to investigate the influence of glass aggregate on the performance of the epoxy–asphalt mixture compared with styrene-butadiene-styrene (SBS) copolymer modified asphalt. The results show that for the two asphalt mixtures, the optimum binder content, void, and density decrease with increases in glass aggregate content. The Marshall stability, soaked Marshall stability, tensile strength ratio, antirutting, and low-temperature property of the epoxy–asphalt mixture are slightly affected by the glass aggregate content, significantly different from those of the SBS-modified asphalt mixture. In addition, the epoxy–asphalt mixture blended with glass aggregate possesses good antifriction and reflective properties. Thus, in the epoxy–asphalt mixture, the high content of glass aggregate can be utilized to attain superior performance without an antistripping agent and mitigate increasing environmental pollution.

Detection of degradation has the potential to improve the long-term performance and integrity of concrete structures and pavements. Conductive surface sensors, specifically conductive paints, have been shown to be effective and adaptable when used as part of crack detection systems. The impact of environmental effects on conductive surface sensors must be known if these sensors will be used on structures or pavements exposed to environmental changes. This paper presents two experiments used to evaluate the effects of temperature and relative humidity on the behavior of a silver-based conductive paint and a more economical nickel-based conductive paint. Environmental effects on sensitivity to cracking and resistance were evaluated. A third experiment is presented that considered different patterns of conductive paint for use in crack localization applications. The results showed that the nickel-based and silver-based conductive paints perform comparably at detecting cracking and can be used over a range of temperature and relative humidity conditions. The patterns evaluated were shown to be effective at localizing cracking over an area, which is promising for application of this technology.

Water greatly affects the mechanical properties of cement bitumen emulsion mixture (CBEM). Its content is usually determined by the minimum voids content of CBEM. However, its effect on the mechanical properties of CBEM has not gained much attention. The effect of water content on volumetric and mechanical properties of CBEM was thoroughly studied to determine a more suitable water content for better mechanical properties. The voids content, indirect tensile strength (ITS), failure tensile strain, stiffness modulus, and critical strain energy density (CSED) of CBEM with different cement contents were investigated. Results indicate that the maximum strength of CBEM does not appear at the water content of the minimum voids content. The water content of CBEM with maximum strength is much lower than that of CBEM with minimum voids content. This is because the strength of CBEM highly depends on the microstructure of hardened cement bitumen emulsion binder. Low water content can help to form a dense microstructure and continual bitumen membrane in cement bitumen emulsion binder, which is beneficial to the strength of CBEM. The mechanical properties of CBEM in both conditions of minimum voids content and maximum strength were compared. CBEM has the maximum ITS and CSED and relatively high failure strain and stiffness modulus in the condition of maximum ITS, the cracking resistance of which can be better than that in the condition of minimum voids content. It is recommended that the optimum water content of CBEM should be determined by the maximum ITS in the mix design.

As the basic chemical components of asphalt binders, the fractions of saturates, aromatics, resins, and asphaltenes (SARA) have crucial effects on the rheological properties of such binders. Thus, two kinds of neat asphalt binders and derived binders with different SARA proportions were studied in this paper. The dynamic rheological properties of two kinds of neat asphalt and the derived binders were tested by frequency sweep tests. Their static rheological properties were tested by creep and stress relaxation tests. The effect of SARA on dynamic modulus, phase angle, creep compliance, and relaxation modulus were analyzed. The results showed that the dynamic modulus increases with increases in asphaltenes or resins content and decreases with increases in saturates or aromatics content. Saturates have the greatest effect on dynamic rheology properties. Shape index $R$ shows a decreasing trend with increases in asphaltenes or resins content and an increasing trend with increases in saturates or aromatics content. Creep compliance and residual relaxation modulus decrease with increases in asphaltenes or resins content and increase with increases in saturates or aromatics content. SARA fractions have important effects on the rheological properties of asphalt binders.

Asphalt binders and concretes modified with polyacrylonitrile (PAN) fiber, styrene butadiene styrene (SBS), and the combination of PAN-SBS were prepared and studied. Both frequency and temperature sweep tests for the binder dynamic shear modulus G*, rutting, and fatigue parameters were carried out. Multiple stress creep recovery (MSCR) test was also conducted on the various modified asphalt binders. The complex modulus E* and flow number (FN) of asphalt concretes (AC) from the modified binders were also examined using asphalt mixture performance tester (AMPT) test. The PAN fiber asphalt binder showed better response in terms of dynamic modulus, fatigue and rutting parameter, nonrecoverable creep compliance and percent strain recovery at 1% fiber content. The hybrid binder ($1\%\mathrm{PAN}+1\%\mathrm{SBS}$) demonstrated overall shear modulus almost twice that exhibited by 2%SBS binder. The hybrid asphalt binder showed the greatest potential for rut resistance, over most of the frequency range, relative to all other binders. It was clear that the combined form of the polymer and the fiber modification has greater rutting resistance potential than the single modification approach generally practiced. The hybrid asphalt binder also showed better fatigue parameter than all the binders within pavement design load frequency range. Results from the AC mix tests verified most of the trends observed from the asphalt binder tests.

Typically, aggregates used for asphalt mixtures consist mainly of natural aggregates such as crushed rock and gravel. Sometimes the natural aggregates are substituted with limited amounts of industrial by-products, such as Reclaimed Asphalt (RA), slag, and waste foundry sand (WFS). Given the importance of overcoming the challenges associated with the management of nonrenewable resources, and to solve the industrial waste stream problems, this article presents the results of fundamental research conducted to assess the rutting and fatigue cracking performance of hot asphalt mixtures with high percentages of by-product aggregates. For this purpose, two full-scale flexible pavement test sections were constructed and tested at the accelerated loading facilities at VTI (Swedish National Road and Transport Research Institute). The accelerated test aimed at evaluating the performance of two developed asphalt mixtures, designated as mix 1 and mix 7, and made up of 98% of industrial by-products (namely, steel slag, WFS, and reclaimed asphalt pavement, in addition to biobased additives). The test sections were constructed in an indoor facility and loaded with a heavy vehicle simulator (HVS) equipped with a half-standard truck axle with dual wheels. The two road sections were constructed using the same construction materials obtained from the same source, as follows: asphalt surface layer of 50-mm thick, 70-mm thick granular base layer, and 160-mm thick subbase layer on top of a 2.6-m thick sandy subgrade soil. Horizontal asphalt strain sensors were embedded in the pavement test sections to assess the mixture’s resistance to fatigue and cracking and the laser surface profiler measurements were used to evaluate the rutting performance under controlled testing conditions. For comparison purposes, the long-term rutting developed in the sections paved with mix 1 and mix 7 was compared to the rutting observed in a previous similar HVS test carried out on a 70-mm thick asphalt surface layer section made only with natural virgin aggregates. The test results showed that mix 1 and mix 7 may suffer from higher rutting at the beginning when the road is open to traffic, as compared to asphalt mixtures of natural aggregate, but subsequently the alternative mixtures resisted the rutting development better with the increase of traffic loading as compared to the conventional asphalt mixtures. The horizontal strain measurements at the bottom of the asphalt layer during testing showed that failure began as cracks initiated at the bottom of the asphalt layer of mix 7 and started to propagate to the surface of the asphalt layer in the last stage of the HVS traffic loading of the test. No fatigue cracking was observed in the asphalt surface paved with mix 1 at the end of heavy vehicle simulation (HVS) testing. The study demonstrated that the adopted by-product hot mix asphalt (HMA) mixtures can substitute the conventional HMA material under the given heavy traffic loading and environmental conditions.

The main goal of this paper is to establish an appropriate fractional derivative model with fewer parameters that can model all the viscoelastic characteristics of asphalt binders. Based on this, the fractional derivative model elements and combination types were selected by analyzing the dynamic viscoelastic data. The model consists of two Abel dashpots in series with a Maxwell element (the model is a fractional derivative model composed of four elements in series, called the FDM-4 model). It was validated by describing both the dynamic and static viscoelastic properties of asphalt binders and by comparison with classical viscoelastic models. The advantages and disadvantages of the models were analyzed. Finally, the fractional derivative model was applied to describe the viscoelastic characteristics of asphalt mastics, and it was proved that the model could well describe the viscoelastic characteristics of asphalt mastics. The results indicate that the elements (an elastic spring and Abel dashpot) connected in series with a linear dashpot are better than those connected in parallel from the perspective of model fitting precision. Increasing the number of Abel dashpots in series in the FDM-4 model has little effect on the fitting results. The FDM-4 model can accurately describe the dynamic viscoelastic behavior, static creep, and relaxation characteristics of asphalt binders and asphalt mastics.

In recent years, considerable attention has been given to the development of special cements capable of reducing ${\mathrm{CO}}_2$ emissions as well as energy and limestone consumption. One option is the use of supersulfated cements (SSCs). SSCs are primarily comprised of blast-furnace slag (80%–85%), calcium sulfate (10%–15%), and an alkaline activator, which is often portland cement, though in a relatively small quantity (around 5%). In this paper, the effects of the proportions of SSC (slag, calcium sulfate, and alkali activator contents) were studied for two slags with different chemical compositions, mainly the ${\mathrm{Al}}_2{\mathrm{O}}_3$ content. The results showed the slag characteristics and the alkaline activator content played a very important role in the process of hydration. The SSC made using high-alumina slag exhibited higher compressive strength (55 MPa at 28 days with 88% slag) and the use of higher activator contents decreased the compressive strength, heat release, ettringite formation, and degree of hydration.

The composite dielectric model of asphalt mixtures is crucial to the use of the ground-penetrating radar (GPR) for detecting compaction, asphalt content, and other quality-related indexes of asphalt pavements. In this study, the interface transition zone between asphalt and mineral aggregate, as well as the mineral aggregate gradation, are considered based on analyses of the microstructure of the asphalt mixture. The effective medium theory and composite-sphere assemblage method are then combined to develop a microstructure-based physical model of asphalt mixtures. A polarizability equation is formulated for a single-mineral aggregate particle with independent interface behavior in which size effects of the particles are introduced. Based on the physical model of the asphalt mixture and the polarizability equation of the single-mineral aggregate particle, composite dielectric models of the asphalt–mineral skeleton structure (AMSS) and asphalt mixtures considering mineral aggregate gradations are generated. Tests and analyses show that the interface effect has a crucial influence on the polarization of the fine aggregate and filler of the mineral aggregate, which causes increasing polarizability in the fine aggregate and filler, as well as corresponding increases in the effective permittivity of the asphalt mixtures. Compared with classic models, the developed composite dielectric model of asphalt mixtures has higher calculation accuracy, with the prediction results more closely matching the test results of asphalt mixtures.

Polycarboxylate (PCE) superplasticizers greatly affect the rheological properties of cementitious materials. Yet, the systematical influence of the PCE structure parameter on the rheological properties of cement paste is not so clear. The authors investigated the effect of backbone methyl group content (backbone stiffness) of PCE samples on the yield stress, residual viscosity, and apparent viscosity of cement pastes at varied water-to-cement ratios ($\mathrm{w}:\mathrm{c}$ ratios). An obvious difference was observed at low $\mathrm{w}:\mathrm{c}$ ratio, which relied on the particle separation distance $H$. The solution viscosity affected the apparent viscosity through the contribution to plastic viscosity at low $\mathrm{w}:\mathrm{c}$ ratio. At high $\mathrm{w}:\mathrm{c}$ ratio, the difference between PCE samples was small at consistent fluidity of cement paste due to consistent packing density and $H$. At low $\mathrm{w}:\mathrm{c}$ ratio, large amount of PCE molecules remained unadsorbed. The value of $H$ approached its largest value and the apparent viscosity of cement pastes depended on the balance effect of $H$ and viscosity of the continuous phase. Due to the high backbone stiffness, PCE of high backbone methyl group content exhibited high adsorption affinity and high solution viscosity, yet a small size of a single molecule after adsorption. At low $\mathrm{w}:\mathrm{c}$ ratio, $H$ was small and the solution viscosity was high. The apparent viscosity of cement paste was therefore high.

This study is centered on the use of ground bagasse ash (GBA) and recycled concrete aggregate (R-CA) as raw materials to produce ecofriendly high-strength concrete (HS-C) with high durability. Specifically, GBA with high fineness was used as a replacement for cement up to 50%wt of the binder, and R-CA was used as a coarse aggregate to produce HS-C. The study involved investigating the water permeability and expansion due to the ${\mathrm{Na}}_2{\mathrm{SO}}_4$ solution present in the HS-C. The results revealed that R-CA had a clear negative influence on the durability of concrete. However, the expansion and the water permeability of recycled aggregate concrete (RAC) reduced when GBA up to 50%wt of cement was introduced as a replacement, and the values were lower than that of the conventional high-strength concrete (CT). Furthermore, the increase in the compressive strength of concrete resulted from the low incidence of capillary pores and pore connectivity in the cement paste, which was due to the filler effect of pozzolanic or hydration products, had significantly affected the reduction in water permeability, whereas the expansion of concrete was not significantly affected.

The strain-softening response and failure of oriented strand boards (OSBs) were investigated both experimentally and numerically. Standard tests were used to characterize the elastic (modulus of elasticity) as well as damage properties (damage height, damage initiation strain, and fracture energy) of OSBs in two principal (parallel and perpendicular) directions. Experimental data were then used in conjunction with a recently developed physically based damage model to simulate the nonlinear response of notched OSB samples under tension using the finite-element (FE) method. Acceptable agreement between the FE simulations and experimental data was found. The results suggest that a strain-softening approach is capable of accurately modeling the damage progression in notched OSB samples.