Journal of Materials in Civil Engineering

Self-healing can be defined as the ability of a material to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on optimized mix composition, or autonomous, when using additionally incorporated capsules containing a healing agent and/or bacteria spores. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria released into the crack from a broken capsule or activated through access of water and oxygen. The critical reviewing of both methods indicates that the autogenous self-healing is more efficient, more cost effective, safer, and easier to implement in full-scale applications. Nevertheless, a better understanding of the mechanism and factors affecting the effectiveness of the process is needed. The main weaknesses of the autonomous method were identified as loss of workability, worsened mechanical properties, low efficiency and low probability of the healing to occur, low survivability of the capsules and bacteria in harsh concrete environment, very high price, and lack of full-scale evaluation.

Properties of concrete are, to a large extent, dependent on the properties of its binding constituent, hydrated cement paste. Therefore, knowledge of properties of hydrated cement paste is crucial for predicting concrete behavior. This paper presents an experimentally informed approach for modeling elastic and transport properties of cement paste. The models used realistic microstructural information—obtained by X-ray computed tomography—as input for property determination. The properties were then determined using discrete numerical models, namely, models based on a lattice approach. Modeling results were compared with literature data, showing excellent correlations. Furthermore, dependence of properties of cement paste on the total porosity, based on the modeling results, was explored. Finally, a correlation between elastic and transport properties for the explored range of portland cement pastes was established. It is seen that the models can be used for property prediction, but also for exploring correlations between different parameters.

Research has shown that polyolefin fiber–reinforced concrete (PFRC) can meet the requirements of standards in terms of the contributions of fiber in structural design. Such results were obtained with fibers embedded in high-performance concrete matrixes. Given that the precracking maximum strength is mainly governed by the matrix properties, a moderate-strength concrete matrix could lead to a reduction in the initial drop of strength after the limit of proportionality. Nevertheless, it was necessary to determine whether residual postcracking behavior would be similar in a poorer matrix. In this study, a moderate-strength concrete matrix with two dosages of polyolefin fibers was produced. The flexural tensile tests showed that it maintained its residual strength and reduced brittleness. All the concrete types tested met the requirements provided in the relevant standards. The study also provides a large comparison with residual strengths found in the literature showing that the contributions of polyolefin fibers were analogous to those cases in which the fibers were embedded in high-performance concrete matrixes. Hence, PFRC is well suited for use in constructive elements designed with low requirements in terms of concrete matrix properties.

The outstanding mechanical and bond strength properties of ultrahigh-performance concrete (UHPC), as well as its long-term durability, make it a suitable material to be used in connections of accelerated bridge construction (ABC). However, the long-term performance and durability of these connections depends on the interface performance between UHPC and prefabricated bridge elements. If debonding failure develops along the interface, the load transfer and durability of these connections may be compromised. This study examined the bond performance between high-strength concrete (HSC) and UHPC under direct tension stress states at different ages and using different surface preparations. The results from this study determined that a sufficient bond strength of UHPC could be assessed even at early ages when good surface preparation was utilized. Furthermore, the properties of the aggregate played a vital role in the interface bond strength. The bond versus slip was investigated at different ages and can be used in future analytical studies to obtain more accurate modeling of HSC–UHPC interfaces.

To identify the key influencing factors and optimal healing conditions for the self-healing ability of bituminous binders, a fatigue-healing-fatigue test was performed under different conditions by the time-sweep mode of a dynamic shear rheometer (DSR). The influence and significance of five factors on healing index were analyzed through a gray correlation analysis. The healing temperature had the most significant correlation with the healing index. In addition, bitumen type, strain size, and degree of damage exhibit significant correlation with the healing index. The effect of healing time is insignificant. This study investigates the flow characteristics of bitumen binder using the viscosity frequency sweep mode of DSR to determine the potential optimal healing temperature. Then, 1stOpt software was used to establish a healing index prediction model to determine the optimal healing time. The optimum healing temperature of #70 matrix bitumen is 47.6°C, slightly higher than the softening point, and the optimum healing time is 48.1 min. The optimum healing temperature of styrene-butadiene-styrene (SBS)–modified bitumen is 76.7°C, slightly lower than the softening point, and the optimum healing time is 30.8 min.

Due to the ever-dwindling level of natural aggregate/asphalt resources and shrinking budgets for infrastructure assets management, engineers have been striving to incorporate more and more recycled asphalt pavement (RAP) materials into pavement maintenance and rehabilitation activities. One critical issue with using RAP is characterizing the actual dispersion characteristics of RAP in the mixture. This study addresses this issue through image analysis and a series of mixture performance tests, including the Marshall stability test, volumetric property test, wheel tracking test, three-point bending test, and freeze-thaw splitting test. The results showed that scanned images of asphalt mixture slices were effective in identifying the dispersion characteristics of the RAP in the mixture. An aggregate five pixels and an aggregate centroid distance of 55 pixels were proposed as the threshold for RAP dispersion, and the dispersion ratio was employed to evaluate the RAP dispersion characteristics of a mixture. With the extension of mixing time, the Marshall stability of the mixture increased but the air voids decreased, which then caused a decrease in the optimum asphalt content of the mixture. In addition, the rutting resistance and cracking resistance of the mixture were significantly improved, whereas the moisture susceptibility was slightly enhanced.

Most recent research has focused on the mechanical strength and durability of geopolymer concrete with heat activation (at different temperatures) and has indicated a limitation for its application in precast industries only. This limitation can be overcome by changing when the ingredients for geopolymer concrete are mixed so that curing can be made at ambient temperature. With this process modification (heat activation of fly ash and alkaline fluid), the modified geopolymer concrete shows a significant enhancement in mechanical strength (compressive, split tensile, flexural, and bond strength) and durability (water absorption, acid attack resistance, and rapid chloride permeability test) compared with conventional geopolymer concrete (heat activation after casting) and the control concrete. The microstructural properties analyzed through a field emission scanning electron microscope (FESEM) with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques show a better interaction of fly ash and activator solution at early ages for such process-modified geopolymer concrete. This accelerates the formation of a crystalline phase from the amorphous phase of fly ash.

The purpose of this study is to understand the complex mechanisms through which the active ingredients of crystalline waterproofing agents change the microstructure of cement-based materials. Microstructural and phase characterization are carried out on cement pastes modified with waterproofing agents through thermogravimetric analysis, scanning electron microscope with energy-dispersive x-ray spectroscopy, and x-ray microcomputed tomography. Two types are investigated—one that is applied onto the surface of existing concrete and another that is incorporated as an admixture into the fresh mix. Samples treated with the waterproofing agents are compared with a sample cured in sodium carbonate solution, one of the key active ingredients. Results indicate that both types of waterproofing agents lead to formation of calcium carbonate. The surface treatment type forms a dense coating, with little penetration into the matrix, whereas the admixture type leads to a measurable decrease in porosity throughout. The sample cured in sodium carbonate solution leads to an increase in porosity due to decalcification shrinkage, which underscores the importance of controlling sodium carbonate content to avoid excessive carbonation.

The bond performance of reinforcing bars to concrete, an indispensable factor in designing reinforced concrete structures, is deeply influenced by the stress states of surrounding concrete. In recent decades, although self-compacting lightweight aggregate concrete (SCLC) has gained popularity in architectural engineering, the bond stress-slip relationship of deformed bars in SCLC under lateral tension remains unknown. In this study, 179 pullout tests were performed to examine the local bond stress-slip behavior of deformed bars in SCLC. In addition, the effects of various parameters on the ultimate bond strength and the slip at the ultimate bond stress, as well as the residual bond strength, were analyzed quantitatively. The results showed that both the bond strength and slip at the ultimate stress decrease with the increase of lateral tension regardless of whether it is in pull-out or splitting failure mode. In addition, an empirical formula was proposed that gives a reasonable prediction of the measured bond stress-slip curve of the SCLC.

A material selected for pavement base layers must possess the structural capacity to withstand stresses and strains caused by vehicle loading and environmental factors. Self-consolidating base material (SCBM) is a variant of controlled low-strength material (CLSM), and it typically uses fine aggregate, pozzolanic material, portland cement, and water. This paper presents findings from research that evaluated mechanical properties and constructability of SCBM and how the addition of steel fiber reinforcement can influence them. The experimental plan included mixes containing no steel fiber (control mix), three steel fiber contents, and two fine aggregate types. The material properties and constructability were assessed based on flowability, compressive strength, indirect tensile strength, and shrinkage. The results show that the addition of steel fiber enhances compressive and indirect tensile strength and reduces shrinkage while maintaining good constructability. Based on findings from the laboratory test program, SCBM was used to construct industry-scale outdoor test sections, and experience gained from the construction process is also discussed in this paper.

Thaumasite sulfate attack was studied on mortars containing portland-limestone cements and various supplementary cementing materials. The resistance of the mortar mixtures against deterioration was quantified by measuring expansion of mortar prisms for 2 years according to current Canadian standards. In order to characterize the products formed from thaumasite sulfate attack reactions in the mortar samples, differential scanning calorimetry (DSC) was employed, and the observations were verified using X-ray diffraction. It was observed that, for the studied mortar samples exposed to thaumasite sulfate attack, thaumasite could be identified using DSC due to its distinct endothermic peak located between 110°C and 119°C. In addition, endothermic peak ranges for ettringite or calcium silicate hydrates and gypsum were found as 88°C–105°C and 120°C–134°C, respectively. DSC was found to be a reliable technique in studying concrete and mortar affected by thaumasite formation, which may be used as a replacement or complement for X-ray diffraction.

The functional performance of pervious concrete pavement surfaces (such as hydraulic, acoustic, and frictional performances) is greatly influenced by the properties of its internal pore structure (such as effective porosity, intrinsic permeability, tortuosity, and pore size distribution). Nondestructive evaluation (NDE) using X-ray computed tomography (CT) and digital image processing (DIP) involves the crucial step of image segmentation of grayscale histograms, which can significantly affect subsequent pore structure analysis and fluid flow simulations. This paper presents a new discharge-based segmentation algorithm capable of predicting non-Darcy permeability of pervious concrete mixtures. The algorithm uses X-ray CT image–based finite-volume permeability simulations to determine the specific discharge at various hydraulic gradients. Experimental results of a falling-head permeability test were used to calibrate and validate the developed finite-volume models. The permeability simulation results from the developed thresholding algorithm were compared against simulation results obtained from 10 different global thresholding algorithms. It was found from the analyses that the developed discharge-based thresholding algorithm predicts non-Darcy permeability characteristics and the effective porosity of the pervious concrete mixtures more accurately than other global thresholding algorithms.

As a new noncontact method for heating asphalt pavement, electromagnetic induction heating has great prospects for application in snow melting and heating-induced crack healing. In this research, different lengths (1, 3, 5, and 7 mm) and amounts (2%, 3%, and 4% by volume of asphalt) of steel fibers were added to the asphalt mixture to achieve the induction heating of the asphalt mixture. The induction heating rate of the steel fiber was tested. The induction heating rate, vertical heating and cooling rules, and the surface temperature uniformity of asphalt mixture samples with different fiber lengths and contents were then studied in detail. Finally, the heating-induced fatigue-damage healing characteristics of samples with different fiber lengths and contents were analyzed by conducting fatigue-healing cycles. The results show that as the fiber length increased, the heating rate of the fiber and asphalt mixture gradually increased, but the increment gradually decreased; as the fiber content increased, the induction heating rate significantly increased. During the induction heating process, a significant temperature gradient appeared in the vertical direction of samples, and the temperature gradient became more significant as the heating time extended. During the cooling stage, the temperature gradient gradually decreased, apart from a slight temperature rise at the middle and bottom of the samples. The fiber content and length had different effects on the heating and cooling processes. As the fiber length and content increased, the uniformity of the samples’ surface temperature deteriorated. In addition, fiber clusters on the surface of samples exacerbated the nonuniformity of the surface temperature. When the fiber length was 5 mm and the content was 4%, the healing effect was the best and the fatigue life recovery rate reached 70.77%. With the increase of fatigue-healing cycles, the healing rate of the samples decreased gradually. The healing rate of the sample with 3% fiber content was the slowest as the fatigue-healing cycles increased.

This paper presents an experimental investigation into the corrosion behaviors and mechanical properties of weathering steel (WS) in a marine atmosphere. Two types of WS (Q420qNH and Q420qNHY) were tested, and carbon steel (Q420q) was chosen as contrast. First, as a simulated marine atmosphere environment, the neutral salt-spray accelerated corrosion test was conducted to study the corrosion mechanism of WS. Corrosion characteristics including corrosion evolution with time and surface morphologies of corroded specimens were obtained and compared among three types of steel. Then, tensile testing on corroded specimens was carried out to investigate the mechanical property degradation of WS. The digital image correlation (DIC) method was used to obtain the full-field strain of corroded specimens during the experiment. The effect of corrosion damage on the mechanical properties of the steels is discussed. Finally, the degradation mechanism of mechanical properties resulting from the local corrosion was determined by analyzing the surface strain of corroded specimens. Results show that Q420qNHY steel with much higher corrosion resistance was more applicable to the marine atmosphere because of the formation of a compact rust layer on the steel substrate surface. The corrosion morphology characteristics of three types of steel were different at the same corrosion time. Q420qNH and Q420qNHY steels presented a similar degradation degree of mechanical properties after corrosion, which was less than that of Q420q steel. However, according to the analysis on degradation of elongation, Q420qNH steel is not applicable to the marine atmosphere. The local corrosion accelerated the development of strain at the fracture section, which eventually resulted in the reduction of elongation with increasing corrosion degree. The different corrosion behaviors and mechanical properties of steels would significantly affect the service performance and life of bridges and should be considered during bridge design.

The use of soil stabilization in place of cutting out and replacing the existing subgrade soil can save significant amounts of resources in roadway construction projects. Also, the possibility of stabilizing a low-grade soil using by-products is economically and environmentally attractive. Considering that, the main objective of this study is to show the technical feasibility of using desulfurization steel slag from the Kambara reactor process (KR slag) as a soil stabilizer. A total of nine soil mixes were evaluated in the laboratory, varying the type of soil and the percentage and type of additives (KR slag and portland cement) used. After laboratory evaluation, two field sections were constructed. The trial sections were subject to repetitive traffic loading using a heavy-vehicle simulator (HVS). Weekly measurements were taken according to the following tests: Benkelman beam, British portable tester, and rutting depth measurements. The soil-KR mix designed with 20% KR slag addition and a poor-grade soil (clay) performed as well as the typical soil modified by cement solution designed with a better-quality soil (sand) modified by 3% cement. The clay soil did not meet standard requirements even when mixed with 10% portland cement. However, the clay soil modified by KR slag not only presented satisfactory laboratory results for roadway use in the base and/or subbase utilization, it also showed excellent field performance.

A new method of preparing expandable polystyrene (EPS) insulation mortar is presented in this work. It consists of using two polymer emulsion adhesives (POEA): commercial water-soluble polyvinyl formaldehyde adhesive (PFA) and polyvinyl acetate emulsion (PAE). The effects of EPS dosage, polymer emulsion adhesive, air-entraining agent, and fly ash content on the performance of EPS mortar were investigated. The workability, mechanical properties, thermal conductivity, water absorption, and softness coefficient of the prepared samples were experimentally studied. The experimental results showed that high-performance EPS thermal insulation mortar can be prepared by limiting the EPS volume fraction to 80%–82%, air content to around 20%, and fly ash content to 20%. The bonding strength and flexural strength were improved as polyvinyl acetate emulsion was added. Also, the drying shrinkage and thermal conductivity were improved with the addition of fly ash.

Aging behaviors of styrene-butadiene-styrene copolymer (SBS)–modified asphalt are complex due to combined effects of hardening of asphalt matrix and degradation of SBS. In order to investigate aging mechanism of SBS-modified asphalt more clearly, a novel method to extract SBS modifier from SBS-modified asphalt was introduced in this paper. Aging methods adopted in this study included thin film oven test (TFOT), pressure aging vessel (PAV), and ultraviolet light (UV) aging. After different aging methods, the physical and rheological characteristics of SBS-modified asphalt were evaluated. Chemical structures and molecular weight of extracted SBS modifier and SBS-modified asphalt were analyzed by Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) tests. The results illustrated that aging led to the degradation of the SBS structures, which could influence the physical and rheological properties of asphalt significantly. According to FTIR and GPC analyses, PAV aging had the obvious influence on the oxidation, fracture, or crosslinking of polybutadiene chain segment, and UV aging had the most obvious effect on degradation of large modifier molecules. Based on this extraction method, the peaks for butadiene structure in FTIR spectrum and the peaks of SBS molecular weight in GPC became increasingly apparent, and changes of those peaks before and after aging were clearer than that based on SBS-modified asphalt. All the previous results indicated that the new extraction method was useful for investigating the aging behaviors of SBS modifier without the influence of base asphalt. Furthermore, methyl index (MI) could be utilized to investigate the aging of SBS modifier based on this new extraction method. Pearson correlation coefficient result showed that the new extraction method was more suitable to characterize the close relationship between the aging of SBS modifier and the changes of asphalt rheological properties after aging.

The current design standards provide strict recommendations to ensure the quality of welds. This study investigates the mechanical properties of welds subjected to elevated temperatures by performing a steady-state tensile test on butt weldments composed of Q345B base metal and E5015 electrodes. The experimental results include the elastic modulus, yield, ultimate strength, and ductility of the butt weldments at temperatures from 20°C to 800°C. Comparison of the results shows that the welding heat-affected zone (HAZ) is vulnerable to fracture when subjected to reheating above 500°C. The comparison indicates that current standards are nonconservative in predicting the deterioration of the elastic modulus. Below 500°C, current Australian recommendations are still applicable to the reduction factors of the yield strengths at a strain level of 1.5% or 2.0%. At 500°C and higher, the butt welds are considered unsafe relative to the recommendation of the current design standards for the reduction factors of the yield strengths. Finally, it is still risky to use the recommendations of the current design standards directly to predict the mechanical properties of butt welds at a high temperature, particularly in the range of 500°C–800°C.

An alkaline-activated, ground-granulated blast furnace slag (BFS) was used as a binder for mortar prepared using river sand. Sixteen mortar mixes with four different BFS:sand ratios (4%, 8%, 12%, and 16% dry weight) were investigated. The BFS hydration of these mortar mixes was activated using four different activator solutions (1 mol): burned oyster shell (OS), calcium hydroxide (CH), sodium hydroxide (SH), and potassium hydroxide (PH). After curing for 3 and 7 days, the unconfined compressive strength (UCS) of the mortar increases with an increasing BFS:sand ratio, regardless of the activator type. The UCS of the mortar increased with increasing pH value of the activator. The mortar activated with OS had similar but slightly lower mechanical properties (60%–90% UCS, 70%–97% peak load strain, 0.78%–100% maximum strain, 40%–114% elastic modulus, 55%–100% toughness) relative to the mortar activated by CH, while the mortars activated by SH had mechanical properties similar to those of the mortar activated by PH. In all mortar samples, activated by different activators, CSH, ${\mathrm{C}}_4{\mathrm{AH}}_{13}$, and ${\mathrm{C}}_4\mathrm{A}\overline{C}{\mathrm{H}}_{11}$ were found. The mechanical properties (strength, peak load strain, maximum strain, elastic modulus, and toughness) of the mortar samples were analyzed.

Bond behavior of coated rebar spliced in concrete has gained significant attention due to the modified interfacial behavior between the coated surface and cementitious materials. This paper proposes an analytical model to describe the bond behavior of enamel-coated rebar spliced in concrete beams. This model considers the strain-softening behavior of concrete in the stress transfer mechanism between spliced rebar and concrete. The local bond strength caused by rebar characteristics and the effect of enamel coating was considered through the unified local bond model. The coupled stress bursting pressure generated by the splice was analyzed using equivalent stress analysis. The proposed model was validated by comparison with the experimental results of 24 concrete beams reinforced with both uncoated and coated rebar. The proposed theoretical analysis and model provide an efficient analytical approach of translating local bond behavior of coated reinforcement to the global bond behavior of lap splices in RC beams. The results indicated a significant coating effect on the load-strain responses of lap splices under tension forces.

Locking point is an important concept in selecting a proper aggregate gradation in the asphalt mixture design. The locking point can be defined as the moment during asphalt mixture compaction at which an aggregate structure becomes stable. Beyond this point, further compaction does not contribute much to the increase in mixture density and can even damage aggregate particles. This study employed two compaction methods, a Superpave Gyratory Compactor and a Marshall Compactor, to investigate the locking points of different asphalt mixtures. For the Marshall compaction method, an accelerometer was attached to the Marshall Hammer to record the response of the asphalt mixtures. For the Superpave gyratory compaction, changes in the height and density of the compacted samples were utilized to determine locking points. A total of ten mixtures was designed and evaluated. All the mixtures were prepared with the same asphalt binder PG 64-22 and aggregates. The aggregates were prescreened by different sieves to control variability in gradation. The results of this study show that it is feasible to determine the locking point for most of the mixtures with an accelerometer. The one exception was the largest aggregate, which experienced particle breakage during compaction. The locking point was found to be dependent on the full range of aggregate sizes of a mixture. Stone mastic asphalt (SMA) mixtures with similar gradation in fine particles showed less variability in locking point. Dense-graded mixtures with smaller maximum aggregate size exhibited lower locking points. These results can be attributed to their higher asphalt content, which served as a lubricant. The 101.6-mm (4-in.) Marshall mold was not adequate for determining the locking point for the mixtures with particles larger than 25.4 mm (1 in.).

The use of recycled coarse aggregate (RCA) can reduce the consumption of natural coarse aggregate (NCA) and preserve the natural environment. The accurate calculation of the compressive stress-strain relationship of recycled aggregate concrete (RAC) is very important in designing the recycled concrete structure. In this paper, experiments on compressive stress-strain based on five strength grades and six replacement rates of RCA from 0 to 60% were designed. The prism specimens of a height-to-width ratio of 3 were used to conduct the experiments under uniaxial compression load. The complete stress-strain curves were obtained by the experiments, and the ascending and descending branches of the experimental stress-strain curves are discussed separately. Based on the experimental results and by introducing the shape parameter $\beta$ of the stress-strain curve, a theoretical model of the stress-strain relationship considering the strength and replacement rate of recycled coarse aggregate was established. Through comparison and analysis, the stress-strain curve of RAC obtained by the suggested model has good fitting accuracy.

This study utilized the concept of surface free energy to assess the effect of binder aging, types of aggregate, and recycled mineral fillers on the moisture susceptibility of asphalt-aggregate systems. A total of 12 combinations of asphalt mastic and aggregates were evaluated. The surface free energy for each mastic type was determined based on contact angle measurements obtained using the sessile drop method. Next, the work of adhesion and the work of debonding for all combinations of asphalt mastics and aggregates were quantified based on their surface free energy components. The energy ratio parameter was used to assess the resistance to moisture damage of each mastic-aggregate combination. Moreover, mixes with different asphalt aging conditions—nonaged, short-term aged, and long-term aged—were evaluated to determine the effect of asphalt aging on moisture susceptibility. The results confirmed that limestone aggregates are less susceptible to moisture damage than granite aggregates. Furthermore, the use of recycled mineral fillers, mainly from recycled concrete aggregates (RCA) and recycled asphalt pavement (RAP), significantly reduces the resistance of asphalt-aggregate systems to moisture damage. Last, the results revealed that asphalt-aggregate systems become less able to resist moisture damage as the asphalt ages.

Asphalt binder acts as a lubricant film between two aggregates during mixing and compaction. The frictional phenomena in an asphalt–aggregate interaction play an important role in mixing and compaction of warm-mix asphalt (WMA). This study evaluates the frictional behavior of WMA with foamed asphalt through tribological characterization. A ball-on-three-plates apparatus assembled inside a dynamic shear rheometer (DSR) is utilized for tribological experimentation. Six foamed asphalts with varying foaming water content (FWC) and a controlled unfoamed asphalt have been tested at various temperatures: 25°C, 60°C, 100°C, and 135°C. These binders were also characterized for rheological properties. Test results show that the foaming process alters the frictional resistance of the foamed asphalt; specifically, the foaming process reduces the coefficient of friction in elastohydrodynamic and hydrodynamic lubrication regimes. Reduced frictional resistance helps in the formation of better coating during mixing and improves the sliding ability between aggregates during compaction at reduced temperature.

The free energy of asphalt cohesion and of adhesion at the interface of the asphalt binder and aggregate are the main parameters that affect mix asphalt fatigue failure in dry and wet conditions. The free energy of cohesion and adhesion within the mix asphalt system can be calculated if the components of the free energy of the adhesion at the interface of asphalt binder and aggregate are clear. Hence, in the present study, the components of the free energy of the adhesion at the interface of the asphalt binder and aggregate were calculated using a universal sorption device and Wilhelmy plate tests, respectively. In addition, an indirect tensile fatigue test was used to determine the fatigue life of mix asphalt. The materials used in this study include asphalt binder with a penetration rate of 85/100 and Nano lime as its modifier. The use of inexpensive nanomaterials such as Nano lime is one way to reduce the fatigue-cracking potential of asphalt mixtures. The results showed that using Nano lime increases the free energy of cohesion and adhesion and, therefore, improves mix asphalt resistance against fatigue cracks in the asphalt binder membrane and the interface of the asphalt binder and aggregate, respectively. In addition, the results of an indirect tensile fatigue test indicated that mix asphalt modified with Nano lime has a greater fatigue life than control mix asphalt in both dry and wet conditions. However, the effect of Nano lime is higher on mix asphalt containing acidic aggregates.

Dredger fill possesses undesirable engineering properties due to high water content, compressibility, and low permeability, causing insufficient consolidation and long treatment periods using a vacuum preloading method. This paper investigates an advanced treatment method using chemically additive polyacrylamide (PAM) on dredger fill combined with a vacuum preloading method via laboratory model tests. Anionic polyacrylamide (APAM, a PAM class based on ionic classification) exhibited better performance on accelerating water discharge, reducing the time for trial filtration tests almost in half, and so was adopted in vacuum preloading model tests. The test results show that the application of APAM reduces 30% to 50% of the dredger fill consolidation time, accelerates the dissipation of excess pore pressure, and reduces the vacuum loss in vertical transition for the whole treatment duration. The vane shear strength post-treatment was observed to increase by 30% to 55% with an additive percentage of $30\mathrm{mg}/\mathrm{L}$ of APAM, which is proposed for the treatment of Tianjin Binhai dredger fill. The results provide a novelty approach to the physical mechanical alteration of dredged fill to break through the unsatisfactory limitation of conventional vacuum preloading treatment.

This study investigated the compressive stress-strain curves of concrete produced with coarse recycled concrete aggregate (RCA) at temperatures in the range of 20°C to 800°C. Three concrete series were produced with coarse RCA replacement levels of 0%, 50%, and 100%. The compressive properties of coarse RCA concrete at elevated temperatures, including compressive strength, modulus of elasticity, peak strain, and complete stress-strain curve, were obtained from the experiment. The experimental results show that both compressive strength and modulus of elasticity diminished with increasing temperature, whereas peak strain increased correspondingly. The effects of coarse RCA replacement level on the relative compressive properties of coarse RCA concrete were indefinite. Based on the experimental results, a model was proposed to generate the compressive stress-strain relationships for coarse RCA concrete in the 20°C to 800°C range.

Several researchers have studied the behavior of particles during shearing to have better insight into the Mohr-Coulomb (MC) strength parameters. In most cases, the movements of particles along the shear band were studied by means of numerical modeling to obtain the velocities and directions of the soil particles. The use of a transparent shear box highlights the original enhancement and contribution in this paper to study the mechanical behavior of particles using particle image velocimetry (PIV) along the shear zone. Previous research using a transparent shear box suffered from several limitations such as obstructed view of the shear zone or using numerical simulation. The tested specimens consisted of sand and reconstituted rock spoils of metagreywacke and shale origins, which were classified according to their shapes and mineralogy contents. Particle shearing behavior was analyzed in detail at various stages throughout the direct shear tests with results complementing the PIV assessments. This novel interpretation technique successfully demonstrated how particle shapes and angularity, mineralogy, and effects of particle dilation and compression under shear can influence the strength parameters.

Airport cement pavement is prone to severe freeze–thaw damage due to the use of deicing chemicals. There is no unified evaluation parameter for analyzing the relationship between the concrete meso-structure and its salt-frost resistance. Therefore, industrial computed tomography (CT) scanning technology was applied in this study to obtain the meso-structure of concrete and the meso-structural parameters of concrete (air content, air void surface area per unit volume, air void distance factor, air void volume fractal box dimension, air void surface area fractal box dimension) that are introduced to characterize its meso-structure. The relationship between each structural parameter and the salt-frost resistance of concrete were analyzed, and a gray correlation model was established to quantitatively compare the significance of each parameter. In addition, the meso-structural parameters were used to analyze the internal structural changes of concrete under freeze–thaw cycles; this analysis mainly included three aspects. First, changes in concrete meso-structure before and after freeze–thaw cycles were analyzed. Second, changes in each meso-structural parameter of concrete under freeze–thaw cycles were tested and calculated. Third, a damage degree index, based on the air void surface area fractal box dimension, was proposed for characterizing the damage degree of concrete. The results showed that air void distance factor had the most significant influence on the salt-frost resistance of concrete in each structural parameter and could be used as the characterization parameter. The depth of the influence of salt frost on the internal structure of non-air-entrained concrete was deeper than its influence on air-entrained concrete. In addition, the damage degree index can quantify the degree of deterioration in concrete meso-structure well.

Gypsum-based composite boards reinforced with mono- and multilayer perforated amorphous ${\mathrm{Fe}}_{78}{\mathrm{Si}}_9{\mathrm{B}}_{13}$ ribbons were fabricated by pouring gypsum slurry directly into molds with prelaid epoxy-resin-coated amorphous ribbons. The influence of structural parameters, including the number of ribbon sequences ($\mathrm{n}=0$, 1, and 2) and the volume fraction ($\mathrm{volume}\%=0\%$, 0.125%, 0.25%, and 0.375%) and porosity (0%, 2%, 4%, and 6%) of the ribbons on the mechanical and electromagnetic interference (EMI) shielding performance of the composite boards was investigated by experimental testing and numerical simulations. The composite boards exhibited strain hardening accompanied by the formation of multiple cracks during bending. As the number of sequences increased, the cracking strength and ultimate strength of the materials increased from $2.48\pm 0.16$ and $2.48\pm 0.16\mathrm{MPa}$ to $4.70\pm 0.16$ to $7.50\pm 0.21\mathrm{MPa}$, respectively. The enhanced mechanical properties of the composites were attributed to the epoxy resin coating and the increased porosity supplying good interfacial bond strength between the amorphous ribbons and the matrix; this was favorable to more fracture energy dissipation. Over a frequency range from 30 to 1,500 MHz, the maximum shielding effectiveness (SE) of the composite board reinforced with double-layered ribbons was approximately 80 dB due to the excellent electrical conductivity and soft magnetic property of the amorphous alloy. The electromagnetic interference shielding effectiveness (EMI-SE) and good mechanical properties of the amorphous ${\mathrm{Fe}}_{78}{\mathrm{Si}}_9{\mathrm{B}}_{13}$ ribbon–reinforced gypsum composite indicate its great potential for use as a high-performance structural and functional material. In addition, numerical simulation results of mechanical properties and electromagnetic shielding effectiveness showed that the finite element simulation and experimental test results were in good agreement; the change trend was basically the same. The mechanical simulation agreed well with the experimental results; the relative error for the ultimate flexural capacity was less than 10%. The numerical simulation value for the electromagnetic shielding effectiveness test was basically the same as the experimental test value under various parameters; thus, the numerical simulation may provide a relatively accessible and cost-effective method for the design and optimization of composites.

This work revealed the mesodamage evolution in blocks-in-matrix soils (bimsoils) under triaixal cyclic loading. Although the macroscopic cyclic stress-strain responses of bimsoil have been well investigated, the mesoscopic damage cracking mechanisms are still not well understood. This work used an artificially prepared bimsoil sample with a rock block percentage (RBP) of 40% (mass ratio) to perform cyclic triaxial testing with a 450-kV industrial X-ray computed tomography (CT) system. For the convenience of damage evolution investigation, the sample was tested with constant stress amplitude and at a low strain level. The mean CT value method and crack extraction method were both used to study the damage evolution during cyclic loading. Results showed that the hysteresis loop on the stress-strain curve had a sparse-dense-sparse pattern caused by the plastic strain accumulation. The damage field distribution in bimsoil is very inhomogeneous and affected by rock blocks. Clear CT images and the CT value of various stages—sample compaction, emergence of a low-density region, crack initiation at rock-soil interface, bifurcation, propagation, and coalescence—were observed. The CT value in the CT images, which is equivalent to sample density, was the most important parameter reflecting the mesoscopic damage evolution. Variation of the CT value in the region of interest (ROI) was influenced by the contact, occlusion, interlock, and separation between the soil matrix and rock blocks. Stress dilatancy caused by the damage cracking behavior had a close link with the evolution of the hysteresis loop, which is controlled by the mesostructural changes during cyclic loading. The paper also reveals the internal relationship between the hysteresis loop area and total crack area during deformation inside the bimsoil sample. The mesodamage evolution of bimsoil under cyclic loading was first documented in this study.

This paper represents an attempt to study the internal structure of sand-sulfur-bitumen (SSB) mixes with the help of effective and quick three-dimensional (3D), high-resolution technology such as X-ray micro-computed tomography coupled with digital image processing tools. Various air void parameters, such as air void content, connected air void content, size and shape of air void, and tortuosity of compacted specimens, were determined and compared with those of a conventional dense graded bituminous mixture. Further, a statistical approach was used to fit the distribution of air void size in SSB mixes based on a lognormal function. The associated scale and location parameters of the lognormal function were used to evaluate the influence of various factors such as type of filler, use of crusher dust, and variation in bitumen content on the distribution of air void size. A substantial improvement in the air void characteristics and tortuosity was observed with the addition of fillers and crusher dust, although the effects of filler type were not significant.

This experimental study examines the influence of different sources and lengths of carbon fiber (CF) on the volumetric properties, volume resistivity, and heat-generation efficiency of electrically conductive asphalt concrete (ECAC). This type of concrete has applications to pavement anti-icing and deicing in critical areas such as airfields where having surfaces free of ice and snow is of paramount importance. This study revealed that increasing CF length decreased the ECAC air void, voids in the mineral aggregate, and increased voids filled with asphalt. The source of CF influenced the electrical conductivity and heat-generation capability of ECAC and decreasing the CF length resulted in volume resistivity reduction and enhancement of heat-generation efficiency. The analyses results obtained from volume resistivity and heat-generation characterizations performed on ECAC cylindrical specimens were used for fabricating ECAC slabs. It was demonstrated that ECAC slab can melt a dense layer of ice under harsh winter conditions simulated in the laboratory environment.

Tests were conducted of the bonding shear strength of different bamboo configurations in terms of grain direction, adhesive, and clamping pressure. The bonding shear tests were carried out with two basic configurations: glued together with the grain in the same direction, and cross-laminated. Five different adhesives were used: emulsion polymer isocyanate (EPI), polyurethane (PUR), melamine-urea-formaldehyde (MUF), hybrid polymer adhesive (HPA), and polyvinyl acetate (PVA). To assess the optimum value, specimens were prepared with three clamping pressures. According to the test results, the most suitable adhesive for glued laminated bamboo surface is MUF; EPI is not effective for bonding laminated bamboo elements, and PVA performs the best for scrimber produced with cross-laminated bamboo. The results also showed that end grain specimens had the highest bonding shear strengths among the four configurations, and that, in accordance with the properties of raw bamboo, cross-laminated types exhibited similar mechanical characteristics in both directions. It can be concluded that the testing method used for cross laminated timber is also suitable for assessing the shear strength of adhesive bonds for cross-laminated bamboo.

To minimize problems of poor bonding and tracking in common tack coats, modified asphalt–based trackless tack coat material (TTCM) was prepared by adding styrene–butadiene–styrene, uintaite mastic asphalt, ethylene-vinyl acetate (EVA) copolymer, and polyethylene (PE) wax to No. 50 base asphalt under high-speed shearing, stirring, and high-temperature static conditions. Through a time-saving orthogonal test and scientific range analysis approach, the optimal dosage of different modifiers determined was No. 50 basic asphalt:SBS:uintaite mastic asphalt:EVA:PE wax as 100:5:6:6:6. Mechanical tests of TTCM revealed track-free time of less than 1 min at 25°C and trackless nature at 60°C. At an optimum dose of $0.5\mathrm{kg}/{\mathrm{m}}^2$, the shear strength of TTCM reached 0.45 MPa, which was 120%–145% higher than many conventional tack coat materials. Dynamic shear rheological testing revealed higher complex shear modulus ($G^{*}$) and smaller phase angle ($\delta$) of TTCM compared with that of base asphalt. Scanning electron microscopy and fluorescence microscopy tests showed distinct uniformly dispersed modifiers and reticulated fine lines in TTCM, which were important for the performance of TTCM. Based on Fourier transform infrared (FTIR) spectroscopy analysis, the proposed modification mechanism suggests that stronger adhesive bonds in TTCM than cohesive forces within the hot-mix asphalt layer contributed to its trackless nature. Each modifier contributed toward the improved high-temperature stability and low-temperature flexibility of the TTCM. Due to its outstanding mechanical performance, cost-effectiveness, and green synthesis approach, the currently designed novel TTCM can be deemed as a potential candidate for highway and construction industries.

With the increasing number of vehicles and dynamic loads, the demand for more roads with higher quality is highlighted. Every year, a considerable portion of the national budget is spent on the rehabilitation of road pavements. Therefore, increasing the resistance of road pavements and extending their service life can greatly reduce the cost of pavement maintenance. A common solution for improving the strength of asphalt mixtures is the use of various additives, such as fibers. This study investigated the effect of ceramic fibers on the mechanical properties of asphalt mixtures. Asphalt mixture specimens modified with ceramic fibers were manufactured with crushed silica aggregates; PG64-16 asphalt binder containing 1%, 3%, and 5% ceramic fibers was used for this purpose. Furthermore, Marshall, indirect tensile stiffness modulus, indirect tensile fatigue, and repeated load axial tests were performed on the specimens. The results showed that the use of 3% ceramic fibers by weight of asphalt binder improves the mechanical performance of asphalt mixtures and significantly increases their resistance to rutting and fatigue damage.

Adding the proper amount of expansive agent (EA) to concrete is an effective way to control shrinkage cracking. Fiber can be treated as a secondary reinforcement for controlling shrinkage and improving the crack resistance and mechanical properties of the concrete. To date, studies on shrinkage for concrete with fiber and expansive agent integration are very limited, especially for hybrid steel and polypropylene (PP) fibers. In this study, shrinkage tests for 21 mixtures of self-consolidating concrete (SCC) with different expansive agent dosages, fiber types [steel fibers (SF), PP fibers, and hybrid steel and PP fibers], fiber contents, as well as the incorporation of expansive agents and fibers were carried out. The shrinkage of the tested SCC at 10 h through 5 days after placement was analyzed to study the effects of different factors on early-stage free shrinkage. To study the effect of curing conditions on shrinkage, both sealed cure (S-Cure) and top-surface exposure cure (TE-Cure) were investigated for comparison. The test results showed that curing conditions had a significant impact on the shrinkage and expansion of the studied SCC mixtures. The shrinkage of SCC under TE-Cure was 5–10 times the shrinkage under S-Cure. The free expansion of expansive SCC (ESCC) under TE-cure was smaller than the free expansion under S-Cure. As the amount of expansive agent increased, the effect of curing conditions on the expansion of concrete change increased. Under both curing conditions, at equivalent fiber factors, the shrinkage-restraining effect of PP fibers on SCC was higher than that of steel fibers. Meanwhile, for ESCC, steel fiber presented a higher restraining effect on expansion than PP fibers.

Loess is a problematic soil, which is often characterized with loose structure and high potential for collapse by water or external loads. In cold regions, the challenge of loess is further compounded by the seasonally frozen weather as the cyclic freeze-thaw action can disrupt the structure of natural loess, resulting in increased compressibility and decreased strength of the loess. A common practice to improve loess properties is to compact loess or chemically stabilize loess using cement, lime, or other binders. Although extensive studies have been conducted on the influence of freeze-and-thaw (F-T) cycles on engineering properties of soils, limited work has been done on freeze-thaw effects on loess and even less work has been concerned about lime-stabilized loess affected by cyclic freeze and thaw. This paper aims to fill such a research gap by performing a comprehensive laboratory study in a closed system to evaluate the impact of cyclic freeze and thaw on engineering properties of compacted loess and lime-stabilized loess, including changes in volume, moisture content, Atterberg limits, stress-strain relationships, modulus, and strength. The test results show that freeze-thaw cycles resulted in increase in soil volume, decrease in moisture content, but negligible change in Atterberg limits. The elastic modulus and peak shear strength of lime-stabilized loess were decreased to the lowest by approximately 15%–25% after three freeze-thaw cycles and the decreasing rate was more significant at a lower confining pressure. However, both the modulus and strength recovered and even exceeded the initial values after 11 F-T cycles.

Corrosive soil has been reported to be a prominent cause of the failure of buried cast iron pipes. Little research has been conducted with a specific focus on the effects of soil acidity and saturation on the corrosion of buried cast iron and subsequent microstructural changes in the corroded cast iron. This paper presents results produced from a comprehensive experimental program designed to determine the coupled effect of soil acidity and saturation on corrosion and subsequent changes in the microstructure of cast iron buried in soil. Relations between corrosion and subsequent microstructural changes in corroded cast iron with affecting factors and time were developed. The study determined that soil with low acidity (pH 5) and high saturation (80%) was the most corrosion-prone environment among the various soil conditions investigated and that corrosion can cause significant changes in the microstructure of cast iron. The significance of these findings is that any changes in the microstructure of cast iron can directly affect the mechanical properties of the corroded cast iron, which are directly related to the service life of corrosion-affected cast iron pipes.

This technical note examines the splitting tensile strength properties of natural sand treated with polyvinyl acetate (PVA) fiber in combination with biocementation using the microbially induced calcite precipitation (MICP) process. Ottawa 20-30 sand was mixed with PVA fiber at five different fiber ratios (0.0%, 0.2%, 0.4%, 0.6%, and 0.8% by weight) and then stabilized using urease-producing bacteria plus urea and calcium chloride (${\mathrm{CaCl}}_2$) solutions. Splitting tensile strength was determined for the treated sand samples. The results showed that the splitting tensile strength and splitting secant elastic modulus increased with increasing in either calcium carbonate content or fiber ratio. The use of PVA fibers together with MICP treatment could also increase the failure strain and the postfailure splitting tensile strength.

To increase the efficiency of biogrouting for coarse sand or gravel, a premixed injection method with or without pH adjustment was developed and adopted for biogrouting of aggregates with grain sizes ranging from 0.75 to 10 mm. The premixed injection method is to inject premixed bacterial suspension and cementation solutions together. This method can reduce the biochemical treatment cycles as compared to the traditional treatment. The shortcoming of this method is that the premixed bacterial suspension and cementation solution tends to form bacterial flocs before the injection. However, the bacterial flocs can be inhibited by adjusting down the pH of the solution and thus enhancing the groutability and efficiency of biogrout. The effect of bacterial flocs on the strength improvement of aggregates was investigated. Based on the testing results, both premixed injection methods with or without bacterial flocs are effective for increasing the strength of coarse aggregates (with grain sizes larger than 2 mm). However, for fine aggregates with grain sizes within 0.75–2 mm, a large difference in the strength was observed between samples treated with and without bacterial flocs. Thus, only the premixed injection method without bacterial flocs (i.e., with pH adjustment) is suitable to be used for aggregates with different grain sizes.