Journal of Materials in Civil Engineering

The addition of recycled aggregate (RA) in self-compacting concrete (SCC) offers compelling opportunities for green and high-end applications of concrete. However, research on the constitutive relationship of the resulting concrete (termed RASCC herein) is sparse. This motivates the current study to look at the compressive stress–strain behavior of RASCC and its variability. A total of 120 cylinders were prepared with waste concrete from different sources. It was found that the workability of the concrete did decrease with the use of RA, especially when recycled fine aggregate was incorporated. The addition of RA had a less pronounced impact on the ascending branch of the averaged stress–strain curve, but increased the steepness of the descending branch markedly. It was also observed that the RA incorporation reduced the modulus of elasticity, peak stress, strain at peak stress, and toughness of the finished concrete. Most notably and importantly, the variability of those four properties was much more sensitive to the incorporation of recycled fine aggregate than to recycled coarse aggregate. Nevertheless, controlling the replacement ratio and using high-strength RA can allow the products to achieve compressive behavior comparable to that of conventional self-compacting concrete. A stochastic stress–strain model for RASCC is developed and experimentally validated.

The progressive damage monitoring and fracture evaluation of plain concrete beam specimens subjected to three-point bending (TPB) are reported in this paper. The objective of the present research is to systematically correlate the fracture behavior of a concrete beam with acoustic emission (AE) data recorded during the present set of experiments. The damage growth and failure mechanisms of the beam specimens are investigated with AE parametric analysis, b-value analysis, and digital image correlation method. Eventually, a reasonable correlation between AE energy and the released fracture energy is established at various stages of loading, which is confirmed with the set of TPB beam experiments and further validated with nonlinear numerical finite-element analysis. The energy released during the cracking processes at different loading stages in the experiment is quantified and systematically analyzed. Acoustic and fracture energies are dependent on active concrete cracking, and their correlation is helpful in determining the extent of damage in the concrete structures. Such a relationship can be used as an operational tool for structural health monitoring of structures as an early warning system supplemented with numerical analysis, a well-calibrated laboratory, and in situ AE experiments.

Attributes of filler play a significant role in the overall performance of asphalt mixtures through their direct influences on asphalt mastic. Alkali-activated slag (AAS), which is currently in the beta stage of development, is a promising and innovative cementitious replacement material. However, mass production AAS for experimental use generates significant quantities of waste discharge. The purpose of this study was to explore the potential of using AAS waste as a mineral filler in asphalt mastic. Properties of AAS waste were assessed and compared to limestone (LS) filler using scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) spectrometry, laser particle size analysis, hydrophilic coefficient, mesoscopic void characteristic, and Rigden void tests. The penetration, softening point, Brookfield viscosity, and rheological properties of the asphalt mastic samples made, respectively, using AAS and LS fillers, were examined using complex modulus (${\mathrm{G}}^{*}$), phase angle ($\delta$), and rutting factor (${\mathrm{G}}^{*}/\sin \delta$) results and two interaction indices ($\mathrm{\Delta }{\mathrm{G}}^{*}$ and $\mathrm{K}–\mathrm{B}–{\mathrm{G}}^{*}$). Furthermore, models used to test relative viscosity (${\eta }_{\mathrm{r}}$) were applied to predict the complex viscosity (${\eta }^{*}$) of the samples. Results indicated that comparing to LS filler, AAS filler was shown to deliver superior compatibility to asphalt matrix, and the properties of the asphalt mastic containing AAS filler were superior to those of the asphalt mastic containing LS filler. Of particular note, the models used to predict relative viscosity demonstrated validity in predicting the complex viscosity of asphalt mastics. The results support using AAS filler as a replacement for LS filler in asphalt mastic. Further research should be conducted to maximize the potential benefits of using AAS filler in asphalt mixtures.

Accidental fires in aged concrete structures can lead to combined damage from corrosion and fire. In this study, we aimed to explore the effects of corrosion and high temperature on the residual mechanical properties of hot-rolled plain and ribbed bars. The results indicated that the corroded steel bars still exhibited ductile failure after high-temperature exposure. Moreover, the combined action of high temperature and corrosion has little effect on the elastic modulus. The residual bearing capacity of the hot-rolled steel bar became smaller under the condition of temperatures above 600°C. When the temperatures experienced by the plain and ribbed steel bars were less than 600°C and 500°C, respectively, the high temperature accelerated the decrease in the nominal yield and ultimate strength. However, the yield and ultimate strengths based on the minimum cross-sectional area remained unchanged with an increase in the cross-sectional loss ratio. Similar to that at room temperature, the ultimate strain of steel bars subjected to high-temperature exposure decreased exponentially with an increase in the cross-sectional loss ratio. The new findings of this study can provide a theoretical basis for the safety assessment of aged reinforced concrete structures after exposure to fire.

Mineral admixtures in portland cement–based concrete, such as rice husk ash (RHA), improve the mechanical strength and durability under normal conditions and ambient temperature. However, more knowledge is needed on the behavior of concretes with these materials when subjected to fire conditions. Fire conditions are characterized by an expressive increase in temperature in the structure in a short period. Thus, this study aimed to evaluate the effect of partial portland cement replacement with RHA in concretes subjected to different temperatures. Parameters examined were mineral composition with X-ray diffraction (XRD), compressive mechanical strength, static modulus of elasticity, and mass loss after heating. The mineral composition of concretes with and without RHA replacement after heating was similar. Partial replacement of cement with RHA improved the mechanical performance with higher compressive strength up to a temperature of 400°C. The static modulus of elasticity degraded more sharply than mechanical strength due to dehydration of cementitious matrix and fissuring. No explosive spalling was observed for all temperatures tested, and the mass loss was similar for both concretes. This indicated no adverse effects in the partial replacement of portland cement with RHA from a mineral point of view.

Compressive behaviors of 12 stub normal-strength concrete (NC) columns were experimentally investigated, which were confined by ultra-high performance concrete (UHPC) jackets. The governing influencing factors consisted of the thickness of the UHPC jacket, shape of specimens, and compressive strength of the core concrete. Generally, the UHPC jacket greatly improved the ductility of the stub columns. The final failure pattern transferred from crushing for concrete stub columns to the expansive crack of the UHPC jacket for UHPC-confined stub concrete columns. Moreover, the thickness of the UHPC jacket was found to greatly affect the compressive strength of specimens. In particular, the circular UHPC-confined stub columns, of lower-strength core concrete, were prone to gain more increments in compressive strengths. Debonding of the UHPC-NC interface was observed in the rectangular and square UHPC-confined stub columns. Enlightened from experimental observations, an analytical model is proposed to predict the axial stress-strain behavior of UHPC-confined concrete columns. It is noteworthy that the UHPC-NC interfacial behavior is identified and accounted for. The accuracy of the analytical model is validated by the reported experimental results. The model provides a useful tool to predict the axial strain-stress relation of UHPC-confined concrete columns in closed-form expressions for design-oriented purposes.

Promoting the utilization of solid wastes such as mineral waste residue in highway engineering is a meaningful way to accelerate the development of green highway construction and to reduce environmental pollution caused by waste residue stacking. To comprehensively evaluate the engineering properties of waste argillaceous gangue–filled subgrade and recommend reasonable construction parameters, the effects of parameters such as moisture content, compaction work, and coarse grain content (CGC) on the engineering properties of waste argillaceous gangue were compared in this study. A multiobjective comprehensive evaluation model based on grey relational degree (GRD) and principal component analysis (PCA) was constructed, and the reliability of the model was verified. The results showed that the mechanical properties of argillaceous gangue are sensitive to various influencing factors. With increased coarse particle content, unconfined compressive strength (UCS) first increased and then decreased, while resilient modulus and California bearing ratio (CBR) gradually increased. The impact of compaction work on different mechanical properties was noticeable. When calculating the comprehensive GRD, the weights of UCS, CBR of unsoaked samples, CBR of soaked samples, and resilient modulus were 0.203, 0.318, 0.278, and 0.201, respectively. The comprehensive performance prediction model can be effectively applied to evaluate the correlation between technical parameters and engineering properties of argillaceous gangue, and the fitting degree reached 98.21%. The model provides a scientific basis for engineering design and construction parameter optimization of subgrade filled with waste argillaceous gangue.

Bayer red mud (RM) is made from aluminum ore using the Bayer process and is considered an industrial waste. The storage of unused RM can cause environmental and geological problems. Although several studies have focused on RM geopolymers, the amount of RM consumed by these synthetic geopolymers is small (usually $<50\%$). Therefore, in this study, a hybrid geopolymer material with more than 90% RM content was developed and made it possible to apply in engineering construction. The consumption of a considerable amount of RM would reduce the massive accumulation of RM and address the shortage of natural construction materials. Experiments were conducted with ground granulated blast-furnace slag (GGBS) as the activator. Two different active GGBSs were selected to stabilize the RM by geopolymerization. The effects of dosage and type of GGBS on the mechanical properties of RM were investigated by conducting unconfined compression tests and disintegration and compression experiments. The experimental results indicated that the type and dosage of GGBS had a significant effect on the mechanical behavior of RM. Based on the unconfined compressive strength (UCS) values and the results of the disintegration and compression experiments, the optimal RM-GGBS mixed geopolymer was determined by orthogonal analysis. Microscopic analysis showed that under optimal conditions, the amorphous phase participated in the geopolymerization process, forming an amorphous geopolymer that improved the mechanical properties of RM.

Polyethylene (PE) and carbon black (CB) were premixed in this study for bitumen modification. The service performance of PE/CB-modified bitumen (PMB) was mainly explored by multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests to reveal the rutting resistance and fatigue life, respectively. Low-temperature properties were evaluated by glass transition temperature ($T_g$) measured by dynamic mechanical analysis (DMA). X-ray diffraction (XRD) results suggested that the crystalline structure of PE was almost the same regardless of different CB loading additions. It was found that the both rutting resistance and fatigue life of PMBs showed nonmonotonic variation with CB loading. The mechanism for this variation was closely related to the microstructure induced by phase separation, CB nanoparticle aggregation and PE crystallinity. As revealed by optical and atomic force microscopy, two different phase structures, network and droplet-matrix structure, can be formed in PMBs when the CB loading changes. In particular, a double percolated network structure can be formed, consisting of a PE-rich network in the bitumen-matrix and CB nanoparticle network within a PE-rich phase. With the presence of this structure, the rutting resistance and fatigue life of PMB can be significantly improved.

The ongoing Syrian civil war began in 2011 and has left more than 130,000 buildings destroyed, 70% of which are RC buildings. When the war is over, it is estimated that the millions of displaced refugees will return within 8 years, thus requiring a rapid urban redevelopment of the country. This study examined the feasibility of reusing concrete from destroyed buildings as recycled concrete aggregate (RCA), and will assist in developing much-needed recommendations for the sustainable redevelopment of Syria’s infrastructure. Although the concept of RCA is not specifically novel, the properties of RCA generated from different sources must be assessed thoroughly to confirm its reuse potential. Never has demolished concrete been so widely available as it is now in parts of Syria, rendering the potential impact of this work enormous. In this study, simple and established methods were implemented to collect and test materials, to simulate more closely real-life scenarios of when the country’s reconstruction is to start. The chemical and physical properties of the aggregate were measured, followed by the determination of fresh and hardened properties of the concrete produced using a mixture of RCA and natural aggregates. For the first time, this study provides evidence that RCA from the rubble of war-destroyed Syrian buildings can be immediately valorized as a sustainable alternative to natural coarse aggregates in concrete; up to 50% replacement can be achieved without significantly affecting the performance of the new concrete.

The high alkalinity and storage of red mud (RM) make it a major environmental problem. In this paper, the mineral composition, hydration process, and microstructure of red mud-cement based grouting materials (RCGM) are studied by means of the differential thermal analyzer, X-ray diffraction (XRD) diffractometer, isothermal calorimeter, and scanning electron microscope. The action mechanism of RM after thermal activation (TRM) and mechanical activation (SRM) on the mechanical properties of RCGM is summarized, respectively. The results show that a small amount of RM, SRM, and TRM can improve the early strength of RCGM, and the effect of TRM is the best. The RM will reduce the late strength of sample. The SRM and TRM still promote the strength of sample, and the compressive strength of SRM-80 and TRM-80 meet the requirements of grouting engineering. The RM, SRM, and TRM don’t change the hydrate phase of RCGM, and hematite and nepheline mainly play a filling role in the material system. A small amount of RM, SRM, and TRM can promote the hydration process of ordinary portland cement (PC), whereas excessive RM, SRM, and TRM can delay the hydration process of PC. Before hydration heat release for 15 h, the RM, SRM, and TRM can accelerate the reaction rate in the early stage of hydration induction, which is independent of activation mode and dosage on RM. Among them, SRM-20 and TRM-20 have the best effect on promoting hydration. The microstructure analysis shows that RM, SRM, and TRM mainly improve the mechanical properties of RCGM through the microfilling. Mechanical activation and thermal activation can improve the activity of RM, and the effect of TRM is more obvious.

Rocks such as Kota sandstone are an excellent construction material. An experimental and numerical study was performed to test Kota sandstone in a large-diameter (76-mm) split Hopkinson pressure bar (SHPB) in a strain rate range of $101–300/\mathrm{s}$. The primary goal of the current study was to optimize pulse shaper dimensions for dynamic testing of rocks. Pulse shapers of diameters 10, 12, 15, 20, 25, and 30 mm and thicknesses 0.1, 0.5, 1.5, 2.5, 5, and 10 mm were used. It was found that the incident rise time increases and the maximum stress drops as the diameter or thickness increases. For a large-diameter SHPB, it is recommended to use a pulse shaper of diameter 15–20 mm and thickness 2.5 mm. These pulse shaper dimensions produce a ramp-like incident pulse that facilitates dynamic force equilibrium and constant strain rate loading in the rock specimens. Also, the inertia-induced stresses in the rock specimens are negligible. A thicker pulse shaper is suggested if higher strain rates are targeted. The inertia-induced stresses in the pulse shaper increase as its diameter increases and decrease as its thickness increases. Especially when the pulse shaper diameter is increased from 20 mm to 25 or 30 mm, the inertia-induced stresses become large enough to cause oscillations in the incident waves.

The development of nanotechnology has facilitated the application of various nanomaterials in concrete over the past decade. Few investigations have characterized early-age properties and cracking potential of concrete with nanomaterials. The present study aimed to expand the limitation by means of an experiment campaign, including a mechanical properties test, free shrinkage measurement, and restrained ring test on high-strength concrete (HSC) with nano-${\mathrm{CaCO}}_3$ (NC). The proportions of NC were 0%, 1%, 2%, and 3% by the mass of cement. The results showed that HSC demonstrated higher mechanical properties with 1% NC incorporated. Adding NC reduced the free and restrained shrinkage of HSC. Stress relaxation and tensile creep were evaluated in this paper. The established relationship between relaxation and creep coefficients was sensibly independent of NC proportions, which contributed to better estimating the stress level in HSC with NC, so as to better evaluate the cracking potential at early age.

The requirements of early strength gain in concrete are indispensable in various structural applications such as precast industry, underwater construction, construction at low temperatures, shotcrete concrete, and so on. Generally, to accelerate the strength gain process in concrete under such applications, conventional hardening accelerators are used, which often suffer from different limitations, such as lowering of ultimate strength and durability properties. Calcium silicate hydrate (C-S-H) seed-based accelerators have the potential to overcome the limitations associated with conventional accelerators. Therefore, they are gradually becoming popular. In this research work, a novel ion-exchange process-based method has been developed and validated for the synthesis of a C-S-H-based accelerator, which successfully eliminated the limitations associated with commercially available hardening accelerators. The synthesis process used inexpensive resources such as agricultural waste to produce a C-S-H seed suspension that is almost free from harmful chemical impurities. Different characterization studies were performed to determine the structural, morphological, and chemical properties of the synthesized C-S-H seed. The heat of hydration and compressive strength studies proved that the material is effective in achieving early strength gains in concrete. The presence of synthesized C-S-H seeds in concrete effectively accelerated the strength gain process by approximately 40% during the initial hours of setting. Therefore, the developed hardening accelerator, when incorporated in concrete, has the potential to reduce the formwork removal time, resulting in the acceleration of the production cycle of precast elements.

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of $0.65–0.69\mathrm{kJ}/{\mathrm{m}}^2$ compared to $0.46\mathrm{kJ}/{\mathrm{m}}^2$ for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, $400\mathrm{J}/{\mathrm{m}}^2$). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered $591\mathrm{J}/{\mathrm{m}}^2$ at its performance grade low temperature ($-16°\mathrm{C}$) and $409\mathrm{J}/{\mathrm{m}}^2$ at $-22°\mathrm{C}$ compared to $429\mathrm{J}/{\mathrm{m}}^2$ for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.

Abstract

To improve the corrosion resistance and mechanical properties of mortars in seawater, this work explored the evolution of biofilm adhered on mortar surfaces with different protective coatings and the mortar properties in the seawater environment. Sulfur-oxidizing bacteria were selected as experimental strains, and epoxy resin and polyurethane as protective coatings. The performance of each group of samples was tested from the 15th day to the 120th day at intervals of 15 days. The evolution and morphology of the biofilms were measured by scanning electron microscopy (SEM), a common camera, ultraviolet-visible spectroscopy (UV-Vis), and ultra-deep field microscope. The properties and microstructure of the mortars were determined by X-ray diffractometer (XRD), thermogavimetric analyzer (TG), energy dispersive spectroscopy (EDS), and electro-hydraulic pressure laboratory machines. The results show that: (1) In a seawater environment, protective coatings can effectively impede the adhesion of biofilms, and the beginning of the rapid growth period of the biofilms is delayed from day 30 to day 60. (2) On day 120, the highest dehydration rate of 0.61% is for the uncoated specimen. In contrast, the epoxy resin group experienced a dehydration rate of 0.57%, and the polyurethane group a dehydration rate of 0.53%. This indicates that a polyurethane coating can effectively hinder the entrance of corrosive media from the seawater, alleviate the tendency of the mortar to swell, delay the corrosion process of the mortar in the seawater, and provide some degree of protection for the mortar.

Practical Applications

Cement-based material is one of the main types of material used in ocean engineering construction. But there are many organisms (micro and large) in the ocean that can damage concrete, among which sulfur-oxidizing bacteria is one of the most widely studied species. In recent years, many antifouling materials have been developed to prevent microbial corrosion and destruction. Based on its cost, convenience, utility, and other comprehensive aspects, a polymer antifouling coating (polyurethane, epoxy resin, etc.) is often applied. This study explored the protection of mortars with polyurethane and epoxy coatings in the presence of sulfur-oxidizing bacteria and monitored the evolution of the biofilms on the surfaces of the mortars. The results show that polyurethane and epoxy coatings cannot completely prevent corrosion damage from sulfur-oxidizing bacteria, and can only delay the corrosion. Further, compared with a epoxy resin coating, a polyurethane coating can more effectively resist damage from the sulfur-oxidizing bacteria and corrosive ions in seawater.

The present study investigated the performance characteristics of concrete paver block (CPB) mixes with incorporated reclaimed asphalt pavement (RAP) aggregates under different curing regimes, namely, continuous water curing (WC), air curing (AC1 and AC2), intermittent water and air curing (WAC), water spray curing (WSC) and heat curing (HC). Seven CPB mixes were formulated by volumetrically replacing virgin coarse and fine aggregates partially and in combination with coarse RAP, fine RAP, and combined RAP fractions. For better refinement of agglomerated particles present in the RAP and to achieve a dense microstructure, the block specimens were fabricated using a design methodology that included a staged mixing approach and time-controlled compaction simultaneously with a vibratory hammer and table vibrator. Hardened CPB specimens were tested to assess mechanical (compressive, flexural, and tensile splitting strength) and durability (water absorption, porosity, and carbonation) properties of the concrete. CPBs fabricated from the considered RAP-inclusive concrete mixes manifested great potential to be used for pavement applications having medium to very heavy traffic when cured with the WC, WAC, WSC, and AC2 curing regimes. Curing regimes WAC and WSC, which involved a combination of water and air curing, were found to be the most effective for the RAP CPB mixes, resulting in superior strength properties. The presence of carbonation was detected in all the RAP CPB mixes when exposed to air curing (AC2) for a prolonged period of time.

In this study, to give a new final disposal to the Dredged Sediments (DS) in the Port of Rio Grande, the manufacture of Compressed Earth Blocks (CEB) with the addition of alkali-activated cement (AAC) is proposed. This binder was produced by mixing Rice Husk Ash (RHA), Carbide Lime (CL), and Sodium Hydroxide Solutions (SHS). The methodology includes AAC optimization for the production of CEBs, considering their performance in terms of unconfined compressive strength (UCS), durability analysis by wetting and drying cycles, and the qualification of the blocks, according to strength and water absorption criteria. The results show that AAC is a satisfactory option to improve the mechanical performance of DS. After 28 days of curing, the CEBs pass the requirements established by the Brazilian standard NBR 8492 to be used in the execution of masonry without structural function in Brazil.

The deformation and degradation behavior of unstabilized ballast and that stabilized with elastomer and geogrid was evaluated using process simulation test (PST) apparatus at various loading frequencies ($f$). The results indicated that elastomer has significantly reduced the extent of both vertical and lateral deformations of ballast. For example, elastomer reduced the extent of vertical settlement ($S_v$) in ballast from 22.76 to 9.83 mm, and the lateral deformation ($l_d$) from 8.14 to 1.95 mm ($f=15\mathrm{Hz}$). It was also seen that the deformation and degradation of both stabilized and unstabilized ballast increased nonlinearly with the increase in the applied loading frequency ($f$). Further, the beneficial effect of elastomer in restraining the lateral flow of ballast was seen over the entire depth of treated ballast, unlike the geogrid, whose efficiency was maximum at its placement location and then reduced at farther locations. Moreover, elastomer has significantly enhanced the resilient modulus ($M_r$) and damping ratio ($D$) of ballast when compared with geogrid-reinforced ballast. For example, the elastomer increased the $M_r$ and $D$ of ballast by 25.9% and 66.6%, respectively, in comparison with an increment of only 15.1% and 25.3% in the case of geogrids ($f:15\mathrm{Hz}$). The $M_r$ and $D$ of ballast were found to be influenced by the effectiveness of the ballast stabilization technique in reducing lateral displacements. Additionally, elastomer has significantly reduced the vertical stress (${\sigma }_v$) at the ballast–subballast interface by 34%. Further, elastomer was found to be more efficient than the geogrid in reducing the dynamic amplification factor (DAF) at any loading frequency. Similarly, elastomer reduced the breakage of ballast by 71% compared with the 40% of geogrid reinforcement ($f=15\mathrm{Hz}$).

In cold climates, early-age cementitious material is easily threatened by frost damage, causing deterioration of material properties. To investigate the hazard and failure mechanism of cement paste due to early frost damage, the cement hydration process was divided into five stages via the electrical resistivity method, and then fresh cement pastes were frozen in five stages and two different temperatures, respectively. Furthermore, mechanical tests and X-ray computed tomography scanning were carried out to characterize the development of frost-related damage. The results indicated that the effect of initial frost time on strength growth is greater than that of freezing temperature, and the cement matrix can be considered completely damaged when frost-related damage occurs before the initial setting. The frost-related texture develops from outside to inside and the porosity of the sample frozen at the first three stages was higher than that of samples frozen at the last two stages. Finally, the frost-related damage could be divided into three types: flow extrusion damage, freezing expansion cracking damage, and flow extrusion-freezing expansion cracking combined damage.

The off-axis embedment behaviors of unidirectional and multidirectional laminated engineered bamboo panels used for glued-laminated bamboo (glubam) structures under dowel-type bolts with three different diameters, 12, 14, and 16 mm, were experimentally studied in this research. The half-hole loading method given by current standards was adopted to perform the embedment tests. Seven different off-axis loading directions from 0° to 90° related to the main bamboo fiber direction at an interval of 15° in the panel plane were considered. The different failure patterns, stress-displacement curves, and the corresponding full-field surface strain measured through the digital image correlation (DIC) method are reported. The loading angles significantly influenced the embedment performance of unidirectional bamboo panel specimens, and the strength values decreased with the increasing off-axis loading angles. A difference of 35% in the strength values between 0° and 90° loading specimens was observed. However, quasi-isotropic embedment properties were noticed for the multidirectional laminated engineered bamboo panels. The capacity functions were provided to predict the mean off-axis embedment strength and characteristic strength values by inputting the characteristic density values into the functions. Compared with the characteristic strength values estimated through the statistical method, with a 95% probability of exceedance and 75% significant level, the conventional capacity-function method underestimated the off-axis embedment strength values, and thus may leading to an overconservative design. The statistical characteristic embedment strength values are suggested to be used to calibrate the safety factor of capacity equations given by wood standards. Results from this research can be used to predict the ultimate strength of glubam joints under complex loading conditions and obtain reliable design values for engineering applications.

For industrial applications in cold regions, a fly ash-amended soil with lignin reinforcement is introduced here. Predictive models were developed for soil shear strength based on two ensemble learning algorithms, to facilitate understanding soil properties with limited prior knowledge. First, over 270 unconsolidated undrained triaxial tests were conducted on the stabilized soil with varying soil moisture contents, percent lignin fiber, confining pressures, and curing conditions (uncured, 15 days curing, and 15 days curing along with freeze-thaw actions). Extreme gradient boosting (XGBoost) and random forest (RF) were then applied to develop the predictive models for the specimens. A parallel genetic algorithm optimized the hyperparameters of both the XGBoost- and RF-based models. Next, monotonicity and sensitivity analyses were carried out with these models, to compare and assess their generalization capabilities. Finally, the peak shear strengths of the specimens finally correlated across different curing conditions. Given different training sample sizes, the XGBoost-based model consistently outperformed the RF-based model, particularly when half of the samples were fed as input. The root-mean-squared error (RMSE), mean absolute percentage error (MAPE), and coefficient of determination (${\mathit{R}}^2$) values of the XGBoost-based model on the test set are approximately $105-135$, $5\%-7\%$, and 0.85, respectively. Some essential features that are overlooked by conventional analysis have been identified with ensemble learning. This study demonstrates the potential of ensemble methods to tackle regression and prediction issues arising in civil engineering with less experimental data.

This study investigated the mechanical behavior of a low-plasticity silt treated by microbially induced carbonate precipitation (MICP). Also, the biogeochemical reactions of the fine-grained soil during MICP treatment were investigated, as soil minerals can react with MICP solutions due to increased pH ($\mathrm{pH}=9$) and generation of carbonate ions. Two types of MICP treatments were investigated: (1) bacterial suspension in the urea medium (UB treatment); and (2) urea medium, bacteria cells, and cementation medium (UBC treatment). The two treatments were applied to silt samples that were then subjected to direct shear tests at different confining pressures (12, 25, and 35 kPa). The relationships of shear stress versus horizontal displacement, compression displacement versus horizontal displacement, and equivalent ${\mathrm{CaCO}}_3$ contents and distributions were measured. Also, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), and Raman spectroscopy were used to investigate the elemental and mineral compositions and microscale morphology of the silt samples. The peak and ultimate shear strengths of the silt samples were improved by the UB and UBC treatments. The improvements of the mechanical properties of UB-and UBC-treated samples are mainly attributed to the precipitations of calcium carbonate, iron carbonate, and iron in the soil.

Abstract

This paper presents the results of three different types of glass fiber-reinforced polymer (GFRP) bars subjected to different harsh environmental conditions. Three types of pultruded GFRP bars, namely, Bar A (13.04 mm dia.), Bar B1 (13.02 mm dia.), Bar B2 (10.19 mm dia.), and Bar C (13.22 mm dia.) were subjected to accelerated aging. GFRP specimens were exposed to four conditionings (alkaline, alkaline with salt, acidic, and water), two temperature regimes (20°C and 60°C), and three time regimes (3, 6, and 12 months). The mechanical strength retention of the bars investigated based on the transverse shear strength (TSS) test, conforming to ASTM D7617M-11 revealed a decline in the shear strength characteristics of specimens proportionally with the exposure time. In general, Bar A, Bar B1, and Bar B2 performed well, but Bar C performed the worst since Bar C exhibited the least mechanical strength retention at elevated temperatures. Scanning electron microscopy (SEM) of the cross section of the conditioned specimens revealed the nature of the evolution of deterioration and the state of glass fibers, polymeric resin matrix, and fiber-matrix interface, validating the decrease in transverse shear capacity of the bars. SEM micrographs showed fiber damage, with debonding occurring at the fiber-matrix interface and cracking of the polymeric resin. Leaching out of glass fibers into the matrix of varying degrees upon conditioning was observed through the X-ray mapping of silicon. Furthermore, strength prediction models developed using multiple linear regression and artificial neural network (ANN) techniques were compared. Coefficients of correlation ($R^2$) of 0.94 and 0.76 and root mean square errors (RMSE) of 7.43 and 12.00 were obtained with models developed using ANN and multiple linear regression, respectively, showing that ANN can be used as a robust tool for GFRP shear strength prediction.

Practical Applications

With glass fiber-reinforced polymer (GFRP) bars possessing properties such as corrosion-resistance, high strength, and being light-weight, it is emerging to be a promising alternative to conventional steel rebars, which are often plagued by durability issues such as corrosion and consequent financial losses caused by its repair and maintenance. The present study makes an effort to contribute to the understanding of the durability performance of GFRP bars exposed to some aggressive environments such as alkaline, acidic, and moisture at room and high temperatures. The effect of these conditions was compared based on variations in shear strength and microstructural characteristics such as damage to the fibers, the polymeric matrix, and the fiber-matrix interface to build confidence in the application of nonmetallic materials in construction.

The large amount of discharge and accumulation of red mud and steel slag has led to the waste of land resources and serious environmental pollution problems. Therefore, the utilization of a large amount of red mud and steel slag in reasonable fields is an urgent problem. At present, the main practical methods include using red mud as a substitute for cement or raw material in cement clinker production and grinding steel slag as a mineral admixture or directly replacing fine aggregates. However, experimental studies on the simultaneous use of large amounts of red mud and steel slag in concrete are extremely limited. In this paper, red mud was used to replace cement (40%–60%) and steel slag to replace fine aggregate (50%–100%) to prepare steel slag fine aggregate red mud–based concrete (SFA-RM concrete). In addition, flue gas desulphurization gypsum (FGDG) was added as a sulfate activator in the concrete to stimulate the potential cementitious activity of red mud and steel slag to prepare the FGDG-activated SFA-RM concrete with improved strength. A total of 18 concrete mixes with different proportions of red mud, steel slag, and gypsum were designed and the mechanical properties, workability, hydration products, and microstructure of these concretes were studied. The results showed that the mechanical properties of FGDG-activated SFA-RM concretes were excellent, the 60 day compressive strength of the SFA-RM concrete reached 43.8 MPa, and the compressive strength of FGDG-activated SFA-RM with 15% gypsum and 100% replacement rate of steel slag improved to 47.1 MPa, which were both better than ordinary concrete. Moreover, the results of X-ray diffraction (XRD) and scanning electron microscope (SEM) tests indicated that the hydration products of concrete mainly included $\mathrm{Ca}{(\mathrm{OH})}_2$, C-S-H gel, ettringite, and zeolite, with small and few micropores as well as dense microstructure.

Soils mixed with recycled waste rubbers have been widely used in geotechnical and geoenvironmental engineering. However, the research on rubber-soil mixtures in deep seasonally frozen regions is relatively lacking, so the application and dynamic properties of expansive soil-rubber (ESR) undergoing freeze–thaw (FT) cycles need further investigation. This study investigated the dynamic properties of ESR undergoing freeze–thaw cycles in terms of confining pressure and frequency using temperature-controlled dynamic triaxial tests. The results show that (1) shear stress and dynamic shear modulus with 5% and 10% rubber content (RC) are similar under freeze–thaw cycles, and both decrease and then increase with the number of cycles; (2) shear stress and dynamic shear modulus are positively correlated with confining pressure and frequency for the same number of cycles; (3) ESR damping ratio decreases with increasing shear strain, with a maximum reduction of 50.65%; (4) variations in ESR damping ratio under the influence of freeze–thaw cycles, confining pressure, and frequency are significant; and (5) ESR damping ratio is optimal when $\mathrm{FT}=12$ and $\mathrm{RC}=10\%$, and is 29.76% higher than that of plain expansive soil.

Once sulfates become limited, the interaction of limestone with metakaolin (MK) is initiated, resulting in the formation of carboaluminates in a blended cement system. In this study, two different types of MKs (sourced from coal mining residue and soft clay) were adopted to examine limestone–MK ratios of 1:8, 1:4, 1:2, 1:1, and 2:1, by fixing the cement and MK content at 55% and 15%, respectively. The optimal limestone–MK ratio of 1:4 was found (equal to limestone content of 3.8%) to achieve the highest compressive strength of 60 MPa due to the formation of more carboaluminate content in both MK blended cement systems. This finding was corroborated with the thermodynamic modeling that the highest hydrates volume was achieved at the optimal limestone–MK ratio of 1:4. An overdosage of limestone reduces its reaction degree, reflecting the fact that excessive limestone content could only acts as filler in the system.

High strength concrete (HSC) has found significant applications in offshore structures, long-span bridges, and tall buildings due to its outstanding strength and durability. There have been concerns regarding the use of HSC in case of fire, especially due to explosive spalling. Polypropylene (PP) fiber has been demonstrated to reduce spalling in concrete. However, the addition of PP fibers adversely affects the concrete’s workability and can lead to non-homogeneous mixes due to fiber agglomeration during compaction. Addition of water soluble polymers in HSC is an innovative approach to avoid spalling under fire circumstances. The present work investigates the influence of polyvinyl methyl ether (PVME) on the hydration of cement, and its pore creation ability in mortars at elevated temperature. PVME was found to reduce the initial rate of hydration of cement, which was confirmed by thermogravimetry analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), isothermal calorimetry and bound water calculations. The rate of hydration increased with time and became greater than that of control samples after 24 h. PVME showed pore creation ability in mortars at high temperatures, which was similar to that of PP-fiber-modified mortars. PVME enhanced the volume of inter-connected pores, which can provide an escape route for gases and moisture and potentially alleviate spalling. It is expected that the present work will form the basis for further assessment and adoption of PVME as an admixture to HSC mixes to reduce its susceptibility to spalling at elevated temperatures.

The current trend in the asphalt industry is to increase the utilization of recycled asphalt pavement (RAP). In general, there are two types of RAP binder in RAP aggregates, the mobilized RAP binder and the immobilized RAP binder. The former can be blended into the virgin binder to coat aggregates during asphalt blending, while the latter can be treated as black rocks because they have already become an outer crust of RAP aggregates. Studies have focused on the mobilized RAP binder quantification and the significance of mobilized RAP binder to mixture performances. However, it remains unknown whether the immobilized RAP binder affects mixture performances. This study developed a laboratory procedure for immobilized RAP aggregates preparation and investigated the contribution of immobilized RAP binder to asphalt-aggregate interaction as well as the performance of 100% recycled asphalt mixtures. The work of adhesive energy and the $K\text{-}B\text{-}{G}^{*}$ model were adopted to characterize the asphalt-aggregate interaction for asphalt mortar. Resilient modulus and dissipated creep strain energy were used to evaluate the stiffness and cracking resistance of 100% recycled asphalt mixtures. Results showed that the immobilized RAP binder can strengthen the asphalt-aggregate interaction and improve the cracking resistance of 100% recycled asphalt mixtures by increasing total asphalt content. However, if the total asphalt content remains the same, the immobilized RAP binder increases stiffness but decreases the cracking resistance of 100% recycled asphalt mixtures.

With the increasing height of new dams, the number of high-water-head and high-flow spillway buildings is gradually increasing, and concretes are required to have better abrasion resistance. Current standards offer a method for evaluating the abrasion resistance of concrete, but when evaluating the abrasion resistance of high-performance concretes, it is necessary to extend the test time to more than 120 h. In this study, an improved way of the current code-specified underwater method was proposed to shorten the testing time, called the high-speed underwater method (HSUM), and the test results of the two methods were evaluated using three-dimensional (3D) laser-scanning technology. It was found that the abrasion efficiency of the HSUM was about twice as much as that of the code-specified method. HSUM resulted in a significant acceleration of the concrete coarse aggregate abrasion process. The average abrasion depth of concrete was between 0 and 6.5 mm (HSUM after 15 h and code method after 30 h), and the abrasion mainly occurred on the surface of slurry, when the abrasion resistance of concrete was obviously affected by the strength and volume of slurry. When the average abrasion depth of concrete exceeded 6.5 mm, it entered the aggregate abrasion stage, and its abrasion resistance was influenced by the aggregate hardness and aggregate content, and the correlation with the slurry strength decreases. The surface roughness parameters $S_q$ and $S_a$ of HSUM concrete increase significantly compared with the code method. HSUM allows for a reduction in experimental time and high performance in evaluating the abrasion resistance of high-performance concretes or concretes with special aggregates (high-strength granite aggregates and cast stone aggregates).

The growth mechanism of layered double hydroxide (LDH) films grown in situ on steel via hydrothermal treatment is still unclear. In this study, the mechanism of ${\mathrm{Co}\text{-}\mathrm{Al}\text{-}\mathrm{CO}}_3\text{-}\mathrm{LDH}$ film grown in situ on a steel substrate was investigated in detail. During the hydrothermal reaction, the in situ growth process of Co-Al LDH on steel involved three steps: (1) hydrolysis of ${\mathrm{Al}}^{3+}$ and etching of the steel surface, (2) hydrolysis of urea and promotion of LDH nuclei, and (3) crystallization of LDH. More importantly, the generation of ${\mathrm{Al}(\mathrm{OH})}_3$ determined the integrity of the LDH film grown on the steel surface, and a suitable heating rate was also the key factor that affected the growth of the ordered and regular LDH nanoflakes. Therefore, this work provides a comprehensive understanding of the in situ LDH growth mechanism on steel and may facilitate optimal LDH film preparation.

Self-consolidating concrete (SCC) may experience autogenous and drying shrinkage due to a high content of cementitious materials, lower aggregate content, and smaller aggregate size, resulting in concrete cracking and other durability issues. In order to solve these problems, shrinkage-reducing materials have been proposed and studied, such as polypropylene fiber, lightweight fine aggregate, and expansive admixtures. However, investigation of the combined effect of the aforementioned three shrinkage-reducing materials on SCC is still unreported. This study examined the influence of polypropylene fiber (0.05%, 0.1%, 0.15% of the volume of the concrete), prewetted lightweight aggregate (10%, 20%, 40% of the volume of the fine aggregate), and expansive agent (0%, 8% of the cementitious materials weight) on the shrinkage of concrete during a seven-day curing period under two curing conditions, sealed cure and top-surface exposure cure. The results showed that it was more effective to mitigate early age shrinkage by adding lightweight aggregate alone than by adding polypropylene fiber alone. In the sealed cure (S-Cure) condition, adding 10% lightweight aggregate compensated for shrinkage, and 0.1% polypropylene fiber content exhibited the highest shrinkage reduction. With the top-surface exposure cure (TE-Cure) condition, 20% lightweight aggregate compensated for shrinkage, and 0.15% content polypropylene fiber showed the highest shrinkage mitigation. It showed that the shrinkage of concrete, which has low polypropylene (PP) fiber content (0.05% and 0.10%) and no expansive agent added, was decreased with the increase of lightweight aggregate content. At a high content of PP fiber of 0.15%, the incorporation of lightweight aggregate did not exhibit significant influence on shrinkage reduction.

To investigate the fracture properties of the rock-concrete interface after fatigue loading, fatigue tests with the maximum loads of 60% and 70% of the ultimate load were carried out under three-point bending (TPB) loading. After 80,000 fatigue loading cycles, the specimens were subjected to quasi-static TPB loading until failure. The fracture parameters—including the nominal initial fracture toughness $K_{1\mathrm{C}}^{\mathrm{ini}}$, the nominal unstable fracture toughness $K_{1\mathrm{C}}^{\mathrm{un}}$, the critical crack length $a_c$, the fracture energy $G_f$, and the characteristic length $l_{\mathit{ch}}$—were obtained based on the experimental results. The test results indicated that the interfacial crack did not initiate in the fatigue tests if the applied maximum fatigue load was lower than the initial cracking load under quasi-static loading. However, microcracks would occur and accumulate around the precrack tip during the fatigue process, which generated a larger damage area than that under the quasi-static load condition. The larger damage area absorbed more energy provided by the applied loading in the subsequent monotonic TPB tests, leading to increases in the initial cracking load and the nominal initial fracture toughness. Accordingly, a distribution model of the nominal initial fracture toughness along the interfacial ligament was derived for the fatigued specimens. Furthermore, a crack propagation criterion based on the nominal initial fracture toughness was proposed and used to simulate the fracture process of the fatigued specimens. Good agreement between the experimental and numerical results validated the proposed distribution model and the crack propagation criterion.

Abstract

The Acoustic Emission (AE) technique is applied to study the failure mode, damage evolution process, and cracking mechanism of reinforced concrete (RC) columns under the coupling effect of exterior compression load and interior reinforcement corrosion. AE signals are collected from different loading stages for corroded and uncorroded RC column specimens. Parameter analyses are conducted to analyze the peak frequency, energy distribution, and phase parameters used to achieve the general changing conditions of AE signals. Fast Fourier Transform is applied to reveal the time-variant rules of signal frequency and energy in different damage stages. Discrete Wavelet Transform is used for a better understanding of the local time-frequency properties of the non-stationary AE signals and optimally interprets the damage evolution process of the RC structure. Results show that the peak frequency has a 3-layered distribution; an obvious “double-peak” trend of the energy distribution indicates two cracking mechanisms: steel/concrete interface damage and aggregate/cement damage. The damage process consists of four stages: micro-crack formation, micro-crack development, crack expansion, and cracking failure. The corrosion behavior remarkably influences the energy distributions of the two cracking mechanisms, the characteristics of the spectra in different stages, and the damage evolution process inside the RC columns.

Practical Applications

This paper studies the failure mode, damage evolution process, and cracking mechanism of reinforced concrete (RC) columns under the coupling effect of exterior compression load and interior reinforcement corrosion via AE signal analysis. The energy distribution and spectral characteristics show significant differences among different cracking stages. Moreover, those important properties and the damage evolution process are also remarkably affected by the corrosion behavior of the steel reinforcement. The practical meaning of those research outcomes are to provide theoretical supports for the application of AE techniques in the health monitoring of RC structures. The changes in the key properties of AE signals measured and analyzed can be used to capture the state changes and locate the cracking stage, which provides important evidence for the safety evaluation of RC structures.

The present paper aims to assess the feasibility of using two wastes, sugar cane straw ash (SCSA) and red clay brick waste (RCBW), in the production of a new sustainable binder for alkali-activated materials (AAM). The RCBW/SCSA mass proportions assessed were $100/0$, $87.5/12.5$, $75/25$, $62.5/37.5$, and $50/50$. The activating solution was composed of NaOH and sodium silicate with a ${\mathrm{Na}}^{+}$ concentration of ${8.3\mathrm{mol}.\mathrm{kg}}^{-1}$ and a ${\mathrm{SiO}}_2/{\mathrm{Na}}_2\mathrm{O}$ molar ratio of 1.3. Moreover, 5 wt.% of calcium hydroxide was added. Compressive strength, the volume of permeable pore space, water absorption of mortars, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy with energy-dispersive X-ray spectroscopy of pastes were carried out in this study. Tests were carried out at 3, 7, and 28 days of curing at 25°C and 1 and 3 days at 65°C. Results showed that the mortars produced with RCBW/SCSA mass proportion of $50/50$ presented an increase of 50% in compressive strength compared to samples with only RCBW ($100/0$) after 28 days of curing at 25°C (39.2 and 26.2 MPa, respectively). Moreover, the presence of SCSA content increases pore refinement and reduces water absorption. Studies on pastes showed that the SCSA favored the formation of N-A-S-H gels with higher silicon content and denser microstructure than the sample with only RCBW. Therefore, it can be concluded that the SCSA can be employed with RCBW in AAM to improve its mechanical properties and generate a denser structure.

Open-graded asphalt friction course (OGAFC) is an asphalt course constructed over a dense-graded and impermeable surface to allow quick drainage of surface water runoff and enable reduction of hydroplaning and splash and spray. OGAFC mixtures demand high-quality aggregates to perform the intended functions while transferring traffic loads to the underlying layer. Steel slag is a byproduct generated during steel production, and large quantities are unutilized in steel-producing countries, including India. This study evaluated the mechanical performance properties of OGAFC mixtures using basic oxygen furnace (BOF) steel slag as replacement for coarse aggregates at percentages of 0%, 25%, 50%, 75%, and 100%. OGAFC mixtures with two types of modified asphalt binders and five percentage replacements of coarse natural aggregates with BOF steel slag were fabricated. The mechanical performance of the OGAFC mixtures was evaluated in terms of rutting resistance (dynamic creep test and Hamburg wheel tracking device test), cracking potential (indirect tensile strength, cracking tolerance index, and semicircular bending test), fatigue life (indirect tensile fatigue test), and modulus properties (indirect tensile stiffness modulus and resilient modulus). The test results indicated that the use of BOF steel slag not only improved the performance of OGAFC mixtures in terms of rutting resistance, cracking potential, and modulus properties, but also increased the fatigue life of the OGAFC mixes. OGAFC mixes up to 100% BOF steel slag content exhibited superior performance compared with the mixtures with natural aggregates.

This paper presents the results of a comprehensive laboratory testing program that was conducted to evaluate the effect of variations in various asphalt mixture properties on changes in the cracking resistance of asphalt mixtures. To this end, a testing factorial consisting of 13 mixes and three asphalt binder content protocols, that is, optimum asphalt binder content (OAC), $\mathrm{O}\mathrm{A}\mathrm{C}+0.3\%$, and $\mathrm{O}\mathrm{A}\mathrm{C}-0.3\%$, were considered. Indirect tension asphalt cracking tests (IDEAL-CT) was conducted on the considered mixtures to examine the interaction effects between mixture characteristics and variations in the binder content on changes in cracking resistance as measured by cracking tolerance index (CTI). Statistical analyses were performed to evaluate the significance of the interaction effects with respect to asphalt mixture type. Regression and artificial neural network models were then developed to predict changes in CTI based on asphalt binder content variation. The results suggested that changes in CTI due to the variation in binder content were significantly influenced by reclaimed asphalt pavement (RAP) content, mixture type, and the type of aggregate used in the production of the asphalt mixture. A good correlation was obtained between mixture characteristics and changes in the CTI values of the asphalt mixtures. The correlation results were further enhanced with the use of artificial neural networks (ANNs).

To obtain a bitumen emulsion paste with a good bitumen film structure and rapid drying rate, the effect of cement content, cement type, and emulsion type on the drying and film formation of bitumen emulsion paste was studied. The drying and film formation mechanism of emulsion was employed to study the drying curve of bitumen emulsion paste. Results indicate that the drying and film formation process of bitumen emulsion paste can be divided into three stages. The solid volume fraction of the beginning of the final stage (${\varphi }_2$) and the maximum particle volume fraction (${\varphi }_m$) are proposed to evaluate the drying and film formation quality of bitumen emulsion paste. Higher values of ${\varphi }_2$ and ${\varphi }_m$ indicate a denser particle packing state and lower residual water content of the final stage, which are beneficial to the drying and film formation quality of bitumen emulsion paste. The ${\varphi }_2$ and ${\varphi }_m$ of bitumen emulsion paste differ slightly with the increasing content of ordinary portland cement. However, these quantitative indexes vary significantly with changing bitumen emulsions with different values of ${\varphi }_2$ and ${\varphi }_m$. Compared with ordinary portland cement, sulfoaluminate cement can lead to a noticeable decrease in ${\varphi }_2$ and ${\varphi }_m$; thus, its addition is harmful to the film structure of bitumen emulsion paste. Overall, to obtain a bitumen emulsion paste with a good bitumen film structure and rapid drying rate, a bitumen emulsion with good drying and film formation quality is recommended.

Due to environmental pollution and the shortage of nonrenewable natural resources in road construction, the use of copper slag as a new material in asphalt pavement has been recently evaluated for its ability to reduce the accumulation of waste and lower the cost of asphalt mixture production. The main purpose of this study was to assess the feasibility of using copper-slag filler as a substitute for lime in warm-mix asphalt (WMA) to enhance its self-healing and thermal/electrical conductivity potential. To this end, an X-ray fluorescence (XRF) test was first conducted to analyze the copper-slag filler constituent elements that affect its microwave heating. Then, the self-healing potential of asphalt samples containing copper-slag filler under microwave heating was investigated using thermal imaging, and an index was presented to analyze the fracture energy and load-bearing capacity at each stage of the fracture-healing test. Moreover, an image processing technique was used to determine its capability for uniform heat transfer. Finally, some tests were performed to study the asphalt mixture heat-transfer potential and determine its thermal/electrical conductivity. The results show that the mixtures containing copper slag had high thermal/electrical conductivity. Thermal conductivity, microwave heating uniformity, and self-healing potential (asphalt resistance against reloading) of asphalt mixtures increased with an increase in the copper-slag filler content. With 40, 50, and 60 s of microwave heating, the samples containing copper slag had an average of 14%, 31%, and 37% better recovery, respectively, than the asphalt samples containing 100% of lime filler.

The development and modification of high volume fly ash (HVFA) concrete using nanomaterials to enhance the strength has advanced significantly of late. However, the long-term behavior of HVFA concrete with nanomaterials, including permeation and durability characteristics, have yet to be studied in detail. This study reports the long-term permeation and diffusion characteristics and the carbonation of nanoengineered HVFA concretes utilizing up to 80% cement replacement with fly ash, hydrated lime, and nanosilica. The 450-day compressive strength of the HVFA concrete was 73 MPa. The air and water permeability indices of HVFA-65 and HVFA-80 concretes (65% and 80% cement replaced) decreased from 0.058 to $0.039\mathrm{Ln}(\mathrm{mbar})/\min$ and $0.3–0.1(\times {10}^{-7}{\mathrm{m}}^3/{\min }^{0.5})$ between 28 and 450 days, and $0.078–0.043\mathrm{Ln}(\mathrm{mbar})/\min$ and $0.5–0.2(\times {10}^{-7}{\mathrm{m}}^3/{\min }^{0.5})$, respectively. These permeation values were significantly lower than the specified indices for low permeability concretes. The presence of pores, ranging from $30\mathrm{\mu m}$ to 1 mm, was observed to be the principal influence on the permeability properties. The pore size and the quantity of pores decreased significantly in the HVFA composites over time. The C─ A─ S─ H gel products formed [$\mathrm{Ca}/\mathrm{Si}=0.43\mathrm{and}\mathrm{Ca}/(\mathrm{Si}+\mathrm{Al})=0.25$] increased both pore discontinuity and the strength of the interfacial transmission zone (ITZ). This increased the packing density in the gel matrix correlated with enhanced durability. The chloride diffusion coefficients of HVFA-65 and HVFA-80 decreased from 3.88 to $0.60(\times {10}^{-12}{\mathrm{m}}^2/\mathrm{s})$ and from 4.06 to $1.61(\times {10}^{-12}{\mathrm{m}}^2/\mathrm{s})$, respectively, between 28 and 450 days. Furthermore, both HVFA-65 and HVFA-80 composites displayed low carbonation coefficients, 2.93 and $4.73{\mathrm{mm}/\mathrm{month}}^{0.5}$, respectively. Calcite was observed at 28 days and was attributed to the carbonation of the hydrated lime. Calcite intensity in the HVFA concretes was observed to decrease up to 90 days; this was attributed to dissolution in pore water to form the more soluble calcium bicarbonate. However, from 90 to 450 days, carbonation led to the accumulating of additional undissolved calcite (calcium carbonate) within the HVFA composites over the long term.

The aim of this study was to evaluate the impact of nanosilica (NS) and gilsonite on the behavior of asphalt binders and stone matrix asphalt (SMA) samples. An asphalt binder with 60/70 penetration grade, 0%, 3%, 5%, and 7% gilsonite, and 0%, 2%, 4%, and 6% NS by the weight of the asphalt binder were used. The rotational viscosity (RV), linear amplitude sweep (LAS), bending beam rheometer (BBR), multiple stress creep recovery (MSCR), and dynamic shear rheometer (DSR) tests were applied to evaluate the physical and rheological behaviors of modified asphalt binders. Also, the wheel track, dynamic creep, indirect tensile strength (ITS), resilient modulus (Mr), and four-point bending (FPB) fatigue tests were utilized to examine the performance characteristics of mixtures. Moreover, a two-factor analysis of variance (ANOVA) was used to analyze the data. The rheological test results showed that gilsonite and NS enhanced the rutting and fatigue resistances of asphalt binders. Gilsonite also reduced the low-temperature resistance of asphalt binders, while NS improved that. The storage stability test showed that gilsonite enhanced the storage stability of asphalt binders. Also, adding NS led to an improvement in phase separation. MSCR test indicated an improvement in the high-temperature performance of base asphalt binder at different stress levels by the addition of gilsonite and NS. Based on the LAS test, gilsonite and NS enhanced the fatigue characteristics of asphalt binders. The sample test results also showed that gilsonite and NS improved the permanent deformation resistance, MR, ITS, fracture energy, and intermediate-temperature properties of samples.

Geopolymers are considered a suitable alternative to portland cement due to their appropriate mechanical properties, the capacity of by-product/waste consumption, and significant contribution to reducing environmental pollution. This study aims to assess the impact of geopolymers based on sugarcane bagasse ash (SCBA) with glass powder (GP) and silica fume (SF) on the mechanical and microstructure properties of poor-graded sandy soils. The geopolymer specimens were prepared with different alkali-activators (NaOH and KOH) and cured for 7, 28, and 91 days to evaluate the effect of activator type and curing period on geopolymerization. The mechanical properties were determined by performing unconfined compressive strength (UCS) test, while scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to evaluate microstructure properties. The results revealed that increasing the SCBA content in the mix significantly improved the UCS and geopolymer gel formation. Also, GP and SF addition improved the UCS of SCBA-based geopolymer specimens. Moreover, toxicity characteristic leaching procedure (TCLP) results illustrate that SCBA-based geopolymer has good environmental performance. Thus, this study has the potential to develop a new eco-friendly geopolymer by using large-volume discarded SCBA and GP for soil stabilization.

The viscoelastic-plastic damage model has been widely used to predict the long-term performance of asphalt mixtures. However, it is challenging for obtaining model parameters to separate the total strain and determine the yield function. This study proposed an improved multistage creep-recovery test to simplify the acquisition of constitutive model parameters. The method was designed to identify the viscoplastic parameters by the equilibrium condition when the specimen was fully hardened and calibrate the damage parameters through the changes of modulus in the process of plastic development. The results indicated the proposed test is an effective method to calibrate the parameters of the viscoplastic damage model, as well as the nonlinearity between the stiffness and strength. In addition, it was found that the sigmoid function may be the more satisfactory choice to fit the cohesion excluding the damage compared with the negative exponential function.

Within the scope of this study, the effect of the main chain length of polycarboxylate-based water-reducing admixture (WRA) on the fresh properties, compressive strength, and water absorption of mortar mixtures containing fly ash was investigated. Three WRAs with the same structure but different main chain lengths and resultantly different molecular weights were used. Effects of the admixtures on the properties of cementitious systems with 0, 15, 30, and 45 wt.% fly ash were investigated. Irrespective of the fly ash substitution level, the fluidity of the mixtures was improved when the admixture main chain length was increased up to a certain level. Possibly beyond a certain main chain length, the entanglement of too large main chains of the polymer to each other reduced the electrostatic effect of the polymer. Thus, the flow properties of the mixtures were affected negatively. The side chain molecular weight (length) of the admixtures was fixed ($\mathrm{2,400}\mathrm{g}/\mathrm{mol}$). However, the molecular weight of the admixtures was adjusted as 24, 48, and $71\mathrm{kg}/\mathrm{mol}$ by changing the main chain length of the polymer. The admixture with $48\mathrm{kg}/\mathrm{mol}$ molecular weight showed the best performance in terms of mortar fresh properties. However, the change in the length of the main chain of admixture did not have a considerable effect on the compressive strength and water absorption of the mortar. In addition, apart from the WRA admixture property, time-dependent flow and permeation properties of the mixtures were affected negatively by the increase in fly ash substitution level.

This study evaluates the effectiveness of a polyurethane polymer adhesive (PPA) in reinforcing a uniformly graded gravel. A series of laboratory tests were carried out to study the permeability, strength, and deformation of gravels improved with different contents of PPA. The permeability of PPA-reinforced gravels under the same compaction effort was observed to decrease as the content of PPA increased, but was still higher than those of sand. PPA-reinforcement can increase the strength while reduce the contraction capability of gravels. Despite of the strength improvement, the ductility of gravels reduced with the increasing content of PPA. Upon shearing, the secant modulus kept decreasing until approaching a stable value, where the decreasing rate became higher as the content of PPA increased. An optimum content of PPA around 4% can be suggested, where a compromise between the moderate ductility and high strength/stiffness of PPA-reinforced gravels can be reached.

This study reports on the development of a multifunctional concrete using graphene nanoplatelet (GnP) and sodium polyacrylate (SP) superabsorbent polymer. A combination of concrete functionalities was convened to improve, i.e., high strength and durability along with smart properties such as self-healing and self-sensing. GnP (0.05% by weight of cement) and SP (0.11% by weight of cement) were dispersed in concrete. Compared to the control concrete mix (no GnP and SP), the compressive strength increased 14% by GnP and decreased 9% by SP, and their combination resulted in a 6% enhancement in strength. The durability performance of concrete samples under coupled degradation mechanisms of freeze-thaw and chloride ion ingress suggested that SP in concrete has a better performance than GnP in concrete. SP in concrete shows self-sealing abilities resulting in less chloride ion penetration. However, the combined effect of both GnP and SP in concrete resulted in the maximum reduction in chloride ion penetration depth under freeze-thaw, a 42% reduction compared to the control mix. Microstructural analysis was conducted and found to resist the effects of freeze-thaw and reduce chloride ion penetration in modified concrete compared to the control concrete mix. GnP developed self-sensing abilities in concrete, resulting in about 12.7% fractional change of electrical resistance under 10 KN of cyclic compressive loading. The synergic impact of GnP and SP possesses a new prospect for developing highly efficient multifunctional concrete.

The drop in internal relative humidity (IRH) affects the early-age cracking risk of concrete. Superabsorbent polymers (SAPs), an internal curing material, are usually used to decrease the drop rate of IRH in concrete and the shrinkage-induced cracking risk of concrete. This study investigated the changes in IRH and distribution of IRH in SAP-modified concrete under sealed conditions and exposed to various ambient humidities. The test results showed that the use of SAPs and additional internal curing water can compensate for water consumption caused by self-desiccation and moisture diffusion (MD) and increase the IRH of concrete exposed to various ambient humidities. However, the degree to which SAPs mitigated the drop in IRH of concrete exposed to outside ambient decreased with increasing ambient humidity. The IRH of SAP-modified concrete increased, and the MD coefficient decreased nonlinearly with increasing ambient humidity. A model for predicting IRH of SAP-modified concrete exposed to various ambient humidities under the influence of self-desiccation and MD was proposed.

The main objective of this study is to evaluate and optimize the crack healing efficiency of hydrogel-encapsulated bacteria in concrete applications. To achieve this objective, Bacillus pseudofirmus was evaluated as the bacteria strain, which was combined with three mineral precursors corresponding to magnesium acetate, calcium lactate, and sodium lactate at two concentrations ($67.76$ and $75\mathrm{mM}/\mathrm{L}$). For each combination, three sets of mortar cubes, along with three sets of mortar beams, were prepared. The mechanical properties of these specimens were characterized by compressive and flexural strength tests. Once the beams were cracked, they were subjected to 28 days of wet/dry cycles in which crack width was monitored. Once the wet/dry cycles were completed, the specimens were retested to determine the strength recovery. In the compressive strength and self-healing efficiency tests, mortar samples prepared with calcium lactate at a concentration of $75\mathrm{mM}/\mathrm{L}$ along with bacteria and yeast extract showed the best performance. With respect to flexural strength recovery, no significant difference was noted among the specimens. Microscopic evaluation revealed a high concentration of calcium-rich crystals (i.e., calcium carbonate or calcium hydroxide crystals) indicative of bacterial activities. A scale-up concrete study was performed based on the best-performing mortar samples and then compared to plain concrete. Results from the concrete analysis indicated that the addition of calcium lactate improved concrete’s flexural strength. However, the plain concrete control specimen displayed superior healing efficiency after being subjected to wet/dry cycles.

Concrete structures constructed with cement-based materials are often at risk of chloride attack and structural damage. This project adds 0%–0.2% content of new, porous three-dimensional (3D) graphene materials into the fresh cement paste to make graphene reinforced cement-based materials. 3D graphene can be well dispersed with only a tiny amount of polycarboxylic acid water reducer. Nanoindentation tests showed that 3D graphene improved the micromechanical properties of hardened cement pastes. Just 0.1% 3D graphene can improve the microstructure and chloride diffusion resistance of hardened cement paste. Finally, a theoretical model was established to explain the barrier effect of 3D graphene on chloride diffusion and to further predict chloride diffusion coefficients in the hardened cement paste with different 3D graphene content by considering the tortuosity factor of 3D graphene. The research results can provide new ideas for applying 3D graphene reinforced cement-based materials.

This study proposed to introduce a combination of crushed granite (CG), superabsorbent polymer (SAP), and expansive agent (EA) into ultrahigh-performance concrete (UHPC) to mitigate the early autogenous shrinkage of UHPC without causing deterioration of its workability and mechanical performance. To this end, the effects of CG, SAP, and EA individually and their combinations on the workability, compressive strength, and autogenous shrinkage of UHPC were investigated. The results showed that CG, EA, and SAP all reduced the autogenous shrinkage of UHPC. However, the addition of CG and EA deteriorated the workability of UHPC, while the introduction of SAP decreased the compressive strength of UHPC. When CG (14.7% vol.), 1% EA, and 0.15% SAP were combined (CG+EA-1+SAP-0.15), UHPC showed the best overall performance. Specifically, the 7-day autogenous shrinkage of the CG+EA-1+SAP-0.15 group was $296.1\mu \epsilon$, which was 68% lower than the reference group (without CG, EA, and SAP); the 28-day compressive strength was slightly improved; and the slump flow was only 1.6% lower than that of the reference group, which was negligible. The results of thermogravimetry analysis showed that SAP could enhance the hydration of portland cement and EA, and could also promote the pozzolanic reaction of ground granulated blast furnace slag and silica fume. The results of mercury intrusion porosimetry demonstrated that the microstructure of UHPC was refined due to the enhancement of hydration by internal curing of SAP. Besides, when CG, EA, and SAP were combined, the total porosity of UHPCs first decreased and then increased when the dosage of SAP increased. Specifically, the total porosities of the reference, CG+EA-1+SAP-0.1, CG+EA-1+SAP-0.15, and CG+EA-1+SAP-0.2 groups were 9.6%, 9.2%, 5.5%, and 9.4%, respectively. The CG+EA-1+SAP-0.15 group had minimum porosity, which was 42.87% lower than reference group. The above results demonstrated that the combined use of CG, SAP, and EA can effectively mitigate the early autogenous shrinkage of UHPC, but the optimal ratio between EA and SAP should be further studied.