Journal of Materials in Civil Engineering

Biochar (BC) is a porous carbon formed by pyrolysis of biomass at high temperatures under anoxic conditions. The use of pulverized BC as a cementitious materials mixture has recently gained research momentum because this usage can lock BC in inert materials and reduce cement consumption simultaneously. This paper presents a review on the use BC particles as an additive or cement replacement in cementitious composites over the last few decades. It comprehensively reviews and discusses the physicochemical properties of BC, as well as the influence of BC on the hydration kinetics, workability, physical properties, mechanical properties, and durability of mortar or concrete. The replacement of cement with 1%–3% BC, in weight, decreases the permeability and increases the mechanism strength of cementitious composites. The properties of the BC-cement composites is closely related to the carbonaceous particle fineness, feedstock, pyrolysis temperature, and treatment method of the BC. Further research is expected to discover BC-based cementitious material for preparing a specific BC for a specific use as cementitious mixture.

The aim of this research is to investigate the sorptivity and capillary coefficient in unsaturated concrete using the capillary water absorption experiment. The effects of water-binder ratio, fly ash content, and aggregate content on the water absorption performance in concrete are compared. The decrease of water-binder ratio, aggregate content, and the increase of the initial degree of water saturation can lead to a decrease in the water absorption ability. With the increase of fly ash content, the water absorption ability first decreases and then increases; the 40% fly ash content had the worst water absorption ability. To forecast the water transport process, an unsaturated flow theory was used to predict the water content distribution in concrete during transport, this theory can well reveal the water distribution in concrete during water transport and the law of water content distribution is consistent with that of the water absorption experimental.

Understanding the mechanical properties of membrane materials in two-dimensional (2D) stress space is critical for structural design and mechanical analysis of membrane structures. In this paper, an experimental study of the warp-knitted fabric PVDF8028 subjected to biaxial loads was performed to expose the detailed mechanical behaviors and determine proper elastic parameters for the fabrics under multiple stress ratios. The least-square method was adopted to calculate the elastic parameters for different stress states, and response surfaces of strain and elastic parameters were used to reveal the mechanical behaviors in detail. Comparison between coated plain-woven and warp-knitted fabrics was used for exhibiting the influences of microstructures and deformation mechanisms on the macroscopic mechanical properties of materials. The results show that the stress–strain behaviors exhibit significant nonlinearities, and could be characterized by appropriate response surfaces. The elastic stiffness response surfaces of loading and unloading processes could form an unbalanced X-shaped cross, and detailed elastic parameters in those two processes could be obtained by corresponding response surfaces. Compared with plain-woven fabrics, warp-knitted fabrics could exhibit more obvious nonlinear characteristics due to the existence of their coiled yarns and lower Poisson’s ratios because of the special noncrimp yarn structure. The differences in macroscopic mechanical properties for these two materials result from the corresponding differences in microstructures and deformation mechanisms.

Based on the positive effect of metal material on the healing property of asphalt binder, this study evaluated the merits of using taconite (an iron-containing filler from iron-mine tailings) to promote the healing performance of asphalt binder. Samples of asphalt binder modified with three different dosages of taconite were tested by a thermal conductivity (TC) device. The presence of taconite can provide TC values in asphalt mastic and thereby allow inductive heating to improve healing in asphalt pavement. Laboratory experiments were used to evaluate the healing property of asphalt mastic containing 10%, 20%, or 30% by weight taconite. The healing property was measured using a healing index based on the complex modulus. The TC values were tested using a new testing method, and then the relationship between TC values and healing performance was analyzed. In the range of content of taconite used in this study, TC gradually increased with increased taconite. The results of the study showed that the presence of taconite improved the healing property of asphalt mastic. For a healing time of 900 s, a loading strain of 5%, and degree of damage of 50%, an increased dosage of taconite led to an increased healing property of modified asphalt binder, although the increase in the promoting effect on healing performance was not significant. This study also evaluated the effect of several factors that influence the healing property of asphalt mastics. The content of taconite, the healing time, the loading strain level, and the degree of damage affected the healing performance of asphalt mastics modified by taconite. Since taconite is a byproduct of mining iron-bearing sedimentary rock in which the iron minerals are interlayered with quartz, chert, or carbonate, our use of this so-called waste from mining and its application in construction is expected to promote resource conservation and recycling while enhancing sustainability in pavements.

The accurate reconstruction of the morphologic organization of reactants would be a crucial aspect in understanding tricalcium silicate (${\mathrm{C}}_3\mathrm{S}$) hydration. However, ${\mathrm{C}}_3\mathrm{S}$ particles are generally regarded as nonporous solids for simplification in most simulation models. This study aimed to analyze the influence of particle internal pores (PIPs) on hydration kinetics and microstructure development in ${\mathrm{C}}_3\mathrm{S}$ hydration. The CEMHYD3D model was modified to generate the ${\mathrm{C}}_3\mathrm{S}$ particles with pores, and its algorithm was accordingly updated. The cases of ${\mathrm{C}}_3\mathrm{S}$ hydration with various internal pore size distributions (IPSDs) and particle porosities (PPs) were simulated using the modified model. The results indicated that (1) the integral absolute errors for the hydration heat obtained from the simulation considering PIPs decreased by 53.3%, compared with that without considering PIPs; (2) the hydration heat difference between the IPSD categories D and E at 50 h was only $0.5\mathrm{kJ}·{\mathrm{kg}}^{-1}$ which accounted for 0.14% of the hydration heat obtained with the IPSD Category E; and (3) for a fixed PP, the dissolution of the ${\mathrm{C}}_3\mathrm{S}$ particle with more small-sized PIPs would be more isotropic than that with less small-sized PIPs.

Rutting is a pavement degradation that can be alleviated by reducing temperature variations experienced by the pavement. These variations can be reduced by utilizing microencapsulated phase change material (MPCM). The objective of this study is to investigate the potential use of a paraffin-type MPCM in mixtures of bitumen mastics to prevent rutting. The studied mastic of bitumen and cement and mastic of bitumen, cement, and MPCM. Multiple stress creep recovery (MSCR) test parameters of stress levels ($0–256\mathrm{kPa}$) and recovery time ($9–40\mathrm{s}$) are investigated to determine rheology properties ($J_{nr}$ and percentage recovery) of the mastics. Performance grade (PG) temperature sweep tests (40°C–80°C) are performed to evaluate complex modulus and phase angle of the mastics $[G^{*}/\sin (\theta )]$. The results show that the presence of MPCM in the mastics leads to higher $J_{nr}$ values and lower percentage of recoveries compared to those using only cement as the filler. Higher $J_{nr}$ values indicate lower stiffness of the mastics. This result is also confirmed by the results of the temperature sweep tests. At 75% MPCM, the stiffness of the mastic is at the same level as that of pure bitumen. At higher temperatures, pure bitumen and all mastics become less viscous, while the presence of MPCM shows nonlinearity in the range of 40°C–50°C. This temperature range is apparently around the phase change temperature of the MPCM. The MSCR test also shows that at 40°C, mastics containing 50% MPCM or less have a complete elastic recovery, shown by their constant $J_{nr}$ values. At 60°C, all mastics have lower $J_{nr}$ values compared to the pure bitumen sample. Hence, it is expected that the presence of MPCM, while reducing temperature variations, does not jeopardize the rutting resistance of the pavement.

Currently, there is a global increase in the use of sustainable technologies in the construction of pavement systems. Cold bituminous emulsion mixture (CBEM) is a promising alternative to hot mix asphalt (HMA) that offers economic, environmental, and energy-saving advantages. However, CBEMs have high water content because of the requirement for prewetting water, in addition to water within the bitumen emulsion. This additional water content causes low early strength and reduces resistance to water damage. To address this, the current study aims to evaluate the influence of water on CBEMs which have been modified with ordinary portland cement (OPC) and an acrylic (AR) polymer, evaluating them in comparison with HMAs. Marshall stability and durability, assessed by means of water damage tests, will thus be used to evaluate the influence of water content for each mix. The acrylic polymer was incorporated into the bitumen emulsion prior to the preparation of CBEMs at various percentages ranging from 0% to 5% of residual bitumen weight. The results indicate that the introduction of OPC and AR generally improves water damage resistance. The CBEM with a mix of OPC and 1.25% AR gave the best performance, showing a 12% increase in resistance compared with HMA with conventional mineral filler (CMF) and a striking 109% increase in resistance compared with CBEM with OPC only.

Geogrid reinforcement effectively controls the rutting of pavements under traffic loads, especially when constructed over soft subgrades. In this study, extensive large-scale model pavement experiments (LSMPEs) were performed to quantify the rut depths of flexible pavements. In all, 20 LSMPEs were performed on pavement sections overlying subgrades of different strengths with California bearing ratio (CBR) values varying from 1% to 5%. Three geogrid types were considered to study the effects of material type [polypropylene (PP) and polyester (PET)] and tensile strengths ($30–60\mathrm{kN}/\mathrm{m}$) on the rutting behavior of flexible pavements. LSMPEs were first performed under monotonic loading to obtain the optimum depth of reinforcement within the base layer of flexible pavement. Thereafter, a series of repetitive load (haversine loading) was applied on paved sections of reinforced flexible pavements using a high-end, linear, double-acting actuator system. Rut deformations were measured at both the surface and the subgrade levels of the model pavements. The rut deformations were found to distinctly vary in accordance with the condition of the subgrade, the thickness of the pavement layers, and the type of geogrid used. The rut depth reduction (RDR) at the pavement surface was found to range from 22% to 69% for PP- and PET-geogrid reinforced base layers. Geogrid reinforcement significantly reduced the rut depths at the subgrade level (as high as 90%) compared to unreinforced sections. In addition, the model pavements were instrumented with the earth pressure cells to measure the vertical pressures transferred to the subgrade due to surface loading. The ability of geogrid reinforcement to distribute loads to wider areas was quantified in terms of the vertical stress distribution angle, ${\alpha }_{\max }$, at the end of the load cycles ($N=\mathrm{100,000}\mathrm{cycles}$). The ${\alpha }_{\max }$ maximum values for geogrid (GG1/GG2/GG3)-reinforced pavements built over weak subgrade ($\mathrm{CBR}=1\%$) varied from 28.4° to 32.2°, while it was 25.7° for unreinforced pavements. Likewise, ${\alpha }_{\max }$ values for geogrid-reinforced pavements overlying a relatively fair subgrade ($\mathrm{CBR}=5\%$) varied from 34.5° to 43.6° against 30.4° for an unreinforced case.

The modification of cement concretes with various silica-containing additives is an urgent task that can significantly improve their physical and mechanical properties, as well as operational characteristics. In this paper, ${\mathrm{SiO}}_2$ sols and nanopowders based on a hydrothermal solution were obtained by a technological method using ultrafiltration membrane concentration. The physicochemical characteristics of silica nanoadditives were measured by dynamic light scattering, the BET (Brunauer–Emmett–Teller) method of low-temperature nitrogen adsorption, scanning and tunneling electron microscopy, and small-angle X-ray scattering and thermogravimetry. Sol and nanopowder with particles $6.6\mathrm{nm}$ in diameter, a specific surface area of ${410\mathrm{m}}^2/\mathrm{g}$, and a density of reactive silanol groups of Si-OH $4.9\mathrm{nm}$ were used as modifiers of the solutions. The level of increment in compressive strength $R_{\mathrm{com}}$ turned out to be lower for all dosages of ${\mathrm{SiO}}_2$ than after modification with the sol. At low ${\mathrm{SiO}}_2$ dosages (0.01%–0.25%), the increment in compressive $R_{\mathrm{com}}$, flexural $R_{\mathrm{flex}}$ strength, and density $\rho$ rose with an increase in the ${\mathrm{SiO}}_2$ dosage much more rapidly than at high dosages (0.5%–3.0%). The relations $\mathrm{\Delta }{R}_{\mathrm{com}}/{[\mathrm{SiO}}_2]$, $\mathrm{\Delta }{R}_{\mathrm{flex}}/{[\mathrm{SiO}}_2]$, and $\mathrm{\Delta }\rho /{[\mathrm{SiO}}_2]$ can be approximated by the same type of equations like $\mathrm{\Delta }R/{[\mathrm{SiO}}_2{]([\mathrm{SiO}}_2])=A/{[\mathrm{SiO}}_2{]}^z$, where coefficients $A$ and $z$ depends on the age of the solid samples. The level of ($R_{\mathrm{com}}^1/R_{\mathrm{com}}^{28}$) for the nanopowder was lower than for sol, especially at the lower dosages of ${\mathrm{SiO}}_2$ 0.01%–0.5% by weight. The ratio $R_{\mathrm{flex}}^{28}/R_{\mathrm{com}}^{28}$ changed in a relatively small range of values from 0.14 to 0.18 for sol and 0.16–0.23 for nanopowders. A modification with the hydrothermal ${\mathrm{SiO}}_2$ sol and nanopowder at dosages of 0.25%–0.50% and higher allows one to bring the grade of cement material to a level of low abrasion. The possibility of modifying concrete products with large dimensions by dosing liquid hydrothermal sol ${\mathrm{SiO}}_2$ and increasing the product’s durability by 3–6 times in a uniform manner is shown.

Relative humidity (RH) and temperature are two major influences on water vapor diffusion in asphalt pavements. However, the combined effect induced by RH and temperature has not been qualified. This study evaluated the RH dependency of Phase I water vapor diffusion and then explored the combined effect caused by RH and temperature. A series of Phase I water vapor diffusion tests at various RH levels were designed and carried out on asphalt mixture specimens using a Gravimetric Sorption Analyzer (GSA). Diffusivity ($D$) and water vapor retention capability per unit mass under unitary gas of water vapor with pressure $P_w$ ($\theta$) were determined by applying a more advanced three-dimensional (3D) diffusion model. $D$ and $\theta$ were then converted into their corresponding values at 1 atmosphere with the same water vapor pressure ($D_{atm}$ and ${\theta }_{atm}$) based on two developed conversion equations. A quadratic function–type model was established between RH and ${\theta }_{atm}$ theoretically based on Henry’s law. A similar quadratic function–type model was also developed between RH and $D_{atm}$ based on the definition of diffusivity in porous materials. Furthermore, two comprehensive models that took both RH and temperature into account were theoretically established and were able to describe the RH-temperature dependency of $D_{atm}$ and ${\theta }_{atm}$. The combined effect of RH and temperature was presented in forms of multiplication.

The utilization of recycled rubber and plastics for asphalt modification potentially has more social and economic benefits than using typical styrene–butadiene–styrene (SBS). However, the availability, compatibility, and stability issues of recycled plastic and rubber in the asphalt limit their application in the field. This study explored an alternative modifier to SBS for asphalt modification by using recycled rubber–plastic blends consisting of recycled polyethylene and tire crumb rubber. The compatibility and rheological properties of the various modified binder blends were characterized by dynamic shear rheometer and optical microscopy. Both recycled rubber–plastic and SBS-modified binder blends were prepared to evaluate the performance of the asphalt mixtures, including rutting, cracking, and moisture resistance. The results showed that the recycled rubber–plastic-modified asphalt could form interacted continuous phases of rubber and plastic, which improved the compatibility of the binder blends and the performance of the asphalt mixtures. Therefore, the recycled rubber–plastic blends can be considered as a potentially suitable alternative for asphalt modification from both performance and economical points of view.

A semicircular bend [SC(B)] test is widely used to evaluate the low-temperature performance of asphalt concrete. However, it is not clear what the proper thickness of a specimen should be, nor the proper notch configuration. This research is targeted to investigate the influence of thickness and notch configurations on stress intensity factors and the fracture energy of asphalt concrete specimens using AASHTO TP 105. Three levels of specimen thickness and three types of notch configuration were set as two variables. Besides, the representative volume element and plane strain status of the SC(B) were discussed. The test results showed the following: (1) the specimen thickness and test temperature did not statistically impact the stress intensity factor; (2) the specimen thickness was significantly impacting on fracture energy; (3) when interacted with the specimen thickness, the notch configuration and test temperature were statistically significant to the fracture energy; and (4) the SC(B) test in this study exhibited the lowest variance in the test results at the condition of $-12°\mathrm{C}$, a semicircular notch, and a 50-mm specimen thickness. In conclusion, the specimen thickness was recommended to be 50 mm for the nominal maximum aggregate size (NMAS) 12.5-mm specimen.

Sugarcane bagasse ash (SCBA) has commendable potential as pozzolanic material on account of silica as an attractive oxide composition; however, the coarser size of SCBA fractions hinders the fullest potential. In this regard, the choice of the comminution process is inevitable. In the present investigation, three sugarcane bagasse ash samples with a variable loss on ignition (less than 20%), but in compliance with the oxide composition requirement of ASTM C618, were selected to assess the effect of grinding on the particle size of SCBA and, in turn, the pozzolanic reactivity of ground SCBA. Four different methods of pozzolanic reactivity were adopted to evaluate the suitable characteristics of SCBA, enhancing the pozzolanicity. The results of the pozzolanic reactivity of ground SCBA showed that a particle size ($D_{50}$) lower than $35\mathrm{\mu m}$ and particles below $45\mathrm{\mu m}$ higher than 60% was a desirable level of grinding in attaining the minimum strength activity index (SAI) (75%). The provided amorphous silica was more than 25%, and oxide composition conformed to ASTM C618. Assessment of the pozzolanic reactivity of SCBA through simple and feasible techniques like the Frattini test and the modified Chapelle test with SAI appears reassuring. The attainment of the suggested level of particle sizes for SCBA through comminution indicates it is a viable method for developing pozzolanic reactivity.

This work explored the feasibility and effectiveness of using recycled polyethylene terephthalate (PET) fibers as an alternative to conventional polypropylene (PP) fibers in preventing the thermal spalling of ultrahigh-performance concrete (UHPC). The effect of PET fibers of varying dosages and geometries on the spalling behaviors of UHPC subject to various heating regimes was studied. The results showed that the PET incorporation into UHPC can effectively prevent the occurrence of heat-induced cracking and spalling. However, compared with PP fibers, a higher dosage of PET fibers was required to eliminate the spalling risk of UHPC. The relatively low mitigation efficiency of PET fibers compared with PP fibers may be attributed to its higher melting temperature, which retarded the formation of interconnected channels. Nevertheless, the incorporation of PET and PP fibers increased the permeability of UHPC even before the heat treatments and fiber melting, which contributed to a reduced spalling propensity of the UHPC.

This study evaluates the surface application of a volcanic ash-based geopolymer for the stabilization of soils susceptible to wind erosion. To achieve this, the mechanical properties of different soil types treated with various geopolymeric mix designs are evaluated using unconfined compressive strength (UCS) tests. The effects of volcanic ash (VA) and alkaline activator (AA) on the stabilization of silty sand soil are analyzed for two different curing conditions and over an extended curing period of 3 to 100 days. As different types of nonplastic fine-grained soil are vulnerable to various modes of wind erosion. The effectiveness of the geopolymer in the treatment of different types of nonplastic fine-grained soils (with fines content between 0% and 100%) is assessed through the UCS tests. Furthermore, the mechanical strength of soil samples prepared by three different preparation methods is evaluated. The impact of crust thickness, activator solution quantity, and curing conditions on the erodibility and friction velocity of three different soil types (clean sand, silty sand, and silty soil specimens) are measured by wind tunnel experiments. The results show that treatment with the geopolymer can notably increase the threshold friction velocity and reduce the soil wind erodibility. It is concluded that proper determination of the geopolymer mix design requires consideration of the soil type, maximum wind speed, and ambient conditions.

The consistency in the quality of as-such received sugarcane bagasse ash (SCBA) samples produced from the sugar industry throughout the sugarcane crushing period is a crucial aspect from the pretreatment point of view for their use in cement-based products. The majority of the reported research used SCBA samples collected from a single source (sugar plant) and at one time. In view of these unattended facets of SCBA, an organized study (characterization and pozzolanic reactivity through various techniques) in a holistic manner was conducted on as-such received SCBA samples collected from two sugar industries having distinct ash collection systems at frequent intervals throughout the sugarcane crushing period to deduce profound conclusions about the reactivity of SCBA in a particular sugarcane crushing period. The results of this study indicate that the physical and chemical characteristics of as-such received SCBA samples collected from a specific sugar industry in a particular crushing period differed to a reasonable extent. For assessment of the pozzolanic nature of the SCBA samples, it is desirable to perform a strength activity index along with the Frattini test. Based on the study, a simple framework was proposed for assessing the variability in the quality of as-such received SCBA.

Peat is geotechnically problematic due to high organic content leading to low strength, high compressibility, high rate, and magnitude of creep. The nontraditional materials like a geopolymer can be used to stabilize the peat due to its low ${\mathrm{CO}}_2$ emission and high strength gain than traditional materials like cement. Therefore, this study presents the viability of rice husk ash (RHA)–based geopolymer to stabilize the Indian peat with a wide range variation of organic content (OC) (21%–79%) and fiber content (FC) (6%–73%). The geopolymer was prepared by adding extra aluminum oxide (${\mathrm{Al}}_2{\mathrm{O}}_3$) with RHA to maintain the atomic weight of silica to alumina (Si/Al) equal to 3. The specimens with binder (${\mathrm{RHA}+\mathrm{Al}}_2{\mathrm{O}}_3$) percentages of 10%, 20%, and 30% by weight of dry peat and alkali/binder ratios of 0.5, 0.7, and 0.9 were activated by sodium hydroxide (NaOH) with molarities (M) of 3, 6, and 9. The results show that the RHA-based geopolymer stabilized peat depends on various factors like the amount of organic content in peat, amount of binder content, concentration of activator, A/B ratio, curing period, and pH. The optimum combination of binder content, concentration, and A/B ratio was found as 20%, 6 M, and 0.7 respectively. At this combination, the unconfined compressive strength (UCS) of treated peat was found 133, 125, and 136 times more than untreated sapric, fibric, and hemic peat, respectively. Further, it was observed that UCS decreases with OC and increases with the curing period The field emission scanning electron microscopy (FESEM) micrograph and X-ray diffraction (XRD) patterns confirm that the pore spaces are filled with cementitious products like zeolite which is further represented by a reaction mechanism.

The interfacial transition zone (ITZ) in concrete is known as the weakest link of the material, and significantly affects the properties of concrete. This study aims to investigate the actual microstructure of the ITZ using microcomputed tomography (micro-CT) in three dimensions (3D). For this purpose, high-resolution synchrotron micro-CT images of materials are used to visualize and examine the 3D ITZ of cement-based specimens. A set of mortar specimens with different water–cement (w/c) ratios as well as different aggregate types and sizes were prepared and compared to investigate the effect of each condition on the characteristics of the ITZ. The microstructural characteristics of the pores and the solid structures of the ITZ are characterized based on the information of grayscale images. The obtained results show the effective investigation on the pore and solid characteristics of the ITZ microstructure by using 3D nondestructive micro-CT; this approach is useful for further detailed investigation of the ITZ.

Dispersive clays are one of the common problematic soils owing to their unstable structure, which causes numerous geotechnical problems in construction projects. One of the main strategies to ameliorate these weak soils is to modify their mechanical properties with additives. Because little research about the influence of nanomaterials on the problematic soils’ characteristics is available, this study aims to evaluate the effect of nanosilica on the mechanical, mineralogical, and microstructural behavior of dispersive clay. A series of experimental tests, including the pinhole, double-hydrometer, and crumb tests, is conducted to determine the dispersivity potential of the soil treated with nanosilica. The Atterberg limits, standard compaction, unconfined compression (UCS), and direct shear tests are also carried out. Additionally, mineralogy and the microstructure of the base soil and treated specimens were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results indicate that adding the optimum amount of 1% nanosilica to the dispersive clay altered the soil characteristic into nondispersive. The liquid limit (LL), plastic limit (PL), and optimum moisture content (OMC) of the treated soil specimens increased; nevertheless, the plasticity index (PI) and maximum dry density (MDD) decreased with the application of nanosilica. Remarkable improvement in UCS, absorbed energy, secant elastic modulus (${\mathrm{E}}_{50}$), and the direct shear strength was achieved in the specimens treated with 1% nanosilica content after 7 and 28 days curing. The formation of calcium–silicate–hydrate (C─ S─ H) gel and substantial reduction of the porous structure were observed through the XRD results and SEM micrograph after 28 days of curing.

To reduce the calcination temperature of belite ($\beta \text{-}{\mathrm{C}}_2\mathrm{S}$)-calcium sulphoaluminate (${\mathrm{C}}_4{\mathrm{A}}_3\$$) cement clinker, hydrothermal curing was applied to mixed raw materials before calcination. The influences of calcination temperature on the mineralogical composition of cement clinker were investigated, and the optimum $\beta \text{-}{\mathrm{C}}_2\mathrm{S}/{\mathrm{C}}_4{\mathrm{A}}_3\$$ ratio was deduced. The phase and microstructure evolution of the hydrated paste were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The compressive strength development was also tested. The results showed that after hydrothermal curing at 95°C, the belite-calcium sulphoaluminate cement clinker can be prepared with a low-temperature calcination of 1,200°C. When the $\beta \text{-}{\mathrm{C}}_2\mathrm{S}/{\mathrm{C}}_4{\mathrm{A}}_3\$$ ratio reached 50%/50%, the cement pastes had the highest 3- and 28-day compressive strengths of 37.34 and 62.94 MPa, respectively. The main hydration product formed in the cement paste was ettringite.

Moisture-induced damage of asphalt pavements constitutes a primary distress. To quantify the extent of moisture-induced damage efficiently, a moisture-induced stress tester (MIST) was developed. This study adopts varying stress cycles of MIST to condition the asphalt mixes without and with reclaimed asphalt pavement (RAP) to ascertain their moisture-induced damage resistivity. Hence, the control mix (0% RAP) and mixes containing 10%, 20%, 30%, and 40% RAP by weight were prepared and conditioned using 0, 1,000, 2,000, 3,500, 5,000, and 10,000 stress cycles of MIST. Thereafter, an indirect tensile (IDT) strength test was conducted on the prepared mixes. Using analytical approaches, the biaxial state of stress was defined to compute the static ($E_{S,H}$) and average modulus ($E_{S,A}$). Increasing stress cycles of MIST decreased the stiffness of control and RAP mixes. The compressive stress–strain curve (SSC) was plotted and utilized to compute the linearity and toughness index (TI) of control and RAP mixes. Increasing stress cycles of MIST were observed to increase the ductility of control and RAP mixes, whereas prepeak linearity was observed to reduce it. The TI increased with the increase in stress cycles of MIST. New moisture damage ratios (MDRs) were computed by utilizing $E_{S,H}$ and $E_{S,A}$ and compared with the commonly adopted tensile strength ratio (TSR). Based on such MDRs, it was concluded that RAP improves the moisture-induced damage resistivity of asphalt mixes. Statistical analysis indicated that both $E_{S,H}$ and $E_{S,A}$ have the potential to be good indicators of moisture-induced damage of control and RAP mixes.

To obtain a precise safety evaluation of concrete structures after exposure to the fire hazard, it is critical to comprehend the residual static and dynamic mechanical properties of concrete after exposure to elevated temperature. In this study, the residual mechanical performance of concrete exposed to different elevated temperatures were investigated under the static and dynamic loading, where the compression test, the splitting test, the ultrasonic pulse velocity (UPV), and the Split-Hopkinson pressure bar (SHPB) test were performed, and the deterioration of thermal performance in concrete was interpreted by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) in detail. Results show that the microstructural change and porosity variation greatly influence the final dynamic mechanical performance subjected to different temperatures. Meanwhile, the effect of strain rate and softening effect due to high temperature also play important roles concerning mechanical performance. Finally, the relationship between the dynamic splitting tensile strength ratio of concrete samples and the temperature is proposed. Meanwhile, the connection between the strain rate and dynamic increase factor under different temperatures was also presented.

The accurate identification and quantification of rock damage are important for the reliable safety assessment of rock engineering. In this paper, stress-strain behavior, passive acoustic emission (AE), and active ultrasonic transmission were measured simultaneously under uniaxial compression to characterize the fracture damage of granites. The deformation and acoustic behaviors with respect to crack initiation and crack damage thresholds were analyzed. Meanwhile, irreversible damage was quantified using different methods. The results show that the marked increase in the AE rate and the average hit energy coincide with the crack initiation stress, ranging from $0.41{\sigma }_c\text{–}0.45{\sigma }_c$ (uniaxial compressive strength), which occurs earlier than the decrease of the $P$-wave velocity and onset of the rock dilation. The moment in which the average hit energy and ratio of low-frequency AEs start to increase rapidly corresponds to the crack damage stress of $0.71{\sigma }_c\text{–}0.74{\sigma }_c$. In addition, the fracture damage was quantified by the crack volumetric strain, dissipated energy, modulus loss, AE characteristics, $b$ value (defined as the log-linear slope of the frequency-magnitude distribution of AEs), and ultrasonic properties. It is revealed that the majority of rock damage accumulates after the crack damage stress, corresponding to the appearance of most high-magnitude hypocenters. Rock damage quantified by dissipated energy and AE energy with clear physical meaning is more reasonable and less subjective. Moreover, the precipitous reduction of the $b$ value, a sharp increase in AE energy, and the ratio of low-frequency AEs prior to peak failure is a perfect precursor of potentially brittle failure.

This study aims to provide engineers with a set of equations to evaluate temperature models for massive footings to avoid the use of high-heat mixtures that can induce excessive expansion. The temperatures of a concrete block and 41 massive footings were measured in the laboratory and construction sites. The equations for the peak core temperature ($T_{\mathrm{PC}}$), peak differential temperature ($T_D$), and form removal time ($t_{\mathrm{FR}}$) are proposed for the thermal resistance of $0.029\mathrm{W}/\mathrm{m}·\mathrm{K}$ for 12.7-mm-thick expanded polystyrene (EPS) and extruded polystyrene (XPS) boards or equivalent. Semiadiabatic temperature rise ($T_R$) curves from 1.1-m elements can be used to model footings up to 1.8 m thick. The gradient temperature increment ($G$) of $0.1°\mathrm{C}/\mathrm{cm}$ is recommended for limestone concrete. The cooling rate ($F_{\mathrm{CR}}$) range of $2.2°\mathrm{C}/\mathrm{day}\le F_{\mathrm{CR}}\le 5.6°\mathrm{C}/\mathrm{day}$ is suggested. $T_R$, $G$, and $F_{\mathrm{CR}}$ used in the equations should be validated with local concrete mixtures.

Stress–time avalanches of recycled polyethylene terephthalate (PET) fiber–reinforced concrete during flexure were investigated based on high temporal resolution signals in this study. Stress drops were extracted based on measurements collected at 100 kHz and modeled as avalanches using the mean field model. Two types of avalanches were observed during flexure of PET fiber beams, i.e., small avalanches collapsed on the scaling regime and large avalanches beyond the regime. The measured stress drop profiles of small avalanches in the scaling regime agreed with predictions from the mean field theory that has been used to model avalanches. When the peak stress was reached after the fracture of bottom concrete, the postpeak avalanche size could exceed the avalanche size at the bottom fracture. Findings from this study could provide essential clues to the understanding of fiber-reinforced concrete during bending.

This paper reports on the effect of addition of nano-calcium silicate hydrate (nano-CSH) seeds on the early-age strength development and microstructural evolution of concrete containing high-volume fly ash (HVFA). Cement replacement levels of 60% and 70% are considered. For each of the replacement levels, 0.5%, 1%, and 1.5% of the mass of fly ash (FA) are replaced with nano-CSH crystals. The early-age compressive strength of concrete was tested at the ages of 1, 3, 7, 14, and 28 days. Microstructural investigations involve thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results show that addition of 1% and 1.5% nano-CSH seeds in HVFA60% and HVFA70%, respectively, can effectively facilitate the formation of hydration products ${\mathrm{Ca}(\mathrm{OH})}_2$ and C-S-H as well as increase the rate of reaction and early-age strength gain at early ages. It was found that the dosages of nano-CSH seeds is a critical parameter in achieving the desired properties.

The Airfield Mat 2 (AM2) matting system typically is employed as an expedient surface for airfields. It usually is emplaced over soft existing subgrades due to logistical, material, and equipment constraints. As a result, rutting is the primary failure mechanism. This problem is accentuated by the issue of traffic wander from landing aircraft. Mechanistic-empirical performance models are used to predict failures in various pavement structures, but this approach typically is confined to static load computations. Two-dimensional axisymmetric finite-element (FE) models can simulate cyclic loading but are restricted to a single point of application. This study properly investigated the soft subgrade deformation of the AM2 matting system under repeated, wandering aircraft traffic, which causes rotation of the principal stress axes and induces variations in excess pore-water pressures in the subgrade. We developed a full three-dimensional (3D) FE model that incorporates traffic wander using a pseudodynamic time-staggered series of tire imprints to represent a moving aircraft. The soft subgrade is modeled by implementing the Multi-Mechanical Model (MMM), a user-defined elastoplastic kinematic hardening model capable of modeling clays under repeated loadings and complex stress histories. The FE model matched well with multiple passes of measured earth pressure cell and single depth deflectometer data from full-scale testing. Results showed that rotation of the principal stress axes and changes in excess pore-water pressures occur in the subgrade because of the moving tire load. Findings suggest that the proposed 3D modeling approach implementing aircraft wander can provide a reliable platform for accurately simulating the subgrade response under pseudodynamic loading conditions.

Stockpiling a cold central plant recycled (CCPR) asphalt mixture may be beneficial to a producer as it allows them to optimize paving and material production. However, no previous studies have been found in the literature, and it is unclear if stockpiling a CCPR mixture has any positive or negative effect on the strength properties of the CCPR mixture. This study investigated the effect of laboratory simulated stockpiling on the strength properties of a CCPR mixture that used foamed asphalt as a recycling agent. To simulate the stockpile, the mixture was stored in buckets to ensure minimal moisture loss, and test specimens were fabricated from the laboratory stockpile at varying time intervals. Moisture content, compaction effort, indirect tensile strength, and dynamic modulus were measured, and AASHTOWare Pavement ME Design was used to determine any change in performance prediction for the laboratory stockpiled mixture. The tensile strength and dynamic modulus decrease significantly within the first three days of stockpiling, after which they remain constant, but the pavement performance prediction showed little effect, highlighting the need for further model development.

In this study, 35VB high-strength bolts used in subtropical, humid climate were tested to determine the causes of fracture failure. Simulated working conditions of a stress corrosion experiment were carried out on bolt #S1. The fracture macromorphology, micromorphology, and phase composition of corrosion products of failed bolt #D1 and simulated stress corrosion bolt #S1, the metallographic structure of the new bolts #N1, #D1, and #S1, and the mechanical properties of #N1 and #S1 were compared and analyzed. It was concluded that the microstructure of #D1 was defective and there were cracks in the crack source region and the crack propagation region. Stress loading and environmental corrosion led to the occurrence of fracture synergistically. It was speculated that the coupling of the environment with stress produced little damage to the bolt in the stress corrosion test, but the environment and stress accelerated the impact on fracture failure.

This research involving two binders, a neat $70/100$ paving grade bitumen and an epoxy-diluted bitumen, evaluated the effect of hydrated lime and limestone filler on the oxidative age hardening of binders. A pressure aging vessel (PAV) unit was used to mimic long-term oxidative aging, and the rheological properties of binders containing fillers were measured using a dynamic shear rheometer. The active nature of hydrated lime with binders was further verified by conducting elongation-to-fracture tensile tests. Results indicate that the effect of the filler reactivity is much more pronounced in epoxy bitumen than in neat bitumen, with the pure limestone filler showing the highest stiffening effect. The epoxy bitumen containing limestone filler was also tougher, showing higher elongation-to-break than the mastics generated with hydrated lime. Even though the epoxy bitumen containing limestone was the strongest and toughest material, it exhibited higher susceptibility to fracture after 80 h in PAV than of the same binder with hydrated lime. This research verifies earlier studies that hydrated lime could improve the low-temperature properties, resulting in the reduction of the deleterious effects of oxidative age hardening in bituminous binders.

Accurate prediction of transport properties for cementitious materials remains a challenge since it is difficult to experimentally obtain the realistic three-dimensional (3D) pore network of cement paste. In this study, the 3D pore network of cement paste is quantitatively characterized using nano X-ray microtomography coupled with the metal centrifugation porosimetry (MCP). First, the MCP technique is carried out to impel the liquid metal into the pore network of cement paste. Subsequently, the 3D pore network of cement paste with the intruded metal is reconstructed using high-resolution X-ray microtomography. Finally, based on the X-ray microtomography images, the transport properties of cement paste including ionic diffusivity and fluid permeability are simulated using a set of lattice Boltzmann transport models. The results show that the metal alloy can significantly enhance the contrast between the pore network and solid phase, and the realistic 3D pore network can be successfully reproduced. For the cement pastes with water-to-cement ($w/c$) ratios of 0.5 and 0.6, the transport properties are dramatically increased with the improving $w/c$ ratio. A similarly dramatic growth evolution of transport properties also occurs when the effective porosity of cement pastes raises from 27.56% to 36.11%.

Welded wire reinforcement (WWR) offers improvements in constructability over conventional rebar but suffers from low ductility because of cold working. WWR is often epoxy coated or galvanized to improve its resistance to corrosion. The associated heating from the coating processes may improve ductility, adding additional value of coating to WWR and improving member performance. The authors hypothesize that epoxy-coated and hot-dip-galvanized WWR have higher strength, stiffness, and ductility than uncoated WWR. To test this hypothesis, experiments were performed to measure the yield strength, ultimate strength, modulus of elasticity, and elongation in uncoated, epoxy coated, and galvanized WWR in D11, D20, and D31 wires. The yield strength and ultimate strength of the WWR were not significantly affected by either coating process; however, the galvanizing process resulted in significant increase in uniform and total elongations. The authors present a case study to compare section ductility in reinforced concrete slabs with uncoated and galvanized WWR elongations at the minimum and maximum allowable reinforcement ratios. Depending on section length and reinforcement ratio, the increase in ductility of galvanized WWR translates to a 10%–50% increase in section ductility.

The results of field tests to evaluate methods designed to make epoxy-coated reinforcement (ECR) more resistant to corrosion are reported. Reinforcing bars coated with epoxies designed to have improved adhesion to the steel, concrete containing corrosion inhibitors, bars with a primer coating containing microencapsulated calcium nitrite applied prior to epoxy application, bars coated with zinc prior to epoxy application, and conventional uncoated bars are evaluated based on corrosion rates and losses using field exposure tests that closely simulate conditions in bridge decks subjected to deicing salts. Coatings are penetrated to simulate damage that occurs during construction. Even when damaged, epoxy-coated bars exhibit significantly lower corrosion rates based on total area than conventional reinforcement. The corrosion resistance of bars with improved adhesion does not increase compared to conventional ECR. Bars with a layer of zinc underneath the epoxy exhibit performance comparable to conventional ECR; this is in contrast to laboratory tests in saturated concrete where the zinc-and-epoxy coated bars exhibited poor performance.

Basalt fiber is commonly used as reinforcement in various civil engineering structures such as concrete panels, domes, bridges, and tunnels. Dynamic characterization of basalt fiber–reinforced concrete (BFRC) using a split Hopkinson pressure bar (SHPB) is carried out in the present investigation. Concrete with characteristic compressive strength of 30 MPa is considered herein to study its static and dynamic behavior. For this purpose, plain concrete (PC) and BFRC with a fiber content of 1% and 2% are investigated. For dynamic behavior, two different diameters, i.e., 76 and 54 mm samples, are prepared with varying slenderness ratios of 0.3 and 0.5. The behavior of PC and BFRC is experimentally studied at different strain rates ranging from 164 to 796/s, with gas gun pressures up to 0.38 MPa. Based on this investigation, it is observed that the strength of the concrete increases with the increasing strain rates, and the dynamic increase factor (DIF) is found to be varying from 0.91 to 3.58.

Rubber powder is widely used to modify base asphalt binder to improve the low-temperature performance and crack resistance of asphalt mixtures. This paper investigates the aging mechanism and performance evolution of rubber-modified asphalt in terms of three levels: rubber powder, rubber-modified asphalt, and rubber-modified asphalt mixture. The multilevel analysis results show that mass loss, phase transition, and melting occur during the process of rubber powder aging, and scanning electron microscope images indicate that the surface morphology of the rubber powder becomes smoother. The aging of base asphalt leads to the volatilization and oxidation of light components, resulting in the production of carbonyl and sulfoxide groups and a reduction in the swelling between the rubber powder and aged base asphalt. The aging of rubber powder leads directly to a significant decrease in the modification effect of the rubber; thus, rubber powder aging plays a more decisive role in the degradation of rubber-modified asphalt than base asphalt aging. By contrast, the performance indicators of aged rubber-modified asphalt are able to reach their highest values due to the effective blending between the rubber powder and base asphalt, which results in an enhanced antiaging capability. The sensitivity of all performance indicators of rubber-modified asphalt to the aging temperature is relatively low, except for the 5°C ductility index. Therefore, the mixing temperature needs to be strictly controlled to a specified value when rubber-modified asphalt is applied in cold areas that require low-temperature stability of the mixture. As for the aged rubber-modified asphalt mixture, the dynamic stability improved significantly, the ultimate tensile strain at low temperature decreased, and the antifatigue performance decreased to different extents under different stress ratios.

Although the uniaxial tensile strength ($f_t$) of concrete is one of the most essential properties in designing and analyzing the tensile performance of a concrete member, a rational consensus to assess it is still lacking because of experimental difficulties. The objective of the present study is to generalize $f_t$ through mathematical analysis based on the plasticity of concrete. The principle of equivalent resultant tensile forces at failure planes is introduced to straightforwardly determine the splitting tensile strength ($f_{sp}$) and modulus of rupture ($f_r$) from $f_t$. The accuracy and reliability of the proposed equations are confirmed at different ranges of the compressive strength and unit weight of concrete by comparing with test data, including 219, 674, and 242 data sets for uniaxial tension tests, splitting tension tests, and flexural tests, respectively. Thus, the present mathematical approaches proved the significance of considering the concrete unit weight and maximum aggregate size in predicting the tensile resistance capacities of the concrete. However, with the variations of the compressive strength and unit weight of concrete, the empirical equations recommended in previous studies and code provisions are insufficient.

High-strength concrete (HSC) has been widely used in civil engineering. HSC is a kind of multiphase composite material with large dispersion. In order to improve the safety of structure or component design, it is of great significance to study the variability of HSC mechanical properties and its variation with time. This paper carries out experimental research on the time-varying properties of C80 fly ash HSC under standard curing conditions, and analyzes the influence of curing time and fly ash content on the mean value and variation coefficient of compressive strength. Based on the compressible packing model (CPM), a compressive strength calculation model of fly ash HSC is established. Because the aggregate distribution characteristics have great influence on strength, the maximum paste thickness is analyzed based on the random aggregate model, a computational model for compressive strength of fly ash HSC considering the randomness of maximum paste thickness is presented further. The results show that the compressive strength values predicted by the proposed model have the same variation rule with predictive values of models in codes containing different fly ash content at different age, and the predictive values of models in codes are all in the prediction range of the proposed model with a 95% guarantee rate. This proposed model not only has a good calculation accuracy, but also has a certain prediction confidence interval, which provides a certain theoretical basis for the random prediction of the compressive strength of high-strength concrete.

This work presents green lightweight reactive powder concrete (GLRPC) as a novel lightweight composite with improved properties by incorporating modified expanded polystyrene beads (MEPS) into green reactive powder concrete (RPC). It provides the advantages of both RPC and lightweight concrete (LWC). Because incorporation of the conventional expanded polystyrene (EPS) beads into the concrete mix results in a considerable loss of mechanical properties, it is necessary to find effective methods to preserve RPC properties as much as possible. The present work is devoted to the thermal modification of EPS. Various mixtures with different replacement levels of total RPC binder paste volume (0%, 15%, 30%, and 45%) with MEPS under different curing conditions (both standard water curing and heat curing conditions) were investigated in terms of their physical and mechanical properties. The results of the experimental study showed that MEPS beads had appropriate distribution into the GLRPC matrix without any considerable segregation. Replacement levels up to 30% of RPC paste volume by MEPS beads result in the development of high-strength lightweight concrete. Further replacement levels lead to lightweight concretes that drop into structural class. The water absorption shows a stronger dependency to curing temperature than replacement level of RPC paste volume with MEPS. The value of water absorption for all the studied mixtures, however, remained less than 2% that is relatively small. The microstructure analysis showed a very dense and uniform interfacial transition zone microstructure (ITZ) with good bonding of cement paste to MEPS beads. The relatively higher compressive strength of GLRPC cured at 200°C could be attributed not only to the development of a denser microstructure, but also to the development of hollow spherical polystyrene beads with hard and stiff shells resulting in an innovative high-tech plastic/cement-paste bonding.

The aim of this study was to examine the effects of different additives on the moisture resistance of asphalt binders using atomic force microscopy (AFM), and to correlate the results with those obtained in macroscale tests. To this end, AFM force spectroscopy was conducted on neat and polymer-modified asphalt binders produced using various warm mix asphalt (WMA) technologies. The technologies considered included Sasobit, Advera, foamed WMA, and Evotherm M1. Furthermore, the asphalt mixtures were prepared using the considered asphalt binders and were tested using the AASHTO T 283 test. The results of this study show that the most significant factor affecting the AFM adhesive forces of asphalt binders is the use of polymer additives. However, the interactions between various chemical groups in asphalt binders and the considered additives differ. Finally, it was found that the effect of aggregate-binder adhesive bonds on indirect tensile strength is greater than that of the binder’s cohesive bonds, as the cracking in this AASHTO T 283 test has more tendency to occur at the interface between the aggregate and the binder due to the high stress concentration.

Microwave-assisted concrete liberation and aggregate recycling is highlighted by many research groups due to its efficient and effective recycling process. In this paper, a series of experiments are conducted to study the heating results of concrete under microwave and conventional heating processes. The temperature variations of concrete under two different heating approaches are obtained. The crack characteristic and material damage during the different heating processes are illustrated. Particularly, the energy efficiency was investigated for two approaches. Results proved that concretes were broken more effectively under microwave irradiation than in conventional furnaces, and the aggregates can be easily separated under the sufficient power input. Scanning electron microscope (SEM) analysis proved that after microwave treatment, intergranular fractures are formed at mortar-aggregate interfaces, few cracks occurred after conventional heating processes. The research proves that, compared with conventional heating, microwave irradiation could liberate concrete and recycle aggregate effectively, with less heating duration and lower energy input required.

Understanding the biaxial mechanical behavior of polypropylene fiber–reinforced expansive self-consolidating concrete (PPESCC) is of critical significance for predicting the response of a structure under multiaxial compression or multiaxial compression and tension. To study the combined effects of polypropylene fiber and expansive agent on strength, the addition of an expansive agent (8% by cementitious material mass) and the volume fraction of polypropylene fiber (0%, 0.05%, and 0.1% by concrete volume) were designed as experimental variables. A series of biaxial compression-compression (C-C) and biaxial compression-tension (C-T) tests on cubic specimens with a side length of 100 mm was conducted. The observed failure mode showed that there was no significant difference in the crack patterns regardless of the addition of expansive agent and fiber content. The experimental results also indicated that although the biaxial compressive strength was affected by the polypropylene fiber content and the incorporation of expansive agent, the normalized failure envelops under biaxial compression are approximately the same for both normal self-consolidating concrete (SCC) and expansive SCC with different fiber contents. Based on previous investigations in the literature, a strength criterion and constitutive model were developed for PPESCC under biaxial compression. Through comparison, the error between the strength criterion model and experimental results is less than 10%. Meanwhile, it was demonstrated that the biaxial C-T strength decreased by 77% on average due to the exertion of tension. The proposed strength formulas for biaxial C-T loading were in good agreement with the experimental data for PPESCC.

Termites are major pests that can secrete formic acid to damage concrete structures. To solve this engineering problem, termite-resistant concrete was prepared by incorporating chlorpyrifos microcapsules. The results showed that the chlorpyrifos microcapsules could resist the alkaline environment and heat from cement hydration. The addition of chlorpyrifos microcapsules had little effect on the hydration of the cement paste, and the microcapsules could be effectively stored in the cement paste. In addition, chlorpyrifos microcapsules changed the workability, and reduced the compressive strength of concrete, though the concrete met the engineering requirements.

Enzyme-induced carbonate precipitation (EICP) has emerged as a soil reinforcement technique in recent decades. To enhance the durability of EICP-solidified soil, a method of EICP combined with polyvinyl alcohol (PVA) is proposed to improve aeolian sand. A cementation solution for $\mathrm{EICP}+\mathrm{PVA}$ was prepared in the PVA solution. Unconfined compression strength, wind erosion, water erosion, and penetration resistance tests were performed to investigate the effect of EICP with different concentrations of PVA (1%, 2%, 3%, 4%, and 5%) on aeolian sand solidification. The durability of aeolian sand solidified by EICP and 3% PVA was examined through freeze–thaw and dry–wet cycle tests. The results demonstrated that the material precipitated from EICP solution is calcite; and that the presence of PVA can improve significantly the unconfined compressive strength, wind erosion resistance, water erosion resistance, and surface strength of EICP-solidified aeolian sand; and that 3% PVA is enough for sand treatment in practical applications. Additionally, $\mathrm{EICP}+\mathrm{PVA}$–solidified aeolian sand had high durability to the freeze–thaw and dry–wet cycles. Scanning electron microscopy (SEM) images revealed films with a network structure in the solidified aeolian sand after adding PVA. Combined with the mercury intrusion capillary pressure test, these tests indicated that the improvement of the performance of $\mathrm{EICP}+\mathrm{PVA}$–solidified sand mainly was due to the fact that the PVA films enhanced cementation between soil particles and between soil particles and calcium carbonate, and because PVA film–wrapped calcium carbonate filled the large-size pores in the soil.

This study monitors the early-age reaction kinetics and measures the heat of reaction of alkali-activated ground granulated blast-furnace slag (GGBFS) using an isothermal calorimeter, and the initial setting and possible product formations by measuring ultrasonic pulse velocity (UPV). The GGBFS was activated with alkaline activator solutions of different concentrations in terms of modulus ratio ($M_s$) and ${\mathrm{Na}}_2\mathrm{O}\%$ content. Results reveal that GGBFS is highly sensitive to the compositions of the alkaline solutions. Increasing the alkalinity of the activator results in better dissolution of species and consequently an increased heat evolution with a relatively shorter setting time. The activator concentration also affects the rate of product formations as well as the morphological features. Activators with higher $M_s$ lead to homogeneous slag morphology. The abundance of silicate species in the alkaline solution also plays an important role in its structural formation. scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDS) microstructural characterizations supports the advanced dissolution of particles in a more alkaline environment. The presence of C-(A)-S-H gels in alkali-activated slag pastes was detected.