Journal of Materials in Civil Engineering

In this study, the effects of some of the important manufacturing parameters of rice husk ash (RHA) on its mechanical performance in mortar mixtures is investigated. All of the presented results belong to a comprehensive experimental program where samples of plain and acid-leached rice husks were slowly heated up to 700°C and combusted at such temperature for different lengths of time, from 0.25 to $16\mathrm{h}$. The obtained ashes were ground for different lengths of time, ranging from 0.33 to $16\mathrm{h}$, and the resulting pozzolans were replaced for cement at different levels (5%, 10%, and 15% by mass) in mortar mixtures with similar flowabilities. The 28-day compressive strengths of the mortars were measured, and the results were analyzed via regression analysis. The analysis outcome suggests that acid leaching does not necessarily lead to better mechanical performance, and precise optimization of other combustion parameters is needed to improve the performance of RHA. Under optimal conditions (acid leaching followed by combustion at 700°C for $16\mathrm{h}$), replacement of 11% cement with such RHA was found to result in approximately 14% greater strength results compared to that of plain RHA-blended mixture and 78% greater strength compared to that of the 100% ordinary portland cement mixture. Despite the significant improvement in strength, it is concluded that acid leaching is not necessarily justifiable considering economic and environmental factors.

Ultraviolet (UV) radiation causes asphalt aging and thus influences its performance. In this research, a composite light stabilizer was prepared to increase the light stability of matrix asphalt. Benzotriazole UV absorber (UV928), a hindered amine radical scavenger (UV4050), and a light screening agent [layered double hydroxide (LDH)] were selected as light stabilizers to modify the matrix asphalt, and their properties were compared using a physical property test and rheological test before and after UV aging. UV aging and a rolling thin-film oven test (RTFOT) were applied to simulate laboratory accelerated aging. The one-component test results demonstrated that three kinds of light stabilizer improved the light stability of asphalt to some extent. However, before UV aging, the addition of light stabilizer caused a great loss of asphalt fluidity and reduced the low-temperature performance of asphalt, which influenced the original performance of matrix asphalt. Therefore, the composite light stabilizer was prepared to weaken the adverse effect of a single material on asphalt. The composite light stabilizer not only improved the fluidity and the low-temperature crack resistance of one-component modified asphalt. Moreover, from the perspective of high-temperature performance, it also reduced the adverse effects of UV radiation on asphalt. This implied that the composite light stabilizer not only reduced the adverse effects of one-component light stabilizer on asphalt but also ameliorated the light stability of matrix asphalt, and the three kinds of light stabilizer had a good synergistic effect.

The object of this research was to study the influence of waterborne epoxy resin on the properties of emulsified asphalt and its microstructure. First, the proportions of curing agent and waterborne epoxy resin were determined based on the test results of three indexes. Then, modified emulsified asphalt emulsion samples with different waterborne epoxy resin contents were prepared. The evaporation residues of the modified emulsified asphalt samples were subjected to the three index tests, dynamic shear rheological (DSR) test, bending beam rheometer (BBR) test, and pullout test. In addition, the performance parameters of the waterborne-epoxy-resin modified emulsified asphalt were compared with those of the neat asphalt and the emulsified asphalt. Last, the microstructures of the modified emulsified asphalt samples were studied with scanning electron microscopy (SEM). The test results indicated that the optimal curing agent to waterborne epoxy resin ratio was $10:1$. As the waterborne epoxy resin content increased, the softening point of the evaporation residue of the modified emulsified asphalt samples increased and penetration decreased. The ductility suddenly decreased. The addition of waterborne epoxy resin significantly improved the high-temperature performance and bond behavior of the modified emulsified asphalt. However, its low-temperature performance deteriorated. The results of the microstructure analysis indicated that when the waterborne epoxy resin content was 10%, the waterborne epoxy resin was more evenly distributed throughout the modified emulsified asphalt. The comprehensive properties of the waterborne-epoxy-resin modified emulsified asphalt were superior to those of neat asphalt and emulsified asphalt.

This study investigated the performance of alkali-activated, cement-based controlled low-strength materials (CLSMs). The CLSM was produced by mixing fly ash, steel slag, sodium hydroxide, and water with bottom ash (BA) aggregate. Properties of fresh and hardened composites were measured, and tests were conducted to determine their microstructure characteristics. Highlighted properties including slump flow, bleeding, unit weight, unconfined compressive strength, and resilience modulus were reported. The results indicated that the inclusion of 10%–30% slag resulted in a stronger CLSM with a higher Ca/Si ratio in the cementitious matrix of its microstructure. Higher slag content in the CLSM also shortened setting time and led to a lower bleeding rate. A mixture containing slag up to 20% of fly ash was recommended for pavement applications. Finally, the economic and environmental impacts were also preliminarily studied.

The damage of asphalt mixture is closely related to its internal material heterogeneity and discontinuity. The mechanical evolution of asphalt mixture is analyzed by meso-mechanics theory, which is very important for revealing the failure mechanism of asphalt pavement. In this paper, the two-dimensional (2D) bending discrete-element model of asphalt mixture was established based on the meso parameters and pictures of the model determined by practical experiments. The process of meso-crack formation and propagation between particles of asphalt mixture under a certain load rate was analyzed. The distribution and transmission of stress and the evolution of the displacement field were also analyzed. The results show that the error between the model bending test and the actual standard test is within 10% (maximum bending strength and maximum bending strain). The model test results show that the discrete-element method can simulate discontinuous and heterogeneous materials well. Under the action of external load, the vertical displacement of coarse aggregate particles is much larger than the horizontal displacement. The displacement of asphalt cement granules is slightly larger than that of coarse aggregate granules. The number of microcracks in the model increases slowly in the early stage and quickly in the later stage. Finally, macroscopic cracks are generated. These macroscopic cracks generally extend along the edges of coarse aggregate particles and where the adhesion of asphalt mortar particles is weak. The force chain diagram between particles in the discrete-element model had both regularity and great discreteness. The results showed that the discrete-element method could not only obtain the internal stress and displacement of the asphalt mixture, but also reveal the mechanical evolution behavior between the particle flows of the asphalt mixture.

A novel statistical framework was developed to quantify the variability of the fitting parameters of the soil–water characteristic curve (SWCC). Reliable estimation of the mean, standard deviation, and associated probability density function (PDF) of the fitting parameters of SWCC is an important tool for addressing reliability-based designs in unsaturated soil mechanics. The assumption of either Gaussian or lognormal distributions may not be valid for representing a high degree of variability associated with fitting parameters. This study aimed to provide the most appropriate continuous PDFs by optimizing the mean and standard deviation such that errors associated with quantile, percentile, and cumulative distribution function (CDF) were as low as possible. A total of 261 and 111 sample points were collected from the most comprehensive experimental works on the fitting parameters of SWCC for clayey and silty soils, respectively. Optimum distributions suitable to the model fitting parameters of SWCC are highly dependent on the type of soil. The most appropriate PDFs for representing the fitting parameters $a_f$, $n_f$, and $m_f$ of Fredlund and Xing’s model were gamma, Weibull, and inverse Gaussian distributions, respectively. Similarly, fitting parameters $a_f$, $n_f$, and $m_f$ for silty soils were represented by inverse Gaussian, Gumbel maximum, and Gumbel maximum distributions, respectively. This study found that the selection of inappropriate PDFs overestimated the probability of failure of unsaturated infinite slopes considerably, by 99.49% and 99.76%, respectively, for clayey and silty soils. Recommended mean, coefficient of variation (COV), and PDF are useful in the reliability-based design of unsaturated soil slopes and in judging the performance of existing infinite and finite slopes.

Geopolymer concrete is reported as the best possible alternative to cement-based concrete. However, the limitation in the attainment of structural strength using ambient curing has restricted the use of geopolymer concrete for cast-in-situ construction. Therefore, the present study aims to develop ambiently cured geopolymer concrete using sillimanite sand as a replacement for river sand. The strength, durability, and microstructural properties of this concrete are evaluated. In the investigation, the fine aggregates of geopolymer concrete were replaced with 25%, 50%, 75%, and 100% sillimanite sand by weight. The test results revealed that the 8-M and 16-M molarity levels are feasible to attain the structural strength. Specifically, the 16-M molarity level with 50% replacement of fine aggregate with sillimanite sand exhibited higher geopolymerization. The suggested range of optimum replacement levels of fine aggregate with sillimanite sand is 25%–50%. An increase in percentage replacement beyond 50% indicates a reduction in compressive strength and durability properties. The microstructural analysis indicates dense interconnection between the gel networks due to the presence of sillimanite sand, uniform distribution of elements in the mix, and the presence of strong Na–Al–Si gel. The sillimanite-sand-containing geopolymer concrete developed using ambient curing resulted in a sustainable product along with higher mechanical and durability property.

This paper aims at presenting an analytical method for evaluating the calcium diffusion coefficient of partially leached cement paste. The analytical method is developed based on a two-scale model of partially leached cement paste. On the first scale, the solid phase in partially leached cement paste is modeled as a two-phase composite material, composed of a matrix of calcium silicate hydrate ($\mathrm{C}─\mathrm{S}─\mathrm{H}$) gel and inclusions of unhydrated cement and undissolved calcium hydroxide (CH) crystal. The relative calcium diffusion coefficient is derived analytically by the differential effective medium scheme. On the second scale, partially leached cement paste is treated as a system consisting of the solid phase and spheroidal capillary pores; the percolation behavior of capillary pores near the critical volume fraction is considered. In combination with percolation theory, the effective medium approach is modified to evaluate the calcium diffusion coefficient of partially leached cement paste. The depolarization factor is expressed in terms of the critical volume fraction of capillary pores, and the percolation exponents are calibrated from computer simulation data. Finally, the validity of the analytical method is verified with computer simulation data and experimental results collected from the literature. It is concluded that the proposed analytical method can predict the calcium diffusion coefficient of partially leached cement paste with reasonable accuracy.

Evaluation of the concrete cracking induced by rebar corrosion is necessary for accurately clarifying the durability and predicting the service life of reinforced concrete (RC) structures. The fact that rust penetration into cracks might decrease corrosion expansion has been realized but not sufficiently investigated. In this paper, a numerical approach in terms of the mesoscopic structure of concrete is used to simulate the corrosion-induced concrete cracking, and the lattice network model to account for rust penetration into cracks is developed by assuming that the movement of rust is driven by moisture convection. The total rust amount is calculated based on Faraday’s law, and the rust expansion is transformed to a radial displacement boundary condition for both uniform and nonuniform conditions. Rust penetration is assumed to be a convection process governed by Darcy’s law. The proposed model is confirmed by comparing cracking pattern, corrosion pressure, surface crack width, mass ratio of penetrated rust to total rust ($\mathrm{\Delta }{W}_{\mathrm{pe}}/\mathrm{\Delta }{W}_{\mathrm{total}}$), and volume ratio of cracks occupied by rust to total cracks ($V_{\mathrm{rust}}^{\mathrm{crack}}/V_{\mathrm{crack}}^{\mathrm{total}}$) with available experimental and numerical results. It is found that the distribution and the amount of penetrated rust are closely related to the volume of cracks and the connection of crack networks. Besides, through sensitivity analysis of influencing factors for rust penetration, it is found that a higher dissolved degree of rust in moisture induces a higher $\mathrm{\Delta }{W}_{\mathrm{pe}}/\mathrm{\Delta }{W}_{\mathrm{total}}$, but it doesn’t influence $V_{\mathrm{rust}}^{\mathrm{crack}}/V_{\mathrm{crack}}^{\mathrm{total}}$. A larger relative water content at the concrete-steel interface will induce higher $\mathrm{\Delta }{W}_{\mathrm{pe}}/\mathrm{\Delta }{W}_{\mathrm{total}}$ and $V_{\mathrm{rust}}^{\mathrm{crack}}/V_{\mathrm{crack}}^{\mathrm{total}}$, while the initial relative water content in concrete has no significant difference on either $\mathrm{\Delta }{W}_{\mathrm{pe}}/\mathrm{\Delta }{W}_{\mathrm{total}}$ or $V_{\mathrm{rust}}^{\mathrm{crack}}/V_{\mathrm{crack}}^{\mathrm{total}}$.

The main purpose of this article is to evaluate the correlation between the indirect tensile strength and the permeability capacity of porous concrete (PC) pavements. The compaction method employed plays a critical role in this correlation. However, even though PC pavements have been studied in many places around the world, using different compaction methods, a profound analysis of these methods has not been carried out yet. This research introduces a study of five different compaction methods: axial compression, gyratory, impact, multilayer impact, and tamping rod, with diverse treatments in each one to obtain the best correlation between the indirect tensile strength and permeability capacity. Results demonstrated that the impact compaction method at 50 blows on only one side of the sample gives the best strength-permeability correlation, with an indirect tensile (IT) strength value of 2.75 MPa and a permeability ($k$) capacity of $0.56\mathrm{cm}/\mathrm{s}$.

Nanosilica has been proven able to strengthen the early-age performance of high-volume fly ash (HVFA) cementitious composites. However, the long-term influence of nanosilica on HVFA composites is yet unclear. This research aimed to investigate the long-term microstructures, strength, durability and volume stability of HVFA mortars incorporating nanosilica. In this study, nanosilica was added to cement mortar where 50% of the binder was fly ash. At the age of 2 years, despite some fly ash particles remaining incompletely hydrated, the benefits of nanosilica could still be retained in HVFA mixtures. The experiments revealed that a 2% nanosilica addition could increase the compressive strength of HVFA mortar by 50% and reduce the water sorptivity, chloride-ion penetration, and drying shrinkage by 80%, 90%, and 13%, respectively. The improvements on the various measurements are attributed to the reduced porosity and refined pore size by nanosilica.

In this study, an experimental investigation of the thermal effect of welding on the mechanical behavior of thermomechanical control process (TMCP) high-strength steel (HSS) Q690CFD is carried out. Twenty-four specimens in four groups with different welding heat input, strength mismatch ratio of weld filler and base material, heat treatment condition [preheating (PH) and postweld heat treatment (PWHT)], as well as mechanical boundary condition during the welding process are designed and tested. The thermal history and cooling rate are monitored and analyzed. The welding residual stress near the weld toe and the microstructure of the heat-affected zone (HAZ), as well as Vickers hardness, are respectively examined with the ASTM hole-drilling method, metallurgical microscope observation, and Vickers hardness tests. The effect of heat input ($q$), mismatch ratio ($r$), heat treatment, and mechanical boundary conditions on welding residual stress, microstructure, and hardness of the HAZ is investigated. The effect of welding heat input on the tensile behavior of the TMCP HSS is studied. Results indict that different heat inputs could have varied cooling times and cooling rates and hence could produce different distributions of residual stress. When the same PH and PWHT is applied, the heat treatment could have better stress-relief effect for the specimens without mismatching. In addition, the width of the HAZ increases steadily with the increase in heat input. A good yield and ultimate strength prediction from hardness can be observed for base steel and welded connections.

Recently, fiber-reinforced concrete (FRC) creep behavior has become a much addressed topic, and the main gap found in the literature is whether cracked FRC is stable in the serviceability limit state. Therefore, this work aims to investigate the creep behavior of steel and polypropylene (PP) FRC by analyzing the growth of the crack opening displacement over time in prismatic specimens subjected to sustained bending. Sustained load tests were also performed on FRC constituents and on the fiber matrix interface in order to evaluate individually their long-term response, and to understand their contribution in bending. Based on a model proposed, the rotation in a plastic hinge located in the crack area could be calculated considering the three mechanisms evaluated—fiber pullout, concrete compression, and shrinkage. It could be concluded that the fiber pullout mechanism plays a primary role in creep deformation in precracked elements subjected to sustained bending loads.

The differences in corrosion between the erosion mechanisms of sprayed concrete (SpC) and ordinary concrete (OC) under sulfate attack at different corrosion ages were investigated in this paper. Here, 10% sodium sulfate was used to corrode SpC and OC under the condition of a 24-h drying-wetting cycle. The microdeterioration process and the change-rule of the durability of the two kinds of concrete are analyzed from the perspectives of microstructure and durability by means of scanning electron microscope (SEM) and relevant laboratory tests. The results show that the erosion products of SpC first accumulate in the original defects, such as pores and holes, whereas the erosion products of OC first concentrate on the surface of the specimen. Thereafter, the original defects in SpC are gradually filled and recracked, whereas OC is directly cracked. As a result, the corrosion resistance and durability of SpC is ultimately better than that of OC to some extent. Moreover, reported experiment data indicate that the damage degree and time of SpC and OC are different, and corrosion products can be detected before the deterioration degree of concrete increased significantly.

This research studies the applicability of alkali-activated cement with a mixture of fine-clay brick waste (FCBW) and palm oil fuel ash (POFA) to manufacture environmentally friendly masonry units. FCBW and POFA were used as a precursor, while a dredged soft clay (SC) was used as aggregate. Sodium hydroxide (NaOH) and sodium silicate (${\mathrm{Na}}_2{\mathrm{SiO}}_3$) solutions were used as the liquid alkaline activator. Effects of NaOH concentration, initial ${\mathrm{SiO}}_2/{\mathrm{Al}}_2{\mathrm{O}}_3$ mole ratio, ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ ratio, and curing conditions on the strength and microstructure of the FCBW-POFA-SC geopolymers were evaluated. The FCBW-POFA-SC geopolymers had a lower total unit weight than compacted SC because NaOH in the geopolymer binder caused a flocculated soil structure. It was found that ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}=70/30$, $10\mathrm{M}$ NaOH, and $\mathrm{FCBW}/\mathrm{POFA}=70/30$ were the best ingredients providing the rigid network of the geopolymer structures. The suitable heat duration of $48\mathrm{h}$ at 80°C accelerated the dissolution rate of the Si and Al and polycondensation in the geopolymer structure, resulting in denser geopolymer gels and early strength gain. With this optimum ingredient and suitable heat condition, 7-day unconfined compressive strength (UCS) of the FCBW-POFA-SC geopolymers achieved the requirement of the Thailand industrial standard for non-load-bearing masonry units ($\mathrm{UCS}>2.5\mathrm{MPa}$). The geopolymer products were found to be sodium aluminum silicate hydrate (N─ A─ S─ H) and calcium aluminum silicate hydrate (C─ A─ S─ H). The research outcome will promote the usage of waste materials for manufacturing environmentally friendly infrastructure in Thailand and other countries.

An innovative preparation method was invented that adds adhesive to gypsum–particle composites. The effects of varying the wood particle to gypsum ratio and melamine-urea-formaldehyde adhesive (MUF) content on mechanical properties and combustion performance were examined and discussed. Microscopic analyses revealed the mechanism of improvement in this innovative gypsum–particle composite (IGP). The ignition point of IGP was high and the heat and smoke release rate low, with the peak release time greatly delayed compared to structural wood-based composites. The mass retention of IGP was greatly increased and its charred appearance slight. The internal bonding strength (IBS), bending strength (modulus of rupture, MOR), and modulus of elasticity (MOE) of IGP with 9.0% MUF content were 3.4, 4.8, and 3.9-fold higher, compared to gypsum board, respectively. IGP with 7.6% MUF appeared to be suitable as load-bearing panels. MUF content positively affected IGP properties and a 7.6% MUF content and $3/10$ wood particle to gypsum ratio were found to be optimal for IGP production. The IBS, MOR, and MOE reached 1.28, 16.10, and 6,861 MPa, such that these composites could be used as building materials. The lateral elastic stiffness and maximum load of IGP nail connections were $313.6\mathrm{kN}·{\mathrm{m}}^{-1}$ and $\mathrm{1,386}\mathrm{N}$ under parallel-to-grain load, respectively.

Fiber-reinforced concrete (FRC) structures are mainly designed using finite-element software. The input parameters used in these methods are based on the material properties of FRC obtained from test results. Because the experimental results of FRC show huge deviations, the material properties determined by an ordinary number of experiments do not give a realistic average value. This work aims to determine the real expected value and deviation of material properties using a semidiscrete analytical (SDA) model (using the average value and deviation of the fiber distribution and the minor deviation parameters of the SDA model). The input parameters of the design software can be determined much more accurately with these results. Finally, the number of experiments obtained can be decreased, and the advantage of adding fibers to the concrete can be effectively achieved.

The amount of municipal solid waste (MSW) generated in the US increases every year, and about 30% of the MSW generated is either recyclable or compostable. Utilization of compost-amended topsoils as a vegetative layer on highway slopes contributes to large-volume beneficial reuse of these materials. This study examines the shear and hydraulic properties of two types of composts, biosolids and leaf compost, and their blends with a topsoil for their potential use on highway slopes. Direct shear and consolidated-undrained triaxial shear tests were performed to obtain the shear strength parameters. Flexible-wall hydraulic conductivity tests and unsaturated hydraulic tests were performed to evaluate the saturated and unsaturated hydraulic behavior of the materials, respectively. Compost addition resulted in an increase in effective friction angle, whereas modest changes were observed in effective cohesion, total cohesion, and total friction angle of the topsoil. Two shape parameters determined via digital image analysis, angularity and relative form of 2-dimensional images, correlated well with the measured effective friction angles of the materials tested. Compost treatment resulted in an increase in saturated hydraulic conductivity and the plant-available water content. Unsaturated hydraulic conductivities of all materials were comparable at the matric potential of field capacity (10 kPa), and the compost-amended topsoils experienced 1–3 orders of decrease in their unsaturated hydraulic conductivities during the drying process.

The present paper looks into the postfire residual mechanical and corrosion behavior of the 2205 duplex stainless steel (DSS) after exposure to 800°C and 700°C (about and under the nose temperature of precipitation, respectively). The discussion focuses on the problems caused by intermetallic precipitation and a comparison of the 2205 DSS with an ordinary constructional steel. Very small amounts of intermetallics may already cause noticeable embrittlement (over 10% reduction of the strain at failure) and degradation of corrosion resistance of the 2205 DSS. Therefore, the reusability of the 2205 DSS, even just after short-time exposure to the intermetallics-formation temperature range, may be compromised. Unlike ordinary constructional steels, the intermetallics-induced problems of 2205 DSS cannot be avoided even when the cooling rate is low.

During earth-rock dam construction, temperature control to reduce the freeze–thaw impact on core-wall clay in cold regions is difficult. To address this challenge, this research developed a phase change material (PCM) incorporated into clay (PCM-clay) to improve the construction efficiency in a cold period. In the preparation of PCM-clay, considerable latent heat was stored by harvesting thermal energy from the environment, which was used for temperature control to extend the winter construction time. The feasibility of PCM-clay as core-wall clay was verified by an analysis of working performance. The results indicate that low-content PCM-clay (7%) is able to protect core-wall clay from freeze–thaw damage in a simulated environment (minimum $\mathrm{temperature}=-4.3°\mathrm{C}$) in a 1-day cycle. The working performance (e.g., shear strength and impermeability) supports that PCM-clay is a promising solution for temperature control of core-wall clay during earth-rock dam construction in cold regions.

Carbonaceous mudstone is a common embankment material with the characteristics of water softening and water disintegration, which often causes the instability of embankments. This paper presents an experimental work on the disintegration characteristics and mechanisms of carbonaceous mudstone under the combined action of load and cyclic drying–wetting. Disintegration tests were conducted by a novel instrument. Afterward, the evolution of disintegration parameters [i.e., coefficient of uniformity ($C_{\mathrm{u}}$), coefficient of curvature ($C_{\mathrm{c}}$), disintegration rate (DRE), disintegration ratio ($Dr$), and fractal dimension ($D$)] during the disintegration process was studied. Finally, the gray relational theory was used to evaluate the impact of disintegration characteristics on the degree of stability of carbonaceous mudstone. The results show that the large particles decrease in number and the small particles increase in number with increasing drying–wetting cycles. Moreover, the DREs of carbonaceous mudstone are very high with final values larger than 10% in all cases. Generally, the larger the load is, the higher the DRE is, while the lower the $Dr$ is. The $D$ increases with the increase of load and number of cycles. The results of gray relation analysis show that the variation in the $Dr$ is the best parameter for characterizing the disintegration of carbonaceous mudstone. The $Dr$ of carbonaceous mudstone decreases with increasing number of drying–wetting cycles under different loads, which can provide a useful reference for the stability analysis and engineering practice of carbonaceous mudstone embankments.

The use of construction and demolition waste is an effective solution to mitigate their environmental impacts and avoid dispose in landfills. This paper aims to evaluate the use of fine recycled-concrete aggregate (FRCA) in grout mixtures used in soil nailing. Compressive strength tests on FRCA grout were carried out at different curing ages and interface shear strength was measured between soil and grout. Properties of a commonly used cement grout are compared with those of sand-cement grout and FRCA-cement grout. Although the FRCA grout shows a lower compressive strength compared to commonly used grout and sand-cement grout, its measured properties still meet the minimum standards requirements. The interface friction angle and adhesion of the FRCA exhibit higher values compared to those measured at the soil–soil interface. The grout mixtures evaluated in this study indicated that it is possible to use 1.126 kg of FRCA for each cubic meter of grout. The consumptions of cement and water were found to be 42% and 24% lower, respectively. This represents approximately 380 kg less of ${\mathrm{CO}}_2$ emissions into the atmosphere per cubic meter. The use of FRCA in soil nail grouting can be a sustainable alternative to reduce environmental impacts, cement consumption, and greenhouse gas emission.

Asphalt pavement contains dynamically changing moisture, and the movement of this moisture will change the relative humidity of the pavement, thereby affecting the dielectric properties of the asphalt mixture. To improve the detection accuracy of nondestructive testing equipment and quantify the influence of relative humidity and frequency on the dielectric properties of asphalt mixtures, a dielectric composite model of asphalt mixtures based on relative humidity and frequency was established through theoretical deduction. The relative dielectric constant and dielectric loss of two asphalt mixtures were evaluated under different relative humidity and frequency conditions to verify the accuracy and reliability of the proposed model. The obtained goodness-of-fit verified wide applicability of the model. To realize the unification of the detection data under different relative humidity and frequency conditions, the relative humidity–frequency equivalence principle was established, and feasibility was verified in experiments that displayed strong applicability within a certain relative humidity and frequency range, thus providing a basis for realizing the conversion of the test results of different nondestructive testing equipment.

Mesoscale numerical modeling is an effective method of representing concrete as a three-phase material. Accurate aggregate geometry representation is an important aspect in numerical mesoscale modeling of concrete to predict mechanical properties as well as the damage initiation and fracture propagation. In this paper, a novel approach of three-dimensional (3D) scanning of aggregates using a structured light 3D scanner is presented, and parametric geometry reconstruction of aggregate geometries using spherical harmonics is carried out. This novel method of scanning aggregates is a faster, safer, economical, and convenient method of obtaining the 3D geometry compared with other methods. A comprehensive database of aggregate geometries is developed, and an innovative aggregate-placing algorithm for these aggregates is presented to develop the mesostructure. In addition to the proposed geometry generation method, a novel parametric-based geometry generation and distribution method for polyhedral aggregate shapes is presented, including flaky and elongated particles. Finally, aggregate transferring methods to finite-element software and mesh generation methods are discussed with the challenges and possible methods to overcome these issues.

Stone matrix asphalt (SMA) is a highly rut-resistant gap-graded asphalt mixture. The inclusion of supplementary materials such as fiber, filler, and polymer-modified bitumen (PMB) makes the layer more expensive to construct. This study examined the rutting and fatigue behavior of SMA mixture by partially replacing virgin aggregates and bitumen with reclaimed asphalt pavement (RAP), thus enhancing sustainability. The study compared the laboratory performance of 20%, 30%, and 40% RAP-added SMA mixtures with that of a conventional SMA mixture. The virgin binders were infused with RAP binder at different proportions and were subjected to rheological testing to evaluate miscibility and performance. The results indicated an improvement in rutting and a decrease in fatigue life, with crumb rubber–modified bitumen (CRMB) offering a higher degree of miscibility than styrene-butadiene-styrene (SBS) PMB when infused with RAP binder. From this study, it can be concluded that in a high-quality SMA surface layer, 20% is the most acceptable amount of RAP content. However, if SMA with CRMB60 binder is used as a binder layer, then 30% of RAP can be used to improve performance.

Internal curing agents are materials that supply additional water for cement hydration, the water being supplied by internal reservoirs (porous and absorbent aggregates). In this study, the potential for a recycled concrete aggregate (RCA) to act as an internal curing agent and chemical sorbent for heavy metal retention was investigated. Mortars were designed with a water/cement ratio of 0.5 and a mix ratio of $1:3$ (cement:fine aggregate; by mass), where 25% of the natural aggregate (NA) was replaced with a lightweight aggregate (LWA) or RCA, under prewetted or dry conditions. Mortars were also prepared with the addition of ${\mathrm{Cr}}^{6+}$ and ${\mathrm{Zn}}^{2+}$ in order to verify the chemical sorbent potential of the aggregate and the retention capacity of mortars designed with internal curing. Results show that the nature and prewetting of the aggregate affect the physical and mechanical properties of the mortars. The prewetted aggregate differs in terms of the period and duration of water release from the period and duration of water release from the pores of the material, modifying the paste microstructure at early ages. The results of the flexural strength clearly demonstrate the efficiency of the internal curing, because cracks in the interfacial transition zone strongly influence flexural strength. Regarding the results of the leaching test, it can be concluded that mortars prepared with RCA without prewetting show greater retention of added heavy metals, retaining 100% of the chromium and more than 91% of the zinc. In relation to mortars with LWA, there was 100% retention for zinc and 94% for chromium. Lastly, it was noted that RCA can be used as an internal curing agent without adversely affecting the final cement material, increasing the potential application of RCA, and can also be used as a chemical sorbent to aid in the solidification/stabilization process of heavy metals.

Superfine stainless wires (SSWs) and carbon nanotubes $(\mathrm{CNTs})/\mathrm{nano}{\mathrm{SiO}}_2\text{-}\mathrm{coated}{\mathrm{TiO}}_2$ (NTs) were used as hybrid micro- and nanofillers to toughen reactive powder concrete (RPC) in this paper. The multiscale synergistic toughening mechanisms of micro- and nanofillers were revealed through theoretical calculation. Experimental results show that incorporating 1.2% by volume SSWs and 1.5% by weight NTs enables the three-point bending strength, first-cracking strength, and bending toughness of RPC to increase by 171.6%, 96.0%, and 572.1%, respectively. The numbers of SSWs being pulled-off at failure are increased by 19.1%, resulting from the addition of nanofillers reducing original flaws and enhancing the interface of SSWs through a nanocore effect at the nanoscale. Meanwhile, the widely distributed core-shell elements and SSWs work together to effectively inhibit the initiation and propagation of cracks by pinning and bridging effect at the microscale, leading to the bending strain-stress curves of RPC with hybrid fillers to have significant strain-hardening and slow strain-softening stages.

The metallurgical and electrochemical behavior of additively manufactured super duplex stainless steel (SDSS) clads on carbon steel [low-carbon steel (LCS)] substrates are investigated in a simulated concrete pore solution. The SDSS clads were manufactured using laser powder bed fusion (LPBF). Passivation and chloride-induced depassivation of the clads were studied as a function of LPBF parameters. It was shown that additively manufactured clads significantly improved the passivation characteristics and increased the chloride thresholds of the LCS substrate. The clads showed a decreasing $\gamma$-austenite phase fraction and increasing $\delta$-ferrite phase fraction with increasing scan speeds. Increasing the $\delta$-ferrite phase fraction resulted in faster passive film formation but lower critical chloride thresholds for the clads. The clads produced with 100-, 600-, and $\mathrm{1,000}\text{-}\mathrm{mm}/\mathrm{s}$ laser scan speeds showed critical chloride thresholds of 4, 2.5, and 1.5 M, respectively. The as-cast SDSS alloy did not show any signs of depassivation until $5\mathrm{M}{\mathrm{Cl}}^{-}$ concentration, whereas LCS substrates depassivated at $0.75\mathrm{M}{\mathrm{Cl}}^{-}$. The study proved the concept of additively manufactured carbon steel rebars with stainless steel clads and is a first step toward producing such rebars.

In this experimental study, the effect of sodium silicate (SS) added into an ultrafine-cement-suspension injection on the strength and permeability properties of grouted sand samples was investigated. The experiment started with a test for identifying the bleeding and viscosity values and setting times. This was followed by injecting sand samples prepared in different gradations with ultrafine cement (UC) with and without SS additive. In the experiments, 1.0, 1.5, 2.0, and 2.5 were used as the water:cement ratios, and 1%, 3%, and 5% were used as the SS additive ratios. Unconfined compression tests were performed on the sand specimens that were successful in the injection tests on days 3, 7, 14, 28, 56, and 90; and permeability tests were performed on days 7, 28, 56, and 90. While viscosity values increased with the addition of SS into the UC, bleeding values and setting times decreased. Injectability slightly decreased with the addition of SS into the UC. The addition of SS into the UC-suspension injection increased the unconfined compressive strength. Injected samples gained strength faster with the addition of SS into the UC. Adding sodium silicate into the UC-suspension injection reduced permeability values. In the experimental study, it was observed that the addition of SS additive into the UC improved the permeability and strength properties of sand samples after injection.

This paper presents an experimental study on the cyclic behavior of steel-fiber-reinforced composite bars (SFCBs) with different slenderness ratios. Twenty-four specimens, including SFCB specimens and corresponding inner steel bar specimens, were designed and tested under cyclic loading. The cyclic tests of the SFCBs proved that their tensile and compressive behaviors were almost identical before the outer fiber layer started splitting or fracturing. Excellent restorability of SFCBs was observed during the hysteretic process. The compressive peak stress of the SFCBs was irrelevant to specific loading modes, i.e., monotonic loading or cyclic loading. The maximum absolute value of the compressive peak stress of the SFCBs (under cyclic loading without lateral confinement) was approximately 50% of their tensile peak stress (under monotonic tensile loading). A bidirectional degradation effect, which could lead to a rapid decrease in strength, was found during the cyclic loading after the fiber’s initial failure. Therefore, a complete fiber failure mode was suggested for the seismic design of the SFCBs once the fiber layer started failing. A new set of simplified hysteretic rules of SFCBs was proposed based on the actual hysteretic properties summarized from the experimental studies. The new hysteretic rules subdivided unloading and reloading curves into two stages based on the stress state variation of the different SFCB materials, and their accuracy was further verified with the test results.

Early-age cracking may occur in high early–strength (HES) concrete repair slabs used for full-depth repairs in jointed plain concrete pavements (JPCPs) due to the early-age volume changes. HES concrete utilizes high cement content and low water-cement ($\mathrm{w}/\mathrm{c}$) ratios, which can cause concrete to experience high temperature rise and increased autogenous shrinkage, and therefore higher cracking potential. Field and laboratory experiments were performed to systematically assess several cracking mitigating strategies, namely paste content reduction and addition of lightweight aggregate (LWA), shrinkage-reducing admixture (SRA), and fiber. It was observed that the initial stress development in most of the field slabs was affected by the moisture migration to the base. The paste-reduced mixture was identified as a potential mix for HES repair slabs. Although inclusion of LWA, SRA, and fiber controlled the moisture loss to the base and subsequently decreased the initially induced tensile stresses, only prewetted LWA demonstrated promising results in minimizing cracking risks.

Although machine learning algorithms to predict the mechanical properties of concrete have been studied extensively, most of the research focused on the prediction of the strength of concrete and only a few studies have focused on concrete creep. This paper analyzed the maximum information correlation (MIC) between concrete creep influence parameters based on the updated Infrastructure Technology Institute of Northwestern University (NU-ITI) database, and the parameters in the database were adopted in the classical creep prediction models for calculation. Three machine learning algorithms (MLAs)—back-propagation artificial neural network (BPANN), support vector regression (SVR), and extreme learning machine (ELM)—were trained with the NU-ITI database to model concrete creep. The SVR-based model achieved high predictive accuracy. Sensitivity analysis of the parameters and feature selection of concrete creep were carried out based on the SVR and the Sobol method. By retraining the SVR model after feature selection, it was demonstrated that low-sensitivity and strongly correlated parameters will increase the robustness of machine learning models.

To further evaluate the compatibility between asphalt matrix and styrene-butadiene-styrene (SBS) modifier using a molecular dynamics (MD) method, MD models of asphalt matrix, SBS modifier, and SBS-modified asphalt were first established. Solubility parameters and interaction energy were utilized to discuss the compatibility between asphalt matrix and SBS modifier. The simulated results indicate that asphalt is compatible with SBS modifier, and the compatibility at 160°C is much better than that at 120°C. The interaction between SBS modifier and asphalt matrix increases their compatibility, and the van der Waals potential energy predominates in the intermolecular potential energy, playing an important role in forming a stable blending system of SBS-modified asphalt. Further, interactions among asphalt components and SBS modifier cannot inhibit the molecular diffusion of each component, lowering the compatibility between asphalt and SBS modifier at 120°C. However, the higher temperature at 160°C inhibits SBS diffusion and increases the interaction and compatibility between SBS and asphalt. This study reveals the segregation mechanism of SBS-modified asphalt.

Aggregate shape properties can greatly influence the overall performance of asphalt mixtures. In this study, shape-controlled aggregates were fabricated and used in porous asphalt mixture (PAM) to assess the effect of aggregate shape properties on the performance of PAM. Three shapes of the aggregates were fabricated, namely cube, cylinder, and sphere. Two parameters, shape factor and sphericity index, were used to define the aggregate shape properties. Results of discrete-element method (DEM) simulation and laboratory measurements were compared to obtain a better understanding on the effect of aggregate shape on the performance of PAM. The results indicated that aggregate shape properties have notable effect on the overall performance of PAM. Spherical aggregates need only a low compaction effort to achieve the design voids-in-total-mix (VTM). For aggregates with the same shape factor, the overall mechanistic properties of PAM generally decrease with increasing sphericity of the aggregates.

Particle-packing theory has been widely applied in the field of composite particle materials, and packing density ($\mathrm{\Phi }$) is an important parameter to evaluate the compactness of particle packing. In this paper, the rheological curves of fresh cement–fly ash–slag (PC-FA-SL) paste at 5 and 60 min resting time were tested through rheometer, and related rheological parameters were fitted by the modified Bingham model. The packing density of composite particles was calculated by the compressible packing model (CPM) and verified by the modified Andreasen model. Results show that with the increasing content of fly ash (FA) and blast-furnace slag (SL), both yield stress (${\tau }_0$) and plastic viscosity ($\eta$) decrease significantly when the addition of FA and SL is less than 20% by weight. For the PC-FA-SL ternary system, ${\tau }_0$ and $\eta$ increase with the development of $\mathrm{\Phi }$. The relationship between ${\tau }_0$ and $\mathrm{\Phi }$ takes on exponential growth (${\tau }_0=a{\mathrm{\Phi }}^b+c$), while the relationship between $\eta$ and $\mathrm{\Phi }$ presents linear growth ($\eta =k\mathrm{\Phi }+m$). Both $b$ and $k$ decrease with resting time developing. Zeta ($\zeta$) potential measurement and hydration heat test were carried out to reveal the relationships between ${\tau }_0$, $\eta$, and $\mathrm{\Phi }$ and rheological evolution of fresh blends.

This work aimed to perform the insight into the performance at early age of cement paste/mortar with calcium silicate hydrate seeds–polycarboxylate (C-S-Hs-PCE) and aluminum sulphate. The performance was evaluated using the setting behavior and compressive strength. Hydration heat liberation, chemical shrinkage, X-ray diffraction, and differential thermal analysis were performed to explore the related mechanism. The results indicate that C-S-Hs-PCE can reduce the setting times of paste and increase the compressive strength of mortar with aluminum sulfate at 6 and 12 h and 1 and 28 days. These results are mainly related to the acceleration hydration of tricalcium silicate and facilitation of ettringite and calcium hydroxide formation. Aluminum sulfate and C-S-Hs-PCE promote the cement hydration in two manners: (1) they significantly enhance the heat flow and end the acceleration period earlier; and (2) aluminum sulfate prolongs the induction period, whereas C-S-Hs-PCE shortens it. These findings provide theoretical guidance for the development of a new alkali-free accelerator as well as the application of C-S-Hs-PCE.

ACI 318 and the fib Model Code 2010 prescribe recommendations for the design of steel fiber–reinforced concrete (SFRC) using performance measured with a four-point bending test (4PBT) per the ASTM C1609 US standard and a three-point bending Test (3PBT) per the EN 14651 European standard, respectively. Different assumptions of the test methods hinder the comparison and direct correlation of studies performed using European and US standards. This study determined the residual flexural tensile performance of 40 SFRC beams using 3PBTs and 4PBTs. The study variables were the dosage (0, 20, 40, and $60\mathrm{kg}/{\mathrm{m}}^3$), the number of hook ends (1, 1.5, and 2), and the tensile strength of the steel fibers. The study assessed the effect of number of hook ends and reinforcement index of steel fibers on the residual strength from 3PBTs and 4PBTs. A model is proposed to correlate the residual tensile performance of the SFRC measured using tests procedures prescribed by European and US standards. The proposed model includes the influence of strain hardening on the relationship between residual strength from 3PBT and 4PBT.

The construction temperature of commonly polymer-modified asphalt for thin overlay is high, and the asphalt is prone to aging, which affects the service life of pavement. In this research, polyurethane (PU) binder was used to replace asphalt to prepare thin overlay mixtures with different gradations at room temperature. The pavement performance of the PU thin overlay mixtures is comprehensively evaluated by comparing with common polymer-modified asphalt mixtures. The results show that the mechanical strength of the PU mixtures is positively correlated with the PU content under the same type gradation. Due to the excellent mechanical strength of PU binder, the mechanical properties and dynamic stability of its mixtures are much higher than that of asphalt mixtures under the same gradation, and the Cantabro loss is also small. Besides, the difference variation is low in water sensitivity between the PU mixtures and asphalt mixtures. The PU mixtures can meet the requirements of low-temperature pavement performance and can also be used in most low-temperature environments. Finally, the evolution model of skid resistance of PU thin overlay mixtures was obtained through accelerated pavement test. It is proved that the PU mixtures have excellent skid resistance and durability. The model can well simulate the development of skid resistance with the number of loading times, which provides a certain reference for research on the durability of polymer and modified asphalt thin overlays.

Variations in the properties of fly ashes from various sources can lead to large variations in the performance of fly ash–blended cement systems. The current study combines analytical and numerical modeling approaches to predict such variations in the hydration behavior of cement paste and compressive strength of mortars with different fly ashes. A microstructural modeling software was used to model the hydration of cement and fly ash. Fly ash parameters such as particle size distribution and reactive content were used to model the variation in fly ash hydration. The fit parameters were determined based on the experimental results obtained from isothermal calorimetry and X-ray diffraction. Heat of hydration and compressive strength results obtained from the modeling agree well with the experimental results. The results also show that modeling can be used not only to determine deterministic quantities such as heat of hydration and compressive strength but also probabilistic quantities like variation in heat of hydration and strength. Such models could be useful for safety parameters in probabilistic design. The model was further used to predict the reduction in variation due to blending of fly ashes from various sources.

In China, the application of asphalt layers in high-speed railway ballastless tracks has two functions. Asphalt layers can be used as a support layer or a waterproof layer; one of these functions is chosen in general design. The main purpose of this work was to apply and evaluate a full cross-section asphalt waterproofing layer in a slab ballastless track. The asphalt layer was intended to support the static and dynamic loads of a high-speed train and protect the internal structure from the effects of environmental temperature. Three types of performance-grade (PG) binders were selected in the asphalt mix design as part of the top surface layer of the subgrade bed of the CRTS III slab ballastless track. These binders (normal, high, and modified-grade binders) are PG64-22, PG70-22, and PG76-22. The efficiency of the asphalt mixture is evaluated through laboratory tests based on permanent deformation and fatigue resistance, and by applying criteria used to assess the mechanical properties in high-speed railways. After analyzing the dynamic response of each layered structure using the 3D finite element model, the laboratory results indicated that the PG76-22, or modified asphalt binder, is suitable for use in ballastless track when applied as a full cross-section asphalt waterproof layer. In addition, the prediction of the model shows that the asphalt waterproof layer performs better than the traditional structure in reducing the stress and vibration of the track.

The seismic performance of honeycomb concrete canvas geocell-reinforced retaining walls with saturated calcareous sand backfill was investigated. Four different shaking table test models were constructed to determine the effect of reinforcement, saturation, and acid rain erosion. Before the shaking table tests, cyclic simple shear tests were conducted to investigate the effect of acid rain on the seismic response of calcareous sand. Then, considering the effects of input accelerations, the seismic response of the retaining walls was examined, along with the acceleration, lateral displacement ratio, lateral acceleration-displacement, dynamic modulus, and excess pore-water pressure. The results indicate that the acid rain erosion reduces the shear modulus of the calcareous sand, which causes larger deformations than those in normal sand in tests. With the accumulation of pore-water pressure under seismic loads the softening response of soil gets significant, and the soil damping increases that restricts the development of the acceleration amplification. The deformation in the reinforced saturated model is larger than the reinforced dry model, and the saturation conditions significantly reduce the reinforcement coefficient and modulus of sand.