Journal of Materials in Civil Engineering

Minimizing the use of nonreplaceable natural resources and relying on renewable materials that generate less waste is a key step in converting masonry manufacturing to a sustainable industry. This research aimed at developing innovative masonry bricks for inexpensive masonry construction, which will lessen the carbon dioxide footprint and firing energy levels during the manufacturing process of bricks without compromising the prescribed mechanical and physical properties of the masonry units. Results are presented from a pilot experimental study on the incorporation of biologically inert by-products of sludge treatment (high-biopolymer sludge and incinerated sewage sludge ash) and waste glass, used as alternatives to natural shale in the manufacturing of low-cost and environmentally friendly masonry bricks. Through characterization tests, it was shown that the developed hybrid bricks containing waste materials satisfy all the quality control criteria set by the masonry industry in terms of a variety of mechanical and physical properties. By using wastes as raw materials to reduce the amounts of nonrecoverable natural resources in brick production, a potentially sustainable solution is developed for masonry construction. Hybrid brick manufacturing also helps to lower the carbon footprint and firing energy and offers an alternative to landfill disposal of the wastes.

The interest in the utilization of granular waste materials as construction fills in lieu of quarried natural aggregates has been increasing recently, resulting in more sustainable and cost-effective industry practices being adopted. This study proposes a mixture of coal wash (CW; a by-product of coal mining) and rubber crumbs (RC; shredding of waste rubber tires) as a potential capping composite for railways. A series of cyclic triaxial tests mimicking typical rail traffic loads were conducted on CWRC mixtures with and without rest periods to gain an insightful understanding of the deformation mechanism of rubber particles. It is found that the inclusion of RC increases the axial permanent strain, the volumetric strain, and the damping ratio, and it reduces the resilient modulus, the shear modulus, and the breakage index (BI). Also, it is found that the mixture with RC recovers part of its energy dissipation efficiency after a rest period is applied, reducing the breakage index further even when the number of load cycles increases. Accordingly, a modified equation is proposed to determine the void ratio, capturing the deformation of the rubber.

Previous studies have reported the effects of aggregate gradation and angularity on the pavement performance of hot asphalt mixtures, while little work has been done on the role of aggregate gradation and morphology related to porous asphalt (PA) mixture performance. The primary objective of this article was to evaluate the effects of aggregate gradation and morphology on the mechanical properties and volumetric characteristics of PA mixtures. Ten PA mixtures, prepared by regulating the percentages of aggregate passing 9.5-, 4.75-, 2.36-, and $1.18\text{-}\mathrm{mm}$ sieves and using two types of aggregate sources, were compared by evaluating air voids, shear strength, Marshall stability, indirect tensile strength, and micromorphology. The analytic hierarchy process method was used to analyze the priority weights of various influencing factors on PA mixture performance. The results indicate that aggregate gradation had significant effects on the performance of the PA mixtures. There was an excellent linear relationship between the percentages of aggregate passing the 9.5-, 4.75-, and $2.36\text{-}\mathrm{mm}$ sieves and the respective mixture air voids. Increasing the proportion of $4.75–9.5\text{-}\mathrm{mm}$ aggregate particles in the PA mixes did not contribute to its moisture damage resistance. The percentage of $2.36–4.75\text{-}\mathrm{mm}$ aggregate fractions was the most critical influencing factor for the PA mixtures’ mechanical properties and volumetric characteristics. Additionally, aggregate morphology does affect PA performance. The permanent deformation resistance and moisture resistance were notably improved as the aggregate sphericity value increased. Based on the test results, the mechanical properties and volumetric characteristics of PA mixtures can be optimized depending on engineering requirements by regulating the aggregate gradation and type.

The recycling of asphalt pavement is a widespread practice around the world owing to its significant social, economic, and environmental advantages. High-modulus asphalt concrete (HMAC) possesses excellent rutting resistance and has received increased attention around the world. While many studies have been conducted on the performance of hot mix asphalt (HMA) containing reclaimed asphalt pavement (RAP), gaps remain in knowledge about producing HMAC containing RAP. This paper aims to investigate the performance of HMAC containing high percentages of RAP by conducting parametric laboratory tests. Design factors, including aggregate gradation, asphalt binder content, recycling agent dosage, and asphalt binder type, are evaluated in the laboratory. Tests conducted include dynamic modulus test, Marshall immersion test, modified Lottman test, three-point bending test, and rutting test. A modified regeneration method with adjusted mixing sequence is adopted to produce a mixture. It was found that low-penetration virgin-grade asphalt binder could produce good-quality HMA, though low-temperature cracking resistance remains a problem. Adjusting aggregate gradation and increasing asphalt binder content could improve its overall performance but not low-temperature cracking resistance. Increasing the dosage of aromatic extract recycling agent could improve HMA’s low-temperature cracking resistance, and a maximum dosage of 6% was proposed. Increasing the penetration grade of virgin asphalt binder with the addition of high-modulus additive could significantly improve its low-temperature and overall performance.

The use of seawater as mixing water for concrete production is one of the most efficient strategies to solve freshwater shortage problems. The purpose of this paper is to investigate the effects of seawater mixing on hydration, microstructure, and strength development of cement pastes. Multiscale tests were used for cement pastes mixed with seawater, NaCl, and ${\mathrm{Na}}_2{\mathrm{SO}}_4$ solutions, respectively. The chloride ions in seawater increased the hydration degree during the process for nucleation and crystal growth and shortened the period for phase boundary reactions as a dominant process. At the age of 28 days, ettringite and Friedel’s salt coexisted for the seawater mixing paste, whereas the ettringite almost disappeared for the deionized water mixing. The seawater mixing led to a less porous cement matrix with much finer pores. Furthermore, seawater mixing enhanced the compressive strength and bending strength at early ages but later the enhancement decreased with curing time. ${\mathrm{Na}}_2{\mathrm{SO}}_4$ in the seawater enhanced the strength of the cement paste before 1 day but later inhibited the strength development.

Glued laminated bamboo (glubam) is a type of engineered bamboo that resembles timber-based glued laminated lumber (glulam). The glubam components are made by laminating 20- to $40\text{-}\mathrm{mm}\text{-}\mathrm{thick}$ engineered bamboo boards; thus, the performance is determined by the quality and properties of the laminated boards. A comprehensive testing program was conducted on typical engineered bamboo boards. The experiments were performed according to the general requirements given by international standards; however, the size of specimens and loading jigs were redesigned according to the modular thickness of typical bamboo boards. Mechanical behaviors and failure modes of the specimens under 15 stress conditions are reported, along with the surface strain distribution recorded through digital image correlation (DIC). A simple design-oriented axial stress–strain model is proposed, and strength values, including the corresponding coefficient of variance (COV), are calculated and provided. A comparison of characteristic strength values between engineered bamboo and typical wood products is also given in this research.

This study investigates the effect of silica moduli (${\mathrm{SiO}}_2/{\mathrm{Na}}_2\mathrm{O}$ ratio) of alkaline activators on the degradation mechanisms of fly ash–based geopolymer (FAG) mortars that are exposed to elevated temperatures of up to 1,000°C. The evolution of the mechanical properties, microstructure, mineralogy, and atomic structure of the FAG with three different silica moduli after the thermal treatment are studied. The results show that silica modulus affects the compressive strength and crack development of geopolymer mortars. Geopolymer mortars with the highest silica modulus have the best thermal stability and volume stability after exposure to high temperatures, as confirmed by the latest cracking initiation and lowest cracking intensity. The mechanism of decreased strength in geopolymer mortars with low silica moduli (owing to crack development) is different from that of increased strength in geopolymer mortars with high silica moduli (owing to further geopolymerization) before 400°C. The crystalline phases of nepheline and albite were observed to appear in the specimen at 800°C and 1,000°C, respectively, which was possibly due to ${\mathrm{Na}}^{+}$ entering into the crystal lattice of mullite and promoting the change of mullite into new crystal phases. Heating processes cause varying degrees of destruction of FAG and form a highly porous and weak structure owing to the sintering process above 800°C. Silica moduli are not an important factor for the gel phase structure of FAG at 1,000°C, which may be related to the same content of ${\mathrm{Na}}_2\mathrm{O}$.

Bamboo is increasingly recognized for its potential as an environmentally friendly and sustainable building material, but the knowledge of its combustion properties and the safety of bamboo building construction are very limited. In this study, experiments were conducted to obtain the combustion behaviors of glue-laminated bamboo (GluBam or glubam) boards by using a cone calorimeter. The tests were carried out at five levels of heat flux: 15, 25, 35, 50, and $70\mathrm{kW}/{\mathrm{m}}^2$. The measured results are compared with those of fir plywood. Glubam generally behaves better than plywood under the same heat flux. A further comparison of the investigation in this study with some measured results in published papers indicates that glubam is less flammable than the laminated bamboo materials and several wood species. The fire safety assessment of glubam is also studied based on fire hazard indices, the charring rate, and fire endurance time. From flammability considerations, glubam has the potential as a substitute for untreated plywood in structural and lining applications and should further be evaluated according to building codes to define its end-use.

The optimization of mixing processes is an effective approach for strengthening the microstructure of the interfacial transition zone (ITZ) in recycled aggregate concrete (RAC). This study used iron oxide to distinguish between residual mortar (RM) and added mortar (AM) in RAC using the normal mixing method (NMM), two-stage mixing method (TSMM), and cement paste encapsulating aggregate method (CPEAM). The ${\mathrm{CaCO}}_3$ contents and pH values of the RM and AM of RAC were investigated separately. The carbonation zone and steel corrosion zone widths of RAC were determined separately based on the ${\mathrm{CaCO}}_3$ contents and pH values, and these widths were compared. The results showed that the TSMM and CPEAM decreased the carbonation and steel corrosion zone widths by improving the microstructures of the ITZs and further decreasing the interfacial effect zones in the RM and AM. In addition, the carbonation and steel corrosion zone widths determined using the RM as samples were higher than those using the AM. Consequently, theoretical models for carbonation and steel corrosion zone widths should reflect the effect of the mixing process.

The physical and mechanical behavior of soil polymer composites tightly depends on the properties and structures of both soil and polymer. This study aims to investigate the effect of glass transition temperature as one of the most important characteristics of adhesive resins of acrylic polymers on the geotechnical behavior of soils that have not been fully covered by previous studies. To achieve that, three similar copolymers of methyl methacrylate-co-butyl acrylate with different glass-transition temperatures of 1°C, 33°C, and 51°C were synthesized, and two representative specimens of cohesive (kaolinite clay) and noncohesive (sand) soils were chosen to perform a full investigation of the consequential changes in the physical and mechanical behavior. A series of laboratory tests, including the Atterberg limits tests, the unconfined compressive strength tests, direct shear tests in soaked and unsoaked conditions, swelling tests, and odometer tests, were conducted on untreated and treated soils with synthesized polymers. The results showed a salient enhancement in the cohesion and the unconfined compressive strength value of both soils. However, the polymer with a glass-transition temperature near to ambient temperature led to a greater increase in the compressive and shear strength of stabilized soil among its peers. Samples treated with the polymer having the lowest glass transition temperature revealed a more compression index (i.e., obtained from odometer tests) and lower unconfined compressive strength. It is also observed that the swelling index and swelling pressure decreased marginally with increasing the glass transition temperature.

Using admixtures to replace part of cement can effectively reduce environmental pollution. Many concrete gravity dams have been planned for Tibet, where the resource of fly ash (FA) is scarce but the resource of tuff is abundant. Compared with the more mature and widely used FA concrete in gravity dams, the application of tuff concrete is rare, and the hardening mechanism of the cement–tuff binary cementation system and the performance of tuff concrete still need to be further studied. In view of this, the hydration and hardening mechanism of the cement–tuff binary cementation system using varying percentages of tuff contents (0%, 25%, and 50%) are discussed, and the mechanical properties (e.g., strength, modulus) and durability performance (e.g., freeze-thaw, carbonization) of tuff normal concrete are investigated in this paper. The microstructure of the cement–tuff system shows that additional tuff powder promotes the hydration of clinker in cement, which increases the calcium hydroxide content [$\mathrm{Ca}(\mathrm{OH}{)}_2$] and leads to a higher porosity at early curing age. Results show that the amount of tuff content is almost positively correlated with porosity. The additional tuff in concrete increases the earlier splitting tensile strength, ultimate tensile value, and drying shrinkage, which also slightly reduces the frost resistance and little affects the compressive strength, tensile strength, elastic modulus, impermeability, and carbonation depth. Tuff normal concrete shows better performance than FA concrete in some aspects. The results show that tuff materials can be used to replace FA, and tuff normal concrete can be applied to the construction of concrete gravity dams in areas where fly ash is scarce and tuff is abundant.

High-performance concrete easily generates early-age cracks due to its sharp and large temperature and relative humidity (RH) changes. The temperature and RH with and without axial compressive stress were experimentally examined in this study. The test results show that the temperature and RH have an obvious coupled effect at an early age. The RH quickly decreases when the temperature sharply and substantially increases and sharply increases when the temperature steeply and substantially decreases. When the stress is applied, a clear abrupt increase in the RH appears, and when the compressive stress is unloaded, a clear abrupt decrease in the RH appears. During the loading, the decrease rate of RH smaller compared with its development tendency without load. The compressive stress has no significant effect on the temperature. Additionally, based on the previous studies and theoretical derivations, the coupled hygro-thermo-chemo-mechanical model of early-age concrete is proposed. The predicted results calculated by the proposed model are in good agreement with the test data in this study and the open literature.

This research investigates the effects of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ and ${\mathrm{Na}}_2{\mathrm{CO}}_3$ on the mechanical and hydration properties of high-volume fly ash (FA) cement (HFC) at three curing temperatures: 25°C, 40°C, and 60°C. Setting time, compressive strength, reaction kinetics, phase assembles, and pore structure were explored. The research found that the hydration of HFC was significantly promoted by the chemical activators at all temperatures. At 25°C, the incorporation of ${\mathrm{Na}}_2{\mathrm{CO}}_3$ and ${\mathrm{Na}}_2{\mathrm{SO}}_4$ decreased the initial setting time by 59% and 50%, respectively, compared to the control sample. This was accompanied by increased heat release from the isothermal calorimetry tests. At the same time, the introduction of ${\mathrm{Na}}_2{\mathrm{CO}}_3$ (HFC-C) increased the early compressive strength by 40%, higher than that of samples with ${\mathrm{Na}}_2{\mathrm{SO}}_4$ addition (HFC-S). While reduced compressive strength was noticed in HFC-C after curing for a long time, resulting from the increased porosity. Furthermore, temperature rise reduced the contribution index (Ci) to the strength development of both HFC-C and HFC-S. On the other hand, the presence of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ contributed to the formation of more ettringite (AFt), while no AFt was detected after the addition of ${\mathrm{Na}}_2{\mathrm{CO}}_3$. Increasing the curing temperature did not strongly change the phase assembles of the hydration products, although the amount of AFt content was observed to increase.

This comparative study investigated the microstructural, thermophysical, and mechanical properties of tea waste–, sawdust-, and wheat husk–incorporated clay bricks. The bricks were prepared by missing clay with different amounts of organic wastes and firing at 600°C and $\mathrm{1,000}°\mathrm{C}$. A transient plane source technique was used to measure the thermal properties of the fired bricks. The calorific values of the tested organic wastes were measured in the range of $15–17\mathrm{MJ}/\mathrm{kg}$. The maximum loss on ignition of tea waste–, sawdust-, and wheat husk–incorporated bricks was measured at about 14.94%, 13.75%, and 9.26%, respectively. The tea waste added–bricks exhibited the highest water absorbance, $20.8\%–35.7\%$, among all the tested samples. The specific surface area of the tea waste–, sawdust-, and wheat husk–added bricks was measured at about 146.43, 139.47, and $167.25{\mathrm{m}}^2/\mathrm{g}$, respectively. Similarly, the pore volume was measured at about 0.192, 0.184, and $0.219{\mathrm{cm}}^3/\mathrm{g}$, respectively. When compared with a reference brick, the compressive strength decreased by $15\%–59\%$ for $2\%–8\%$ by weight of tea waste, by $12\%–59\%$ for $2\%–10\%$ by weight of sawdust, and $31\%–69\%$ for $1\%–4\%$ by weight of wheat husk in the brick. However, the compressive strength of the waste-added bricks was still in good agreement with Pakistan building code standards.

Microbially induced carbonate precipitation (MICP) was used to treat Bayer-process red mud, a waste product of the aluminum industry. Changes in the unconfined compressive strength (UCS), calcium carbonate content and distribution, leaching of metal ions, pH value, and stress-strain characteristics were measured, and the effects of MICP on red mud were evaluated. The results showed that MICP was effective and efficient in red mud treatment. This method could overcome the adverse effects of complex mineral composition, fine particle size, strong alkalinity, and the presence of toxic and hazardous materials characteristic of red mud to produce urease to decompose urea, precipitate carbonate, and strengthen red mud. After treatment, the red mud experienced a significant increase in strength, whose UCS increased up to 1,395 kPa, and a transition from strain hardening to strain softening behavior was observed. In the process, the heavy metal ions in the red mud could also be fixed in the form of carbonate precipitation. Mechanistic studies suggested that the red mud changes were entirely due to the calcite, which were in a state of aggregation and had a relatively large volume. In addition, they acted as a framework to agglomerate red mud particles. Through the action of cementation, the red mud particles aggregated and changed from a loosely distributed (scattered) form to a tightly bound block morphology. This had nothing to do with the carbonation reaction of the active calcium minerals contained in the Bayer-process red mud.

Medium-density polyethylene (MDPE) pipes are extensively used for gas distribution systems in Canada and worldwide. MDPE pipe material possesses time-dependent mechanical properties that govern the performance of the pipes in service. In this research, an extensive laboratory investigation is carried out to investigate the time-dependent behavior of MDPE pipe material. Uniaxial tensile tests are conducted with samples (coupons) cut from the wall of a 60-mm diameter MDPE pipe. A tensile test with a sample of the full cross section of the pipe is also conducted to investigate the influence of sample type on the test results. The test program includes uniaxial testing at various strain rates ranging from ${10}^{-6}/\mathrm{s}$ to ${10}^{-2}/\mathrm{s}$ to capture the effects of loading rates, creep testing, and relaxation testing. The program revealed that the stress-strain responses of MDPE pipe material are highly nonlinear and strain rate-dependent. However, the strain rate effect is negligible below ${10}^{-6}/\mathrm{s}$, which is termed herein as the “reference strain rate.” A numerical technique for modeling time-dependent behavior is proposed using the features available in a commercially available finite element software, Abaqus. In this technique, strain rate-dependent stress-strain models are used to simulate loading and unloading responses, and a power-law type creep-law model is used to simulate the creep/relaxation behavior. The proposed modeling approach successfully simulated the test results.

The determination of the postcrack tensile properties of steel fiber–reinforced concrete (SFRC) after exposure to elevated temperatures is a current methodological challenge. The objective of this research is to evaluate the applicability of the double edge wedge splitting (DEWS) test to characterize the postcrack tensile properties of SFRC after exposure to elevated temperatures. Results show that the DEWS test has reduced scatter and facilitates the interpretation of results with diminished frictional interaction between the apparatus and the specimen. The results in terms of coefficient of mechanical degradation were comparable to those obtained by bending tests in literature, which highlights the suitability of the DEWS test to be adopted in future researches and guidelines. The postcrack tensile properties were not significantly affected up to $\sim 300°\mathrm{C}$ and a linear reduction ratio was verified with the increase in temperature. Additionally, the constitutive model proposed may reproduce the effect of temperature on the tensile stress-strain behavior of the SFRC and is a valuable input for hygro-thermo-mechanical numerical models oriented to simulate the mechanical behavior of structures made with SFRC.

Two kinds of binders, microbially induced carbonate precipitation (MICP) and ordinary portland cement (OPC), were used separately to produce macroporous pervious concrete (MPC). Furthermore, the macro- and micromechanical properties of these two binders and MPCs produced with them were compared. The results revealed a significant difference between the effective porosities of samples produced with MICP and OPC. In addition, the MPCs made with MICP had a higher elastic modulus in comparison to those made with OPC. Moreover, MPCs produced with MICP required less cement to achieve the same compressive strength as those produced with OPC. Finally, investigation of the boundary of MICP binder and aggregates revealed that there was no interfacial transition zone between the aggregate and the MICP binder as existed between OPC and aggregates.

The objective of this study was to develop artificial neural networks to predict the viscosity of rubberized asphalt rejuvenated reclaimed asphalt pavement binders. Eight variables were selected as input factors, namely, viscosity measuring temperature, rubber blending time, reclaimed asphalt pavement blending time, original binder blending time, rubber content, reclaimed asphalt pavement content, blending temperature for aged binder, and asphalt type. Two viscosity analysis models, backpropagation artificial neural networks and genetic algorithm modified artificial neural networks, were developed in this study. It was found that both artificial neural network models were effective in predicting the viscosity of rubberized asphalt rejuvenated reclaimed asphalt pavement binders. Through sensitivity analysis, blending temperature for aged binder, viscosity measuring temperature, original binder blending time, and reclaimed asphalt pavement blending time were found to be important variables that contributed to the binder viscosity. On the contrary, the asphalt type and rubber blending time were found to be less important. As a result, the viscosity of rubberized asphalt rejuvenated reclaimed asphalt pavement binders changed significantly with the blending temperature, blending time of the aged binder, and blending time of the original binder. Both backpropagation artificial neural networks and genetic algorithm modified artificial neural networks viscosity models were validated using data collected from prior studies, and the results were barely acceptable.

In this study, a calcined illite clay from Bailén, Jaén, Spain, was valorized as a substitute of metakaolin in the synthesis of new geopolymeric materials. The raw materials, raw clay and commercial kaolin, were pretreated at 750°C (4 h). Several samples (0%–100% by weight of clay) were activated by mixing NaOH solution and sodium silicate solution. The specimens were cured (60°C and 99% relative humidity) for 24 h, then demolded and kept at ambient conditions for 7, 28, and 90 days. The prepared geopolymers were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Physical, mechanical, and thermal properties were determined. The results indicated that the specimens based on the illite raw clay and metakaolin present an amorphous consolidated appearance, characteristic of the polycondensation reactions. The incorporation of up to 50% by weight of raw clay provided geopolymers with higher mechanical strength (39.6 MPa) and bulk density ($\mathrm{1,455}\mathrm{kg}/{\mathrm{m}}^3$), lower apparent porosity (19.6%), and similar although slightly higher thermal conductivity ($0.25\mathrm{W}/\mathrm{mK}$) than control geopolymers containing only metakaolin as a precursor after 28 days of curing. Control geopolymers presented compressive strength, bulk density, apparent porosity, and thermal conductivity of 23 MPa, $\mathrm{1,251}\mathrm{kg}/{\mathrm{m}}^3$, 41.03% and $0.224\mathrm{W}/\mathrm{mk}$, respectively, at the same age of cured geopolymers. The mechanical properties increased with curing time due to a greater advance of the geopolymerization reaction. Therefore, this illite clay can be thermally activated together with metakaolin to obtain geopolymers with suitable technological properties. The results demonstrate that the finished materials can be used for construction applications.

This article reports the experimental study of the influence of the fiber volume content in steel fiber–reinforced concrete (SFRC) on the acoustic emission (AE) characteristics. Plain concrete and SFRC specimens with various steel fiber contents were tested under unconfined uniaxial compression in the laboratory. Both AE testing and ultrasonic pulse velocity (UPV) methods were used to study the fracture process in the specimens. During the fracture process, the generated AE and axial compressive strain were recorded. The differences in AE characteristics of plain concrete and SFRC specimens were discussed. An absence of a considerable amount of AE for a certain period was observed (silent period of AE) near the peak load for SFRC specimens. The AE-based $b\text{-}\text{value}$ suddenly decreased near the peak load during the fracture process in plain concrete. However, in the case of SFRC specimens, a sudden decrease near the peak load was not observed, and the $b\text{-}\text{value}$ decreased gradually until failure, at which point it attained its minimum value. More AE related to shear cracking was observed in the case of SFRC specimens. This was due to interlocking between steel fibers, cement matrix, and coarse aggregates. AE testing is useful for studying the material characterization of SFRC, and is beneficial for assessing damage in structures constructed with SFRC.

This study presents the fracture behavior of synthetic fiber-reinforced structural lightweight aggregate concrete (SynFR-SLWAC) by experimental and analytical studies. Experimental studies include testing of 15 specimens for understanding mode-1 fracture response. Analytical studies include developing multilinear stress-crack width relations through inverse analysis. SynFR-SLWAC is made using sintered fly ash aggregate (SFA) with varying volume fractions of monofilament macro synthetic (0.2%, 0.4%, and 0.6%) and a small fraction of micro synthetic fibers (0.02%). The effect of synthetic fiber addition on the crack arresting mechanisms of SynFR-SLWAC is studied using the digital image correlation (DIC) technique. The stress-crack width relations are obtained from the experimental load-crack mouth opening displacement (CMOD) curves using inverse analysis. Additionally, empirical equations are proposed for predicting the stress-crack width relationship for SynFR-SLWAC with different fiber volume fractions. Fracture energy increased significantly with an increase in fiber volume dosage at larger values of crack width. Hinge width of SynFR-SLWAC reduced when compared to normal density concrete made of natural coarse aggregates.

In this paper, waste engine oil was used as the base oil to produce a competent rejuvenator for the recycled asphalt mixture based on the Design-Expert surface response method. From the surface response in terms of penetration, ductility, softening point, glass transition temperature, and mass-loss percentage, the optimum waste engine oil-based rejuvenator had 5% plasticizer, 6.33% antiaging agent, and 7.3% fusogen. The thermogravimetric (TG) analysis indicated that the prepared rejuvenator possessed excellent thermostability at 200°C. The optimum dosage of the rejuvenator was determined as 6% by the weight of asphalt binder based on the penetration, ductility, and softening point results. Then, the effects of the rejuvenator on the asphalt binder properties were evaluated through Fourier transform infrared spectroscopy (FTIR), dynamic shear rheometer (DSR), and differential scanning calorimetry (DSC). The binder test results implied that the rejuvenator significantly reduced the glass transition temperature of aged asphalt and restored the chemical composition, which also increased the rheological properties. Subsequently, the effects of the rejuvenator on the asphalt mixture properties were also evaluated through freeze-thaw splitting, beam bending, and dynamic stability tests. The mixture test results showed that the rejuvenator effectively increased the moisture resistance and low-temperature cracking resistance of aged asphalt mixture, which yielded comparable mixture properties with virgin asphalt mixtures.

A new approach to incorporate scrap tire material into concrete was investigated, in which two reclaimed waste tire components, carbon black and fuel oil, were used to replace a portion of water. The effect of liquid tire content to water ratios from 5% to 40% on an otherwise typical concrete mix were assessed, and compressive and flexural strength, flexural toughness, modulus of elasticity, and several fresh concrete properties were determined. Results were compared with typically expected results of traditional shredded tire mixes with equivalent tire content. It was found that the liquid tire mixes had significantly smaller losses of compressive strength and workability than did shredded rubber mixes; increased flexural strength compared with traditional concrete mix; and significantly decreased stiffness compared with traditional and shredded tire mixes.

Bituminous pavements frequently fail at an early age well below the predicted design life, which in turn necessitates taking rehabilitation actions to recover the serviceability to an acceptable level for users. Two rehabilitation techniques have been the focus of the engineering community: a traditional method known as the mill and fill and the other, which attracts increasing interest, is to take advantage of an interlayer before resurfacing. This rehabilitation technique is more challenging from the theoretical point of view since the traditional test methods need to be adapted to capture the mechanical properties that, in the presence of the interlayer, may emerge. On this ground, the focus of this paper is to gain an in-depth understanding of mechanical properties developed at the interface between two asphalt layers as in an unreinforced case and between a layer of paving fabric (a system composed of binder and synthetic fabric) and asphalt layers as in a reinforced case. To achieve this goal, three main properties were addressed: the antireflective property of the interface against crack propagation was examined via a modified three-point bending test (3-PBT) by calculating the J-integral and measuring the crack width below and above the interface. Besides, the stiffness properties in two perpendicular directions at the interface were separately studied through novel approaches to find out the possible mechanical effects induced by the interlayer on structural responses of a composite structure. The experimental results derived from this study revealed that the reinforced interface, including the paving fabric, had about 5 times the higher capacity in delaying the propagation of bottom-up cracking than the unreinforced one. However, this promising result was accompanied by 2.5 and 1.5 reductions in bonding quality and dynamic modulus, respectively, at the reinforced interface, which in turn necessitates introducing the real mechanical behavior of the reinforced system into design methods.

This research investigated the effects of usage of basalt fiber (BF) in cement mortars at elevated temperatures. Compressive strength, mass loss, and microstructure characteristics, including petrographic analyses and scanning electron microscopy (SEM) images of cement composites, were investigated. BF was added in the mortars at five different ratios: 0%, 0.5%, 1%, 1.5%, and 2% by volume of the mix. The mortars were subjected to temperatures of $23°\mathrm{C}$, $200°\mathrm{C}$, $400°\mathrm{C}$, $600°\mathrm{C}$, and $800°\mathrm{C}$. The mixture with 1% BF had the best residual compressive strength at high temperatures, so that is considered to be the optimum dosage. The lowest amount of mass loss at each temperature was for specimens with 2% BF. The results indicate that adding BF to the mixes decreased the mass loss. Petrographic and SEM images showed that with increasing temperature, the part of the microstructure which began to deteriorate first was the interfacial transition zone between cement matrix and fiber. BF has a significant function in spreading the cracks, and acts like bridge between two parts of cement paste.

The purpose is to enhance the working properties of waterborne epoxy resin and improve the quality of cold pavement binder usage. In this study, a modified waterborne polyurethane/epoxy composite was prepared. The influence of the type and content of the polyurethane on the working properties of a composite was studied. The optimum composition and ratio of the composite were determined. The properties of the waterborne epoxy at different working conditions and treatment times were analyzed. The long-term evolution law of property of waterborne epoxy was clarified. The correlation between different working properties of waterborne epoxy was studied. The results show polyurethane can improve the working properties of waterborne epoxy resin. Considering the tensile, bending, and bonding properties, the suitable type of polyurethane is toluene diisocyanate-polybutylene adipate (TDI-PBA), and the suitable content is 15%–20%. With the increase of hydrothermal aging time, the strength of waterborne epoxy resin increases 5%–10%, the flexibility reduces 6%–12%, and the bonding property decreases 70%–75%. After polyurethane modification, the property stability of waterborne epoxy resin is enhanced. The retention rate of the bonding property increases significantly, at approximately 120%–150%.

Portland limestone cement (PLC) has been used in all classes of concrete in Florida since 2017. In order to comprehensively use PLC, this study investigates the effects of cementitious paste volume (CPV), water to cementitious materials ($\mathrm{w}/\mathrm{cm}$) ratio on PLC concrete mixes with or without incorporation of the blended aggregate optimization (BAO) technique. The prelimary results indicated that CPV and aggregate gradation affected the workability, and $\mathrm{w}/\mathrm{cm}$ ratio mainly influenced strength in PLC concrete. Using a lower CPV can improve the electronic resistance and durability of PLC concrete. The findings of this research can help design the proper PLC concrete mix with low cost and environmental impact.

The properties of asphalt and aggregate in the warm-mix asphalt (WMA) containing recycled asphalt pavement (RAP) are critical to the mixture performances. This study quantified the effects of the morphological properties of WMA-containing RAP through the gray correlation analysis. The properties of asphalt and aggregate involved in this study included RAP content, two-dimensional morphological properties of recycled coarse aggregate, three-dimensional angle of recycled coarse aggregate, and surface free energy of recycled asphalt. The high-temperature performance represented by dynamic stability, low-temperature indicated by maximum bending strain, and moisture susceptibility characterized by the tensile strength ratio were chosen as the criteria for evaluating the impacts of different factors. The results showed that the RAP content had the greatest influence on high-temperature performance, followed by recycled asphalt’s surface free energy (SFE), and aggregate sphericity. The irregular shape factor of aggregate particles significantly influenced the mixture’s low-temperature properties. The SFE of asphalt was pivotal to the moisture susceptibility, and samples with higher SFE of asphalt presented better moisture damage resistance.

With the increase of sewage discharge, concrete sewage pipelines with small diameters are always under a fully flow-through operation stage and consequently suffer severe corrosion. To understand the deterioration process, concrete specimens were submerged in an accelerated sewage environment. The experimental results indicated that the main cause of the submerged concrete deterioration was corrosive media produced by a large number of acid-producing bacteria (APB) and sulfate-reducing bacteria (SRB) in the anaerobic environment of sewage. The corrosion process resulted in the increase of the ${\mathrm{Ca}}^{2+}$ concentration in the environment; the decomposition of hydration products; and the formation of amorphous silica gel, ${\mathrm{CaCO}}_3$, and AFt. The deterioration evolution of concrete in sewage was a combined effect of dissolution, decomposition, and expansion. After immersion in sewage for 6 months, the surface pH of concrete decreased from an initial 12.6 to 5.0, and the mass loss of concrete was as great as 15.9%. The corroded concrete can be classified into four zones from the surface to the innermost layer. The outmost layer was a strongly deteriorated zone, which was white and porous, and was composed of calcium carbonate, gypsum, and amorphous silica gel. The inner adjacent layer was a separation zone, which was yellow, and had microcracks due to the accumulation of expansive AFt crystals. Next to this zone was a white visible transition zone, which developed across the cracks and was dominated by ${\mathrm{CaCO}}_3$ and AFt crystals. The innermost layer, called the inapparent transition zone, almost had no visible sign of deterioration; however, some decomposition and dissolution of hydration products also occurred, except calcium silicate hydrate.

The application of photocatalysts on pavement engineering to degrade automobile exhaust has become a hot topic for researchers. However, the effect of photocatalysts on pavement materials has not been fully investigated. The primary purpose of this study is to explore the effect of a typical photocatalyst titanium dioxide (${\mathrm{TiO}}_2$) on the chemical structure and properties of asphalt through laboratory experiments and molecular dynamics (MD) simulation. Performance tests indicated that the physical properties of asphalt modified by ${\mathrm{TiO}}_2$ changed more significantly compared with that of calcium carbonate (${\mathrm{CaCO}}_3$) and silica (${\mathrm{SiO}}_2$), which might be due to the smaller particle size of ${\mathrm{TiO}}_2$. Atomic force microscopy (AFM) and Fourier infrared spectrum (FI-IR) analyses demonstrated that the addition of ${\mathrm{TiO}}_2$ resulted in a smoother asphalt surface and a disappearance of the bee structure. Using ${\mathrm{TiO}}_2$ would not accelerate the aging process of asphalt. Moreover, the MD simulation results indicated that a more significant interaction existed between ${\mathrm{TiO}}_2$ and asphalt than that of ${\mathrm{CaCO}}_3$ and ${\mathrm{SiO}}_2$, which resulted in a tighter asphalt molecule and smaller free volume distribution in the ${\mathrm{TiO}}_2\text{-}\mathrm{asphalt}$ system.

Fillers have been commonly used to replace a portion of cement in ultra-high-performance concrete (UHPC) for economic and eco-friendly purposes. However, mostly only the type and amount of filler are addressed, and limited efforts have been made on the size and shape effects of filler. This study used inert mineral fillers with different morphologies (approximately spherelike versus needlelike) to study the effect of the shape and different particle sizes (fineness) within the same filler type to study the effect of the size. A systematic study was carried out to investigate these effects on the workability, strength, hydration, modification of the particle-size distribution (PSD), and microstructure of the designed nonfibrous UHPC matrixes. The mixture proportion design is based on a modified Andreasen and Andersen model, and three mixtures devoid of fillers were prepared firstly to study the effect of superplasticizer dosage on the UHPC matrix to determine the saturation dosage. Results reveal that larger-sized approximately spherelike filler (limestone or quartz) results in a slightly negative effect on the strength, whereas larger-sized needlelike wollastonite enhances the strength of the mixture. The mixtures with 20% substitution of cement by the seven different fillers obtained increased workability, decreased cost, and higher strength or no more than 4% strength reduction compared with the control mixture devoid of filler. This quantification of size and shape effects of fillers will provide an effective theoretical basis, and particular fillers could be intelligently chosen in the engineering practice for the production of UHPC.

Due to the limitations of sorting technology, mixed recycled coarse aggregate, which mainly includes recycled concrete coarse aggregate and recycled brick coarse aggregate, accounts for a large proportion of recycled aggregate. This paper proposes a grading method for mixed recycled coarse aggregate to ensure satisfactory concrete performance. Distribution of specific density, saturated surface dry density, water absorption, and crushing value of mixed recycled coarse aggregate, as well as the effect of recycled brick coarse aggregate content, on the four parameters of mixed recycled coarse aggregate are investigated in this paper. The water absorption and crushing value were selected as the main grading indexes of mixed recycled coarse aggregate by using the weighted grey analysis method. According to the analysis results of the nonlinear fitting curves between the property indexes of mixed recycled coarse aggregate (water absorption and crushing value) and the performance parameters of mixed recycled coarse aggregate concretes (cubic compressive strength, prism compressive strength, splitting tensile strength, static modulus of elasticity, and the flexural strength), the mixed recycled coarse aggregates were divided into two categories; Categories I and II are used for structure and nonstructure uses, respectively.

Advanced numerical modeling of high-strength concrete ($f_c>60\mathrm{MPa}$) structures designed to withstand severe thermal conditions requires detailed and reliable information on the mechanical properties of the material exposed to elevated temperatures. The only uniaxial compressive strength variation with temperature is not enough to satisfy the large number of parameters often required by advanced nonlinear constitutive models. For this reason, a complete experimental investigation is required. The paper takes a commonly used high-strength concrete ($f_c=73\mathrm{MPa}$) as an example to describe a comprehensive experimental approach instrumental to the parameter definition and calibration of common constitutive models for concrete. The present study not only studied the overall compressive and tensile behavior of the case study material, but also investigated the effect of elevated temperatures on the specific fracture energy and the evolution of internal damage, in residual conditions after a single thermal cycle at 200°C, 400°C, and 600°C.

In this paper, a new class of self-consolidating ultrahigh-performance concrete (UHPC) was investigated. The UHPC featured a compressive strength higher than 150 MPa with self-consolidating characteristics desirable for modular construction. This paper describes the development and characterization of UHPC, its large-scale processing techniques with conventional equipment, its verification with internal and surface microstructure analysis techniques, and the structural behavior of large-scale steel plate UHPC (S-UHPC) beams under out-of-plane loads. Based on a particle size distribution study, an optimum packing density was achieved in the mixture that uses an uncommonly used undensified silica fume. The physical parameters of the ingredients and the resulting microstructure after hydration are considered essential for the design of self-consolidating UHPC materials. Distinguishing the three phases of the material after hydration using three-dimensional X-ray microtomography allowed the quantitative analysis of the UHPC microstructure. The internal microstructure study showed a significant reduction of macropores in UHPC compared to mortar specimens, which confirmed the physical attributes behind the improved material characteristics. A microstructure study of the material was also performed using scanning electron microscopy. In addition, a comparison of the experimental results of four large-scale steel plate concrete (SC) beam specimens cast with either conventional concrete or UHPC materials under three-point shear loading indicated that the developed UHPC materials significantly enhanced the ductility and capacity of the S-UHPC beams.

Cellular concrete is an alternative to conventional concrete as a low-density and high-insulating building material. The eco-cellular concretes (ECCs) based on geopolymer technology have been recently introduced by the scientific community. A form of ECC was studied, in which the fluid catalytic cracking residue and the blast furnace slag were employed as precursors, the rice husk ash was utilized as an alternative silica source in the activator, and the aerating reagent was replaced with recycled aluminum foil. Field emission scanning electron microscopy, optical microscopy, and ImageJ version 1.48 software (National Institutes of Health) were employed to characterize the void distribution. Bulk density and porosity were determined by hydric tests. The results revealed that lowest densities without strength loss were obtained when the cementing matrix had a homogeneous void system: similar spacing between pores, narrow size ranges, and nonconnected pores. A relationship was established between open and closed porosity with density and thermal conductivity.

The present study evaluated the effects of six different bitumen film thicknesses (0, 0.2, 0.4, 0.6, 0.8, and 1 mm); four polishing levels of aggregate [220, 400, 600, and 800 Silicon Carbide (SiC)]; three moisture conditioning temperatures (25°C, 40°C, and 60°C); and three different aging levels of bitumen (143°C, 163°C, and 173°C) on interfacial strength of basaltic-unmodified bitumen system using binder bond-strength (BBS) test. Further, two different basaltic aggregates were procured, and their interfacial bond with three different types of bitumen, namely, unmodified (VG30), polymer-modified (PMB40), and crumb rubber–modified (CRMB60) was evaluated. The results showed that basaltic aggregate with higher porosity (and thus higher rate of moisture absorption) showed lower bond strength, although the polishing level of both aggregates was kept at 220 SiC. Further, PMB40 had higher bond strength followed by VG30 and CRMB60, depicting the influence of crumb rubber particles on interfacial bonding behavior of CRMB60. The study showed that 220 SiC polished aggregates having 0.8-mm bitumen film thickness and conditioned at 40°C can provide appropriate results on aggregate-bitumen bond strength using the BBS test, which supports the recommendations provided in AASHTO T 361. Thus, the authors believe that the BBS test may be beneficial in evaluating aggregate-bitumen bond strength in the field.

Roller compacted concrete (RCC) is a dry concrete with zero slump and is constructed in layers. RCC dams are generally weak in interlayers. The bond strength and the permeability of the interlayer affect the performance of the dam structure and its safety. In this study, the mechanical characteristics and the permeability of the interface layer of RCC were investigated by considering three key parameters, including water-to-cementitious materials ratio (w/cm) of concrete, water-to-cementitious (w/c) ratio of bedding mortar, and time interval between pouring each layer. More than 300 RCC specimens were prepared. The bond strength of the interlayer was measured using the direct shear test and the direct tensile test. The permeability of the interlayer was evaluated by conducting the water permeability and the sorption tests. Scanning electron microscopy (SEM) was utilized to investigate the microstructure of interlayers. The analysis of variance (ANOVA) was utilized to identify the statistical significance of experimental parameters, which were the w/cm ratio of concrete, w/c ratio of bedding mortar, and time interval on the strength and permeability properties of RCC. Additionally, the relationship between the variables and responses was determined using the response surface method. Finally, the optimal mix design was achieved by multiobjective optimization based on target strengths and water permeability. Joint condition of the RCC layer was affected by the age of the joint and bedding layer. Results showed an increase in the time interval led to a reduction of bond strength and high permeability of the joint. Furthermore, by increasing the cement content of the bedding mortar, the shear and tensile strengths were improved, and the permeability coefficient was reduced considerably.

This technical note evaluated hybrid asphalt binders modified with a combination of styrene-butadyene-styrene (SBS) and postconsumer ground tire rubber (GTR). These hybrid blends were evaluated in laboratory mixture experiments against more traditionally modified binder using either SBS or GTR. Mechanical properties measured during laboratory experiments were supplemented with a literature review, followed by a discussion of trade-offs between these modification options within the context of a sustainability triple bottom line of environment, economics, and social well-being. This technical note also discussed test sections containing hybrid binders and how some state departments of transportation have incorporated hybrid binders into their specifications. Overall, this work suggests that performance leans toward SBS, sustainability leans toward GTR, economics sometimes leans toward GTR, and social well-being benefits from consideration of all these factors simultaneously. A hybrid binder containing 1%–2% SBS and 3%–8% GTR should allow for high-temperature grading increases and the use of GTR in a wider range of mix types than have historical approaches.

The vibration reduction effect of compacted stone mastic asphalt (SMA) mixture with rubber particles or rubber powder has been widely explored, but the vibration reduction effect of common SMA mixture has not received enough attention. To explain the vibration reduction effect of compacted SMA mixture, the vibration attenuation test on tires was designed to simulate the attenuation characteristic of automobile tires in vertical vibration. Meanwhile, the influence of material composition and paving thickness on the vibration characteristics of compacted SMA mixture was also analyzed. Results show that compared to the compacted SMA mixture with different nominal maximum size of aggregate, the vibration attenuation coefficient of compacted SMA-13 mixture is higher than SMA-5 and SMA-10 mixtures, and the difference between SMA-16 and SMA-13 is slight. The vibration reduction effect of compacted the SMA-13 mixture is associated with asphalt type, content of coarse aggregate, and asphalt binder, but the design of the mixture proportion should also be combined with pavement performance. The vibration attenuation coefficient of compacted SMA mixture with Styrene-Butadiene-Styrene block copolymer (SBS)–modified asphalt is slightly larger than that of the high viscosity–modified (HVM) asphalt mixture. Through comprehensively considering different influencing factors, the mineral aggregate gradation and the dosage of asphalt binder are found to be the dominant factors that affect the vibration reduction effect of the compacted SMA mixture. The research results can provide some references for improving the comfort of passengers and optimizing the design of asphalt mixture in environmentally sensitive areas.

Permeable concrete is required to have adequate strength, water permeability, and freeze-thaw resistance as pavement material. The purpose of this research is to improve the properties of fiber-reinforced permeable concrete (FRPC) based on orthogonal experimental design by adjusting water-cement ratio ($\mathrm{w}/\mathrm{c}$), target porosity, volume content of polyacrylonitrile fiber (PANF), and polypropylene plastic fiber (PPF). Computer tomography (CT) is applied to generate the three-dimensional (3D) pore structure model of optimized FRPC for permeability prediction and seepage flow simulation by the computed fluid dynamics (CFD) method. The results show that the FRPC with $\mathrm{w}/\mathrm{c}$ of 0.37, target porosity of 20%, PANF volume content of 0.16%, and PPF volume content of 0.25% can obtain reasonable strength (compressive $\mathrm{strength}>20\mathrm{MPa}$, flexural $\mathrm{strength}>2.5\mathrm{MPa}$), high water permeability (permeability $\mathrm{coefficient}>20\mathrm{mm}/\mathrm{s}$), and adequate frost resistance (freeze-thaw $\mathrm{cycles}>200$). The permeability coefficient obtained by numerical simulation shows error less than 10% in comparison with experimental results. The relationship of seepage velocity and pressure gradient confirms to Darcy-Forchheimer’s law and the critical Reynolds number for optimized FRPC with aggregate sizes of $10–15\mathrm{mm}$ is 21.92.

In order to reduce the disposal of industrial byproducts and the environmental impacts associated with ordinary Portland cement (OPC) production, it is encouraged to use industrial byproducts to replace OPC for soil stabilization. In this context, this study attempts to use three industrial byproducts, including ground granulated blast furnace slag (GGBS), ladle slag (LS), and phosphogypsum (PG), for soft clay stabilization. The GGBS-LS was used as the main binder, and the PG was used to enhance the strength development of GGBS-LS-stabilized soft clay. The GGBS-LS-PG-stabilized clay with different binder contents and $\mathrm{PG}:(\mathrm{GGBS}+\mathrm{LS})$ ratios were prepared and cured for different periods and then subjected to different tests, including unconfined compressive strength (UCS), one-stage batch leaching, X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy analysis. The results indicated that the addition of PG could effectively enhance the strength development of GGBS-LS-stabilized clay. With $\mathrm{PG}:(\mathrm{GGBS}+\mathrm{LS})$ ratios of 10%–20%, the GGBS-LS-PG-stabilized clay could achieve higher 28-day and 112-day strength than that of OPC-stabilized clay. The leaching of Pb and Zn from the GGBS-LS-PG-stabilized clay was three to five orders of magnitude lower than that of raw LS and could satisfy the three common drinking water regulations. The addition of PG produced more ettringite in the stabilized clay, enhancing the strength development of stabilized clay. The findings indicate that the three industry byproducts can replace OPC to stabilize soft clay, which has significant benefits in both cost and sustainability.