Journal of Materials in Civil Engineering

The disposal of waste slurry from construction engineering is attracting more and more attention due to the thorny issues related to high water content (dewatering is difficult and time-consuming). The use of chemical flocculants is proposed in this study, and organic, inorganic, and composite flocculant are designed to identify the characteristics and efficiency of slurry-water separation. The influence of flocculant type and dosage on slurry settlement and its associated mechanisms are studied by a set of sedimentation column, particle size distribution, and scanning electron microscopy (SEM) tests. The experimental results prove that organic, inorganic, and composite flocculants can promote the efficiency of slurry-water separation, although inorganic flocculants may perform relatively worse in comparison with organic and composite flocculants. The conditioning performance of organic flocculants is sequentially anionic polyacrylamide (APAM) > polyacrylamide (PAM) > amphoteric polyacrylamide (ACPAM) > cationic polyacrylamide (CPAM), while their optimum dosage is 300, 300, 400, and $400\mathrm{mg}/\mathrm{L}$, respectively. The combined formulation of $\mathrm{APAM}+{\mathrm{FeCl}}_3$ improves the conditioning of slurry owing to the charge neutralization, net capturing, and sweeping ability. The flocculating effect causes an aggregation of fine particles, and this induces a decrease in the amount of fine particles and an increase in the fraction of coarse flocs. The SEM results prove that the slurry particles tend to be arranged in a parallel manner and the flocculant induces an agglomeration of fine particles owning to a series of physicochemical reactions. The previous discussions can provide an experimental framework for the development of slurry-water separation technology on waste slurry from construction works.

Manufactured sand (MS) has been increasingly used as fine aggregate for concrete. This paper proposes a prediction of the compressive strength of concrete with manufactured sand (MS-concrete) based on an ensemble classification and regression tree (En_CART) method. A data set containing 1,350 original measured strengths of 328 concrete mixtures from actual engineering projects were used for training and testing. The cross-validation and experimental data from the literature were also used for validation, both indicating that the En_CART model provides an accurate and robust prediction. The comparison of En_CART with various machine learning methods, including artificial neural network, linear regression, Gaussian process regression, random forest, and support vector machine regressions, indicates that the En_CART model indicates superiority in predicting the compressive strength of MS-concrete. Based on the proposed model, the evolution of compressive strength is analyzed. The importance analysis indicates that age is the most significant factor influencing the compressive strength of MS-concrete, and stone powder content presents approximately 25% of the age contribution. The compressive strength of MS-concrete was found to first increase and then decrease with increasing content of MS. The optimal content of MS slightly increases with an increase in the strength level of MS-concrete. Stone powder, at certain MS content, is also found to indicate remarkable improvement in the compressive strength of MS-concrete. The optimum content of stone powder in MS is higher for MS-concrete with lower strength and lower for MS-concrete with higher strength.

The present research evaluates the technoeconomic performance of alkali-activated slag (AAS) concrete in comparison with ordinary portland cement (OPC) concrete. Seventy-five AAS mixtures with a wide range of mixture proportions are produced, moist-cured, and tested for their workability (slump or slump flow) and compressive strength. The relative ${\mathrm{CO}}_2$ emission and material cost of the mixtures are also analyzed in comparison with OPC concrete. Regression analyses are carried out to model the mixtures’ consistency and compressive strength and relate them to the governing factors [i.e., $(\mathrm{Na}+\mathrm{K})/\mathrm{Si}$, $\mathrm{Ca}/\mathrm{Si}$, and ${({\mathrm{H}}_2\mathrm{O}/\mathrm{Solids})}_{\mathrm{vol.}}$]. The extent of the effects and the interactions of such factors on the strength and slump of AAS concrete is quantitatively determined. A multiresponse optimization method with the aim of maximizing the strength for a targeted slump range while minimizing the relative cost and ${\mathrm{CO}}_2$ emission is introduced, and the mixture proportions yielding such conditions are identified. The results suggest that at molar ratios $(\mathrm{Na}+\mathrm{K})/\mathrm{Si}=0.55$, $\mathrm{Ca}/\mathrm{Si}=1.01$, and volume ratio ${({\mathrm{H}}_2\mathrm{O}/\mathrm{Solids})}_{\mathrm{vol.}}=1.0$, workable AAS mixtures ($\mathrm{slump}=90\mathrm{mm}$) could be produced with strength values exceeding twice the amount and ${\mathrm{CO}}_2$ emissions half that of OPC concrete while maintaining the material cost increase below 40%.

Pervious concrete, extensively applied in sustainable urban drainage systems, is prone to clogging. From the perspective of the clogging particle size relative to the pore size, clay particles easily pass through pervious concrete. However, drying may increase the potential of clay clogging. A laboratory study was performed to examine the effect of drying on clay clogging of pervious concrete and the mechanism of clay clogging. Five slurries of different clay concentrations were prepared to clog pervious concrete specimens under two exposure methods, namely, drying and no drying, which were applied after the clay slurry was added to the specimen. After clogging, 30 pressure washing cycles were applied to each specimen, and the permeability was measured after each washing cycle. Moreover, the dried clay-clogged specimens were scanned by computed tomography (CT) before the 1st washing cycle and after the 30th washing cycle. The measurements revealed that more than 80% of the total retained particles were within the depth range $20–70\mathrm{mm}$ below the specimen surface, and the most highly clogged layer was found in this range. The permeability of specimens clogged with undried clay almost recovered to the initial value after only five washing cycles. Clay drying may cause difficult-to-recover clogging due to two factors, namely, drying increases particle-to-particle cohesion and particle adhesion to pore walls, and drying causes particles to shrink to form aggregates that are larger than the pore size. This study facilitates the development of effective pavement maintenance strategies.

To improve the self-healing performance of styrene-butadiene-styrene/multiwalled carbon nanotube composite modified emulsified asphalt (SMEA), three representative types of nanofibers were used to reinforce SMEA, and their effects on self-healing properties of SMEA were discussed by the developed self-healing evaluation methods. Test results indicate that basalt (BS) nanofiber without shape memory performance not only decreases the ductility and low-temperature cracking resistance of evaporation residue of SMEA after self-healing but also lowers the self-healing performance of SMEA. On the contrary, polyethylene terephthalate (PET) nanofiber and polytrimethylene terephthalate (PTT) nanofiber improve the ductility and low-temperature cracking resistance of SMEA. Further, PTT nanofiber with a stronger shape memory property more obviously increases the self-healing performance of SMEA than PET nanofiber. Additionally, the self-healing index of dissipated energy ratio ($H{I}^3$) before and after self-healing is more suitable to characterize the self-healing performance of nanofiber-reinforced SMEA. Finally, PTT nanofiber-reinforced SMEA shows satisfactory repeated self-healing performance. PTT nanofiber at the content of 0.35% is proposed to reinforce SMEA, developing more durable modified emulsified asphalt for the maintenance and repair of asphalt pavement.

As preservative asphalt, microsurfacing is an effective solution in preventive repair and maintenance, which consists of well-graded fine aggregates, polymer-modified cationic bitumen emulsion, water, and chemical additives in order to control the breaking time of bitumen emulsion. Due to the use of polymeric bitumen emulsion and fully crushed aggregates, these mixtures produce an increase in shear strength, abrasion resistance, and rutting resistance of asphalt surfaces. According to the researches conducted and the substantial role of filler in the strength of asphalt mixtures, and also owing to environmental impacts and high energy consumption of traditional cement filler. In this study, three mixtures containing fillers (microsilica slurry, quicklime, and combination of cement and quicklime) with slow setting bitumen emulsion, and the mixture of cement filler, as the control mixture, were used for laboratory survey and comparison of the effects of different fillers on the performance of microsurfacing asphalt mixture. Based on International Slurry Surfacing Association (ISSA) A143 guideline and ASTM D6372 standard, the performance of samples was assessed by wet cohesion, wet track abrasion, and loaded wheel tests. The findings demonstrate that the utilization of alternative fillers has a better performance in rutting, stripping, and abrasion compared to the control mixture owing to their appropriate physical, chemical, and mechanical features.

Acidic environments constitute serious chemical threats to concrete-like cementitious materials. The purpose of this study is to experimentally investigate the degradation of alkali-activated slag/fly ash mortars with different slag/fly ash ratios: $80/20$, $60/40$, and $40/60$ in acidic environments. Mortar samples were exposed to three different types of aggressive acidic solutions: phosphoric acid, sulfuric acid, and a mixture of phosphoric acid and sulfuric acid maintained at a constant pH value of $2.5\pm 0.5$ for a period of 150 days. Results showed that, for all mortar samples, the aggressivity of the phosphoric acid is greater compared to the other acids. Moreover, samples with a slag/fly ash ratio of $60/40$ demonstrate the highest resistance against the three types of acidic environments. In addition, it shows that the degradation process of alkali-activated mortars can be divided into two degradation stages: an early stage and a subsequent stage. The chemical-reaction dominated early degradation stage is described by using Hill function, whereas a diffusion process–dominated subsequent stage is simulated with Fick’s second law. Finally, the results of theoretical analysis predicted that the degradation depth of alkali-activated slag/fly ash mortars exposed to sulfuric acid environment ($\mathrm{pH}=2.0$) for 50 years could be reduced by about 52%–60% compared to that of an ordinary Portland cement (OPC)-based mortar.

Urbanization in China has been producing a huge quantity of construction and demolition waste, of which clay brick waste accounts for a substantial proportion. For reducing waste disposal, the clay brick waste has been reutilized in concrete production by employing the aggregate replacement or cement replacement methods. However, with these methods, the clay brick waste tends to have an adverse effect on the mechanical performance of the concrete produced, especially at high replacement rate. Herein, a novel method, the paste replacement method (PRM), was applied, in which clay brick fines (CBF) were made by crushing and grinding clay brick waste and reused to partially replace the cementitious paste (water + cementitious materials). The compressive behavior of the concrete produced was tested. The results showed that the CBF added based on PRM increased compressive strength and elastic modulus, caused little change to Poisson’s ratio, and decreased the lateral dilation of the concrete. More importantly, it reduced the cement content by up to 29.4% and the cement factor (cement content to strength ratio) by up to 62.3%.

This study examines the effects of five biomodifiers on the aging and rejuvenation of biomodified rubberized bitumen. It further discusses the challenges associated with restoration and reuse of aged bitumen, especially bitumen located in a geographic area with high ultraviolet intensity. Exposing bitumen to oxidation changes its colloidal stability, whereas the content of asphaltene increases, and the content of aromatics decreases as aging progresses. In addition, bitumen’s evolution during aging includes oxidation, aromatization, chain scission, and carbonization, which alters bitumen’s molecular structure and subsequently its restoration capacity. To revitalize aged bitumen, a need exists to restore bitumen’s molecular conformation. The latter becomes more complex when rubber molecules are involved because the presence of polymeric structures and carbon black in tires could have counteracting effects on bitumen’s aging. The polymer structure can degrade and act as a sacrificing agent, whereas carbon black might work as an ultraviolet blocker and free radical scavenger. In addition, the presence of other modifiers, such as bio-oils, could alter the evolution of aging. To study the interplay of modifiers on the aging evolution of rubberized bitumen, this study compares the resistance to the ultraviolet aging of various biomodified rubberized bitumens. It further examines the efficacy of a rejuvenator to restore each aged bitumen. This study found that not all biomodified rubberized bitumens had similar restoration capacity. The results indicated that bitumen containing a wood-based modifier has the least signs of aging among all scenarios studied. This finding can be attributed to the presence of a significant content of furfural in the wood-based modifier that helped reduce molecular-level changes. After aging, each specimen was rejuvenated using a biobased rejuvenator. The success of rejuvenation was tracked using the rejuvenating index calculated based on the extent of the changes in the chemical and rheological properties of rejuvenated bitumen. Aged wood-based rubber modifier was found to need the lowest dosage (5.7%) of the rejuvenator to be restored, followed by corn stover (8.3%), miscanthus (8.4%), waste vegetable oil (9.81%), and castor oil-based rubber modifier (10.87%). The study results indicate that the composition of biomodified rubberized bitumen not only affects its evolution during aging but also its rejuvenation capacity.

Ultrahigh performance concrete (UHPC) is an advanced composite material that exhibits superior compressive and tensile strengths as well as negligible permeability. Although the mechanical properties of UHPC are extensively investigated, the bond strength between UHPCs cast at different times due to the construction process or its application is not fully understood and needs to be quantified. The interface between precast UHPC (PC-UHPC) and cast-in-place UHPC (CIP-UHPC) cold joints is subjected to various stress conditions ranging from tension, shear, compression-shear, and tension-shear. To date, no comprehensive study has been conducted to consider all possible stress conditions at the interface. The objective of this study is to quantify the effect of roughness on bond strength at the UHPC-UHPC cold joint under tension, shear, and a combination of compression and shear stresses. Roughness on the interface of the precast UHPC was achieved using commercially available formliners with five mean texture depths ranging between 1.32 and 4.28 mm. The interfacial parameters, such as cohesion and shear friction, which have not been identified for cold UHPC joints, were determined. Specimens prepared with a mean texture depth of 4.28 mm experienced the highest bond strength under the most tested stress conditions. The results indicate that the interface, which was ultimately without fibers, experienced cohesion values that were lower than the reported values from some design codes. The friction coefficients were higher than the maximum reported value from the design codes.

Streptomyces-induced calcite precipitation (SICP) was used to bind loose dredger fill into soil columns. The composition, microstructure, strength, and permeability of the soil columns were studied. The X-ray diffraction (XRD) results show that the cementitious material of calcium carbonate was found in the soil columns. The morphology of the soil columns with and without streptomyces was the sheet and the block structure, respectively. The compressive strength of the soil columns was highest (2.29 MPa) when the content of streptomyces was 30%. The compressive strength of the soil columns with streptomyces was higher than other groups when the medium solution pH was 9, although the hydraulic conductivity of the soil columns containing streptomyces (15% of calcium oxide) was similar to those without. Under the optimal bacterial powder content of 30%, the average resulting content of calcium carbonate was 12.73% in the soil columns. Compared with microbially-induced carbonate precipitation (MICP), the SICP process did not release ammonia gas during biomineralization. Therefore, the SICP technique is environmentally friendly for the cementation process.

The compression property of basalt fiber–reinforced polymer (BFRP) confined coconut shell (CS) concrete (CSC) was examined. The mix ratio of plain concrete as reference was fixed to be $0.60:1:1.23:2.05$ for water: cement: sand: stone aggregate by weight, while the stone aggregate was replaced with CS by 25%, 50%, 75%, and 100% in volume. Three groups of BFRP tubes, i.e., 2-, 4-, and 6-layer tubes, with a height of 200 mm and an inner diameter of 100 mm were built. An axial compression test was carried out to examine the strength and deformation capacity enhancement of concrete due to BFRP. Strains in the axial direction and hoop direction, axial force, and failure modes were discussed. Results indicated that the strength of CSC decreased quickly with an increase of the CS replacement ratio. However, with the confinement of the BFRP, the strength and deformation capacities were respectively improved by 1.39–2.65 times and 5.53–9.95 times in comparison with that of the plain concrete. The results also indicate that inclusion of CS changed the failure mode, i.e., BFRP confined plain concrete failed with a vertical crack and BFRP confined CSC was damaged with a horizontal crack.

This paper investigated the deformation (dynamic creep) behavior of foamed bitumen stabilized mixes (BSM-foam) that incorporates recycled asphalt pavement (RAP) material. The influence of temperature and stress level on the deformation behavior of these mixes was studied. The permanent deformation indicators that were determined using the laboratory tests on BSM were also compared with those of the conventional hot mix asphalt (HMA). From the comparative studies using dynamic creep tests, it was noted that the three-stages (primary, secondary and tertiary) of the creep curve that are usually seen for HMA were also observed for BSMs. The mathematical models that are commonly used to fit the different stages of the creep curve of HMA were found to be applicable to predict the creep behavior of the BSMs. In general, it was found that the BSMs behave similarly to that of HMA in terms of permanent deformation in that a steady-state strain rate was achieved before failure. From the repeated load axial test (RLAT) tests, it was noticed that the BSMs are less temperature-sensitive to deformation compared to HMAs. BSMs showed 20%–45% less of an increase in permanent deformation compared to HMA when test temperature increased from 30°C to 50°C. This study also investigated the applicability of the time-temperature superposition (TTS) principle for secondary stage permanent strain data obtained from RLAT tests. The RLAT tests were conducted at three temperatures and three stress levels to develop the dynamic creep master curve. It was observed that the TTS principle is applicable for secondary creep data of BSMs.

Serious environmental pollution will occur if corn stalk materials are discarded randomly or burned in open air. This study presents a possible method for using corn stalk materials to make fibers used in stone matrix asphalt (SMA) mixtures to address this problem. To obtain an in-depth understanding of the application of corn stalk fibers in SMA mixtures, basic properties such as high-temperature, low-temperature, moisture susceptibility, and fatigue performance, and the dynamic modulus were researched. The performances of SMA mixtures with lignin fibers and basalt fibers were studied as comparative research. Corn stalk fibers and basalt fibers, used as composite fibers, were incorporated jointly into the SMA mixtures, and the performance was evaluated. The test results showed that the high-temperature, low-temperature, and moisture susceptibility performance of SMA mixtures with corn stalk fibers can meet the specification requirements. The addition of corn stalk fibers and basalt fibers in SMA mixtures improved the high-temperature, low-temperature, and fatigue performance of SMA mixtures and had comparable dynamic moduli. A content of 0.6% corn stalk fibers is recommended for SMA mixtures. For the application of composite fibers, contents of 0.4% corn stalk fibers and 0.2% basalt fibers currently are recommended for SMA mixtures. In general, corn stalk fibers can be used in asphalt pavement, and the application of corn stalk fibers can reduce construction costs and environmental pollution.

Isophorone diisocyanate (IPDI) was encapsulated successfully within double-layered shells, and final microcapsules showed outstanding self-healing functions in cement paste. The well-dispersed microcapsules had a diameter of $347.0\pm 103.4\mathrm{\mu m}$, shell thickness of $3.1\pm 0.4\mathrm{\mu m}$, and core fraction around $74.8\%\pm 1.9\%$ by weight. The diameters of microcapsules were adjustable by varying agitation rates. The beginning weight-loss temperature of microcapsules was 200°C, implying good thermal stability. The final microcapsules affected slightly the workability and setting time of fresh self-healing cement paste. Although the mechanical strength of hardened self-healing cement paste was decreased with the increase of microcapsule concentrations, the open porosity was improved obviously from 33.5% (control samples) to 31.8% when 5.0% by weight of microcapsules was introduced. The interfaces of microcapsules were compatible enough with cement paste without obvious delamination. Especially, the self-healing cement paste showed outstanding self-healing functions in open air when 10.0% by weight of microcapsules was introduced.

The purpose of this paper was to study the aging behaviors of high-viscosity asphalt (HVA). Three kinds of asphalt binders [base asphalt, styrene-butadiene-styrene-modified asphalt (SBSMA), and HVA] were treated with rolling thin-film oven test (RTFOT) and pressure aging vessel (PAV). Temperature sweep (TS) test and multiple stress creep recovery (MSCR) tests were conducted on all samples to test the indexes of rheological properties, and chemical compositional changes were monitored by attenuated total reflection (ATR)–Fourier transform infrared spectroscopy (FTIR). The results show that the values of complex modulus ($G^{*}$), storage modulus ($G^{\prime }$), loss modulus ($G^{″}$), and rutting factor ($G^{*}/\sin \delta$) of all asphalt binders increase with the severity of aging. Additionally, after PAV, the values of phase angle ($\delta$), $J_{nr}0.1$, and $J_{nr}3.2$ of base asphalt gradually decrease, while those of SBSMA and HVA increase. After PAV, the rutting resistance of the base asphalt improves, while that of SBSMA and HVA deteriorates. The aging deteriorates the temperature sensitivity of base asphalt, SBSMA, and HVA but improves their homogeneity. Moreover, the effect of aging on the temperature sensitivity and the micromorphology structure of polymer-modified asphalt (PMA) is greater than that of base asphalt. The rheological aging index and FTIR spectroscopy test result shows that the aging resistance of SBSMA and HVA is better than that of base asphalt. Based on the aging sensitivity analysis and the correlation analysis, the storage modulus is the most sensitive to aging, and the loss modulus aging index could be used for the aging evaluation of HVA.

The acceptance of geopolymeric systems in construction industry as an alternative to portland cement has paved the way for using it in the strengthening of reinforced concrete structures. In this regard, a study was carried out to develop a novel method of strengthening reinforced concrete beams by jacketing using ultrafine blast-furnace slag-based geopolymer. The reinforced concrete beams were in a fully damaged, partially damaged, or undamaged state prior to jacketing. Geopolymer concrete (GPC) exhibited appreciable performance as a jacketing agent. The results of GPC-jacketed beams in terms of strength, ductility, and stiffness degradation were superior compared to portland cement concrete (PCC). GPC-jacketed beams exhibited appreciable performance even at the early age of three days. The levels of damage also influenced the behavior of the jacketed beams.

Quantifying the features of concrete cracking is of significance for assessing the bearing capacity and durability of concrete structures. However, there is a lack of efficient and reliable observation and description of the crack features, particularly for very early-age concrete. In this study, a high-precision, noncontact laser scanner is used to dynamically obtain the 3D point cloud data of the cracks in concrete starting from casting until the age of 24 h. A crack point extraction method based on the local density of the scanned points is proposed to recognize the crack points, which are then connected according to the nearest neighbor principle to form crack elements. By setting the angle and the distance thresholds, the crack elements are clustered and expanded into independent cracks, and further, the crack sets. The calculation methods for both the length and the width of the independent cracks as well as the long and the short axis of the crack set are proposed from the scanned 3D data, and thus, the cracks are quantified from one and two dimensions in terms of the independent crack and the crack set, respectively. The reliability of the crack extraction method based on the measured 3D point cloud data is compared to and verified by the traditional crack viewer method. The results of this study can provide a strong algorithm support for intelligently detecting concrete cracks and for predicting crack development.

It is common to perform small-scale prototyping before large-scale application of three-dimensional (3D) printing technology and in this case size effects can have an important effect. There has been limited study to date on the size effects associated with 3D printing technology. Plaster and polylactic acid (PLA) were selected as typical inorganic and organic 3D printing materials. Binder jetting was used to print cube plaster specimens for compressive testing and fused deposition molding was used to print PLA beams for flexural testing. Five sizes were used for both plaster and PLA specimens. The experiments found that the compression strength of the plaster specimens decreased by 46% and the bending strength of the PLA specimens decreased by 15% and 39% relative to two printing schemes with the size increasing. Microstructural analysis using a digital image correlation technique were used to understand the specimen size effects observed. Existing size effect theories were used to model experimental results and recommendations are given regarding modeling efficiency. The paper provides experimental evidence on how the size of specimens produced by 3D printing technology influences properties and microstructure.

Microwave heating is a novel and promising method to remove mortar that adheres to aggregates in recycled concrete. A systematic experiment was carried out to evaluate the heating results of mortar-aggregate composite materials after microwave heating with different power and irradiation times. It was revealed that the surface temperature and heating rates of the mortar and aggregate linearly increased with the irradiation time and powers level. After microwave treatment, macrocracks generated along the mortar–aggregate interface and penetrated the mortar matrix until the mortar broke. Moreover, based on the push-out tests, it was found that the interface bond strength of mortar-aggregate after microwave treatment was much lower than that of the untreated specimens. The influence of the temperature difference on the residual bond strength is also discussed in this study. The parametric study confirmed that the bonding strength between mortar and aggregate after microwave heating is reduced. This experimental investigation could provide a basis and reference for microwave-assisted concrete recycling for industrial applications.

This study examines the effect of weathering on bituminous composites containing polyphosphoric acid (PPA). PPA has been commonly used in bitumen to increase bitumen’s stiffness and elastic properties. However, the effect of PPA on bitumen’s properties is highly affected by the interplay between PPA and other bitumen modifiers such as liquid and solid additives. Wax-based additives generally reduce PPA’s efficacy, and a mineral additive such as montmorillonite (MMT) clay increases PPA’s efficacy. MMT has been typically used to enhance the resistance of a bituminous matrix to aging. This paper uses laboratory experiments to evaluate changes in the properties of bitumen containing PPA and MMT when exposed to water. Samples were conditioned in water at 60°C for up to 100 h, and their thermomechanical properties were evaluated at different intervals. The study results showed that the presence of PPA in bitumen alleviates the swelling of MMT when montmorillonite-doped bitumen is exposed to water. However, extended water exposure reduces the elastic properties of bitumen. This is attributed to PPA’s losing its branches as water promotes the separation of PPA’s branches from its backbone, leading to a reduction in binding energy between bitumen and PPA. The latter was reflected in a rapid loss of bitumen’s elasticity, healing capacity, and shear thinning, as water conditioning continued.

The increased use of polyester-polymer concrete (PPC) overlays on bridge decks throughout the United States has created a need for more comprehensive information about their field performance. The objectives of this research were to evaluate the performance of PPC overlays constructed using two methods of deck preparation and enable further development of a new PPC specification. The scope of the research included nondestructive testing of two PPC test section placements and three PPC bridge deck overlay placements during and after construction. Specifically, hardness tests were performed on the test section placements, and hardness, skid resistance, acoustic impact-echo, and vertical electrical impedance tests were performed on each of the bridge deck overlay placements. In situ PPC properties were documented, and new recommendations regarding hardness testing, skid resistance testing, patching, and surface preparation were developed based on the findings. The results of the research demonstrate the use of nondestructive testing for evaluating the performance of PPC overlays and informing specification development.

Construction and demolition (C&D) waste has been annually generated in high volume due to a mega-scale of the construction industry. It causes the environmental problem of waste management requiring numerous landfill disposal areas. C&D waste can be mainly used as recycled concrete aggregate. However, C&D materials are needed for more effective utilization. Applications in road pavement are recommended to overcome this problem. Therefore, this study examined the use of recycled concrete aggregate (RCA) as a full replacement for natural aggregate (NA) in a hot mix asphalt (HMA) mixture for a heavy-duty asphalt surface. A modified thermal-mechanical beneficiation method was employed to improve the RCA abrasion resistance to meet the Los Angeles abrasion (LAA) requirements for HMA aggregates. Then, the heavy-duty dense-graded HMA was mixed with beneficiated RCA (BRCA) (HMA-BRCA). The HMA mixture with NA (HMA-NA) was utilized as a benchmark. A series of laboratory performance tests on the Marshall stability and flow, resilient modulus (MR), dynamic modulus, and tensile strength ratio (TSR) was performed in conjunction with x-ray diffraction (XRD) analysis. Test results revealed that HMA-BRCA demonstrated better Marshall stability and flow and had a better MR than HMA-NA. However, HMA-BRCA and HMA-NA demonstrated almost identical dynamic modulus characteristics. Nevertheless, HMA-BRCA was more susceptible to moisture than HMA-NA, as indicated by the substandard TSR of HMA-BRCA. Further analysis showed that the breakage of BRCA particles during the mixing and compaction processes led to tighter packing of the HMA aggregate matrix, which was the cause for the improved strength, modulus, and deformation characteristics of HMA-BRCA. Furthermore, a relatively thinner asphalt binder film and the presence of calcite (retained from the original mortar) lead to the poor moisture damage resistance of HMA-BRCA. Therefore, moisture susceptibility is an issue when RCA is used in an HMA mixture, even though the RCA was treated to meet all HMA aggregate requirements. A solution by using an antistriping agent would be carefully considered.

Concrete structures are susceptible to cracking, contributing to the penetration and transport of deleterious agents, which may compromise their durability. At the end of the 19th century, a natural capacity of the concrete in sealing cracks was noted, which would later be called autogenous self-healing. This article aims to explore the effect of fly ash contents in autogenous self-healing of conventional concretes using different test tools. Therefore, the durability of the material was indirectly assessed. The age of cracking was also analyzed. Concrete specimens with different fly ash contents (0%, 12%, and 27%) were cracked by compression at 7 and 28 days. Subsequently, durability tests were performed on the day of cracking and after 84 days under wetting and drying cycles to stimulate self-healing mechanisms. The results demonstrated the beneficial effects of self-healing on concrete containing fly ash when the analyzed parameter is more focused on the concrete bulk of the test specimens (ultrasonic pulse velocity and resistance to chloride ingress). When the analyzed parameter is related to the surface of the specimens (resistance to carbonation), the effect of cracking is more evident in concrete without fly ash.

The determination of styrene-butadiene-styrene (SBS) content in SBS-modified asphalt (SBSMA) is crucial in road quality control. In this study, a polystyrene (PS)-based index, which is an alternative indicator for the current polybutadiene (PB)-based index of SBS content determination in specification based on the Fourier transform infrared spectroscopy test, was proposed to provide a more accurate measurement. The influences of the types of base asphalt/SBS modifiers/solvents, sulfur stabilizers, and aging on SBS content determination were investigated based on both of the two indices. The results show that the PS-based index has higher accuracy and is recommended as the indicator in the content determination. The selections of the types of the base asphalt/SBS when preparing the calibration samples should correspond to those of the testing samples to avoid the measurement deviation. Trichloroethylene solvent has an interference influence on the characteristic peak of PB in SBSMA. The sulfur and aging both have a double-sided effect on the SBS content determination. Furthermore, the fluorescence microscopy test and the four-component test were conducted to correlate the compatibility of asphalt with SBS and the stability of the asphalt colloidal structure. The gel permeation chromatography test was also used to verify the influence of aging on the SBS content determination.

Cross-laminated timber (CLT) is an innovative wood product that can be used to build midrise and tall wood construction as an alternative to concrete, masonry, and steel. As floor, roof, and wall made of CLT is subjected to out-of-plane bending, rolling shear (RS) failure of cross-layers can arise prior to bending failure of the outermost layers, which governs the load-carrying capacity of CLT. In fact, the global deflections of CLT depend on the rolling shear modulus of cross-layers, which is much lower than shear modulus parallel to grain. Therefore, it is necessary to determine and improve the rolling shear strength and modulus of cross-layers. In this paper, several test methods were firstly summarized, after which the main influence factors on rolling shear properties were reviewed. Finally, seven configurations of hybrid CLT with three layers were tested to assess the rolling shear properties of hybrid CLT, in which the outer layers are made of Spruce-Pine-Fir (SPF) and the cross-layer is made of different materials such as birch, compressed wood (CW), laminated veneer lumber (LVL), Parallel strand lumber (PSL), plywood, oriented strand board (OSB), and glued laminated bamboo (GLB). The CLT made of SPF was also tested, whose rolling shear properties were regarded as reference. The rolling shear properties of GLB are about twice as high as those of SPF. Other materials do not exhibit superior rolling shear properties to SPF. The compressed wood shows a significant ductility in rolling shear failure.

This study focused on the frequency-dependent damping properties of recycled aggregate concrete (RAC) and provided new insights into the damping mechanism of RAC. Cyclic compressive loadings at low frequencies were applied to RAC with five replacements of recycled coarse aggregate (RCA) to evaluate the damping properties of RAC. A nanoindentation test was conducted to investigate the nanomechanical properties of cementitious nanophases in RAC and analyze the damping mechanism. It is found that the damping parameters (loss factor, loss modulus, and hysteretic energy) of RAC decrease with the increasing loading frequency from 0.05 to 1.0 Hz. The damping of RAC is more frequency-sensitive than that of natural aggregate concrete (NAC). A linear relation among the damping parameters and the mortar content of RAC is established. With the increasing RCA replacement from 0% to 100%, the loss factor and hysteretic energy of RAC increase, and the loss modulus firstly increases and then decreases when the RCA replacement is larger than 50%. Nanoindentation results show that the mechanical hysteresis of cementitious nanophase in RAC is inversely proportional to the storage modulus, and the loss modulus is approximately proportional to the storage modulus. A decrease in mechanical hysteresis and hysteretic energy of cementitious nanophases with an increase in loading frequency may be the nanoscale mechanism for the frequency-dependent damping of RAC.

The size effect on the axial compressive performance of laminated bamboo lumber is studied through compression tests on three groups of short columns with different heights and section sizes. The failure modes, bearing capacity, strain distribution, and deformation capacity were analyzed. Based on the test results, three groups of stress-strain models of laminated bamboo lumber with different sizes are presented. The simulated results were in good agreement with the test results. The slope method and the parameter method were used to calculate the size effect coefficient and the results showed that the linear regression parameter analysis method is more efficient for analyzing the size effect. It is concluded that the size effect coefficients of compressive strength, ultimate load, elastic modulus, ductility, and compressibility are 0.043 ($1/23.26$), 0.6676 ($1/1.52$), 0.064 ($1/15.63$), 0.0529 ($1/18.90$), and 0.133 ($1/7.52$), respectively.

Foamed concrete has been widely used in building energy conservation and insulation engineering, and its fire resistance is very important for buildings under fire. However, due to high porosity and permeability, the properties of foamed concrete are liable to change under high temperatures. Therefore, it is essential to evaluate the performance and functional evolution of foamed concrete at high temperatures. In this study, foamed concrete specimens with three different densities were treated at five different temperatures. The changes of macroscopic appearance and pore structure for the foamed concrete specimens under high temperature were analyzed to reveal the damage mechanism of temperature effects on foamed concrete. Besides, the high-temperature effect on the mass loss, water absorption, and compressive strength of the specimens were investigated. In addition, a prediction model of compressive strength for the foamed concrete considering the coupling effect of temperature and density was proposed.

Natural soil formation processes involve variable particle size distributions that vary spatially within a deposit, giving rise to an array of soils that transition from one general soil type to another within essentially similar deposits. Characterization of such transition soils in the active zone is something past research has largely overlooked. An evaluation of the unsaturated strength behavior of a transition soil was carried out on a native mid-Atlantic silty sand. A suite of unsaturated consolidated drained axisymmetric triaxial shear tests was performed, and the stress–strain and volume change characteristics of the transition silty sand under different values of matric suction, confining pressure, strain rate, and fines content were investigated. It is found that the triaxial shear strength increases with increasing matric suction, confining pressure, strain rate, and fines content. The volumetric strain increases with increase in matric suction and confining pressure, and it decreases as fines content and strain rate are increased. The experimental results are used to further validate a state-dependent constitutive model for unsaturated soils that was recently proposed based on the theory of bounding surface plasticity and the framework of hyperelasticity. It is shown that the model simulations are in good agreement with the experimental data.

The success of self-healing cementitious materials relies on their ability to repeatedly heal over the lifetime of the material. Vascular networks have a distinct advantage over other self-healing techniques whereby the healing agent in the network can be routinely replenished. The aim of this study was to develop a multiuse vascular network that can be reused over the lifetime of a structure to enable repeated self-healing events in cementitious materials. The feasibility and self-healing efficacy of novel two-dimensional (2D) vascular networks in concrete beams were tested on laboratory-scale specimens before being trialed in situ on larger, structural-scale elements. The vascular networks were formed via linear interconnecting hollow channels filled with a healing agent that is delivered to zones of damage under an externally supplied pressure. This technique was reproducible at large scale and channels were refilled over a test period of 6 months. Of the two healing agents used in this study, sodium silicate (SS) proved easier to handle and supply into the vascular network, but cyanoacrylate (CA) offered greater strength recovery (up to 90%) in a relatively short time scale. The presence of flow networks in the cover concrete tended to act as a crack initiator and this was particularly evident in the larger-scale specimens. Nevertheless, the potential to enhance and enable multiscale healing in cementitious materials has been demonstrated.

Prediction of creep and recovery of asphalt binders using limited experimental data can reduce instrumental stress and save time. A simple methodology, using generalized Burger’s model (GBM) and time temperature superposition principle (TTSP), has been proposed to predict the creep and recovery response of asphalt binders at different temperatures. The proposed methodology has been validated using six different asphalt binders at a stress level of 3.2 kPa. It is found that the proposed technique offers reasonable prediction of unrecoverable creep compliance and percentage recovery with a percentage error of $\pm 10\%$.

The ability of latex to notably improve the performance of asphalt pavements has established the material as a favorable modifier in asphalt systems. However, the high viscosity of latex-modified asphalt (LMA) binders significantly increases the production temperature of asphalt mixtures. One effective way to resolve this problem is by employing foaming technology, which was investigated in this study. Diluted methanol was used as a foaming agent due to its lower boiling point and energy consumption compared with water. Asphalt binder of penetration grade $60/70$ was utilized as the binding agent. Latex accounted for 6% of the total weight of the asphalt binder. In this study, 1% water and 3% diluted methanol were added as foaming agents. The basic and rheological properties of asphalt binders were examined via different tests, for example, softening point, decay curves, rotational viscosity, torsional recovery, and dynamic shear rheometer. The findings showed that the presence of latex contributed to higher softening point, viscosity, elastic property, and rutting resistance to improve the pavement durability. The foaming agents (water or diluted methanol) decreased the viscosity and improved the expansion ratio producing better workability and aggregate coating during mixture production.

This paper evaluates the long-term mechanical properties (up to 1 year) of alkali-activated slag concrete produced with recycled coarse aggregate (AAS-RA) and natural coarse aggregate (AAS-NA). The AAS-RA achieved a compressive strength of 35.20 MPa at 28 days and improved to 37.52 MPa at 365 days. This corresponded to a reduction in strength of 12.2% at 28 days and 7.7% at 365 days when compared with AAS-NA concrete. The flexural strength of both AAS concretes decreased with age, displaying a 10% and 11.8% drop after 1 year for AAS-NA and AAS-RA concretes, respectively, compared with that achieved at 28 days. However, the splitting tensile strength remained constant for the entire period. Furthermore, the elastic modulus of both AAS concretes decreased between 28 and 90 days; however, beyond 90 days, AAS-RA concrete maintained a constant elastic modulus while AAS-NA showed further decreased with time, such that by 365 days the AAS-NA had a 10% lower value than the AAS-RA concrete. This is attributed to alkali activation continuing beyond 90 days, producing additional C-A-S-H/C-S-H gel. This resulted in the combined effect of disjoining pressure and self-desiccation, which increased propagation of cracks and crack widths at later ages. However, in the AAS-RA there was also an increase in bond strength between the C-A-S-H gel and old cement paste (C-S-H gel matrix) on the recycled coarse aggregate, which resulted in a greater elastic modulus for the AAS-RA concrete. Experimentally observed long-term mechanical properties were compared with the predicted values in Australian and American Concrete Institute (ACI) codes. However, further studies are required to identify specific amendments required for these codes for the design of structural members manufactured from AAS concrete with recycled aggregate.

Replacing more than 50% of the cement in concrete with fly ash produces high-volume fly ash (HVFA) concrete, which likely reduces the life-cycle cost and environmental footprints of concrete. In cold climates, the susceptibility of HVFA concrete to freezing–thawing cycles is a durability concern if no appropriate measures are taken. This study modeled the degradation of dynamic modulus of elasticity of HVFA concrete during the freezing–thawing cycles. A four-phase sphere composite model considering the unhydrated fly ash particles in HVFA concrete is proposed to interpret the change in dynamic modulus of elasticity. The modeled values were in good agreement with the measured values; therefore, this model sheds new light on the deterioration of HVFA concrete caused by freeze/thaw damage cycles. Parameter analysis clarified the influence of the key factors in this model.

Polyester-coated fabric has been widely used in membrane structures. However, the mechanical properties of polyester-coated fabric at elevated temperatures have not been well studied, limiting its applications in the fire-resistant analysis. This work concerns the temperature effects on the mechanical properties of the polyester-coated fabric membrane material from four common brands, with an experimental study on polyester-coated fabric specimens at 23°C, 70°C, 100°C, 150°C, 200°C, 230°C, and 250°C under uniaxial loading, respectively. The results indicate that the elastic modulus and the ultimate tensile strength of polyester-coated fabric membrane material decrease with temperature increasing. The breaking elongation first increases and then decreases with increasing temperature. The results are utilized to obtain simple empirical equations by applying membrane structure design and fire-resistant analysis. Change laws for elastic modulus, ultimate tensile strength, and breaking elongation with temperatures are proposed as equations; the constitutive relation of polyester-coated fabric membrane material with temperatures is also fitted by one two-stage equation. Of considerable significance is promoting the research of membrane structure design and fire-resistant analysis.

Pavement service and antiaging performance of single-component polyurethane-bonded porous mixtures (PPMs) were studied. The influence of the adhesive–aggregate ratio on PPM volumetric properties and pavement service performance was analyzed by testing PPM air voids, water permeability coefficients, dynamic and Marshall stabilities, Cantabro loss rates, $-10°\mathrm{C}$ bending-failure strains, and the British pendulum number (${\mathrm{BPN}}_{20}$). Four-point bending fatigue tests conducted after ultraviolet (UV)-accelerated aging were used to characterize PPM antiaging performance. The results showed that PPM air voids and connected air voids were negatively linearly correlated with the adhesive–aggregate ratio. PPM and an open-graded friction course (OGFC) asphalt mixture, with identical connected air voids, did not have significantly different water permeability coefficients, indicating that polyurethane- or asphalt-film connected-pore surfaces did not significantly impact water permeability. PPM dynamic and Marshall stabilities, Cantabro loss rates, and $-10°\mathrm{C}$ bending-failure strains were much better than those of the OGFC asphalt mixture. These pavement service performance indicators increased, whereas ${\mathrm{BPN}}_{20}$ decreased with increasing adhesive–aggregate ratio. When the adhesive–aggregate ratio reached 5%–6%, there was an inflection point in the trend of the pavement service performance, which can be used as a criterion to determine the optimal adhesive content. After 1 simulated year of aging, changes in the PPM initial bending-stiffness modulus $D_{S_{\mathrm{ini}}}$ and the antifatigue damageability $D_{S_{\mathrm{ini}}}$ were significantly better than those of the OGFC. UV aging nonlinearly influenced PPM $D_{S_{\mathrm{ini}}}$ and $Ds$. The influence of UV aging on $D_{S_{\mathrm{ini}}}$ and $D_{S_{\mathrm{ini}}}$ initially were large and, small and gradually decreased and increased, respectively.

This study evaluated the mechanical properties of hybrid (mixed-species) cross-laminated timber (CLT) panels made of low-value sugar maple (Acer saccharum) and white spruce (Picea glauca). The modulus of elasticity (MOE) of the laminations was measured with a nondestructive method. Three-layer hybrid CLT panels with layup combinations of sugar maple–white spruce–sugar maple and white spruce–sugar maple–white spruce were prepared to evaluate the effects of layups on the performance of the CLT samples. The mechanical properties of hybrid CLT panels were evaluated with different layups and both melamine- and resorcinol-based adhesives. Both long-span and short-span third-point bending tests were conducted to study the flexural and shear behavior of each CLT panel type. It was found that the influence of adhesive types was not significant. The mechanical properties of the hybrid CLT panels with sugar maple surface layers were improved significantly compared with those of the current standard layups. Both bending tests were simulated with finite-element analysis based on measured and reference material properties. The simulated results of each case were in good agreement with the test results.

Silane coupling agents (SCAs) are a type of antistripping agent for improving the adhesive property between acidic aggregate and hydraulic asphalt. To evaluate the modified effect, find the optimal dosage of SCA, and study the modified mechanism at different dosages, the surface free energy (SFE) component, energy parameters, and the energy ratio were used to analyze the energy required in the asphalt-aggregate-water three-phase transformation. Additionally, the functional group index of organosilane and hydroxyl were used to evaluate the SCA binding effect at the asphalt–aggregate interface using Fourier transform infrared (FTIR) spectra. The results showed that with the increase of SCA, the SFE and FTIR parameters almost increased initially, reached the maximum at the 1.0% by weight, and then decreased. This indicates that the SCA can serve as a molecular bridge to improve the adhesive property between acid aggregate and hydraulic asphalt with the optimal dosage of 1.0% by weight. Insufficient SCA could not modify the adhesive property effectively, and excess SCA led to the hydrogen-bond association and SCA depolymerization, resulting in an adverse effect.

Adobe has been extensively used as a viable construction material in various hot and arid climatic regions throughout the world for several centuries. Adobe bricks, primarily made out of clay, remain in an unsaturated state for the majority of their life span. These unsaturated bricks are vulnerable to weathering, erosion, cracking, and strength degradation due to changes in moisture and drying–wetting cycles imposed by climatic events and seasonal changes. However, limited information exists in the literature regarding the effect of suction and degree of saturation on the mechanical response of unsaturated adobe. The main objective of this study was to experimentally examine the effect of suction on the shear strength and dilatancy of the adobe used for the repair of a 1,500-year-old adobe castle, the Izad Khast Castle, in Central Iran. We tested the index, physical, mineralogical, and microstructural characteristics of the adobe. After determining the drying and wetting paths of the soil water retention curve (SWRC), we built and employed an osmotic direct shear device to evaluate the shear strength extensively and dilatancy of the adobe under various matric suctions (0, 200, 400, and 800 kPa) and vertical stresses (39, 66, and 122 kPa) without and with the application of drying–wetting cycles. The tested adobe exhibited a significant suction hardening with a brittle behavior along with the shear-induced dilation. Increasing suction prompted a notable rise in the effective angle of friction and a linear increase in dilatancy of the adobe. Applying drying–wetting cycles led to a less brittle response accompanied by a decrease in the peak shear strength. The findings offer new insight into the mechanical behavior of unsaturated adobe, which can contribute toward the preservation and maintenance of historical and contemporary adobe structures.

Ultra-high-performance concrete (UHPC), despite its superior mechanical and durability properties, has a high ${\mathrm{CO}}_2$ footprint owing to its high portland cement content. This drawback can be offset to a notable extent if a high volume of supplementary cementitious materials can be utilized to produce UHPC while maintaining mechanical and durability properties that are comparable to those of conventional UHPC. In this study the effects of high-volume cement replacement by Class-F fly ash (up to 70% by mass) on the mechanical, durability, and microstructure properties of UHPC are investigated, with the aim of encouraging moderate- to low-volume cement use in UHPC (from 600 down to $300\mathrm{kg}/{\mathrm{m}}^3$). Environmentally friendly-UHPC (ECO-UHPC) mixes, which have ${\mathrm{CO}}_2$ footprint intensities of less than $5\mathrm{kg}/{\mathrm{m}}^3/\mathrm{MPa}$, have been synthesized with different replacements of cement by Class-F fly ash. Results suggest that concretes with ultrahigh strength ($>150\mathrm{MPa}$) and a strength greater than 100 MPa can be prepared with up to 40% and 70% replacements, respectively, without employing any special curing or fibers. A model has been developed to predict the compressive strength of fly ash–based UHPC from the contents and chemical compositions of its binders. UHPCs made with up to 60% cement replacement by Class-F fly ash exhibit durability properties comparable to that of UHPC without fly ash, in terms of water absorption, initial rate of water absorption, and corrosion risk. The depth of carbonation remains below the detection limit of 0.5 mm, up to 70% replacement.