Journal of Materials in Civil Engineering

The main objective of this research is to develop a sustainable and environment-friendly asphalt binder based on the reutilization of waste engine oil (WEO) alongside crumb rubber (CR), two major waste materials of the automobile industry. This composite modification eliminates the limitations and the negative effects of solo application of these waste modifiers, including the poor workability and pumpability of the CR-modified binder, as well as compromised rutting resistance of the biobinder modified with WEO. Besides investigating the high-temperature properties of the composite-modified binder with CR and WEO, for the first time, a new method is presented to analyze the influence of the preparation parameters on the performance of the binder and optimize the whole production process. For this purpose, the design of experiment was conducted with the aid of the central composite design (CCD) method, and the rheological properties of the binders were evaluated by rotational viscosity (RV), dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) tests. Based on the results of rotational viscosity at 135°C and the unaged and RTFO-aged rutting factor values at 58°C, regression models were established and analysis of variance was carried out on the preparation parameters. Overall, test results indicated that the addition of 5%–10% blending content of WEO in the composite-modified binder could achieve a satisfactory rutting resistance while improving its workability and pumpability. On the other hand, although the content of WEO had the most significant influence on the rheological properties of the binder samples, other parameters including preparation temperature and time also had influence to some extent. Additionally, optimum values of the preparation parameters were determined, and the production process was optimized.

While self-healing concrete has been increasingly studied this past decade, research on the self-healing of a crack after repeated loading is still scarce. Studying this topic is of utmost importance because structures in practice are subjected to repeated damage, causing a variety of crack openings. Hence, this paper presents an evaluation of the self-healing properties of aged concrete containing a combination of crystalline admixture (CA) and expansive agent (CSA), and submitted to repeated loading. Pre-cracked at 218 days old by means of a three-point bending test, the prisms were reloaded every three weeks and healed in wet/dry cycles in between. After two loadings, they were reloaded a third time until failure. Two types of reloading procedures were carried out: (1) reloading to the same residual crack width; and (2) reloading with increasing crack width. Self-healing was assessed with water permeability measures before and after each reloading, macroscopic observations of the cracks, and mechanical recovery. The results showed that two phenomena occurred with opposite effects: damage versus healing. The magnitude of both processes depends on the reloading procedure. When reloading to the same crack width, the damage effect was lower than the healing effect, indicating that the healing products provided sealing even after repeated loading. When reloading with an increasing crack width, the damage effect was greater than the healing effect, but the healing rates were higher than reloading to a constant crack width, because of the creation of new fresh crack surfaces that healed faster. In any case, multiple damage slows down healing but the self-healing process continues. This confirms the long-term healing potential of cracked structures made of, or repaired with, self-healing concrete.

To investigate the influence of methyl styrene block copolymers (SMC) modifier on the fatigue performance and damage evolution of recycled asphalt mixture (RAM), RAM with reclaimed asphalt pavement (RAP) ratios of 30%, 50%, and 70% and 90# asphalt mixture were used for four-point bending fatigue test. The fatigue performance and damage evolution process of RAM were analyzed using the stiffness attenuation rate and the relative change rate of dissipated energy (RDEC). Linear amplitude sweep (LAS) tests and atomic force microscopy (AFM) tests were carried out for mixed asphalt in the mixture. The results show that under the same test conditions, with the increase of RAP content, the damage development of RAM is faster, and the fatigue damage resistance is worse. Compared with 90# asphalt mixture, RAM has better fatigue resistance. The fatigue property of the mixed asphalt is better than that of the 90# asphalt. With different RAP contents, the modulus changes of RAM and mixed asphalt are almost the same on macro and micro scales, which proves that the difference of fatigue performance between 90# asphalt mixture and RAM probably is caused by asphalt. A fatigue failure criterion based on the peak dissipation energy is proposed for the LAS test, and the applicability and accuracy of the criterion were proved by grey correlation analysis. Under this criterion, the power function model is introduced to describe the development process of fatigue damage in LAS test, which has high fitting reliability.

Styrene-acrylic organic emulsion was synthesized, prepared, modified by silane coupling agents, and added to metakaolin-based geopolymer. Combining mechanical properties, x-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and energy-dispersive x-ray spectroscopy/scanning electron microscopy (SEM-EDS), the effect of organic emulsion on the properties of geopolymer was analyzed. Results show that the flexural strength of the organic-inorganic hybrid geopolymer formed after adding the modified emulsion was significantly improved. Adding an appropriate amount of organically modified emulsion can improve the mechanical properties of geopolymer cured for 3 days. When adding 0.5 wt% modified emulsion (A-151), the 28-day flexural strength of the hybrid geopolymer reached its maximum value, which was 25.81% higher than that of pure metakaolin-based geopolymer. After the emulsion was added, the compressive strength of geopolymer samples decreased slightly, which may be related to the increased moisture brought by the emulsion and the viscosity of the emulsion. The increased flexural-to-compressive-strength ratio of samples indicate that the toughness of the geopolymer was improved. It was found using SEM-EDS that the organic phase has good compatibility with the inorganic matrix, and the organic phase participates in the polymerization of geopolymer.

The use of reclaimed asphalt pavement (RAP) in asphalt mixtures is an expedient and cost-effective solution against rutting failure, but its performance against fatigue and thermal cracking is unsatisfactory and causes the pavement to deteriorate sooner than expected. Rejuvenators can improve RAP performance under various operating conditions through stiffness recovery and binder healing. In this paper, waste cooking oil (WCO) and styrene butadiene styrene (SBS) polymer were used to evaluate the rheological behavior of reclaimed asphalt binder (RAB). The modified RAB has been evaluated using chemical composition, linear amplitude sweeping (LAS), and bending beam rheometer (BBR) tests. The results of the LAS test showed that the fatigue life of RAB containing WCO was about 6 to 9 times longer than the control RAB specimen at the strain level of 2.5% and 5%. The results of the BBR test also indicated the good performance of the WCO. Thus, the WCO used in this study was expected to enhance the fatigue performance and thermal cracking of RAB. To evaluate the behavior of RAP containing RAB and additives on the fatigue response before and after self-healing, four-point bending beam test (4PBB) was employed. The results showed that besides improved fatigue life of hot-mix asphalt (HMA) produced with RAP- and RAB-containing additives, it had a longer fatigue life after self-healing. The specimen containing WCO had a better performance than the specimen to other samples.

The use of carbide sludge (CS)-ground granulated blast furnace slag (GGBS) for clay slurry treatment has shown superior strength performance compared to ordinary Portland cement (OPC). To achieve a maximum level of unconfined compressive strength (UCS) of the CS-GGBS-treated slurry, there is an optimal level of CS, but this content varies with soil type and GGBS content. Optimal CS content is conventionally assessed by evaluating the UCS at 28 or 56 days. In this study, a rapid test method is proposed to estimate the optimum CS content in a few hours by measuring the pH, instead of UCS, of the CS-GGBS-treated slurry. Results show that the 28-day and 56-day UCS versus CS content curves of CS-GGBS-treated slurries are quite similar to their one-hour pH profiles. Hence, the pH versus CS content profile could be used to estimate the optimum CS content, i.e., the minimum CS content required to obtain a saturated $\mathrm{Ca}(\mathrm{OH}{)}_2$ solution was estimated as the optimum CS content. The CS-GGBS-treated slurry with an estimated optimum CS content based on initial pH achieved a high strength level ($\ge 91\%$ of the maximum UCS) after curing for 28 and 56 days. Furthermore, the thermogravimetric analysis (TGA) results indicate that excess CS addition beyond the optimum CS content led to the generation of more hydrotalcite phases, but less calcium silicate hydrate (CSH), which contributed to the strength difference.

Recycled aggregate concrete (RAC) has been gradually used in practical engineering owing to the maturity of waste-concrete recycling technology. However, the disposal of waste RAC in different environments remains challenging. Second-generation recycled concrete aggregates (second RCAs) prepared by crushing waste RAC can further promote the sustainable development of the construction industry, in which the mix-proportion design method of RAC used in different environments is key in determining the feasibility of recycling second RCA. In this study, to investigate the usability of second RCA, five typical concrete mix-design methods were selected to prepare RAC with a service life of 50 years for freeze-thaw (F–T) environments in cold regions: the ordinary concrete design method, high-performance method, saturated surface-dry aggregate design method, equal mortar volume method (RAC-E), and overall calculation method (RAC-A). The frost resistance of RACs and the physical properties of second RCAs were investigated, and the economy of recycling waste RAC with different mix-proportion design methods was evaluated via value engineering analysis. The results showed that after 350 F–T cycles, the mass loss and relative dynamic modulus of elasticity of RAC-E and RAC-A were better than those of specimens prepared via other methods. Compared with the original RCA, the second RCAs obtained using waste RAC in the F–T environment performed better, and their water absorption was reduced by 23%. A value analysis of the RAC–waste RAC–second RCA circulation system showed that RAC-A exhibited the highest value coefficient. Both the equal mortar volume and overall calculation methods can be used for the mix design of RAC in the F–T environment; however, the latter is a better method owing to its higher value coefficient and lower calculation error.

Due to the fast-growing number of cars, the amount of scrap tires is quickly increasing across the world. Because buried tires need a long period of time to dissolve, the accumulation of scrap tires in different countries has caused several social, economic, and environmental issues worldwide. Many researchers in geotechnical engineering have utilized scrap tires in various forms for soil reinforcement in recent years. A by-product of waste tire processing is waste tire textile fiber (WTTF). These WTTFs are classified as special wastes, and they are frequently buried or burned in violation of international law. This study experimentally shows that these materials could be recycled and mixed with soil to improve the mixture mechanical properties. A complete series of small-scale laboratory tests, including direct shear test, Brazilian tensile test, permeability test, and swelling test, was conducted to examine the possibility of reusing WTTFs as soil-reinforcing agents. Five different fiber percentages (FPs), i.e., 0%, 0.5%, 1%, 2%, and 4%, of soil dry weight were mixed with the soil and the mechanical behavior of the mixture was investigated. The test results suggest that adding fiber to the soil improves both its shear and tensile strengths. The material ductility increases by adding the fiber to the soil as well. Further, the soil mixed with the fiber has a greater permeability coefficient and has less swelling potential. The mixture with these improved mechanical properties can cause less lateral pressure in case of being used as a backfill material. As a result, rather than being buried or burned, these wastes could be utilized to enhance the mechanical properties of various types of soils in geotechnical applications. The testing procedures and results are reported, discussed, and compared with those from the literature.

Short fiber–reinforced clay mortar is known as an important structural material in traditional and rural buildings because it not only provides superior mechanical properties but can also be easily produced by the rapid, low-cost molding process. The adhesion of the fibers to clay mortar has a significant role in the mechanical characteristics of fiber-reinforced mortar. In this study, interfacial shear stress (ISS) between nine different fibers and clay mortar was investigated by performing the Microbond test. Based on the findings, date palm fiber, hollow polyester, and polypropylene, respectively, demonstrated the highest degree of ISS with clay mortar; nevertheless, the lowest degree belonged to goat hair, acrylic, and wool, respectively. The critical lengths of the fibers to be embedded in the mortar as the short fiber reinforcements were calculated. The highest critical length belonged to glass fibers and date palm, respectively, and the lowest values belonged to acrylic, polyester, polypropylene, and wool, respectively.

This paper aims to investigate the effect of internal and external humidity differences on the distribution characteristics of the carbonated zone of cement-based materials. Carbonation tests with ambient humidity and pore water saturation as the influencing factors were implemented. The calcite content of the mortar along the depth of carbonation was presented. The rationality of the carbonation model was verified by the calcite test results, and the effect of internal and external humidity differences on the carbonation zone distribution of cement-based materials was analyzed by the model. The results showed that the test results of calcium carbonate and the simulation results can clearly distinguish the completely and partly carbonated zones of cement-based materials. The effect of pore water saturation on the distribution of the carbonated area was conspicuous, but the difference in pore water saturation cannot change the variation of the extent of the carbonated zone with ambient humidity. The change regularities of fully and partly carbonated zones with humidity differences were obtained.

Formulation of highly workable reactive magnesium oxide (MgO) cement (RMC)–based composites is critical to their wider adoption in the construction industry. Yet, the performance of the binder with the presence of chemical admixtures is not well understood. This study assessed the influence of polycarboxylate ether (PCE)–based superplasticizers on the hydration and carbonation kinetics of RMC. Its application was also demonstrated. RMC-based composites were prepared with conventional aggregates, superplasticizers to aid workability, and fibers to control cracking induced by volume changes under both hydration and carbonation. Two carbonation methods were utilized: 20% ${\mathrm{CO}}_2$ in a carbonation chamber and ${\mathrm{CO}}_2$ in an enclosed plastic bag to emulate a low-technology carbonation process. Highly workable RMC-based mortar mixes were achieved with a superplasticizer content of 2% by weight, despite the presence of 0.2% by volume polyethylene microfibers. The admixtures slowed down the hydration rate and altered the morphology of the hydration product. Compressive strength of 32.7 MPa was attained after 7 days under 20% ${\mathrm{CO}}_2$ in a carbonation chamber compared with 15.6 MPa under carbonation inside the plastic bag condition. The crystalline carbonation products within the exterior regions were dominated by nesquehonite. A significantly reduced carbonation level was observed within the interior regions due to the formation of the carbonation products and the resulting pore refinement within the exterior regions. Also, the PE fibers provided a crack control mechanism, and their failure mode was characterized by pullout. The finalized mix was successfully applied for the construction of a large-scale architectural structure.

Confocal scanning laser microscopy (CLSM), Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) were performed to analyze the changes in apparent morphology, the functional groups, and glass transition temperatures of warm-mix rubber-modified asphalt under freeze–thaw cycles to describe the evolution mechanism of the low-temperature performance of asphalt binders under freeze–thaw cycling at the microscale level. Using the bending beam rheometer (BBR) test, the relaxation and delay characteristics of the asphalt binders under freeze–thaw cycling were quantitatively analyzed using the parameters fitted by Burgers model, and based on the dynamic shear rheometer (DSR) test, the low-temperature evaluation indices of the asphalt binders were calculated using the Christensen–Anderson–Marasteanu (CAM) model. Regression analysis of the related performance parameters was carried out, so as to describe the evolution of the low temperature performance of asphalt under freezing-thawing cycles at the macroscopic level. It was indicated that freeze–thaw cycling reduced the low-temperature performance of the asphalt binders. Compared to water freeze–thaw cycling, salt freeze–thaw cycling caused a greater degree of damage to the surfaces and changes in the related parameters of the asphalt binders. Also, the addition of warm-mix additives (EM and SDYK) changed the low-temperature performances of the rubber-modified asphalt (60MCR). After freeze–thaw cycling, the rubber-modified asphalt with SDYK (0.6S-60MCR) showed lower degrees of change of characteristics describing low temperature performance than those of the rubber-modified asphalt (60MCR) and rubber-modified asphalt with EM additive (1E-60MCR), indicating its superior resistance to anti-cracking ability at low temperatures.

The split Hopkinson pressure bar (SHPB) was used to carry out impact compression test on the concrete, granite, and concrete-granite combined samples with different interface roughness. The effect of interface roughness on stress wave propagation was studied, which was the result of competition between the strengthening effect of interface bonding force on the transmission ability of stress wave and the weakening effect of rough fluctuation on stress wave propagation. The failure mode of components in the concrete, granite, and combined samples were compared and analyzed; the failure patterns of concrete components were mainly massive, granular, or even powdery, and the rock components existing in combined form were mostly split along the groove position of the interface. After analyzing the crushing characteristics and energy dissipation characteristics of samples, the energy absorption characteristics of the two components in combination and the influence of roughness on the mechanical characteristics of the composite were explored based on the difference in the block characteristics of the concrete, granite, and the composite.

Mineral fillers are a vital part of asphalt mastic and mixtures that are known to have a major role in the mixtures’ performance. A better understanding of the effects of the filler properties on asphalt mastic is important to control the distresses of the asphalt mixtures. This study evaluates the effects of physical and chemical properties of filler on fatigue and bond strength of asphalt mastic. Twelve asphalt mastics are prepared in the laboratory using three types of asphalt and four types of fillers. A filler to binder ratio of 1 (by mass) is used for all mastic sample preparation in the laboratory. Rigden voids (RV), fineness modulus (FM), calcium oxide (CaO), and methylene blue value (MBV) are used as properties of the filler for characterizing the fillers. The fatigue cracking behavior of asphalt mastic is evaluated using linear amplitude sweep (LAS) test, and asphalt bond strength (ABS) test is used to evaluate the interfacial bond strength between aggregate samples and mastics. The results from LAS test showed that the rolling thin-film oven (RTFO) aged mastic with a high percentage of FM containing filler has a better fatigue life than RV, CaO, and MBV containing filler. For pressure aging vessel (PAV)-aged mastic, the overall test result indicated that the fatigue cracking resistance of mastic is dependent on the interaction between base asphalt binder and filler type. The failure criteria of the LAS test method is an important parameter to characterize the mastic properties. The LAS and ABS test methods reveal that mastics prepared with high MBV and low CaO containing filler have better bond strength and worst fatigue performance. The bond strength performance of the mastic prepared with high FM filler is worse than base asphalt. FM, MBV, and CaO are major filler properties that could influence the asphalt mastic’s fatigue and bond strength performance.

Recycling waste materials has become popular in the pavement industry because of its potential for significant environmental benefits, conservation of natural resources, and sustainability. This study investigated the feasibility of simultaneously recycling waste steel slag and tire rubber in bituminous pavements and analyze the moisture susceptibility of asphalt mixtures made of these solid wastes. The physical and chemical characteristics of the aggregates and the adhesive behavior of the aggregate–bitumen system were explored to determine their impact on moisture sensitivity. Accordingly, two different methods, freeze–thaw splitting test and fracture energy tests, were employed to assess the moisture stability of mixes in a multiple freeze–thaw environment. The microstructure of the interface between the aggregate and bitumen was investigated, and the long-term moisture damage process of the mixes was clarified and verified. The results indicate that the natural hyperalkalinity and porous structure of the steel slag have a favorable effect on the adhesion performance. Cohesive failure was found to be the primary mode of failure of loose asphalt mixtures in a multiple freeze–thaw environment. We tentatively propose that the adhesion energy loss is a secondary failure mode of the loose asphalt mixtures. The addition of 100% steel slag and asphalt rubber had the greatest impact on improving the long-term moisture resistance of the asphalt mixtures. The present work is beneficial for the practical application of waste tire rubber and steel slag in highway engineering.

Warm-mix asphalt (WMA) is a group of technologies focused on reducing the viscosity of the asphalt binder (or binder) to produce asphalt mixtures at a reduced temperature compared with that specified for conventional hot-mix asphalt mixtures. The WMA technologies include two main groups: foaming and additives. The additives can be classified as synthetic-chemical or natural-based. This study aims at assessing the feasibility of optimizing the WMA additives dose by maximizing the adhesion between the asphalt binder and the aggregate at their interface in WMA mixtures. Adhesion is quantified using energy parameters derived from surface-free energy measurements (SFE), including three WMA additives (Carnauba wax, a natural-based warm-mix additive, Sasobit, and Evotherm). Accomplishing this objective required measurements of SFE for four different asphalt binders, and corresponding WMA-modified asphalt binders were performed. The results suggest the possibility of identifying a WMA-additive dose that maximizes adhesion at the binder–aggregate interface in terms of resistance to fracture (i.e., adhesive failure) and moisture damage, and the wettability of the binder. In addition, the results showed that the inclusion of Carnauba wax as a warm-mix additive yielded equivalent adhesion at the binder–aggregate interface compared with the response of the other commercially available WMA additives evaluated (i.e., Sasobit and Evotherm). Additional studies at the mixture level are recommended to validate further the conclusions obtained in this study.

White ultra-high performance concrete (WUHPC) was prepared with limestone powder (LP), silica fume (SF), and metakaolin (MK) to meet low carbon requirements. The influence of the mineral admixture on fluidity, strength, and whiteness of WUHPC was studied by orthogonal experiments and variance analysis. The effects of nano-${\mathrm{TiO}}_2$ (NT) on fluidity, strength, whiteness, impermeability, and the photocatalysis of WUHPC were also investigated. Results shown that the fluidity of WUHPC was decreased with increased concentration of NT. The compressive and flexural strength of WUHPC reached $198\mathrm{MPa}/44.4\mathrm{MPa}$ when the NT content was 1%. The whiteness of WUHPC increased and then decreased with increasing NT content. The water absorption of WUHPC continuously increased when the NT content exceeded 1%. The photocatalytic rate of WUHPC continuously increased to 18 times greater when NT increased from 3% to 10%.

This work investigated the setting performance of alkali-activated slag (AAS) pastes prepared with various activators including sodium hydroxide (NH), sodium carbonate/hydroxide (Nc/NH), and sodium silicate (NS) solutions using in situ attenuated total reflectance Fourier transform infrared spectroscopy (FTIR). Also, the AAS slurry samples at the initial and final setting moments were characterized by multiple microscopic techniques [i.e., X-ray diffraction (XRD), thermogravimetric analysis (TGA), FTIR, and field emission scanning electron microscopy (FESEM)]. The results showed that a higher concentration of NH activator leads to more rapid setting reaction and more calcium-aluminosilicate-hydrate (C─ A─ S─ H) formation in AAS at the setting moments. In AAS prepared with carbonate-rich activators, early-age precipitation of carbonate phases (e.g., gaylussite and calcite) contributed substantially to the initial setting completion; afterward, the C─ A─ S─ H precipitation played a decisive role in final setting realization. In NS-activated slag systems, a relatively high silica modulus in activators facilitated the plasticity loss of fluid paste due to the early precipitation of C─ A─ S─ H products formed by the rapid reaction of aqueous silicates from activators with the calcium ions released from dissolving slag particles. This study contributes to identification of characteristic molecular and microstructural features of AAS that are correlated well with the setting moments.

Pseudoboehmite is a hydrated aluminum oxyhydroxide obtained from inorganic precursors by the sol-gel process. It is used as a precursor to alumina and as a reinforcement in obtaining nanocomposites. Cement-reinforced composites with this nanomaterial were obtained in concrete and mortar. Pseudoboehmite with sodium polyacrylate was used to promote a deflocculation of pseudoboehmite particles, which tend to agglomerate in the material. The obtained material was added to the concrete to improve its workability and strength. The new concrete was characterized by slump tests and mechanical tests. Our results revealed that the incorporation of pseudoboehmite with sodium polyacrylate significantly increased the compressive strength and improved the workability of the concrete. Multiple experiments evaluated compressive strength, ultrasound speed, and nanomaterial characterization. Using the Weibull method in mortars, we verified that the pseudoboehmite brought visible benefits as the characteristic stress increased by 17.5%. This increase was observed with the addition of 3% by weight of pseudoboehmite.

To evaluate the fatigue-creep damage coupling effect of asphalt mixture under different loading frequencies, three tests—tension-compression fatigue, direct tensile fatigue, and static creep—were carried out with haversine cyclic loading at four loading frequencies of 5, 10, 20, and 50 Hz, respectively. In this research, the elastic modulus was selected as a damage variable for evaluation, and the evolution of fatigue damage and creep damage was analyzed by the Chaboche model and the Kachanov model, respectively. Then, based on haversine fatigue stress decomposition, tension-compression fatigue damage, direct tension fatigue damage, and creep damage under four loading frequencies were compared, and the fatigue-creep damage coupling model under those loading frequencies was established. The results indicated that, with the increase in loading frequency, the corresponding damage under the same standardized coordinate decreased, the growth rate of the damage evolution curve decreased, and the damage increased more rapidly when the asphalt mixture was damaged. It was found that the direct tensile fatigue damage of the asphalt mixture under repeated loads was not the direct superposition of pure fatigue and pure creep damage, but a coupling effect of fatigue-creep damage. In the direct tensile fatigue tests, the fatigue-creep damage coupling effect was negative and during the coupling effect the creep effect was more obvious. The model proposed in this result can better characterize the fatigue-creep damage coupling effect and damage evolution process of asphalt mixtures under different loading frequencies.

Considering ${\mathrm{CO}}_2$ emissions during production and re-mineralization during hardening, natural hydraulic lime (NHL) has been deemed an ideal cementitious material based on ${\mathrm{CO}}_2$ cycling. However, the preparation of NHL has rarely been reported. In this study, NHL clinker was prepared by calcining calcite tailings, and NHL was obtained by digesting the clinker. The results showed that the performance of the prepared NHL when calcining the calcite tailings at 1,200°C for 1 h and digesting the clinker at $20°\mathrm{C}\pm 2°\mathrm{C}$ and $70\%\pm 5\%$ RH (relative humidity) for 8 days met the requirements of NHL5 standard lime mortar. Furthermore, carbonation of the prepared NHL5 was studied, showing that the pore size of the hardened NHL5 mortar was refined during carbonation, and its compressive strength also improved. The prepared NHL5 could be an environmentally friendly cementitious material owing to its utilization of waste, relatively lower energy consumption, and higher ${\mathrm{CO}}_2$ recycling rate.

A systematic laboratory-based experimentation was carried out by replacing the fine aggregates in M35-grade concrete with varying dosages of fly ash (FA) and bottom ash (BA). Multiple linear regression (MLR) analysis was carried out to predict the compressive strength of the proposed ultrahigh-volume ash concrete at 28 and 90 days and the results of predicted versus observed strengths are discussed. ANOVA was analyzed using the Excel add-in named XLSTAT—Basic by Addinsoft. Durability studies were also carried out in terms of resistance to chloride penetration to ensure the serviceability of the developed mix designs. Finally, life-cycle assessment (LCA) was carried out and the mixes were evaluated in terms of emissions and embodied carbon. The mixes containing either only FA or a combination of both FA and BA revealed enhanced strength properties as compared to the control sample. However, the mix containing only BA failed to achieve the necessary strength requirements. Furthermore, the predicted equations for compressive strength at 28 days and 90 days exhibited a minor difference between the $R^2$ and adjusted $R^2$ indicating their statistical significance. The $R^2$ of 0.858 and 0.837 observed for C28 and C90 respectively indicate that the proposed models can predict the strengths of ultrahigh-volume ash concrete with high accuracy. These equations were then validated from the findings of published literature and found to be within an acceptable degree of variance.

Porous asphalt concrete (PAC) has the benefits of good drainage performance and excellent skid resistance. In double-layer porous pavement, the top layer ensures good pavement performance, and the bottom layer maintain the lateral drainage capacity with the air voids content. However, there is no uniform layer thickness design for double-layer porous asphalt pavement. This study determined the optimum asphalt binder contents of PAC-13 mixtures, and investigated the influence of high-viscosity modifier on the PAC-13 mixture. The laboratory properties related to filed performance were obtained, including high-temperature stability, water stability, high-temperature performance, low-temperature performance, and water permeability. The PAC-13 mixture modified with 10% high-viscosity modifier C (HVM-C) and 0.4% polyolefin was used as the mixture for the top layer, and the PAC-13 mixture modified with 3.3% HVM-C and 0.4% polyolefin was used as the mixture for the bottom layer. The optimum binder content was found to be 4.8% for top-layer PAC-13 mixture and 4.7%–4.8% for bottom-layer PAC-13 mixture. In terms of rutting resistance performance, there was an increasement of 14.6% for the dynamic stability indicator when the HVM-C content increased from 3.3% to 10%. The low-temperature performance, moisture sensitivity, and permeability of the tested mixtures met the standard requirement.

A set of 48 cyclic and 12 monotonic large-scale direct shear tests was performed to assess the interface properties of sand–rubber composite along a nonwoven geotextile layer. Rubber content, semiamplitude of the shear displacement, and applied normal stress all were varied to determine the cyclic, postcyclic, and monotonic interface response of the composite system under shear loading. The test results show that adding 40% granulated rubber to pure sand caused approximately 50% reduction in the maximum mobilized interface shear stress as the loading cycles progressed. The addition of granulated rubber to the sand decreased both the damping and the shear stiffness of the interface for all values of displacement amplitude and normal stress; in particular, for the energy dissipation, the observations were associated with the higher linearity of the stress–strain relationship when adding rubber, thereby reversing the typical trend of higher damping at smaller strains or displacements. In addition, an increase in the displacement amplitude value yielded a reduction in the secant shear stiffness, but contrarily increased the damping ratio of the geotextile–composite soil interface. An increasing trend of the hardening factor was observed through the initial cycles of loading for the samples containing 40% granulated rubber, which was ascribed to the increased densification capability of the sand–rubber mixture with the progression of the loading cycles; however, this response was not captured for the pure sand–geotextile interface.

Recycling waste steel slag for asphalt pavement construction can reduce energy consumption and preserve nonrenewable natural resources. However, the moisture susceptibility of steel slag asphalt mixture (SSAM) in severe freeze–thaw regions should be taken into consideration. In light of this, three types of fibers (basalt fiber, polyester fiber, and lignin fiber) and rubber powder were blended into the SSAMs, and their freeze–thaw damage characteristics were investigated. First, the optimum bitumen and fiber content of SSAMs were determined based on Marshall design using response surface methodology. Then, the air voids of SSAMs were identified through X-ray computed tomography (CT) technology, while the effects of the fiber and freeze–thaw cycles on the moisture stability of SSAMs were investigated. Moreover, the enhancement effects of the fibers were analyzed using scanning electron microscopy (SEM). The results show the optimum fiber content of different fiber-reinforced SSAMs are 0.35%, 0.29%, and 0.23%, respectively, and the optimum bitumen content is 6.7% for all cases. The effect of freezing–thawing leads to an increase of the air voids in the middle part of the specimen, whereas the incorporation of fibers weakens the adverse action of freezing–thawing and effectively improves the moisture stability of the SSAMs. Furthermore, the network structure formed by basalt fibers in asphalt mastic significantly improves the integrity of the SSAM. Additionally, basalt fiber reinforced SSAM shows the best resistance to moisture damage.

This article aims to propose an asphalt mixture with deicing and permeable functions to address the dilemma of excessive stormwater runoff during summer and ice accumulation in winter for pavement in southwest China. A peeling test and ice melting test were first conducted to select one powder and one granular anti-icing additive for better deicing performance. Then the effects of anti-icing additive contents on deicing and pavement performance of deicing permeable mixtures were investigated to select the best content. Additionally, the effect of immersion treatment on the pavement performance of deicing permeable mixture was analyzed. The results showed that the rise in additives content would help to improve deicing performance, as expected, regardless of additive type. The optimal content of the powder additive was reached by replacing 80% of the mineral powder, and the optimal mass ratio of granular type was 5% of the mixture. The addition of additives weakened the low-temperature performance and water-stability performance of the permeable mixture, whereas a high-temperature performance was observed when granular additive was adopted. The pavement performance of the mixture with granular additive was better than the mixture with powder additive under different immersion treatments. Overall, the granular anti-icing additive is recommended for use in a permeable mixture. This research is helpful and may provide guidance for the design of deicing permeable asphalt mixtures.

Magnetic fly ash is a potential alternative responsive additive to achieve magneto-rheology control of cementitious materials; it reduces the cost of magnetic particles and also is beneficial to preparing sustainable binder materials. This paper estimates the magnetic force between micrometer-sized fly-ash particles in cementitious suspensions. Four cases, regarding different selections of particle distance and different characterizations of magnetic properties of fly ash, are considered. The correlations between theoretical calculated parameters and experimental rheological properties are discussed. Results show that fly ash should be separated into magnetic and nonmagnetic parts to better estimate the magnetic force between particles. For the case of two neighboring magnetic fly-ash particles in cementitious suspensions, the estimated magnetic yield parameter, describing the relative magnitude of magnetic force to the resistance of the suspension, can be used as an indicator to describe whether the fly-ash cement paste shows rheological response to an external magnetic field. The intensity of the magneto-rheological response can be correlated to the average magnetic force calculated by considering the even distribution of magnetic fly-ash particles in nonmagnetic solid suspensions.

Cement addition and pozzolanic reaction in construction and demolition waste recycled aggregates can stabilize the base of pavements chemically. A way to control and explore the maximum benefits of it is necessary. This study establishes a mix between recycled cementitious and red ceramic-waste aggregates with hydrated lime to enhance pozzolanic reactivity in the material and achieve the best mechanical properties compared with those of a portland cement or recycled concrete aggregate itself pavement base layers. Chemical tests (Chapelle and thermogravimetry), physical tests (grain size distribution, density), and mechanical tests [unconfined compressive strength (UCS) and resilient modulus (RM)] were conducted. The increase of hydrates in the fine fraction of the mixes and the recycled aggregate itself correlated with the resulting increase in UCS and RM. The limited contribution of the self-cementing reaction of recycled cementitious aggregates was quantified, resulting in an UCS of 1 MPa and RM of 1,000 MPa. The pozzolanic reaction of cementitious and red ceramic aggregates with hydrated lime achieved an UCS of 8.4 MPa and RM of 2,800 MPa, values closer to those achieved by a portland cement stabilized pavement base (5.4 MPa and 4,500 MPa, respectively).

The mechanical properties of rigid polyurethane foam (PUF) will be significantly affected because of the existence of water when applied in dam repair and road maintenance. The related studies generally consider the effects of water and matrix on the mechanical properties of rigid PUF. However, PUF is a three-phase composite consisting of water, air, and matrix in practical engineering. Its mechanical properties are subject to the combined effects of these three composites at the same time. In this case, an improved three-phase viscoelastic model was proposed to quantify the effects of water, air, and matrix on the compressive mechanical behavior of rigid polyurethane foam immersed in water (WRPF). Based on the improved viscoelastic model and piecewise method, a compressive strength prediction model of WRPF was developed to describe the change of WRPF’s compressive strength during the full-service life. Then uniaxial compression tests and electron microscope tests were conducted to verify the rationality of the model. Results show that water and air have reinforcing effects on the compressive property of WRPF in the short-term, unsaturated absorption stage. In contrast, water has weakening effects on its compressive property in the long-term, saturated stage. Finally, at different stages of water absorption, a semitheoretical and empirical formula was developed from the prediction model and the experimental data from compressive tests.

From the perspective of the features of effective vertical and overhanging construction, the spray-based three-dimensional (S-3D) mortar printing technology has promoted the application of 3D printing in construction fields. Carbon fibers were used to optimize the mechanical performance of S-3D printed mortar. The effects of carbon fiber volume (0%, 0.5%, 1.0%, 1.5%, and 2.0%) and length (3 and 5 mm) on the working properties, printing accuracy, mechanical properties, and microstructural properties of the S-3D printed mortar were studied comprehensively. The test results showed that the S-3D printed mortar with the 1.5 vol% and 3 mm length carbon fiber (L3-V1.5 specimen) showed optimal printing accuracy in the single-layer and accumulative thickness tests. The S-3D printed L3-V1.5 mortar had the maximum flexural strength, which increased by 53.06% and 39.96% at 7 and 28 days, respectively, more than those of its cast counterparts. In addition, the S-3D printing process enhanced the interlayer bonding strength, and the ultimate interlayer splitting strength of the S-3D printed L3-V1.5 mortar increased by 2.16% and 3.33% at 7 and 28 days, respectively, more than those of the cast mortar without carbon fibers. The S-3D printing process improved the carbon fiber alignment and compactness and, thus, the mechanical properties of the S-3D printed mortar.

Synthesized nanocalcium-silicate-hydrate (C─ S─ H) was successfully employed as an accelerator in portland cement. C─ S─ H nanomaterials were produced in this study utilizing a process that used separate nucleation and growth steps with varied solvent compositions. The effects of the water/alcohol volume ratio (W/A) in the combined solvent on the calcium silicon ratio, particle size, morphology of C─ S─ H nanomaterials, and compressive strength of portland cement were studied. The results reveal that when the W/A ratio decreased, the calcium to silicon (Ca/Si) molar ratio reduced, and the morphology of the C─ S─ H nanomaterials turned from micalike to mixed lamellar and granular, then to granular with a wrinkled surface, and finally to foillike. When the W/A was $3:1$, the small particles (100 nm) of C─ S─ H nanomaterials had the highest W/A, whereas the large particles ($>200\mathrm{nm}$) had the highest W/A. C─ S─ H nanomaterials offered calcium silicate hydrate nucleation sites, altered C─ S─ H gel development modes, and enhanced the number of hydration products. The composition, particle size, and shape of C─ S─ H nanomaterials all influenced the compressive strength of the cement paste.

Over the last 20 years, many polymer-based additives have been used in asphalt modification. The extensive utilization of these additives and their inability to biodegrade create environmental concern for humans. Therefore, discovering affordable and naturally occurring asphalt polymers has become prominent. In this study, a new asphalt modifier was produced under laboratory conditions by synthesizing boron oxide with rosin (colophony resin), which is naturally produced from pine trees. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC)/thermogravimetric (TG), and X-ray powder diffraction (XRD) analyses were used to determine the microstructural characteristics of the produced modifier. The SEM analysis showed that the new modifier was distributed homogeneously the asphalt matrix, the FTIR and XRD analyses showed that a chemical synthesis had taken place, while the DSC and TG analyses determined the thermal structure characterization and temperature range of the modifier. The rheological properties of the modified asphalts were investigated by conducting penetration, softening point, ductility, flash point test, rotational viscosity (RV), and dynamic shear rheometer (DSR) tests. The results showed that the new modifier could be produced in a laboratory environment, the temperature sensitivity of the original asphalt was reduced by 48% with a 3% additive rate, and the modified asphalt provides a wide range of usage in hot climates. Conclusively, the boron-added resin compound (BARC) additive did not adversely affect the workability and pumpability properties and the BARC-modified asphalt binders significantly increased the rutting resistance.

Production of calcium sulfoaluminate (CSA) cement from solid industrial wastes consumes enormous amounts of wastes and provides an environmentally friendly binder for the construction sector. However, carbonation of CSA cement is much faster than that of portland cement. Silane was used to reduce water absorption of portland cement concrete and thus promote its carbonation resistance. To clarify the effect of silane on carbonation resistance of CSA cement prepared from solid industrial wastes, three silanes, including glycidoxypropyltrimethoxysilane (GOPTS), vinyltrimethoxysilane (VTMS), and dodecyltrimethoxysilane (DTMS), were employed in this research. Their influence on early-age hydration and water absorption of CSA cement mortar was investigated. Accelerated carbonation was performed. The results show that GOPTS and VTMS retarded early-age hydration of CSA cement and slightly decreased 28-day compressive strength, whereas DTMS had less influence. All three silanes decreased water absorption of mortar. However, they bring about more pores larger than 200 nm, which would facilitate the spread of ${\mathrm{CO}}_2$ in mortar. Nevertheless, other than silane’s effect on water absorption and the pore structure of mortar, carbon chain length of silane determines the carbonation resistance of CSA cement mortar. DTMS accelerates carbonation due to its long chain, but, GOPTS and VTMS, with shorter chains, promote resistance of mortar.

The manufacture of asphalt pavements causes various environmental problems due to bitumen’s hazardous nature. Aging of bitumen yields undesirable properties, which may cause several adverse effects on asphalt performance. Use of antiaging agents for bitumen modification results in improved aging resistance, hence such agents confer environmental benefits by reducing the consumption of bitumen owing to lower maintenance requirements and the reduced volume that needs to be produced. Therefore, it is important to develop new antiaging agents and investigate their benefits to the asphalt industry. This study investigated the use of different rates (1%, 2%, and 3%) of linear alkyl benzene sulfonic acid (LABSA) as a bitumen antiaging agent through chemical and rheological characterization on unaged, short-term-aged, and long-term-aged samples using Fourier transform infrared spectroscopy and dynamic shear rheometer (DSR). A chemical aging index (CAI) and various rheological aging indexes, obtained by the construction of master curves and crossover temperatures were calculated to evaluate the variation of aging effects by LABSA addition. The detailed experiments showed that LABSA-modified samples exhibited better aging resistance compared to neat (base) bitumen. Additionally, the statistical analyses of all aging indexes were investigated to obtain the relationship between chemical and rheological aging indexes. The determination coefficient ($R^2$) and scatter index (SI) results showed that the rheological behavior of bitumen against aging could be evaluated based on chemical behavior and vice versa. Moreover, it was concluded that short-term aging and long-term aging effects should be evaluated separately to determine the relationship between different aging characteristics of samples.

The corrosion of steel fibers is a direct cause of the deterioration of steel fiber-reinforced concrete in chloride environments. This study mainly investigated the corrosion behavior of steel fibers exposed to NaCl solutions with $\mathrm{pH}=7$, 10, 11, 12, and 13. The corrosion rate of the steel fibers was calculated according to the change of the diameter and ultimate tensile load. The electrochemical parameters of the steel fibers corrosion were continuously monitored. The morphology of the steel fibers affected by chloride attack was observed by scanning electron microscope (SEM). The results reveal that the corrosion rate of the steel fibers decreased as the pH of the NaCl solution increased from 7 to 13, and it was very small at $\mathrm{pH}\ge 12$. According to the open circuit potential, corrosion potential, corrosion current density, and electrochemical impedance spectroscopy, the steel fibers exhibited a high corrosion tendency and corrosion rate when exposed to NaCl solutions with $\mathrm{pH}\le 12$. However, they exhibited low corrosion tendency in the chloride solution with $\mathrm{pH}=13$. The surface roughness of the steel fibers exhibited only a slight increase after exposure to the NaCl solution with $\mathrm{pH}=13$ for 180 days.

In view of the excellent bonding capacity, rapid hardening, and high early strength, magnesium phosphate cement (MPC) functionalized with impedance matching agent of expanded polystyrene (EPS) and absorber of Mn–Zn ferrite that exhibits excellent electromagnetic wave absorption performance (EWAP) is fabricated to shield the construction of buildings against the ever-increasing electromagnetic radiation hazards. Influences of EPS and Mn–Zn ferrite contents and layers of specimens on the reflection loss (RL) of MPC in the frequency range of $1–18\mathrm{GHz}$ are systematically investigated. Test results demonstrate that EPS and Mn–Zn ferrite significantly enhance the EWAP of MPC due to the porous structure effect by EPS and multiple magnetic loss effects by Mn–Zn ferrite. MPC with double-layer structure shows an optimal EWAP as featured by a peak RL value of $-23.2\mathrm{dB}$ and a bandwidth of 17 GHz below $-10\mathrm{dB}$. The electromagnetic energy absorbing mechanisms of MPC are further analyzed with scanning electron microscopy/energy disperse spectroscopy (SEM/EDS) and X-ray diffraction (XRD) results. In view of structural strengths, the modified MPC is able to repair damaged concrete of prefractured specimens, which ensures the reliability and rapidity of electromagnetic radiation protection.

The grain–grain interface of cement, which is composed of the complex needle-shaped microstructure of calcium silicate hydrate (C-S-H), is crucial in the development of the mechanical properties of cementitious composites. These C-S-H needles grow radially outward from the grain surface. This work proposes a combined experimental and modeling approach to incorporate the finer details of these needle geometries and the distribution of mechanical properties in an interface-based multiscale mechanical model for hydrating tricalcium silicate (${\mathrm{C}}_3\mathrm{S}$). At micrometer and sub-micrometer length scales ($<5\mu \mathrm{m}$), electron microscopy images revealed that the geometrical nature of these needles at the grain interface varies with days of hydration. The mechanical properties of C-S-H at the nanoscale were observed to be higher at the inner core and reduced toward the outer product. The model developed can incorporate the details of these needle microstructures and their mechanical properties at the microscale and can predict the bulk properties of hydrated ${\mathrm{C}}_3\mathrm{S}$ at higher scales.

Steel slag needs aging treatment before being used for the coarse aggregate of asphalt mixtures because it has volumetric instability due to the hydration of calcium oxide. This paper investigates the effect of hydration products on the bonding properties between asphalt binder and steel slag coarse aggregates subjected to natural aging treatment. A scanning electron microscope, a fluorescence microscope, and X-ray diffraction testing were used to study the surface morphology, microstructure, and mineral phase of the hydration product layer generated on the aggregate surface of steel slag. A modified water boiling test was conducted to evaluate the water stripping resistance of asphalt film with different boiling times. Pull-off testing on real steel slag aggregates was performed to investigate the effect of the hydration product layer and surface treatment on the bonding strength and interface failure mode. Test results indicated that the hydration products exhibited a loose and porous structure and formed an interlayer to prevent the asphalt film from directly adhering to the aggregate surface of steel slag. The hydration product layer could improve the initial stripping resistance but impair the long-term stripping resistance with increased boiling time. The interlayer of hydration products tended to be the weakest link between asphalt film and steel slag aggregate when subjected to pull-off strength damage. The bonding strength showed a negative linear relation with the stripping rate of asphalt film. After steel slag surface treatment with water-based capillary inorganic waterproofer, the pull-off failure of hydration product layer was avoided and thus improved the bonding strength between asphalt film and steel slag aggregate. The bonding strength and failure mode between asphalt-slag adhesion could be well examined by using pull-off tests. Better insights into asphalt–slag adhesion are useful to design durable asphalt mixtures containing steel slag aggregate.

Asphalt pavement failure is directly related to the traffic and climate effects. Temperature and moisture severely impact pavement service life. It is known that moisture changes the stiffness and stress–strain distribution and all the mechanical behaviors of the mixture/structure. There is a huge interest in studying the impact of water on the behavior of flexible pavements, mainly on freeze–thaw regions under tropical climates with high rainfall levels. The scope of the present paper was to check the susceptibility to moisture-induced damage of dense asphalt mixes produced and applied on highways in Brazil’s southernmost region using different laboratory tests: visual adhesion of coarse aggregate; tensile strength ratio (TSR), and dynamic modulus ratio (DMR). Thus, this study evaluated the morphological, chemical, and mineralogical properties of aggregates from 11 quarries, as well as the interaction between aggregates and the respective bituminous binders. Rocks with high Si contents performed worse in visual adhesiveness tests; chemical ratios such as Fe/Si above 1 and Ca/K above 5, as well as the rougher texture of aggregates, considerably improved the coating, reducing the failures in adhesion. Results of TSR and DMR, after applying the induced moisture damage cycle, indicated greater susceptibility to conventional binders than mixtures containing modified binders in their composition. The action of moisture damage for most mixtures caused a reduction in strength and stiffness, warning of a decrease in the binder’s ability within the mixture, completely changing the distribution of efforts within the structure. Therefore, from this study, it is possible to suggest using DMR instead of TSR to assess susceptibility to moisture damage.

The suitability of the rapid, relevant, and reliable (${\mathrm{R}}^3$) heat of hydration and bound water tests for measuring the reactivity of various supplementary cementitious materials (SCMs) and their blends with calcium hydroxide (CH) was investigated in this study. These tests have been recently standardized in current standards. The test was carried out on pastes of fly ash (FA), slag (S), kaolinitic calcined clay (K), limestone (LS), and their blends. A detailed analysis of the heat of hydration and bound water measurements specified according to the ${\mathrm{R}}^3$ test was carried out. A good correlation was found between the two types of test results and also between the reactivity test results versus strength activity index measured using cement mortar compressive strength. The formation of hydration products in the ${\mathrm{R}}^3$ test paste specimens was also studied using X-ray diffraction (XRD). The hydration products for SCMs formed in the test were similar to those reported in cement systems. It was seen that the interactions in the blended SCMs with CH were also similar to those reported in cement pastes. Further, the microstructure of the specimen was studied using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis, and the overall hydration of various SCMs was studied. The influence of the proportions of the SCMs in the blended SCMs and that of fineness were also investigated. The applicability and limitations of this test method for SCMs and their blends were discussed.

This paper summarizes the results of the first comprehensive laboratory study that was conducted to evaluate the effect of using different aramid fiber properties (types, lengths, and dosages) with different combinations on the performance of dense-graded asphalt mixtures reinforced with aramid fibers. Asphalt mixtures with two different aramid fibers (Fiber A and Fiber B) were prepared. For each type of fiber, two lengths and four doses were considered. The semicircular bend (SCB) test, indirect tensile asphalt cracking (IDEAL-CT) test, and the overlay tester (OT) were conducted to evaluate fracture resistance and reflection cracking resistance of prepared mixtures, along with the asphalt concrete cracking device (ACCD) test for evaluating the low-temperature cracking resistance, the Hamburg wheel-tracking (HWT) test for evaluation of rutting susceptibility. Cost analysis was also done to evaluate the feasibility of adding aramid fibers to the asphalt mixtures. Results of the conducted tests indicated that the effects of adding aramid fibers to asphalt mixtures vary depending on the type of aramid fiber and its properties. In general, the addition of the Type A and Type B aramid fibers to the unmodified performance grade (PG) 64-22 mixtures resulted increasing their fatigue lives by 104% and 65%, respectively. Adding Type B fiber [short aramid/polyolefin fiber blend with 12.5 mm (0.75-in.) length] or long Type A fiber (wax-treated aramid fiber with a length of 1.5 in.) to the PG 64-22 mixtures resulted in improving the cracking resistance of reinforced mixtures. In addition, doubling the suppliers’ recommended dosage of each fiber type resulted in significantly lower cracking resistance values. The fibers did not improve the resistance to low-temperature cracking for asphalt mixtures. However, the rutting and moisture susceptibility results for fiber-reinforced mixtures were satisfactory compared with the unreinforced mixtures. Results of cost analysis indicated that the addition of aramid fibers to the mixtures resulted in a significant reduction of construction cost for these mixtures to the values between 27% and 37%. The optimum formulation of both aramid fibers for the purpose of improving cracking resistance of asphalt mixtures was found as 1.5-in. length at the supplier recommended dosage for Type A aramid fiber, and 0.75-in. length and the supplier recommended dosage for Type B aramid fiber.

Coal mine filling requires a safe, lightweight, and high-strength filling material, but current commonly used aeration agents, such as hydrogen peroxide, which produces the combustible gas ${\mathrm{O}}_2$, and aluminum powder, which produces the explosive gas ${\mathrm{H}}_2$, are not suitable for coal mine filling. In this paper, a new inorganic composite aeration agent, namely sodium bicarbonate and potassium aluminum sulfate, which produces inert gas ${\mathrm{CO}}_2$, was developed. The effects of this composite aeration agent admixture (at contents of 0%, 2%, 4%, 6%, and 8%) on the properties such as fluidity, setting time, compressive strength, and water resistance of sulfoaluminate cement paste with high water-to-cement ratios were investigated systematically. The evolution of the microstructure and pore structure of this foamed material was determined using X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), and scanning electron microscopy (SEM). The results showed that when the amount of aeration agent was 8%, the 7-day compressive strength of the prepared sulfoaluminate cement–based foamed material with a dry density of ${600\mathrm{kg}/\mathrm{m}}^3$ was 1.2 MPa. Compared with the control group, the setting time was shortened by 87%, dry density was reduced by 42.1%, 7-day compressive strength was increased by 47.5%, and water resistance was increased by 45.4%. The composite admixture not only formed uniform bubbles within the sulfoaluminate cement paste but also produced in situ calcium carbonate, which promoted the hydration of sulfoaluminate cement and made the microstructure of the hardened paste denser. The results provide new materials for coal mine foam filling, which can be applied to corner gas control and foam filling in mining areas and coal mine fire prevention.

For ground improvement via microbially induced carbonate precipitation (MICP), the spatial distribution of biocementation considerably affects the mechanical performance of soil. This study systematically assessed the ${\mathrm{CaCO}}_3$ spatial distribution in sand columns with various grouting strategies. ${\mathrm{CaCO}}_3$ dispersion along the radial and vertical directions was quantitatively evaluated. Furthermore, a series of biochemical monitoring experiments was conducted to investigate the MICP process in sand. The results indicated that the reversed and downward chemical solution grouting and high rates of microbial grouting all promoted ${\mathrm{CaCO}}_3$ vertical uniformity. Moreover, the grouting strategy slightly affected the dispersion degree of radially distributed ${\mathrm{CaCO}}_3$. The variation coefficient basically ranged from 0.1 to 0.3. However, the variation coefficient for radially distributed ${\mathrm{CaCO}}_3$ along the vertical direction was significantly affected by the chemical grouting direction. The biochemical monitoring results indicated that 38% ${\mathrm{Ca}}^{2+}$ was even consumed near the chemical solution outlet in the chemical solution grouting process. The initial ${\mathrm{Ca}}^{2+}$ concentration during the intermittent period gradually decreased along the chemical solution grouting direction. The ${\mathrm{CaCO}}_3$ vertical distribution was controlled by a combination of the total MICP reaction time, biomass, and ${\mathrm{Ca}}^{2+}$ availability in the intermittent phase. Different ${\mathrm{CaCO}}_3$ distributions resulted in each grouting strategy exhibiting specific applicable engineering requirements. Furthermore, the carbon footprint was preliminarily evaluated. The results in this study provide references for the selection of grouting strategies for the MICP technique in engineering applications.

Solar thermal energy is a technology that collects radiant energy from the sun to generate heat or electricity. Thermal energy storage is required to compensate for the solar thermal energy variations across time scales, and a popular strategy is storing thermal energy in hot water tanks. Due to superior strength and durability, ultrahigh-performance concrete (UHPC) is exploited to construct such water tanks for applications at 200°C. Therefore, the mechanical strength and microstructure of UHPC after long-term temperature-pressure load (autoclaving) is studied. The compressive strength of UHPC can stay robust due to the accelerated formation of hydrates, while the flexural strength is vulnerable to long-term autoclaving due to the transformation of amorphous calcium silicate hydrate (C-S-H) to more ordered phases. The main hydrates in autoclaved samples are poorly crystallized C-S-H, hydroxylellestadite, and hydrogarnet. The porosity of autoclaved samples is not strictly related to the mechanical strength, and the influence of hydrate assemblage outweighs that of porosity on mechanical strength after long-term autoclaving. The partial replacement of cement by limestone powder can decrease crystalline hydrates and increase poorly crystallized C-S-H, which densifies the microstructure and enhances the mechanical strength. However, excessive poorly crystallized C-S-H aggravates the thermal mismatch between the matrix and quartz aggregates after autoclaved samples cool to room temperature, leading to interstice in matrix-quartz interfaces and, thus, reduced mechanical strength. Therefore, an appropriate addition of limestone powder is required to induce the hydrate assemblage with appropriate poorly crystallized C-S-H, ensuring durable UHPC structures under autoclaving.

To evaluate the structural safety of corroded prestressed concrete structures, it is necessary to define the deteriorated mechanical behaviors of corroded prestressing steel strands. However, no standard provides a quantified relationship between the level of corrosion and the residual mechanical properties, and no consensus for such quantification has been reached. The aim of this study was to provide a test database for the residual mechanical properties of corroded prestressing steel strands. Strands recovered from aged bridges were naturally corroded, and an evaluation method for the corrosion level was suggested. In addition, corrosion assessment criteria were suggested based on characteristics of the corrosion appearance.

Lightweight concrete is applicable to skyscrapers and structures with a large size or long span, as well as the fabrication of reinforced concrete units in modular construction. With reduced self-weight, it is essential to maintain sufficient mechanical strength to avoid the increase in structural member size that lowers the efficiency in space utilization and headroom. In this study, by incorporating lightweight aggregate sourced from industrial by-products into foamed concrete, an experimental program was conducted to develop a lightweight concrete mix that has strength-to-density ratio superior to existing mixes reported in the literature. Scanning electron microscopy was performed to understand the rationale behind the improvement.