Journal of Materials in Civil Engineering

Fly ash is introduced to strengthen the durability of magnesium oxychloride cement (MOC) solidified sludge, developing a more sustainable method for waste sludge disposal. The effect of curing age, fly ash dosage, and $\mathrm{MgO}/{\mathrm{MgCl}}_2$ molar ratio on strength, microstructure, durability, and cementation products of MOC-solidified sludge was identified. Fly ash weakens the compressive strength of solidified sludge and prevents its long-term strength deterioration. The amount of brucite and magnesium silicate hydrates (M-S-H) gels increases with curing age, and the crystal shape of phase 5 becomes more robust when fly ash is added. Fly ash grains fill the pore space, enhancing the long-term strength and durability, but an excessive dosage of fly ash weakens the porous structure. The higher the fly ash dosage, the better the mass stabilization and strength retention. In particular, the strength of solidified sludge exposed to freeze–thaw cycles was enhanced for the dewatering and ice hardening effect. The results indicate that fly ash promotes the durability of MOC-solidified sludge, and the fly ash-MOC blend is proved a profitable and sustainable material for sludge solidification.

The aging of asphalt binder is one of the most serious problems related to using binder in asphalt pavement. Therefore, understanding the effect of aging on the chemistry and rheology of asphalt binders is important to achieve proper durability and longevity in asphalt pavement design. The chemical properties of asphalt binder and the ratio of maltenes to asphaltenes change during the aging process. Many studies have investigated the immediate effect of recycling agents (RAs) on aged binder properties, but understanding the behavior of restored binders in the next period of pavement service is quite limited. This study aims to evaluate the immediate and long-term influence of different RAs in restoring the chemical properties of aged asphalt binders. Three different types of RAs, namely aromatic extracts, paraffinic oil, and naphthenic oil, were used to modify the blended binder in this study. The chemical properties of the modified blended binders were characterized by a saturates-aromatics-resins-asphaltenes (SARA) fractionation analysis, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and elemental (carbon, hydrogen, nitrogen, sulfur, and oxygen) analysis. The results indicated that RAs have restored the chemical and microstructural properties of the aged binder. The relatively limited increase in colloidal index (CI) due to aging in the restored binders indicated that the RAs have performed well in maintaining the stability of the colloidal structure of binder in the long-term aging. Paraffinic oil performed better than the other two RAs in maintaining the chemical composition and colloidal stability of binder.

The aggregate skeleton and its evolution under external loads are crucial to evaluate the mechanical properties of the asphalt mixture. This study developed a method to identify the three-dimensionally (3D) aggregate skeleton based on geometry information. The proposed method can identify the evolution process of the aggregate skeleton during loading in the finite element method (FEM). Random models based on the Gilbert–Johnson–Keerthi (GJK) algorithm are used to study the influence of the concave–convex degree of the gradation curve and the magnitude of the creep load on the aggregate skeleton during the creep process. The results indicate that the aggregate skeleton undergoes three stages during creep: aggregate redistribution, skeleton formation, and skeleton failure after reaching the ultimate load, while the increase of load causes the aggregate skeleton to lose its bearing capacity faster. More coarse aggregate raises the strength of the aggregate skeleton, but it is more likely to break down quickly once it reaches the strength. More fine aggregate enhances the stability of the aggregate skeleton. The proposed identification method can serve as a general tool to investigate the evolution process of the internal aggregate structure of the asphalt mixture.

Different fine materials that constitute either industrial or mining by-products were incorporated as filler materials in self-compacting (SC) mortars, aiming at improving their sustainability. More specifically, two common by-products of the cement industry—cement kiln dust (CKD) and bypass dust (BPD)—were evaluated together with the fine content (PeP) of residuals of perlite mining (RoM) before and after further grinding or thermal treatment, yielding the fine material products $\mu$-silica (MS) and expanded perlite (EP), respectively. The five by-products, two limestone fillers (MP20/80), and pumice were incorporated in SC mortars, for which the last two types served as reference fillers. The effect of all fillers on the rheology, strength, and hydration of the mortars was comparatively evaluated with respect to their nature, size, shape, and inherent pozzolanic reactivity. The results illustrated that all prepared mixtures achieved the rheological criteria of self-compaction, developing satisfactory strength and altered hydration heat. The examined by-products proved to be equivalent alternative fillers for SC mortars, increasing their sustainability, which is significantly burdened with the increased grinding needs of the limestone fillers.

Metakaolin (MK)-based geopolymer is an emerging alterative to cement, but the quantitative understanding of its pore structure is lacking. Prior studies are limited to phenomenological investigations of the influence of activator modulus and concentration, liquid/solid ratio, or curing temperature. This study characterized the pore structure of a MK-based geopolymer using mercury intrusion porosimetry, gas adsorption, and scanning electron microscopy and revealed the quantitative correlation between its pore structure and geopolymerization degree. Most pores in the MK-based geopolymers were from 10 to 100 nm—noticeably smaller than that of OPC paste ($<\mathrm{1,000}\mathrm{nm}$). A denser microstructure can be achieved by increasing the degree of geopolymerization through lower activator modulus or higher activator concentration. The liquid/solid ratio and curing temperature also influenced the geopolymer microstructure mainly by changing the initial distance between MK particles and affecting the water loss during curing, respectively. These findings provide guidance for studying the shrinkage and chloride resistance of geopolymer concrete, among other properties.

This paper is based on the basic mechanical properties and volume deformation test, as well as the characterization of hydration products and microstructure properties such as x-ray diffraction (XRD), scanning electron microscope (SEM), and mercury injection method (MIP). The effects of ${\mathrm{CO}}_2$ curing on the mechanical properties, hydration product composition, and microstructure of magnesium oxysulfate (MOS) cement were studied. The results show that the carbonation properties of MOS cement are closely related to the standard air curing age after demolding. The ${\mathrm{CO}}_2$ curing immediately after demolding is not conducive to the development of compressive strength of MOS cement, while the compressive strength of MOS cement in standard air curing for 14 or 28 days after demolding is increased during ${\mathrm{CO}}_2$ curing. The ${\mathrm{CO}}_2$ can prevent the continuous hydration of residual MgO to form $\mathrm{Mg}{(\mathrm{OH})}_2$ or 5·1·7 phase, which affects the development of the compressive strength of MOS cement. The appropriate addition of low-calcium fly ash (L-FA) can compensate the effect of ${\mathrm{CO}}_2$ on the mechanical properties of MOS cement. During ${\mathrm{CO}}_2$ curing, some $\mathrm{Mg}{(\mathrm{OH})}_2$ is transformed into an amorphous phase to increase the compactness of its microstructure and a small amount of $\mathrm{Mg}{(\mathrm{OH})}_2$ reacts with ${\mathrm{CO}}_2$ to form ${\mathrm{MgCO}}_3·3{\mathrm{H}}_2\mathrm{O}$. The results provide an important theoretical and experimental foundation for the further study of the effects of ${\mathrm{CO}}_2$ on the properties of MOS cement and the use of ${\mathrm{CO}}_2$ curing modification.

First, porous asphalt (PA) pavement possesses a lower strength and lifetime compared to typical dense-grade asphalt mixtures due to its large empty space structure. Second, PA pavements’ fatigue life and durability are affected significantly by climate factors; the two most critical factors being aging conditions and moisture actions. Third, because of the environmental concerns connected with producing or repairing asphalt pavements using only virgin materials, studies have recommended reusing reclaimed asphalt pavement (RAP) materials. On the other hand, their use in road pavement is negative to the fatigue performance of asphalt pavements, especially PA. Therefore, modifying PA mixtures containing RAP to address the mentioned issues is necessary. Researchers have found that modifying asphalt mixes using nanotechnology is one of the more effective methods. The four-point bending beam fatigue test is one of the most dependable tests to assess the fatigue performance of asphalt mixtures, and evaluating the fatigue resistance of nano-modified PA mixes containing RAP under laboratory conditions by performing this test is essential. This study aims to investigate the fatigue behavior of different compounds of PA mixtures modified with nano zinc oxide (NZ) (0%, 2%, 4%, 6%, and 8%) containing various contents of RAP materials (0%, 25%, and 50%) under normal, long-term aging, and freeze–thaw (F–T) cycle conditions. Moreover, the self-healing capability of these PA samples was evaluated using this test by performing two 24-h recovery periods following the first and second loading. It can be inferred from the result that although adding RAP and inducting long-term aging and moisture-damaged conditions negatively influenced PA mixes’ fatigue lives, incorporating NZ caused increases in these values by averages of 114%. Besides, results indicated that applied rest periods were observed to significantly impact PA specimens’ self-healing capability, resulting in longer fatigue life for them. On average, conventional and NZ-modified PA mixes with/without RAP could recover up to 32 and 48% of their fatigue resistance in all conditions.

The calculation method of asphalt film thickness was proposed by considering the specific surface area of coarse and fine aggregates [computed tomography (CT) and Blaine test methods] and the wrapping effect of fine particles ($<0.075\mathrm{mm}$) on the aggregates to investigate the optimal asphalt dosage of asphalt mixtures. The effect of asphalt film thickness on the pavement performance of asphalt mixtures was studied. The optimal asphalt film thickness determination method for asphalt mixtures is proposed based on the pavement performance. The study shows that the asphalt film thickness of $4.4\mathrm{\mu m}$ has the best high-temperature performance. The higher the asphalt film thickness, the better its low-temperature performance, water stability, and fatigue performance. The optimal asphalt film thickness is selected according to the performance requirements of the asphalt mixture in different structural layers and environmental conditions.

Waste ethylene-propylene-diene monomer (EPDM) rubber and tire pyrolytic oil (TPO) derived from waste tire pyrolysis have shown promising results for their use in asphalt binder modification. However, their incorporation has shown improvements mainly either on rutting or fatigue behavior of the resultant asphalt binders. Composite modification may be a viable option to achieve improved performance with these two materials. The aim of this study was to evaluate the rheological, morphological, and chemical properties of asphalt binders produced through both individual and composite modifications using waste EPDM rubber and TPO. For composite modification, two different blending schemes were used: (1) sequential addition of TPO and EPDM rubber to the heated base asphalt binder; and (2) premixing of TPO and EPDM rubber prior to addition to the heated base asphalt. In the latter case, before being added to the base asphalt, TPO premixed EPDM rubber was conditioned at two temperatures (25°C and 90°C) to see the effect of different conditioning temperatures in composite modification. Firstly, the conventional properties of all the binders in the unaged state were assessed, followed by the evaluation of short-term-aged binders for Superpave and Shenoy rutting parameters, frequency sweep, zero shear viscosity, multiple stress creep and recovery, and Burger’s modeling. The long-term-aged binders were evaluated through the Superpave fatigue parameter, Glover-Rowe parameter, and linear amplitude sweep. Fourier transform infrared (FTIR) spectroscopy and optical microscopy were used for chemical and morphological analyses. The premixing of EPDM and TPO accompanied with conditioning at 90°C imparted a synergistic effect with improvements in both rutting and fatigue performance of binder. The improvement in performance attributes was ascribed to the preswelling of EPDM rubber with TPO, which was evident from the morphological analysis. FTIR provided evidence of chemical interaction between EPDM rubber and TPO during the conditioning and blending processes.

A concrete expansion joint can be damaged due to certain conditions. The performances in terms of temperature sensitivity and adhesion of used sealant materials in concrete caulking have strong relations to the joint service life. In this work, a composite-modified asphalt-based sealant (AS-M) with added styrene-butadiene-styrene (SBS), crumb rubber (CR), and tackifier resin (TR) modifiers was prepared, and its microstructure, high-temperature viscoelasticity, low-temperature crack resistance, and adhesion properties were evaluated, with two commercial finished sealants (AS-A and AS-B) as a reference. Specifically, Fourier transform infrared spectroscopy (FTIR) was used to analyze the chemical compositions of asphalt sealants, and the results showed that the physical blending and chemical reactions coexisted in the self-prepared sealant. A good compatibility and continuous structure for each sealant could be observed by fluorescence microscopy (FM). A dynamic shear rheometer (DSR) experiment was conducted to characterize the viscoelastic properties at high temperatures. The self-prepared sealant obtained the highest complex modulus, phase angle, and deformation resistance ability; the composite modifiers showed an outstanding modified effect. The glass transition temperature ($T_g$) was measured by dynamic mechanical analysis (DMA) testing. The $T_g$ value of the self-prepared sealant was similar to that of the commercial sealant with SBS modifiers, whereas the stress relaxation modulus at a low temperature of the self-prepared sealant was the lowest, indicating that the combination of the modifiers made it obtain a better stress relaxation ability at low temperatures. The self-prepared sealant possessed the best interface adhesive capacity between sealant and aggregate based on surface free energy theory. The experimental results showed that the asphalt sealant modified by SBS/CR/TR has excellent performances in various properties and can be used for concrete caulking.

Recycled engine oil bottoms (REOBs) are widely used in asphalt binders for modification and cost saving. However, more early road failures have appeared on the pavements constructed with REOB-modified asphalt binders in North America, leading to the bans and limits of its use and the interest in REOB’s quantification in asphalt binders. This study aims to systematically introduce a quantifying method via liquid-state nuclear magnetic resonance (NMR) techniques. One base asphalt binder, two REOB resources, and eight blend samples were measured by ${}^1\mathrm{H}$ NMR, ${}^{13}\mathrm{C}$ NMR, and heteronuclear single-quantum correlation (HSQC) NMR. Peaks at 1.1 and 1.4 ppm in ${}^1\mathrm{H}$ spectra and peaks at 31.2, 38.1, and 59.5 ppm in ${}^{13}\mathrm{C}$ spectra were found only in REOB samples and asphalt samples containing REOBs and derived from polyisobutylene (PIB). The indexes of peak ratio and area ratio could well characterize the relative contents of REOB within a certain concentration range. Finally, an obvious peak at (1.4 ppm, 59.5 ppm) (F2, F1) was found and suggested as a characteristic peak of REOB via the HSQC NMR test.

Toothed metal-plate connector (MPC) is a cost-effective connection method, easy to install with high assembly efficiency for manufacturing engineered timber trusses. In this study, In order to combine the advantages of the MPC with glued laminated bamboo (glubam) structures, a total of 136 MPC glubam joints, divided into 22 groups according to testing parameters, were tested and analyzed. Design strength values of the anchorage strength of metal plate tooth embedded in glubam, the tensile and shear strengths of toothed metal plate in glubam joints were provided in reference of the existing timber code specifications. The results show that the linear interpolation formula provided by the existing design code largely overestimates the anchorage strength of metal plate tooth embedded in glubam for the nonorthogonal loading directions. An angular equation expressed as the loading direction is therefore proposed. The design shear strength of aligning the major axis (tooth slot direction) of the metal plate parallel to the plate longitudinal direction is higher than that of aligning plate major axis perpendicular to the plate longitudinal direction, especially for the combined shear and tension loading. The design tensile and shear strengths of the MPC glubam joints are obviously larger than those of the Class I MPC timber joints given in the Chinese Standard, indicating that the MPC glubam is hopeful to be alternative to replace the MPC timber structures such as roof truss systems.

The last generation of cement hydration accelerators relies on the seeding effect induced by amorphous calcium silicate hydrate particles. However, little is known about the effect of variables, such as the degree of crystallinity and morphology, on their performance. In this work, particles with a $\mathrm{Ca}/(\mathrm{Si}+\mathrm{Al})$ molar ratio of 0.83 and different proportions of aluminum substitution for silicon were synthesized under hydrothermal conditions. X-ray diffractograms, nuclear magnetic resonance spectra, and scanning electron microscopy images showed that this altered the degree of crystallinity, structure, and morphology of the particles. Nevertheless, the addition of the synthesis products to cement pastes and their subsequent study by isothermal calorimetry and mechanical tests showed that the variables with the largest impact on cement hydration are the dosage and the proper dispersion of the particles. In fact, the use of a dispersing agent is highly recommended while drying of the particles should be avoided to prevent irreversible agglomeration processes from taking place.

This study aims to investigate the effect of pore physical and chemical microstructure factors on the durability properties of self-compacting concrete containing metakaolin and silica fume. This study identified the pore physical microstructure characteristics including pore size distribution, total porosity, pore connectivity factor, and the volume of large and small capillary pores. The pore chemical microstructure factors, including the concentration of potassium and sodium ions, were analyzed. The durability of self-compacting concretes including electrical resistance, chloride ion migration, and resistance to rebar corrosion (using rebar corrosion rate) was evaluated. The self-compacting concrete mixtures were considered based on the water-to-cementitious materials ($\mathrm{W}/\mathrm{Cm}$) ratios of 0.35, 0.45, and 0.55 and using silica fume substituting 0% and 8% of cement by weight, Also, for $\mathrm{W}/\mathrm{Cm}$ of 0.45, metakaolin and silica fume and cement were considered as the binder. Results indicate that in self-consolidating concretes (SCCs) without pozzolans, the volume of the large capillary pores affects the rate of rebar corrosion. No significant relationship was observed between the pore physical microstructure characteristics and rebar corrosion rate of pozzolanic SCCs.

Concrete face rockfill dam (CFRD) is a commonly used and cost-effective type of dams. However, random cracks are often seen in the face slab concrete (FSC) of a CFRD during construction, largely due to the shrinkage caused by concrete temperature gradients, drying, and cementitious hydration. This study aims to improve the cracking resistance of FSC by using shrinkage compensating and cracking control materials. In this study, 5.0% by weight MgO-type expansive agent (MEA) or 0.1% by weight carbon nanotube (CNT) was added to a reference FSC (FSC-REF) selected from a CFRD. Fresh and hardened state properties of the developed concrete were tested. Different properties such as hydration heat, capillary pressure, mechanical properties at various ages, drying and autogenous shrinkage, thermal expansion coefficient (CTE), pore structure, and cracking resistance at early age of the FSC mixes (FSC-REF, FSC-MgO, and FSC-CNT) were determined. The results showed that the CNT addition lowered the capillary pressure and reduced the risk of plastic shrinkage cracking, while it also reduced drying and autogenous shrinkage of FSC. The addition of both CNT and MgO had little influence on the heat of hydration of FSC, but these slightly improved the axial tensile properties of FSC. CNT reduced the thermal expansion coefficient of FSC, whereas MgO increased it. Both CNT and MgO decreased the total porosity of the FSC, and the CNT addition significantly reduced the number of mesopores. The temperature-stress test results showed that MgO/CNT improved the cracking resistance of the FSC at early age under both temperature matching curing mode and constant temperature curing mode. Based on measured properties, CNT can be considered a promising additive for cracking control of FSC.

The durability of alkali-activated slag grouting materials (AASGMs) has attracted significant research attention. This paper investigated the mechanical properties and microstructure of AASGMs mortars and pastes immersed in a flowing 5% ${\mathrm{NaHCO}}_3$ solution. Compared with the strengths of AASGMs immersed for 3 days, the flexural and compressive strengths of AASGMS immersed for 56 days increased by 11.1% and 37.8%, respectively. The leaching depth of AASGMS immersed for 56 days was 0.627 mm. The AASGMs had good antiflowing ${\mathrm{NaHCO}}_3$ solution deterioration performance. The leaching process of AASGMS in flowing ${\mathrm{NaHCO}}_3$ solution was divided into three stages: (1) neutralization of residual alkali in gel pores; (2) decalcification of calcium aluminate silicate hydrate (C-A-S-H) gels in the surface and intermediate layers to form calcium carbonate and silica gels; and (3) leaching of calcium and silicon in surface layers from calcium carbonate and silica gels.

Geotextile filters are used widely in overflow hydraulic structures to prevent long-term particle loss and internal erosion in cohesionless soils. Filter criteria have been proposed and developed for the geotextile filter design. The geometric properties of a geotextile filter typically are described in terms of its characteristic opening size ($O_F$), which should consider the different physical characteristics of the soil being protected. To investigate the filter criteria, this study used a percolation approach to determine the optimum value of $O_F$ considering the abilities of geotextile to retain soil, and numerical simulations were conducted of the filter–soil system. Different limit states of the filtration system, considering the retention, permeability, porosity, and thickness criteria, were studied. The statistical fractal method was used to consider the broad gradation of soils and their nonlinear properties, and network models composed of particles and constrictions were generated to simulate the erosion process. The proposed approach can serve as an appropriate guide for the design of geotextile filters applied to the cohesionless granular soils.

The surface roughness prior to adhesive bonding plays an important role in enhancing the durability of composite materials. To obtain deep insight into the effect of aggregate surface roughness on the interfacial properties of the asphalt–aggregate system, molecular dynamics simulations were carried out. Different surface nanostructure patterns, including groove, grid, and pillar, were generated with predefined roughness ratios in both acidic mineral (quartz) and weak alkali mineral (calcite) models. The influences of surface nanostructure on interfacial interaction energy, tensile bond strength, and the interlocking effect were investigated. In general, the van der Waals energy dominates the interaction energy between asphalt and aggregate surfaces at a low roughness ratio, whereas electrostatic interaction dominates the interaction energy in surfaces at a high roughness ratio because of the unsaturated atoms introduced by the surface nanostructure. Moreover, the presence of surface nanostructures results in the adsorption of more asphalt chains, strengthening the interlocking effect. By increasing surface roughness, the interfacial failure mode under tensile stress gradually transfers from adhesive failure to cohesive failure. In light of the aforementioned observation, a schematic illustration of the bond strength along with surface roughness was obtained.

This study was conceived to develop the optimum mix for cement-stabilized bamboo fiber–reinforced clay bricks for low-cost farm settlements. The concept was concerned with the provision of houses in rural areas as incentive to encourage youth participation in farming activities and at the same time reduce rural–urban migration. The input factors for the composite development were bamboo fiber (BF), sand proportion, and cement dosage. Mixture of the input materials were carried out per experimental runs obtained by the Box-Behnken approach. Responses analyzed were apparent porosity, water absorption, and compressive and flexural strengths. The results showed that the responses were significantly affected by the experimental factors. The developed models for each response were certified statistically fit for response prediction. Also, response surface plots revealed that each response was dependent on the interactive patterns between the input factors. An optimization procedure was carried out, and the optimum mix was 0.99%–1% by weight BF, 27.24% by weight sand and 24.82% by weight cement, yielding 13.78%, 12.66%, 8.86 MPa, and 1.98 MPa for apparent porosity, water absorption, compressive strength, and flexural strength respectively. A confirmation experiment carried out yielded error < 5% for each of the parameters, validating the models. Therefore, the optimum mix can be used in the development of low-cost clay bricks with the purpose of building low-cost farm estates for improvement of agricultural activities for the purpose of engaging more youth in farming.

Porous asphalt pavement have been widely employed for various functions. However, due to its large voids and small contact area between particles, the reflective cracks results from semirigid base layer shrinkage cracking and buttom-up fatigue cracking are easy to occur, under long-term multifield coupling influenced by load, temperature, water, light and other factors of natural conditions. Therefore, improving asphalt crack resistance is a key issue. Using an overlay test with a high-viscosity porous asphalt mixture (HPA-13) as a control object, a multi-index evaluation was performed to test the anticracking performance of an epoxy porous asphalt mixture (EPA-13) under different temperatures and aging conditions. Results showed that epoxy asphalt binders can considerably improve the anticracking performance of porous asphalt mixtures; under the standard condition of 25°C, the number of loading cycles ($N$) of EPA-13 was 7.5 times higher than that of HPA-13. However, EPA-13 was greatly affected by low temperature and aging conditions; in particular, under the low temperature condition of 10°C, $N$ decreased by 93.5%. In the multi-index evaluation of crack resistance, the gray correlation degree of each evaluation index followed the order of the allowable failure times with ($J$) > cumulative fracture energy ($G$) > displacement at the maximum load of the first cycle ($L_F$) > fracture energy of the first cycle ($G_F$) > average fracture energy ($G^{*}$) > maximum load of the first cycle ($F$). It is recommended to use $N$, $J$, and $G$ to evaluate the crack resistance of porous asphalt mixtures.

The primary objective of this study was to investigate the constitutive relations and damage properties of concrete in complex stress states with different stress paths under high pressure. Monotonic hydrostatic pressure, cyclic hydrostatic pressure, uniaxial stress with lateral confinement, and multiaxial proportional stresses were applied in tests. High stresses reaching up to 500 MPa under the aforementioned four loading paths were achieved through a true triaxial testing system. A series of uniaxial tests were carried out after triaxial tests to evaluate the damage degree of concrete. Microscopic observations were also made to visualize the changes of microstructures of the specimen before and after the triaxial compressive tests. The most important finding of this study is that concrete suffers damage even before it is loaded to the ultimate strength under multiaxial compressive stress states, different from the commonly used concrete models that assume the concrete damage only occurs in the strain softening stage. This means the conventional deviatoric strength theory alone may not be sufficient to model concrete material damage under complex stress states, instead the combined effect of hydrostatic and deviatoric stress should be considered together in predicting the concrete material damage. This study also found cyclic hydrostatic loads could induce more severe damage to concrete than monotonic hydrostatic loads with the same stress amplitude.

In this work, the feasibility of incorporating different industrial wastes in the production of ultrahigh-performance fiber-reinforced concrete (UHPFRC) is investigated. Five different blends of UHPFRC were produced, partially replacing coarse sand with copper slag (CS) and cement and/or silica fume with ground-granulated blast-furnace slag (GGBFS). The replacement percentages ranged between 50% and 60% in all cases. This study focuses on the development of an UHPFRC using waste without special treatments and available in the Andalusia, Spain, market to reduce the cost of concrete. An extensive experimental program was carried out to analyze workability and mechanical properties. Results obtained showed a significant reduction in environmental and economic cost without loss in the UHPFRC performance. One of the main conclusions was that partial replacement of GGBFS increased the compressive and flexural strength at later ages (matching the traditional UHPFRC at 28 days) even when a small decrease was observed at early ages. In addition, the partial replacement of coarse sand by CS resulted in a UHPFRC with a compressive and flexural strength similar to the traditional UHPFRC at different ages.

To optimize the rheological properties of warm-mix asphalt and analyze its ultraviolet (UV) aging behaviors, organic montmorillonite was selected to modify the Sasobit warm-mix asphalt. 3% Sasobit was added into the hot mix asphalt to prepare warm-mix asphalt; and then, three different contents of organic montmorillonite (1%, 2%, and 3%) were added to modify the warm-mix asphalt compositely. Subsequently, the road performance and UV aging behaviors of prepared asphalt were evaluated by some rheological indicators; and then, the modification mechanism was investigated by micro testing methods, including Fourier transform infrared spectroscopy (FTIR) test and Fluorescent microscope (FM) test. Results show that with the introduction of Sasobit, construction workability and high-temperature properties of hot mix asphalt were improved, while its fatigue performance and low-temperature properties were decreased. Fortunately, adding organic montmorillonite into the prepared warm-mix asphalt can significantly optimize its fatigue performance while having little influence on its low-temperature properties. UV aging test results show that $DSRFn$ is the most sensitive indicator to characterize the UV aging behaviors of asphalt. Meanwhile, $DSRFn$ aging indexes of warm-mix asphalt and those with 1%–3% organic montmorillonite were reduced by 28.88%, 46.41%, 48.55%, and 46.15%, respectively, compared with that of hot mix asphalt, indicating that Sasobit warm-mix asphalt has superior aging resistance than hot mix asphalt and that the addition of organic montmorillonite can further improve this ability. Microscope test results confirm that the intercalated structure or exfoliated structure may be formed in the asphalt binders, thereby enhancing the rheological properties. In accordance with the presented results, it is recommended that the optimum content of montmorillonite is 2%, which can promote the prepared asphalt samples to obtain excellent rheological properties.

In this study, the usability of calcium carbonate-polyethylene compound (PEC) was investigated as an alternative to styrene-butadiene-styrene (SBS), which is one of the most used additives in bitumen modification. The softening point, penetration, rotational viscosity, bending beam rheometer, dynamic shear rheometer, multiple stress creep recovery, and fourier transform infrared spectroscopy tests were applied to the bituminous binders. To reveal the effectiveness of PEC modification, the PEC and SBS modified binders were compared in terms of performance and cost. As a result, with the use of PEC in bitumen, penetration decreased, whereas softening point, viscosity, and rutting parameters increased. PEC also improved the low-temperature performance of pure bitumen. PEC modification offered low-stress sensitivity and made the binder suitable for heavy traffic conditions. When all experiments were evaluated together, it was determined that 9% PEC modification gave similar or better results than 4% SBS modification in terms of performance and cost. Consequently, it was revealed that PEC can be used as a good alternative to SBS in bitumen modification.

A massive amount of recycled asphalt pavement (RAP) is produced in road construction and maintenance, and using rejuvenators to rejuvenate RAP can have a significant economic benefit. At present, a biorejuvenator is used to rejuvenate RAP to alleviate the problem of low efficiency of the mineral oil rejuvenator. But the oxidation resistance of bio-oil is poor, it is easy to develop a wax deposit at low temperature, and the cost is much higher than mineral oil. To avoid these adverse effects of the biorejuvenator, a new mineral oil rejuvenator was developed by response surface methodology and solved the problem of low efficiency of mineral oil rejuvenator simultaneously. The rejuvenating effect of rejuvenator on aged asphalt was studied by a force ductility test (FDT), multiple stress creep and recovery (MSCR) test, Fourier transform infrared spectroscopy (FTIR) test, dynamic shear rheological test (DSR), antiaging performance test, and diffusion test. The results showed that the self-developed rejuvenator can restore the traditional physical properties of aged asphalt. In comparison with other commonly used rejuvenators, the self-developed rejuvenator had a significant antiaging performance and diffusion performance. Compared with aged asphalt, the chemical structure of recycled asphalt had not significantly changed, the aged asphalt was only diluted and dissolved by the rejuvenator. The addition of the rejuvenator improved the rheological properties, but was not conducive to high-temperature deformation resistance. The deformation recovery rate of recycled asphalt was positively correlated with the addition of the rejuvenator, and it showed excellent elastic deformation behavior under low stress. A comparison study indicated that a reasonable dosage of rejuvenator can restore the physical properties to the same approximate level as virgin asphalt. The recommended optimum dosage of the rejuvenator developed in this study was 5%. Finally, the prediction equation model of performance index and the dosage of rejuvenator was established, and the effect of the dosage of rejuvenator on the performance of recycled asphalt was quantitatively analyzed.

Today, high-viscosity modified asphalt (HVMA) is widely used in drainage asphalt pavements. However, due to its high construction temperature, HVMA is prone to thermal oxidative aging, which reduces its life cycle and increases the maintenance costs of asphalt pavements. In this study, the effects of warm-mix additives on the physical, rheological and chemical properties of HVMA were studied to determine optimum warm-mix conditions. First, the effects of warm-mix technologies (foam warm mix, Sasobit, Evotherm, and GLWBR at 3%, 3%, 0.8%, and 0.8%, respectively) on the physical and rheological properties of HVMA were studied. Then, two aging methods [thin film oven test (TFOT) and pressure aging vessel (PAV)] were applied to simulate the short-term and long-term thermal oxidation processes of HVMA and evaluate the influences of different warm-mix technologies on HVMA aging. The results showed that the four warm-mix technologies, especially foam warm mix and Sasobit, reduced the construction temperature of HVMA. In addition, warm-mix technologies also improved the high-temperature rheological properties of HVMA; however, they had adverse effects on the low-temperature cracking resistance of asphalt. Based on asphalt aging index fluctuations, it was evident that warm-mix technology was not conducive to the antiaging performance of HVMA, and foam warm mix had the weakest influence on the antiaging performance of high-viscosity asphalts. Furthermore, according to the results of an analysis of the carbonyl changes in aging asphalts, asphalt aging index can be applied to predicting the degree of aging of warm-mix HVMA.

The application of polypropylene (PP) to asphalt pavement construction, as one of the measures to dispose white waste, has suffered from many challenges. Meanwhile, the emerging nanomaterials for asphalt pavements has exhibited great potential and drawn the attention of many researchers. Therefore, in this study, the novel graphene/carbon black nanocomposite (GC) was selected to improve this dilemma by compounding with PP in different approaches. First, three kinds of asphalt binders incorporated with PP and GC were prepared by mechanical mixing. Subsequently, the temperature sweep, frequency sweep, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) have been performed to evaluate the rheological properties of PP/GC composite-modified asphalt binders. In addition, the low-temperature tensile fracture behaviors of the different modified asphalt were investigated through the force-ductility testing machine (FDTM). Moreover, the microstructure and chemical composition of the different modified asphalt binders were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The experimental results confirmed that PP and GC synergistically increased the mechanical strength and high-temperature rutting resistance of the asphalt binder. As a result, the incorporation of GC significantly improved the stress sensitivity of the PP/CG composite-modified asphalt under repeated loading. Wherein, the polypropylene/GC masterbatch (PGC) modified asphalt, prepared by premixing process, exhibited superior fatigue-damage tolerance and low-temperature cracking resistance. SEM and FT-IR data revealed that the addition of GC facilitated the formation of a strong network structure of PP in the asphalt matrix by physical coblending. This study may cast some light on the application of PP and GC for asphalt modification.

Copper slag (CS) is a by-product generated during the process of copper metal smelting. The influence of CS on the mechanical performance, hydrate assemblage, and mechanism of the cementitious system was investigated by multiple methodologies to accelerate the sustainable development of the copper industries. The results revealed that adding 10% by weight of CS was beneficial to developing compressive strength. However, the strength decreased significantly if too much CS was incorporated. This adverse effect can be mitigated by prolonging the curing age. Besides, the evolution of mechanical performance was explained by multiple microscopic studies. More ettringite (AFt) and monosulfate (AFm) were formed in the paste containing 10% by weight of CS at 28 days, which filled the space and improved the strength. For the paste containing 30% by weight of CS, the backscattered electron images suggested that more than 60% of incorporated CS participated in the hydration at 200 days and developed an additional C─ (A)─ S─ H with a higher atomic ratio of Fe/Si and Al/Si, resulting in a dramatic improvement in compressive strength. Finally, the hydration mechanism of CS in the cementitious system was established based on the dissolution test combined with the theory of cement hydration.

Usual-temperature synthetic pitch (USP) is a modifier that can efficiently reduce the mixing temperature and improve the overall engineering properties of warm-mix asphalts; however, few studies are reported for its application in cold patch asphalt. In this article, cutback asphalts were prepared with USP, bitumen, biodiesel, an antistripping agent, and a tackifier. Referring to a series of single-factor analyses on the cutback asphalt viscosity, the reasonable dosage ranges for the USP, antistripping agent, and tackifier were first determined. Based on these, a four-factor and four-level orthogonal test plan was proposed to guide the selection of some potential appropriate mix design schemes. The recommended mix design schemes were then screened out by successively examining the physical properties, adhesion, workability, Marshall stability, high- and low-temperature rheological properties, and compatibility. Two design schemes with mass proportions of 6:18:0.3:6 (Scheme 1) and 6:20:0.4:2 (Scheme 2) for USP, diluent, antistripping agent, and tackifier, respectively, were finally selected. The engineering properties of the prepared specimens meet the standard requirements. Compared with Scheme 1, Scheme 2 presents better Marshall stability and high- and low-temperature performance. The proposed mix design schemes can guide the preparation of USP-modified cold patch asphalts and promote their application in practice.

In this study, bond failure tests were carried out on eight beam anchorage specimens after accelerated corrosion, and the crack widths on the concrete surface and the nonuniform corrosion characteristics of the reinforcing bars were analyzed. The testing results show that the pitting volume and maximum crack width on the concrete surface both increase exponentially as the mass loss rate increases. According to the testing results, the pitting coefficient and uniform coefficient are introduced to reflect the effect of the pitting corrosion and uniform corrosion, respectively, on the bond strength, and as these two coefficients increase, the bond strength greatly decreases. In addition, based on the maximum crack width on the concrete surface, bond strength and peak slip models are developed, and a bond stress–slip model of the nonuniformly corroded reinforcing bar is proposed, combined with that of uncorroded reinforcing bar. It is proved that the proposed models provide good predictions.

A series of laboratory tests including flow consistency, viscosity, one-dimensional compression, and permeability were conducted on the fiber-reinforced cemented waste slurries obtained from a construction site to evaluate the fiber efficiency on the flow behaviors and compressibility-permeability properties. Results indicated that the fiber efficiency did not increase with increasing fiber length in this study because the waste slurry was composed of high montmorillonite and illite contents in this study. Fiber had a limited effect on the flow behaviors of the slurry mixture because the slurry reinforced by short fibers exhibited dispersive soil particles and fibers in the suspension. Longer fibers can bridge the soil particles and contribute to an aggregated fiber–soil matrix. A perfect fiber network with soil particles could be obtained at fiber content of 0.8%, where a well-fitted trendline can be obtained between slump flow and viscosity with high fiber efficiency. The cement content was found to dominate the compressibility of soil at higher water content. Fiber lengths in the range from 3 to 8 mm exhibited effective fiber reinforcement in terms of hydraulic conductivity. It is recommended to reinforce the waste slurry at fiber content of 0.8% with the optimal fiber length between 6 and 8 mm for the cemented waste slurry in this study.

In this study, the mechanical properties and microscopic structure of concretes containing natural coarse aggregates (NCAs), recycled concrete aggregates (RCAs), and recycled asphalt pavement (RAP) aggregates are investigated. The replacement percentage of NCA with RCA and RAP was equal to 0%, 50%, and 100%. The study results showed that using RCA and RAP decreased the concrete’s mechanical properties, including a 14%–30% reduction in compressive strength and a 43%–53% loss in the modulus of elasticity. The target compressive strength can be obtained if a modified mix design is used, but the modulus of elasticity is still reduced. Also, the stress-strain curves for the uniaxial compressive test on RCA and RAP concretes showed that the strain at the maximum stress, ${\epsilon }_0$, increased by 22% and 27% for RCA and RAP concretes, respectively, in comparison with the NCA concrete. In addition, it can be concluded that the ascending branch of the stress-strain curves had a lower slope for both RCA and RAP concretes, and the ultimate strain reached, ${\epsilon }_{cu}$, for RCA concrete decreased and for RAP concrete was up to two times higher than the NCA concrete. The toughness of specimens showed that RCA concretes had higher brittleness, while RAP concretes had higher toughness than NCA concretes. Also, analyzing the microscopic structures of specimens using scanning electron microscopy images showed that the interfacial transition zone is remarkably affected when RCA and RAP are utilized, which was the main reason for changing the behavior of RCA and RAP concretes.

In this study, the effect of multiwall carbon nanotubes (MWCNTs) on various properties of a fired clay brick was investigated and subsequently compared with other kinds of bricks. MWCNT doped bricks and traditional bricks were prepared in laboratory conditions and commercially available bricks were obtained from a nearby manufacturer. Each group of bricks were subjected to various tests such as visual examination, dimension tolerance test, efflorescence test, water absorption test, impact resistance test, soundness test, hardness test, structure test, compressive strength test, and scanning electron microscopy (SEM) imaging. An extensive characterization of soil, water, and MWCNT was carried out. X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) were done to characterize soil in addition to basic consistency limit tests. MWCNT was characterized using XRD, SEM-EDS, and Fourier transform infrared spectroscopy (FTIR). Soil passing through a 425-μm sieve was used to manufacture MWCNT doped brick (0.01% of water by weight) and traditional bricks. The compressive strength of MWCNT doped bricks was 53.9% and 45.52% more as compared to commercially available and traditional bricks. An adequate reduction in water absorption was recorded when compared with traditional and commercially available bricks. Economic analysis was also carried out, which marked an increase of $0.0134 per brick in the manufacturing of MWCNT doped bricks.

Rejuvenators as environmentally-friendly materials can restore the properties of aged bitumen physically or chemically. A proper dosage of a rejuvenator can achieve the desired properties of bitumen. Thus, this study proposed a method, the empirical double-logarithmic formula and calibration, based on physical properties to determine the appropriate rejuvenator dosage within aged bitumen for the desired properties. Three different rejuvenators were selected to restore recycled/aged bitumen extracted from reclaimed asphalt pavement (RAP) to a similar level as that of neat bitumen with penetration of 70–100 (reference bitumen). The initial estimation of rejuvenator dosage was determined by the viscosity of rejuvenators and recycled bitumen using an empirical double-logarithmic formula; the penetration and softening point of one rejuvenated bitumen were applied to calibrate the rejuvenator dosage within recycled bitumen. After the determination of the rejuvenator portion within recycled bitumen, rejuvenated bitumen was compared with reference bitumen regarding penetration, softening point, Fraass breaking point, complex modulus, phase angle, and PG upper temperature; the properties of rejuvenated bitumen over aging degree (short-term aging and long-term aging) were also compared with that of reference bitumen using softening point, Fraass breaking point, complex modulus, phase angle, rutting factor, and fatigue factor. It was found that this method can accurately calculate the rejuvenator dosage in recycled bitumen with a few available physical parameters; the rejuvenated bitumen showed similar equivalent properties as reference bitumen, and the three rejuvenators have a lasting effect on recycled bitumen. Therefore, this method is recommended for calculating the rejuvenator dosage of recycled bitumen due to its convenience and less demand for tests.

A chloride binding model consisting of physical adsorption and chemical ion exchange was proposed. Chemical binding was quantified based on the thermodynamic equilibrium of the relevant hydrated phases while physical adsorption was modeled by a Freundlich-type isotherm. Comparison of the proposed model results with experimental chloride binding data in the literature was found to be satisfactory. The implementation of the model in the Nernst-Planck-Poisson (NPP) reactive transport NPP model accurately predicted the free and total chloride concentration profiles in the analyzed cement paste and concrete specimens. The results of the traditional chloride diffusion model based on Fick’s second law were compared with the NPP model and it was discovered that estimating the apparent diffusion coefficient by a well-established formula and using it in Fick’s model gave a significantly erroneous estimation of the free and total chloride profiles compared to the corresponding experimental data. Finally, in the NPP model it was determined that chloride transport by diffusion was limited to the region near the exposed surface while in the concrete bulk it was dominated by electromigration.

The physical and chemical properties of three kinds of laminations relative to the bonding properties of three-layer hybrid cross-laminated timber (CLT) were studied. The density of the parallel layer lamination of CLT was $640.47\pm 61.85\mathrm{kg}/{\mathrm{m}}^3$, and the perpendicular layer laminations for CLT larch wood, poplar, and oriented strand board (OSB) were $392.51\pm 40.14$, $343.73\pm 17.16$, and $384.41\pm 12.93\mathrm{kg}/{\mathrm{m}}^3$. Block shear bond strength (BBS), wood failure percentage (WFP), and delamination rate (DR) of the hybrid CLT specimens were also determined. The results showed that the three kinds of hybrid CLT prepared with polyurethane (PUR) adhesive had good bonding properties under 1.2 MPa of bonding pressure. The BBS values of CLT with larch wood, poplar hybrid, and OSB hybrid were 2.32, 2.41, and 1.98 MPa, respectively; furthermore, their WFPs were all greater than 80%, and their DRs were 9.32%, 0.37%, and 0.11%, respectively. Regarding the relationship between perpendicular layer material properties and bonding properties, analysis revealed that delamination performance was strongly correlated with pH, buffer capacity, and the surface free energy of the perpendicular layer, whereas the WFP and BBS values had a strong correlation with pH and buffer capacity. Density was determined to be unrelated to bonding performance in the CLT prepared in this experiment. Microscopic analysis of the bonding line proves that the PUR adhesive can effectively penetrate into three different laminations under a bonding pressure of 1.2 MPa and form enough nails to ensure bonding strength.

The rheological properties and performance of binders are often explained using the chemical composition of binders. The present study explored the effect of SARA fractions (saturates, aromatics, resins, and asphaltenes) and colloidal stability on the rheological properties of ethylene vinyl acetate (EVA) modified binders. The effect of short-term and long-term aging on SARA fractions and colloidal stability of EVA-modified binders was also examined. The base bitumen (VG40) was modified with EVA-18 polymer (1% to 7%, varied with an increment of 1%) to produce EVA polymer-modified binders. Penetration, softening point, elastic recovery, complex shear modulus (G*), phase angle ($\delta$), Superpave rutting parameter (${\mathit{G}}^{*}/\sin \delta$), temperature and frequency sensitivities of the Superpave rutting parameter, and multiple stress creep and recovery (MSCR) test parameters of the binders were determined and correlated with the polar components (resins and asphaltenes) of EVA-modified binders. The elastic recovery, percent recovery measured in the MSCR test, temperature and frequency sensitivities of Superpave rutting parameter, and fatigue lives of binders estimated from the linear amplitude sweep (LAS) test were correlated with the colloidal stability index of binders. The temperature and frequency sensitivity of the binders decreased with EVA polymer modification. Colloidal stability of bitumen increased with increased content of the EVA polymer modifier in base binder VG40. The effect of aging demonstrated a decrease in the colloidal stability of bitumen. The polar fractions (resins and asphaltenes) of binders were found to correlate well with (1) different consistency/stiffness parameters such as penetration, softening point, and complex modulus (G*); (2) elastic response represented by elastic recovery, phase angle, and percent recovery measured in the MSCR test; (3) permanent deformation (rutting) resistance measured by ${\mathit{G}}^{*}/\sin \delta$ and nonrecoverable creep compliance (Jnr) measured in the MSCR test; and (4) temperature and frequency sensitivities of Superpave rutting parameter. The correlations obtained for resins are observed to be better than those developed with asphaltenes. Colloidal stability index is found to correlate well with elastic recovery, percent recovery measured in the MSCR test, temperature and frequency sensitivities of the Superpave rutting parameter, and fatigue lives of binders estimated from the LAS test.

High-performance concrete (HPC) is known as a material of high strength and high durability. This investigation is focused on the influence of the use of rubber waste tires on the physical, mechanical, and durability characteristics of HPC. Tire-rubber residues were used in the contents of concrete at 7.5%, 15%, and 30% in relation to the sand mass. Eleven mixtures were tested in the experimental program. To improve the mechanical strength of rubberized concrete, superficial treatment of the rubber was carried out with calcium carbonate and silica fume. From the results obtained, the following are notable: reduction of the area between the rubber and the cement paste, increased resistance to compression and traction of the concrete with treated rubber, and lower water absorption value and void index, evidencing the benefit of this type of surface treatment. Regarding the durability, electrical resistivity, chloride ion penetration, and carbonation tests, high-strength rubberized concrete shows the potential to be used in aggressive environments.

The durability of concrete structures that have been in service for a long time under the coupled action of stray current and salt-brine environment has become increasingly important. Because of the excellent mechanical properties of steel fiber–reinforced concrete (SFRC), erosion experiments of SFRC were carried out to study issues such as the erosion depth, strength loss, ion migration, and microscopic morphology changes of SFRC under the action of stray current in a salt-brine environment. The color test and compressive strength were used to characterize the penetration depth of chloride ions and the strength loss of concrete, respectively. The titration method was used to detect the chloride and sulfate ion content. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to characterize the microscopic morphology and composition; the finite-element method and discrete-element method were used to explain further and verify the mechanism of SFRC corrosion. This research showed under the action of an electric field, chloride ions transport faster than sulfate ions. The strength loss of SFRC is caused mainly by the erosion and expansion of steel fibers. Products such as gypsum and ettringite are generated only in the cathode area, which also reduces the strength of SFRC to a certain extent.

The study of corroded metal materials in building structures is the basis for analyzing and evaluating the residual bearing capacities of existing structures. In this study, the corrosion behaviors and residual properties of two types of low-alloy steel and a 6061-T6 aluminum alloy were investigated under different corrosion times in an acetic acid spray environment. Scanning electron microscopy (SEM) and three-dimensional (3D) laser scanning were performed. Uniaxial tensile tests were conducted on the three metal materials with different corrosion levels. The test results showed that the corrosion rate of the aluminum alloy increased with corrosion time, and the corrosion rates of the low-alloy steels decreased with corrosion time. The pitting of the low-alloy steels was shallow and wide; the pitting of the 6061-T6 aluminum alloy was narrow and deep. Characteristic parameters are proposed for the pitting morphologies of the low-alloy steels. The corrosion depths of the pitting were more inclined toward a generalized extreme value distribution. Simplified models and evaluation indexes were defined for the stress-strain relationships of the three materials. The two types of low-alloy steel were reduced to 60% of their original engineering strength, and the engineering strength of the aluminum alloy was reduced to 85%. Methods are proposed for evaluating the residual mechanical properties of different structural materials with different corrosion behaviors.

Flue gas desulphurization (FGD) gypsum is a kind of industrial solid waste containing impurities (i.e., heavy metal ions ${\mathrm{Zn}}^{2+}$ and ${\mathrm{Ni}}^{2+}$), which may lead to threats to the ecological environment and public health. To safely use the FGD gypsum, this study investigated the mechanical strength, releasing property of ${\mathrm{SO}}_4^{2\text{-}}$ and leachability of heavy metal ions of a series of FGD gypsum (40%) based mortar with various cement to slag ratios. The hydration process, pore structure, and morphology of the sample were then characterized and analyzed by isothermal calorimetry, ${}^1\mathrm{H}$ low-field nuclear magnetic resonance (NMR), and scanning electron microscope with energy dispersive X-Ray analysis (SEM-EDx). It was found that the highest mechanical strength could be obtained when the C/S ratio was 1:5, and the decrease of C/S ratios from 4:2 to 1:5 leads to less ${\mathrm{SO}}_4^{2\text{-}}$ releasing from the mortar. The heavy metal leachability of the mortars is lower than that of the limitation of solid waste stipulated by the specification of GB5085.3-2007, and less of the heavy metal are leached from the sample as the C/S ratios decrease. The heat flow for the paste sample with 40% of FGD gypsum was delayed as the cement to slag ratio decreased from 5:1 to 2:4. In addition, the released amount of ${\mathrm{Zn}}^{2+}$ ions linearly decreases with the pore size of gel pores and capillary pores but increases with the pore size of macropores, and the ettringite in the paste exhibits the transformation from the needle to the clubbed shape when smaller cement to slag ratio was used. This work helps to understand how to reduce the heavy metals leachability of FGD gypsum from cementitious material and provides baseline for safely using the FGD gypsum for the preparation of building materials.

Recycling of phosphate tailings (PT) in cement production can reduce the amount of this solid waste and its consequent pollution. This paper used high content of calcined PT as an alternative to light-burned magnesia to prepare magnesium oxysulfate (MOS) cement. Thermal decomposition properties of PT at calcination temperature of 600°C–900°C were studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compressive strength, XRD, Fourier-transform infrared spectroscopy (FT-IR), and SEM were conducted to study the effects of the calcination temperature of PT (600°C–800°C) and the dosage of calcined PT (50%–100%) on the strength development and hydration mechanism of MOS cement. Results showed that the main component of PT, dolomite, partially decomposed into magnesium calcite, periclase, and calcite at 700°C; decomposed further into calcite, periclase, and lime at 800°C; and finally decomposed into lime and periclase at 900°C. The periclase sourced from calcined PT reacted with the MOS system to form brucite and $5{\mathrm{Mg}(\mathrm{OH})}_2{·\mathrm{MgSO}}_4{·7\mathrm{H}}_2\mathrm{O}$ (517 phase). Gypsum also was formed in the reaction. Brucite, 517 phase, and gypsum worked with the unreacted PT to build the structure and provide the source of strength. MOS paste prepared with 60% PT calcined at 700°C had the highest compressive strength, 63 MPa, at 28 days of all the mixtures. The paste prepared with 50% PT calcined at 700°C had the highest strength retention value, about 68%, after 56 days of water immersion. This study provides a method for the efficient use of PT by incorporating it into MOS cement after calcination.

This paper describes an experimental investigation into the properties of ambient cured one-part alkali-activated materials (AAMs). Mixes incorporating waste glass (WG), ground granulated blast-furnace slag (GGBS), fly ash (FA), and sodium metasilicate pentahydrate were assessed in terms of workability, water absorption, physical and mechanical properties, and environmental impact. Microstructure investigations on selected mixes were also carried out. The GGBS-only mixes had low workability and high early strength that declined over time, whereas FA-only mixes had virtually no strength. Equal proportions of WG and GGBS provided similar fresh properties to those of GGBS mixes yet comparatively higher strengths and a positive strength time gradient. Mixes incorporating 50% GGBS, 25% FA, and 25% WG had the best balance between mechanical properties and workability, with compressive strengths above 40 MPa suitable for structural applications. An increase in activator content from 14% to 21% enhanced the strengths by 39.1%–54.6%. The flexural strengths were largely proportional to the compressive strengths, the water absorption properties were like those of cement mortars, and dry densities depended on the proportions of the constituent binders. Finally, the AAM mixes had between 53% and 72% less embodied carbon compared with a corresponding cement mortar.

In the process of making steel, around 10%–15% of slag is produced. In the last decade, several studies have proposed the application of steel slag as geomaterial. However, its potential application as a subgrade material in river embankments (artificial banks to protect the adjacent land against flooding) has been unexplored hitherto. This study assessed the geotechnical properties of steel slag, riverbank sand, and their various blends. First, the index properties, microstructure, and mineralogy of the slag and sand were evaluated. Then, the strength properties of slag and sand were assessed via the direct shear test at different relative densities and blends. The hydraulic conductivities of the proposed blends were also assessed, and the pH of their effluent discharge was evaluated. The optimal slag-sand mix for strength was found to be $1:7$ (slag content 12.5%), which improved the friction angle of sand from 27° to 37°. The hydraulic conductivities of all the proposed blends were observed to be in the range of ${10}^{-5}\mathrm{m}/\mathrm{s}$, equivalent to that of riverbank sand. Hyperalkalinity of the leachate was observed during the hydraulic conductivity tests. The findings from the present study reveal that substituting a small proportion of riverbank sand with slag improves its strength considerably. However, there are geo-environmental concerns over its application in river embankments due to the hyperalkalinity of the effluent.