Journal of Materials in Civil Engineering

Temperature field analysis is the precondition of studying the heat and mass transfer and durability of a concrete building; thermal conductivity is a key parameter that affects the distribution of the temperature field of concrete. Through reasonable assumptions and simplifications, the relationship between the micro-microscopic composition of concrete and its macroscopic thermal conductivity is established, and a multiscale theoretical model of thermal conductivity considering the influence of interface transition zone (ITZ) is proposed. The model can predict the thermal conductivities of concrete and its components at an arbitrary saturation. Subsequently, the influence of saturation, water-cement ratio, volume fraction and type of coarse aggregate, and sand ratio is researched. Moreover, according to the prediction results of the proposed model, a mesoscale simulation of the concrete temperature field is carried out. The results demonstrate that the presence of aggregate and ITZ leads to the isotherm deflection and abruption at the junction of the phases. Meanwhile, the heat flux density at the corners of the polygonal aggregate is significantly higher than at other positions; the phenomenon, first named the “corner effect” in the research, causes the temperature field distribution of concrete containing polygonal aggregates to be more uneven than that of circular and elliptical aggregates, and it is more likely to produce temperature-induced cracks. The research helps explain the influence mechanism of material components on the thermal conductivity of concrete and the distribution of its temperature field and provides a basis for the fine simulation of concrete thermal crack growth and creep at variable temperatures.

The design service life of 100 years is an essential requirement for modern corrugated high-density polyethylene (HDPE) pipe grades used in road drainage systems. Whether the recycled pipes guarantee performance and can be substituted for virgin pipes is also an issue in the process of being clarified. Furthermore, the variety of area characteristics and the specific serving conditions of the pipes significantly affect pipe service life. Therefore, the University of Sherbrooke and the Quebec Ministry of Transportation (MTQ) recently collaborated to conduct a project on the long-term performance of recycled and virgin HDPE pipes supplied by local manufacturers. This project included investigating stress-crack resistance (SCR) and predicting the service life of new corrugated HDPE pipes fabricated by Canadian manufacturers as well as corrugated HDPE pipes in field service in Quebec under natural aging. Notched specimens were cut directly from the HDPE pipe liner to evaluate their SCR. In addition, four exposure conditions were used: freeze–thaw cycles and exposure to saline, acidic, and alkaline solutions to predict the remaining lifetime of pipes. The SCR was investigated with the Florida test method in water at 3.10 MPa (450 psi) and 80°C, 4.48 MPa (650 psi) and 80°C, and 4.48 MPa and 70°C in compliance with FM 5-573. The data points at elevated temperatures were then shifted to predict the service life of pipes at lower service conditions with the Popelar’s shift method (PSM) and the rate process method (RPM), both of which are extrapolation methods. The results show that, before immersion in different solutions, the recycled could guarantee 100 years of service life as virgin pipes under service conditions of 10°C and 3.45 MPa (500 psi). After immersion, the decrease in SCR was related to the two steps of elevated temperature in the conditioned test and the Florida test, along with the harsh environment of the conditioned test. Moreover, RPM proved better than PSM, because the latter yielded nearly scattered, nonlinear data points.

A standard method for the mix design of pervious concrete (PC) is not available. This study provides a novel framework, based on film thickness index (FTI), for the mix design of PC. The developed methodology is tested and validated on pervious paver blocks (PPB), fabricated at varying FTI and water-cement ($\mathrm{w}/\mathrm{c}$) ratios. Laboratory testings and statistical analysis are performed to understand the effect of FTI and $\mathrm{w}/\mathrm{c}$ ratio on various properties of PPB. A procedure has been proposed to select the optimum FTI and $w/c$ ratio to achieve the targeted desired properties. An increase in FTI reduces the porosity and infiltration rate (IR) while increases the compressive strength and abrasion resistance. Statistical inferences indicate that FTI significantly affects the porosity, IR, and skid resistance of PPB. For the gradation used in this study, PPB fabricated with 0.4 mm FTI at a $0.3\mathrm{w}/\mathrm{c}$ ratio shows a good balance between the functional, strength, and pore characteristics. The output of the present study reveals that FTI-based methodology can be effectively adopted for the mix design of PPB, or any other form of PC. More studies are required to appreciate the applicability of the proposed framework.

In this study, sodium hypophosphite (SHP) was used to modify polycarboxylate superplasticizer (P-PCE), and the properties of P-PCE on $\beta$-calcium sulfate hemihydrate ($\beta \text{-}\mathrm{HH}$) were systematically investigated. The results showed that P-PCE could exhibit better fluidity and more retarding effect compared with the conventional polycarboxylate superplasticizer (C-PCE). The reason might be ascribed to the higher adsorption ability of P-PCE because of its stronger complexing capacity with calcium ion, which was induced by the phosphonate and phosphinate groups in the P-PCE molecule. Additionally, PCE played an important function in hindering the calcium sulfate dehydrate (DH) crystallization instead of the dissolution of $\beta \text{-}\mathrm{HH}$, resulting in the retarding effect. This new type of PCE can show great potential in gypsum engineering.

The present study envisaged the development of a novel admixture based on the composites of amino trimethylene phosphonic acid and boric acid (AB) that exhibited an intense inhibition of the hydration effects for Portland cement. The study was aimed to lay a solid foundation for the utilization of AB in large volume concrete by reducing the temperature control measures. The setting time at different temperatures, and the compressive strength of the cement pastes containing AB were examined. The hydration characteristics of the Portland cement containing AB were investigated using isothermal calorimetry measurements, X-ray diffraction, thermogravimetric analysis, Zeta potential, and scanning electron microscope. The results showed that the fitting curves for the setting time of amino trimethylene phosphonic-based material (ATMP) exhibited a linear relation in the concentration range of 0.02% to 0.40%. However, the fitting curves for the setting time of AB presented an exponential relation in the concentration range of 0.02% to 0.20%, and exhibited a linear relation at the addition dosages from 0.20% to 0.40%. It was observed that, at 0.40% concentration, the initial and final setting times of the AB sample was longer by 1,954 min and 3,767 min, respectively, than those of the ATMP sample. ATMP and AB exhibited intensive retarding effects at higher temperatures, and the temperature adaptability of both ATMP and AB was excellent. The reduction in the cumulative hydration heat and heat evolution rate effect in the Portland cement was significantly higher in AB than ATMP. AB substantially inhibited the formation of ${\mathrm{Ca}(\mathrm{OH})}_2$ (CH) and ettringite (AFt) than ATMP. Thus, the inhibition of cement hydration by AB was clearly superior to that of ATMP, which could be attributed to the inhibition of ${\mathrm{C}}_3\mathrm{S}$ and ${\mathrm{C}}_3\mathrm{A}$ hydration by AB.

Supersulfated cement (SSC) consists essentially of blast-furnace slag and calcium sulfate. It can be considered an alternative to Portland cement because its production minimizes the environmental impacts caused by the exploration of raw materials and ${\mathrm{CO}}_2$ emissions. However, the long-term durability of SSC still needs to be studied. In this article, the influence of the composition of the SSC in the attack by sodium and magnesium sulfates was analyzed, varying the source (gypsum and phosphogypsum) and content (10% and 20%) of calcium sulfate. The source of calcium sulfate did not significantly influence the resistance to sulfate attack, but it did change the mechanical strength of the SSC. The results showed that at the end of two years, all SSC samples were resistant to sodium sulfate attack; SSC pastes naturally formed a large amount of ettringite at early ages, preventing expansion at later ages. The SSC containing more calcium sulfate was the only mixture resistant under magnesium sulfate attack. A higher content of calcium sulfate in the composition of SSC can reduce the rate of diffusion of sulfate ions and improve their resistance to attack by magnesium sulfate. The lower formation of C─ S─ H, together with a higher content of calcium sulfate, provided an SSC with the best performance under magnesium sulfate attack.

In this research, a combined experimental and analytical program was conducted to study the effect of the single and hybrid fibers [polyvinyl alcohol (PVA) and steel] on the material characteristics of the sustainable high-strength self-compacting concrete incorporating a 100% replacement ratio of aggregate with granite industry by-product. The experiment includes 13 mixture compositions to understand mechanical and impact properties. The analytical investigation comprises statistical analysis of impact behavior, optimized mix compositions, and regression analysis between mechanical properties. The sustainable cementitious composites were made with 100% recycled fine aggregate, different volume fractions of PVA and steel fibers (0%, 0.5%, 1.0%, 1.5%, and 2.0%), and a constant proportion of Class F fly ash as partial replacement of cement. Mechanical properties of hardened concrete were studied in terms of compressive strength, splitting tensile strength, and three-point flexural tests. Specimens were subjected to repeated drop-weight, ultrasonic pulse velocity, and water absorption tests to determine impact resistance, integrity, and durability. It was discovered that incorporating fibers into fully recycled fine-aggregate concrete improves the material’s properties, which was found to be highly dependent on the use of single or hybrid fibers, their types, and their content. The energy-absorbing and energy-dissipating capability of samples was improved remarkably with the addition of fiber volume dosage. The best efficiency was for the mixture with 1.5% hooked-end fibers according to the higher values of mechanical and impact properties and the lower cost.

Based on exposure tests in a natural tidal environment, free chloride concentrations in concrete with different fly ash contents and exposure times were tested, and the apparent and instantaneous chloride diffusion coefficients of different fly ash contents were analyzed. Microstructural parameters such as porosity were analyzed using nuclear magnetic resonance (NMR) test results. The time-dependent model and analysis method of stable time for microstructural parameters is presented, and the time-dependent and stable time of microstructural parameters with different fly ash contents were studied. The relationship between stable time for chloride diffusivity and stable time for microstructural parameters was analyzed. Results show that chloride concentrations and chloride diffusion coefficients both have a linearly increasing relationship with exposure time and fly ash content increase. The stable time for chloride diffusion coefficients decreased as fly ash content increased. The total porosity and contributive porosity of large capillary pores (100–1,000 nm) generally decreased with the increasing exposure time, which is consistent with the time-dependent chloride diffusion coefficients. Increasing fly ash content had an obvious effect on reducing the contributive porosity of large capillary pores (100–1,000 nm) in concrete. The stable time for contributive porosity of large capillary pores (100–1,000 nm) decreased with increasing fly ash content. Whether fly ash was added or not, the contributive porosity of large capillary pores (100–1,000 nm) stabilized at first, and the stable time was the most important factor affecting the stable time for instantaneous chloride diffusion coefficient of concrete, providing a reference for predicting the stable process of macroscopic permeability from a microscopic view.

The current study aims to construct a synthetic polymer (or family of polymers) with superior plasticizing properties in a highly alkaline medium. An invented laboratory-prepared superplasticizer (SP), namely phenol-formaldehyde sulfonilate (PFS), was synthesized, and its performance was measured against two types of commercial superplasticizers [naphthalene-based (Nb) and polycarboxylate-based (PCb)]. Fourier transform infrared (FTIR) and gel permeation chromatography (GPC) tests were performed to verify the admixture’s stability in a highly alkaline medium. The interaction between different SPs and alkali-activated slag (AAS) surface was investigated via zeta potential and adsorption measurements. The flowability, setting time, and compressive strength developments were evaluated for AAS mixes. The hydration products’ morphologies and phase compositions were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD). The results reveal that the prepared PFS SP has a high stability against the highly alkaline medium. The dispersing efficiency of PFS SP resulted from the highly negative zeta potential value ($-49.8\mathrm{mV}$) compared with Nb ($-41.5\mathrm{mV}$) and PCb ($-15.8\mathrm{mV}$), as well as its high adsorption percentage as PFS, Nb, and PCb adsorbed by 18.5%, 9.2%, and 3.7%, respectively. The PFS SP enhanced the physicomechanical properties for AAS because it combined several advantages at the same time compared to commercial superplasticizers; for instance, AAS pastes admixed with PFS SP have superior workability, acceptable setting time, and high early strength.

The consumption of natural resources by the construction industry has increased in an unprecedented manner, which has been coupled with a consequential trail of immense environmental impacts due to unsustainable practices. This study was undertaken to develop a sustainable brick from a combination of waste glass and oil palm industry waste. The focus of this study was to provide a sustainable brick that contributes to minimal environmental impact and better insulation capability to enhance thermal comfort levels. The developed bricks showed an acceptable strength of 7.21 MPa, which complies with the standard criteria for non-load bearing bricks. Additionally, thermal conductivity was found to be approximately $0.38\mathrm{W}/{\mathrm{m}}^2\mathrm{K}$, an improvement of almost 50% compared with common red clay brick. In addition, the numerically obtained conjugate heat transfer analysis of the thermally efficient sustainable hybrid (TESH) brick revealed that thermal resistance offered by TESH brick is approximately four times that of fired clay brick. This research also analyzed the embodied energy consumption and environmental impact assessment of TESH bricks. The results pointed to the sustainability aspect of the developed TESH bricks having positive impacts relative to commercially available red clay bricks.

This study aims to compare the microstructural and mechanical properties of lightweight polymer concrete (LPC) and lightweight ordinary cement concrete (OCC) before and after exposure to a corrosive acidic environment. In this regard, LPC mixes were prepared with five different unsaturated polyester resin contents (15%–27%) and combinations of lightweight expanded clay aggregate (LECA) and natural river sand. Thereafter, specimens were exposed to sulfuric acid solution for up to 90 days. In addition to visual inspections, physical and mechanical properties [mass and volume changes, compression strength, and modulus of elasticity (MOE)], petrographic inspections, and scanning electron microscope investigations were carried out. Mechanical results showed that LPCs had by far better mechanical features compared with OCC, where at the optimum mix comprised of 24% polymer, reduction of 6% for compression, and 7% for MOE was observed, whereas these values were respectively 70% and 55% for OCC at the same conditions. Outcomes of microscopic observations indicated that increasing the polymer content resulted in strengthening the bond between binder and aggregates where pores were filled by resin. In addition, the impact of the acidic solution on the LPC mixes was less pronounced than for OCC mixes, and lamination of the matrix and affected polymer areas were reduced in LPC mixes with a resin content of 24% and 27%. After 90 days, a slight reduction in properties of LPC specimens and degradation was observed due to the reaction of the acid with the surface of LPC specimens.

Most geopolymer research claims a substantial reduction in carbon dioxide emissions compared with ordinary portland cement concrete. However, geopolymer concretes are not all equally eco-friendly. The environmental benefits of geopolymer concrete cannot be taken for granted. Modeling emissions is necessary to assess the environmental impact of each geopolymer mix. Unfortunately, only studies concerned with carbon dioxide emissions care to provide sophisticated emissions modeling. Such modeling is practically nonexistent for other geopolymer studies; because function-oriented geopolymer research tends to assume the environmental eminence of their designed mixes. This research reviews the last 7 years of geopolymer concrete research to assess the sustainability of the mixes designed by researchers worldwide and to highlight any bad environmental practices in the mix design. The nominal ${\mathrm{CO}}_2\text{-}\mathrm{e}$ equivalent emissions for geopolymer concrete mixes varied from 56 to $661\mathrm{kg}\text{-}{\mathrm{CO}}_2/{\mathrm{m}}^3$ for the surveyed mixes. ${\mathrm{SO}}_{\mathrm{x}}$ and ${\mathrm{NO}}_{\mathrm{x}}$ emissions reached $\mathrm{1,865}\mathrm{g}\text{-}{\mathrm{SO}}_{\mathrm{x}}/{\mathrm{m}}^3$ and $\mathrm{1,161}\mathrm{g}\text{-}{\mathrm{NO}}_{\mathrm{x}}/{\mathrm{m}}^3$, respectively. Finally, this paper recommends a simple method for estimating a nominal carbon dioxide emissions value, which can be easily implemented in future geopolymer research.

The construction sector adversely affects the environment. In this research, biowaste and electronic waste are used as raw materials to produce lightweight cement blocks. Cement-like material was synthesized using cockleshells and rice husk ash as raw materials, and the filler used in the cement blocks primarily consisted of nonmetallic fractions (NMF) of printed circuit board (NMF residue). The NMF residue was characterized by X-ray diffraction and exhibited prominent peaks corresponding to ${\mathrm{SiO}}_2$ and ${\mathrm{Al}(\mathrm{OH})}_3$. Morphological examination of the NMF residue revealed irregularly-shaped particles with an average size of 29.2 μm. The use of NMF residue as fillers adversely affected the compressive strength of the lightweight cement blocks. Nevertheless, when the NMF residue content did not exceed 15 wt.%, the average compressive strength was 3.83–4.63 MPa and the average density was ${1.086–1.19\mathrm{g}/\mathrm{cm}}^3$, which are within the acceptable ranges specified by the Thai Industrial Standards Institute. The concentrations of hazardous elements, such as Pb, Hg, Cr, Cd, As, Be, and Ni, were in the range 0–220 ppm, below the limits set by the Restriction of Hazardous Substances Directive. This study highlights a synergistic approach to waste utilization in the fabrication of lightweight cement blocks suitable for practical applications.

Three types of textile fabric waste, namely Kevlar, Nomex, and Cordura Nylon, were investigated in this study. The effects of the fiber parameters: volume fraction (0.1%, 0.3%, and 0.5%), length (6, 12, and 24 mm), and use of 1D fiber (width of 0) versus 2D woven fabric fiber (width of 3 and 6 mm) on strength properties, flowability, and shrinkage were studied to determine the optimum textile parameters. The pore structure, microstructure, and fiber-matrix interfacial properties of the optimised mixtures were then characterized by means of X-ray micro-CT, SEM, and nanoindentation at 7, 28, and 90 days. Results showed that the optimized parameters for three types of fabric fibers are 1D fiber (width of 0), length of 12 mm, and volume fraction of 0.3%. This optimized design provided an enhancement of strength and shrinkage resistance. Pore refinement was pronounced in the case of hydrophilic Kevlar and Nomex fibers. However, this also correlates to inferior performance in shrinkage resistance of mortar compared to hydrophobic Cordura Nylon. The fiber-matrix ITZ thickness was dependent on fiber size, while the wettability of fibers (i.e., hydrophobicity or hydrophilicity) was observed to affect the phase distribution in the vicinity of the fiber surface. Furthermore, a large volumetric proportion of the structure is porous in nature (more than 50%) in the region of the fiber-matrix interface after 7 days. With the increment of curing age, the microstructure at the fiber interface becomes denser due to the hydration of the clinker phase facilitating the growth of CSH and CH phases.

This study focused on the enhancement of the pozzolanic properties of thermally activated (calcined) mica clay (MC) by mixing it with smectite clay waste (SCW) from oil bleaching. Mica clay consists of small amounts of kaolinite, montmorillonite, illite, quartz, and carbonates, whereas smectite clay contains montmorillonite, an amorphous phase, and organic impurities. Samples were prepared by adding 10%, 30%, and 50% by weight SCW to the mica clay, followed by thermal activation at $600°\mathrm{C}–800°\mathrm{C}$ for 1 h, and finally milling after cooling. The obtained product was used as supplementary cementitious materials (SCMs). It was determined that the increase of calcination temperature and the amount of SCW additive improved the pozzolanic activity of the mixtures. The addition of 30% by weight SCW to the mixture calcined at 800°C increased the pozzolanic activity by 40%, whereas the addition of 50% by weight SCW increased the activity of the mixture by more than 1.5 times compared with that of the simple mica clay. The increase in the pozzolanic activity of the mixture was associated with the partial decomposition of the clay minerals throughout the combustion process and the presence of an amorphous phase from SCW. The obtained results show that combustion at 800°C of the mica clay mixture containing 30% SCW accelerated the early hydration of portland cement, and the samples containing the additive clearly exhibited signs of pozzolanic reaction after 28 days of hydration. The replacement of up to 15% by weight portland cement with the investigated additive increased the compressive strength of the samples.

Basalt fiber (BF) has been proven to play a positive role in strengthening the toughness of concrete. At present, there are many studies that investigate its compressive and tensile behavior. However, concrete is often subjected to shear action in practical engineering. In order to explore the shear dynamic performance of BF reinforced concrete (BFRC), a systematic direct shear dynamic performance experiment was carried out using BFRC specimens with four different fiber lengths and four different fiber contents while considering the influence of earthquake magnitude strain rate. The experimental results showed that BFRC had an obvious strain rate effect, and the increase in strain rate significantly increased the shear stress of BFRC. As either the BF content or length increased, the concrete shear dynamic increase factor first exhibited an increasing trend followed by a decreasing trend. Based on the comprehensive analysis of static and dynamic data, the shear stress and dynamic increase factor of BFRC reached the maximum values at the fiber content of 0.2% and BF length of 6 mm, and the corresponding shear stress and dynamic increase factor were 10.48 MPa and 1.29, respectively. According to the general trend analysis, the plastic deformation capacity of BFRC was gradually improved with the increase of BF content and length. Meanwhile, scanning electron microscopy (SEM) and computerized tomography (CT) technology were used to systematically analyze the stress mechanism of BFRC from the microscopic point of view. Overall, this study provided a theoretical basis for the application and development of BF in concrete.

Cracking risk of cementitious materials remains one of the serious problems in the construction and highway field. Here, a series of pH-sensitive microgels with different anionic content and crosslinking density have been successfully synthesized and applied in cement mortar. The absorption behavior and pH sensitivity of microgel in aqueous solutions were determined. The effects of microgel on hydration degree, autogenous shrinkage, and compressive strength of cement mortar were studied. Experimental results indicate that the microgel exhibits less desorption in the pore solution and releases water timely in pH from 12–13. Despite the different anionic content of microgels, the addition of microgel with moderate crosslinking density is $0.19\%\sim 0.31\%$, which can alleviate the autogenous shrinkage of cement mortar. The compressive strength of mortar can be increased by about 5.7 MPa by the microgels with low anionic content and moderate crosslinking density, thereby showing excellent internal curing effect.

In this paper, active MgO was used as the alkali activator, and the early hydration kinetics and microstructure development of MgO-activated slag were explored by means of the hydration heat test, X-ray diffraction (XRD), thermogravimetry (TG-DTG), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), and scanning electron microscopy–energy dispersive spectrometry (SEM-EDS). Three types of MgO were selected based on reaction time ($\mathrm{R}\text{-}\mathrm{MgO}<\mathrm{M}\text{-}\mathrm{MgO}<\mathrm{S}\text{-}\mathrm{MgO}$). The other two variables in this study include MgO content and curing age. The research results show that S-MgO is more suitable as an alkali activator and the total hydration heat of S-MgO-activated slag is much lower. The second exothermic peak is more obvious with the increase of MgO content. The main early hydration products of S-MgO-activated slag were a hydrotalcite-like phase, C-S-H gels, and C-A-S-H gels; the early main hydration product of R-MgO-activated slag was brucite. With the increase of MgO content, the total porosity decreases, i.e., the total porosity of the S-MgO specimen is the smallest, followed by the M-MgO specimen, and the total porosity of the R-MgO specimen is the largest. With the increase of S-MgO content, the processes of crystal nucleation and crystal growth are accelerated. When the S-MgO content is 20% by weight, the phase boundary reaction process and diffusion process of the MgO-activated slag system accelerates, which is more conducive to the diffusion, recombination, and precipitation of hydration products. This study provides an experimental and theoretical basis for the use of green alkali activator.

To gain a better understanding of the microscopic damage mechanism of different asphalt mixtures under the action of ice swelling, the authors use the stochastic modeling method combined with MATLAB and Ansys to conduct a thermal–mechanical coupling analysis of open-graded friction course (OGFC) and asphalt concrete (AC) under continuous freezing conditions. The results show that without considering other heat sources, the internal temperature of a structure will increase with time and gradually maintain the same periodic change as the external temperature. Under the same environment, internal moisture will freeze quickly in approximately 15 s. The freezing rate is related to the size of the pores and the temperature difference between the inside and outside of the ice crystals but is less related to the gradation type of the mixture. In structural analysis, the stress and strain will increase with the porosity under the same gradation type. At the same time, the stress in the bonding surface is always approximately twice the stress value in the asphalt mortar, and the strain is less than that in the asphalt mortar. In different grading types, although the strain of OGFC is smaller than that of AC, the overall frost heave stress is significantly larger than that of AC. Therefore, this study not only provides a reference for the dynamic study of ice crystals but also reveals the internal damage mechanism of the two types of asphalt mixtures.

The emergence of strain-hardening cementitious composites (SHCCs) improves brittle cracking of concrete materials. SHCC has the characteristics of strain hardening and multiple cracking under tensile load. In this study, 10 groups of SHCC were developed by incorporating polyvinyl alcohol (PVA) fiber into cement-based materials with high-content fly ash. Testing variables included water/binder ratio, sand/binder ratio, fly ash and cement content, and sand particle. The tensile test on the thin-plate specimen and compression test on cylindrical specimen were carried out. In addition, the double-edge notched plate specimens with relative notch lengths of 0.2, 0.4, and 0.6, respectively, were tested. The results showed that the average ultimate tensile strain of SHCC was 403 times that of ordinary concrete, and the peak compressive strain was about four times higher than ordinary concrete. The ultimate tensile strain of SHCC with high-volume fly ash ratio is generally higher than the low-volume fly ash ratio group. The failure mode of SHCC was ductile with good energy dissipation. Also, SHCC compressive strength is mainly adversely affected by the water/binder ratio and the ratio of cement to fly ash. With the increase of compressive strength, the angle of the failure face was reduced under compression. The acoustic emission (AE) activity captured the initiation and development of cracks at the three stages in the notched specimens under tension. With the increase of the notch length, the fracture energy calculated by the tensile stress–crack mouth opening displacement (CMOD) curve decreases.

This study investigated replacing microsilica with waste glass for preparing ${\mathrm{MgO}\text{-}\mathrm{SiO}}_2$ formulations to form magnesium-silicate-hydrate (M-S-H). The mechanical performance and microstructural development of the samples were supported by an assessment of their environmental impact. The obtained results indicated that microsilica can be partially replaced by waste glass (i.e., 50% by weight replacement) in ${\mathrm{MgO}\text{-}\mathrm{SiO}}_2$ formulations without sacrificing the compressive strength of samples, whereas the complete replacement with waste glass did not reveal favorable outcomes in terms of performance. The reactivity and solubility of the silica source played a key role in the formation of M-S-H, which contributed to the strength development in samples containing microsilica. Alternatively, samples containing waste glass as their only silica source revealed limited M-S-H formation and brucite, accounting for their poor mechanical performance. The predetermined treatment of waste glass should be carefully chosen, which could also affect the outcomes of the life cycle assessment (LCA).

Abstract

Given the importance of pavement surface, many transportation agencies have developed technical specifications to serve as a baseline for ensuring the quality of initial pavement roughness after paving works, monitoring it over time as an indicator of serviceability, and then referring to it as a threshold for strategic scheduling of pavement repair and maintenance works. Past studies have shown that various external factors are involved in determining pavement roughness; however, how principal asphaltic design parameters may affect initial pavement roughness has not been examined so far. To close this gap, this study investigated the contribution of the basic concepts of the Marshall mixture design method and individual constituent properties by analyzing the international roughness index (IRI) values of the asphalt wearing course of nine different roads with a total length of 435 km. The evidence from this study suggested that the strongest relationship at the mixture level was observed between Marshall stability and IRI, whereas optimum bitumen content had no influence on IRI. At the ingredient level, among various material properties, the specific gravity of fine aggregate was found to have the most pronounced effect on IRI. Consequently, particular attention should be devoted to these two factors to further improve IRI values at the mixture design stage.

Abstract

Once put into service, asphaltic pavements experience detrimental deteriorations because of repeated load-based stress and environmental conditions that result in an increase in pavement roughness. Defined as “irregularities of pavement surface,” roughness is used for rating road serviceability, assessing paving quality, monitoring network condition, and optimizing investments in preservation, rehabilitation, and reconstruction of pavements. Furthermore, roughness is known to affect pillars of riding safety and driving costs. Correspondingly, most transportation agencies around the world developed technical guidelines to determine the initial roughness of the pavements newly opened to service. To improve these guidelines, more factors affecting initial pavement roughness should be uncovered. Bearing this in mind, the study presented in this paper strives to examine the comprehensive factors of asphalt design parameters and material properties to elaborate on what affects initial pavement roughness at the design level. The study results demonstrated that the strength of the paving mixture and the density of fine particles used in the mixture are of great importance for initial pavement roughness. Hence, in order to construct sustainable and cost-effective road pavements with desirable roughness, the impact of these two factors should be considered when designing asphalt mixtures.

This paper proposes a reconfiguration of the rapid chloride permeability test (RCPT) using a time-domain reflectometer (TDR) to quantify the transport properties of concrete. The current RCPT test requires soaking the specimens for $18\pm 2\mathrm{h}$ to facilitate the ionic movement during the test. A voltage source is constantly applied over a 6-h period, and the charge passed is measured to qualitatively interpret the penetrability of concrete specimens. In this study, oven-dry specimens were used to measure the time-dependent dielectric constant as a key output of the TDR measurements and characterize the actual ingress of the chloride solution over the 6-h test period. The measured dielectric constant was used in the self-consistent and complex refractive index (CRI) models to establish the volumetric solution content relationship with time. Furthermore, this relationship was employed to estimate the transport properties in terms of diffusion and permeability coefficients of roller-compacted concrete (RCC) specimens. It was also used to establish a relationship between the charge passed and the volumetric content of the solution. Test results showed that the diffusion coefficients of RCC specimens are in order of ${10}^{-8}{\mathrm{m}}^2/\mathrm{s}$, and permeability coefficients are in the order of ${10}^{-6}{\mathrm{m}}^2/\mathrm{s}$. Additionally, the charge passed exhibited a linear relationship with the volumetric content of the solution.

The internal structure of the asphalt mixture plays a vital role in performance because it addresses gradation, air void distribution, and mixture packing. Although the quantification of the effect of the internal structure on the mechanical behavior of hot mix asphalt cannot be achieved through experimental work, the internal structure can be characterized through image-based analysis. Recent studies used imaging techniques to understand how the internal structure influences the performance of a mixture. This study attempted to quantify the interlocking properties of hot mix asphalt using three-dimensional (3D) and two-dimensional (2D) image analyzing processes and correlate the result to the locking point concept. Two types of aggregates (limestone and gravel), one type of bitumen PG64-22, and two types of asphalt mixtures—surface and base (binder)—were utilized in this study. Two software packages were used to process and analyze the captured images: iPas2 for the 2D analysis and Avizo Fire version 9.7 for the 3D analysis. Three parameters were utilized to quantify the interlocking properties, such as the number of contacts between aggregates per volume and area, ratio of interlocked particles to total number of particles, and contact area and length. This study’s results show that 3D and 2D image processing represent promising nondestructive methods to quantify asphalt mixtures’ interlocking properties. The parameters evaluated in this research indicated that the locking point definitions LP3/2-2-3 are the most appropriate to quantify the interlocking of the asphalt mixture.

This study aims to investigate the moisture and salt-erosion resistance of asphalt-calcined bauxite systems (ACBSs). The effects of the type of asphalt, aged asphalt, polymer modifiers, and grade of calcined bauxite on the moisture and salt-erosion resistance are evaluated by the pull-off strength and flaking rate of ACBSs after water immersion and neutral salt spray. The results show that a lower grade of asphalt is beneficial for the moisture resistance of an ACBS. Styrene-butadiene-styrene (SBS), antistripping agents, and polyphosphoric acid (PPA) improve moisture resistance, whereas rubber powder reduces it. Although the short-term thermal oxygen aging process can improve moisture resistance, high temperatures can result in the failure of the ammonia antistripping agent. The crystallization erosion from salt increases the moisture damage caused by water. The addition of modifiers and nonammonia antistripping agents can improve salt-erosion resistance; however, PPA has a weaker effect on salt-erosion resistance. Because the higher strength of the interface prevents moisture and salt erosion, an ACBS with a higher grade of calcined bauxite has higher moisture and salt-erosion resistance.

Supplementary cementitious materials (SCMs) play a significant role in improving the durability of cement-based materials by restricting moisture and aggressive ion transfer through capillary pores. Phosphorous slag (PS), as a SCM, is a waste product that seems to be capable of enhancing durability and mechanical properties of cement-based materials because of its chemical components. In order to investigate its effects, fresh and hardened cement mortars prepared with various amounts of PS were studied in this research project. Moreover, surface area is a key factor in SCM performance. Therefore, the effects of surface area on PS performance were also investigated. The main results show that various amounts of PS have an insignificant effect on the results of flow table tests, regardless of surface area. However, PS significantly improves the capability of cement mortars to retain their initial workability. Plus, as surface area increases, the capability of PS-incorporated mortars to retain their initial workability improves. Additionally, findings of hardened mortar analysis show that the pozzolanic reaction of PS occurs slowly and it can be argued that the impact of PS on hardened mortars does not depend on surface area. For example, findings show that the effects of the lowest and highest surface areas tested are about the same on compressive strength, electrical resistivity, and chloride diffusivity. Plus, the mechanical and durability properties of PS-incorporated mortars are usually lower than those of reference mixtures after short periods of moist curing. By contrast, PS-incorporated mortars have better mechanical and durability properties in comparison with reference mixtures after longer periods of moist curing. In order to shed light on PS performance, its performance was compared with a well-known SCM, silica fume (SF). The outcomes show that PS is not as active as SF. Interestingly, PS contributes to strength gain after longer periods of moist curing, while SF improves mechanical and durability properties even after short periods of moist curing.

To study the splitting tensile damage characteristics of concrete, this paper conducted Brazilian disc split tensile tests on concrete and mortar with three water-cement ratios and four loading rates, respectively. Acoustic emission (AE) technology was used for real-time. The test results indicate that in the early loading stage of Brazilian disc specimens, a small number of microcracks are primarily generated at the interface between aggregate and mortar, and microcracks and macrocracks are generated simultaneously at the peak stress. The peak frequency characteristics of AE explain the strength enhancement principle and strain rate effect of concrete damage. The curves of AE cumulative ringing and AE energy counting reflect the internal damage activity of concrete and mortar specimens at different stress stages. Finally, a model that conforms to the macroscopic performance of the concrete dynamic splitting tensile test was established based on the discrete element method (DEM) and Hertz–Mindlin bond model. The simulation was compared with the actual analysis to verify the effectiveness of the parameters. The evolution of concrete damage space was studied through the discrete element simulation results, and the three evolution stages of damage space were summarized, which confirmed that the DEM plays an essential role in the field of micromechanics.

Intelligent compaction (IC) has been successfully used for soil and base compaction of highways. However, the application of IC technology to monitor the construction quality of asphalt pavement faces complications with compaction processing. This study monitored the compaction process of asphalt layers using an IC-based method. The compaction data were first collected during the construction of a local road in Mardan, Pakistan, including IC data, in-place density, and temperature at the asphalt layer surface. The collected IC data were then used to compute the intelligent compaction measurement values (ICMVs). The support vector regression analysis was performed to predict the roller amplitude and in-place density using the ICMVs. To explore the correlations in compaction measuring/monitoring indicators, this study also explored the correlations between the ICMVs with core density, temperature, and amplitude. Experiment results indicated that the predicted roller amplitude values from the support vector regression model were close to the measured ones. There were high correlations between the roller amplitudes and temperatures with the compaction measurement values (CMVs). In contrast, the correlation between the in-place core densities and CMV values was low. Additionally, the CMVs of the backward pass were higher than the forward one in each compaction cycle because the pavement density increased and the air void decreased after each forward pass.

The waste of scrap rubber and asphalt mixtures brings a serious problem of environmental pollution and resource waste, which is inconsistent with the principles of sustainable development and a circular economy. A waste-utilizing rejuvenator was developed using scrap rubber, waste engine oil (WEO), aromatic furfural oil (AFO), and antiaging agent, among others, in this investigation. This work aims to explore the influence of the rejuvenator on properties of recycled asphalt binders. The recycling effect of the rejuvenator was first evaluated by conventional tests, followed by the characterization of saturate (S), aromatic (A), resin (R), and asphaltene (A) fractions and colloidal structures. Subsequently, the evaluation indicators were optimized by gray relational analysis (GRA). Finally, the viscosity composition characteristics were analyzed by the composite viscosity theory. The results indicated that the rejuvenator can significantly restore the consistency, workability, and low-temperature flexibility of aged asphalt binders, and a rejuvenator content of 8%–12% is acceptable. The rejuvenator can effectively replenish the components lost during the aging process. Hence, SARA fractions in the aged asphalt binder are balanced and the colloidal structure is restabilized. Penetration, ductility, and viscosity are recommended as evaluation indicators according to GRA, and the percentage change of SARA fractions is worth noting. The modified model can accurately predict the viscosity of recycled asphalt binders at 65°C and 85°C because it considers the difference in viscosity between the rejuvenator and the aged asphalt binder. This provides the possibility to design the composition of recycled asphalt binders.

Nonuniform or segregated asphalt mixture has been critical in asphalt pavement construction, accelerating pavement damage and reducing pavement service life. Existing uniformity quantification methods have not considered the aggregate skeleton structure that impacts the mixture loading and durability. Under the isotropic hypothesis, this paper proposed a nondestructive, real-time, and rapid approach to measuring asphalt mixture uniformity using image processing technology (IPT). A total of 1,188 images were first collected from a new construction site and then preprocessed to identify the coarse aggregate. The aggregate particle and skeleton structure factors were obtained, including particle quantity and position distribution, particle axial length ratio, particle orientation, and distance between particles. We used the entropy weight method to combine these four factors to propose a uniformity quantification index (UQI). Finally, UQI was compared with two existing uniformity quantification indices in evaluation consistency. The results show that the uniformity level ranked by the UQI was more consistent with the visual observation than the other two indices. Among the four factors, the particle quantity and position distribution, particle axial length ratio, and distance between particles correlate well with the asphalt mixture uniformity. Moreover, for the considered asphalt mixtures, stable quantification results need a minimum image size of 250 by 556 mm. Even smaller image sizes produced misleading uniformity quantification results.

In this paper, secondary recycled concrete was modified using basalt fiber (BF) and nanosilica (NS) to form modified secondary recycled concrete (MSRC), to promote the recycling of concrete. The flexural toughness and influence of pore size distribution of the MSRC were analyzed through the four-point flexural mechanics test and nuclear magnetic resonance test, respectively. The results showed that with an increase in the content of BF and NS, the fracture of the coarse aggregate increased and the flexural strength of MSRC increases. According to different evaluation standards, the flexural toughness of the MSRC exhibited a similar trend in different evaluation standards. As the NS content increased, the equivalent flexural strength increased, and as the BF content increased from 2 to $4\mathrm{kg}·{\mathrm{m}}^{-3}$, the equivalent flexural strength decreased. Additionally, scanning electron microscope and nuclear magnetic resonance spectroscopy showed that NS and BF had significant influence on the pore structure of the MSRC. When the BF content was $2\mathrm{kg}·{\mathrm{m}}^{-3}$, the content of micropores was minimal; and with further increase in BF content, the content of micropores increased, the internal defects increased, and the flexural toughness decreased. Moreover, with the increase in NS content, the content of internal pores decreased and the flexural toughness increased. Therefore, the results showed that BF and NS had a significant toughening effect on the MSRC.

The objective of this study was to obtain insight into the synthesis and structural changes of organo-montmorillonite (OMT) by tailoring montmorillonite (MMT) with the help of a quaternary ammonium salt. The OMT was prepared as a precursor to the development of enhanced asphalt rubber (AR) product. The dimethyldioctadecylammonium chloride (DDAC) provided the required thermodynamic driving force for changing the polarity of hydrophilic MMT to organophilic when both materials were mixed at 80°C under constant stirring for about 12 h. The newly synthesized OMT and base MMT were thoroughly characterized by using particle size analyzer, zeta potential, infrared (IR) spectroscopy, powder X-ray diffraction, and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) measurements encompassing 20,936 data points. The SEM images of OMT depicted the grafted fibrils of long-chain aliphatic hydrocarbons. At the same time, EDX indicated the exchange of sodium and magnesium cations with carbon and nitrogen of the DDAC. Comparison of the IR spectra for reactants and OMT powders concluded that water molecules were removed and methyl/methylene functional groups were inserted in the OMT. The 100 basal reflections of OMT were 1.894 nm, while that of untreated MMT was 1.522 nm, which corroborated the intercalation of the long alkyl chains of the DDAC, a cationic surfactant in the OMT. The study established a simple method for the preparation of OMT to be used as an AR modifier for roadway applications supporting the utilization of nanoclay material in resolving storage stability issues and enhancing properties of recycled rubber–based asphalt products.

Antiaging effects of two inorganic nanoparticles [4% nano-titanium oxide ($\mathrm{nano}\text{-}{\mathrm{TiO}}_2$) and nano-zinc oxide (nano-ZnO)] on asphalt were investigated by liquid-state nuclear magnetic resonance (NMR) spectroscopy, multiple stress creep recovery (MSCR) tests, and linear amplitude sweep (LAS) tests. The rheology test results showed that rutting and fatigue performance of asphalt binder increased with the addition of nano-oxides, and the addition of nano-ZnO showed improved rutting resistance and fatigue life compared with $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$. ${}^1\mathrm{H}$ NMR spectroscopy shows that the aromatic hydrogen ratios and branchiness index (BI) of asphalt decrease significantly after aging. It indicated that some isomerization and dehydrogenation occurred during the aging process. After adding nano-oxides into asphalt binder, the aromatic hydrogen content and the number of branched chains in asphalt susceptible to oxidation are further reduced, which slows the aging degree of asphalt. ${}^{13}\mathrm{C}$ NMR spectroscopy shows that the content of aromatic carbon is the key factor affecting asphalt aging. After original asphalt aging, the aromatic carbon ratios decreased, and adding nano-oxides into asphalt binder, whereas two kinds of nano-oxide-modified asphalt have different trends of aromatic carbon ratios. The antioxidant mechanism of $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ is to inhibit the loss of aromatic carbon, whereas the oxidation of nano-ZnO-modified asphalt either inhibits the reaction of aging or causes sufficient aromatization to offset the influence of different degrees of asphalt aging.

In order to solve the current problem of insufficient toughness of epoxy asphalt and immiscibility between resin and asphalt binder (not aged) in epoxy asphalt, nanomodifiers (${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$) were prepared by a biomimetic mechanism from chitosan (CS), calcium ions (${\mathrm{Ca}}^{2+}$), and graphene oxide nanoplatelets (GOs). In ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$, CS connects GOs through calcium ion coordination bonds and amide bonds. ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}\text{-}\text{modified}$ epoxy asphalt was prepared by directly adding different percentages of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$ to epoxy asphalt. Then, the properties of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}\text{-}\text{modified}$ epoxy asphalt were analyzed through macro and micro tests. The macroscopic tests included tensile, cyclic, and stress relaxation tests. The microscopic tests included fluorescence microscopy (FM) and scanning electron microscopy (SEM) tests. Tensile tests showed that after adding 0.05% ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$ to the total mass of epoxy asphalt, the tensile strength and fracture toughness of epoxy asphalt increased by 29.6% and 20%. Cyclic tensile tests showed that ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}\text{-}\text{modified}$ epoxy asphalt had greater consuming work recovery capacity, and stress relaxation tests showed that the addition of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$ delayed the relaxation modulus decline of epoxy asphalt. The infrared spectrum, scanning electron microscope, X-ray diffraction, and Raman spectra of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$ in the micro test can show the successful synthesis of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$. FM and SEM of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}\text{-}\text{modified}$ epoxy asphalt showed that the addition of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}$ could reduce the particle-size distribution of the asphalt phase in epoxy resin and establish a miscible bridge between epoxy resin and asphalt, which led to the improvement of macroscopic mechanical properties of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}\text{-}\text{modified}$ epoxy asphalt. Finally, the modification mechanism of ${\mathrm{GOs}\text{-}\mathrm{CS}\text{-}\mathrm{Ca}}^{2+}\text{-}\text{modified}$ epoxy asphalt was proposed by combining macroscopic and microscopic test results.

Bacterially induced calcium carbonate precipitation is a newly developed technic in geotechnics and is suggested for soil liquefaction problems in an environmentally friendly process. The utilization of bacterially induced calcium carbonate precipitation in degraded stone conservation, and monument reinforcement is newly proposed. In this study, calcium carbonate biologically produced by Bacillus licheniformis was used as a consolidator cement. The results showed that the biological treatment could increase the uniaxial compressive strength (UCS) of stone to more than 500 kPa in dry samples. The permeability of the samples reduced from $8\times {10}^{-4}\mathrm{cm}/\mathrm{s}$ in untreated samples to around $5.5\times {10}^{-6}\mathrm{cm}/\mathrm{s}$ in biologically cemented samples. The bacterium was also able to reduce water vapor permeability and water absorption by capillary tubes and by the bulk of the stone. SEM analysis showed a wide range of calcium carbonate polymorph genesis effective in pore alteration processes. Elemental analysis coupled with SEM was also indicative of primarily the role of the calcium carbonate precipitation in plugging and the distribution pattern of calcium carbonate within the pores. Data from UCS showed that biological cementation could be considered a convenient alternative to consolidate historical monuments and improve durability.

Cracks are one of the factors that can weaken reinforced concrete structures (RCSs), and are associated with a reduction in concrete durability. RCSs could encounter concrete crack issues due to high temperature as a result of fire. Over time, unrepaired concrete cracks can spread on the surface and trigger serious damage to the structure. Therefore, the repair of concrete cracks is essential. In the present laboratory study, cubic concrete specimens with dimensions of $150\times 150\times 150\mathrm{mm}$ were exposed to heat at 600°C and 800°C. Then, the ability of two calcium carbonate-producing bacteria, Sporosarcina pasteurii and Bacillus sphaericus, to repair thermal cracks was evaluated. After aging for 28 days, the specimens were placed in a furnace at 600°C and 800°C for 1 h, with a 5.5°C increase per minute. The efficiency and effectiveness of the two microorganisms on the specimens was then evaluated for compressive strength, water absorption, and water capillary absorption. The tests indicated that the microorganisms had a substantial ability to repair both surface and deep cracks; both types of cracks were completely filled and repaired by the calcium carbonate deposits, and the compressive strength of specimens repaired by the microorganisms increased by 31%–93%. Furthermore, water absorption decreased by about 30%–43%, and capillary water absorption decreased by 15%–31%. Scanning electronic microscope (SEM), X-ray diffraction (XRD), and stereo microscopic images further confirmed the high activity of the microorganisms in the production of calcium carbonate deposits.

Abstract

This paper presents the results of an experimental study investigating the recyclability of ground granulated blast-furnace slag (GGBFS) base geopolymer concrete as recycled aggregates (RAs) for both geopolymer concrete (GPC) and portland cement concrete (PCC). The effects of partial (0%, 25%, 50%, and 100%) replacement of recycled geopolymer concrete aggregates (RGAs) with natural aggregates (NAs), as fine and coarse aggregate, in either type of recycled geopolymer concrete (RGPC) and recycled portland cement concrete (RPCC) under ambient-cured conditions in similar laboratory circumstances was evaluated. The results were compared with those of recycled concrete counterparts made by recycled cement concrete aggregates (RCAs). A wide range of basic and mechanical properties [i.e., density, compressive strength, ultrasonic pulse velocity (UPV), tensile strength, flexural strength, and modulus of elasticity, water absorption, and shrinkage] along with scanning electron microscopy (SEM) analysis was investigated. The results highlight the high potential of RGAs in both RGPC and RPCC in terms of compressive and tensile strength with only an average reduction of 10% to 15% in 50% substitution of RGAs with NAs. However, there seems to be an incompatibility in using the heterogeneous type of recycled concrete aggregate and binder, which led to more dispersion of test result values. The results in the modulus of elasticity showed a negligible decrease of 3% to 6% by RAs substitution with NAs compared with the control samples. The reductions in flexural strength, water absorption, and shrinkage of RGPC were found to be slight, more than RPCC, which seems to be mainly attributed to the differences in properties and characteristics of geopolymer paste than the influence of RAs content. However, further incorporation of RAs content of more than 50% was found to lead to more significant negative effects in all recycled concrete groups, but the substitution of 50% RGAs to NAs as an optimum mixed proportion due to promising results can be considered for more investigation.

Abstract

GPC is known as a sustainable alternative to PCC, admittedly with more compatibility with the environment. By expanding the use of GPC in the construction industry in the near future, the end-of-life strategies of this material should inevitably be considered as an upcoming concern according to sustainable development policies. Although recycling and reusing of PCC has been widely investigated in many studies for years, the applicability of using GPC itself as a recyclable material to be used for recycled concrete has been barely studied. Therefore, this study compares the properties of slag-based geopolymer recycled concrete with conventional cement-based recycled concrete. The results indicate the promising potential of GPC recyclability for partial replacement of recycled aggregate with natural aggregate and acceptable mechanical properties and durability as a sustainable material for the construction industry. The geopolymer recycled concretes recorded better compressive and tensile strengths and similar modulus of elasticity compared with cement-based recycled concrete. Additionally, the results in flexural strength, water absorption, and shrinkage of cement-based recycled concrete indicated a better behavior over time, which is more attributed to the characteristics of geopolymer binder rather than recycled aggregates. However, incorporation of RAs content of more than 50% was found to lead to more adverse effects in all recycled concrete groups.