Journal of Materials in Civil Engineering

In this paper, the time-dependent properties of rheological parameters (${\tau }_0$, $\eta$, $A$) and electrochemical parameters ($R_b$) are investigated by preparing sulphoaluminate cement pastes with different water-to-cement ratios ($\mathrm{W}/\mathrm{C}$) of 0.3, 0.4, and 0.5, respectively. A new rheological microstructure model is proposed by combining hydration kinetics with a newly introduced hydration stage, with electrochemical parameter $R_b$. Meanwhile, the time-dependent nature of rheological parameters was evaluated by electrochemical parameters. The experimental results show that the time-dependent properties and microstructural evolution are closely related to the water content of cement paste. Based on hydration kinetics, the reconstruction curve of hydration rate conforms to the Krstulović–Dabić model and the hydration mechanism belongs to NG-I-D (where NG, I, and D stand for nucleation and crystal growth, interactions at phase boundaries, and diffusion, respectively). The time-dependent property of electrochemical parameter $R_b$ can be divided into four stages, which conform to the mathematical model of $R_b=kt$. However, the hydration mechanism that dominates those four stages is different. In addition, the rheological parameters (${\tau }_0$, $\eta$, and $A$) have a good linearly time-dependent relationship with electrochemical parameter $R_b$. As an in-situ nondestructive method, the electrochemical analyzer is feasible to monitor and evaluate the time-dependent properties of cement rheology.

Corrosion of reinforcement bar caused by chloride ions diffusion is a crucial durability problem for concrete structures. Deoxyribonucleic acid (DNA) is a new type of corrosion inhibitor. Previous research has concentrated primarily on the influence of DNA on the corrosion of reinforcement bar caused by chloride salts in simulated concrete pore solution and cement-based materials, with scant attention to the chloride diffusion behavior of cement-based materials with DNA. In this work, the chloride diffusion behavior of cement-based materials with DNA was studied using chloride binding isotherm, chloride rapid migration (RCM), and natural diffusion tests. The composition, content, and morphology of the hydration products and pore structure were monitored using X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests. The results show that DNA can improve the chloride-binding capacity and enhance the chloride diffusion resistance in cement-based materials. The lowest chloride migration coefficient and chloride diffusion coefficient were found in cement mortar with 4% by weight DNA, which were 45.58% and 42.36% lower than those of the reference group, respectively. DNA can stimulate the cement hydration reaction to produce more C-S-H gels and can increase the $\mathrm{Ca}/\mathrm{Si}$ ratio of C-S-H. This is conducive to physical chloride adsorption. DNA can be combined with calcium ions to form insoluble aggregates that can fill the pore structure of mortar. Mortar with 4% by weight DNA maintained the lowest porosity, which effectively enhanced the chloride diffusion resistance.

Recycled gypsum powder from waste drywalls is a new alternative that has been recently introduced for partial cement replacement in concrete for construction applications. It has been shown that the recycled gypsum, alongside fly ash, can partially replace cement in concrete to some extent without hurting the required properties of concrete. In this paper, the impact of recycled gypsum content on the durability of concrete (hereafter called gypsum concrete) exposed to different environmental exposures is evaluated. A total of 153 concrete cylinders ($100\times 200\mathrm{mm}$) with different recycled gypsum contents (0%, 10%, and 20% of cement replacement) were considered. Each mix was exposed to air-dry, freshwater, seawater, freshwater–air dry cyclic, and seawater–air dry cyclic conditions. The specimens were tested in compression loading after 1,000, 3,000, and 6,000 h of exposure. Recycled gypsum used in this research was in two types of a powder with fine particles only (hereafter called fine gypsum) and in the form of mixed fine, coarse, and paper particles (hereafter called whole gypsum). Other mechanical and physical properties of concrete such as absorption, volume change, and ultrasonic pulse velocity were analyzed. It was observed that the compressive strength of the specimens with 10% and 20% fine gypsum content at Day 28 was about 36% and 40% lower than that of the control specimens, respectively. However, the strength gap was reduced to about 16% and 7% at the end of 6,000 h in the air-dry condition. The specimens submerged in freshwater and seawater showed a rate of strength gain higher than that of the control specimens, bringing the compressive strength of the gypsum concrete specimens slightly higher than that of the control specimens after 6,000 h exposure. Overall, recycled gypsum in combination with fly ash not only does not hurt the long-term strength of concrete but also can enhance the strength under certain conditions, mostly those exposures involving water exposure.

The development of tests, standards, and specifications necessitates the establishment of technical validity while concurrently optimizing costs associated with the testing requirements. AASHTO TP 125-16 recommends the utilization of the bending beam rheometer (BBR) as a simple, rapid, relatively cost-effective, and reproducible method for assessing the low-temperature properties of asphalt concrete mixtures. However, the standard does not provide specific guidance regarding the representative sample size necessary for the BBR test. Therefore, this study used statistical techniques to calculate the sample size by scrutinizing data for two variables, i.e., creep moduli (stiffness) and stress relaxation capacity ($m$-value), which were obtained from testing a variety of asphalt concrete mixtures. In this regard, distinct asphalt mixtures were meticulously prepared and subjected to laboratory testing. A representative sample size of eight thin-beam specimens was determined. This recommendation was validated by sampling five different asphalt mixtures from pavement construction projects. It was found that testing and analyzing trimmed means of only eight specimens from a 2 in. thick asphalt concrete layer was adequate to represent the global low-temperature performance of those five pavement sections. So, an asphalt mixture’s low-temperature performance can be completed in 2 h by testing only eight specimens in the BBR without sacrificing accuracy and practicality. Therefore, this study contributes to a possible application of the BBR during pavement construction.

This research aimed to enhance the ultraviolet aging and long-term thermal oxidation aging resistances of styrene-butadiene-styrene (SBS)-modified asphalt simultaneously. For this purpose, antioxidant 1222–intercalated ultraviolet (UV) shielding material layered double hydroxides (LDHs) (LDHs-1222) were prepared and added into SBS-modified asphalt as an antiaging agent. The effect of LDHs-1222 on the physical properties, high and low temperature rheology, and chemical composition of SBS-modified asphalt was investigated. Meanwhile, the aging properties of the asphalts after short-term or long-term thermo-oxidative aging and 7-day ultraviolet aging were investigated. The results showed that LDHs-1222 significantly improved the resistance of SBS-modified asphalt to short-term thermo-oxidative, long-term thermo-oxidative, and UV aging while having less impact on the physical and rheological properties than LDHs. Compared with SBS-modified asphalt, the softening point increment, aging indices of viscosity, complex modulus and carbonyl index, and SBS index decrement of the asphalt with LDHs-1222 were significantly reduced, and their growth rates were significantly slowed, indicating that the aging rate and degree of SBS-modified asphalt were reduced by the addition of LDHs-1222. SBS-modified asphalt with 4% LDHs-1222 exhibited superior resistance to long-term thermal oxidation and UV aging compared to asphalt with an equivalent amount of LDHs.

This paper proposes a new method of reusing uncalcined coal gangue (UCG) as a mineral admixture in magnesium ammonium phosphate cement (MAPC) blended with fly ash (FA). The effects of UCG on setting time, workability, hydration heat release, mechanical properties, hydration products, and microstructure of MAPC composites were systematically investigated. The results indicate that the addition of UCG decreased the maximum hydration temperature and extended the setting time of MAPC composites. The compressive strength of MAPC was improved by introducing an optimal amount of UCG. The XRD results showed no new crystal phase in UCG-0 (with 20% FA and 0% UCG) and some secondary hydration products, such as berlinite and lizardite, were observed in MAPC with UCG. The addition of UCG was found to inhibit the generation of dittmarite and promote the development of struvite. Results showed that differences in the crystal morphology of struvite and dittmarite influence the compressive strength of MAPC composites.

One of the most important factors influencing concrete durability is permeability. Permeability testing is conducted according to certain standards to measure the water permeation in concrete. After the test, the concrete specimens should be positioned under the concrete breaker jack and split into two sections to measure the permeability. In general, it is difficult to use the majority of permeability tests to determine concrete permeability in situ. As a result, the permeability and compressive strength of concrete with various strength classes were measured in this study by using the novel “cylindrical chamber” and “friction transfer” tests. Permeability-reducing admixtures, including Fibrous microsilica gel and waterproof, were used in several specimens that were subjected to 0, 50, 100, and 150 freezing and thawing cycles. A cylindrical chamber device can quantitatively display the permeation volume and rate of any liquid into concrete. By comparing the results of the nondestructive cylindrical chamber test with the standard destructive test, it was observed that there is a 97.6% correlation coefficient between the results. This correlation coefficient demonstrates the high accuracy of the cylindrical chamber test in measuring water permeability within concrete without the need for sample breakage. Furthermore, by comparing the results of the friction transfer test with the standard destructive test, a 94.2% correlation coefficient was observed. This correlation coefficient indicates the high accuracy of the friction transfer test in assessing the compressive strength of concrete without the need to break the concrete. In addition, the process of rising permeability rate has a greater value for low cycles. However, it progressively becomes smoother for higher cycles, in such a way that, on average, the permeation volume increased by 71% in the first 50 cycles, 21% in the second 50 cycles, and only 8% during the third 50 cycles. In concrete specimens without additives, the value of permeability rate increases under freezing and thawing cycles by approximately 36% and 19%–22% in specimens containing permeability-reducing admixture.

The environmental friendliness, good thermal performance and sustainable development of rammed earth structures have attracted the attention of numerous researchers and engineers in recent years. Nevertheless, the fire safety of rammed structures has not been extensively studied. The primary objective of this study is to investigate the mechanical properties of stabilized and unstabilized rammed earth exposed to direct fire under short elapsed time and high temperatures using a kiln. Rammed earth specimens with various mix designs were prepared and then exposed to high temperatures. Afterward, destructive and nondestructive tests were performed. Additionally, microstructural analysis was preceded to evaluate the change in chemical composition and microstructural of rammed earth specimens. The majority of the stabilized specimens exhibited thermal instability at 700°C. These specimens lost up to 85% of their compressive strength and 15% of their weight and change in their chemical composition. Under direct fire exposure, the rammed earth’s mechanical properties were not greatly impacted due to the short elapsed time. Compressive strength was increased in unstabilized (clay) RE specimens. A correlation between destructive and nondestructive properties was proposed. This study can be considered in the mix design of RE that experiences high temperatures.