International Concrete Abstracts Portal

In this study, a chloride adsorption test was performed to depict the chemical evolution of pore solution for cement hydration. It was found that the amount of chloride adsorbed by the AFm phase and the calcium-silicate-hydrate (C-S-H) phase decreased with the increasing pH of the pore solution. The stability of Friedel’s salt tended to decrease with the increasing pH of the pore solution. Notably, in the C-S-H phase, the decrease in the amount of chloride adsorption resulting from an increase in the pH level was larger when the Ca/Si ratio was higher. Based on these works, multiple regression analysis was performed to examine the correlation between the chloride adsorption density of cement hydrates and the experimental variables involved, including the pH of the pore solution and the amount of chloride-ion penetration. The pH of the pore solution was predicted based on cement hydration and pore-chemistry theories, and these results were combined with the experimental results, considering the changing chemical characteristics of the pore solution during each temporal stage of cement hydration. The amount of chloride-ion adsorption in fly ash (FA) and granulated blast-furnace slag (GBFS) was larger than in ordinary portland cement (OPC) due to the decreased pH of the pore solution resulting from the consumption of calcium hydroxide.

Firstly, the proposed static test was carried out on eight fly ash foamed concrete walls with different axial compression ratios μ and steel ratios ρ. Secondly, the quantitative analysis method of wall damage was proposed based on the crack development theory, and the real damage index was proposed. Then, through theoretical analysis and curve fitting, two kinds of seismic damage models— energy method and Park-Ang-W—were proposed, and the damage values were calculated to compare with the real damage values. Finally, the Park-Ang-W model was used to analyze the parameter expansion of 16 Abaqus wall models with different axial compression ratios μ and steel ratios ρ. The results show that the damage evaluation index based on crack development theory can effectively reflect the damage of fly ash foamed concrete walls. The accuracy of the energy method model is not high at the low number of cycles, and the error is less than 20% at the high number of cycles. The Park-Ang-W model has an error of approximately 10% at a high number of cycles, which better reflects the true damage of the specimen. The axial compression ratio μ has little effect on the wall damage, with a maximum effect range of 6.7%. Increasing the reinforcement ratio can effectively reduce the wall damage, with a maximum effect range of 12.6%. The results of the study provide a theoretical basis for the future application of fly ash foamed concrete in construction projects.

The focus of this study is to determine the optimum length of micro (average diameter less than 0.3 mm) and macro (average diameter greater than or equal to 0.3 mm) hemp fibers subjected to tensile loading in a cement paste mixture. Optimizing the length of the fibers to carry tensile loading for concrete members is important to minimize waste of hemp material and to provide the best performance. This study evaluated three water-cement ratios (w/c): 0.66, 0.49, and 0.42 (fc′ = 17.2, 24.1, and 27.6 MPa [2500, 3500, and 4000 psi], respectively). Because of the high cost of cement, replacement of cement with fly ash was also part of the program to determine if the addition of fly ash would have a negative impact on the performance of the hemp fibers. The results show that hemp micro- and macrofibers bonded to the cement matrix and carry higher tensile loads at higher w/c. Statistical analysis (regression modeling) shows that the optimum length for hemp macrofibers is 30 and 20 mm (1.18 and 0.79 in.) for microfibers.

In this study, low-carbon ultra-high-performance concrete (UHPC) was designed by adding fly ash-based mineral admixtures (SD-FA). The improved Andreasen & Andersen model was used to obtain SD-FA, which was then used to replace part of UHPC cement, to achieve the effect of low-carbon emission reduction. The effects of the composition and dosage of cement-based materials, the water-cement ratio, the composition of sand, the steel fiber content, and the lime-sand ratio on the properties of UHPC were studied, and the design of the batches was optimized. On this basis, the performance changes were analyzed at the micro level. The results show that when the 1~3 grade fly ash content after screening treatment is quantitative, the densest stacking is theoretically reached. The SD-FA optimized design improves the bulk density of UHPC and realizes the dense microstructure of UHPC. Under the optimal mixing ratio, its processability is guaranteed and the mechanical properties are enhanced.

Reinforcing seawater sea-sand concrete (SSC) with basalt fiber reinforced polymer (BFRP) bars can adequately resolve chloride corrosion issues. However, the multiple-element ions in seawater and sea sand can increase the concrete alkalinity and accelerate the degradation of BFRP bars. This study aims to enhance the durability performance of BFRP-SSC beams by regulating concrete alkalinity. A low-alkalinity SSC (L-SSC) is designed by incorporating a high-volume content of fly ash and silica fume. A total of 16 BFRP-SSC beams were designed based on the current standards and prepared using normal SSC (N-SSC) and L-SSC. The beam flexural performances before and after long-term exposure are characterized through the four-point bending test. The test results indicate that exposure in the simulated marine environment can reduce the load-bearing capacity and change the failure mode of BFRP beams with N-SSC. After exposure at 55°C for 4 months, the load-bearing capacity of the BFRP-SSC beams was reduced by 70.0%. Moreover, a slight enhancement of load-bearing capacity and ductility of the BFRP-L-SSC beams was observed due to the enhanced interface performance with further concrete curing. Furthermore, the long-term performance of the sand-coated BFRP bars is better than that of the BFRP bars with deep thread. The load-bearing capacity of the BFRP-L-SSC beams increased by approximately 20% after 4 months of accelerated aging due to concrete strength growth, and the BFRP-L-SSC beams maintained the concrete crushing failure mode after exposure. Finally, a loadbearing capacity calculation model for the BFRP-SSC beams is proposed based on the experimental investigation, and its prediction accuracy is higher than that of the current standards. This study can serve as a valuable reference for applying BFRP-SSC structures in the marine environment.