No abstract

Aerated concrete (AC), such as cellular concrete, autoclaved aerated concrete (AAC), and non-autoclaved aerated concrete (NAAC), having excellent insulation properties, is commonly used in buildings located in cold regions, such as Nur-Sultan in Kazakhstan, the second coldest capital city in the world, because it can contribute to a large energy saving. However, when the AC is directly exposed to the repeated freeze and thaw (F-T) cycles, its F-T resistance can be critical because of lower density and scaling resistance of the AC. Moreover, the evaluation of the F-T resistance of the AC based on the durability factor (DF) calculated by using the relative dynamic modulus of elasticity may overestimate the frost resistance of the AC due to the millions of evenly distributed air voids in spite of its weak scaling resistance. In the present study, the F-T resistance of NAAC mixtures with various binary or ternary combinations of ground granulated blast-furnace slag (GGBFS) and micro-silica was assessed mainly using the ASTM C 1262/C1262M-16 Standard Test Method for Evaluating the Freeze-Thaw Durability of Dry-Cast Segmental Retaining Wall Units and Related Concrete Units. Critical parameters to affect the F-T resistance performance of the NAAC mixture such as compressive strength, density, water absorption, air-void ratio (VR), moisture uptake, durability factor (DF), weight loss (W loss ), the degree of saturation (S d ), and residual strength (S res ) were determined. Based on the determined parameter values, frost resistance number (FRN) has been developed to evaluate the F-T resistance of the NAAC mixture. Test results showed that all NAAC mixtures had good F-T resistance when they were evaluated with DF. Binary NAAC mixtures generally showed higher S d and W loss and lower DF and S res than those of ternary NAAC mixtures. It was determined that the S d was a key factor for the F-T resistance of NAAC mixtures. Finally, the developed FRN could be an appropriate tool to evaluate the F-T resistance of the NAAC mixture.

Reactive Powder Concrete (RPC) is a newly emerging concrete material that is being used for various applications where high-strength concrete is required. RPC is obtained by removing coarse aggregates and adding fine powders such as silica fume into the concrete mixture. This research has focused on the proportioning and characterization of RPC mixture to be used as a material for energy storage pile application. For mixture parameters, the water-to-binder ratio (WB), silica fume (SF) content, and normal and warm temperature curing have been selected. The relative flowability, penetration resistance, setting time, drying shrinkage, and compressive and flexural strengths were evaluated. Based on the test results, the mixture with WB = 0.22 and SF = 20% was the best mixture with the highest tensile strength and other characteristics. Response surface methodology (RSM) was used to design the experiments and find the optimum mixture proportions to achieve the highest compressive strength. The optimum WB and SF content to achieve the highest strength for combined ages (7 days, 28 days, and 56 days) was determined to be WB = 0.213 and SF = 20%. Through the comparison between the test results and the required strength from analytical simulations, the RPC studied in this paper was deemed to be suitable for the energy storage pile.

The purpose of this study was to investigate properties of non-autoclaved aerated concrete (AC) with quadruple cementitious mixture containing silica fume (SF) and ground granulated blast furnace slag (GGBFS) on the basis of Response Surface Method (RSM). Compressive strength and porosity for 9 different mixtures have been determined and the prediction models for these properties have been developed using regression analyses. The combination of 5% SF and 20% GGBFS was found to be useful for strength development and reduction of porosity in the AC.

Aerated concrete (AC) is widely used in the construction industry due to lightweight and advanced thermal properties. In this research, thermal conductivity (λ) of non-autoclaved AC was characterized with Response Surface Methodology (RSM). The effect of fine aggregates with different Al2O3 contents on the minimal λ value was analyzed using RSM. Test results show that sand with higher Al2O3 content has more influence on lower λ of AC. The regression models were significant and applicable to analyzation and prediction of λ of AC with good accuracy.