Comparison of Fly Ash, Pva Fiber, Mgo and Shrinkage-Reducing Admixture on the Frost Resistance of Face Slab Concrete via Pore Structural and Fractal Analysis

Abstract

Face slab concrete suffers from serious frost damage in cold regions in China, how to improve the frost resistance of face slab concrete in cold regions is one of the important issues in concrete faced rockfill dam (CFRD) design and construction. The results in this paper indicate that the frost resistance of concrete can be improved by adding fly ash, fiber, MgO and shrinkage-reducing admixtures (SRA), and the efficiency is in the sequence: (fly ash + fiber) > fiber > fly ash > MgO > SRA. The incorporation of 0.8 kg/m 3 PVA fiber and 20 wt% fly ash together enhances the compressive strength and tensile capacity of concrete by 6-7 % at late age, whereas the addition of 6 wt% MgO or 1 wt% SRA reduces the compressive strength and tensile capacity by about 4-10 % at various ages. The Ds of concrete added with fly ash, fiber, MgO and SRA is within the range of 2.619-2.796. The frost resistance of concrete correlates linearly with the air void parameters, pore structures and Ds. The utilization of fly ash and/or PVA fiber refines and optimizes the pore structure, thus increasing Ds and improving the frost resistance. On the contrary, MgO and SRA in this study are less effective in refining the pores than PVA fiber and fly ash, thereby producing smaller Ds and relatively weaker frost resistance.

Comparative Study on the Mechanical Strength of SAP Internally Cured Concrete

“…It is consistent with the results of this paper. Tong (Tong, 2018) also pointed out that SAP has a negative effect on the flexural strength of concrete or mortar. This can be attributed to the following facts: firstly, all the strength of SAP concrete decreases with the increase of SAP and internal curing water, which increasing the total watercement ratio.…”

“…According to RILEM (Mechtcherine et al, 2014), when SAP releases internal curing water, it shrinks and leaves air voids behind, which act as weak spots in the material structure, decreasing the flexural strength. Tong (2018) pointed out that the existence of pores due to the shrinkage of SAP is a kind of defect in the concrete.…”

“…After the SAP particles lose water, a large number of honeycomb holes are left in the hardened concrete stones, thus reducing the effective cross-sectional area. The pore structure of SAP concrete has been modified by SAP particles, similar to the effects caused by fly ash, silica fume and other additive admixtures (Wang et al, 2020a;Wang et al, 2020b;Wang et al, 2020c). At the same time, it easily causes stress concentration when the concrete specimen is compressed.…”

Effect of Tuff Powder Mineral Admixture on the Macro-Performance and Micropore Structure of Cement-Based Materials

“…The above MIP results could be used to characterize the porosity distribution and evolution of tuff powder-cement paste, but fail to characterize the complexity of the internal pore structure. For this purpose, the relevant literature applies the fractal theory to analyze the pore structure of cement-based materials (Wang et al, 2020a;Wang et al, 2020b). The fractal dimension of the pore surface (Ds) is introduced to quantitatively characterize the surface characteristics of the irregular pore structure of tuff powder-cement paste.…”

“…The fractal dimension of the pore surface (Ds) is introduced to quantitatively characterize the surface characteristics of the irregular pore structure of tuff powder-cement paste. Studies have (Wang et al, 2020a;Wang et al, 2020b;Wang et al, 2020c;Rahman, 1997) shown that the surface fractal dimension value is primarily related to the pore distribution characteristics. The Ds is within the range of 2-3.…”