Pore Structure and Compressive Strength of Tailings Concrete under Dry-Wet Cycles of Chloride Attack

Abstract

To investigate the relation between pore structure and compressive strength, ordinary portland cement (OPC) concrete (C), tailings concrete (T), and tailings concrete mixed with steel fiber (TF8) were subjected to dry-wet cycles of chloride attack for 30, 60, 90, 120, 150, and 180 days and subsequently to compressive strength tests. The pore structure was examined using a concrete pore-structure analyzer. For the purpose of analysis, the pore size was divided into three regimes, 0–60, 60–500, and 500–4,000 μm, and the corresponding air content, pore chord length frequency, and fractal dimensions were calculated. The macroscopic and microscopic properties of the concrete were analyzed, and the relations among the compressive strength, fractal dimensions, and pore structure of concrete were studied. Results show that the compressive strengths of OPC concrete, T, and TF8 all increased first and then decreased over the course of the experiment. Turning points were identified at 60, 90, and 90 days, respectively. The compressive strength of OPC concrete varied with age to lesser extent than T or TF8. The air contents of T and TF8 were much greater than that of OPC concrete. Air content of OPC concrete exerted a negative effect on the compressive strength, whereas no clear relationship between air content and compressive strength was observed in T or TF8. The air content and fractal dimensions appear to be closely correlated with compressive strength in large-pore-size OPC concrete and in small-pore-size T and TF8. The most sensitive pore size affecting the properties was found to be 500–4,000 μm for C and 0–60 μm for T and TF8. Tailings and steel fiber can significantly improve the early compressive strength of concrete. Although there is attenuation in later stages of erosion, TF8 can basically replace OPC concrete.