Study on Sulfate Resistance Durability of High Volume Recycled Aggregate Concrete Solidified by Soil Solidification Rock

Concrete incorporating soil solidification rock (SSR) and recycled aggregates offers a viable solution to mitigate the depletion of natural aggregate resources and to decrease carbon emissions associated with cement production. Concrete, however, is susceptible to degradation when exposed to severe environmental conditions, such as sulfate attacks, during its service life. The objective of this dissertation is to assess the durability of SSR-cured high-performance recycled aggregate concrete (RAC) materials under sulfate attack. The RAC is formulated by integrating cement-silica fume reinforcement with recycled aggregates (RCA) as a substitute for natural aggregates and SSR as a substitute for Type P.O. 42.5 cement. Sulfate resistance of the soil-consolidated high-admixture RAC was investigated through sulfate dry and wet cycling tests, supplemented by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The study reveals that an increase in RCA content correlates with a reduction in sulfate erosion resistance; however, the interaction between cement-silica fume and the recycled aggregate surface enhances the formation of Calcium-Silicate-Hydrate (C-S-H) gel, thereby improving the surface integrity of RCA and sealing the pores and cracks, significantly enhancing sulfate durability. The findings demonstrate that as the concentration of soil coagulant is increased from 9% to 15%, the sulfate resistance of RAC improves, as evidenced by a 18% increase in the Kf lift-off value and a 1.38% reduction in mass loss rate. SEM analysis reveals that the TR-100-12 concrete exhibits a complete C-S-H gel matrix, with the cement-silica fume treatment reducing surface porosity and minimizing interfacial transition zones between the mortar and aggregate, resulting in a denser structure. XRD and FTIR analyses suggest that sulfate exposure leads to an increase in gypsum content and a decrease in calcite content within the concrete matrix.