Using recycled aggregate and powder from high-strength mortar waste for durable cement-based materials: Microstructure and chloride transport

The large-scale application of high-strength mortar in engineering will inevitably generate a significant amount of high-strength mortar waste in future, but there has been relatively limited research to date on the reuse of high-strength mortar waste as recycled building materials. Therefore, this paper studied the microstructure and chloride transport in cement-based materials using recycled fine aggregate (HCRA) and recycled powder (HCRP) derived from high-strength mortar waste or from high-strength mortar waste separated from high-strength concrete waste recycling. HCRA had much better physical and mechanical properties than ordinary recycled aggregate. HCRP contained some active components, and mixing appropriate HCRP refined paste pore structure; besides, reducing HCRP particle size could further refine the pore diameter of HCRP doped mortar. The strength of mortar first raised and then declined with the increment of HCRA replacement, but the strength decreased as HCRP was incorporated. Incorporating HCRA slightly reduced the chloride migration in mortar, and the mortar with HCRA had better chloride resistance than the mortar with recycled fine aggregate crushed from ordinary mortar waste. Mixing appropriate HCRP could reduce the chloride diffusion coefficient and chloride concentration. Reducing HCRP particle size further declined the chloride transport in HCRP blended mortar, and the mortar with HCRP had superior chloride resistance to the mortar with ordinary recycled powder. Mixing HCRA and HCRP both raise the chloride binding capacity. Particularly, fully recycled mortar with 100% HCRA and 30% HCRP exhibited even better chloride resistance than reference mortar. Incorporating appropriate HCRA and HCRP could prepare durable cement-based materials with good chloride resistance.