Study on the mechanical properties and hydration of red mud-limestone powder ultra-high-performance concrete
Ultra-high-performance concrete(UHPC)has been widely studied and applied in the world because of its excellent mechanical properties and durability.However,as a ce-ment-based material with high cement content,UHPC can lead to higher production costs and greater environmental harm.The use of supplementary cementitious materials(SCMs)to substitute the cement in UHPC has become an effective way to reduce cement consump-tion.In recent years,red mud(RM)is frequently used as a supplementary cementitious ma-terial to partly replace cement.However,previous studies have shown that incorporating RM may undermine the performance of UHPC due to its low reactivity.It is well known that the aluminum phase in cementitious materials can synergistically interact with carbonate to promote the production of hydration products and improve the performance of the matrix.Since RM is rich in aluminum phase,a sustainable UHPC is developed in this study by a synergistic use of RM and limestone powder(LP)to partially substitute cement.The effects of the admixture amount of RM on the mechanical properties,hydration,pore structure and carbon emission of UHPC are investigated through mechanical tests,calorimetry analysis,X-ray diffraction,porosity tests and carbon emission tests.The results show that UHPC in-corporated with RM and LP generally exhibits lower early-age strength than the reference mix,but its late-age strength develops more rapidly due to the synergistic reaction among RM,LP and cement.As the RM dosage increases,the main exothermic rate peak occurs earlier and the hydration reaction is accelerated owing to the nucleation effect and high alka-linity of RM.The coupled addition of RM and LP could lower the porosity of UHPC matrix due to RM's filling effect and the synergistic effect among RM,LP and cement.Moreover,the incorporation of RM and LP effectively reduces the carbon emissions of UHPC.
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