Study on mechanical and shrinkage properties of ES-UHPC

• Early-age mechanical and shrinkage properties of ES-UHPC was investigated. • Compressive strength of ES-UHPC slightly decreased with increase in TEA content. • The effect of the combination of different early strength agents was studied by theoretical analysis. • The CaO expansion agent was used to reduce the shrinkage of the ES-UHPC. • The optimal combination of early-strength agents is obtained to prepare the ES-UHPC. Some road and bridge projects to be repaired require materials that can quickly and easily obtain high mechanical properties. Added early strength agents are commonly used to improve the early strength of Ultra-high performance concrete (UHPC). Previous studies focused primarily on improving the early strength of UHPC, and few studies on how to reduce early age shrinkage of UHPC. This paper selected two inorganic early-strength agents, lithium carbonate (Li 2 CO 3 ), nano-calcium carbonate (NC), and two organic early-strength agents, calcium formate(CF), triethanolamine(TEA),and an CaO expansion agent, which are commonly used. Experimental studies were carried out for single and compound early-strength agent systems in a cement-based UHPC system. The results showed three early-strength agents (NC, Li 2 CO 3 ,CF) reduced the setting time and improved the early-strength of the UHPC. TEA had an adverse effect in the both single and compound systems. The 1-d compressive strength of the group(L0.15N3P10) reaches 84.5 MPa, with good workability and lower shrinkage. It can be used to prepare early strength ultra-high performance concrete (ES-UHPC) at room temperature. In terms of strength, shrinkage, and workability, it is suggested that the combination content of Li 2 CO 3 is 0.15%, NC is 3%, and the expansion agent is 10% for fast repair and reinforcement projects.