Experimental study of marine ultra-high-performance concrete with coarse aggregate (UHPC-CA)

Reported are the results of an investigation of the effects of coarse aggregate type and content on the workability, mechanical properties, and long-term durability of ultra-high-performance concrete (UHPC). UHPC specimens were prepared with four types of aggregates - granite, limestone, quartzite, diabase - and five content levels - 0, 200, 400, 600, 800 kg/m3. The specimens were cured by steam for 48 h and by standard for 28d. The matrix and the interfacial transition zone (ITZ) were analyzed by scanning electron microscopy (SEM) and by microhardness testing. The results show that the workability of the UHPC with quartzite coarse aggregate is better by 5-30 % than those of the UHPC with the other three coarse aggregates. Further, the UHPC with granite and limestone coarse aggregates are found to have the highest compressive and splitting tensile strengths at content levels of 200-400 kg/m3 and 600-800 kg/m3, respectively. It is shown that the granite coarse aggregate significantly improves the long-term durability of UHPC. In all cases, the workability and the autogenous shrinkage decrease linearly with the coarse aggregate content, while the compressive strength, the splitting tensile strength, and the abrasion resistance increase significantly. The optimal coarse aggregate content for resistance to chloride ion penetration is found to be approximately 600 kg/m3. The steam curing is shown to enhance all properties compared to the standard curing, notably improving chloride ion resistance. Microhardness and SEM analysis confirm a denser cementitious matrix structure following steam curing.