Effects of coarse aggregates on physical and mechanical properties of C170/185 ultra-high strength concrete and compressive behaviour of CFST columns

摘要

The demand for and use of ultra-high strength concrete (UHSC, f(ck) > 90 N/mm(2)) in high-rise construction have become attractive nowadays, even in countries with seismic activities. However, the poor ductility of it is one of the key concerns leading to the code restrictions on its application even it is infilled into the steel tubes (CFSTs). To study the strength and ductility, this paper presented an experimental work on physical and mechanical properties of UHSC in terms of workability, density, elastic modulus, compressive strength, modulus of rupture and splitting tensile strength; and compressive behaviour of CFSTs using the UHSC, considering the effects of curing age, specimen size, coarse aggregate size and proportion. The test results revealed that the workability of UHSC could be improved by mixing the larger-size coarse aggregates which had little influence on its density; the coarse aggregate size affected the compressive strength in both ways: beneficial and adverse, and the final effect should be determined by its proportion; different from the normal strength concrete (NSC), the UHSC specimens with cylinder shape and larger-size had higher strength than those with cubic shape and smaller-size. It is concluded that, by replacing base material of the UHSC with 38% ordinary coarse aggregates having a maximum size of 10 mm to form the double-tube CFSTs, the ductility can be improved with the axial load capacity not affected. (C) 2019 Elsevier Ltd. All rights reserved.