Assessment of changes in compressive strength of deep beam elements made by pumping self-compacting concrete bottom-up

Abstract

This experimental work investigates into the effect of a change in the compressive strength of concrete along the length and height of monolithic deep beams made of high performance self-compacting concrete (HPSCC). In the tests, three different HPSCC mixes were used in which the amount of silica fume differed (0, 5 and 10% by mass of cement). The binder content (550 kg/m3) and the water-binder ratio (0.32) were fixed. Experimental deep beams, measuring 1.60 m in length, 0.16 m in width and 0.48 m in height, were cast. Two variants of concrete mixture casting were considered in this work: from the top and from the base of the formwork system with a single casting point at one edge. No significant changes to the compressive strength along the element span were observed in the tests, independently of the casting variant or the mixture composition. However, a tendency was observed for the compressive strength to undergo a reduction with an increasing distance between the samples and the concrete casting point. On the other hand, the tests showed that independently of the concrete casting variant, the mixture composition or the distance to the concrete casting point, in the upper parts of the elements there was a concrete layer of poorer quality and lower compressive strength. The reduction of the compressive strength of the top sample with respect to the bottom one was in the range 6.1 - 15.0% for the top-down concreting and 1.0 - 10.3% for concreting from the bottom of the formwork. Casting the self-compacting mixture from the bottom of the formwork yielded a satisfactory degree of the strength homogeneity in the test element. This variant of casting may be used in practice as an alternative way of laying an self-compacting concrete mix.