Effect of placement characteristics on SCC lateral pressure variations

Lateral pressure exerted by fresh concrete on vertical formwork systems controls significantly the design of the formwork systems. Several factors including, material properties, placement conditions, and formwork characteristics can affect formwork lateral pressure. This paper presents the results of an extensive experimental work aimed at studying the influence of concrete temperature (10-32 °C), casting depth (up to 13 m), placement rate (2-30 m/h), waiting period between successive lifts, as well as concrete thixotropy on lateral pressure characteristics. The increase of concrete temperature is shown to accelerate the stiffening rate of the concrete leading to reduction in initial lateral pressure. For highly thixotropic SCC mixture even at very high casting rate of 30 m/h, the initial lateral pressure is limited to 26% of the equivalent hydrostatic pressure at casting depth of 10 m and to 70% at the shallow casting depth of 3 m. These pressure values can drop further (about 25%) when the casting rate reduces from 30 to 2 m/h. Interruption of concrete casting with a waiting period of 30 min can reduce lateral pressure up to 15%, especially for highly thixotropic concrete.