Owing to enhanced filling ability, self-consolidating concrete offers accelerated casting and superior quality control during construction. However, its high fluidity and high placement rate increase the lateral pressure on the formwork, necessitating an extensive supporting system to retain fresh mixtures in a desired shape. Current recommendations of formwork design for self-consolidating concrete adopt the concept of hydrostatic pressure, even though the measured pressure could be less than the recommended level. This study shows that mineral admixtures such as processed clays can appreciably lessen the formwork lateral pressure. In addition, the correlation between the formwork pressure response and the loss of slump flow is derived, providing an approximate method to estimate the reduction in formwork pressure. (C) 2010 Elsevier Ltd. All rights reserved.