Mix Proportioning of High Performance Self-Compacting Concrete using Response Surface Methodology
Abstract
High performance self compacting concrete (HPSCC) is typically proportioned with mineral and chemical admixtures leading to relatively high material cost. Such cost can be tolerated in high value added applications specially when cost savings can be realized using HPSCC in terms of reduction in size of reinforced concrete members. Efforts are still needed to reduce material cost of HPSCC to gain wider acceptance in variety of applications. Proper material selection and sound mixture proportioning can achieve this [1]. The derived statistical Response Surface Methodology (RSM) is targeted to develop cost effective HPSCC mixtures [2]. RSM can be used effectively in analyzing the cause and effect of the process parameters on response. This paper presents an experimental program in which RSM are employed to optimize a four-component concrete containing fly-ash subjected to six performances criteria. The four key mixture constituents used in the models included cement, fly-ash, and high range water reducer and water binder ratio. The modeled response that included were the compaction factor, compressive strength, split tensile strength and flexural strength at 28 days. The anticipated responses are not expected to vary in linear manner with selected variables; a central composite plan was selected to enable the model of any response in a quadratic manner. Therefore each of the four selected mixture constituents is studied in five distinct levels corresponding to codified value-2,-1,0,1,2.A total of 31 mixture combinations were used in the experimental design which consisted initially of a matrix 24(=16) factorial design plus seven central points and eight star points. The derived models are valid for a wide range of mixtures with ranges of water binder ratio of 0.28-0.44, cement content of 400 to 600 kg/m3, fly-ash 0 to 10% (by weight of mass cement and HRWR dosage of 1 to 3% (by weight of mass cement).
