Assessing the compressive strength and elastic modulus of high-performance GGBS concrete

Abstract

The mechanical properties of High Performance Concrete are crucial for structural design to achieve expected advantages over conventional concrete. For example, the efficient prefabrication of precast concrete requires sufficient early-age strength so that early striking time and transport can be achieved. The stiffness of prestressed concrete significantly determines the prestress loss as the deformation of concrete is strongly related to the elastic modulus. The studies of the mechanical properties of High Performance Concrete involve the correlation between the compressive strength and the elastic modulus. There are also many influencing factors that strongly affect these mechanical properties. Ground granulated blast-furnace slag (GGBS), as a by-product from a steel plant, is a widely used supplementary cementitious material in Ireland. The advantages and disadvantages of using GGBS are both vital for assessing this material in concrete manufacture. It is necessary to quantify the influence of GGBS on both the strength and elastic modulus under various conditions. There are many conventional methods that can be used to accelerate the development of concrete after mixing to varying degrees. Thus both the strength and elastic modulus are affected by these techniques under a faster growth rate. The individual effect of one accelerating method and the combined effect of several methods together are both of importance for determining the growth path of concrete strength and stiffness. Numerical prediction of the compressive strength and elastic modulus is commonly introduced in many standards and books through different formulae. The comparison of calculated values and actual results provides a reliable method of determining the accuracy of those formulae. For different countries with more complicated situations, modified formulae with new variables and constants should be proposed based on experimental work for more accurate prediction. This research recommends values for constants and indices in the predicted equations used by practitioners for both strength and stiffness using Irish aggregates and GGBS, together with rapid hardening cement, an accelerating admixture and thermal curing in the high strength precast industry.