Effects of curing temperature on the hydration of GGBS concrete and the use of electron microscope particle analysis

Abstract

It is a common concern that ground granulated blast-furnace slag (GGBS) blended CEM I concrete lacks sufficient early-age strength, which may prevent its application in cast-in-place structural concrete. This has been identified in the present study through GGBS activity index tests and compressive strength tests of GGBS blended concrete specimens. Current codes for GGBS used in concrete require a minimum early-age hydraulic activity and a specific surface area. The particle size distribution (PSD) of GGBS can also affect the physical and mechanical properties of concrete, but this cannot be sufficiently addressed by the standard testing methods. This paper proposes a quantitative assessment method which can quickly determine the particle shape and PSD of CEM I cement and GGBS samples based on electron microscope image analysis. This method of assessment offers the potential to work as an important supplementary method to the existing testing methods adopted by the cement industry. In addition to the particle shape analysis, CEM I and GGBS samples were also characterised based on isothermal calorimetry, scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. These tests were conducted at 20°C and 38°C curing to investigate the effect of curing temperatures.