Study of the degree of hydration of concrete by means of image analysis and chemically bound water

This article deals with the effect of both initial temperature and subsequent high curing temperature on the degree of hydration of normal strength concrete at the age of 28 days. Variations in compressive strength were observed and presented previously. Here, their causes are investigated through a difference in the hydration state in relation with the initial mixing and curing conditions. We present two ways of measuring the degree of hydration and compare the results, first by means of an original technique of image analysis on flat polished sections observed by scanning electron microscope, and second by classical measurement of the chemically bound water. Two kinds of specimens are studied. Cylinders of 11 cm × 22 cm were prepared with two different temperature formulae of constituents: 20°C (water)—20°C (aggregate)—20°C (cement); and 20°C (water)—70°C (aggregates)—70°C (cement), so as to obtain an initial temperature of the mixes between 20°C and 50°C, respectively. Specimens were sealed and cured under either controlled laboratory conditions or simulated conditions of hot weather. In each case, all the specimens were stored in water up to 28 days.