DENSITY AND POROSITY STUDIES OF HYDRATED PORTLAND CEMENT

Abstract

The density and porosity of hydrated Portland cement are usually measured using aqueous saturated solutions of Ca(OH)[ 2] as a medium on cement in the d-dried state. However, measurements made with a comparison pycnometer using helium, and conventionally using an aqueous saturated solution of Ca( OH)[2] and methanol show that the porosity and density values obtained using aqueous solutions are too high. The assumption that d-dried hydrated Portland cement does not rehydrate even when exposed to water is incorrect. The values obtained with helium and methanol as media are very similar. Measurements were made on pastes having w:c ratios of 0.4, 0.6, 0.8, and 1.0 using helium as a medium from samples dried only from 11% r.h. to beyond d-dry. At 11% r. h. the density values, after correction, were 2.34 g/cm[3] using helium and 2.35 g/cm[3] using the aqueous solution. It is concluded that the properties of d-dried hydrated cement that led to the concept of gel pores are due to partially collapsed interlayer spaces. Gel pores as such do not exist.