Materials Chemistry and Physics 71 (2001) 76–83 Physico-chemical characteristics of some polymer cement composites M. Heikal a,∗ , I. Aiad b , M.M. Shoaib c , H. El-Didamony c a Institute of Efficient Productivity, Zagazig University, Zagazig, Egypt b Egyptian Petroleum Research Institute, Cairo, Egypt c Faculty of Science, Zagazig University, Zagazig, Egypt Received 30 January 2001; received in revised form 10 February 2001; accepted 6 March 2001 Abstract The electrical conductivity of cement pastes can give an indication of the initial hydration of the cement pastes and early formation of products. In this study, sulphate-resisting cement (SRC) pastes were prepared with different doses of two synthesised admixtures, namely phenol formaldehyde sulphonate (PhFS) and melamine formaldehyde sulphonate (MFS). This work is aimed to evaluate the effect of PhFS and MFS on the hydration reaction of cement pastes during the first 24 h by determining the initial, final setting times and the electrical conductivity changes, as well as the effect of these polymers on the hydration progressing up to 90 days by determining the chemically combined water content and gel/space ratio of each paste at different intervals of time (1, 3, 7, 28 and 90 days). © 2001 Elsevier Science B.V. All rights reserved. Keywords: Sulphate-resisting cement (SRC); Setting time; Electrical conductivity; Polymer and gel/space ratio 1. Introduction Portland cement is a multi-component system, its hydra- tion is a rather complex process consisting of individual chemical reactions having series of thermodynamic and kinetic characters, which depend on both chemical and phys- ical parameters. Hydration is a chemical process that from the anhydrous material through several chemical reactions leads to the formation of hydrates. The reaction of cement with water proceeds at different rates for the various mineral phases and involves both hydrolysis and hydration process, then its four major phases start to hydrate. Some phases such as calcium aluminoferrite (C 4 AF) and tricalcium aluminate (C 3 A) are the hydrates at very early stages of hydration. The silicate phases such as -dicalcium silicate (-C 2 S) and tri- calcium silicate (C 3 S) need some time for initial setting [1]. Abbreviations in cement chemistry : C = CaO, S = SiO 2 , A = Al 2 O 3 , F = Fe 2 O 3 The production of Portland SRC is expected to increase because of the attack of sulphates in soil and ground water. SRC is exposed to severe sulphate action when the con- struction is exposed to aggressive media such as sulphates, ∗ Corresponding author. seawater and/or ground water. Low C 3 A and comparatively high C 4 AF contents of SRC means that it has high strength but because -C 2 S represents a high value, the early strength is low. The heat developed by SRC is not much higher than the heat of Portland cement. Therefore, it could be argued that it is theoretically an ideal cement for massive structures exposed to seawater or ground water. Superplasticizers are now widely used in the production of concrete with excellent workability, for easy placement without reduction in cement content and strength. These admixtures are extremely effective for dispersing cement particles in water. The dispersion mechanism has been de- scribed in terms of electrostatic repulsive forces between the cement particles followed by adsorption of charged super- plasticizer molecules. Several reports have been concerned with the improvement of the strength and development of Portland cement using admixtures [2–4]. Concrete admix- tures or superplasticizers have been used to reduce the water of consistency and to improve the workability of cement pastes and consequently concrete, leading to improvement in mechanical properties and resistance towards environmen- tal deterioration, chemical attack and moistures. Polymeric concrete admixtures which act as water reducer decrease the total porosity, therefore the relationship between porosity and electrical resistivity in cementitious systems were stud- ied [5]. Electrical conductivity is an important parameter to 0254-0584/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0254-0584(01)00346-7