Influence of superplasticizer and curing on porosity and pore structure of cement paste

Most concrete produced today contains admixtures. Superplasticizers (SP) are used for the purpose of improving workability and reducing the water to cement ratio; therefore producing more durable concrete. SP cause better dispersion even at high water to cement ratio. Although SP improves the dispersion of particles, it is not quite clear how the addition of SP affect the porosity and pore size distribution of cement paste. The purpose of this study was ro examine the influence of one type of SP on porosity and pore size distribution under different curing regimes. Paste specimens with and without SP were prepared at constant water to cement ratio of 0.45. Specimens were cured for 28 days and some for six months. Specimens were exposed to high temperature (45 degrees C) and normal temperature curing (20 degrees C) and also subjected to different relative humidities (similar to 100%, 55% and 25%). Curing at high temperature was carried out to simulate temperature in hot climates. Tests on porosity and pore size distribution were conducted using mercury intrusion porosimetry. The results show that the inclusion of SP decreases the total intruded pore volume of paste. The dominant pore diameter, however, does not seem to be affected and the percentage of pores smaller than 100 nm increases in the presence of SP. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.