THE INFLUENCE OF PULVERIZED-FUEL ASH UPON THE HYDRATION CHARACTERISTICS AND CERTAIN PHYSICAL PROPERTIES OF A PORTLAND CEMENT PASTE

In order to examine the effects produced by the presence of pfa upon the hydration characteristics of an ordinary portland cement, comparisons were obtained using two equivalent pastes. One of these pastes was prepared with an ordinary portland cement and the other with a blend containing 30 parts by weight of pfa and 70 parts by weight of the opc. Both pastes were made so as to have a water to solids ratio of 0.47 by weight. The chemical composition and the physical characteristics of the starting materials are shown. The following quantitative measurements were made after 0.25, 0.5, 1, 1.5, 2, 7, 14, 28, 65, 100, 275 and 365 days hydration at room temperature: 1) compressive strength (at ages greater than 1.5 days); 2) total porosity (at ages greater than 1.5 days); 3) chemically bound water; 4) calcium hydroxide (portlandite) content; 5) hydration of the individual cement phases; 6) reaction of the "glassy" phase in the pfa. Two distinct mechanisms are shown to occur. At early ages the pfa does not make a strong contribution to strength but, as a fine powder, it accelerates the hydration of the cement. The pozzolanic reaction becomes apparent at normal temperature if curing has continued beyond fourteen days. (TRRL)