EFFECT OF LIMESTONE ON THE HYDRATION CHARACTERISTICS OF PORTLAND-POZZOLANA CEMENT MORTARS

The aim of this work is to utilize some Egyptian by-products such as granulated blast-furnace slag (GBFS) and fired clay or waste clay bricks known as Homra to produce economic blended cement. The effect of addition of limestone as a filler on the hydration characteristics of such blended cements was investigated.
The effect of artificial pozzolana (waste clay bricks) and GBFS in the absence and presence of limestone on the physico-chemical and mechanical properties of the hardened cement pastes was studied.
A various dry cement blends were prepared by mixing of ordinary Portland cement (OPC) with waste clay bricks (WCB) or GBFS as partial replacement of OPC (0, 10, 20 and 30%) and the optimum constitution was established as 10%. Other cement blends were also prepared by partial replacement of OPC by limestone (LS) (0, 2.5, 5.0 and 7.5 %) and the optimum composition was found to be 5%. This was followed by mixing of the optimum constitution of 85 % OPC: 10 % GBFS: 5 % LS and 85 % OPC: 10 % WCB: 5 % LS blends. Each of cement blend was mixed with water using the standard water of consistency and the setting time was determined.
The physico-chemical properties of the hardened mortars, made of each cement blend with a ratio of 1:3 of cement blend:sand a water/solid ratio of 0.50, were tested for compressive strength, chemically combined water content and free water content at different ages of hydration of 1, 3, 28 and 90 days. In addition, thermal analysis and X-ray diffraction analysis were carried out on some selected samples.