Estudo da influência do calcário cru e cinzas volantes nas propriedades físico-químicas e mecânicas do cimento portland produzido em moçambique

Abstract

The present work presents a proposal for the reuse of industrial waste, thus minimizing the environmental problems caused by them, and reducing the energy consumption necessary for the production of Portland cement, rationalizing the consumption of clinker. In the contents of 25% and 30% by weight, the Portland cement clinker was replaced by fly ash and raw limestone. From these, test pieces were molded, which were subsequently subjected to physical and mechanical tests with the purpose of evaluating the possible alterations or variations that the incorporation of these materials in the cement could cause in comparison with the standard Portland cement, which in this case was Portland cement 100%. In all, about 140 physical, chemical and mechanical tests were carried out. The results obtained indicate a loss of mechanical resistance with the introduction of fly ash and raw limestone in the cement composition. They also indicate that the physical-chemical properties such as fineness, setting time, are extremely influenced by the presence of these materials, where there is a substantial increase in the setting time, especially in cement with fly ash, and a notable divergence in terms of fineness. In relation to 100% Portland cement, the cement partially replaced by fly ash, proved to be thinner as opposed to that substituted by raw limestone. With the presence of a material with pozzolanic characteristics in cement, such as fly ash, it is important to evaluate the reactivity of this material in cement. From values ​​of compressive strength at 28 days, of cement not replaced and replaced by fly ash at 25%, the percentage of pozzolanic activity in percentage was determined, which was not more than 82.7%. Not exceeding 85%, recommended by the standard, the material cannot be considered pozzolanic. Among a series of pros and cons, cements synthesized with fly ash and raw limestone reached the minimum values ​​acceptable by the standard, in relation to the physical-mechanical requirements, with classes 32.5N and 42.5N allied, with the exception of cement 30 % replaced by raw limestone, which according to the same standard, has no classification because it does not have the minimum resistance for any type of current Portland cement. The incorporation of fly ash up to 30%, raw limestone up to 25% is recommended, from an environmental and economic point of view, although the experimental results obtained through mechanical and physical-chemical tests demonstrate the weakening of some properties, these values ​​are found above the minimum limits acceptable by the standards.