CHARACTERISATION OF LIMESTONE AND FLY ASH FOR A RATIONAL USE IN CONCRETE

摘要

In the recent years, the use of supplementary cementitious materials, such as fly ash and slag, in the production of concrete has spread rapidly, especially due to environmental and economical reasons. Great attention is now paid to blended cements in order to understand the interaction between the admixture and the "fines", which include, besides cement, fly ash, slag, silica fume and fillers, which may cause problems of incompatibility. Among the most important parameters to investigate is the tendency of fillers to adsorb the admixture, and the kinetics of adsorption. In fact, if a polymer is slowly adsorbed by the fines, more of it is then available for the dispersion of the "fines". On the other hand, if the admixture is rapidly adsorbed by the "fines", its dispersing effect is short lived. Another important parameter, which plays a key role in the kinetics of adsorption, is the internal porosity of the filler. The shape and the size of the pores might, in fact, affect the mode and the rate of adsorption. Therefore, it is very important to investigate the chemical and the physical properties of these materials, in order to understand and overcome the problems of incompatibility. In this paper, results of investigation on two types of "fines" (limestone and fly ash) are reported. The "fines" were characterized by means of adsorption analysis, mercury intrusion porosimetry, laser granulometry and chemical analysis with the aim to highlight possible problems of incompatibility. The performance of these materials was then evaluated by testing in mortars, and the results correlated to their chemical and physical characteristics.