The Influence of Different Pozzolanic Admixtures on Structure and Properties of Concrete

As known, pozzolana is a natural or artificial material containing silica or alumina (mainly silica) in a reactive form. By themselves, pozzolanas have little or no cementitious properties. However, in a finely divided form and in the presence of moisture they will chemically react with alkalis to form cementing compounds. The silica and alumina in a pozzolana has to be amorphous, or glassy, to be reactive. When silica containing e.g. fly ash is added to concrete the pozzolanic reaction occurs between the silica glass (SiO2) and the calcium hydroxide (Ca(OH)2) or lime, which is a by-product of the hydration of Portland cement minerals. The hydration products produced fill the interstitial pores reducing the permeability of the matrix [1]. Ca(OH)2 (hydrated lime) is produced by the reaction of hydrolysis of Portland cement minerals and water. Due to its limited solubility, particles of hydrated lime form within interstitial spaces. With a continuing supply of moisture, the lime reacts with the fly ash pozzolanically, producing additional hydration products of a fine pore structure. The pozzolanic reaction is as in Calcium hydroxide + silica = tricalcium silicate + water: 3Ca(OH)2 + SiO2 = 3CaO · SiO2 + 3H2O [1-3]]. The main aim of given studies was to perform a comprehensive investigation of relationships between concrete mix composition containing additive of different pozzolanic materials and mechanical strength and microstructure. As pozzolanic admixtures micro and nano size silica, powder of glass and ashes of biomass were used. Obtained series of samples were tested in order to compare their properties