Enhancement of cementitious properties of alkali activated low reactive volcanic ashes: effects of curing regime and cassava peel ash replacement.

Abstract

The present study aims at improving the cementitious properties of alkali activated low reactive volcanic ashes. It has two Major parts. It assesses the influence of three curing regimes of fresh pastes and powder of cassava peel ash on cementitious properties of two low reactive volcanic ashes. After the characterisation of starting raw materials, some characteristics on elaborated alkaline cement pastes were determined. Volcanic ashes denoted Vn and Ma and cassava peel ash (CA) have respectively 26, 18 and 72 % by mass of reactive phase. In the first part of this study, the cement pastes obtained from alkaline activation of Vn and Ma powders were cured for a fixed period in three regimes: sealing in a polyethylene bag at ambient temperature (SSP25), oven drying at 60 °C (ODS60) and maintaining in open atmospheric air of laboratory (SOA25). Results obtained revealed that SSP25 regime enables good dissolution of reactive phase but cement products express low durability and mechanic strength. The ODS60 and SOA25 regimes lead to cementitious products with fairly high durability and mechanical strength. According to thermal analysis results (TGA / DSC), the differences observed on these three curing regimes for cement paste are related to hygrometric water of the reaction medium. In the second part of this study, the low reactive phase content in Ma (18 % by mass) led to search for an improvement of its reactivity in alkaline medium. This consisted of substituting Ma powder with 0 to 30 % by mass of CA powder. Thus, the substitution of Ma with CA made it possible to optimise the activation of this precursor in alkaline medium. In synergy with Ma, the substitution of 30 % by mass of CA enabled the lowering of initial setting time of paste and the enhancement of compressive strength of the cementitious product to about 60 and 733% respectively. Moreover, the substitution of Ma with CA diminishes the magnitude of efflorescence. In fact, the presence of arcanite (K2SO4) in CA assures a chemical reaction with excess Na+ ions (responsible of efflorescence) of synthesised product for the formation of aphthitalite (K3Na(SO4)2. Hence, during alkaline activation of volcanic ashes, ODS60 and SOA25 regimes are best suited for paste curing and CA powder behaves as an additional precursor.