The effect of marble powder on physico-mechanical and microstructural properties of kaolin-based geopolymer pastes

Abstract

As an alternative to ordinary Portland cement (OPC), alkali-activated materials (AAMs) have more recently been studied and found to have certain suitability in reducing ecological footprint of OPC binding systems. Nonetheless, due to recent concerns over the availability of certain precursors used AAMs (such as the reduction of coal fly ash availability), this study utilized marble powder in various quantities to replace the naturally available kaolin as precursor. This composite use of natural precursors has been entertained to assimilate the production of carbon zero AAMs. To evaluate the physico-mechanical and microstructural characteristics of the materials, 48 mixes with different sodium (Na) concentrations, curing temperatures, and marble powder content have been used. The results show that rising curing temperature is more effective than other variables, such as the Na and marble powder content on the physico-mechanical performance of tested geopolymers. In this regard, it is found that a very high Na content can have adverse effect on the properties, potentially due to altered Na/Si, Na/Al ratio in the mixes. Furthermore, the inclusion of marble powder is found to be effective in decreasing the overall porosity up to similar to 31% and enhancing the physico-mechanical properties of the specimens cured at 20 and 80 & DEG;C. Nonetheless, results show that when specimens containing marble powder are exposed to higher curing temperatures (above 80 & DEG;C) the presence of marble powder adversely affects physico-mechanical properties. It is concluded that this phenomenon is caused by the dehydration of chemically bound water in higher temperatures when marble powder is used. This result is further confirmed by microstructural tests.