Study On Hydration Mechanism Of Cement-Pozzolana Gelation System

Natural pozzolanic materials are richly available in Yunnan province of China, yet relatedinvestigation on its compositions and cementitious properties was rarely conducted, which in alarge extent affects its application.In this paper, it had launched investigation on chemical compositions and lithofacies ofpumice and basalt and had evaluated pozzolanic activity of pumice, basalt and fly ash in terms ofSpecific strength. The results showed that, the total amount of SiO2, Al2O3 and Fe2O3 accountedfor 86.11% and 83.62% in pumice and basalt respectively and Pumice was of porous glassceramics phase.The primary mineral of Pumice consisted of volcanic glass and pyroxene andBasalt was of patchy and the matrix grain structure and mainly consisted of plagioclase andpyroxene. Activity of pumice powder was significantly higher than that of basalt powde. Givencontent of 10% and 20%, activity index of pumice powder was higher than that of classâ… fly ash.With content of 30% or higher, the activity index of pumice powder decreased, lower than classâ… fly ash. The optimal content of pumice powder, basalt powde rand fly ash were respectivelyabout 20%, 10% and 40%.In later hydration, with increase of specific surface area of basalt, theactivity index did not show an upward tendency solely, approaching the peak when surface areacoming to 500m2/kg.It had explored influence of pumice and basalt upon strength of composite cementitioussystem. The results showed that mortar strength of the composite cementitious are lower thanreferenced cement cementitious system, and strength decreased with pozzolanic materialscontent, yet strength decreasing magnitude was mitigated with aging, which in a way reflectedthe fact that pumice and basalt contribution to strength development was primarily manifested inlater hydration stage and later strength of composite cementitious system was superior toreferenced cement. Pumice powder mortar compressive strength was higher than asalt powdermortar, and pretty close to fly ash mortar. At 90d, the microstructure of cement - fly ashcementitious was observed to be the most compacted, followed by pumice cementitiouscementitious system. Late hydration, basalt cementitious system with surface area of 500m2/kgwas considered the best in terms of activity, strength and microstructure.Based on heat releasing rate curve and hydration kinetics model, it investigated the effect of pumice, basalt on hydration process and reaction mechanismthe of the Moderate Heat PortlandCement cementitious system. The results showed that incorporating pumice, basalt and fly ashinto cement could delay exothermic peak produced by C3A hydration and final set time In whichCement - Basalt cementitious system final setting was delayed most seriously. Compared withModerate Heat Portland Cement cementitious system, the total heat hydration amount ofComposite cementitious system was reduced to different extent. Pumice and basalt had adverseeffect on cement clinkerin at accelerating stage yet it was reversed in stabilizing stage. In thelight reaction rate, it could be ranked from fast to low as cement - fly ash system, cement -pumice system and cement - basalt system.