Effect of microcrystalline and microfibrillated cellulose on the evolution of hydration of cement pastes by thermogravimetry

Abstract

The interest in the use of cellulose fibers of increasingly smaller sizes in cementitious materials has increased in recent years. This paper brings new contributions in this field showing from respective paste thermal analysis data, how microcrystalline cellulose (MCC) and microfibrillated cellulose (MFC) affect differently the formation of Class G cement pastes hydration products from early (2 h) to later hydration ages (672 h). Pastes containing 0, 0.25 and 0.5% of cellulose per cement mass and a water/cement mass ratio of 0.45 were cured at 23 °C, and the TG/DTG tests were carried out after 2, 6, 12, 24, 168 and 672 h. The results show that the pastes with MCC and MFC additions presented higher total combined water content than the reference paste, especially after 24 h of hydration. However, this is strongly related to the quantity of water adsorbed by different celluloses and their concentrations in the mixture. Comparing cellulose pastes, MFC pastes showed lower total combined water up to 28 days, attributed to the fiber’s microfibrillar form. No higher amount of calcium hydroxide was formed in the presence of cellulose, but it was more crystalline than that obtained in the reference. Other hydrated phases (dehydration from 200 to 400 °C) are differently affected by the presence of the celluloses, the highest formation occurring for 0.25% MCC paste. This behavior was attributed to an additional cure of these mixtures related to morphological characteristics and water retention capacity of cellulose.