Mechanical properties and water absorption of steam-cured mortar containing phase change composites

Steam curing is a common method used in the production of precast concrete components. However, the formation of microcracks and large pores during steam curing process are very detrimental to the longterm performance of cement-based materials. The use of phase change materials may be a potential method for improving disadvantages caused by steam curing. Phase change composites are prepared by implanting paraffin into diatomite, expanded graphite, and mixture of diatomite and expanded graphite. They are represented by D/P, EG/P and D/EG/P in turn. The thermal properties and static water contact angle of phase change composite (CPCM) are tested. The mechanical and water absorption properties of steam-cured mortars with CPCM are investigated. Results indicate that the latent heat values of EG/P, D/P and D/EG/P are 80%, 30% and 36% of the values for pure paraffin, respectively. The CPCMs exhibit hydrophobic properties due to the roughness of solid surface. The presence of CPCM greatly improve the water resistance of steam-cured mortar without sacrificing mechanical properties, and steamcured mortar with 1 vol% D/P has the best performance. The possible reason is that D/P reduces the porosity and improves porous microstructure of steam-cured mortar. The cracks and holes in the mortar matrix can be covered and filled with paraffin from D/P by SEM analysis. There is no interfacial gap between D/P and the mortar matrix through SEM analysis, which promotes the formation of a dense and strong mortar matrix. Therefore, the addition of an appropriate CPCM is helpful to improve the durability of the steam-cured cementitious materials. (C) 2020 Published by Elsevier Ltd.