Thermal and moisture performance parameters of high toughness engineered cementitious Composite(ECC) with PVA fibers

PVA fibers-reinforced engineered cementitious composite (PVA-ECC) has good mechanical properties and broad application prospects in construction. But researches on the performance of it as a building envelope are limited. To provide a basis for the study of the heat and moisture transfer performance of PVA-ECC as a building material, this work investigated the thermal and moisture properties of PVA-ECC by experimental methods. The dry density and porosity, capillary water absorption curve, isothermal moisture absorption curve and the relationship between water vapor permeability and relative humidity were measured. The results show that the dry density of PVA-ECC is 1715 kg/m(3), and the porosity is 20%. The capillary water absorption coefficient of PVA-ECC is 9x 10(-3) kg.m(-2) .s(-0.5), and the capillary saturated moisture content is 59.84kg.m(-3). The water vapor permeability of PVA-ECC is 3.21 x 10(-9) kg/(m.s.Pa) in the relative humidity range of 15%-33%, while it is 1.196 x 10(-8) kg/(m.s.Pa) in the relative humidity range of 81%-100%. Different empirical adsorption isotherm models are used to fit the isotherm adsorption curve of PVA-ECC. The BET model shows the best effect among these models. The variation of the thermal conductivity of PVA-ECC affected by moisture content is studied and the applicable fitting expression is obtained. The results show that as the moisture content increases, the thermal conductivity gradually increases, but the growth rate decreases. Over all, PVA-ECC has low water absorption, vapor permeability and thermal conductivity. Combined with its advanced mechanical properties, It can be speculated that the PVA-ECC has the potential to be used as a building envelope material.