Experimental investigation of moisture buffering capacity of sprayed hemp concrete

This study deals with dynamic characterization of hydric behaviour of sprayed hemp concrete. The measurement of moisture buffer value (MBV) is held according to the NORDTEST protocol (Rode, 2005). Specimen are exposed to daily cyclic variation of relative humidity: 8 h at 75%RH and 16 h at 33%RH the test is held under isothermal conditions (23 degrees C). The experimental set-up is validated by comparison of moisture buffer value measured on cellular concrete with values given in the NORDTEST project for the same kind of material. Results show that sprayed hemp concrete has an excellent moisture buffer capacity (MBV = 2.15 g/(m(2) %RH)). So, it is an excellent hydric regulator that improves hygrothermal comfort and reduces energy needs. Moisture effusivity is then calculated from sorption and water vapour permeability value and from dynamic test of MBV. The results (respectively 5.8 x 10(-07) and 4.8 x 10(-07) kg/(m(2) Pa s(1/2)) show a slight discrepancy between values obtained from steady-state and from dynamic conditions. Finally, the penetration depth for daily cyclic variation is estimated about 5.8 cm for sprayed hemp concrete. Also, the experimental data set can be used for benchmarking buffering models. (C) 2012 Elsevier Ltd. All rights reserved.