Characterization of the granular packing and percolation threshold of reactive powder concrete

Reactive powder concrete (RPC) is a new cement-based material developed thr ough microstructural engineering. RPC is composed of very fine powders: san d, crushed quartz and silica fume, all with particle sizes comprised betwee n 300 and 0.02 mum, and a low water content, WIC < 0.20. A very dense matri x is achieved by optimizing the granular packing of these powders. This com pactness confers to RPC ultrahigh strength and durability. The hydration ki netic of the cementitious matrix using electrical conductivity and isotherm al calorimetry is presented. A linear relationship between the logarithm of conductivity ln(<sigma>) and the degree of hydration alpha, has been found : ln(sigma) = A(nu) - B-nu x alpha where A(nu) depends on the nature and the dosage of the different mineral a nd organic components, and B-nu is an invariant related to the granular pac king. From 19 different RPC compositions, an average value of 12.1 with a s tandard deviation of 1.7 were found for B-nu. The capillary porosity percol ation threshold was also deduced from this relationship. It has been found that when the degree of hydration is equal to 26%, the capillary pore space is discontinuous. This last result is in agreement with the prediction of the NIST microstructural model by Bentz and Garboczi [D., Bentz, E. Garbocz i, Percolation of phases in a three-dimensional cement paste microstructura l model, Cem Concr Res 21 (2) (1991) 325-344]. A continuous determination o f the degree of hydration based on electrical conductivity is proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.