Mix design method for plant aggregates concrete: Example of the rice husk

This article proposes a method for the mix design of concretes based on plant aggregates. Its principle consists in determining the packing density of the plant skeleton for a specific mode of implementation and then in proportioning the binder paste which will occupy the residual intergranular pore volume. The paste is consisted of the binder, the effective water, the possible additions and admixture, and trapped air and/or entrained air. For a given volume of air (and additions), the quantities of cement and effective water are then adjusted to achieve the targeted performances, based on the law of Féret. However, for this type of concrete, the large volume of entrained air (also) depends on the quantity of cement and water present in the mixture, the intensity of the mixing and the casting mode. A model describing the residual air volume must then be calibrated from tests carried out with the components of the concrete that it is desired to manufacture. The problem of the formulation can then be solved by using a numerical optimization module. An example applied to a rice husks concrete is presented here.