An investigation into the effect of material composition on the fundamental properties of permeable concrete

The use of permeable concrete in the construction industry has been increasing around the world during the last few years. The fundamental properties of permeable concrete must thus be comprehensively evaluated and elucidated in order to obtain the full benefits of this material. This research investigated the effects of material composition on the mechanical properties (compressive strength, stress-strain behaviour and the modulus of elasticity) and on the hydraulic properties (porosity ratio and permeability) of the permeable concrete. Eight different permeable concrete mix designs were prepared with two aggregate sizes in two different proportions, different sand ratios, two aggregate to cement ratios and a constant water to cement ratio. The target 28-day compressive strength was designed to be between 15MPa and 35MPa. The porosity ratio was designed to be between 25% and 15%, whilst the permeability was designed to be between 12mm/sec to 2mm/sec. A review of the published literature revealed no standard experimental procedure for determining the stress-strain behaviour and the modulus of elasticity of permeable concrete using the strain gauge method. The only method in use was the platen-to-platen method. This research involved the development of a testing method for determining these properties using the strain gauge method. The results are compared with those that were obtained using the platen-to-platen method. A significant difference was found between the properties that were measured by these two methods. A semi-empirical equation to represent the complete stress-strain behaviour for unconfined permeable concrete is proposed as part of this research. Various existing models for low-strength concrete and normal-strength concrete were used and compared with the experimental data. Various parameters were studied and their relationships were experimentally determined. The only parameters needed to run the new model is the ultimate compressive strength and the density. The proposed semi-empirical stress-strain equations were compared with actual cylinder tests results under axial compression; the new model gives a good representation of the mean behaviour of the actual stress-strain response of the permeable concrete.