Anisotropy and macro porosity in wet sprayed concrete: Laminations, fibre orientation and macro pore properties measured by image analysis, PF test, water penetration and CT scanning

Sprayed concrete typically contains large, irregularly shaped macro pores. These are a product of the spray application and are different to spherical pores formed by an air entrainment agent for frost protection. Image analysis, capillary suction and pressurised saturation (PF test) and CT scanning were used to measure and analyse the macro porosity in specimens taken from 20 different panels sprayed in four series with varying accelerator doses, varying spraying distances and angles and varying sprayed concrete mixes. Macro porosity measurements by image analysis (3.8–7.5 %) and CT scanning (4.7– 10.1 % measured on five specimens only) were higher than measurements by pressure saturation (2.5– 4.9 %). The macro porosity increased with increased set accelerator dose. 9–20 % of the of the PF macro pore volume filled with water when submerged at atmospheric pressure. The shape of the macro pores was measured to be non-spherical, with 50 % of length/width ratios greater than 1.5. The macro pores were measured to tend towards orientation parallel to the substrate. Likewise fibre orientation was measured by CT scanning to tend towards orientation towards parallel to the substrate. Water penetration tests were done on specimens with the water pressure applied parallel and perpendicular to the direction of sprayed concrete application. Water penetration was measured to be very low parallel to the direction of application, but much higher perpendicular to the direction of application, due to macro porosity and laminations in this direction, indicating the importance of execution in wet spraying of concrete.