Improvement of hydraulic concrete surface quality by different controlled permeability formwork liner

To enhance the improvement effect of controlled permeability formwork liner (CPFL) on the surface quality of concrete, two kinds of modified CPFLs were prepared by adjusting the pore size and stiffness. The effects of modified CPFLs on the three-dimensional surface morphology of concrete, the surface rebound strength, and the pore structure at different depths were analyzed by using three-dimensional image scanning, the rebound method, and the image recognition technology. The results showed that after using modified CPFLs with smaller average pore size and higher stiffness, the surface roughness of concrete was reduced by 54%, the coefficient of variation for surface strength was controlled within 0.067∼0.074, the porosity was decreased by 17.9%∼22.9% and the improvement depth of the concrete was increased to 20 mm. Compared with ordinary CPFL, modified CPFLs had more advantages in reducing the surface roughness of concrete and improving the uniformity of surface strength distribution. Modified CPFLs can significantly reduce the number of pore, porosity and pore fractal dimension of the concrete surface, and the improvement depth of the concrete is greater compared to ordinary CPFL. Reducing pore size and increasing stiffness can effectively enhance the improvement effect of CPFL on the surface quality of concrete.