Influence of materials and processes on the robustness of apparent porosity control methods for fair-faced concrete

Abstract

Fair-faced concrete is a new type of concrete that directly uses the surface of concrete as the facing, with good surface integrity, no chiseling and repairing after forming, and no need for decoration. In recent years, it has developed rapidly after being introduced into China, but there are some problems, the stability of pore control is difficult and the formation mechanism is insufficient. It also exists chromatic aberration. Aiming at the formation mechanism of apparent pores in fair-faced concrete, by changing raw materials and mix ratio of fair-faced concrete, adjusting raw materials, construction process and formwork parameters, this paper put forward the control interval of high robustness parameters of fair-faced concrete with few apparent pores and excellent aesthetic grade. It makes it possible to prepare fair-faced concrete repeatedly and stably with a good economy. It also has good guiding significance for practical projects. The material parameters included initial gas content, maximum particle size of coarse aggregate, plastic viscosity coefficient, initial dynamic yield stress and bleeding rate. Construction process parameters included vibration frequency, vibration time and vibration amplitude. Formwork parameters included release agents with different contact angles. The results show that the initial gas content of the fair-faced concrete slurry was 2%–3%, the particle size of the coarse aggregate was 5 mm–25 mm, the plastic viscosity coefficient of the fair-faced concrete slurry was 5 Pa·s-10 Pa s, the yield stress was 100 Pa–200 Pa, the water secretion rate was 8%–10 %, and the vibration frequency was 10,000 times/min-12,000 times/min. When the vibration time was 20 s–25 s, the vibration amplitude was 1.0 mm–1.2 mm, and the contact angle was 102°–112°, the apparent porosity of the fair-faced concrete could be controlled well.