Research on mix proportion and nitrogen release property of porous concrete with recycled aggregate

Q. Huang, L. Lu, C. Gong, S. Wang, P. Zhao, W. Zong
University of Jinan,
China

Keywords: porous concrete, recycled aggregates, mix proportion, release of nitrogen nutrients, permeability, compressive strength, void ratio

Summary:

Using the adsorption property of porous structure of materials prepares planting concrete with fertilizer efficiency release property for plants growth. The purpose of this study was to develop planting concrete which could release nutrient for plant growth. Recycled aggregate from waste crushed concrete as porous aggregates and urea as fertilizer were used in this study. Due to the high water absorption, poor quality of recycled aggregate and planting concrete sensitive to water-cement ratio, there proposed a method for estimating the water-cement ratio while prepared planting concrete using recycled aggregate. The compressive strength, void ratio, water permeability, release of nitrogen nutrients and alkalinity of planting concrete with added urea were examined. The optimum mix proportions were employed to prepare planting concretes using limestone aggregates as reference sample. The void ratio and water permeability of planting concrete incorporating recycled aggregate were higher than with limestone aggregate but the strength of planting concrete using limestone aggregate was higher than planting concrete with recycled aggregate. The water-cement ratio suited for recycled aggregate to prepare planting concrete was 0.334, which indicated that the theoretical calculation of water-cement ratio method was feasible for preparing planting concrete with recycled aggregate. During the water-cement ratio was 0.334 and aggregate-cement ratio was 5.0, the total and connected void ratio, compressive strengths and coefficient of water permeability of planting concrete using recycled aggregate could up to 43.32%, 38.21%, 5.0MPa and 5.44cm/s, respectively. While connected void ratio was in the range of 29~38%, the results demonstrated a linear relationship between connected void ratio and coefficient of water permeability of all planting concretes. The alkalinity of planting concrete with urea was lower than without urea in early curing age and alkalinity of all planting concrete using recycled aggregate were tended to 8.2. Nitrogen nutrients could release from planting concrete and the release rates were in the range of 25%~92%.