Investigation On The Properties Of Porous Concrete Using Recycled Concrete Aggregate As Partial Replacement Of Coarse Aggregate.

Abstract

Porous concrete is an environmentally friendly concrete that contains zero fine aggregates, creating a significant pore that allows the concrete to be water permeable. Thus, it is an important way to control health and pollution hazards due to surface ponding of water on roadways by allowing water downward through the pores, thereby minimizing flooding risks, reducing runoff, and improving groundwater water recharge. However, this type of concrete has not been considered in the Ethiopian market. Likewise, demand for fresh aggregate is still high while natural resources are reducing. Accordingly, attempts have been made to avoid the gap between demand and supply of fresh aggregates. Therefore, the utilization of recycled coarse aggregates from construction and demolition wastes serves as a sustainable solution, which reduces the overall cost and environmental pollutions. This study aims to investigate the properties of porous concrete expermentally using recycled concrete aggregate in the ratio of 0%, 15%, 30%, 45%, and 60% replacement by weight of natural coarse aggregate. For this experimental study of concrete grade ranging between 2.8 MPa to 28 MPa , five different groups with 75 cubes of size 150mm* 150mm* 150mm and 60 cylinders of size 200mm* 100mm of total 135 samples were casted, and conventional curing method for 7, 14, and 28 days was adopted. To determine the behavior of the concrete, workability (slump and compacting factor test), fresh density, compressive and split tensile strength were evaluated. In addition to those properties, porosity and permeability properties of the concrete were also evaluated. The fresh concrete property test result shows that increasing the percentage of RCA decreases the degree of workability and fresh density as compared to the control mix. In a similar manner, compressive and split tensile strength of concrete decreases by 54.70 % and 24% respectively with an increasing percentage of RCA. This indicates that there is an indirect relationship between workability, fresh density, compressive, and split tensile strength with that of RCA. Oppositely, the test result for porosity and permeability shows that increasing the percentage of RCA increases the porosity ratio up to 16%, coefficient of permeability by 35.66%, and decreases concrete strength respectively as compared to the control mix. This also indicates, the strong linear relationship between porosity, permeability, and percentage of RCA. The optimum quantity of RCA for the most favorable compressive strength (17.37MPa) was observed at 30% of RCA. A regression model was also developed to determine the degree of workability using compacting factor test . From the result, cofficent of determination (R 2 ) shows that compacting factor test values are 88% accurate to determine the workability of fresh porous concrete. Generally, the finding of this research shows that the use of recycled concrete aggregate for porous concrete production and its application is practicable.