Effectiveness of Spent Coffee Ash in Concrete Permeable Pavement Bricks

This paper utilized the principle of circular economy to recycle spent coffee grounds, which are pyrolyzed into coffee ash biochar for the preparation of permeable concrete pavement bricks. This process can solve the problem of spent coffee grounds disposal and positively affect the economy and the environment. After comprehensive comparison, the coffee ash at 500°C, 650°C, and 800°C was selected as a cement substitute to replace 5%, 10%, and 15% of cement for the production of permeable pavement bricks, and orthogonal tests were conducted to investigate the effect of coffee ash in the application of permeable concrete pavement bricks, with mechanical properties, permeability, and frost resistance as the evaluation indexes. Through the experiment, it is found that with the increase of coffee ash content, the mechanical properties of permeable pavement bricks show a decreasing trend. Under the optimal water-cement ratio, the compressive strength of the specimen with a 5% spent coffee ash (SCA) content increased by 47.7% compared to the 15% content, the flexural strength increased by 64.1%, and the splitting tensile strength increased by 32.4%. The water permeability coefficient is not much different. This paper shows that the application of SCA in concrete permeable pavement bricks is feasible, and explores the application of SCA in permeable bricks and the trend of its effect on their performance. The experimental results were evaluated through range analysis and analysis of variance to determine the optimal combination of individual characteristics that can be used for different performance requirements.