Evaluation of pervious concrete performance with pulverized biochar as cement replacement

Manufacturing cement in the industry is responsible for most of carbon dioxide (CO2) emissions to the atmosphere, while producing biochar (BC) reduces CO2 emissions to the atmosphere. Replacing a portion of cement with BC will be a win-win alternative to curtail CO2 emissions and simultaneously lock up BC. However, the mechanical performance and properties of concrete with BC as a cement replacement, especially pervious concrete, have not been well understood. In this study, we comprehensively study the porosity, water permeability, water absorption, evaporation, compressive strength, splitting tensile strength, solar reflectance, and microstructure morphology of pervious concrete samples that are prepared by replacing a portion of cement with pulverized BC. The replacement ratio, in weight, is set as 0%, 0.65%, 3.2%, 6.5%, 9.5%, and 13.5%, respectively. It is found that the BC content has little and/or no impact on the porosity and water permeability of the BC pervious concrete samples considered here, and that the water absorption increases with BC contents. BC pervious concrete samples show both the greater compressive strength and splitting tensile strength than conventional ones when the BC content is 0-6.5%, above which these strengths are compromised. The reason is that a small amount of BC will promote cement hydration, so hydration products generated in a higher amount respect to those without BC contribute to the development of the strength of pervious concrete. It is also found that 6.5% BC in the cement paste can decrease an albedo of 0.05, this decrease, however, can be compensated by the water absorption increment and strength improvement. Based on our findings, it is speculated that producing pervious concrete by replacing up to 6.5%, in weight, of cement by pulverized BC is feasible to curtail CO2 emissions and lock up BC.

Automated summary

The study found that replacing a portion of cement with biochar in pervious concrete has little impact on porosity and water permeability, but increases water absorption. When the biochar content is 0-6.5%, the compressive strength and splitting tensile strength of pervious concrete are higher than conventional concrete, but compromised above 6.5%.