A Comparative Study on Water and Gas Permeability of Pervious Concrete

The water and gas permeability of pervious concrete play essential roles in rainwater infiltration and plant root respiration. In this study, the gas and water permeability of pervious concrete samples were measured and compared. The water permeability was tested using the constant water head method and several water heads were measured for inspection, in which the permeability varied with the application of the pressure gradient. The permeability of gas was measured using a new simple gas permeameter, which was specially manufactured for measuring the gas permeability of pervious concrete under a stable pressure difference. A series of different gas pressure gradients was applied to test whether the gas permeability was a function of the applied pressure. Both the gas and water permeability of pervious concrete were found to decrease with an increased applied pressure gradient, which did not conform to the Klinkenberg effect (gas slippage effect). When comparing the gas permeability and water permeability of pervious concrete, we found that the water permeability was 4–5 times larger than the gas permeability

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

Innovative high-strength, high-permeability concrete for large-scale applications in permeable subgrade of highway tunnel

The durability of concrete roads in mountainous regions may be reduced due to underground water infiltration and surface water erosion within highway tunnels. A promising solution is the use of pervious concrete as a drainage subgrade layer to drain away the water, and then to prevent water-induced pavement damage of pavement. For pervious concrete to be an ideal drainage layer for high-traffic loads, it must have compressive strength and permeability coefficient exceeding 25 MPa and 15 mm/s, simultaneously. However, traditional pervious concrete tends to emphasize either in high-strength or high-permeability, depending on its porosity. This study introduces an innovative proportion design method of pervious concrete, which enables higher compressive strength and permeability coefficient by adjusting its skeleton structure, and thus catering to high-traffic load applications. In addition, the workability and setting time of pervious concrete were optimized according to the local environmental conditions, facilitating large-scale and efficient paving of the drainage subgrade. As a result, a drainage subgrade layer with a 28-day compressive strength of 26.43 MPa and permeability coefficient of 18.86 mm/s was successfully applied in a highway tunnel. This study provides a theoretical framework and technical support for widespread application of pervious concrete in drainage subgrade of high-traffic load road