Evaluation of engineering performance, carbon dioxide emission and cost analysis of pervious concrete composed of biochar and lightweight expanded clay aggregate

This work describes the effect of biochar (BC) and lightweight expanded clay aggregate (LECA) on the engineering properties (compressive strength, density, porosity, water permeability and sound absorption), CO2 emission and cost analysis of pervious concrete. 1–50 wt% of biochar was used as a filler and 25–100 wt% LECA was used as a coarse aggregate. Moreover, the porosity values determined by the traditional method and a method using an air pycnometer were compared. The results indicated that the strength, density and sound absorption coefficient of the pervious concrete increased with increasing biochar contents up to 10 wt%, but decreased with increasing LECA contents. The porous nature of the LECA was responsible for the increased porosity and water permeability. A comparison of the porosity test methods for these materials showed that the air pycnometer method was fast and effective for samples of density <1000 kg/m3. The cost of pervious concrete containing biochar (sample BC50L0) and LECA (sample BC10L100) would be 1.7 – 2.2 times greater than a control sample (CT) without these additives. This drawback was offset in the biochar-containing samples by their lower total CO2 emission. By contrast, the total CO2 emission from the samples containing LECA was increased due to the high temperatures involved in the manufacture of the LECA. The optimum mixture for a biochar-pervious concrete incorporating LECA is sample BC10L25, which meets the ACI standard and provides a lower CO2 emission than CT. Thus, this suggests that a future challenge would be to develop a pervious concrete containing low-cost biochar and retaining the low-CO2 emission properties of LECA.