Effects of fly ash and silica fume on alkalinity, strength and planting characteristics of vegetation porous concrete

Supplementary Cementitious Materials (SCMs) have been utilised for decades to lower the OPC concrete's alkalinity. However, the usage of SCMs to lower the alkalinity of Vegetation Porous Concrete (VPC) is limited. The present study examined the effects of Fly Ash (FA) and Silica Fume (SF) on the alkalinity, strength and planting properties of VPC. Since the Coarse Aggregate Size Ratio (CASR) has a substantial impact on the VPC strength, the current-study also examines the influence of CASR on the void content, strength and planting properties of VPC. The blending of cement with FA and SF reduced the alkalinity of the VPC, and that increasing the dose rate of FA and SF lowered the alkalinity of the VPC even more. The pozzolonic reaction of FA and SF in the VPC consumes CH crystals to form C–S–H gels, and the reduction in the quantity of CH crystals causes the pH of the VPC to decrease. Consequently, the plant's root length growth and LRWC improved by 7.91% and 4.95%, respectively. The inclusion of FA decreased the compressive strength due to the lower activity of the FA with the cement matrix; however, the accelerated pozzolanic reaction between Ca(OH)2 and SiO2 in the SF enhanced VPC strength. Despite an increase in CASR improves the aggregate interlocking property and the strength, it also reduces the void content of the VPC. The reduction in VPC pores hampered root mobility through the concrete, delaying root development and reducing the availability of water and nutrients.