Photovoltaic’s silica-rich waste sludge as supplementary cementitious material

Waste sludge, a solid recovered from wastewater of photovoltaic-industries, composes of agglomerates of nano-particles like SiO2 and CaCO3. This sludge deflocculates in aqueous solutions into nano-particles smaller than 1000 nm. Thus, this sludge is potentially hazardous waste when is improperly dumped. Due to its high content of amorphous SiO2, this sludge has a potential use as supplementary cementitious material (SCM) in concrete. In this study the main properties of three different samples of photovoltaic silica-rich waste sludge (nSS) were physically and chemically characterized.
The effects on the hydration kinetics of cement pastes by the addition of nSS in the designed slurries were determined using an isothermal calorimeter. Finally, the compressive strength tests of standard mortars with 7% of cement replacement were performed to determine the puzzolanic activity of the waste nano-silica sludge. The results demonstrate the nSS can be utilized as SCM to replace portion of cement in mortars, thereby decreasing the CO2 footprint and the environmental impact of concrete.

Author: G. Quercia, J.J.G. van der Putten, H.J.H. Brouwers

Section: Waste utilization

Keywords: waste, photovoltaic, nano-silica, SCM, pozzolanic