Impact of accelerated carbonation on OPC cement paste blended with fly ash

•Accelerated carbonation tests are performed on fly ash blended cement pastes.•Porosity, liquid water saturation and chemical content evolution are quantified.•We can quantify the average molar volume evolution of C-S-H during carbonation.

Cement is a huge carbon dioxide producer. Supplementary cementitious materials can help reduce this outcome. However, carbonation of these blended cements remains an active subject of research. Accelerated carbonation tests (10% CO2, 25 °C and 62% RH) are performed on fly ash blended cement pastes. Experiments are performed at varying ages of carbonation (1 to 16 weeks) to measure the evolution of the carbonation depth over time and to quantify key parameters: thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP) and gamma ray attenuation method (GRAM). The total porosity decreases with a rearrangement of the microstructure due to carbonation and the creation of big capillary pores for the paste with the highest contents of fly ash (60 vol.%). The C-S-H molar volume evolution during fly ash-blended cement carbonation is calculated using a method combining MIP, TGA and GRAM formerly successfully applied to OPC paste in a paper published in the same journal.