Pore Structure Changes of Blended Cement Pastes Containing Fly Ash, Rice Husk Ash, and Palm Oil Fuel Ash Caused by Carbonation

Abstract

In this paper, the effects of carbonation on pore structure of blended pozzolan cement pastes were investigated. Ordinary Portland cement ͑OPC͒ was partially replaced with ground palm oil fuel ash ͑POA͒, ground rice husk ash ͑RHA͒ and classified fine fly ash ͑FA͒. The strength, total porosity, specific surface area, and pore size distribution were tested. In general, incorporation of pozzolans increased the total porosity of blended cement pastes in comparison to that of OPC paste. Carbonation of pastes under 5% CO 2 and 50% relative humidity ͑RH͒ for 28 days resulted in filling of the pore voids and possible attack on calcium silicate hydrate ͑CSH͒ depending on the type of pozzolan used. After carbonation, total porosity decreased and specific surface areas of the blended pozzolan cement pastes reduced indicating the infilling of voids. Pore size distributions of POA and RHA pastes were different to those of FA pastes. Large pores of the POA and RHA pastes were increased indicating coarsening of pores owing to possible attack on CSH. It is possible that POA and RHA were highly reactive and hence their uses resulting in severe carbonation compared to use of FA.

Mortars and Concrete Incorporating Palm Oil Fuel Ash and Fly Ash

“…This is because fine particles size of FA improves the packing effect of coarse POFA hence produced a denser blended concrete. This statement was also supported by Isaia et al, [10] and Rukzon et al, [23]. They stated that incorporation of fine pozzolans in blended concrete improves the strength of concrete due to synergic effects.…”

On blended cement and geopolymer concretes containing palm oil fuel ash

“…Chindaprasirt and Rukzon [33] indicated that the incorporation of FP caused the carbonation depth to decrease compared to cases in which coarse particles were used. They demonstrated that the amount of SP required was reduced by FP and that the mortar strength was improved compared to coarser POFA concrete.…”

“…Chindaprasirt and Rukzon [33] reported that the total porosity of mixed cement pastes can be increased compared to that of OPC paste when POFA is employed. When these pastes were subjected to 50% relative humidity (RH) and 5% CO 2 for 28 d, the pore voids were filled, and attacks on C-S-H were likely to occur.…”

Effects of Carbonation on the Microstructure of Cement Materials: Influence of Measuring Methods and of Types of Cement

“…In contrast, other authors have reported an increase in the specific surface area after carbonation; e.g., Da Silva et al (2002) and Chindaprasirt (2009) conducted mercury porosimetry studies on concrete, Arandigoyen et al (2006) investigated nitrogen adsorption on cement pastes that consisted of a mixture of cement and lime and Kim et al (1995) examined the carbonation of portlandite and C-S-H.…”