Influence of cement type on resistance to attack from two carboxylic acids

Abstract

In a number of circumstances, concrete may be required to possess resistance to organic acids. These are frequently carboxylic acids. This paper examines the effect of two such acids-acetic and butyric-on hardened cement paste specimens made from three cement types-Portland cement (PC), a combination of PC and fly ash (PC/FA), and a calcium sulfoaluminate cement (CSA). Specimens were exposed to solutions of the acids and deterioration characterized in terms of mass loss and pH measurements, micro-CT scanning, and chemical and mineralogical analysis. Additionally geochemical modelling was used to further examine the mechanisms involved during acid attack. The CSA cement was most resistant to attack, with the PC paste displaying the least resistance. This resistance has been partly attributed to the higher acid neutralization capacity of CSA cement. However, this paper demonstrates that the enhanced performance is most probably the result of a denser microstructure.

Biodeterioration of concrete in agricultural, agro-food and biogas plants: state of the art and challenges

“…For acids with soluble calcium salts (acetic acids and other volatile fatty acids, lactic acid), calcium salts do not form under immersion conditions and chemical attack results in a progressive dissolution of all hydrated and anhydrous phases of the cement matrix (depending on the pH and concentration of acids). Calcium, magnesium, sulfur and alkalis are leached, leaving a porous skeleton of Si-Al gel [27][28][29][30][31][32][33] (Fig. 1).…”

Deterioration of stone and concrete exposed to bird excreta – Examination of the role of glyoxylic acid

“…In the case of the two 372 cement pastes and limestone there is a slight increase in pH. This behaviour has not been observed in 373 the case of similar monoprotic organic acids present at the same concentration in contact with cement 374 paste specimens (Dyer 2017), since the materials typically do not have the capacity to wholly neutralise 375 the acid. These results strongly suggest the precipitation of acid species from solution in the exposure 376 tank.…”

“…Given that the mode of deterioration of cement by 759 glyoxylic acid is acidolysis, an alternative approach is the combination of Portland cement with 760 pozzolanic materials such as fly ash or latent hydraulic materials such as GGBS. This approach works 761 { PAGE \* MERGEFORMAT } because it limits the levels of portlandite present, whose dissolution is most immediate and which leads 762 to a significant loss in strength (Dyer 2017). The use of calcareous aggregate may provide a means of 763 further neutralising the acid.…”

Thermodynamic Modeling and Experimental Validation of Acetic Acid Attack on Hardened Cement Paste: Effect of Silica Fume

“…Concrete made of ordinary Portland cement (PC) usually has a lower acid resistance compared to concrete made of calcium aluminate cement (CAC) or mixtures of Portland cement and supplementary cementing materials (SCMs). The pozzolanic additives with high silicate (such as silica fume) and aluminate content (such as slag, metakaolin and fly ash) lead to a lower concentration of Portlandite in the hydrated paste and densification of the microstructure, both increasing the acid resistance [ 3 ].…”

“…Beneath the completely decalcified layer of silica gel, a partially degraded layer forms that are characterized by Portlandite dissolution only. This leads to a gradient of the pH with decreasing values from this layer towards the outer layer or the concrete surface [ 3 ].…”