Geopolymer (GP) binders are an appealing alternative to Portland cement (PC) binders as they have the potential to reduce the CO 2 emissions associated with the cement and concrete industry. However, their durability in aggressive environments needs thorough examination if they are to become a viable alternative to traditional Portland cement (PC) materials. This study investigated the effect of increasing slag content and activator dosage on the sulfuric acid resistance of fly ash GP binders. Their performance was also compared with that of neat PC mixes using various physical and microstructural techniques. The results show that increasing the slag content of fly ash GPs decreases porosity, but makes the reaction products more susceptible to sulfuric acid attack. It was also found that increasing the alkaline activator dosage of fly ash GPs has little impact on sulfuric acid resistance. Finally, GP binders displayed superior sulfuric acid resistance than their PC counterparts.

2018). Sulfate and acid resistance of lithomarge-based geopolymer mortars. Construction and Building Materials, 166,[537][538][539][540][541][542][543][544][545][546][547][548][549][550][551][552][553] ABSTRACTThe resistance of room temperature cured geopolymer mortars (GPM) against chemical attacks, i.e. sodium and magnesium sulfate solutions, and sulfuric and hydrochloric acid solutions, was evaluated. GPMs were formulated using a lithomarge precursor (low-purity kaolin) to achieve 28-day characteristic compressive strengths of 37.5 and 60 MPa. Their performance was compared with those of equivalent Portland cement mortars (PCMs) having the same paste volume and strength grade. GPMs with both strength grades showed superior performance against sulfate attack when compared to PCMs. No visual deterioration was observed in GPMs, the mass and length changes were relatively small, and no changes to the microstructure were detected -in contrast to severely deteriorated PCMs.As confirmed by visual observations and lower mass loss, GPMs showed better resistance to attack by both acids than PCMs. GPMs provided a better quality (lower permeability) of an acid-degraded layer, lowering the degree of further deterioration. The main mechanisms of the matrix deterioration of GPMs in both acids was dealumination of the hardened binder, with a higher degree of changes detected for sulfuric acid.

Abstract:Traditional Portland cement (PC) concrete has been used for many years in the agricultural industry for the construction of silos and silage effluent storage facilities. However, the acidic nature of the silage effluent produced by silage has led to severe degradation of PC concrete which in turn has significant environmental and financial implications. This study compares the resistance of PC and geopolymer (GP) mortars and pastes to silage effluent over 12 months. The GP samples displayed increased resistance to silage effluent in terms of mass and strength loss. Analysis of microstructure suggests that the increased stability of the reaction products is the main factor behind increased silage effluent resistance when compared with PC. It was also found that pulverised fuel ash (PFA) and ground granulated blast furnace slag (GGBS) blends with a higher PFA content may offer increased long term silage effluent resistance due to the nature of the main binder gel produced in PFA dominant systems.

The concrete mixes used in this study had 28 d mean strengths of 50 and 30 MPa and also had Portland cement (PC) partially replaced with ground granulated blast-furnace slag (GGBS) and fly ash (FA). These mixes were the same as those used in a UK-based project that involved casting of blocks, walls and slabs. The strength development of ‘equivalent’ mortar mixes was determined in the laboratory for curing temperatures of 10, 20, 30, 40 and 50°C. High curing temperatures were found to have a beneficial effect on the early-age strength, but a detrimental effect on the long-term strength. GGBS was found to be more sensitive to high curing temperatures than PC and FA, as reflected in its higher ‘apparent’ activation energy. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse–Saul function (i.e. concrete strength gain rate varies linearly with temperature) was not sufficient to account for the improvement in early-age strengths resulting from high curing temperatures. The Arrhenius-based function, on the other hand, overestimated them because of the detrimental effect of high curing temperature on strength starting from a very early age. Both functions overestimated the long-term strengths, as neither function accounts for the detrimental effect of high curing temperatures on the ultimate compressive strength.

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