The effect of delayed ettringite formation on fine grained aerated concrete mechanical properties

Abstract

Delayed ettringite formation (DEF) is a chemical reaction with proven damaging effects on the mechanical properties of hydrated cementitious composite (concrete). Ettringite crystals can cause cracks and the widening of cracks due to pressure on the crack walls caused by the positive volume difference in the reaction. In this paper, we investigated the potential to utilise the positive volume difference in DEF in order to improve the mechanical properties of hydrated fine grained aerated concrete. Fine dispersed crystallisation nuclei, achieved by adding air-entraining agent (AEA) and by short vibration of specimens, are presented as the main requirement for such improvements. Control tests of expansion and mechanical properties were performed on samples of concrete with and without AEA by inducing DEF. The microstructure of fine grained aerated concrete was examined with an optical microscope and scanning electron microscope. We found that the controlled DEF, which is guaranteed by adding AEA and with the formation of uniformly dispersed air bubbles, which are crystallisation sites for ettringite crystals, improves the mechanical properties. The specimens with induced DEF were measured and found to have a 6.8% increase of compressive strength.

Ultrasound irradiation as an effective tool in synthesis of the slag-based catalysts for carboxymethylation

“…The internal structure of the untreated desulfurization slag represents a crystallized ettringite phase over agglomerates [42] . Heterogeneous morphology of the starting material underwent significant transformations under the treatment.…”

Sustainable use of magnesite mine waste in self-compacting concrete and its study on strength, microstructure, cost and CO2 emission

“…In contrast, secondary ettringite formation (thick and long needle-like structure) was only observed in the 50MWFA mix (figure 6(d)). Primary ettringite formation involves the development of strength, while secondary ettringite formation (delayed ettringite formation-DEF) lessens the strength of SCC [72]. Batic et al (2000) stated that C-S-H gel's ability to absorb sulphate rapidly in early ages and release the same in later stages is responsible for secondary ettringite formation [73].…”

Mechanical Behavior of Crushed Waste Glass as Replacement of Aggregates

“…It can be seen in Figure 7e that the binding property of the CWG powder cement and the pozzolanic property of the glass powder results in good bonding. Etringite formation is an important issue in Portland cement concretes due to early phase hydration [51,52]. Although the hydration of glass powder and cement show similarities, some ettringite formation is seen in Figure 7e.…”