Topic
Ettringite
About: Ettringite is a research topic. Over the lifetime, 2702 publications have been published within this topic receiving 67056 citations. The topic is also known as: woodfordite.
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TL;DR: In this article, the authors used micro-analysis to check if traces of sulfate crystals are present in the cement paste and found that large amounts of ettringite, gypsum and brucite were probably one of the determining factors causing failure of cement paste.
Abstract: Normally, concrete technologists attribute salt weathering, salt crystallization or physical attack to the deterioration of concrete that is partially exposed to sulfate environment. However, there are few convincing evidences supporting this view. The purpose of this paper is to check by means of extensive micro-analysis if traces of sulfate crystals are present in the paste. This would enable to verify in a direct way whether salt weathering really causes cement paste damage or not. In this research, cement paste and cement–fly ash paste specimens were partially exposed to sodium sulfate and magnesium sulfates solution under a constant storage condition (20 ± 2 °C, and 60 ± 5% RH) and a sharply fluctuating environment (40 ± 2 °C and 35 ± 5% RH for 24 h, then 10 ± 1 °C and 85 ± 5% RH, also for 24 h) respectively. ESEM and SEM images, combined with EDS and XRD analysis, were employed for micro-analysis. The experimental results indicate that Na2SO4 crystals or MgSO4 crystals could not be identified in the cement paste or the cement–fly ash paste, both under constant and fluctuating exposure conditions. Instead, large amounts of ettringite, gypsum and brucite were found and identified as probably one of the determining factors causing failure of cement paste. On the other hand, salt crystallization could be observed in the calcium carbonate crystals, the carbonated products of hydrated cement paste.
30 citations
TL;DR: In this article, a pore solution study was undertaken to provide additional understanding of the hydration behavior of high-calcium fly ash in fly-ash-water pastes.
30 citations
TL;DR: In this paper, a supersulphated phosphogysum-slag (SSC) concrete was used for concretes, and the compressive strength reached 38.6 MPa after 28 d, close to PSC concrete and OPC concrete.
Abstract: Supersulphated phosphogysum-slag cement (SSC) is a newly developed non-burned cementitious material mainly composed of phosphogysum (PG) and ground granulated blast furnace slag (GGBFS), with small amount of steel slag (SS) and clinker (CL). SSC is a kind of environmentally-friendly cementitious material due to its energy-saving, low-carbon emission, and waste-utilization. We prepared concretes with supersulphated phosphogysum-slag cement, and studied the mechanical properties, microproperties and resistance to chloride penetration of concrete in comparison with those of portland slag cement (PSC) and ordinary portland cement (OPC) concrete. The test results show that the compressive strength of SSC concrete can reach 38.6 MPa after 28 d, close to PSC concrete and OPC concrete. Microanalyses indicate that large quantities of ettringite and C-S-H, and little amount of Ca(OH)2 are generated during the hydration of SSC. The dense cement paste structure of SSC is formed by ettringite and C-S-H, surrounded unreacted phosphogysum. The property of resistance to chloride penetration of SSC concrete is better than PSC and OPC concrete due to the fact that SSC can form much more ettringite to solidify more Cl−.
30 citations
TL;DR: In this paper, the influence of three doses of expansive agent on fresh state and on compressive strength and magnitude of free expansion under two curing environments was evaluated on a reference mixture of self-compacting concrete (SCC).
Abstract: Expansive concretes based on the formation of ettringite from calcium sulfoaluminate agents are presented as an effective alternative to minimize the problems derived from shrinkage and low tensile strength at the early ages of the concrete. However, determining the mechanism responsible for the expansion is still a controversial issue today. In this study, the influence of three doses of expansive agent on fresh state and on compressive strength and magnitude of free expansion under two curing environments was evaluated on a reference mixture of self-compacting concrete (SCC). The microstructural evolution of the hydrates and anhydrous related with the expansive phenomena was also studied. From our observations it seems that an eminently amorphous ettringite is formed and that this ettringite would be strongly related to expansion. As a result, the influence of the ratio w/cementitious material and curing environment on the magnitude of the expansion as well as the influence of this on the mechanical properties of the SCCs was identified.
30 citations
TL;DR: In this article, the results of the substitution of the calcium based additive by one alternative additive based on magnesium, an industrial byproduct named PC-8, in the stabilization of five different sulfate soils were analyzed.
30 citations