Hydration mechanisms of hybrid cements as a function of the way of addition of chemicals

Abstract

In this study fly ash contents of up to 50% were used to produce binders with mechanical strength greater than or equal to type CEM I 42.5R cement (reference). The specific aim pursued in this research was to determine whether the procedure used to add the chemical activator (in solid or liquid form) can affect strength development in the cement or the nature of the reaction products formed. Two experimental procedures were deployed: (a) the chemical activator was dissolved in the mixing water; (b) the chemical activator was ground, as a solid, into the fly ash. The solid-state method induced slightly higher mechanical strength than when the activator was dissolved in hydration water. The way the chemical activator was added affected not only early age reaction kinetics, but also the nature and composition of the reaction products, the liquid state favoring the formation of phases AFt and AFm. K E Y W O R D Salkali activator, calorimetric, cement, fly ash, mechanical strength

Hydration of polyphase Ca3SiO5‐Ca3Al2O6 in the presence of gypsum and Na2SO4

“…Previous studies have demonstrated a significant increase in the overall reactivity and mechanical properties, when high volume fly ash blends are activated with Na 2 SO 4 . [1][2][3][4][5] However, the current understanding of the effect of Na 2 SO 4 on the hydration of Portland cement systems is rather limited, and new knowledge is required to understand the fundamental mechanisms, potentials, and limitations of such systems.…”

Effect of high temperatures on the mechanical behaviour of hybrid cement

“…The difference may be attributed to the formation of a smaller amount of hydrates in the HYC, particularly AFm and AFt phases and of hydrates with less water in their structure. C-S-H gels are deemed to take up more water in their structure than C-A-S-H or N-A-S-H gels (24). The endothermal peak at 430 °C to 450 °C related to portlandite dehydroxylation (1, 3) was much more intense in OPC than in HYC (Figure 3), an indication that more portlandite formed in the former than in the latter.…”

“…Hybrid alkaline cements (HYCs) are a new group of cements, developed by combining knowledge of traditional Portland and alkaline cement chemistry (11,(20)(21)(22)(23)(24). They are characterised by low clinker content (20 % to 30 %) and a high proportion of supplementary cementitious materials (SCMs).…”

“…To elude that effect while increasing the fraction of SCMs to 70 % or 80 %, a solid or liquid alkaline activator is added. The inclusion of alkaline activators raises the pH of the aqueous phase and lowers Ca(OH) 2 solubility, partially hastening alite hydration (22), while at the same time expediting the initial SCM reaction (24). Accelerating the hydration reactions of both OPC and SCMs shortens setting times and improves early age mechanical strength.…”

Development of a technology for utilizing the electroplating wastes by applying a ferritization method to the alkaline­activated materials

“…One of the promising ways for comprehensive disposal of industrial wastewater treatment products is to use them as components for water mixing and for the filler of alkaline cements [7]. These materials have unique performance properties, and include in their composition to 95 % of waste and related industrial products (fuel ash [8], blast furnace granulated slags [9], etc.…”