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Resumen de Eco-cements containing belite, alite and ye’elimite. Hydration and mechanical properties

Diana Londoño Zuluaga

  • Cement industry is one of the major contributors for greenhouse gases emissions, releasing about one ton of carbon dioxide per ton of ordinary portland cement (OPC) fabricated. For these reasons, there is a growing interest in the development, characterization, and implementation of alternatives. The term “alternative eco-friendly cement” refers to a man-made mineral material that, reacts with water to produce a hardened mass which can be used in concrete or mortar. This is the case belite-rich cements. The major problem of these cements is the space between the extremely fast reaction of ye'elimite and the slow reaction of β-belite. A possible solution is the activation of belite clinkers by the production of cements that jointly content alite and ye’elimite, known as belite – alite – ye’elimite (BAY) cements.

    This PhD Thesis is focused on the design, synthesis and characterization of a BAY cement, with and without fly ash addition; as well as the deep understanding of the joint hydration mechanism of alite with ye'elimite. In addition, for the sake of comparison, a blended of two commercial cements (belite and calcium sulfoaluminate) was prepared, which mineralogy was similar to BAY.

    One of the objectives of this thesis has been to obtain a BAY clinker with the major jointly content of alite and ye’elimite from natural raw materials. The maximum obtained percentages of alite with ye’elimite were 16.0 and 12.1 wt% respectively, presenting an alite/ye’elimite ratio of ~1.3. These phases were associated with 60.3 wt% C2S, 2.3 wt% C12A7, 7.0 wt% C4AF and 2.3 wt% C3A in the clinker.

    Another objective has been to understand the water-to-cement (w/c) ratio effect, the superplasticizer content and the addition of fly ash (FA) in the hydration mechanism and mechanical properties of BAY. The influence of w/c ratio found on the mineralogy was only in the stratlingite/katoite ratio, where the increment of w/c ratio favored the precipitation of stratlingite instead of katoite; in the compressive strength of BAY mortars were improved by decreasing the w/c ratio. The effect of the superplasticizer on the hydration behavior showed that the polycarboxylate affects the kinetic of mayenite (C12A7) hydration; therefore, it inhibited the competitive hydration reaction between ye’elimite and mayenite. The use of fly ash in pastes and mortars did not show enough direct evidences of pozzolanic effect. Nevertheless, it was found that the increment in partial replacement increased the mechanical properties during the hydration time.

    With the aim of understanding the influence and behavior of jointly hydration of alite and ye’elimite, mixtures of alite and ye’elimite (orthorhombic and pseudocubic) systems with two alite/ye’elimite ratios (1.37 and 2.74) were prepared. The results showed that alite hydration was highly affected by the hydration kinetic of ye’elimite, and independently of the alite/ye’elimite ratio, the increase of w/s ratio favored the hydration degree of alite and the respective precipitation of stratlingite. Therefore, decrease the stability of AFt.

    Finally, the “commercial binder” B83 shows the same hydrated mineralogy than. Particularly, B83 presented less hydration degree of alite at 180 days than BAY. This low hydration degree favored the ettringite stability without any evidence of AFm formation.


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