One of the actual problems of the further sustainable development of construction industry is solution of energy and resource saving problems during production and reduction of harmful emissions. Building materials based on gypsum raw compared to cement materials of analogical purpose are characterized by low energy consumption, as well as better ecological indicators. However, gypsum materials without modifying additives have low strength and water resistance which limits their application to the area of internal processing of rooms with a relative humidity of up to 60 %.
Among the known ways to increase strength and water resistance of gypsum compositions the most effective from a technical and economical point of view is introduction into their composition lime and active mineral additives (AMA) which during the hydration process form waterproof and high-strength products in the structure of gypsum stone. Metakaolin is used in the work as AMA.
The article deals with the results of determining the influence of gypsum brand (G-4, G-5 and G-10) on the composite binder properties and the stone characteristics of system “gypsum – quicklime – metakaolin”: compressive strength, water resistance, shrinkage. Technological parameters for the preparation of composite gypsum-lime binders: water-powder ratio W/P = 0.8; the temperature of the mixing water is T = 12 ° С.
For samples with gypsum G-4 and G-5 the increase in strength for 28 days of hardening was 59% and 50% respectively, and for a stone with gypsum G-10 the drop in strength was 52% compared with pure gypsum stone in its normal density. It was established that for receiving without clinker composite gypsum-lime binder the most optimal is using building gypsum brand G-5. On the basis of such a binder, a stone with a compressive strength of up to 8 MPa and a coefficient of softening of 0.46 was received.
It was established by X-ray analysis that the main products of binder hydration are calcium sulfate dihydrate CaSO4·2H2O, Ettringite 3CaO·Al2O3·3CaSO4·32H2O, Portlandite Ca(OH)2 and Calcite CaCO3. The presence of these crystalline phases was confirmed by respective thermal effects on the curve derivatogram. According to thermogravimetric measurement the amounts of Portlandite and Calcite were calculated.
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