Study On The Water-resistant Of Cementitious Composite Based On Gypsum

Gypsum products have many good properties, such as energy-saving, lightweight, heat insulation, etc. As a kind of air-hardening gelling material, water-resistance is very bad. This is the big disadvantage to prevent the development and application of Gypsum.Many methods were used to improve the water-resistance in this paper, namely, organic matter coating, inorganic chemical reaction and hydration mineral closed pores. The paper analyzed the water-resistance mechanism of the above methods and provided a reference for the preparation of gypsum-based composites production.Firstly, the modifier types were explored through the polyvinyl alcohol(PVA),Ethylene Vinyl Acetate emulsion(EVA), Barium chloride, Sodium silicate, Sodium methyl metasilicate and ZKY water-resistant additive. The water absorption of Gypsum products was largely reduced when added moderate PVA, Barium chloride and Sodium methyl metasilicate, On the contrary, EVA, Sodium silicate and ZKY additive had little influence on its water absorption.Further, different dosages of modifiers influence properties of Gypsum products included the mechanical properties, volume stability and water-resistant.The results show that PVA and Barium chloride increased its mechanical properties on dry condition, while Sodium methyl metasilicate decreased it. Although Barium chloride had little influence on the 28-day wet flexural strength, it obviously reduced its wet compression strength. Barium chloride and Sodium methyl metasilicate improved the volume stability of the material. And when 5% of PVA can improve the volume stability. When 3% of PVA, 15% of Barium chloride and 8% of Sodium methyl metasilicate were mixed respectively, the softening coefficient reached the highest.Through orthogonal test of barium chloride and aluminate cement, the effect of compound admixture on the mechanical properties, volume stability and water-resistant property were studied. show that when the ratio of water to binder was 0.53, Barium chloride was 10%, Aluminate cement was 20%, 28-day softening coefficient reached the highest.Through orthogonal test of Barium chloride and PVA, the effect of compoundadmixture on the mechanical properties, volume stability and water-resistant property were studied. The results show that when the ratio of water to binder was 0.53, Barium chloride was 15%, PVA was 3%, the 28-day softening coefficient of flexural reached the highest.Moreover, when the ratio of water to binder was 0.53,Barium chloride was 20% and PVA was 1%, 28-day softening coefficient of compressive reached the highest.The analysis on XRD and SEM shows that the blank sample of Gypsum product is mainly made up of CaSO4·2H2O. The main form of Gypsum product is long columnar crystal, and it also consists of small number of short columnar and tabular crystal. The modifiers can change crystal morphology. EVA, Barium chloride and Polyvinyl alcohol can reduce the porosity. Sodium silicate, ZKY additive and sodium methyl metasilicate can produce amorphous substance in crystal and protect crystals contact point. Sodium methyl metasilicate, compound admixing Barium chloride and PVA can densify the crystal structure.