Study On The Composition And Properties Of New Type Of Magnesium Oxychloride Cementious Composites

With the characteristic of energy conservation and environmental protection, magnesium oxychloride cement (MOC cement) has many excellent engineering performances. And there are many resource advantages to develop magnesium oxychloride cementious composites in China. But MOC cement is limited in many engineering applications because of its poor water resistance and absorbing moisture in high humidity atmospheres. Overcoming this cement's technical defects by modifying with admixtures and developing a new type of magnesium oxychloride cementious composites can help us expand this material's application scope, utilize magnesia resources rationally and effectively, and take its advantages in energy conservation and environmental protection.The influences of the molar ratio of MgO/MgCl2 on the strength retention coefficient (kcn) and absorbing moisture of the samples had been investigated firstly to obtain a basic raw material proportion with excellent performance. Then this basic proportion was modified by a series of admixtures respectively. And the influences of chemical admixtures, mineral admixtures and polymer emulsions on the MOC cement's properties were discussed. Then an Orthogonal Experiment was designed to study the influences of different admixture blends on MOC cement's properties. Some checkup experiments were implemented and an optimum mix proportion was obtained. Magnesium oxychloride cement concretes taking sawdust, perlite and EPS particles as lightweight aggregate were prepared respectively. The influences of different kind of aggregate and mix amount of water-reducing agent on concrete's performances were investigated lastly. The main conclusions were draw as following.1. Chemical admixtures, mineral admixtures could improve MOC-cement samples'water resistances performance and restrain bittern accumulation. The sample with phosphoric acid obtained the optimum performance; when the mix amount of phosphoric acid reached 1%(wt), kcn=1.100, and the phenomenon of bittern accumulation hadn't happened on the sample after it had had been located in artificial climate box for 72 hours. Polymer emulsions had strong adverse influences on MOC cement's performance.2.The optimum mix proportion of modified MOC cement was:the molar ratio of MgO/MgCl2=7,the mix proportions of fly ash, silica fume,phosphoric acid and ferrous sulfate were respectively 40%,15%,1%,4%;the sample's properties of this proportion were that:kcn=1.083, the dissolution rate of chloride ion (Cl28) was 1.422%,and the phenomenon of bittern accumulation hadn't happened on the sample.3. With the same bulk density (ρb), the properties of different magnesium oxychloride concrete without modifiers were different.MOC-sawdust concrete had the highest flexure strength; MOC-perlite concrete obtained the highest compressive strength and the lowest expansion; the water absorption rate of MOC-EPS concrete was lowest.4.As the increase of mix proportion of lightweight aggregate, the bulk density(pb), strength(R) and water resistance(kcn) of new type of magnesium oxychloride cementious composites decreased, while the water absorption (β) and C128 of the samples went up. The water-reducing agents selected hadn't remarkable water reduction function in this material system, but their air entraining function had negative impacts on composites'performances.5.The tendency of expansion curve of modified MOC-sawdust concrete and modified MOC-perlite concrete was that the expansion (St) went up and then went down as the cure time'extending until the 30th day after the samples had been prepared; meanwhile the tendency of expansion curve of modified MOC-EPS concrete was that the St went up as the cure time'extending until the 24th day after the samples had been prepared.