Research On The Froms And Expansion Property Of MgO In Cement Clinker

MgO expansion in cement is one of the roots causes poor cement stability, and thus the national standards strictly limited the content of MgO in cement. Meanwhile, MgO expansion can be exploited to compensate for the shrinkage of the cement concrete. This paper studies the morphology and expansion properties of MgO, designed to further understanding of the law of MgO expansion. That can help us to take full advantage of the high magnesium limestone resources and improve the durability of concrete, to guide the research, production and application of high magnesium cement.In this paper, with the help of chemical analysis, petrographic analysis, XRD, SEM and EDS, we studied the morphology of MgO and the firing properties of clinker. As well, we researched the hydration and expansion properties about the high magnesium clinker under the different hydration temperature and content of fly ash, we discussed the internal relations and mechanism between MgO and it’s expansion properties. The results show that:(1) The content of periclase in clinker increased with the MgO, and its increasing rate will slow down when the MgO content is high enough. In this work, the MgO content of this transition point is about7.0%.(2) Improve the calcination temperature and speed up the cooling rate can both reduce the amount of periclase formation in clinker, In the high MgO and low heat clinker, improve the aluminum rate will adjust the balance of the liquid viscosity and liquid content, to make the content of the periclase decreased. The improvement of the silicon rate will also decline the periclase content, but the degree of influence is relatively weak.(3) The forms of MgO are closely related with the vitreous material in clinker. When the MgO content increased or the cooling rate accelerated, there is much more vitreous material in clinker which enfolds more amorphous MgO and that makes the proportion of periclase to MgO declined.(4) An appropriate amount of MgO can help to improve the clinker firing, but will reduce the performance of clinker firing with too much content, for example, about9.0%in this experiment. In addition, in the high MgO and low heat clinker, the increase in the rate of aluminum helps to improve the performance of clinker firing, but the raise of silicon rate will reduce the clinker firing performance. (5) Within a certain range, the higher the content of the periclase in clinker, the greater the cement expansion coefficient, and the growth of the expansion coefficient consistent with the increase of the amount of periclase. Improve the curing temperature can greatly promote the hydration of periclase, such as the cement sample with7.0%MgO content in this experiment,45℃under conservation20d can get the conversion rate of periclase as the20℃under conservation500d.(6) The influence of fly ash on the hydration expansion of periclase includes the expansion stress buffering effect and the periclase hydration reaction inhibition effect.This work shows that the existing forms of magnesium in clinker influenced by the MgO content, calcination temperature, cooling rate and the ratio of cement, and the periclase is the root of the expansion, and the expansion of the cement is closely related to the application of the supplementary cementitious materials.Therefore, in the actual production and application of high magnesium cement, we can use to control the MgO content, optimization of process parameters and mixed with supplementary cementitious materials to design and control the expansion properties.