Research Of The Mechanism Of Cement Paste Agglomeration

With the rapid development of the cement production and consumption, more attention has been paid to the cement quality. The problem of cement paste agglomeration (CPA) during the cement hydration was found a long time ago. But it has been not thought highly of from then on. The research of CPA was not enough made to explain its mechanism and no good method was proposed to solve the problem. So the users and producers had to get much loss. The more important is that the cement with CPA is passed the cement national standards though it affects the properties during its using. So the research in this paper might be valuable for some practical applications in the national standards and for the development of theory.Stemming from the water sieve analysis method, a test method of CPA was proposed. Effects of cement quantity, hydration temperature, cement fineness, water cement ratio, gypsum addition, and hydration time on the particle weight (PW) of CPA were studied. The feasibility of this test method was discussed. The standard deviation results of PW show that the reliability, stability and fidelity of the test method are good. The regulation of CPA in different conditions can be revealed by the test method. It is the effective method of the study of CPA.In this paper, some exterior factors of CPA were analyzed. It was shown that PW increases along with the growth of hydration temperature, but with the decrease of environment humidity. These factors have different influence ability to CPA. Larger particles will be built if PW grows. On the other hand, the quicker the hydration speed is, the more PW is. This point shows that CPA is connected with cement hydration speed.After PW under the different exterior factors was studied, it was shown that PW increases along with the growth of cement fineness, but with the decrease of gypsum addition. All above factors and cement ingredients were analyzed, and it was revealed that C3A is the primary of the interior factor of CPA, compared with the other cement minerals. In order to study the C3A influence rate, several C3A content clinkers were produced. The result shows that PW is higher and particles are larger if C3A content in clinker is more. And C3A influence ability is stronger than all the other factors.In this paper, hydration products were discussed by means of XRD and SEM. Above all, the mechanism of CPA is that C3A hydrates more quickly in the cement hydrationsystem. Its hydration product becomes a semipermeable membrane coating (SMC) which can envelop cement particles and prevent them to hydrating. That is the formation mechanism of large particles of CPA. Cement in the big particles can hydrate partly because water can go through SMC but cement particles can not. Two phases are formed by reasons of difference concentration in the hydration system. In the end CPA appears. Experiments show that the high content of C3A is, the larger PW is. The cause is cement hydration will be accelerated, and SMC will be formed rapidly become more thick in the cement with more C3A. Any factors which result in accelerating cement hydration can induce more PW, which is the mechanism of the exterior factors. So CPA would be avoided when the content of C3A is decreased or influence ability of the exterior factors is feeble. Hereby, the production of cement with CPA will be deceased as long as the content of C3A is decreased. And CPA will be controlled as long as the use of the cement with CPA is controlled.