Study On The Mechanism Of Portland Cement Hydration On Phosphorous And Fluoride Of Phosphorus Slag

The application of phosphorus slag (PS) in the cement industry has two aspects, one is used as raw materials for cement clinker producing to improve the burnability; secondly, it can be used as cement admixture. However, phosphorus slag can cause a negative impact on Portland cement when used as cement admixture. The effects mainly include two aspects, one is a long setting time, sometimes the initial setting time is up to 12 hours; Secondly, the early strength is very low. These two factors severely handicap the applications of the phosphorus slag as cement admixture.In order to improve shortcomings of phosphorus slag, chemical methods to stimulate the activity of phosphorus slag were used to improve the hydration rate and shorten the setting time of phosphorus slag. It can be concluded that CaO heightens the strength of 3 days and 28 days of phosphorous slag cement. The 3 days strength of samples can increase 0.5Mpa (2.0%/growth rate) compared with phosphorous slag cement mixed with no CaO; the 28 days strength of samples can increase 4.7MPa (12.2%/growth rate). NaOH (Na2CO3), together with the compound of CO(NH2)2or NaCl, can accelerate the hydration of phosphorous slag cement. Moreover, the combination of NaOH combined with CO(NH2)2 or NaCl is more effective. According to the reaction rate of phosphorus slag, the stimulation function of activator to phosphorus slag, mainly occurs in the early-age hydration of phosphorus slag, and the late-age of which increase slowly. As for example of NaOH, the reaction ratio of 1 day is 24.12%, but the 28 days merely increase 4.96% more than that of 1 day.Meanwhile, mainly focusing on the retarding effect of phosphorous slag to the cement, the study brings forward phosphate slag soaking solution substituting water soaking, which is also called the method of the cement single mine (tricalcium silicate and tricalcium aluminate) hydrating in phosphorous slag soaking solution. Then, by means of chemical bound water, the technic XRD, SEM, hydration heat rates and many other methods, it is feasible to investigate the influence of the phosphorus and fluoride in phosphorus slag cement on the hydration process of cement single mine. The studies show that the soluble phosphorus and fluoride in phosphorus slag can obviously put off the hydration of cement single mine. From the SEM photograph, because of the delayed effect of phosphate and fluoride in the hydration process, a few pores can be obseved in the micro-structure of 3 days hardened paste, whereas the chance of cracks is reduced. As seen from the hydration heat curve, compared with the hydration process in the water solution, tricalcium silicate soaking in the phosphate slag solution emits sharply less heat. Furthermore, insoluble calcium phosphate retard cement single mine hydration, and insoluble calcium fluoride almost takes little effect on the hydration rate of aluminum tricalcium silicate. By comparison with the hydration of tricalcium silicate soaking in the water solution, the first exothermic peak of immersing in the phosphate slag solution is obviously lower, and the induction period prolongs, which consequently delays the appearance of the second exothermic peak. The characteristic, reflected from the whole exothermic curve, takes on a phenomenon that the exothermic peak is low, and the appearance of the peak is delayed.