دانلود رایگان مقاله اثر خاکستر بادی و عامل درجه بندی بر خواص ملات با روش شناسی سطح پاسخ

Abstract

In this study, the concept of Response Surface Methodology (RSM) was presented to optimize and compare the effect of fly ash and grinding agent on the cement compressive strength at 7, 28 and 90 days. This method showed that the optimum paste mix design with the fly ash (FA) to binder at 0%, clinker (KK) to binder at 66.4% and debit grinding agent (GA) to binder at 306 kg/t produced a spread compressive strengths of the hardened paste at 29.0, 38.0 and 50.4 MPa after 7, 28 and 90 days of curing, respectively. The fly ash began to play a significant role for the compressive strength after 28 days of curing, whereas grinding agent was reactive after 7 days of curing, indicative of time dependent contribution of fly ash and grinding agent to the development of compressive strength. These were further supported by the SEM microstructure analysis. Such a delayed involvement of fly ash and grinding agent in the cement chemistry should be taken into consideration with care when translating laboratory research results typically based on 28 days strength to field practice where a shorter curing is typically provided for cost reasons.

4. Conclusion

In this investigation, the experimental results of the optimization of mix ratio of the cement paste for the desired spread percentage of the fresh paste and the maximum possible compressive strengths of the hardened pastes for 7, 28 and 90 days, allowed making the following conclusions: – The link between the cement compressive strength at 7, 28, 90 days and the percentage of clinker, fly ash and the grinding agent debit is presented by linear model. – the best values of compressive strength at 7, 28 and 90 days can be achieved at the same time by fixing the percentage of clinker at 66.4%, fly ash at 0% and the grinding agent debit at 306 kg/t. – The compressive strength of pastes significantly increased with the increase of grinding agent debit but with the decrease of fly ash. Such a grinding agent and clinker play a significant role in the development of compressive strength at different age of curing, whereas the addition of grinding agent was found effective in supporting the chemistry in cement paste at early age (i,e., 7 days) and later curing stages, especially after 90 days of curing. – During hydration, the grinding agent develops the cement hydrates and a crystal system of cement which increases the cement compressive strength. – SEM microstructural analysis supported delayed contribution of fly ash and grinding agent to the development of compressive strength at late age of the hydration. Consequently, even the grinding agent is used with a low dose (306 kg/t) it has a double effect and it presents better results than fly ash. On the one hand, it facilitates the grinding of the clinker by improving the cement fineness and on the other hand it develops the cement quality by increasing its compressive strength at young age and in the long term. Therefore, the grinding agent presents a good cement additive.