The study determines the reasonable particle composition, evaluates the actual cement grain composition of some typical rotary kiln cement factories, points out technological and technical solutions to achieve the composite particle composition. management, will help the cement industry choose investment, production more efficiently in cement production in the short term, as well as in the long term, is a necessary job
In Vietnam, the research on the composition of cement grain size and its use to improve the quality of cement, so far has not been properly mentioned. The assessment of the fineness of cement today is mainly based on the criterion of residual on the sieve and measurement of the ratio. According to TCVN 6260:1997, for cement mixed with PCB30, the residual amount on sieve 008 is <12% and the density is >2700 cm2/g. But with TCVN 4030:2003, the basis for assessing the fineness of cement is the residual amount on sieve 009 and the ratio criteria. Thus, in terms of quality indicators have been lowered, contrary to the requirements of improving the quality of cement of society and the progress of cement science.
Survey results of many cement samples at production facilities show that: Although the fineness determined through the 0.08 sieve is similar and is consistent with the provisions of Vietnamese Standards, their proportions are different. quite different (from 2700 to 4000 cm2/g). The physical and mechanical properties, especially the strength of the cement, are also significantly different.
Up to now, production facilities have only been interested in grinding output and product quality that satisfy the requirements of TCVN, but there has not been a statistic or a scientific research project that has given the ingredients. optimal cement particle size and therefore, there is no basis interested in studying whether the particle composition of their products is reasonable.
The study to determine the reasonable particle composition, evaluate the actual cement particle composition of a cement production facility to give a reasonable particle composition solution to help the cement industry improve the quality of cement and reduce the cost. product.
The experimental results show that the grain size range of 0 - 5 mm has a decisive influence on the 1-day age intensity, the 5--10 mm particle size range mainly affects the 3- and 7-day age intensity, and the 10-day grain size range. – 20 mm determines the age intensity one month and later. From the experiment, it can be seen that if the same type of clinker but with the content of particle size range of 0 - 20 mm varying from 45, 50, 65 and 80% can be obtained the corresponding cement grades 60, 70 and 80. MPa.
The authors of the USSR Cement Scientific Research Institute have studied the influence of cement particle composition on some properties of cement, showing that:
- The particle size range < 5 mm reduces the time to start setting, increases the compressive strength of cement hardens under normal conditions as well as autoclaving, increases the overall porosity and permeability coefficient, increases the shrinkage deformation of the cement. cures under normal conditions as well as by autoclaving. In general, this grain-size range has the main positive role: increasing compressive strength and increasing crack strength.
- The grain size range of 30 - 60 mm has the effect of prolonging the setting time of the cement in addition to increasing the porosity and shrinkage of the sample like the fine grain band (< 5 mm).
- The large grain size range (>60 mm) significantly increases the porosity of the cement stone while tending to increase the crack strength, which can be considered as a result of frame formation in the cement stone. bamboo shoots in the presence of this grain size range.
Based on the above research results, the optimal cement grain size range in terms of strength when cement has a particle composition (in % by mass) is as follows:
- Particles < 5 mm account for < 20%
- Particles 5 - 20 mm account for 40 - 45%
- Particles 20 - 40 mm account for 20 - 25%
- Particles > 40 mm account for 15 - 5%
Cement size less than 40 mm plays a major role in the strength of cement stone. At the same time, multi-grained cement gives the optimal "micro-concrete" structure of cement stone.
Cement particle size less than 40 mm is confirmed through the American standard ASTM specifying the fineness of cement and additives according to the sieve size of 45 mm (ASTM 430 - 96, ASTM C 150 - 99, ASTM C 595 - 00, C 1157 – 00). In ASTM C 959 - 00 also specify fineness - residual amount on 45 mm sieve for admixture for cement is < 20%.
Từ các kết quả nghiên cứu trên thấy rằng khi tăng độ mịn của xi măng tới khả năng tối đa kỹ thuật cho phép nhằm tăng hoạt tính xi măng, tăng hàm lượng phụ gia sử dụng, giảm hàm lượng clanhke, nâng sản lượng xi măng.
Tác giả thuộc Viện Nghiên cứu khoa học xi măng – Liên Xô nghiên cứu ảnh hưởng của độ mịn đến hoạt tính của xi măng trên cơ sở clanhke nhà máy Pôđônski và xỉ Rustasvski đã đi đến nhận định: Hiệu quả sử dụng clanhke tăng mạnh khi chuyển từ xi măng pooclăng (OPC) sang xi măng pooc lăng xỉ (PCB) khi tăng độ mịn của xi măng và xỉ. Việc tăng độ mịn của xi măng cho phép sản xuất tắng sản lượng tới 25%. Trong bảng dưới đây nêu các số liệu về ảnh hưởng của độ mịn của xi măng đến hàm lượng phụ gia (xỉ) trong xi măng.
