The calcium to silicon ratio is the molar ratio of the total CaO to the total SiO2 in the constituent materials of autoclaved aerated concrete, written as C/S. The basic reason why aerated concrete can have high strength is that the calcareous materials and siliceous materials in aerated concrete have reasonable C/S and interact under autoclaved curing conditions, and the interaction between CaO and SiO2 The hydrothermal synthesis reaction generates new hydration products with suitable quantity and alkalinity of hydration products.
According to the “Practical Lectures on Production Technology of Aerated Concrete” compiled by the China Aerated Concrete Association, from the perspective of the two main types of autoclaved aerated concrete in my country, the C/S of cement-lime-fly ash aerated concrete is It is appropriate to control it at about 0.8; while the cement-lime-sand aerated concrete is between 0.7 and 0.8.
The calcium to silicon ratio not only affects the amount of hydration products, but also directly affects the phase composition of hydration products. The main effect of improving the strength is the calcium silicate hydrate. As the calcium-silicon ratio increases, the hydration product increases, and the strength increases. When the calcium-silicon ratio is at the best C/S (or at a smaller When a certain C/S within the optimal C/S range of the variation range, there is a peak in intensity, and the intensity is reduced if it is greater than this optimal C/S or less than this optimal value. When the calcium to silicon ratio is at the optimal value, and under the conditions of a reasonable autoclaved curing system, the final hydration product Tobmullite crystals and CSH(Ⅰ) are in equilibrium and coexist in an appropriate ratio, so that the hydration product has Optimal crystallinity, so that autoclaved aerated concrete can obtain high strength and high durability. When the calcium to silicon ratio is less than the optimal C/S, the amount of hydration products is insufficient, the hydration layer on the surface of the unhydrated particles is thinned, the cementing ability is weakened, and the strength of the product is reduced. When the calcium to silicon ratio is greater than the optimal C/S, on the one hand, calcium silicate hydrate with lower strength and higher alkalinity is formed in the hydration product, on the other hand, the hydration layer is too thick and lacks a strong framework, resulting in Decrease in intensity.
For a certain type of autoclaved aerated concrete, certain materials and production processes, C/S has an optimal value. The best C/S is the main factor to control the alkalinity, quantity and type of suitable hydration products, and it is an important and key technical index for the excellent performance of autoclaved aerated concrete.
When the autoclaved aerated concrete has the best C/S, the best crystallinity will be formed under the conditions of a reasonable autoclaved curing system to ensure its high strength, high durability and small drying shrinkage value. Only under the best C/S conditions and reasonable autoclaved curing system conditions can it be possible to produce high-quality products that meet the requirements of GB11968.
However, as mentioned above, since the national standard GB11968 stipulates two levels of superior product and qualified product for the strength grade, it is obviously to tell people that whether the strength grade meets the requirements of the superior product or the qualified product, the products are all In line with the regulations of GB11968, as long as qualified products can enter the construction market; in addition, what the enterprise pursues is economic benefits and strives to reduce product costs, as long as the products meet the requirements of qualified products. Therefore, it has been suggested that the C/S used can be lower than the best C/S when the strength reaches the highest value, so that the amount of calcium material can be reduced, and the product cost can be easily reduced. C/S is completely unnecessary to pursue strength. The best C/S when the highest intensity is reached, and it has realistic economic benefits. The best C/S is not a fixed value. It is related to the variety, quality of raw materials, fineness, production technology, technical parameters, etc. of autoclaved aerated concrete. It needs to be adjusted and determined through small tests, pilot tests and production verification. Good C/S. The higher the SiO2 content in the siliceous raw material, the more hydration products will be generated when the C/S is the same, and the higher the product strength will be. For siliceous raw materials with low SiO2 content, to obtain more hydration products to meet the needs of high strength, higher C/S is required. For example, the C/S of ash aerated is higher than that of sand aerated. /S. The calcium to silicon ratio C/S of ash aerated air should be 0.75~0.80, and the C/S of sand aerated air should be 0.65~0.75.
At present, whether it is production practice or scientific experimental research, the important role of the optimal calcium to silicon ratio is often overlooked, because the production of enterprises does not pursue the strength level of the blocks to meet the superior requirements, and scientific experimental research, such as the experimental research mentioned above Most of the goals are for the strength level to meet the requirements of qualified products specified in GB11968.
Therefore, for decades, companies producing high-quality autoclaved aerated concrete products are rare. If we change the decades-old tradition of producing qualified products of low-grade products—autoclaved aerated concrete blocks and produce high-quality products, we should be guided by high-level product standards, stimulate the enthusiasm of enterprises to produce high-quality products, and eliminate backward ones. And crude production process equipment and production technology, pay attention to the important influence of calcium-silicon ratio, water-to-material ratio and autoclaved curing system on the performance of autoclaved aerated concrete products, adopt the best calcium-silicon ratio, suitable water-to-material ratio and reasonable Of course, the autoclaved maintenance system of the company is also inseparable from the use of high-quality raw materials and strict production process management.
Post time: Sep-01-2020