The challenge related to waste management has become a serious worldwide environmental problem. Highly sustainable solutions, which do not involve reworking the material and are based on waste utilization, are sought. Such waste as used casting compounds, which so far has been used, among others, in construction, road construction, mining and cement production. Descriptions of the use of various waste moulding compounds, such as waste quartz compounds with water glass, quartz chamotte and quartz bentonite can be found in the literature. Due to the high content of quartz and low toxicity of bentonite sandmix, an attempt was done to use them for the production of sand-lime products. The aim of this article is to determine the suitability of the waste material as a substitute for quartz sand in the production of sand-lime products. The usability of waste was determined by laboratory tests of physicochemical characteristics of the finished silicates. Sand, which is a carrier of silica, was replaced with used moulding compounds with fractions up to 0.5 mm, in the weight amounts of 5.5, 11 and 16.5%. Applying up to 11% of used casting materials as a substitute for quartz sand with a lime content of 5.5% in the raw material mixture has a clearly positive effect on compressive strength. However, the higher share of sand substitution in the mixture weakens the mechanical features of the obtained materials. The absorptivity of the finished products increases with the increase of the inserted additions’ amounts. The influence of significant amounts of casting compound additives on the microstructure of calcium-silicate products was studied as well. It was stated, that they affect the location of the tobermorite in the volume of the autoclaved material.
Sand-lime products are characterized by advantageous features: compressive strength, thermal accumulation and acoustic insulation. Product features are resultative choice of decisions made at individual stages of the production process: method of thickening the raw material mixture, time and temperature of autoclaving and the pressure of saturated steam. The above factors may affect on the characteristics of sand-lime products not only directly, but also through other factors. However, there is no suggestion in the literature about the relationship between these factors. The aim of this article is to find answers to the following questions: which stage of the technological process is the most important? What impact does the individual stages have on each other? Whether and to what extent modification of a given stage will affect the compressive strength of finished products? The authors carried out an analysis using the DEMATEL method to identify factors that have a key influence on autoclaved materials. The results show that using the right amount of water in the raw material mixture is the most important factor. To a slightly lesser extent, proper selection of amount of the quick lime is important. The least important factor is the method of forming silicate products. Although the time of autoclaving has a large contribution in the creation of the impact network, however it is caused by the influence of thermal and humidity conditions, the amount of lime, water and, in the low extent, the molding method.
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