Influence of secondary raw materials on synthesis of tobermorite in lime–silicate composite

Abstract

Crystalline calcium silicate hydrate (CSH) phases, primarily tobermorite, arise in the microstructure of autoclaved aerated concretes (AACs) during autoclaving, which affects the concrete's important characteristics. Calcium oxide/hydroxide and silicon oxide are the feedstocks for the hydrothermal reactions. When producing AACs, aside from commonly used raw materials, it is also possible to utilize secondary raw materials rich in silicon oxide. The use of such secondary raw materials provides the opportunity for the construction industry to lower its impact on the environment. This work describes the investigation of individual added secondary raw materials' influence on the microstructure of AAC. The tested materials were as follows: high-temperature fly ash, FBC ash, slag, ground container glass, and zeolite. The materials were mixed with quicklime at a molar ratio of calcium oxide to silicon oxide of 0.73 and 1.0. Autoclave reactors were used for the synthesis of tobermorite under laboratory conditions. Autoclaving took place at 170 and 190 • C with hydrothermal soaking times of 4, 8, and 16 h. The additive with the most significant impact on microstructure was fly ash, while ground container glass showed the greatest influence on mechanical characteristics. K E Y W O R D S autoclaved aerated concrete, fly ash, glass, secondary raw material, zeolite How to cite this article:Černý V, Kulísek K, Húšt'avová J. Influence of secondary raw materials on synthesis of tobermorite in lime-silicate composite. ce papers. 2018;2:439-444. https://doi.

Utilization of Waste Glass in Autoclaved Silica–Lime Materials

“…In the case of white glass (WG), the pores visible in the SEM images did not cause such an effect. As in the study by Černý et al [49], the use of container glass contributed to a significant increase in compressive strength. In the present study, the increase in strength of the material is observed, which is also linked to the formation of tobermorite during the autoclaving process [50,51].…”

“…In the WG sample (Figure 9a), the hydrated lime silicates took the form of small plates with rounded edges, resembling clover leaves in shape, which are closely spaced and arranged at different angles. These silicates can be identified as tobermorite (Figure 9d), whose high content may be related to the increased compressive strength of this sample [46,[49][50][51]. In this sample, however, a lot of pores occurring between the produced plates are observed.…”

“…There are more of these pores than in other samples tested and they may be the reason for increased water absorption results (Figure 7). According to Černý et al [49], the high strength achieved by autoclaved materials may be due to the presence of tobermorite, which can be increased by using suitable raw materials. However, this effect may be diminished when the raw materials used increase the porosity of the material, as may be the case with fluidised bed ash in the zone around the ash grains.…”