Structure and phase investigations on crystallization of 11 Å tobermorite in lime sand pellets

The present work examines the crystallization behaviour of 11 Å tobermorite and its dependence on the reactivity of different silica sources (quartz sand, grain-size ≤ 0.30 mm; quartz powder, grain-size ≤ 0.08 mm; inflated clay sand, grain-size ≤ 0.50 mm and raw perlite, grain-size ≤ 1 mm). The influence of different C/S ratios (calcium/silica ratio: 0.53, 0.83) was also investigated. For simulation of the industrial production process of lime sand products, a synthesis of lime sand pellets was carried out with a hydrothermal treatment (T = 200 °C, t = 40.5 h). The C–S–H phases were characterized by ESEM, EDX and X-ray powder diffraction.The investigations revealed that the grain-size, C/S ratio and porosity of the silica sources influence the formation of 11 Å tobermorite. A formation of 11 Å tobermorite using inflated clay sand with a grain-size ≤ 0.50 mm and a high porosity was only found with a C/S ratio of 0.53. This indicates a negative influence of an increase of lime content inside the synthesis mixture for tobermorite crystallization.Besides, a formation of xonotlite inside big pores of the lime sand pellet with inflated clay sand could be observed. The formation of portlandite and calcite was detected in all samples. The amount of calcite increased with the grain-size and with a higher C/S ratio.