Recent progress in microsilica-gel bonded no-cement castables

This paper focuses on the recent advance in no-cement technology, mainly focusing on their properties, benefits, and prospects when calcium aluminate cement is replaced by a “dry-version” silica binder, using microsilica powder to replace silica-sol. A microsilica-gel bond system has been designed using microsilica powder and a tailor-made dispersant package to give excellent flow and to control the setting behaviour of the NCCs. The flow, set-behaviour and mechanical properties have been studied in comparison with silica-sol bonded NCCs and cement-bonded low cement castables (LCC). The microsilica-gel bonded NCCs not only exhibit higher flow, better workability and adequate green strength compared to the silica-sol bond system, but also entail easier handling, storage, and transportation thanks to the all-in-the-bag solution. The microsilica-gel bond system contains only a minor amount of cement as gelling agent; hence, the hot properties are much better than that of LCCs. Phase transformations and bond mechanism were investigated by SEM and XRD techniques after pre-firing at 1400 and 1500°C. Furthermore, the effect of drying agents on both lab- and industrial-scale explosion resistance was studied. The drying behaviour and explosion resistance of microsilica-gel bonded NCCs was further significantly improved by using a speciality drying agent (EMSIL-DRY™); a perfect 400 kgs block was produced with no problems using a fast-firing program (20°C to 850°C at a heating rate of 50°C).