The investigation on the structure and properties of medium cement refractory castable with clinker aggregate

Abstract

The aim of this work was to modify the phase composition and the structure of medium cement refractory castable (MCC) by complex additives for improving the durability of the lining of the energy equipment. The additives used for the said purpose include: composite deflocculant – for improving the mechanical properties; ground quartz sand – for improving the alkali resistance; an additive of carbon fiber and of a mix of carbon and polypropylene fibres – for modification of the microstructure of castable. In addition, clinker calcium aluminate aggregate will ensure improved mechanical properties of the material and increase its resistance to abrasion. It was found that during the hardening of cement paste and refractory binder, densified hydrate microzones are formed on the surface that vesture the carbon fiber. After processing at the temperature of >500°C, ~6 µm diameter and ~5 mm long microchannels are formed in the binder after burning-out of the carbon fiber. In the layer around a microchannel, densified microzones remain. Next, carbon fiber and a mix of carbon fiber and polypropylene fiber increase the cold crushing strength (CCS) of clinker based MCC after 3-day hardening and after firing at the temperature of 800–1200 °C. The indicator of thermal shock resistance of castable was also conducted. Carbon fiber additive do not protect the castable against explosive spalling on thermal processing at the temperature up to 1000°C with the rate of 40 °C/min. It was found that specimens with a mixed carbon and polypropylene fiber additive do not explode and remain undamaged. As a result of the investigations, the ground quartz sand additive improves the alkali resistance of clinker based MCC. Depending on the content of the additive, the resistance of castable to the impact of K2CO3 increases from 3 (without ground quartz sand additive) to 6–8 cycles (with this additive) (1100 °C – cooling in air). The investigation shows that when K2CO3 affects castable with ground quartz sand additive, a protective layer is formed on its surface that prevents the potassium carbonate salt degradation products from penetration into the structure of castable. On summarizing the obtained results of the investigation of castables, it may be noted that use of clinker calcium aluminate aggregate and composite deflocculant in MCC enables to ensure the following properties of the castable: CCS – > 95 MPa; bending strength – ≥ 17 MPa; shrinkage – 0.28%, thermal shock resistance – 10 cycles (950 °C – cooling in water); density – ~2450 kg/m3; abrasion resistance – 4.5 cm3.