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Technical Paper


FACTORS INFLUENCING THE BEHAVIOUR OF CASTABLES DURING INSTALLATION - HOW CAN THE ROBUSTNESS BE IMPROVED?


Sebastian Klaus1 , Dagmar Schmidtmeier1 Zhou3


, Dale Zacherl2 , Zhang Ju3


1Almatis GmbH, Frankfurt/Ludwigshafen, Germany; 2 China; 4


Abstract


The behaviour of refractory castables with regard to wet mixing, flow over time, and setting and strength development depends on the composition of the mix and external factors such as ambient temperature, water quality, intensity of mixing, etc. Variation of the castable behaviour in those properties mentioned above can challenge the whole installation, and bring into operation countermeasures on site. Sometimes these countermeasures are detrimental to the performance of the installation, e.g. through consequential increased water demand and higher porosity. The paper discusses the impact of raw materials and ambient conditions on castable properties and also considers solutions to improve the robustness of castables.


Introduction


In general, conventional castables can be considered more robust due to their higher cement content when compared to low and ultra-low cement mixes. The latter mixes provide higher performance in use but are more sensitive to changes in installation conditions. Their formulation is also more complex, including various fine matrix components and additives for dispersion and setting control. The raw materials, especially in the matrix fines can have a significant influence on the robustness of low and ultra- low cement castables. Trace contaminations and variations in homogeneity within raw materials, under- or over-dosage of small amounts of additive, aging behaviour in the ready dry-mix, and different wet out times depending on the mixing intensity are examples of these influences.


, Andreas Buhr1 , Tadahiro Kaneko4


, Marion Schnabel1 , Jerry Dutton5


Almatis Inc.,Leetsdale, PA, USA; 3 Almatis Limited, Nagano Iwakuni, Japan; 5 , Rainer Kockegey-Lorenz1 Stourbridge, UK


Ambient conditions such as temperature and humidity have a big impact on castable properties, in particular on the setting behaviour. Ambient conditions during storage and installation are not usually well controlled and due to the time lapse between castable production and usage, the adjusted setting times may not meet the requirements for on-site installation some months later. In order to overcome problems associated with too low or too high ambient temperatures during the installation, heated or cooled water is sometimes used, even if the effect might be questionable. Alternatively additives for retarding or accelerating the setting time are added to the mixer on-site. Schnabel et al. [1] and Kockegey-Lorenz et al. [2] reported on the adjustment of setting time with citric acid. Dosage levels were in the range of 0 – 0.08% and small increases of citric acid resulted in the desired extension of working time but also lead to undesired strong retardation of the main cement hydration and a weakening of the reaction. The papers also provided recommendations for a more robust way of setting time re- adjustment by using dispersing aluminas [3] as retarder and hydratable alumina Alphabond 300 as accelerator.


Today’s trend in raw material and castable development focuses on both optimisation of the castable properties and on the robust behaviour and easy installation in order to achieve the best overall performance. This helps to make processes such as castable production, testing and installation smooth and less prone to error. The paper will present results from trials in the laboratory performed under defined conditions for systematic investigation of e.g. impact of water dosage and the influence of dry mix and mixing water temperature. The trials will also provide information on the robustness of additive systems at these different ambient temperatures.


, Yunpeng Qingdao Almatis Co., Ltd., Qingdao,


Table 1: Typical product data – dispersing aluminas November 2017 Issue ENGINEER THE REFRACTORIES 11


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