Factors influencing consistency of strength of high alumina cement

Location and dispersion in the strength response of high alumina cement (SECAR 80) are explored in a series of factorial designs of experiments. The factors considered are water/cement ratio, cement/aggregate ratio with aggregate grade, the use of sodium hexametaphosphate powder as a deflocculant during mixing, compacting pressure in the mould, curing time under water after setting and testing age. In addition, controlled exposure to elevated temperature and humidity are used to simulate environmental 'noise' effects. The results generally confirm expectations from the previous literature for factor effects on average strength, while the use of this deflocculant is shown to have a strong negative effect on strength so that it cannot be recommended. However, additional analysis also indicates the factors that contribute most to variably in strength and factor levels that provide some resistance to environmental 'noise' effects. It is demonstrated that an appropriate mix and preparation design may provide an element of 'robustness' against these.