The major contribution towards strength development in OPC or blended cements containing SCMs is from C-S-H gel. Does C-A-H phases contribute towards strength development? If in calcium aluminate cements C-A-H phases are the only phases that contribute to the strength, then the C-A-H must be having some contribution in the development of strength in OPC or blended cements containing SCMs
C-A-H contributes towards setting of concrete in initial stages other than that it does not contribute towards strength of concrete
Thanks for your answer Charan, but in the case of Calcium aluminate cements, the phases that are formed are Calcium aluminate hydrates only and they achieve high strength in roughly 24 hours
The difference between calcium aluminate cements and composite cements is that the latter also contain gypsum and sometimes limestone. These will react with the aluminate phases to form AFm phases, so except for with very high replacement levels, you won't often see C-A-H phases, and then they will only be at low levels.
Usually what you observe in systems with high alumina SCMs (meta kaolin, fly ash) is an increased uptake of aluminium by CSH, compared to normal OPC systems. Therefore, in this cases is more accurate to talk of CASH rather than just CSH. The amount of aluminium incorporated in CSH varies with age, and also depends in the amount and quality (in terms of aluminium content) of the SCM used. A second interaction would be the formation of AFm phases. When you also have limestone in the system, the alumina phases provided by the SCM can react and form monocarboaluminate and hemicarboaluminate, which further contribute to space filling and therefore, to strength. The publication below can provide some further insights regarding this interaction mechanism.
Article Cement Substitution by a Combination of Metakaolin and Limestone
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