Co-precipitation of ettringite of rapid and slow formation. Consequence: Expansive Synergic Effect. Its demonstration by mortars and concretes

Several prior papers have shown that enough pozzolans can bring about rapid formation ettringite (from its Al 2 O 3 r- ). It has likewise been found that the formation rate of this ettringite is higher than the of slower forming ettringite originating from OPC (from its C 3 A). In this context: What type of effect will they ultimately produce? Addition? Synergism? Antagonism? or perhaps Inversion of final expansive action?. To reply to these questions, 4 PC and 12 blended cements containing 20%, 30% or 40% metakaolin, were tested using the ASTM C 452-68, EN 196-1 and RT-86:ΔL tests and also concrete specimens. The experimental results have shows that the joint precipitation in a common sulfate medium, of ettringite from pozzolan and from OPC, was always more synergic than additive , and the technical consequences of the Expansive Synergic Effect may be classified as beneficial, adverse or indifferent according to its sulfates content in excess is more or less adequate.