Expansive Synergic Effect of ettringite from pozzolan (metakaolin) and from OPC, co-precipitating in a common plaster-bearing solution: Part I: By cement pastes and mortars
✍ Scribed by Rafael Talero
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 771 KB
- Volume
- 24
- Category
- Article
- ISSN
- 0950-0618
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✦ Synopsis
and ''slow" forming ettringites Synergies a b s t r a c t Several prior papers on this subject have shown, with XRD and SEM techniques and Le Chatelier-Ansttet (L-A), ASTM C 452-68 and RT-DL tests, that almost all pozzolanic additions can bring about the rapid formation of ettringite, ett-rf, a process dependent upon their reactive alumina, or Al 2 O rÀ 3 , content, which may be vitreous or amorphous (tetra-or penta-coordinated). It has likewise been found that the formation rate, V f , of this ettringite from pozzolans origin is higher than the V f of slower forming ettringite, ettlf, originating from the C 3 A in OPC; consequently, the size of the ett-rf is % 10-fold smaller.
To describe the interrelationships between their expansive processes, a terminological analogy is drawn between the rapid and slow formation of ettringite, on the one hand, and drugs interaction, on the other. A common development in the treatment of certain diseases and as a result of hospital practice, drugs interaction may be quantitative or qualitative and is denominated, based on the final outcome, to be additive synergy, partial antagonism, competitive antagonism, potentiation synergy, non-competitive antagonism or physiological and functional antagonism. In this context, the key questions relating to the development of the two types of ettringite when forming together in a common plaster-bearing solution are: What will the outcome of the expansive effects be? What type of effect will they ultimately produce? Addition? Synergism? Antagonism? or perhaps Inversion of final expansive action?
To reply to these questions, 16 cements -4 Portland cements and 12 blended cements containing 20%, 30% or 40% metakaolin (M pozzolan) -were tested using the L-A, ASTM C 452-68 and EN-196-1 tests. Specimens of all 16 types of cement were made for L-A, ASTM C 452-68 and EN-196-1 testing and several direct and indirect parameters were measured, as follows:
-Increase in diameter, DØ (%); diameter growth rate, Vcø(=DØ (%)/day); and Vicat Needle Penetration, VNP (mm), for L-A specimens, and -Flexural and compressive strengths for ASTM C 452-68 and for