Is the addition of 5% to 15% Limestone interground with quality clinker detremintal to strength?
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K G
Limestone has better grindability in comparison to clinker; hence will be ground finer during inter-grinding. It does not react with alkalies released during cement hydration. However it acts as a inert filler during concrete hardening, resulting in refinement of pore structure and corresponding increase in strength. The percentage addition should be decided by conducting trials. http://www.drjdbapat.com
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Dr J D Bapat
Forgot to mention that when we changed precast vibrated C 45 strength using 360 kg CEM I 52.5 R cement to precast SCC 180 kg CEM 52.5 and added 180 kg GGBS and 180 kg GCC we reached easily C 65! In general, GCC will add to early and 28 day strength though at high amounts you might see a drop of 10% after one year.
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Boudewijn Piscaer
Thank you Boudewijn and Dr Bapat,
Another question on the subject: Does the addition of ground Calcium Carbonate to cements make concretes produced with such binders more suseptable to Thaumasite attack (in the absence of limestone aggregates), and if so at what level of addition would this become critical?
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K G
First of all, I am not a cement chemist, so there are many more people far more competent to answer this. But let me tell you a real story that demonstrates the opposition we got from clinker producers when we introduced GCC on a big scale for the Dutch pre-cast Self Compacting Concrete market, more as a "separate" mineral stabilizer then OPC replacement. A Thaumasite (we called it Traumasite) case in the UK was shown in Germany as a threat.
It was investigated by the University of Kassel and considered a too far out extreme case where aggressive pyrites and constant moisture under low temperature was present.
Since then the expansion of GCC, both in cement (CEM II LL) and concrete, cannot be stopped. Since 90% of durability problems are due to corrosion, a denser concrete by using GCC is far out weighing potential extreme thaumasite problems somewhere.
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Boudewijn Piscaer
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