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
A recent PhD thesis of Olga Chowaniec at the EPFL has confirmed what we know already from practice a long time. Calcium Carbonate is NOT inert but act as a catalist. The higher the CaCO3 content, the better. Our experience, first for SCC, comes from > 90% CaCO3 which is not necessarily the quality that you find in OPC quarries.
In the prescriptive EN 197 CEM II B L (or LL) goes to 35% addition, but we have made special mixes for civil works containing 590 kg with 90 kg OPC.
Again I like to stress that performance does not come only from reactivity, but also from mechanical packing. Ground Calcium Carbonate (GCC) can provide the finer fractions as DDr J D Batap indicated.
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Boudewijn Piscaer
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