1156 posts
Milling additives Question 1
What ratios can be suggested for ternary blending of cement with PFA and GGBS. Taking into account that the cement will be of Cem I quality and we would like to achieve a 32.5MPa product.
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1156 posts
Re: Milling additives
The ratios for blending GGBS or fly ash to achieve a 32.5MPa product will depend on the hydraulic activity of the individual components. The only way to define these ratios is going to be by the process of producing trial mixes and physical testing of concrete made from the mixes. It may be possible to add up to 65 per cent GGBS as this material is both cementitious and pozzolanic. The limit of PFA addition will be much lower, perhaps around 25 per cent, as this is only pozzolanic.
1156 posts
Milling additives Question 2
We are using synthesised calcium sulphate anhydrite from a nearby aluminium plant. This calcium sulphate (96 per cent purity) is fine in form and free from moisture. In addition to CaSO4 this material contains 2.0 per cent CaF2. Can calcium sulphate be used as an alternative retarder for the natural gypsum? Your expert opinion on the solubility of this synthetic calcium sulphate anhydrite is appreciated.
1156 posts
Re: Milling additives
The solubility of anhydrite varies dependent on the temperature history to which it has been subjected. However, I am sure this will be a good material to use as a set-controlling additive in your cement. You may need to use it in combination with your natural gypsum or you may be able to replace your natural gypsum with 100 per cent of this material. The only way to find out will be to conduct trials with the synthetic CaSO4.