The effect of nitrobenzene and aminobenzoic acids on the hydration of tricalcium silicate: a conduction calorimetric study

The hydration of tricalcium silicate (C₃S) in the presence of 0.004, 0.008 and 0.016 mol.% (with respect to 100 g of the silicate) of benzole acid, o-, m- and p-nitrobenzoic and aminobenzoic acids, was followed by conduction calorimetry. Benzoic acid at 0.004 and 0.008 moles behaved as a delayed accelerator of hydration, whereas at a dosage of 0.016 moles it performed as an accelerator by decreasing the onset of the induction period and promoting the earlier appearance of the main exothermic peak. The m- and p-nitrobenzoic acids accelerated the hydration of C₃S, whereas o-nitrobenzoic acid acted as a retarder. Both m-and p-aminobenzoic acids retarded the hydration by delaying the appearance of the main exothermal peak. o-Aminobenzoic acid showed a similar effect to that of the reference at early times by not affecting the induction period and the maximum rate-of-heat peak. However, it increased slightly the amplitude of the main exothermic peak. The compounds that promoted the appearance of a heat peak at periods of 1 h or earlier exhibited an acceleration effect. In the presence of retarders this peak did not appear.