| Abstract | Six phosphonates including three acids Aminotri(methylenephosphonic acid) (ATMP ); 1-Hydroxyethylidene-1 ,1-diphosphonic acid (HEDP) and Diethylenetriaminepenta(methylenephosphonic acid) (DTPMP) and their corresponding Na-salts Na5ATMP;Na4HEDP and Na@JTPMP were added to Portland cement in dosages ranging from0.03% to 0.09%, at a constant water:cement ratio of 0.35 and their conductioncalorimetric behaviour was investigated up to 72 hrs. The induction period, the time toattain the maximum heat effect and the integral heat developed at different times weredetermined. All phosphonates increased the induction period, from about 3 hrs togreater than 72 hrs with respect to the reference cement, with an induction period of 2hrs. The acid phosphonates were more effective retarders than their corresponding salts. At a concentration of 0.05% the induction period extended from 10.1 to 21.1 hrs with the acids and only from 4.1 to 16.2 hrs with the salts. DTPMP was the most effective retarder among all the phosphonates, a concentration of 0.05% produced an induction period of21.1 hrs and an exothermic inflection at 42.4 hrs compared to values of 2.2 hrs and 7.9 hrs respectively for the reference. The corresponding salt (Na@JTPMP) was the most efficient of all the salt retarders. At a concentration of 0.05%, the induction period was extended to 16.2 hrs and the exothermal inflection to 31.4 hrs. In most instances the degree of extension of the induction period increased with the dosage of retarders. Phosphonates appear to be much more efficient retarders than many other retarders used in concrete practice. |
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