Research engineer, Concrete Materials Research Department, Construction Technology Laboratories, Portland Cement Association, Skokie, Ill.
Concretes containing high-range water reducers (HRWR) based on naphthalene (NHRWR) and melamine (MHRWR) condensation products were batched, mixed, and tested at temperatures of 7, 16, 23, and 32°C (45, 60, 73, and 90°F). The amount of HRWR necessary to obtain a fixed slump and water-cement ratio was found to increase with a decrease in temperature below 23°C (73°F) and to remain fairly constant from 23 to 32°C (73 to 90°F). Slump loss showed a significant increase with an increase in temperature across the entire range studied. Mixtures containing melamine-based HRWR exhibited somewhat higher rates of slump loss than did those containing naphthalene-based HRWR when a cement containing a moderately high tricalcium aluminate (C3A) content was used. No consistent differences in slump loss were found between the two admixtures when a cement with a somewhat lower C3A content was tested. At the dosages used in this study, HRWR exhibited significant, though not excessive, retardation of set. It was found that certain combinations of HRWR and lignosulfonate or hydroxycarboxylic acid type retarders can have a moderating effect on slump loss at elevated temperatures.
Paper ID: CCA10176J