Cold Weather Construction Materials. Part 2. Field Validation of Laboratory Tests on Regulated-Set Cement for Cold Weather Concreting.

摘要

The Army carries on construction projects in localities where the concrete placing season is shortened considerably by the cold climate. This study evaluates regulated-test cement, which is a fast setting, rapid strength gain cement, that appeared to have great promise and would allow concrete to be placed at ambient temperatures as low as 15 F. Both mortars and concretes made with regulated-set cement were studied in the laboratory with favorable results, so the laboratory results were validated with field testing. Two 12-ft by 12-ft by 8-in. test slabs were cast in January 1975 when the mean ambient temperature was approximately 15 F. The only differences in the two slabs were the concrete mixture temperature and air entrainment. The slabs received no special protection from the ambient temperatures. Neither slab obtained any appreciable compressive strength at 1 day but slab 1 had approximately 1200 and 2000 psi at 7 and 28 days, respectively, while slab 2 had 2200 and 3300 psi, respectively. The concrete in both slabs was wetter than intended. Since there was no strength gain at day 1, whereas there had been in laboratory tests of approximately the same concrete mixture but with an earlier shipment of regulated-set cement, a sample of cement from the field test was brought to the laboratory for comparison with the cement used in the laboratory tests. Chemical and physical tests indicated that there was a difference in chemical composition; the laboratory shipment had a higher sulfate content. This difference points out the need for a responsive purchase specification, which is presently not available. Keywords: Cold regions; Regulated set concrete.