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|Title:||Cold weather construction materials. Part 2, Regulated-set cement for cold weather concreting : field validation of laboratory tests|
|Authors:||Cold Regions Research and Engineering Laboratory (U.S.)|
Structures Laboratory (U.S.)
United States. Army. Office of the Chief of Engineers.
Houston, Billy J.
Hoff, G. C. (George C.)
Cold weather construction
|Publisher:||Concrete Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||CTIAC ; 45.|
Abstract: The U. S. Army carries on construction projects in localities such as Alaska, the northern tier of the United States, northern Europe, and the Arctic where the concrete placing system is shortened by the cold climate. At ambient temperatures below 50°F, concreting operations become more expensive since Corps of Engineers specifications require freshly mixed and placed concrete to be protected from low ambient temperatures maintenance in cold regions program was. The overall military construction and initiated to locate and evaluate existing and new cementing materials that would allow concrete to be placed at ambient temperatures as low as 15°F. A relatively newly developed cement called "regulated-set" cement, which is a fast setting, rapid• strength gain cement, appeared to have promise and was selected for a detailed study. Both mortars and concretes made with regulated-set cement were studied in the laboratory. Test results were favorable, so the decision was made to validate the laboratory results with field testing. The U. S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL) located in Hanover, New Hampshire, was selected for the prototype study. Two 12- by 12-ft by 8-in. test slabs were cast in January 1975 when the mean temperature in New Hampshire was approximately 15°F. Test cylinders, push-out cylinders, drilled cores, and beams were tested for strength at various ages. The only difference in the two slabs was the concrete mixture temperature. Slabs 1 and 2 had concrete temperatures at discharge from the mixer of 33°F and 49°F, respectively. The higher temperature in slab 2 was accomplished by heating the water prior to mixing. The slabs received no special protection from the ambient temperatures. Neither slab attained any appreciable compressive strength at 1 day, but slab 1 had compressive strengths of 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 due to inexperience with the continuous batching and mixing equipment. Since there was no strength gain at 1 day age whereas there had been a strength gain in laboratory tests of approximately the same concrete mixture but with an earlier shipment of regulated-set cement, a sample of the cement was brought to the laboratory for comparison with the earlier cement. Chemical and physical tests indicated that there was a difference in chemical composition. The factor suspected of being most significant in causing significant early strength gain in the laboratory cement sample and none in the CRREL cement was sulfate content. The earlier shipment had a higher sulfate content. These differences point out the need for a responsive purchase specification which is presently not available.
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