Technical Note N-1300 RAPID-HARDENING CONCRETE FOR REPAIRING NAVY CONCRETE STRUCTURES IN ANY GEOGRAPHIC REGION

摘要

Concrete mixtures, consisting of common aggregate, high-early-strength portland cement, accelerators (either generic or proprietary), and seawater, were investigated in the laboratory to determine their compressive strength and also their strength of bond to old concrete. The various constituents were stored in the atmosphere at temperatures of 33, 63, and 93 F, and the concretes were mixed in the atmosphere at these temperatures. The cylindrical test specimens were cured and tested at these temperatures in the atmosphere and in seawater pressurized to simulate a hydrostatic head of 60 feet. Strength tests were made at ages 1 hour, 4 hours, 24 hours, and 7 days. Correlation of the strength data with logistic and economic factors showed that rapid-hardening concretes, having adequate compressive and bond strengths and costing less than similar concretes incorporating proprietary accelerators, can be produced by using either calcium chloride (4.0% for low slump concrete and 6.5% for high slump) or calcium nitrate (6.5% for either low or high slump). The recommended concrete mixtures, intended for placement either in the atmosphere or in harbor waters at any depth to 60 feet, may be used by Seabees in restoring damaged or deteriorated Navy concrete structures situated either ashore or underwater in any geographic region. (Author)