Rapid strength gain concrete repair mixtures that cure within 4 to 12 hr were used to carry out full-depth slab repairs on a section of Interstate highway. The mixtures included a calcium-chloride accelerated mix, a very early strength mix developed by the Strategic Highway Research Program, and a "fast-track" mix previously used for early opening of concrete intersections. Before carrying out the repairs, job materials and mix designs were obtained and used to develop correlations between pulse velocity, maturity, and early strength of concrete. Maturity functions based both on Nurse-Saul and Arrhenius (equivalent age) approaches were developed. To account for heat rise of the concretes in actual sections, laboratory correlations were carried out by curing test cylinders in a specially insulated curing box. Pulse velocity and maturity functions were used to predict in situ strength gain of concrete in instrumented test repair sections. Temperatures were monitored through the depths of the test slabs during the initial 8 hr of curing. Temperatures at mid-depth ranged from 60 deg C to 70 deg C (140 deg F to 160 deg F) for these mixes. After 4 hr of curing, the very early strength mix exceeded 14 MPa (2,000 psi) compressive strength, as determined by in situ methods. The other two mixes gained strength at a slower rate.
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