Specifications for 18 grade crossing bridges of the New Jersey Garden State Parkway, involving production of 324 girders, called for a minimum of 4,000 psi before determining and stress transfer. Thus the key factor was fast strength gain. Realizing these strengths in one day instead of 28 days was essential for successful and economical production. The required fast strength gain was obtained by investing in a 150-hp boiler for generating steam, a couple of lines of 3 inch pipe, two recording thermometers, and tarpaulins to form a kiln. Steam was introduced under the tarpaulins through one-eighth inch diameter holes spaced under the tarpaulins through pipes on each side of the casting beds. Temperature increase was limited to one degree per minute. Steam curing continued from noon until 6:00 am the following day. Under the tarps the thermometers recorded 140 degrees F., while internal girder temperatures remained constant at about 160 degrees. Experience on this project indicates that it is important to have a continuous record of the temperature range in order to be certain that the temperatures are high enough during the critical period of steam curing. It was also found that the temperature under the tarps should be at least 100 degrees, and preferably in the range of 110 to 140 degrees. The three other factors which most directly influenced the strength and quality of the concrete were rate of temperature rise in the enclosure, uniformity of temperature throughout the enclosure, and the curing time.