We have an acute cement shortage in our area and have to use portland cement that is very hot. The cement comes directly from a cement mill only seven miles away and is too hot when it arrives to hold one's hand in it. We are worried about what this does to our strengths. Our compressive breaks seem to be all right, though erratic. Sometimes a seven-day strength result will be almost as high as the 28-day strength is expected to be.
The effect on strength will depend on how hot the fresh concrete gets. The temperature of the fresh concrete should not be higher than 90 degrees F in hot weather, according to the Recommended Practice for Hot Weather Concreting, ACI 605. This can be readily accomplished by using cold water or ice, depending on how hot the other materials are. A simple calculation based on a specific heat of 1.00 for water, 0.22 for cement and 0.22 for aggregate shows that in a mix containing 470 pounds of cement at 150 degrees F. 3,300 pounds of aggregate at 70 degrees F and 260 pounds of water at 70 degrees F the concrete temperature would be 77.6 degrees F. making no allowance for cooling by evaporation. Thus the hot cement is likely to raise the temperature of the other materials no more than about eight degrees F. If compressive strengths are erratic, it is undoubtedly for some other reason. The unusually high seven-day strengths would be caused by something other than hot cement.