Based on the results of this investigation certain conclusions were arrived at relative to Portland cement concrete using Dolomitic limestone sand as the fine aggregate. The most important of these are as follows:

1. Fresh concrete continues to gain strength while in the frozen state.

2. Freezing and then thawing of fresh concrete does not have an appreciable effect on the twenty-eight day ultimate strength, and the concrete, if given time to recover, will compare favorably with concrete cured under normal conditions.

3. Freezing of concrete immediately after pouring has a greater effect on the twenty-eight day ultimate strength of the concrete than has freezing for the same period at a more advanced age within the twenty-eight days.

4. Concrete cured at 65°C. tends to increase its twenty-eight day ultimate strength, providing the water lost through evaporation is replaced.

5. High early strength concrete can be obtained by curing ordinary Portland cement concrete at high temperatures.

Based on the results of compression tests performed in this investigation, Dolomitic limestone sand has been found to be satisfactory as the fine aggregate for Portland cement concrete; verifying what Messrs. Broyles and Brown had said in 1936 and 1937 respectively.

What has been done in the way of concrete research at Virginia Polytechnic Institute is satisfactory for relatively new concrete using Dolomitic limestone sand as the fine aggregate; but it is wondered how this concrete will stand up over a long period of time. Professor Hartman and Dr. Holden have inaugurated some long time studies at the Institution, but there is still much room for further investigation. Dolomitic limestone rock has proven itself worthy when used as the coarse aggregate for Portland cement concrete. It is up to time and future research to prove the worth of its sand used as the fine aggregate.