On the basis of freezing and thawing tests of air-entrained concretes having poor quality cherts as course aggregates subjected to three different treatments for improving durability, the following conclusions have been derived: 1. Removal of cherts lighter than the BSSD specific gravity of 2.5 by heavy liquid definitely improved the durability of the concrete. 2. Combining 50 percent durable aggregate (1/2"-1/4" size) with 50 percent cherts (1"-1/2" size) did not show any significant improvement in durability over that containing 100 percent chert. 3. As much as 12 percent chert could be blended with durable aggregate without an appreciable reduction in durability. / Master of Science