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(ii) Laboratory Tests
Chemical Resistance (CIGMAT CT-1 or modified ASTM G 20): In order to study chemical resistance, the ASTM G 20 test was modified for use with coated concrete and clay brick materials. This method is intended for use as a relatively rapid test to evaluate the acidic resistance of coated specimens under anticipated service conditions. In this test, 76 mm (3 inch) by 152 mm (6 inch) cylindrical cement concrete specimens were used. Specimens were prepared by stripping the molds from the concrete cylinders, leaving the base in place. Dry and wet cylindrical specimens were coated on all sides, except the base, and tested. For the test, two radial holes were drilled into the specimen approximately 15 mm (1/2 inch) deep.
As shown in Fig. 7 (a), the specimen was immersed in a selected test reagent to half the specimen height in a closed bottle. For coated concrete specimens changes in (1) amount of calcium leached into the in test medium (2) weight of specimen (3) appearance of specimen and (4) pulse velocity (ASTM C 597) of the specimen were measured at regular intervals. For coated clay bricks, no calcium measurement was done except in the case of cemetitious coatings. The three test reagents selected for this study are (1) deionized water (pH = 6) and (2) 1 percent sulfuric acid solution (pH = 1; representing the worst reported condition in the wastewater system). Control tests are performed with no holidays. Over 60 specimens were tested for each coating material.
Fig. 7: Chemical tests on coated materials with holidays
Bonding Strength: These tests are being performed to determine the bonding strength (pull-off strength) between the concrete/clay brick and the coating material over a period of time.
CIGMAT CT-2 or modified ASTM D 4541: In this test, a 51 mm (2 inch) diameter circular area was used for testing. Coated concrete blocks were cored using a diamond core drill to a predetermined depth to isolate the coating, and a metal fixture was glued to the isolated coating section using a rapid setting epoxy. Tests are planned for each of the coating materials over a period of several years. The test configuration is in Fig. 8.
Fig. 8: Pull-off test method load frame arrangement