Therefore, a test is needed to identify the mix properties that enhance surface durability. This test will help concrete producers use the best possible ingredients, help contractors understand the best possible construction techniques, and help researchers pave the way to advanced pervious concrete applications.Test concepts
To solve this problem, the team worked through several criteria the test should fit:The test should use existing, readily available equipment.The specimens should be easy to fabricate.The test specimens should be as light as practical.You should be able to perform the test in the lab or field.Lab-cast specimens should be representative of field conditions.For wide adoption, the test should be quick and easy to run.The test should be repeatable.
Several existing test methods were considered but discounted:ASTM C 944 is a standard test for concrete abrasion resistance and was ruled out because it did not test a representative sample area and is not readily available.ASTM C 779 is another test for concrete abrasion resistance and was not chosen because the specimen size would be too heavy.ASTM E 303 is the British Pendulum test for skid resistance. The team liked the concept of a swinging pendulum as a tool to dislodge aggregate, but decided this pendulum was not heavy enough to be efficient.ASTM C 39 is the standard test for compressive strength of concrete. Many of the factors that impact raveling resistance probably also impact compressive strength, but the results of this test are impacted by more than just the surface properties.
But one commonly used test presented some opportunity. ASTM C 131, commonly called the LA Abrasion Test, measures abrasion resistance of aggregates. The team thought the apparatus might be used for testing raveling resistance in pervious concrete if the test is not too aggressive. The team focused on this effort.Developing the test
The standard ASTM C 131 procedure uses a sample of aggregate that is placed in a steel chamber, with up to 12 steel balls, which is spun for a set number of revolutions. In developing this test for pervious concrete, all options were open for consideration and study. The team considered specimen size and geometry, the number of specimens to put in the machine, the number of revolutions for a test run, and the number of balls to be used.
For the first round of evaluation, a single 4-inch-high, 4-inch-diameter cylinder was placed in the machine without any balls. The specimen was weighed before testing, and then again after 50, 100, and 500 revolutions of the machine. The mass loss was calculated as a percentage of the original specimen mass. An identical specimen was tested with the full complement of 12 balls.ASTM C 131, commonly called the LA Abrasion Test, measures abrasion resistance of aggregates.
At 50 revolutions, there was little abrasion of the coarse aggregate. After 100 and 500 revolutions, the aggregate abraded significantly. The intent of the test is not to test aggregate durability, but to test the ability of the cement paste to hold onto the aggregate.
Thus, researchers decided to set the test at 50 revolutions, after which the team determined the presence of the steel balls had no impact on the durability of mix in this test. The teams conducted further tests after eliminating the steel balls, considering them unnecessary.
The next round of testing focused on varying cylinder size and number. Single and multiple 4-inch-diameter, 8-inch-tall cylinders were tested. Larger cylinders broke in half in some tests, thus skewing the results with larger surface areas to ravel.