Measurement of concrete permeability
thesisposted on 15.10.2010, 11:30 by Raymond W. Hudd
A comparison was made between a number of laboratory and in-situ concrete permeability test methods. The laboratory tests used measured air, water, and water vapour permeability, whilst the in-situ tests used were the Initial surface absorption test, the Figg air and water tests, and a new in-situ method called the Egg test; a non-destructive surface test which measures air permeability properties. An initial set of tests were carried out on six concrete mixes with water: cement(w/c) ratios between 0.3 and 0.8. These tests showed that problems existed with both the laboratory and in-situ test methods. Some of these problems arose from the preparation of specimens or test procedures and these were overcome with practice or by modifying the test methods. However, it was found that a major problem is moisture in the concrete which decreases it's measured permeability. Further tests were carried out on a second set of concrete specimens with the same mix proportions as the first and a set of mortar specimens with w/c ratios ranging from 0.3 to 1.1 and cement: sand (c: s) ratios from 1: 1 to 1: 5. Results from tests on oven dry specimens were used to compare the different methods and showed that few simple relationships existed between the different methods. Comparing the test results with the mix proportions showed that in the majority of cases, the measured permeability values increased as the w/c ratio increased, but the relationships between the tests results and c: s ratio were more complicated. After these tests had been completed, specimens from twenty six of the mixes were retested after being conditioned to various different moisture contents. The results of these tests showed that in most cases there was a rapid increase in measured permeability as the specimens dried, followed by a slower increase (in some cases a decrease) as the specimens approached an oven dry condition. To complement this study a number of methods were examined for measuring in-situ moisture content. The most promising of these was a non-destructive method which operated by measuring the electrical permittivity of the material it was placed against. Because the electrical permittivity varies with the amount of water in the concrete, it is largely independent of the type material being tested. Results from this test showed a shallow linear drop from saturated to approximately half of the saturated moisture content, followed by a steep drop towards the oven dry condition.
- Architecture, Building and Civil Engineering