Abstract
Determining the water permeability of concrete in structures remains a challenge because of difficulties in removing the influence of its moisture content. Saturating concrete with water could be one option, but this is not easy to achieve on site. This paper reports a testing programme carried out to assess the reliability and effectiveness of two field saturation methods, viz. vacuum saturation and ponding. The water permeability test results after applying the vacuum saturation and ponding were compared with that obtained after incremental immersion. It was found that ponding was unable to remove the influence of moisture, whilst vacuum saturation was effective for wet concretes. The results obtained from the electrical resistance measurements after incremental immersion suggested that the water permeability of concretes can be accurately determined by carrying out in situ permeability tests if the near surface region up to a depth of 25 mm is fully saturated.
Highlights
Concrete has the reputation as a strong and durable material [1, 2]
An investigation by Yang et al has indicated that to remove the influence of moisture on air permeability of high-performance concrete (HPC), the relative humidity in the near-surface region should be less than 60% [7] as opposed to the value of 80% proposed by Basheer and Nolan for NCs [10]
The vacuum saturation and ponding are considered as possible approaches for field use, whilst the incremental immersion is considered as the ‘reference’ method, as the previous work [13] has shown that reliable water permeability results can be obtained after incremental immersion of HPCs
Summary
Concrete has the reputation as a strong and durable material [1, 2]. the occurrence of durability problems and some catastrophic failures of reinforced concrete structures since 1970’s have caused deep concerns to civil engineers in their ability to design and construct durable reinforced concrete structures [3]. The permeability of cover concrete has been considered as a key parameter to assess the durability of concrete structures and numerous methods for measuring the in situ permeation properties of normal concretes have been proposed [4,5,6] They are not effective for distinguishing the permeation characteristics of very low permeability concretes, such as those typically associated with high-performance concrete (HPC), because of their low sensitivity to variations in permeation characteristics. An investigation by Yang et al has indicated that to remove the influence of moisture on air permeability of HPCs, the relative humidity in the near-surface region (from surface to 20 mm depth) should be less than 60% [7] as opposed to the value of 80% proposed by Basheer and Nolan for NCs [10] As this moisture condition is not easy to reach for HPCs on site, an alternative could be to measure their permeation properties by carrying out in situ water permeability tests. The vacuum saturation and ponding are considered as possible approaches for field use, whilst the incremental immersion is considered as the ‘reference’ method, as the previous work [13] has shown that reliable water permeability results can be obtained after incremental immersion of HPCs
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