Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578843
Title: Rapid assessment of the potential chloride resistance of structural concrete
Author: Abu Hassan, Zahiruddin Fitri
Awarding Body: University of Dundee
Current Institution: University of Dundee
Date of Award: 2012
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Abstract:
This present study benchmarked the chloride resistance of concretes mixes at the limit state of BS 8500-1:2006 using the newly published CEN TS12390-11. Of the three allowed methodologies, the immersion test was carried out. At least two water-cement ratios were produced for each mix design to enable normalisation of the results. The performance of concrete was compared on the basis of equal compressive strength, i.e. 40 and 50 N/mm2 and an equal water-cement ratio of 0.45. In addition to the CEN TS 12390-11:2010, rapid test methods NT Build 492 and a steady-state migration test UNE 83987:2009 were also conducted. Selected concretes were also tested for cyclic wetting in artificial sea water and evolution of chloride diffusion over the test period. The ageing factor of concrete mixes, which describes the development of diffusion coefficient (D) from the unsteady to steady-state determined from this research was compared with those reported in The Concrete Society Technical Report 61. Test specimens for highway exposure were also produced for future research work. CEN has just agreed and published (at the time of the writing of this thesis) a test methodology for chloride resistance as a technical standard (CEN, 2010). The test method underpins the equivalent durability performance approach. Therefore, the use of this test was investigated in terms of evolution of the chloride diffusion, and effect of cyclic wetting and drying in artificial seawater exposure. As the test method is slow, (3 months to complete), other rapid test methods were also studied on the same specimens. The results from these tests were compared to look for the possibility of having a faster test methodology for chloride durability. Overall, the results showed that concrete mixes at the limiting value of BS 8500-1:2006 have a wide range of performance between 0.3 × 10-12 m2/s and 20 × 10-12 m2/s regardless of the test methods. Ranking of concrete according to performance shows that this changes with age. This is the same for all test methods although the rate of change is different between different test methods. However, the ranking of concrete at equal compressive strength and equal water-cement ratio follows the general order of (from best to worst) ggbs> fly ash> silica fume> limestone> CEM I. It was also postulated that there is a limit to the benefit of reducing water-cement ratio to improve durability. This is because of at very low water cement ratio, concrete may develop autogenous cracking that is detrimental to the porosity. Using the CEN TS 12390-11:2010 it was found that CEM I, fly ash and silica fume mixes follows the same ageing factor proposed by Concrete Society Technical Report 61 although ggbs shows a different ageing factor. The improvement of ggbs quality was attributed to this change. It was also found that 90 days test duration was optimum as a shorter period risks giving a non stable diffusion rate whilst longer than 90 days shows insignificant change in Dnss values. Exposure of selected concrete specimens to cyclic wetting and drying in artificial seawater elevated to 1 M NaCl equivalent shows reduced chloride diffusion. However, the mechanism controlling this is not clear. The thesis showed that some of the limiting value requirement for BS 8500-1:2006 does not meet the durability requirements for chloride resistance. There are some concrete mixes recommended that performs poorly in testing. The research reported also provides further understanding of the new CEN TS 12390-11:2010 in terms comparative ranking of cements up to the point of comparative performance between other tests methods. Validation of the ageing factor for chloride durability is also provided as well as the need for updates in the age factor values due to changes in the nature of cements.
Supervisor: Jones, Martyn Sponsor: Ministry of Higher Education, Malaysia ; University of Malaya, Malaysia
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.578843  DOI: Not available
Keywords: Concrete durability ; Chloride resistance ; Diffusion test ; Migration test ; Age effects
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