Abualgasem, Jumma (2014) The effect of wetting and drying cycles and carbonation on thaumasite formation. PhD thesis, University of Sheffield.
Abstract
Thaumasite form of sulfate attack is having great attention since its
discovering in series of foundations supporting motorway bridges in the UK
in the late nineties of the last century. This is mainly due to its destructive
effect on concrete structures, and the lack of information about its
formation mechanisms. This research conducted a study on the effect of
wetting and drying, carbonation and the effect of water to cement ratio on
the thaumasite formation, and whether these effects are linked with other
parameters such as cement type and sulfate concentration or not. 10
different mixes were produced based on four binder types in this study
namely 100% CEM I, 90% CEM I + 10% Limestone filler, 50% CEM I + 50
%PFA and 30% CEM I +70%GGBS. A series of mortar samples of two types
were prepared 50 mm cubes and 40 × 40 × 160 mm prisms. The samples
were kept in three different solutions contain BRE DS3,DS4 based on
magnesium sulfate MgSO4.7H2O in addition to deionised water. Two
different temperatures 5°C and 20°C were also used to confirm the
formation of thaumasite at ambient temperatures (20°C) and to accelerate
its formation at 5°C. The effect of wetting and drying cycles on thaumasite
formation was studied and compared with samples immersed continuously
in the same solutions for 12 months.
Powder-sulfate interaction and its effect on thaumasite formation was
studied by grinding mortar samples to a fine powder, thus eliminating the
permeability effect and enabling physical factors that affect the rate at which
solutions can be transferred through the mortar to be separated from
chemical factors that affect the rate at which the chemical reactions take
place.
Visual observations, mass and length changes were used to assess the
mortar deterioration, along with X-ray diffraction, infra-red spectroscopy
and SEM that were used to determine the mineralogy of deterioration
products.
For the cyclic wetting and drying exposure regime the results showed that
wetting and drying cycles significantly delayed thaumasite formation
compared with control specimens.
For powder samples, it is found that thaumasite is readily formed in these
powders after 3 months of exposure to sulfate solutions including GGBS
and PFA samples, on the other hand cubes and prisms, exposed to the same
solutions for 24 months showed no signs of deterioration.
Thermodynamic modelling was used to predict the deterioration products for
powders samples and good agreement between predicted and observed
results was found.
Metadata
Supervisors: | Cripps, John and Lynsdale, Cyril |
---|---|
Keywords: | Thaumasite, wetting drying sulfate attack, carbonation. |
Awarding institution: | University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Civil and Structural Engineering (Sheffield) |
Identification Number/EthosID: | uk.bl.ethos.619098 |
Depositing User: | Mr Jumma Abualgasem |
Date Deposited: | 22 Sep 2014 08:15 |
Last Modified: | 03 Oct 2016 11:18 |
Open Archives Initiative ID (OAI ID): | oai:etheses.whiterose.ac.uk:6899 |
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