Abstract
The effect of supplementary cementing materials (SCM) on internal sulphate attack in mortars was evaluated. Different types and levels of SCM were investigated where a mixture of hemihydrate and calcium carbonate fillers were used in the mixtures as a source of sulphate and carbonate, respectively. In addition, mixtures containing aggregates with high sulphate content were also examined to understand the role of sulphate from aggregate on the expansion. It has been found that the internal sulphate attack can be reduced through the use of SCM with high reactive alumina such as Metakaolin. It was hypothesised that the beneficial effect of Metakaolin lies in its ability to reduce ion mobility within the matrix, and perhaps raise the alumina/sulphur in the system favoring the formation of non-expansive monosulphoaluminate. However, at high levels of sulphate, none of the SCM provided successful protection against internal sulphate attack.
Highlights
This thesis is on the mechanisms and mitigation techniques of internal sulphate attack focusing primarily on two types of phases or types of sulphate attack; Ettringite formation/attack and Thaumasite sulphate attack (TSA)
This type of fly ash has shown improved durability when it comes to conventional sulphate attack, mitigating Ettringite formation, whether it is used with ordinary Portland cement (OPC), Portland Limestone Cement (PLC) or sulphate resistant Portland cement (SRPC)
The levels of sulphate used in this study are for the purpose of investigating the effect of supplementary cementing material (SCM) and cannot be used as to set limits for a safe level of sulphate in concrete
Summary
There has been research conducted by European Scientists on the Sulphate resistance of Concrete as early as the 19th Century with reported cases in Canada of damage due to the presence of sulphate as early as 1908. (Marchand, Odler, and Skalny 2003a). The damage on concrete was due to excessive sulphate ions and is commonly referred to as Sulphate attack. Examples of this type of concrete deterioration include but not limited to expansion, cracking, spalling, strength loss and loss of adhesion which reduces the service life of the concrete (Collepardi and Mario 1999). Ettringite formation that occurs during hydration, known as Primary Ettringite Formation (PEF), does not result in any expansion. The formation of Ettringite after concrete has hardened due to presence of excessive amounts of sulphates is known as Secondary Ettringite Formation (SEF). Excessive amounts of sulphates resulting in an imbalance of sulphate will turn the available aluminate phases (Tricalcium Aluminate and monosulphoaluminate) into Ettringite. Mechanisms and mitigation techniques will be reviewed to obtain a better understanding on the subject
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