Detecting load induced thermal damage in concrete

• Main Author: Stein, Robert
• Other Authors: Petkovski, M. ; Engelberg, D. L.
• Published: University of Sheffield 2015
• Subjects: 624
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678077

Ordinary Portland cement based materials that are subjected to mechanical load during heating experience Load Induced Thermal Strain (LITS). LITS is known to have a significant effect on material strength and loading stiffness1 and may completely suppress thermal expansion in the loaded axes2. It has been proposed that LITS occurs as a result of a mechanical damage mechanism known as Load Induced Thermal Damage1 (LITD) which occurs in the microstructure of the hydrated material. This investigation has undertaken to characterise the pore structure of LITS affected concrete in order to quantify any microstructural changes and verify the LITD hypothesis. Pore structure was chosen as the principal feature for investigation due to its inherent relationship with mechanical strength and permeability along with the range of quantifiable features through which it can be described. Mercury Intrusion Porosimetry, Backscattered Electron Image Analysis and X-ray Computed Tomography were employed to characterise LITS affected, heat only and unconditioned control specimens. Specimens were characterised both ex-situ and in-situ in the case of X-ray Computed Tomography using a purpose built thermo-mechanical loading rig. Experimental results indicate that in terms of total porosity, LITS affected specimens do not appear to differ from those which experience only heating. However, evidence is presented of other developments in the material pore structure which can uniquely be associated with LITS. These include data from the ex-situ characterisation of pore size distribution and interfacial transition zone porosity along with in-situ data relating to pore volume during fracture testing following conditioning. These observations provide new insight into macrostructural observations made on material strength and permeability in existing research. Evidence from this investigation does not provide substantive support for the LITD hypothesis and further research into the calcium-silicate-hydrate structure of OPC based materials is required to develop a better understanding of LITS development.