| Popis: |
This research investigated shrinkage of low carbon cement concrete to assess its subsequent effects on cracking and corrosion affecting the overall durability. The low carbon binder compositions considered were 40% and 60% slag, 30% fly ash and 20% to 65% limestone calcined clay cement (LC3). Shrinkage was monitored for both paste and concrete. Furthermore, microstructural properties such as phase assemblage, rate of hydration, and pore structure of the paste samples were studied. The cracking potentials of concrete mixes were evaluated using ring test. The self-healing potential of the binder compositions was examined by laser microscopy and Micro-CT techniques. To study the corrosion of steel reinforcement in a marine environment, the corrosion potential of embedded reinforcement in artificially cracked samples was investigated using the linear polarization method. The location of corrosion onset in relation to the presence of cracks was also identified using the Micro-CT technique. The deciding factor governing the extent of autogenous shrinkage for any given low-carbon mix was the pore structure refinement due to hydration at any given age. Complementing the shrinkage results, LC3 cracked the earliest compared to plain, fly ash based and slag-based concrete. The early-age cracking of concrete depended on the rate of shrinkage development rather than the magnitude of shrinkage. In spite of the crack healing, corrosion initiated and propagated for all steel embedded in paste sample. Therefore, autogenic self-healing showed negligible influence on durability related to corrosion. Low carbon cement with higher replacement levels showed general corrosion along the length of the mild steel due to weak steel paste interface in addition to the pitting corrosion. Therefore, this thesis highlights the secondary effect of binder composition in corrosion propagation. The overall shrinkage-related durability was significantly dependent on the hydration of the binders. Furthermore, the shrinkage caused by numerous factors including hydration, microstructure evolution, and drying was related to subsequent features of concrete such as the formation of cracks and the potential of corrosion propagation. Therefore, shrinkage, cracking and corrosion were investigated in a holistic and systematic manner and the overall shrinkage-related durability of low carbon cement and concrete was assessed. |
