Cement Changes and their Effects on Shrinkage and Durability of Concrete
Sharma, Achintyamugdha Surendra
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In this work, the effects of different cementitious combinations on drying shrinkage and durability of concrete are investigated. Shrinkage is caused due to loss of water from concrete due to evaporation. Cement paste is the most vulnerable part of concrete to shrinkage. As concrete consists of cement paste and aggregates, the latter pose as restraints to the shrinking paste. As a result, tensile stresses are formed thereby leading to the formation of cracks. Cracks in concrete are responsible for the ingress of deleterious chemical ions such as, Chloride and Sulfate ions, which may form expansive compounds. Chloride ions also induce corrosion of steel reinforcement bars. Prior literature has indicated that coarser cementitious systems lead to less shrinkage in concrete. Additionally, tri-calcium silicate (C3S) and tri-calcium aluminate contents in cement also influence the extent of shrinkage in concrete. However, the extensive use of such cement in concrete as per current industry standards will be challenging. Therefore, in this study investigations are made with Type IL (10) portland limestone with or without supplementary cementitious materials (SCMs), such as fly ash, and engineered nanomaterials such as nanosilica, to develop concrete with similar shrinkage performance as compared to coarse ground portland cement, without adversely affecting other engineering properties of concrete. Key engineering properties include workability, degree of hydration, compressive and splitting tensile strengths, electrical resistivity, setting time, and bleeding. Portland limestone cement used in this study has a partial replacement level of 10% of portland cement with limestone. Although, ASTM C595 allows up to 15% replacement with limestone, current industry use is limited to ~5%. Micro-cracking tendency of selected concrete mixtures from this study is also investigated by using fluorescence microscopy and micro computed tomography (µ-CT). In this study, life cycle assessment (LCA) studies are conducted on select cementitious combinations to quantify the benefits of such replacement of portland cement. Additionally, life cycle cost analysis (LCCA) is also performed to determine feasibility of cost. Results show that Type IL portland limestone cement can be an effective alternative for reduced shrinkage strain and enhanced durability properties.
Doctor of Philosophy