Physico-chemical changes in cementitious systems through the use of non-standard cementing materials and their influence on ionic transport

The use of non-standard supplementary cementing materials (SCM) that are by-products or waste products from different processing operations is gaining increased acceptance in concrete. These materials contribute to the cause of sustainability of concrete and can potentially improve concrete properties. This thesis focuses on understanding the behavior of cement pastes and/or concretes modified with novel SCMs such as vitreous calcium alumino-silicate (VCAS), glass powder, or nano-silica and compare it with the performance of cement pastes and/or concretes modified with silica fume and fly ash as cement replacement materials. The long-term durability characteristics evaluated in this study (for concrete and pastes specimens) are resistance to chloride ion penetration, and resistance to calcium ion leaching.;The chloride ion penetration resistance is evaluated using a combination of conventional tests such as the rapid chloride permeability test (RCPT), the non-steady state migration (NSSM) test, and steady state conduction (SSC) test along with advanced characterization techniques such as electrical impedance spectroscopy (EIS) and equivalent circuit modeling. The chloride transport resistance is seen to increase with increase in replacement material content, especially at later ages. It is found in this study that performance of glass powder modified concretes is similar to that of fly ash and VCAS modified concretes as far as chloride transport is considered. Different microstructural parameters based experimental results and models are developed to monitor microstructural changes during the non-steady state migration test. It is observed that these microstructural parameters are able to capture the changes in the material as a result of age, incorporation of cement replacement materials, and chloride ingress. Evidence of pore structure changes (Friedel's salt formation and deposition) is also provided based on changes in values of electrical circuit elements in the model as well as thermal analysis and X-ray diffraction data.;Leaching of calcium ions from cement pastes when exposed to two different leaching media (deionized water and 6 M ammonium nitrate solution) is studied. The parameters related to calcium ion leaching studied are the mass loss, increase in porosity, and changes in calcium hydroxide and C-S-H contents. All the modified pastes show better calcium ion leaching resistance (in deionized water or 6 M ammonium nitrate) than the plain cement paste even though reasons for this behavior are different and are studied in detail. A new approach to separate the porosities created as a result of calcium ion loss from CH and C-S-H is presented. Calcium equilibrium curves are developed using thermogravimetric analysis, stoichiometric equations of cement hydration and pozzolanic reaction, and porosity measurements. The coupling of calcium ion leaching with further cement hydration/or pozzolanic reaction is quantified for the pastes subjected to leaching in deionized water. A simple and effective method to calculate the calcium dissolution front from CH loss during leaching is also detailed. A ranking system to evaluate the performances of different cement replacement materials in slow and accelerated leaching conditions is also presented.