PhD Oral Exam - Seyed Javad Mirvalad, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The use of Portland Limestone Cement (PLC) as a greener alternative to Portland Cement (PC) dates back to 1960s. In Canada, PLC was first introduced in 2008 with the limestone content limit of 15%. While the use of PLC alone in sulfate exposure is prohibited according to CSA A23.1, the limit of 15% is mainly to ensure a suitable level of mechanical and durability performance. Improving the performance of PLC and decreasing its clinker content is very appealing since it can contribute to reducing the carbon and energy footprint of cement industry. Calcium carbonate nanoparticles (NC) have been shown to be effective in accelerating cement hydration in ultra high performance concretes and concretes with high levels of supplementary cementing materials, but their effect on durability has been rarely studied.

In this research, limestone cement was made by blending micro limestone powder with general use cement at 15%, 20%, and 25% content levels. NC was used as an additive at 1%, 2%, 3%, and 4% and heat of hydration using isothermal calorimetry technic was evaluated. Based on the results of this test, 2% addition of NC was selected as the most favorable addition level and was used in mortar samples for further durability investigations. Additionally, the same mixtures were made with the addition of 2% nano silica (NS), which is a one of the most widely-used nanoparticles in cement, in order to put the efficacy of NC in perspective. Several mechanical and durability measures such as compressive strength, volume of permeable voids, sorptivity, bulk electrical conductivity, bulk electrical resistivity, and expansion due to ettringite and thaumasite sulfate attack were studied on mortar samples.

The results showed that 2% NC addition was significantly effective in improving durability of mortar samples. Also, 2% NC addition was found to be more effective than 2% NS addition in improving all of the measures except for compressive strength. Moreover, considering durability performance, it was concluded that, with the 2% NC addition, limestone content limit of 15% can be safely increased to 20% and even to 25% if sulfate resistance is not required.