No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

<p>The use of supplementary cementitious materials (SCM) decreases the environmental impact of the cement industry. SCMs are commercial by-products that possess pozzolanic properties. Recycled glass powder, classified as a SCM, when added as a cement replacement reacts with the available lime in the cement to form calcium silicate hydrate (C-S-H) products. In contrast with other SCMs, glass is siliceous and thus the reaction can also cause alkali silica reaction (ASR) which causes expansion and cracking. This study was completed in order to characterize the chemical reactions and their rate using a simplified system that mimics glass particles in hardened cement paste.</p> <p>Silica powder was added to solutions containing calcium hydroxide and/or sodium hydroxide. The rate of dissolution of the silica was monitored as well as the composition of the reaction products. Dissolution rates of silica with varying concentrations of silica, calcium hydroxide and sodium hydroxide, were fitted to the Hixson-Crowell cubic root law. The precipitate composition of the reaction product was represented by means of triaxial plots. It was found that silicate ions enter the solutions containing sodium hydroxide and containing both sodium hydroxide and calcium hydroxide. The rate is proportional to the quantity of sodium ions in the solution and to the pH. Also, higher concentrations of silica generally cause higher dissolution rates. The solutions with a pH of 13.48 and with lower silica concentrations created reaction products that were similar to C-S-H while the solutions with higher pH levels formed ASR after thirty days. The C-S-H prevented further dissolution of the silica. The formation of the ASR reaction products did not prevent further dissolution of the silica and they continued to dissolve until most of the silica had entered the solution.</p> / Master of Applied Science (MASc)

Heavy metals like cadmium, lead and zinc pose a significant threat to human health and environment. Several factors such as pH, EH, organic matter and clay content of the soil affect the bioavailability of such heavy metals in the environment. The presence of several naturally occurring minerals such as calcite (calcium carbonate, CaCO3) and calcium oxalate (CaC2O4.) in the environment significantly influence the fate and transport of some of the heavy metal cations. Sequestration of heavy metals such as cadmium (Cd) and zinc (Zn) from solution by calcite has been clearly demonstrated in the literature. However, studies on heavy metal sequestration by calcite and calcium oxalate from a multi-metal environmental that represents real world situations are rare. In this contribution, column flow studies of Cd and Zn sequestration by calcite exposed to influent solutions saturated or non-saturated with calcite and containing either 1 mg/L of Cd, 1 mg/L of Zn or combined 1 mg/L of Zn and Cd, followed by desorption of the sequestered metals were conducted. Complementary scanning electron microscopy (SEM) coupled with electron dispersive x-ray spectroscopy (EDS) data were generated. Kinetic studies show that reaction rates of Cd and Zn with calcite are governed by a simple rate law with reaction orders of less than 1 (0.02 - 0.07) indicating at least mathematically, the occurrence of reactions that went to completion if the reaction orders did not change. When the influent solution contains a single cation, the rate of Zn removal from solution by calcite and calcium oxalate is greater than Cd removal rate. However in a multi-cation environment, cadmium removal rate was greater than zinc removal rate. MINTEQA2 a geochemical equilibrium speciation model was used to compute the equilibrium between the various species in the cation-calcite environment. Complimentary desorption studies and surface SEM/EDS analysis indicate that the removal of Cd and Zn from solution by calcite and calcium oxalate is probably due to precipitation/complexation reaction. The SEM and EDS results appear to confirm the presence of a precipitate on the mineral surface in the case of the influent solution containing Zn. The current research also examines the effect of citrate, a commonly present urinary tract species on calcium oxalate dissolution. The dissolution studies indicate that citrate solution is capable of dissolving sodium oxalate at high pH. The dissolution of calcium oxalate results in the release of heavy metals that were previously sequestered within the mineral. Results show that a greater percentage of zinc was removed than cadmium, from calcium oxalate due to its dissolution by citrate. / Engineering

Many people experience a romantic breakup at some point in their lives, but people's reactions can vary considerably. A common way of coping with the dissolution of a romantic relationship is to seek support and opportunities to talk with close others. Although talking with social network members may prove helpful for some, the Social-Cognitive Processing (SCP) model posits that interpersonal interactions can hinder emotional recovery and adjustment if the disclosers feel the social network members are responding in a socially constraining way. As a result of perceiving social constraints, individuals may try to avoid thinking and talking about the breakup altogether, which, in turn, may interfere with the cognitive processing necessary to move forward from the breakup. The current research marked the first time the SCP model was explored with regards to the dissolution of romantic relationships, and it evaluated the utility of the SCP model in potentially explaining the variable nature of adjustment to a romantic breakup. One hundred and seventy-four eligible participants completed this online study. Participants completed various questionnaires pertaining to their previous relationship and subsequent breakup, their feelings and experiences following the romantic dissolution, their tendencies to think about the breakup, and the degree to which they discussed the relationship dissolution with others and the reactions they received during these conversations. In support of the SCP model, the results indicated that social constraints were associated with greater psychological distress. Furthermore, avoidance partially mediated the relation between social constraints and psychological distress as levels of social support decreased. This suggests that higher levels of social support might help buffer against engaging in avoidance in response to social constraints. In an initial attempt to examine whether the extent of avoidance displayed varied as a function of a dispositional variable (i.e., self-monitoring), no support was found. Future research should continue to investigate additional factors that may moderate the relation between social constraints and psychological distress through avoidance. / Psychology