Abstract

This thesis covered the second phase of a study that focused on the reactivity of recycled concrete aggregate (RCA) produced from concrete affected by alkali-silica reaction (ASR). The first phase investigated the reactivity of ASR-affected RCA and the use of Supplementary Cementing Materials (SCM) as a preventive measure. The second phase was carried out to study the efficacy of lithium nitrate, when used individually and in combination with SCM, in suppressing the reactivity of RCA. The use of different dosages of lithium nitrate combined with SCMs reduced expansion due to ASR. However, the expansion results showed that increasing the dosage of lithium beyond a certain level does not help in suppressing the expansion. The high reacitivity of the tested RCA was attiributable to its relatively high alkalis and calcium hydroxide contents that fuel further ASR. The alkalis consumed or contributed from RCA were evaluated through leaching the aggregate particles in distilled water and alkaline solutions at different molarities with and without lithium nitrate. Alkalis consumption was found to decrease when lithium was presented in the leaching solutions. Examining RCA samples under scanning electron microscope (SEM) showed that the crushing process of the RCA exposes fresh surfaces of the reactive virgin aggregate and creates cracks within the particles that provide an easy path of alkalis to reactive sites within the RCA. Examination of the composition of ASR gel showed that exposing the RCA to lithium solution decreased the calcium content and Ca/Si of the gel. This could add to the suggested mechanisms by which the lithium mitigates ASR.

Highlights

  • 1.1 GeneralConventional concrete aggregates usually contain natural fine and coarse aggregates

  • When recycled concrete aggregate (RCA) that was affected by Alkali-Silica Reaction (ASR) is used as partial or full replacement for coarse aggregate, some of the alkalis contained in the aggregate contributes to raise the available alkalis in the pore solution, and the ASR expansion obtained from that type of RCA was found to be similar to the one obtained from the original natural aggregate

  • For the material investigated in this thesis the following conclusions are drawn: 1. ASR-affected RCA was found to be as reactive as the original natural aggregate used which was reactive siliceous limestone (Spratt)

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Summary

A Thesis Presented to Ryerson University

I hereby declare that I am the sole author of this thesis. I authorize Ryerson University to lend this thesis to other institutions or individuals for the purpose of scholarly research. Waleed Mikhaiel I further authorize Ryerson University to reproduce this thesis or dissertation by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. Ryerson University requires the signatures of all persons using or photocopying this thesis.

General
Objective
Organization of thesis
General Recycling of concrete is a relatively simple process
Recycled concrete
Recycled concrete Applications
General Alkali-Silica
Alkali Silica Reaction Mechanism
Adequate moisture content
Other Factors affecting ASR
Test methods to evaluate expansion due ASR
Petrographic examination (ASTM 295) ASTM C295-03
Accelerated Mortar Bar
Concrete Prism
Accelerated Concrete Prism Test method In 1992, Rance and
Limiting the alkali content in concrete
Use of Supplementary Cementing
Use of Lithium Salts Since McCoy and
Coarse Aggregates
Lithium Nitrate LiN03
Mix procedures
Concrete mixes
Scanning Electron Microscopy (SEM)
Alkali Contribution Test
ASR concrete prisms
Effect of SCM binary blends
Effects of SCM ternary blends
Effect of lithium nitrate on RCA reactivity
Effect of using lithium nitrate with SCMs
Dilution effect of the reactive aggregate
Composition of Gel and Residual Paste
Effect of lithium on the alkali consumption
Conclusion
Recommendations
Full Text
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