Date of Award

2014

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

Sub-Department

Civil Engineering

First Advisor

Fabio Matta

Abstract

Use of polymers as partial replacement for Portland cement in cement mortar and concrete can diminish several drawbacks of these composites such as low tensile strength and strain capacity, high permeability and low adhesion. Main reasons for the use of polymers are to improve damage tolerance, adhesion, and resistance to water permeation. Various polymers with a wide range of physical and mechanical properties have been used in fabrication of cementitious composites. Typical polymer content for such composites is 5% to 20% (by the weight of cement) for both mortar and concrete. There are also drawbacks associated with the use of PMMs which become critical at higher P/C ratios. These limitations include but are not limited to high cost; vulnerability to high temperatures, chemical attack, and UV radiation; and storage and handling issues such as odor, toxicity, flammability, and combustibility. Therefore, finding ways to reduce these drawbacks and maintain the advantages PMMs have to offer is of great interest to engineers and researchers.

In this work dopamine (DA) is introduced as a potential monomer for production of high-performance polymer-modified mortar (PMM) composites at small polymer-cement (P/C) ratios of 0.1-0.5%, i.e. two orders of magnitude smaller than P/C ratios used in common practice. Formation of a PDA-cement co-matrix is examined and different factors affecting the characteristics of such system are discussed. In particular, the role of P/C ratio in formation and distribution of PDA network and effect of PDA network on mechanical properties of PDA-cement systems are studied and different mechanisms are discussed. 7- and 28-day compressive strength and splitting tensile strength of newly-formulated composites were tested at different P/C. Morphology and microstructure of PDA-cement matrix were studied using scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) analysis of samples obtained from fracture surfaces. The effect of PDA on drying shrinkage and early-age cracking resistance of mortar was also evaluated using ASTM ring test. Incorporation of PDA at P/C of 0.5% improved compressive strength, tensile strength, and shrinkage cracking on average by 55%, 27%, and 69%, respectively.

Rights

© 2014, Nima Zohhadi

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