Date of Graduation

12-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Murray, Cameron D.

Committee Member

Hale, W. Micah

Second Committee Member

Zhang, Shengfan

Third Committee Member

Braham, Andrew F.

Keywords

compressive strength; concrete; flexural strength; magnesium phosphate cement; mix design; modulus of elasticity

Abstract

Magnesium phosphate cement (MPC) is a rapid-setting alternative cement typically used as a quick repair material. MPC has gained popularity in recent years due to its ability to reduce CO2 emissions, its strong chemical resistance, and potential use in large scale applications. There is currently limited research on the properties of MPC when varying the proportions of its ingredients. Several hardened concrete properties were analyzed on concrete mixtures made with MPC. A mix design process for MPC concrete is proposed based on testing of 300 MPC paste mixtures and 115 MPC concrete mixtures. A standardized mix design process is imperative for MPC to gain broader application in practice. The first chapter examines only paste mixture properties. Setting times, compressive strengths, and flow values are strongly affected by mixture characteristics such as the magnesia to phosphate molar ratio (M/P), water to binder ratio (w/b), chosen phosphate component and replacement rates, set retarder type, set retarder dosage, fly ash type (class C or class F) and replacement rate. This study found that lower M/P, higher w/b, higher set retarder dosages, and inclusion of class C fly ash provided longer setting times and higher flow values. Higher M/P, lower w/b, lower set retarder dosages, and no addition of fly ash provided higher compressive strengths. This work should aid in future studies seeking to develop non-proprietary MPC formulations. The second chapter investigates hardened properties of MPC. Compressive strength testing was conducted on 109 MPC mixtures and flexural strength, modulus of elasticity, and ultrasonic pulse velocity testing on 73 MPC mixtures. Eight different mixture design parameters were examined in this study to understand their effects on hardened properties. These included M/P (4, 6, 8), w/b (0.18, 0.2, 0.22), aggregate type (limestone, dolomite, trap rock, sandstone), aggregate size (#57, #7), aggregate percentages (50%, 60%, 70%), paste to aggregate ratio (0.5, 0.7, 1), replacement rates of class F fly ash (20%, 40%, 60%), and set retarder dosages (4%, 6%). Existing relationships between compressive strength and other engineering properties were found to be generally applicable to MPC concrete despite the major differences in chemistry. Demonstrating how to achieve specified hardened properties of MPC could encourage the use with this material in practice. The third chapter proposes a mix design process based on the already familiar American Concrete Institute (ACI) 211 document for portland cement concrete mix design. The effects of mixture parameters such as M/P (4, 6, 8), w/b (0.18, 0.2, 0.22), aggregate type (limestone, dolomite, trap rock, sandstone), aggregate size (#57, #7), aggregate percentages (50%, 60%, 70%), binder to aggregate ratio (0.5, 0.7, 1), replacement rates of class F fly ash (20%, 40%, 60%), and set retarder dosages (4%, 6%) on setting time, slump, slump flow, and compressive strength values detailed in the other chapters were used to recommend optimal starting values for trial mixture designs. The result is a mixture design process able to produce an initial mixture design with adequate workability and strength properties for MPC concrete.

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