Degree

Doctor of Philosophy (PhD)

Department

Engineering Science

Document Type

Dissertation

Abstract

The issue of concrete cracking poses a significant challenge, leading to the accelerated deterioration of civil infrastructure. In response to this concern, a new class of materials called Engineered Cementitious Composites (ECCs) has been developed over the past three decades to address the inherent brittleness of conventional concrete. Guided by fiber/matrix micromechanics and fracture mechanics principles, ECCs exhibit pseudo-strain-hardening behavior (PSH) with tensile strain capacity ranging from 1 to 8% at low fiber content (i.e., 1 to 2 vol.%). More recently, there has been a growing interest in geopolymer-based ECCs known as Engineered Geopolymer Composites (EGCs). By eliminating the need for energy- and emission-intensive Portland cement, EGCs are considered more environmentally friendly compared to ECCs. EGCs are emerging as a sustainable alternative that maintains the desirable characteristics of ECCs while reducing the environmental impact associated with traditional cement production.

The objective of this study was to develop and evaluate the factors influencing the physical, mechanical, and fiber bridging properties of engineered geopolymer composites (EGC). Specifically, binder composition, aggregate type, aggregate content, fiber type, fiber length, fiber treatment, and fiber content were examined. For comparative purposes, the fresh (i.e., workability and setting time) and hardened (compressive strength) of the geopolymer binders and mortars were determined. Additionally, and fracture toughness test was conducted on the geopolymer mortars.

The results revealed that the potassium (K)-activated MK-based EGCs manufactured with 12 mm ultrahigh molecular weight polyethylene (UHMWPE) at 0.8 vol.% fiber content achieved exceptionally high tensile strain capacities of up to 8% (i.e., similar to Grade 60 steel reinforcement) compared to 0.8 vol.% 10 mm UHMWPE fibers and 1.6 vol.% polyvinyl alcohol (PVA) fibers. Moreover, the composites manufactured with 50 mol.% potassium and 50 mol.% sodium (i.e., K/Na) resulted in higher physical, mechanical, and fiber bridging properties and shorter setting times compared to potassium. Furthermore, based on the compressive and tensile properties, the optimum aggregate content for river sand and microsilica sand were found to be 45 vol.%. Nevertheless, the composites manufactured with river sand generally exhibited higher tensile strain capacities at 1 vol.% 12 mm UHMWPE fiber content. However, upon incrementing the fiber content (i.e., from 1 to 1.5 vol.%), the K/Na composite with 45% MS and 1.5 vol.% UHMWPE fiber content exhibited a tensile strength of 4.62 MPa and a tensile strain capacity of 3.15%. Among the MK-based EGCs in this study, the composite with plasma treated 12 mm UHMWPE fiber emerged as the best-performing, boasting an impressive compressive strength of 59.4 MPa, a tensile strength of 6.65 MPa, and a tensile strain capacity of 6.26% with an average crack width of 44.4 µm. These findings pave the way for the design and implementation of MK-based EGCs in various engineering applications.

Based on the workability and compressive strength of the K-activated MKFA-based geopolymer mortars, the optimum metakaolin to fly ash content used in the manufacturing of MKFA-based geopolymer composites was determined to be 50 mol.% metakaolin and 50 mol.% fly ash. The results of the geopolymer composites manufactured with 4 wt.% silica fume revealed that many composites exhibited pseudo strain hardening behavior, yet they did not achieve the minimum tensile strain capacity of 2% to be classified as an EGC. However, the composites manufactured with K/Na,10 wt.% silica fume, 45 vol.% RS, and 1.75 vol.% 12 mm UHMWPE fibers exhibited a tensile strain capacity up to 4.57%. Life cycle assessment revealed that the carbon footprint of the EGCs design mixes was lower than the ECC baseline, where the production of potassium hydroxide was the highest contributor.

Date

2-26-2024

Committee Chair

Hassan, Marwa

Download

Available for download on Thursday, February 25, 2027

Share

COinS