Development of self-healing concrete structures and the quantification of their value in the context of enhancing the delivery of a major highway project

Moore, Thomas 2024. Development of self-healing concrete structures and the quantification of their value in the context of enhancing the delivery of a major highway project. MPhil Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis describes the investigation of a novel polymer concrete reinforcement system, where testing is carried out on polymer specimens, standard concrete specimens and large site trial structures. Traditional steel reinforcement is a well understood and tested material however, it suffers from corrosion which reduces the durability of reinforced concrete. Therefore, reducing or removing steel and replacing it with inert polymer reinforcement could increase the durability of concrete structures and reduce maintenance costs. Individually, the novel polymer reinforcement unit is known as a “Spheritet” however, when cast into a cementitious matrix, the cementitious composite is referred to as Tetcrete. Spheritets have been designed and developed via research at Cardiff University supported by the polymer knowledge and manufacturing capabilities at the University of Bradford. Tetcrete is one output of the research carried out under the Resilient Materials 4 Life programme grant. Objective one of this thesis analysed tensile, creep and relaxation results for two polymer specimens as well as Tetcrete, results from prisms, cubes, cylinders and three large culverts. This is to establish the performance of the raw polymer materials as well as the concrete and Tetcrete, primarily the strength, crack propagation and healing potential. Polymer testing was carried out on dog bone specimens to determine the tensile and creep data for Polyoxymethylene (POM) and Polyethylene terephthalate (PET), with POM currently being used for Spheritets. POM tensile results achieved an 11.7 % greater peak load than PET. For creep testing PET achieved a 14.4% lower displacement at 72 hours than POM with both proving similar relaxation recovery percentages of 31.3 and 29.7 % after 24 hours for POM and PET respectively. The material data sheets suggested that PET should outperform POM, which was true for creep and relaxation but not peak load. Therefore, the creep rate was lower for PET than POM however, the ultimate tensile load was lower. This could be due to a small sample size for testing and the lack of environmental chamber. ii For objectives two and three cementitious specimens were cast using a low strength CEM V/A concrete mix containing 50% supplementary cementitious materials (SCM’s), SCM materials are mineral admixtures that improve the properties of fresh and/or hardened concrete. The CEM V/A mix design includes 50% ordinary Portland cement (OPC) and 20% Ground granulated blast furnace slag (GGBs), 10% silica fume (SF) and 20% Fly ash (FA). The lab specimens and culverts were then positioned outside and monitored. The experiments aimed to determine the strength, deflection, healing potential and durability via water absorption and water flow testing of spheritets as opposed to traditional steel reinforcement, complementing steel reinforcement and control specimens. The culverts were loaded using a jacking mechanism with strain/load, displacement, monitored over time to compare the performance of the steel reinforced concrete culverts against that of the steel reinforced concrete and spheritet culverts (i.e. steel reinforced Tetcrete). The best performing Tetcrete specimen provided a 37.9 % lower failure load than the best performing control specimen however, the addition of Spheritets did allow two additional rounds of flexural testing due to increased durability. Steel-reinforced Tetcrete specimens showed a failure load capacity of 7.6 % greater than steel reinforced concrete specimens alone. Moreover, the load required to achieve a crack width of 0.2mm, was 21% higher in the steel-reinforced Tetcrete culverts than in the steel-reinforced control culvert. Both Tetcrete with steel and steel only specimens showed healing potential, with one prism of each providing a 100% crack closure. Tetcrete results were impacted by thermal expansion of the Spheritets during the drying stage prior to initial surface absorption testing where considerable surface cracking appeared compromising the flexural, displacement and healing results. This research is novel as whilst polymer materials have been utilised previously this study focuses on a specific geometric shape, where the reinforcement can be incorporated “randomly” whilst also providing a consistent distribution, unlike fibres. This will increase the potential to provide optimised designed standards as the reinforcement position can be defined in a similar manor to that of traditional steel reinforcement. Additionally, the concrete mix used is not widely utilised and aims iii to complement the Spheritets by enhancing the self-healing potential due to reducing crack opening size. Reduced carbon concrete is becoming more prevalent to reach our net zero goals, this thesis aims to provide insight into one avenue of this field. Future works will continue to test polymer materials with a key avenue being the thermal expansion that occurs within a cementitious matrix due to Spheritets.

Item Type:	Thesis (MPhil)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1). Self-healing Concrete 2). Polymer reinforced concrete 3). Tetcrete 4). Spheritets 5). Autogenous concrete 6). Supplementary cementitious materials
Date of First Compliant Deposit:	7 March 2025
Last Modified:	07 Mar 2025 11:45
URI:	https://orca.cardiff.ac.uk/id/eprint/176695

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