title: Development of chloride resistant self-healing concrete with bio-agent immobilised polymer
Creators: name: Mohammed, H
Publisher: name: Liverpool John Moores University
Year: 2026

description: Cracking of concrete and degradation are the major problems in today’s concrete structures in the UK. Repair and maintenance of existing RC structures costs the UK government £50 billion per year. Most of these repairs (conventional repair) can last just 10 to 15 years. In addition to these technical aspects, the repair costs are usually very high. To achieve the sustainability targets, of the United Nations’ Intergovernmental Panel on Climate Change (IPCC) to reduce global greenhouse gas (GHG) emission 40% - 70% by 2050, it is essential to reduce the environmental impact of reinforced concrete (RC) structures. Recyclable thermoplastic polymers might be a solution by filling the voids and/or reducing the conduction contact area for corrosive components of the environment. Since the root cause of most of the structural failure is attributed to concrete cracking, there is a compelling economic incentive to develop a concrete that can treat and repair the damage all by itself. Bacteria based self-healing concrete development, is relying on calcium carbonate (CaCO3) precipitation. The CaCO3 formed by bacteria in the cracks is a brittle material and mainly useful for healing of static cracks, the use of polymer will protect the bacteria in/ around the cracks and the combination can show a larger degree of elasticity that might allow to keep even a dynamic crack sealed. The goal of this research was developing self-healing concrete composites by immobilising bio-agents into the polymers. The use of bacteria-based solutions to complement the polymer modified concrete might be an opportunity by potentially enabling the re-use or increase the quantity of polymers incorporated and simultaneously taking advantage of polymers’ elastic/ductile properties to heal concrete cracks in a complementary way to the calcium carbonate formed due to bacteria metabolism. This is the hypothesis of this work. The research started by analysing the influence of polymers on the mechanical and durability properties of concrete. A total of seven types of thermoplastic polymers were selected for this study, that they have not been considered before in the durability of infrastructures. The polymers are: ε-caprolactone (PCL), Polymorph, low density polyethylene copolymer with Ethylene-vinyl acetate (LDPE/EVA) granular and powder, general polyethylene (GPE), plastomer with ethylene–vinyl acetate EVA (N-228) and thermoplastic elastomers (TPE) (SEEPS); they were used as fine aggregate replacement (3 and 5%) and as a bio-agent carrier in concrete. Initially the experimental work was conducted to investigate the influence of the polymers and their replacement percentages on the mechanical and durability properties of concrete. As a result, the contribution of polymers leads to a 2–15% concrete strength increase. The durability properties such as open porosity, capillary water absorption improved for all the polymers except for TPE inclusion. For most of the polymers studied, their effect on preventing water migration via capillarity seems to occur 2-3 days after exposing concrete to water. The substitution of natural fine aggregates with some polymers leads to a reduction of chloride ion migration into the concrete samples, indicating that some of them stop free chlorides inside concrete. 5% LDPE/EVA leads to the higher restricted movement of free chloride migration as the coefficient decreased by 64% in comparison to plain concrete. This research then compares the performance of the three types of polymer modified concrete (TPE, LDPE/EVA, and PCL) if bacteria-based solutions are used. S. oneidensis MR-1 is a facultative anaerobic iron respiratory bacteria (IRB) that was selected to be investigated in this study. Experiments on the fresh, mechanical and durability characteristics of polymer and bio-polymer modified concrete, as well as the impact of nutritional media (Tryptic Soy Broth (TSB)) quantity (0.5L and 1L) were conducted. As a result, the bio-polymer (bacteria immobilised polymer) with 0.5L nutritional medium performed better when compared to 1L. Polymers and the bio-agent contributed to an increase in overall compressive strength, Bio-TPE and bio-LDPE/EVA exhibited a compressive strength of 75 MPa at 90 days. The contribution of bio-agent reduced concrete porosity from 12% to 2-4%. The water absorption via capillary was reduced by 85% in bio-polymer modified samples when compared to plain concrete. The chloride ion transfer was significantly reduced with the addition of polymers and the bio-agent, the improvement was 55 to 67% for 0.5 and 1L TSB at all ages. Surface electrical resistivity for bio-polymer modified concrete improved by 66%. According to the experimental outcomes, S. oneidensis could effectively induce calcium precipitation in the pH above 12. Through 16S rRNA gene sequencing it was confirmed that S. oneidensis can remain dormant up to 3-years in concrete. The maximum crack healed was 1.84 mm at 7 days, and completely fill the surface pores of 7.5 mm at 28 days after curing in water and TSB. Using SEM-EDS and FT-IR analyses, the healing material produced on or inside the cracks was investigated, and it was determined to be CaCO3.