Development of high shrinkage Polyethylene Terephthalate (PET) shape memory polymer tendons for concrete crack closure

YesThe shrinkage force exerted by restrained shape memory polymers can potentially be used to close cracks in structural concrete. This paper describes the physical processing and experimental work undertaken to develop high shrinkage die-drawn Polyethylene Terephthalate (PET) shape memory polymer tendons for use within a crack closure system. The extrusion and die-drawing procedure used to manufacture a series of PET tendon samples is described. The results from a set of restrained shrinkage tests, undertaken at differing activation temperatures, are also presented along with the mechanical properties of the most promising samples. The stress developed within the tendons is found to be related to the activation temperature, the cross-sectional area and to the draw rate used during manufacture. Comparisons with commercially-available PET strip samples used in previous research are made, demonstrating an increase in restrained shrinkage stress by a factor of two for manufactured PET filament samples.Thanks must go to the EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and to Costain Group PLC. for their industrial sponsorship of the project and author

Large Scale Application of Self-Healing Concrete: Design, Construction, and Testing

Materials for Life (M4L) was a 3 year, EPSRC funded, research project carried out by the Universities of Cardiff, Bath and Cambridge to investigate the development of self-healing cementitious construction materials. This paper describes the UK's first site trial of self-healing concrete, which was the culmination of that project. The trial comprised the in-situ construction of five concrete panels using a range of self-healing technologies within the site compound of the A465 Heads of the Valleys Highway upgrading project. Four self-healing techniques were used both individually and in combination with one another. They were: (i) the use of microcapsules developed by the University of Cambridge, in collaboration with industry, containing mineral healing agents, (ii) bacterial healing using the expertise developed at Bath University, (iii) the use of a shape memory polymer (SMP) based system for crack closure and (iv) the delivery of a mineral healing agent through a vascular flow network. Both of the latter, (iii) and (iv), were the product of research undertaken at Cardiff University. This paper describes the design, construction, testing, and monitoring of these trial panels and presents the primary findings of the exercise. The challenges that had to be overcome to incorporate these self-healing techniques into full-scale structures on a live construction site are highlighted, the impact of the different techniques on the behavior of the panels when subject to loading is presented and the ability of the techniques used to heal the cracks that were generated is discussed.The work reported in this paper was carried out as part of the EPSRC funded project Materials for Life (M4L), reference EP/K026631/1 and supported with PhD studentship funding from Costain Group PLC

A shape memory polymer concrete crack closure system activated by electrical current

YesThe presence of cracks has a negative impact on the durability of concrete by providing paths for corrosive materials to the embedded steel reinforcement. Cracks in concrete can be closed using shape memory polymers (SMP) which produce a compressive stress across the crack faces. This stress has been previously found to enhance the load recovery associated with autogenous selfhealing. This paper details the experiments undertaken to incorporate SMP tendons containing polyethylene terephthalate (PET) filaments into reinforced and unreinforced 500 × 100 × 100 mm structural concrete beam samples. These tendons are activated via an electrical supply using a nickelchrome resistance wire heating system. The set-up, methodology and results of restrained shrinkage stress and crack closure experiments are explained. Crack closure of up to 85% in unreinforced beams and 26%–39% in reinforced beams is measured using crack-mouth opening displacement, microscope and digital image correlation equipment. Conclusions are made as to the effectiveness of the system and its potential for application within industry.EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and Costain Group PLC for industrial sponsorship of the project and autho

Self-healing concrete full-scale site trials

The development of a self-healing concrete aimed at improving the durability of concrete structures has been the focus of Materials for Life (M4L), a 3 year research project conducted by the universities of Cardiff, Bath and Cambridge. This interdisciplinary research has culminated in the UK’s first site trial of self-healing concrete on the A465 Heads of the Valleys section two project in South Wales hosted by one of the main industrial sponsors Costain Group Plc. The trial, which follows on from a series of small-scale laboratory experiments, comprises a number of concrete wall panels which contain combinations of the self-healing techniques studied during the project. These techniques include (i) encapsulation of healing agents led by Cambridge University, (ii) healing via bacterial action led by Bath University, and (iii) the use of shape memory polymer (SMP) based systems for crack closure and delivery of healing agents through vascular flow networks by Cardiff University. This paper presents the design, methodology and initial results of the site trial. The degree of self-healing is quantified via visual measurements of the crack aperture. An insight is offered into which of the combinations of techniques has shown the most promise for a selfhealing concrete solution for use within the construction industry. At a later stage of the project the regain in mechanical load and stiffness after damage and the reduction in permeability compared to that of the damaged concrete will also be assessed