Use of Recovered Toner Powder to Enhance Durability, Engineering and Sustainability Performance of Structural Concrete Elements

The working life of reinforced/prestressed concrete elements is often determined by serviceability limit state which is governed by the movement of harmful moisture into the structure and propagating/initiating corrosion of steel reinforcement. Recovered toner powder (RTP) is a highly engineered hydrophobic waste material currently being sent to landfill (approximately 5000 tonnes per annum, classified as hazardous due to its fine particle) which has the potential to modify the water resistance of concrete and provide a greater performance level. The project will consist of four phases:

Phase 1: Concrete Microstructural Characterisation and Optimisation

Using mercury intrusion porosimetry, nitrogen adsorption and micro-computed tomography, the influence of RTP on concrete microstructure and reinforcement interfacial transition zone will be determined. A parametric study will allow RTP content to be optimised with the particle size distribution of the cements considered (CEM I, II, III).

Phase 2: Water Resistance and Durability Study

Using water penetration and sorptivity techniques, the project will examine water movement within optimised RTP concretes as well as chloride ingress/carbonation resistance, the main causes of corrosion of embedded steel. This will provide data for modelling of service life (initiation and propagation periods) of structural elements.

Phase 3: Engineering Performance and Service Life Modelling

Compressive/tensile strength and E-value of concrete elements will be examined to assess the impact of optimised RTP contents. The outputs of this along with Phase 2 will allow numerical modelling of concrete elements under selected exposure conditions to determine alignment with intended working life requirements in BS EN 1992 and BS 8500.

Phase 4: Sustainability Study

Using industry embodied CO2 figures (Mineral Products Association), a comparison of cradle to gate sustainability in conjunction with the outputs from Phases 1-3 will allow an iterative approach to materials selection to provide optimised concretes based on engineering performance, serviceability requirements and up-front carbon.

Benefits to Structural Engineers: Enhancing the service life is beneficial to structural engineers and clients. The use of RTP has the potential to provide greater protection to embedded carbon steel and hence lower intervention and maintenance costs for key structural elements which are often difficult to access. RTP may also allow greater optimisation of construction materials (and hence resources) allowing structural engineers to achieve greater performance with less materials (key for reducing embodied up-front carbon) and contribute to significant reductions in capital, lifecycle and whole life costs of structures.

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