Introduction

Emissions data suggests that 30-50% of all carbon emissions arise from activities in the built environment. The global population is expected to reach 9bn by 2050, with 67% living in urban areas. Meeting strict emissions reductions targets (in the UK – an 80% reduction by 2050) and facilitating global low-carbon design is therefore a major challenge for structural engineering.

Concrete is the world’s most widely used man-made material. The manufacture of cement accounts for a large proportion of global raw material expenditure and at least 5% of global CO2 emissions. Recent research has made it possible to cast geometrically complex concrete structures, capitalising on a key advantage of this fluid material. These developments allow new architectural expression, and the new geometries allow us to save considerable amounts of material through design optimisation.

This new potential is being held back by current methods for reinforcing concrete. Although the steel rods that we use can be bent into standardised shapes, any further complexity adds considerable cost to the construction process.

With the goal of achieving low carbon concrete design, two major challenges exist: 1) to reinforce structures with complex geometries and 2) to provide durable and resilient structures. Meeting both challenges would allow us to capitalise on the fluidity of concrete to meet long-term emissions reductions targets. This will require a completely new approach to design and construction of concrete structures.

This proposal will completely replace internal steel reinforcement with a knitted composite reinforcement cage made from carbon fibre tows. By fabricating this reinforcement in exactly the right geometry, we will provide exactly the right strength exactly where it is needed. This will be transformative for concrete construction, and will greatly simplify the reinforcing of more efficient concrete structures to help the UK meet its ambitious targets for emissions reductions. 
Introduction

Objectives

1) To demonstrate that CFRP can be woven into geometrically appropriate 'cages' for the reinforcement of concrete beams (mechanical properties)

2) To develop an outline manufacturing process, supported by prototypes and influenced by industrial methods using in aerospace and mechanical engineering, that can produce the cages (production and manufacturing aspects)

3) To develop a reliable method for the design of the internal reinforcement, that provides flexural and shear capacity, accounts for concrete confinement and can be implemented in three-dimensional design methods (design and mechanical properties)

4) To complete outline life cycle analysis of the construction process and compare it to steel construction to demonstrate the potential of the proposal going forwards (economic properties)


Progress

  • The technical developments performed in this project provide the basis for a novel alternative reinforcement technique to reinforce structures having complex geometries, which are difficult to reinforce with conventional steel. 
  • A new method of manufacturing CFRP shear reinforcement for optimised concrete beams by winding carbon fibres around a bundle of FRP reinforcing bars was developed.
  • The method is well suited to automation and mass production of entire reinforcing cages.
  • Fabric formwork and the flexibility of the winding process greatly reduces technical limitation on the shapes that can be built.
  • The effectiveness of the reinforcing material is established by mean of flexural tests conducted on real scale optimised beams subject to a uniformly distributed load.
  • WFRP, when used in the required quantity and in an appropriate geometry, is able to prevent shear failure of such members.
  • Existing FRP provisions can be conveniently used to predict the behaviour of FRP optimised beams, through a section-by-section analysis.