The Properties of Concrete and Concrete Structures
Research Topics in Concrete
Dr. Roger P. West
The slump test is quick but not particularly accurate. It has long been known that it is a poor indicator of the true flow behaviour of concrete. Better indications can be obtained using specialist equipment designed to measure concrete flow characteristics. The department developed a lab-based rheology measurement system, which has been very successful. Work is now underway to develop a portable system suitable for on-site use.
Numerous projects have explored novel concrete mixes. These projects range from light-weight concretes for embankment construction, concretes formed using recycled paper waste, deliberately porous mixes designed for lining wells and many others using various grades of PFA etc.
Novel Reinforcement systems
The department has been involved in developing and testing prototype reinforcement systems. The Wireball system developed by Bjorn Svedberg has been the main focus of this work. This system replaces or supplements traditional bar reinforcement with interlocking reinforcement spheres. This system confines the concrete efficiently and this enables the concrete to develop greater compressive stresses. This reinforcement technique is suited to column reinforcement and testing has shown that it improves the performance of columns subjected to seismic loading.
The structural and creep performance of concrete reinforced using glass reinforced plastic bars has been investigated to assess its suitability for use in a marine environment.
The department has done extensive work on different fibre reinforcing systems including both steel and synthetic fibres. The research on the alignment of steel fibres within a concrete slab is quite novel. When fibres are mixed randomly within concrete only a small fraction of the fibres will be aligned usefully. However, if the position and alignment of the fibres is controlled then maximum benefit can be gained. Work is ongoing on the active alignment of steel fibres using magnetic fields. The results to date are very promising. One interesting use of the fibres has been to apply an electric current through the fibre-saturated layer: this results in an elevated internal temperature which accelerates drying of the slab.
Concrete and Impact
The department has undertaken research into the behaviour of concrete under impact. This research has been of a fundamental nature. The samples were testing under both active and passive confinement thus modelling different states of tri-axial stress. This work has been undertaken in conjunction with the late Professor Simon Perry.
Wireballs are open sphere’s of wire, spun in three orthogonal directions. With rings added, they form a unique type of reinforcement for concrete in which the confinement of concrete contained within the sphere is enhanced. The performance of concrete construction details for seismic loading have been tested by carrying out full scale structural testing using Wireballs within the conventional reinforcement. These tests involved cyclically loading test pieces at high strain. This research has been undertaken with Dr. Broderick as the principal investigator.
Drying out of concrete slabs
This is an area of very active research. The presence of moisture within newly constructed floor slabs can delay placement of floor finishes. Accelerated drying can unfortunately cause problems later and has led to the failure of many floor coverings. Work is ongoing on the development of analytical models that will be helpful in dictating how drying can be accelerated without leading to long-term problems.
Telemetry for concrete testing
Many sensors in concrete, thermocouples, strain gauges, transducers etc. require wiring back to a data-logger and from there to a computer. The department has been working in conjunction with a local manufacturer, Tramex, to develop wireless systems whereby radio signals are used to transmit readings to a nearby computer directly.