Scientists at ANSTO have moved a step closer to solving a mystery that has puzzled technologists for thousands of years - how concrete sets. The eventual spin-off for Australian industry could be more durable and stronger concrete materials and that will mean cheaper and longer-lasting buildings.
The scientists, at ANSTOs Materials Division, have been investigating ways to encapsulate low level radioactive waste in concrete. The work requires a fundamental understanding of the complex changes that occur as concrete hardens. People have long known how to make concrete. The ancient Romans were masters of the craft. It is at least 2,000 years since the ancient engineers first heated limestone (calcium carbonate) and minerals to make a substance which when powdered and mixed with water set into a material of remarkable strength.
The scientists, at ANSTOs Materials Division, have been investigating ways to encapsulate low level radioactive waste in concrete. The work requires a fundamental understanding of the complex changes that occur as concrete hardens. People have long known how to make concrete. The ancient Romans were masters of the craft. It is at least 2,000 years since the ancient engineers first heated limestone (calcium carbonate) and minerals to make a substance which when powdered and mixed with water set into a material of remarkable strength.
But despite painstaking research, no-one has ever been able to work out how concrete sets. Even the most advanced scientific techniques - like X-ray crystallography - have failed to solve the mystery. Part of the problem is that the concrete gel - the material formed as cement sets - is amorphous, not crystalline, and cannot be examined by conventional methods.
The ANSTO team working on a very modern problem believes it is getting close to answers to some very old questions. With the help of funding from the Department of Industry, Science and Resources, ANSTO is collaborating with the American Centre for Advanced Cement Based Materials (ACBM) on better methods for testing concrete durability, a quality dictated by the chemical reactions that take place as concrete hardens.
The ANSTO team - Professor Terry Sabine, Dr Bill Bertram, Dr Laurie Aldridge and Mr Kevan Harder, all of the Materials Division, and Dr Michael James, of the Physics Division - has been collaborating with ACBM on the work for five years.
The scientists have been using advanced equipment overseas, which exploits neutrons generated in research reactors. The instruments - ultra-small-angle neutron scattering spectrometers - are effectively "neutron microscopes". They use neutrons produced in research reactors to probe the structural differences in particles smaller than a grain of talcum powder. Neutrons bombard the sample, and are scattered by the nuclei of the atoms like balls on a billiard table.
The scattering pattern enables scientists to generate a picture of the material's structure. The instruments are commonly used to study plastics and biologically active molecules, and can probe concrete at the molecular level.
The scattering pattern enables scientists to generate a picture of the material's structure. The instruments are commonly used to study plastics and biologically active molecules, and can probe concrete at the molecular level.
The ANSTO scientists want to know the extent to which the water molecules bind to the gel particles. Professor Sabine and Dr Bertram have formulated a theory to interpret the spectrometer results. The theory has enabled them to determine the chemical and structural interactions taking place in setting cement.
The ANSTO research has been accepted for publication in the prestigious physics journal Acta Crystallographica A, and the new theory is already being applied by overseas scientists to interpret scattering from amorphous materials.
The team will now use the theory to combine the ultra-small-angle neutron scattering results with data from the Australian Small Angle Neutron Scattering spectrometer, AUSANS, to "see" particles ranging from atomic dimensions to sizes that can be seen by an optical microscope. The AUSANS instrument, which uses neutrons produced by ANSTO's HIFAR research reactor at Lucas Heights, has just become operational.
"The success of our work can be put down to a close collaboration between physicists and material scientists both in Australia and overseas," Professor Sabine said.