Quarry aggregate reserves are depleting rapidly, particularly in some desert regions of the world. Worldwide Quarry aggregate production is about 4.5 billion tonnes, and Australia alone consumes about 130 million tonnes of aggregates annually. Moreover, the production of 1 tonne of natural crushed aggregate emits 7.4-8.0 kg of CO2. In addition, emissions from trucks as well as the use of crushers, which result in large dust and particulate emissions, contribute to the increase global warming. Furthermore, the quarrying removes resources, impacts on the natural drainage patterns, and adversely affects the environment from the quarrying processes.
Quarry aggregate reserves are depleting rapidly, particularly in some desert regions of the world. Worldwide Quarry aggregate production is about 4.5 billion tonnes, and Australia alone consumes about 130 million tonnes of aggregates annually. The process energy and greenhouse gas emissions from Quarry aggregate is around 7.4 to 8.0 kg CO2-e per tonne. Aggregate demand is also increasing with the expansion of construction with the annual production of premix concrete in Australia is about 30 million cubic metres. Between 3‒5 % of concrete delivered to site remains unused and goes to landfill or crushing plants.
To address this problem RMIT University and Cycrete and undertaking research on the manufacturing of coarse aggregates from wet mix waste concrete. The project is assessing the performance of the reclaimed material as both a supplementary aggregate mixed with conventional aggregate and also as the sole aggregate. The material recovered includes both coarse aggregates and fines. The research is testing a series of mixes produced using this manufactured coarse aggregate with the replacement of quarry aggregate by 25%, 50%, 75% and 100%. This includes physical, chemical, mechanical and durability properties of the aggregate and the concrete. In addition, RMIT are assessing environmental and economic costs/benefits of the process.
It has been estimated that the annual fly ash generation from coal power plants in Australia had reached 14 million tonnes in 2015 with the worldwide fly ash production anticipated to increase up to approximately 2000 million tonnes in 2020. At present between 35-45 percent of fly ash is being utilized in construction while the balance is disposed of in landfills and storage lagoons at significant cost. As the fly ash waste continues to accumulate there is pressure on the coal power industries to find a solution for its disposal. At the same time, natural aggregate reserves are depleting fast. The production of 1 tonne of natural crushed aggregate emits 7.4-8.0 kg of CO2. In addition, emissions from trucks as well as the use of crushers, which result in large dust and particulate emissions, contribute to the increase global warming. Furthermore, the quarrying removes resources, impacts on the natural drainage patterns, and adversely affects the environment from the quarrying processes
RMIT University are currently undertaking an extensive research programme with and Polyagg Ltd who have patented a methodology for a manufactured geopolymer coarse aggregate using low calcium fly ash. The technology for the manufacture of this geopolymer coarse aggregates uses novel techniques employing high pressure and reduced temperature production methods. The reaction mechanism of the geopolymer coarse aggregate is similar to that of fly ash based geopolymer concrete where the silicates and aluminates in low calcium fly ash react with highly alkaline activators and produce a sodium-aluminosilicate gel. This geopolymeric gel consists of a three-dimensional network of silicon and aluminium atoms linked by oxygen atoms in a four-fold coordination. The use of this novel aggregate in concrete has the potential to reduce the reliance on conventional aggregate quarries as well as utilizing a waste material, hence reducing the environmental impacts.
The research has utilized a range of advanced analytical and microscopic techniques to asses physical, chemical, mechanical and durability characteristics of the aggregate microstructure. This has included comparison with conventional aggregates, which have shown that the geopolymer aggregate has similar performance characteristics as standard lightweight aggregate. In addition, the reaction kinetics and pore development of the geopolymer aggregate have been studied. Furthermore, RMIT has undertaken environmental and cost benefit analysis on the use of the material as a structural lightweight aggregate.
