Humphrey Wallis - British Geological Survey - Environmental Science Centre
Simon Holyoake - British Geological Survey - Environmental Science Centre
NI Products Used: LabVIEW, LabVIEW FPGA Module, LabVIEW Real-Time Module, CompactRIO
The term ‘construction minerals’ describes materials used by the construction industry, for example in road making, concrete, house construction, and as railway ballast. The largest component of construction minerals, and the most mined materials in the world, are ‘aggregates’ – a term used to describe granular material suitable for use on their own or with binders such as cement, lime, or bitumen.
These aggregates are typically produced by crushing rock (such as limestone, igneous rock, and sandstone), which is an energy intensive process. Reducing the size of solids in the mining and quarrying industry consumes an estimated five percent of artificially generated energy in the developing world.
Increased Efficiency, Reduced Carbon Footprint
As has become common place, the minerals industry faces increasing pressure to reduce carbon emissions in line with government targets. A key area to consider is the energy required to crush certain aggregates, which must be balanced with the energy costs associated with transporting them from quarries to construction sites.
Currently, the energy consumed crushing rocks is calculated using the ‘Bond Work Index’, which was defined by 1945 by American mining engineer, Fred C. Bond. We sought to investigate and improve these theorems by building a prototype ‘Bond-impact test rig’, employing the latest technologies, high-precision instrumentation, and new experimental methodologies.
Prototyping the Rock Smashing Test Rig
Armed with LabVIEW software and a CompactRIO embedded controller, which we had acquired for a previous project, we set out to create an in-house prototype for the Bond-impact test rig. Because the functionality of the CompactRIO controller is entirely defined by software, even down to the hardware level, it offers the utmost in flexibility. This meant we could quickly repurpose our existing equipment without going through another purchasing process. This greatly improved the time and cost required to arrive at a functioning prototype.
Once an engineer gains experience and proficiency in LabVIEW, it becomes the ultimate tool to quickly transform ideas into solutions. The prototyping process was further accelerated by technical support and application guidance from the NI application engineering team. A steep learning curve could be a critical obstacle that could stall the prototyping process, but due to the flexibility and reusability of the NI platform and the support from the NI engineering team, we made rapid progress on the prototype.
The apparatus consisted of two 10 kg hammers suspended on a pendulum on either side of a sample. On release, the two hammers impact the rock sample repeatedly until it is broken down into construction aggregate. Throughout the experiment, the hammers relay their angular position through high-resolution rotary encoders, which we coupled with the CompactRIO using an NI-9403 digital I/O module and processed on the onboard FPGA.
The data we gathered helped us determine the initial potential energy of the system. If we combine this data with the return height of the hammers, we can calculate the energy absorbed by the impact. This provided a better understanding of the actual energy absorbed by the samples, something that was not achievable with previous test rigs.
The Value of Our Bond-Impact Test Rig
The energy consumption values derived from our test rig compared well to real-world values measured by jaw-crushers, showing much improved accuracy compared to existing methodologies. Additionally, we gained further insight as we can separate the energy consumed in crushing the rock from the energy consumed by the crushing machinery itself.
British Geological Survey’s Bond-impact test-rig helped us establish, demonstrate, and validate an improved theorem for energy consumed in aggregate crushing. The improvements were well received and have gained commercial traction.
Considering that a single kilometre of motorway requires approximately 30,000 tonnes of aggregate, the scale of this additional insight to energy expenditure becomes very significant. Our improved Bond-impact tester, controlled by CompactRIO, empowers the construction industry to better assess where energy is expended and make informed decisions for efficient manufacturing and reduced carbon footprint. The NI platform provided a low-investment opportunity for the British Geological Survey to prove that a data-driven approach to rock crushing can significantly boost energy efficiency within the construction industry.
British Geological Survey - Environmental Science Centre