Purest quality limestone

Limestone for the production of cement in the Ash Grove Cement Company plant has been quarried here in Louisville since 1929. Ash Grove, a part of the CRH plc group, one of the world’s leading manufacturers and suppliers of building materials for the construction industry, is one of the largest cement producers in the USA and Canada. The extraction of the material in the quarry has been contracted out to North American Mining (NAM).

Even though the quarry in Louisville has been in operation for almost 100 years, the valuable limestone reserves are far from exhausted. The geological situation has, however made extraction a more difficult task, as the remaining limestone strata are interlayered with shale. Due to this, quarrying with conventional methods such as drilling and blasting would have led to contamination of the material. Ash Grove therefore decided to use a Wirtgen Surface Miner from NAM for the job. As the 280 SM(i) enables selective extraction of resources, it guarantees outstanding material purity and is ideal for use in areas with sensitive infrastructures.

Limestone – shale – waste rock – clean separation is the name of the game

The 280 SM(i) cuts, crushes and loads the extracted material in a single pass. This means there is no need for pre-crushing or conventional extraction methods such as drilling and blasting. This not only reduces the otherwise enormous costs, but also enables quarrying or mining in areas that are difficult to access or sensitive areas where it’s hard to get permits for drilling and blasting.

For Ash Grove, the use of the Surface Miner in the quarry in Louisville opens up entirely new opportunities for the extraction of limestone. The extraction of the material takes place selectively, layer-by-layer: the valuable primary resource, limestone, is cleanly separated from waste rock such as shale before crushing takes place – with exceptional power and efficiency. Considering a compressive strength of 110 MPa (16,000 PSI) for the limestone in the quarry, the 280 SMi achieves a mean cutting rate of approximately 400 t/h – with 87.5% of the material extracted being crushed into pieces smaller than the targeted maximum size of 7.6 cm (3 in). In the waste rock (shale and overburden), the machine achieves a mean cutting rate of approximately 650 t/h. The cut and crushed material is loaded directly into ready and waiting 70-ton dump trucks. The process is fast and continuous: a fresh truck is filled with crushed limestone every four minutes – around the clock and on five to six days a week.

Minimal wear and exceptional manoeuvrability

Due to the high compressive strength (extreme hardness) of the limestone, the cutting tools used here are subjected to enormous stresses. The 280 SM(i) in use in Louisville is ideally prepared to take on this challenge and achieves maximum cutting rates with minimal pick wear. ‘The machine does a great job. I really appreciate the round-shank picks and the toolholder. They make it so easy to replace worn picks and get back to work again after only a couple of minutes’, reports a clearly impressed David Ashby, who has more to say about the machine: ‘One of the advantages of the sliding counterweight and the 90-degree slewing angle of the discharge conveyor is that they let you work right up to the high sides of the quarry. Although the machine is very big, it’s still very useful for working in tighter spots. The machine’s manoeuvrability is simply fantastic.’

Environmentally friendly technology

Apart from its efficiency, the machine above all impresses with a range of environmentally friendly aspects: the reduction of extraction processes from 4 to 1, lower exhaust emissions, less noise and less dust not only makes the everyday work on the site much easier, but also offers new opportunities for quarrying rock close to populated areas. ‘We can now extract limestone from deposits we could hardly have reached before’, explains Nic Haubruge, Business Development Manager at North American Mining. ‘In many cases, we simply can’t use drilling and blasting anymore. And this machine has now enabled us to develop new deposits with minimal dust emissions, minimal noise pollution and no vibrations.’

Excellent support from Wirtgen

The team from North American Mining was particularly impressed by the comprehensive support provided by the entire Wirtgen crew – from service to sales management. Regardless of whether we needed training on the spot or help on the phone: we could always count on the expertise and experience of the Wirtgen service technicians in every respect. David Ashby’s résumé: ’The support provided by the Wirtgen crew here on our site was absolutely amazing. That made loads of things much easier for me. It was definitely a real team atmosphere.’