Introduction

Production and process technologies are a key aspect of any aggregate operation. The type of equipment and process configuration used is largely dependent upon the local market for construction materials, company experience and preferences, acceptance of new ideas and attitudes towards capital investment, the legacy of past production (especially in older operations) and the nature and geology of the mineral exploited. The responsibility for producing aggregate from as quarried mineral usually falls to a site production or quarry manager; these and students of quarry management will be the primary user of information in this section of Goodquarry.com.

Primary aggregates are produced from two main types of quarrying operation, crushed rock (Photo 1) and sand and gravel (Photo 2). Crushed rock aggregate is produced from hard, strong rock formations including igneous (andesite, basalt, diorite, dolerite, gabbro, granite, rhyolite, tuff), metamorphic (hornfels, gneiss, quartzite, schist) and sedimentary (sandstone, limestone) rock. It is produced from quarries that are much larger and deeper than sand and gravel pits, and involve large investments with quarry outputs that are typically in the range 100 000 to 5 million tonnes per annum (tpa). Sand and gravel is produced from naturally occurring deposits derived from the erosion of particles that were transported and deposited by water, wind or ice. Sand and gravel pits are usually shallow, sometimes only five or six metres deep. Operations are likely to be shorter term than for crushed rock and, with progressive restoration normally following closely behind extraction, the working area at any given time is usually comparatively small. They typically produce 10 000 to 1 million tonnes per annum (tpa), with most in the range 100 000 to 300 000 tpa.

Primary aggregate is produced by extraction and processing; most extracted mineral cannot be used as dug and processing prepares it to be used as a construction material. Extraction, also known as quarrying, involves removing mineral from the ground and delivering it to a production plant in a form suitable for processing. Processing is typically carried out in a production plant and involves crushing, milling and screening. The key parameters for aggregates are particle size and distribution, particle shape, physical and mechanical properties and lack of contaminants.

Photo 1. Panorama of limestone quarry

Photo 2. Sand and gravel washing plant

The information presented in Production and Process Technology is split into six sections:

• Aggregate production summary this gives a brief explanation of aggregate production, products, and quarry fines and waste;
• Production good practice this outlines good practice for the operation of quarry crushing and washing equipment, with an emphasis on quarry fines minimisation;
• Technology: extraction and crushing this gives an explanation of the processes and technology involved in extraction and crushing of aggregate;
• Technology: washing plant this gives an explanation of the processes and technology involved in washing aggregate;
• Technology: dry processing this gives an explanation of the processes and technology involved in drying, air classification and screening of aggregate;
• Future technology and practices this is a forward look at the issues that will drive developments in aggregate production technology and processes.