The rapid growth of South Africa’s urban areas has put immense pressure on existing construction material resources, as there is increasing demand for land use for infrastructure, housing, recreation and industrial activity. The quality of aggregates is a critical component in determining the use and life of infrastructures. It is therefore important that the aggregates supplied are affordable, durable and secured for long term supply. The report focuses on the relationship between aggregate and sand sales and the impact on the construction industry.
Furthermore, the report establishes the link between Outcome Six of Government priority areas, which identifies infrastructure network as one of the key areas in unlocking the economic growth of the country. The infrastructure build programme had played a key role in South Afica’s sustained economic growth since the 2008/09 economic downturn, with R1-trillion spent on economic infrastructure. The report also seeks to avail relevant informationto decision makers when carrying out large magnitude infrastructure network projects as identified by the National Development Plan, focusing on measures that will contribute to South Africa’s economic transformation.
Aggregates are granular raw materials, including gravel, crushed stone and recycled concrete that are used in residential construction and commercial construction. Public funded infrastructure projects consume most aggregates, usually for use in road construction. Aggregates are vital to the construction industry which maintains and enhances the country’s built environment and transportation infrastructure. The quality of aggregates is a critical component in determining the use and life of infrastructures. It is therefore important that the aggregates supplied are affordable, durable and secured for long term supply.
The rapid growth of South Africa’s urban areas has put immense pressure on existing construction material resources as there is increasing demand for land use for infrastructure, housing, recreation and industrial building activity. The widespread use of aggregates result not only from its general availability and low value but also from the fundamental role they play in developing and sustaining modern society and economy. Traditionally, sources of aggregate were found close to their demand locality due to the high cost of transportation resulting in quarries located on the outskirts of cities and towns. However, in numerous instances, these deposits have been depleted and new sources further away had to be found resulting in greater transportation costs. Urban development itself has, in recent times been responsible for the rapid depletion of readily available deposits. Hard rock aggregate quarries are often located on the slopes of hills and mountains, usually resulting in the defacing of areas of natural scenic beauty. Growing environmental awareness increasingly influences the exploitation of such resources in localities of this nature.
Before any project of a large magnitude can be undertaken, especially those identified by the Presidential Infrastructure Coordinating Commission (PICC), it is essential that an investigation of quality aggregate availabiltyis conducted. This will ensure thatdecision makers are aware of the position and spatial extent of potential construction and building materials during land-use planning.
South Africa has various types of rocks which are characterised as aggregates which are widely distributed in abundance in a variety of geological environments. Coarse aggregate are derived from a wide variety of parent bedrock materials. The three main groups of coarse aggregates are:
Igneous rocks – Andesite, basalt, dolerite, felsite, gabbro, granite, granodiorite, norite, rhyolite and syenite.
Metamorphic rocks – Granite-gneiss, granulite, hornfels, quartzite and slate.
Sedimentary rocks – Quartzite, sandstone, greywacke, shale and tillite.
A good concrete aggregate must be clean, chemically inert, and durable and roughly cubic in shape after crushing and of a size grade suitable to make concrete of desired physical qualities. Natural sand consists of loose grains which are commonly the result of the chemical weathering and/or physical breakdown of rocks. The range of particle sizes is dependent on the original texture of the source rock and the state and degree of weathering. Natural sands include alluvial/eluvial sands, aeolian/windblown sands and marine/beach sands. Sand accumulates in rivers, on beaches, as dunes and in valleys between mountains. Manufactured sand is produced by the mechanical crushing or milling of rock and gravel. Mine-dump sand being a waste product in the mining industry can also be classified as manufactured sand.
Most hard rock material used to produce coarse aggregate is sourced from open pit quarries and waste dumps. Quarrying usually requires drilling and blasting, after which the rock is extracted by means of bulldozers and draglines. The broken rock is transported to a processing facility for scalping, the process which involves the removing of unwanted materials, such as clay. The scalped material is then crushed to obtain the desired fragment size. The resulting material is then screened to obtain aggregates of the desired grade (Fig.1). In some instances, blending is done to meet customer’s specification. Natural sand is dug from the ground often using hydraulic excavators. The quality and final use of the sand usually determines the amount of processing necessary. The sand undergoes complementary processing including washing and scrubbing, primarily to make them cleaner before being stockpiled to go on to their end use. It is now a common practice to further beneficiate the aggregate into:
- Ready-mix concrete
- Bricks and paving material
Compiled By: Refiloe Motsie – Refiloe.email@example.com Eulendah Malematja – firstname.lastname@example.org Issued by and obtainable free of charge from The Director: Mineral Economics, Trevenna Campus, 70 Meintjies Street, Arcadia, Pretoria 0001, Private Bag X59, Arcadia 0001 Telephone (012) 444-3531, Telefax (012) 341-4134 Website: http://www.dmr.gov.za