Synergies between aggregate supply and infrastructure development in western Ghana

One limiting factor on the development of an economy can be the availability of affordable resources. One such resource is aggregate, a collective term for stone, sand, and gravel, which is a critical component of a nation’s infrastructure. Cities are literally made of aggregate. It is in the cement used to make sidewalks, bridges, buildings, and their foundations. It is used to make roads, in the beds in which they lie and in the asphalt with which we pave them.

The demand for aggregate depends as much on a country’s size as its stage of development. More aggregate is needed where development is occurring, and less is used where infrastructure is merely being maintained. In Ontario (a province of Canada), for instance, the annual per capita demand for aggregate is nearly 15 tonnes, but this number falls to 9 tonnes for the US, and only about 4 tonnes for the UK.

In Ghana, as in other tropical countries, the availability of aggregate is limited by the climate, which normally precludes formation and preservation. This lack of aggregate has an impact on Ghana’s development. It increases the costs of building relative to temperate countries in which aggregate is more common, and is reflected in an annual per capita usage of 4 tonnes of aggregate. Observed demand is much higher, but the market is unable to supply aggregate in the amounts required.

The bedrock in the southern part of Ghana is excellent source material for aggregates, but the local aggregate industry is poorly developed and unable to supply large amounts of material for construction.

Although large road contractors operate their own quarries and use modern methods to crush aggregate, local markets are served by small operations where aggregate is crushed by hand in an extremely time-consuming and labour-intensive method. The products of such quarries are limited to crushed stone and sand and generate copious amounts of dust, which poses environmental concerns.

Marine aggregate production may be a way forward for Ghana.

Marine aggregates can be used for any application common to standard aggregates, including housing and road construction, pipeline construction, and land reclamation or beach replenishment. Marine aggregates can be used in fashioning concrete block or roofing tiles. Typically, marine operations target aggregates which are most suitable for quality construction products, which consist of varying gradations of clean sands and gravels formed from relatively hard granite and quartzite bedrock.

Transport costs, which are normally the limiting factor for aggregates on land, are minimized, as the aggregates can be loaded and transported by barge. Reduced cost of transport extends the delivery range, so that marine aggregate can be used to supply distant markets, even in other countries. Furthermore, transporting aggregate by barge has a smaller environmental impact than by truck.

Offshore aggregate materials represent an entire range of materials from sands to boulders, which can be processed into a variety of value-added products. The material has been naturally washed and sorted and is of high quality, and the various by-products (specialty aggregate products, gold, industrial minerals) can be separated entirely by mechanical means, requiring no chemical processing.

International protocols for marine mining have been developed to minimise environmental impacts. Disruption to ocean floor ecosystems can be reduced through a combination of judicious exploitation of the seafloor combined with remediation. As the distribution of seafloor species are dependent on the granulometry of the seafloor, thorough mapping of the seafloor (using acoustic methods backed up by sampling) enables the mining to be tailored to the areas with the best granulometry, and to leave refuges from which life may spread into the remediated areas. Coastal erosion problems are minimised by moving the operations sufficiently far offshore to reduce beach erosion and noise.
Summary

Benefits of offshore aggregate production include: 1) increased supply and increased quality of aggregate, reducing costs of development and maintenance; 2) reduced transport costs (barging) and reduced environmental impact on coastal regions; 3) quarries which supply aggregate at present can be used to produce quarried stone products, which have a higher-value than crushed stone.