Context
South Africa’s national parks (SANParks) conserve the country’s rich diversity of flora and fauna through a system of 21 national parks, including three world heritage sites and the world-renowned Kruger National Park (KNP). The Kruger National Park offers a wildlife experience that ranks with the best in Africa. Established in 1898 to protect the wildlife of the South African Lowveld, this national park is unrivalled in the diversity of its life forms and a world leader in advanced environmental management techniques and policies. Kruger is home to an impressive number of species: 336 trees, 49 fish, 34 amphibians, 114 reptiles, 507 birds and 147 mammals.
The National Environmental Management Protected Areas Act requires SANParks to create destinations for nature-based tourism in a manner that is not harmful to the environment. SANParks embarked on a commercialisation programme to increase funds for SANP’s core function, nature conservation. The principle is to have private operators build and operate tourism facilities within the national parks, under stringent and monitored conditions.
Amongst other things, the construction and operation of roads requires careful consideration of social, environmental and financial factors.
Specification
SANParks released a manual (Specifications for the Construction of Roads in the Kruger National Park and Concession Areas) which compiled a set of uniform and functional guidelines for the construction of new roads and the upgrading and maintenance of existing roads within the boundaries of the Kruger National Park. Key excerpts from the manual are shown below.
12.10 The use of alternative stabilising agents in road construction
- General
The dwindling supplies of natural sources of road building material in the KNP are being further curtailed by the high cost of exploitation and rehabilitation of borrow pits and under the present circumstances several environmental considerations. This fact gives greater emphasis to the need for improving the utilisation of marginal, sub marginal and problem in situ materials through stabilisation techniques. Some of the most important advantages of stabilisation are:
- The strength of the material is increased;
- Durability and resistance to the effects of water are improved;
- Wet soils can be dried out; and
- The workability of clayey materials can be improved.
Although soil is an abundant natural resource, many types cannot be used for construction purposes due to the lack of a suitable and affordable stabilisation technology. There are many stabilisers that are marketed as a replacement for the conventional stabilising agents, such as cement, lime, etc. From a risk management point of view, there is reluctance by engineers to employ these so-called replacement stabilisers. The marketing of these products is done conventionally by product representatives who may lack objectivity. The role of an independent materials engineer to act as an “honest broker” is often missed.
Key point #1: Stabilisation can have environmental advantages, but choice of an appropriate stabilisation technology requires expertise and objectivity.
2.5 Cement additives are mainly used to improve the strength and reduce the water permeability of concrete products. Because of high costs very few of these additives have been used in road stabilisation successfully.
The only product that has been used with success in and outside Southern Africa is a non-toxic liquid concrete additive for use in building and road construction by the name of Renolith. It allows concrete to be made without coarse aggregate, instead is using soil as the filler. Renolith and Portland Cement together bind and waterproof the soil particles to form a stable and durable polymer with improved compressive load bearing and flexibility. Renolith may be applied by using in situ material, such as sand, clay, any clay/sand/silt mix, sea sand etc.
Key point #2: Renolith and cement has been successfully used to form roads from a variety of in-situ materials including sand, clay, any clay/sand/silt mix, sea sand etc.
2.6 Cement additives are normally successful under most circumstances, but very expensive. Renolith has been applied successfully in areas, where construction material was not available, by the utilisation of the in situ material. In several cases pure sand and even clayey material were used to construct base courses successfully. Although the initial cost of the product seems to be high, savings of almost 40% on the construction of pavement layers were generated, because no construction material of whatever nature was imported. The cement content varies between 2% and 8% per m2.
Key point #3: Construction cost savings of 40% were achieved.
Conclusion
Stabilisation of in-situ materials can provide multiple advantages to road construction and maintenance, particularly in environmentally sensitive areas such as the Kruger National Park. Most stabilisation techniques are only suitable in limited scenarios. Renolith and cement has been successfully used to form roads in Southern Africa from a variety of in-situ materials including sand, clay, any clay/sand/silt mix and sea sand. Construction cost savings of nearly 40% were achieved.
