Civil Engineering June 2022 | Vol 30 No 5

Civil Engineering June 2022 25 In their submission for the Fulton Awards, the contractors, Zana Manzi Joint Venture, stated that the construction of the dam provided abundant employment for resi- dents of the villages surrounding the dam. Back in 1995, the construction of a multiple arch RMC dam near the Bakubung Gate of the Pilanesberg National Park in the North West was also very labour intensive, calling for 9 000 person-days of employment for its construction. The dam is now known as Lengau Dam. Another important advantage of RMC is costs. Financially, savings of between 30% and 60% can be realised when compared to other dam building tech- niques. A lesser known, but very useful application for RMC, is the construction of culverts and small arch bridges. CONSTRUCTION METHODOLOGY The typical construction method for RMC involves spreading a layer of mortar between 100 mm and 200 mm thick. Rocks are then pushed into the mortar until bedded against underlying rocks. The largest possible rocks – ranging in size from 10 kg to 40 kg – are placed first and packed as closely together as possible to reduce the amount of mortar required. Smaller stones (spalls) are then pushed into the larger gaps between the large stones to reduce the mortar volumes even further. When this is complete, the next layer of mortar is placed. The construction material is self- supporting, so there is no need for pressure-resisting shutters. Formwork is sometimes used to shape the structure, but the outer leaves of masonry are gener- ally built by more skilled masons, using stiffer mortar. These leaves contain the layer of more workable mortar laid by less skilled labourers who can be employed to build the inner section. The cost savings are due to locally sourced sand and rock – either naturally occurring boulders or quarried rock. Without the need for formwork, cement is the only imported material and, with careful construction, the cement content can be reduced to well below 300 kg/m 3 . In more rural areas, this cost saving could even be higher. But ultimately, the major advantage offered by RMC is the use of unskilled labour. Any municipality looking to increase the labour content on civic infra- structural development should consider using RMC where possible. Experience has shown that for a given structure the person-days for construction using RMC are between five to nine times higher compared to using alternative construc- tion methods and materials.  The RMC construction of Lengau Dam required 9 000 person-days of employment