Civil Engineering June 2021 | Vol 29 No 5

38 June 2021 Civil Engineering S outh Africa has gradually followed suit, with many municipalities and their engineering teams now also specifying precast concrete reservoirs in the early phases of water augmentation projects to overcome many of the chal- lenges associated with constructing these structures using in-situ methods. Located in large cities and rural areas, South Africa’s more recent precast concrete reservoir projects range from 10 Mℓ to 35 Mℓ. Together, these projects constitute about 350 Mℓ of water storage capacity. Reservoirs can be constructed signifi- cantly faster using the precast concrete system than cast-in-place methods. By saving time, this modular approach mitigates the potential risk of project delays and cost overruns. Considering the level of control that prefabrication offers in terms of curing, temperature, mix design and formwork, precast concrete technologies also provide additional quality assurance. These are among the key factors that regulate the quality of civil engineering construction projects, including reservoirs. Based on international best practice in precast concrete reservoir construc- tion, a unique approach that was designed and developed in South Africa for unique African conditions is being deployed in the country. The system comprises a precast concrete roof, as well as a vertically prestressed and hori- zontally post-tensioned wall structure. However, the real innovation lies in the way it is constructed on site to ensure a water-tight structure. FAST AND EFFICIENT ROOF CONSTRUCTION A typical precast concrete roof structure comprises hollow-core slabs (HCS) that are placed on precast concrete beams that are, in turn, supported by prefabricated columns. The precast concrete columns are connected to the in-situ bases via cast-in components, or “column shoes”. These are secured to the hold-down bolts in the same manner as a conventional steel structure. Various column base con- figurations can be implemented to meet project specific requirements and their designs consider a minimum safe bearing capacity of 200 kPa at founding level. The precast concrete beams are then installed onto the receiving columns and secured with dowels that protrude from the columns. Willie de Jager Managing Director Corestruc South Africa refines construction of precast concrete reservoirs Precast concrete has helped to accelerate construction and mitigate risks in complex civil engineering projects the world over, including on demanding reservoir projects that traditionally use cast-in-place concrete methods. This modular approach saves time in constructing reservoirs