Construction World June 2015

PROJECT PROFILE

CEMENT and FLY ASH Metolong’s innovative Project information • Client: Sinohydro • Project start date: 2012

Project background The Metolong Dam project is the major struc- ture in the Metolong Dam and Water Supply Programme (MDWSP) that will provide a new raw water supply for Lesotho’s capital, Maseru, and the generally impoverished surrounding areas. The region has historically suffered from water shortages and the scheme will improve water delivery to domestic users and the country’s textile industry, an impor- tant source of employment. Metolong Dam is a 83 m high roller compacted concrete (RCC) dam with a design crest length of 280 m, constructed on the Phuthiatsana River, approximately 35 km from Maseru. Contractor, Sino- hydro, established an on-site batch facility to provide the estimated requirement of 330 000 m³ of RCC and 40 000 m³ of conven- tional vibrated concrete (CVC). The Beijing based contractor is a global top-ranking construction and hydropower group that is involved in a range of projects on the African continent, and has worked on major interna- tional projects such as China’s Three Gorges Dam, the world’s largest dam. Fly ash Ash Resources, Lafarge South Africa’s leading fly ash company, had established a relationship with Sinohydro three years previously on a project in Zambia and were also supplying fly ash for other sections of the MDWSP. This facilitated the initial introduction of Lafarge South Africa to Sinohydro as a major, technically sophis- ticated company that could supply all of the contractor’s requirements for cement and fly ash. It was both commercially and practically of interest to Sinohydro and was in line with the recently introduced ‘One Lafarge’ approach to major infrastructure developments, aimed at ensuring customers receive the optimum all-round benefits from the company’s resources. It further reflects Lafarge South Africa’s policy of building long term relationships by delivering true value. In South Africa, cement for water infra- structure projects is traditionally dominated by CEM I products. Engineers and contrac- tors are cautious about changing estab- lished practice, whereas Lafarge SA had phased out CEM I cements and, some years earlier, had developed a complete range of innovative fly ash extended products. The challenge that the company faced was to

convince the project team of the merits of its CEM II product. Technical innovation Realising that Heat of Hydration would be a significant concern, Lafarge SA proposed their premium technical cement, Power- crete Plus CEM II 42,5R. This formulation is a Low Heat cement and also has the capa- bility of being extended further on site with additional fly ash. The engineers and the contractor were not familiar with this versatile, high performance product. It took a two-year determined selling campaign, with strong technical support from Lafarge SA’s highly regarded accredited civil engi- neering testing facility, Quality Department Southern Africa (QDSA), to achieve a change in the technical mindset and the commercial breakthrough. A significant selling point was the same quality and source of fly ash being incorporated in the cement as would be used for on-site concrete batching. The role of QDSA Arising from discussions with the consult- ants and main contractor Sinohydro, QDSA was requested to conduct laboratory eval- uations of the RCC (Roller Compacted Concrete) mix and the CVC (Conventional Vibrated Concrete) mix. The outcome was that based on QDSA’s recommendation, Powercrete Plus premium technical cement and DuraPozz® classified siliceous fly ash from Ash Resources’ Lethabo facility were used as binder material, with the RCC mix containing 66% and the CVC mix (grade 25/38) 52% fly ash respectively. Trials using the CEM II Powercrete Plus achieved similar results to those obtained during a trial mix programme by the consult- ants using a type CEM I product. This impressed both the consultants and the contractor, whose previous experience did not include RCC dams constructed using a CEM II cement. A significant factor in favour of Powercrete Plus was that it is a Low Heat Cement with a typical Heat of Hydration

• Project end date: End of 2014 • Main contractor: Sinohydro • Principal agent: Metolong Authority • Consulting engineer: Arcus GIBB

value of 227 J/g, compared with the EN 197-1 criterion of < 270 J/g at 41 h. Throughout the dam’s construction, QDSA has continued to provide technical support. Its laboratory is equipped to under- take Heat of Hydration testing in accord- ance with EN 196-9, and Lafarge’s cement team supplies the consultants with Heat of Hydration results, together with Powercrete Plus batch chemical analyses on a monthly basis. This gives the client the security of confirmed consistent levels of fly ash exten- sion in the product. Cement performance Lafarge’s Powercrete Plus has performed exceptionally well, exceeding the contrac- tor’s expectations. The consistent quality of the product and its good strength performance has enabled the contractor to systematically reduce the cement content of some of the mixes from the initial design levels. Quality fly ash extending concrete performance The use of Ash Resources’ classified fly ash, DuraPozz®, has become virtually a standard component of concrete for controlling the heat of hydration in major water retaining structures. This is now especially the case since DuraPozz® complies with the new and more stringent SANS 50450 specification for category ‘S’ fly ashes. The consistent

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It was both commercially and practically of interest to Sinohydro and was in line with the recently introduced ‘One Lafarge’ approach to major infrastructure developments, aimed at ensuring customers receive the optimum all-round benefits from the company’s resources.

CONSTRUCTION WORLD JUNE 2015