A new national record has been achieved at the De Hoop dam, in Limpopo, when 103 600 m³ of concrete was placed in 23 days, more than double the previous record of 40 600 m³ placed in a month at the Wolwedans dam.

The Department of Water Affairs (DWA) on Tuesday announced that the new record was achieved late last year, by using a new, locally developed roller-compacted concrete (RCC) mix.

The R2,547-billion De Hoop dam is currently the largest construction site funded and implemented by the DWA and forms part of a water resources development project aimed at supplying water to existing and new mines, as well as potable water to the surrounding communities from the Steelpoort and Olifants rivers.

The DWA reported that the concrete was placed between November 4 and 27, with a peak hourly production of 329 m³. The African record for concrete placed in one month is 175 000 m³.

The new RCC mix with which the national record was improved, was developed on the De Hoop dam site and halved the time spent on concrete placement by eliminating certain processes, such as skin concrete and the adding of grout.

De Hoop dam contractor’s representative Johan van Niekerk said that the team working on the De Hoop dam received input from Spanish RCC expert Francisco Ortega in developing the immersion vibrated roller-compacted concrete (IVRCC) mix, which would be labelled as a local product, but used globally in construction.

“The IVRCC is a high paste mix with easy application. The mix’s required density is obtained without difficulty and its properties reduce segregation. It also eliminates the need for skin concrete because of its improved impermetability,” he noted.

Van Niekerk added that IVRCC was an improvement on grout-enriched RCC, as well as grout-enriched vibrated RCC, as it has a high rate of placing, easily double the speed of traditional RCC, with an excellent concrete surface finish.

Construction on the dam, which would be the 13th largest in the country with a 347-million m³ reservoir capacity, started in 2007 and was expected to be completed by April 2012, after the initial deadline of April 2011 was extended, owing to construction challenges.

Van Niekerk explained that environmental challenges and power supply delays interrupted construction and delayed the project’s completion date.

“The biggest challenges came from a six-month delay in road construction, owing to contractual difficulties, as well as problematic geological conditions, resulting in further excavations with more concrete that had to be placed,” he noted.

Further challenges to the project included the awarding of tenders by the State procurement system, labour and local community issues and skills shortages.

However, the DWA used 80,5% local labour during the project, spending more than R6-million on training. The project also achieved 95% compliance in its environmental audits and 96% compliance in its safety audits, with 5,3-million hours worked to date.

Impoundment of the De Hoop dam was expected to start by April 2011.