One concrete truck after another delivered its load ‘round the clock – from Friday morning until Sunday midday.  The objective – to win a marathon readymix concrete relay – a race against time and too-high temperatures which could compromise the quality of the largest pour NPC Concrete has poured to date on the South Coast.  The prize – the strategic success of the huge 1800 cubic metre pour of the base for the new clinker silo at the NPC CIMPOR cement plant at Simuma, one of the largest and technically demanding concrete pours in Southern KZN in recent years.

The project’s dimensions were challenging, to say the least – a continuous readymix concrete pour to produce the 1,8 metre deep, 35 meter diameter silo base.  The R75 million silo, which will approach 60 metres in height when complete, will be another important fixture in NPC CIMPOR’s ongoing expansion programme designed to meet the province’s cement demands.  Now that the base pour is complete, acknowledgement for a job well-done is shared by a team of players from NPC Cement, NPC Concrete and NPC Aggregate as well as contractor Stefanutti Stocks and the engineers, Kantey & Templer.

The non-stop truck relay ran from the NPC Concrete wet batch ready-mix plant at Margate Quarry to Simuma and back, with the company’s Park Rynie concrete plant on the Mid-South Coast held ready in reserve – just in case it was needed.  Additional Mixer trucks were brought in from other plants in the NPC Concrete network. In the end, twenty-six mixer trucks  were used to successfully complete the pour.  

NPC Concrete Technologist Rolf Schutte was concerned about the amount of heat that
is generated during the hydration of large quantities of cement.  During the heat build-up, the
warmer inner section of the base could still be expanding while the outer areas had already
stiffened.  During cooling, under these circumstances, the inner section of the pour could pull
away from the outer section causing unacceptable cracking, although much of the cracking
might go unnoticed. 

Taking into consideration the length of the ready-mix delivery trip, and that the concrete would be pumped with NPC’s 36 metre boom pump, Schutte proposed a strategy which would limit the cementitious content of the ready-mixed concrete without compromising on design strength.  He designed the mix using a blend of NPC CIMPOR’s new limestone cement with 40% NPC CIMPOR Slagmore as well as an appropriate admixture.  Cement content was further reduced when Schutte and the Consulting Engineers agreed that it was only necessary for the design strength to be reached at 56 days instead of the typical 28 days.


NPC Concrete and NPC Aggregate Managing Director Avi Bhoora noted that, in conjunction with the contractor and engineers, the successful project was an NPC CIMPOR event all the way.  “Our NPC Concrete team, with support of our in-house specialists such as Schutte, have demonstrated their capabilities and willingness to go the extra mile to ensure our clients’ success.”   In four years, NPC Concrete has grown from two concrete plants to six, including Sterkspruit in the Hillcrest region, Umlaas Road near Pietermaritzburg, Tinley Manor on the North Coast, the new King Shaka International Airport and Park Rynie in addition to Margate on the South Coast. 

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