In a housing market that is desperate for quality, robust and affordable homes, advanced building technology frontrunner, Sanjo Fabtech Sterling has been collaborating with construction materials leader, AfriSam, to deliver just that in Thembisa.

At the heart of the 500 unit, fast tracked housing project is Sanjo Fabtech Sterling’s advanced, lightweight wall technology, delivering solid four-storey ‘walk-up’ residential buildings that will be ready by mid-year. According to Jonathan Peel, director at Sanjo Fabtech Sterling, the walling systems used in Thembisa have recently also been used in upmarket Sandton apartments and hotel projects.

AfriSam is supplying an innovative lightweight readymix solution designed and developed by Sanjo Fabtech Sterling’s sister company, SanteQ Liteweight Building Technology, for the Thembisa project. The lightweight concrete mix designs combine recycled polystyrene with SanteQ’s specialised concrete mixes.

The readymix infill for the walling system is supplied by AfriSam and pumped into the void between the fibre cement boards which acts as permanent formwork. The polystyrene creates mechanical air bubbles, reducing the weight of the walls by 50 to 75% when compared to traditional masonry materials, and offering distinct design and engineering benefits.

“Due to dolomitic soil conditions in the Thembisa area, the weight advantage of the walls significantly reduced the design of the raft foundation.” says Peel. “Despite their lighter weight, the walls are as solid as brick and mortar, pass the ‘knock test’ and provide better sound and thermal insulation.”

“Delivering from our nearby Olifantsfontein plant, we could provide Sanjo Fabtech Sterling with 48 to 102 cubic metres a day of their special mix in our readymix trucks,” said Luigi van der Made, AfriSam’s readymix operations manager. “Using four of our six cubic metre capacity readymix trucks, we were able to add the polystyrene on site and create a homogenised mix.”

The special lightweight concrete mix – which does not use coarse aggregate – includes fine and coarse sands as well as fly ash with the cement. CHRYSO® Omega 140 AFR ZA, a high range, water reducing plasticiser is also included to increase the slump while reducing the water requirement.

“Keeping a constant supply flowing with four dedicated readymix trucks, we ensured that the mix remained consistent, workable and cost-effective,” says van der Made. “The final infill mixture was then be pumped into the walls, speeding up the construction process.”

He notes that the process had to be closely controlled to prevent residual polystyrene in the readymix trucks from contaminating any other process back at the plant. This required a careful cleaning process, which also included a recycling circuit to separate the polystyrene and return it to SanteQ for recycling.