How we test every concrete pour

Every column, beam and slab in our towers is made of reinforced concrete, and the strength of that concrete decides how well the building carries its load for decades. That is why we test every pour, not just some. Here is what happens on site.

Concrete arrives in transit mixers from the batching plant with a delivery note showing the grade, such as M30 or M40, the mix and the time it was loaded. Our site engineer checks the note before the first bucket is poured, and rejects any truck that has been on the road too long, since concrete starts to set within about 90 minutes.

Before pouring, a slump test is done. A cone is filled with concrete, lifted off, and the amount the concrete sinks is measured. It shows whether the mix has the right water content: too stiff and it will not fill the formwork properly, too wet and it will be weaker.

During the pour, a technician fills sets of 150 mm steel cube moulds from the same concrete. Each set is labelled with the tower, floor, element and date. The cubes are cured in water on site and taken to a testing laboratory, where they are crushed in a press at 7 days and 28 days. The 28-day result must meet the strength required for the grade. After the pour, slabs are kept wet for at least 7 to 14 days by ponding or wet hessian. All results go into a register for each tower, and buyers can ask to see the records for their tower during a site visit.