Function over form

Concrete suppliers in the region have to get to grips with a number of issues as they try to keep up with the demand for their product in the construction industry. Hugo Berger looks at the range of additives which are helping them overcome their dilemmas.

As the temperature soars in the GCC summer, ready mix concrete suppliers are facing a battle against the clock.

The intense Gulf heat speeds up the hydration of concrete, putting pressure on concrete suppliers to ensure their products are delivered to construction sites on time.

As concrete only has a limited lifespan - about two hours in the summer months - if it is not transported from plant to site quickly it is easily spoiled.

In Dubai, the race against time to get concrete from plant to site is intensified by the city's infamous traffic gridlock.

A solution used by many ready mix suppliers is a carefully blended recipe containing additives.

These not only keep the mixture from hardening during transportation, but also improve its workability when it arrives at its destination and is ready for pumping.

Vishal Sharma, general manager, construction chemicals, Conmix, says there are a number of new chemicals which the firm adds to concrete to keep it fresh.

He says controlling temperature during concrete pours was vital to the stability of buildings.

In the case of mass concrete structures there will be an increase in the temperature during the hydration of cement.

As the cement water reaction is exothermic, meaning it releases heat energy, the temperature rise within a large concrete mass where the heat is not easily dissipated, such as the core of the building, can be very high.

If the temperature difference between the core and the surface exceeds 20C then there was a chance of developing thermal cracks in the structure.

Sharma says that because of this, it is vital that the right types of additives are used during the mixing stage.

The use of materials such as fly ash or ground granulated black furnace (GGBS) slag can help control the placement temperature of concrete.

He says: "Water reducing and set-controlling admixtures can be used to keep the concrete plastic in massive blocks longer, so that successive layers can be placed and vibrated before the previous layer sets."

"By using admixtures the water content in the mix can also be reduced, and hence for the same water to cement ratio, the cement content in the mix will be reduced. Low cement content means less heat generation."

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