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BASF Innovations // X-Seed®

T

11-05 :: May/June 2011

Crystals from BASF make Concrete Harden Faster and Reduce Carbon Emissions

hey’re everywhere, although we hardly spare a thought for them in everyday life – precast con-

crete components. Whether it’s bridge girders, sewer pipes, staircases or railway sleepers: millions of these structural elements are industrially prefabricated and installed directly on-site. With X-Seed®

, BASF has

succeeded in introducing an important innovation in this area. Because this hardening accelerator not only allows precast concrete units to be produced more rapidly and in better quality, it also considerably red- uces energy consumption and the associated emis- sions of the greenhouse gas carbon dioxide (CO2

).

How does it work? The main ingredient of concrete is cement, which is obtained by firing limestone, clay and minerals at high temperatures to produce cement clinker. This process consumes enormous amounts of energy.

The coarse-grained clinker is finally ground into a fine, gray cement powder which hardens after mixing with water. Chemically speaking, calcium silicate hydrate (CSH) and other compounds crystallize out of the cement during this process to form a compact artificial stone in which the aggregate substances like sand and gravel also contained in the concrete are embedded.

Prefabricated components are produced by pouring the still liquid concrete into formwork molds made of

wood, metal or plastic. Only when the concrete has hardened sufficiently can this casting mold be open- ed and the component removed. At ambient tem- peratures of around 20° Celsius (68° Fahrenheit) it takes around twelve hours until the concrete is hard enough – valuable time during which the formwork cannot be re-utilized. To speed things up, the liquid concrete is often heated with steam. Although this accelerates the hardening process, it also demands much additional energy. Moreover, this treatment can lead to internal thermal stresses, discolorations and a coarser surface of the finished concrete part.

“X-Seed® makes heat curing with all its disadvantages

largely superfluous,” explains Dr. Michael Kom- patscher, responsible for BASF’s European precast concrete component market. “With this additive, concrete hardens just as fast at 20° Celsius (68° Fahrenheit) as it otherwise does at 60° Celsius (140° Fahrenheit). And by a brilliantly simple method – be- cause all it involves is adding something that’s alrea- dy present in the concrete anyway: calcium silicate hydrate.”

More precisely, it’s the countless millions of tiny CSH crystals with a diameter of several nanometers suspended in liquid in X-Seed®

. Because of their

nanosize, more very homogeneously distributed cry- stallization seeds can be accommodated in the same