Polyester concrete, if not concrete, what else?

Polyester concrete is a name commonly given to a composite that in effect is not concrete at all! Traditionally concrete is a composite of cement, gravel, sand and water. Contrary to traditional concrete, the binding agent in polyester concrete is not cement but a polyester resin. Except polyester, such polymers can be used in concrete as (Poly) Methyl Meth Acrylate (PMMA), epoxy pre-polymer, and furfuryl alcohol. So the name polymer concrete may be the preferred choice, even though it still contains the word concrete.

Compared to traditional concrete, polymer concrete is a relatively new invention. It was first used on a commercial scale in the early nineteen fifties. Especially the lightweight facade elements produced then were very popular. A special application of polyester concrete may be seen in the Fast Ferry project by Hans Slemmer and WTS Architects in Vlissingen. The facade is constructed of elements poured onto a rubber mat co-developed with WTS Architects. First a cast was made of a wave structure in the beach sand formed at low tide. Then a section of 2 x 3 meters was enclosed with formwork and plaster poured in. Then another model was made. Once cured, the plaster models were released, transported to the factory and enclosed with carpentry work, with the plaster models serving as bottoms for the mold. The next step was making rubber casts of the plaster models. The rubber casts were the basis for the final mold into which the polyester concrete was poured. Once thoroughly cured the elements were blasted, making the stone’s grain visible creating a coarse textured appearance. The elements were then screwed visibly onto the underlying facade construction.

Slender Dimensioning
In addition to its excellent weather-proof and fire-retardant qualities, polymer concrete offers various benefits over (Portland) cement concrete. Once cured, polymer concrete has a smooth and level surface. This surface is non-capillary, preventing water and grime to penetrate the concrete and creating a waterproof surface. Compared to standard concrete, polymer concrete is three to five times more lightweight and three to ten times stronger. This allows for facade elements with more slender dimensioning and a more lightweight underlying facade construction. Elements can achieve even more slender dimensioning by reinforcing the concrete with glass fibers, metal mesh or carbon fibers. Also complex three-dimensional shapes can be realized. Project NUVO 2000 by Kjeli Kuizinga is a good illustration of how a smooth three-dimensional shape can be achieved using polyester concrete.

An intermediate form of polymer concrete and traditional concrete is Polymer Glass-Fiber Reinforced Cement (PGVC). Traditional concrete cannot be reinforced with glass fibers because of the alkaline reaction between cement and glass. This problem can be remedied by using PGVC. PGVC consists of glass fibers encapsulated in a polymer resin which attaches to both glass fiber and cement. At the same time the polymer resin forms a barrier between the glass fibers and the cement, preventing an alkaline reaction. As with Polymer concrete, PGVC enables the creation of highly precise and slender details.

Extra Additives
Because polymer concrete shrinks when curing, extra additives are used. In the ninety seventies mainly gravel was the visible additive, but nowadays also other materials like stone, glass, shells or metal particles are used. In principle any dry material not absorbing moisture can be used. Examples of added materials in polymer concrete may be seen in several samples by PP Gevelbouw. These experimental samples incorporate shells, glass and metal particles.

Surface Treatment
The surface of polymer concrete can receive a range of treatments. The concrete can be polished, removing thin layers from the top coat with fine polishing disks. An alternative is water blasting or sand blasting the concrete giving the concrete’s appearance a deeper perspective. With the Vectogram cutting technology images can be made in the concrete without applying prints that fade over time. This technology is based on conversion of a digital image into 256 gray values. These gray values are converted via special software into a three dimensional milling pattern subsequently applied to the surface via a computer controlled milling machine.

Drawbacks of Polymer Concrete
Using polymer concrete has its drawbacks. The polymers are more expensive than Portland cement and the visco elasticity of polymer concrete is relatively high, varying from 20 to 50 GPa (Portland cement concrete: 20 – 30 GPa). Plus, polymer concrete is difficult to manipulate on site. To achieve the desired result manipulation and curing must occur in a controlled environment. Consequently, facade elements are almost always prefab elements entailing the customary maximum dimensions.
Another consequence of prefabrication is that the facade’s appearance always has visible joints. This need not be a drawback when due allowance is made for the resulting line patterns.

Polyester concrete is not concrete, but then what is it? It is a composite offering many benefits and only a few drawbacks. It provides many potential forms and technical possibilities, and can be used in more than facades alone. Perhaps this article gave you inspiration?