Dupont Zemdrain: A concrete problem solver

"A foolproof way to get high quality, high finish and highly impermeable concrete? You must be joking!" said an experienced structural consultant recently. The consultant admitted that he had been putting up exposed concrete structures, water retaining concrete structures and bridges for years, and had struggled with these basic issues all through. Dupont Zemdrain, then, is a dream comes true for him and many others.

What is Zemdrain?

DuPont Zemdrain are form liners used in civil engineering applications like bridges, tunnels, dams, water tanks and waste water treatment plants. To be precise, it is a controlled permeability formwork liner where longer life concrete is required in a project.

Why use form liners for concrete?

Concrete is a porous material and many of the problems with durability start with the quality of the surface of concrete. Aggressive elements like oxygen, salts, carbon dioxide and moisture attack the outer layer of concrete can penetrate it. Once these elements enter, they systematically decrease the strength and durability of concrete by increasing its porosity and over time, causing cracks and fissures. Dupont Zemdrain provides a near non-porous, dense skin with minimal capillaries guarding the concrete from liquid and gas attacks, by adding to its resistance.

What is Zemdrain made of?

It comes as a sheet made up of fine polypropylene fibers with numerous pores creating an air and water permeable membrane. Both sides of the fabric exhibit their individual properties and functioning.

The draining side is composed of either embossed black coarse fibers as in Zemdrain Classic or of a plastic uniquely shaped plastic grid as in Zemdrain MD. This side does the collection and evacuation of excess air and water from the concrete.

The filtering side holds back the cement particles giving a strong covercrete. The fine fiber bonded composition does not stick to the concrete. These are grey for Zemdrain Classic and white for Zemdrain MD. There is no release agent applicable for the product.

How exactly does it work?

When lining the formwork the material in fact drains away excess water from the cover zone of the concrete. The concrete so left behind is a protective and strengthening cover for the core and reinforcement that are guarded against aggressive elements. The surface is free from blowholes as it disperses air bubbles.

The Zemdrain treated concrete shows the properties of low porosity, greater strength and aesthetically enhanced surfaces. The draining side of the sheet collects air and water that are then evacuated at the shutter interface. The filtering side holds back the cement particles at the surface of the concrete. It is then most suitable for controlled permeability formwork lining for projects requiring long life concrete. This is true for civil engineering applications like bridges, tunnels, dams, water tanks and waste water treatment plants.

The Zemdrain advantage

Zemdrain offers a concrete structure with superior durability without additional treatment or chemicals due to the low w/c ratio obtained in the concrete cover zone. The liner allows a regulated evacuation of excess water and air from the fresh concrete while retaining the cement particles. There is no vacuum or soaking effect as the drainage is by gravitation. The cement type, additives used and the quantity of excess water determine the time taken for the process. Some of the excess water is retained by the sheet and goes towards the curing of the concrete.

Apart from the strength advantage the concrete offers resistance enhancement towards carbonation, freeze-thaw with salt, chloride diffusion, microbiological growth and reduced permeability.

Zemdrain Classic is the first generation product that has proved its performance on over 1 million square meters of concrete surface across the globe. Zemdrain MD, the second generation product was launched in 1997 and is already in use in several hundred sites worldwide. The installation process requires tensioning around the formwork to avoid folds for Zemdrain Classic. It can be used as a curing membrane when left on the concrete prior to its stripping. Zemdrain MD, the second generation product in the line, is stiffer and easier to fix.

As compared to 20% wastage generated in using Zemdrain Classic, only 2-5% waste is generates when you use Zemdrain MD. The new product is also easier to install and uses less manpower. Plus, it can be re-used up to three times, whereas Classic is not normally used more than once.

The last word

The panacea cure for exposed concrete structures and their related issues certainly seems to have arrived with Dupont's Zemdrain.

Zemdrain is now here in India and though it's been introduced recently, its popularity in such a short span of time is proof that this is a product that has, proverbially speaking, hit the nail right on the head.