Posted by Eric Boullenois - 15 April, 2020
Water may seem to be a very simple substance, but that is not the case! Most of the people working in water industry are well aware of this fact and face the challenges of water management every day. I already introduced the topic of the multiple challenges of water containment in the article The challenges of water containment. Now, I would like to explain why carefully protecting and waterproofing the concrete structure is key to ensuring the durability of a water storage project and to explain pros and cons of the most common and latest technologies on the market.
In water management, and in the water management industry, water goes through a long chain of processes from the dirtiest state to the purest, which is often classified as human drinking water. Along this chain, the water is stored several times in tanks for treatment and is gradually purified.
For economic reasons, these tanks usually are made of concrete. The first question is whether concrete water tanks need to be protected, or indeed always need to be protected? The short answer is: protection is not always needed, but always recommended! Why?
The main reasons are:
- What we call “water” is not only H2O and the water in water treatment plants contains many other substances which are aggressive to the concrete and will reduce the service life of the tank and/or will increase maintenance requirements.
- The concrete surface will always retain a certain roughness and porosity which is not ideal for the cleaning of the tank and can allow the development of algae and bacteria.
- Local regulations in many countries forbid the use of concrete in contact with human drinking water. In such cases the use of a protective membrane is required.
For these reasons, concrete water tanks are more and more often coated.
Several competing technologies are available on the market and they all have advantages and disadvantages. The following paragraphs review these technologies starting with the latest technology available.
Membrane based on Xolutec technology
Xolutec™ is the latest technology introduced to the market, and is the result of several years of development work with the objective of solving the problems of concrete in challenging environments, e.g. wastewater treatment plants. By optimizing the intermolecular interactions between the resin building blocks, an enhanced cross-linked polymer network (XPN) is created, allowing unique properties for many different solutions. The main benefits for users are reduced cost of ownership as a result of longer maintenance cycles and less downtime, or long-lasting aesthetics and increased durability. An innovative waterproofing and concrete protection system based on Xolutec™technology is MasterSeal 7000 CR.
Polyurea (PUA) membranes
PUA coatings came onto the market a few years after cementitious and epoxy coatings. The application process requires the material to be hot sprayed, allowing an extremely short curing time of only a few seconds. Once cured, polyurea membranes show very high crack bridging properties without mesh.
Epoxy coatings are very common in the market and was introduced many years ago. It is also available in two versions: (1) systems without mesh: are the simplest systems with often one layer of primer for adhesion to concrete and two layers of epoxy coating; (2) systems with mesh: These systems incorporate a mesh embedded in the first layer of the system, to distribute tensions created by the opening of cracks in the substrate and avoid its reflection in the coating.
Cementitious coatings have been used to protect concrete for many years. This can be considered the oldest technology on the market and can be divided into two categories: (1) flexible coatings with polymer additives; (2) rigid coatings. Both categories consist of a mixture of cements, sands, some admixtures and in case of flexible coatings also polymers.
The summary provided in the table above shows how each technology has its pros and cons. It is extremely important, depending on the specific conditions on the job site (structure of the tanks, concrete quality, surface quality, new job or refurbishment, …), to ensure that the technology and the solution applied actually fit the job site requirements. In particular cases, two technologies can be combined, e.g. the MasterSeal P 770 Primer, based on Xolutec technology, bringing resistance to humid substrate, can be combined with MasterSeal M 689 system, a hot spray PUA membrane for fast application and high crack bridging properties.
The storage of drinking water requires additional care and it is strictly governed by national standards which provide approval for commercial products.
National regulations vary in terms of acceptance procedures applied for membranes and coatings intended to be in contact with drinking water. Normally all regulations require the evaluation of substances migrated into water after a certain period of immersion. Additionally, it is very often the case that all the ingredients used in the formulation of the products need to be checked and ensure that they are in the so-called “positive lists”. And in some other cases, the behavior of the membrane against microbiological growth or even flavor and taste checks are required before approval.