Chemical Resistance of Ultra High Performance Concrete

Densit concrete showed relatively good acid resistance and should open new areas of application. Source: Fattuhi and Hughes 1986

A few weeks ago, a dear colleague asked me about my experience with UHPC and chemicals for a special project. I realized that actually not much has been done in recent years while in the early days this has been a very important property especially related to industrial floors. I had to look in my old files to find a very old article and I realized again that much of this information is actually lost. ?

Earlier in 2018 I wrote an article about my experiences with concrete and UHPC in a sewage treatment plant in the Netherlands in 1987 – 1989. Chemical Resistance of Ultra High Performance Concrete compared to 3 types of concrete in a sewage treatment plant in the Netherlands: 1987 - 1989 | LinkedIn

One of the main business area's of Densit A/S (the first commercial UHPC company founded to commercialize the inventions of Hans Henrik Bache from Aalborg Portland) when founded in 1983 were Industrial Floors and this was one of the 4 original divisions (1. Security Industry, 2. Civil Engineering, 3. Wear Protection, 4. Research & Development New Applications). For especially industrial floors but also for Wear Protection, chemical resistance is very important since both are used in various industries with often products which potentially can attack and/or penetrate concrete and therefore require repair and/or replacement on a frequent basis. Especially in the chemical industries but also in the food processing industry and abattoirs the products themselves and/or the products used for cleaning can seriously affect good quality concrete. Concrete often must be provided with a chemically resistant coating to prevent this deterioration, but with high mechanical loads, high and/or low temperatures and moisture, the applied coating or thin screed can quickly wear out or even detach from the concrete floor.

The resistance of different UHPC toppings has been evaluated by practical and laboratory experiments in the laboratory of Aalborg Portland in Denmark. The UHPC topping materials are consisting of a range of products with different properties and chemical resistance. The chemical resistance from the cured UHPC samples is, because of the high density, much higher than that from a traditional cement based topping or a good quality concrete (C45). The most important component of UHPC is still cement (Portland Cement or calcium aluminate cement) and cement is not or poor resistant against a large amount of, mainly chemical, products. Corrosion or chemical attack from an industrial topping is however depending on many other factors, which are not, or bad to simulate in a laboratory test. For that reason, difference must be made between the following 3 points:

1. The resistance of the material used or to use.??
2. The resistance of the material used or to use under laboratory conditions.
3. The resistance of the material used or to use in the practical situation.

It is also possible that there are special requirements from the authorities for so-called fluid tight constructions in certain industries as required in the Netherlands and Germany for example. Important factors which also strongly influence the total service life of a cement-based toping or floor which is subjected to chemical products are:

• Composition of the industrial floor: type of binder, type of fillers and type of aggregates.
• Age of the industrial floor: with cement-based floors the chemical resistance must be determined after min. 28 days due the increasing chemical resistance.
• Permeability of the industrial floor: penetration with or without pressure.
• Permeability of the industrial floor: shrinkage in the plastic phase and temperature changes in the fresh concrete.
• Permeability of the industrial floor: efficient curing of the industrial floors.
• Permeability of the industrial floor: (micro) cracks and crack width.
• Permeability of the industrial floor: auto healing with certain circumstances.
• Permeability of the industrial floor: joints and connections.
• Permeability of the industrial topping or overlay: crack-bridging system.
• Wear resistance and impact resistance: in case of damages where the medium can penetrate in and what will reduce the total thickness of the floor.
• Slopes in the industrial floor: a relatively large slope will result in a high flow of the medium but can also result, with strong acids, in a relatively fast washing out of the surface.
• Temperature: of the surrounding construction and from the medium.
• Concentration of the medium.
• Combinations of mediums.
• The period of the chemical load: temporary when some spillage, only in case of emergencies, all the time.
• The period of the chemical load: cleaning and cleaning with what.

Practical and laboratory test during the last 40 years is showing that cement-based materials with a high density, made possible using a large amount of very fine fillers and a very dense packing, have a good or even extreme good resistance against chemicals. In a comprising test in 1986 a very dense UHPC concrete was compared with different types of concrete, concrete with micro silica and concrete protected with different coatings like styrene butane latex and hydroxypropyl methyl cellulose. A large number of cubes (25) with dimensions 100 mm were produced for compressive strength tests and a test in a bath where all the time sulphuric acid was added in the water (concentration 2,08% and pH 1,37) what was pumped through during 28 and 46 days. The corrosion was measured by brushing with a steel brush and weighting the cubes afterwards.

Densit concrete, where the dry materials of specially graded Portland cement and silica fume are supplied ready proportioned and mixed by the manufacturer, showed both very good acid resistance and very high strength (165 MPa). Source: Fattuhi and Hughes 1986

The results showed the very good performance of the very dense UHPC concrete, the coatings where only a protection for a short time and the addition of styrene butane latex resulted in a much lower compressive strength of the concrete. The very dense concrete cubes where showing a very high resistance and the attack was uniform over the whole surface, the total weight loss was only 3,4% compared to 13,6 to 25,4% for the other cubes.

?Also, from practical tests we learned that a very dense concrete, compared to a reference concrete of a good quality (40 MPa), has a very good chemical resistance against for example: animal fat, fertilizer, animal food, sugar solutions, milk, salts, oil, etc. For that reason, many UHPC floors are placed in the meat- and meat processing industry and in the food- and food processing industry.

The next points are important to judge the chemical resistance of an UHPC topping:

• Temperature: of the surrounding construction and of the medium.
• Concentration of the medium.
• Possible combinations of different mediums.
• The period of the chemical load: temporary when some spillage, only in case of emergencies, all the time.

With a constant load of strong acids, it will be necessary to apply an extra protective layer form an epoxy or resin on the UHPC topping. The advance is than that even when some mechanical damage occurred in the protective layer, that the subbase is still protected and that the medium cannot go thru the UHPC topping during a very long period. During a shutdown period the protective layer can be repaired easily since the UHPC topping is only attacked at the surface and not penetrated by the medium.

?The resistance of UHPC toppings against chemical attack has been evaluated by laboratory experiments in the laboratory of Aalborg Portland in Denmark. The next tests are done with a traditional Portland based UHPC with a binder content of approximately 20% and a calcium aluminate cement based UHPC with a binder content of approximately 20%.

?The experiments were carried out using different acids and were done on specimens with the size 50 x 50 x 20 mm. The test procedure was carried out as a comparison test between specimens made of UHPC materials and a reference Portland cement mortar with a water/cement ratio of 0,40. All specimens were cured in water for 28 days prior to immersion into the acid bath. The acid bath was kept at constant temperature and pH-value. After 28 days or longer in the acid bath weight losses were reached. Some of the specimens were subjected to cleaning using a steel brush before being weighed to remove material. Results appear in the tables below.

Please take note that a laboratory test is not always representative for an actual situation, which are in most cases less bad but sometimes much worse. Also, when these UHPC products are used for industrial floors they have, due the way of placing and finishing, a much higher density than the small specimens tested.

In the food processing industry, it is important to check what products, temperatures, actual spillage and cleaning products are used. A surprisingly very fast deterioration (1 – 2 years) of the UHPC toppings with a slope of 1 cm/ m1 occurred in a production facility for pickled vegetables once occurred. While brine itself is harmless for UHPC in Industrial Flooring and Wear Protection, the combination of hot water containing vinegar, sugar, brine, product and cleaning with citric acid resulted in very fast superficial damage and a protective layer was necessary.

To avoid potential failure, it is thus recommended to test the specific product in in the laboratory with samples and, because the local circumstances are often not known or even kept secret and thus therefore difficult to copy in the laboratory, to make a trial area in the production facility of the client.

I used that approach when a large producer of fruit drinks wanted to have a UHPC topping in its production facilities in Germany. We tested all possible fruit drinks, combinations of fruit drinks and cleaning products in the laboratory and on a trial area in the production facility. A failure in the industry, for whatever reason, is much more expensive than the application of the UHPC topping and the consequences of an unforeseen and unwanted production stop are large and expensive. ??

Peter Buitelaar

Amsterdam, 11 December 2024