Chemical Resistance of Ultra High Performance Concrete compared to 3 types of concrete in a sewage treatment plant in the Netherlands: 1987 - 1989
Introduction
Recently I have read an interesting article from Jon Belkowitz (Intelligent Concrete LLC) on LinkedIn regarding the chemical resistance of concrete in an aggressive environment of a sewage. That reminded me of one of the first research projects I did with Ultra High Performance Concrete (Densit) in my position as development manager in the R&D department of the Dutch contractor J.G. Nelis (now part of Royal BAM Group). J.G. Nelis obtained a license from the Danish Densit A/S to market and apply the World’s first Ultra High Performance Concrete Densit in the Netherlands in 1985. I already used Densit Ultra High Performance Concrete for wear protection in hydraulic and pneumatic transport systems and cement-, steel - and coal fired power plants since 1985 for a service company. I was hired by J.G. Nelis to develop the products further for civil engineering applications. The materials were used as industrial floors (toppings) in the heavy industry and chemical industry and for various prefab applications as drain covers and drains.
Research project Rioolzuiveringsinstallatie (Sewage treatment plant) West in Amsterdam
The department of Public Works of the city Amsterdam expressed their interest to use this new Ultra High Performance Concrete for rehabilitation and renovation of their sewage treatment plants and to possible replace normal concrete in certain parts of the new to construct sewage treatment plants. We had some very good experiences with the use of Ultra High Performance Concrete in two chemical factories in the northern part of the Netherlands where several 100 tons are used for drains, drain covers and chemical storage tank foundations. We suggested to initiate a testing program in combination with other concrete types to not only get an opinion about the chemical resistance of the Ultra High Performance Concrete but also to get an objective comparison with more traditional types of concrete as used in the Netherlands. I thinks that that was the right approach since chemical attack in a sewage treatment plant is depending on many factors and in this way we avoided discussions and questions later.
Corrosion in a sewage system and sewage treatment plant
Wastewater treatment plants handle some of the most corrosive and aggressive liquids and solids known to process engineering. Pipes, tanks, pumps, and all the instrumentation that measures flow, level, pressure, temperature and other parameters are exposed to high concentrations of organic and inorganic compounds, sewage and industrial waste, corrosive chemicals, solids and microbiological organisms of all forms, as well as various gases. Even the infrastructure is subject to corrosion. The interaction of the primary components of sewage typically produces secondary chemicals and gases with even greater toxic and/or corrosive properties. Microorganisms cultivated at different stages throughout the wastewater stream produce a multitude of chemical and gaseous by-products – hydrogen sulphide (H2S) being a very common and particularly damaging by-product of MIC related bacteria. Sulphur-reducing bacteria (SRB), for example, reduce sulphates to sulphites in an anaerobic environment to produce hydrogen sulphide - H2S gas. Other aerobes, most commonly different strains of Thiobacillus, will oxidize the sulphur to sulphuric acid - producing pH values as low as 1.0, and attacking the concrete basins and most metals it comes in contact with.
Concrete at different parts of a sewage treatment plant may be exposed to sulphuric acid produced by microorganisms, sulphates and chlorides – containing water, to permanent submersion in water and constant flow, as well as to changeable temperatures of freezing and thawing. Occurrence of such conditions may cause problems to concrete, including cement dissolution, macro- and micro-cracks, as well as chipping and corrosion of the reinforcing steel. The process taking place is very complex and a good description can be found in 1.
Based on an earlier tests [2] from 1986, with different concrete samples in a hydraulic channel with acids, it was concluded that: “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)". This while standard mixes with the addition of micro silica didn’t show any improvement. Also tests made for the development of nuclear waste unit for use in shallow land burial [4] showed promising results for Densit UHPC in an aggressive environment. The early (1983) work of Carolyn M. Preece showed excellent corrosion protection of steel reinforcement in Densit UHPC [5].
Concrete samples
We decided to make 4 series of each 3 samples (12 samples in total, dimensions 400x200x60 mm) plus all the necessary cubes (150x150x150 mm) for compressive strength tests to control the quality of the concrete produced. In the samples a plastic tube was casted to create a slot for the fixation of a rope to hang the samples on a tube above the water level. In 8 samples a welded mesh reinforcement is used to observe possible corrosion of the steel. All samples were weighted, photographed and sieve analysis were made from the silica sand and aggregates.
Sample location
On February 17th 1987 the 12 samples were placed in 3 sets on 3 locations of the so called first intake tank where the heavy residue and particles are sinking to the bottom of the tank and the light residue and particles are floating. By hanging them just above the water level in a closed manhole it was expected to have the maximum possible chemical attack on the samples. The pH value at the bottom part of the samples, thus close to the water level, was 3 – 4 and the pH value at the top of the samples was 1 – 2. The denomination is thus extremely to ultra acidic and extremely aggressive to concrete. Analysis were also made from samples of the water in the tank.
Observations
On 2 dates (May 11th 1987 and May 17th 1988) the samples are taken out, pH values at the surface is measured, deteriorated concrete is removed with a steel brush, photographs are taken and samples are placed back at their location. Unfortunately, during handling the unreinforced Densit sample felled and broke at the top, a hole was drilled (very difficult) to hang it back again. On September 18th 1989 8 samples which have been exposed for 21 months, had to be removed due to maintenance work at that location. The samples are taken out, pH values at the surface is measured, deteriorated concrete is removed with a steel brush, photographs are taken and samples were transported to the workshops of J.G. Nelis in Haarlem. On September 25th 1989 the samples were cleaned with low pressure water and a soft brush to remove all residue, photographed and the final weight was taken. With a steel plate frame corresponding with the original thickness of 60 mm the layer thickness of the lost concrete due to chemical attack was measured on 20 spots on both sides by using the grid (50 x 50 mm) with holes in the steel plate. Samples were cut in smaller blocks to determine deeper penetration and deterioration of the cement matrix. Unfortunately due to the renovation works all samples were removed in 1990.
Conclusions
The photographs taken after 21 months exposure shows serious corrosion of Portland Cement concrete, Blast Furnace Cement concrete and Fly Ash Cement concrete. Remarkable is that with all samples there is more erosion around the area of the hole where a rope was used to hang the samples just above the water level. Possible because the rope was always soaked with water of condensation and had close contact with the concrete surface.
The slices cut also showed, after a chemical analyse in the laboratory, a penetration of the chemicals in the cement matrix, there was not a large difference between the samples of Portland Cement concrete, Blast Furnace Cement concrete and Fly Ash Cement concrete. But after cleaning the surface there was no penetration of chemicals in the cement matrix of the Densit UHPC samples. The dept of concrete disappeared due to the chemical corrosion showed some serious erosion in the samples made of Portland Cement concrete, Blast Furnace Cement concrete and Fly Ash Cement concrete. In the traditional concrete aggregates were easy removed from the surface while in the Densit UHPC there was still good adhesion between the aggregates and the binder. The Densit UHPC showed almost no erosion and often the dept was measured of a bughole or air void and in sample DS 181201 No.: 10 at the area around the drilled hole at the backside (black top sample) due to breaking off of parts of the concrete.
Densit UHPC showed a much better resistance compared to traditional concrete in a sewage treatment plant while deterioration was much less also penetration of the Densit UHPC was not possible due the extremely dense micro structure of the cement matrix. A more optimum mix design with smaller aggregates and hybride fibers and a more efficient casting could have resulted in even better results. The corroded Densit UHPC could, compared to other concretes used, be repaired easy after a high pressure water cleaning.
In 1992 – 1996 Densit A/S initiated with several European partners a BRITE EURAM II projects to develop a durable repair mortar (DURAP) and application methods for rehabilitation of sewage pipes and concrete structures.
Peter Buitelaar
[email protected]
References
1. Elzbieta Stanaszek-Tomala and Maria Fiertaka, Biological Corrosion in The Sewage System and The Sewage Treatment Plant”. World Multidisciplinary Civil Engineering-Architecture-Urban Planning Symposium 2016, WMCAUS 2016.
2. Vincke, E., Boon, N., Verstraete, W., 2001. Analysis of the microbial communities on corroded concrete sewer pipes - a case study. Applied Microbiology and Biotechnology, 57 (5-6): 776-785.
3. Fattuhi, N.I. and Hughes B.P., “Resistance to acid attack of concrete with different admixtures or coatings”. The International Journal of Cement Composites and Lightweight Concrete, Volume 8. Number 4, November 1986.
4. Brodersen, Knud, “Development of waste unit for use in shallow land burial”. RIS? Chemistry Department 1986. Work performed in frame of the Indirect Action Programme (1980-1984) of the European Atomic Energy Community: "MANAGEMENT AND STORAGE OF RADIOACTIVE WASTE".
5. Preece, Carolyn M., Arup, Hans and Fr?lund, Thomas, “Electrochemical Behaviour of Steel in Dense Silica-Cement Mortar”. Proceedings of the Canmet/ACI First International Conference on the use of Fly ash, silica fume, slag and other mineral by-products in concrete. July 31 – August 5, 1983 Montebello, Quebec, Canada.
6. Peter Buitelaar, “Research concrete corrosion in sewage treatment plant West, Amsterdam” Internal report J.G. Nelis December 1989.