Prepared by M. Donadio, Market Development Manager, TM Refurbishment, Sika Services AG, Switzerland

Transcription

1 Sika Services AG, Switzerland Sewage treatment plant protective coating long term investigation Dated: April 2013 Version : n Sewage treatment plant protective coating long term investigation Prepared by M. Donadio, Market Development Manager, TM Refurbishment, Sika Services AG, Switzerland Phone: +44 (0) / Fax: +44 (0) /12

2 Table of Contents Abstract Introduction Plant overview In-Situ Tests Inspection and Testing Systems Tested Product Evolution Site Inspection Laboratory Testing and Analysis Definition of Terminology The 2008 Investigation Measurements and Results Tensile strength of the concrete Summary of the Test Zones Inspection and Condition Pollutants Concentration Assessment and Conclusion Current Situation Phone: +44 (0) / Fax: +44 (0) /12

3 Abstract Concrete structures in sewage and waste water treatment plants often suffer severe damage due to chemical attack from the aggressive water and acidic gases produced by the sewage. These in-situ investigations carried out over a very long period of 17 years, allow the differentiation of different concrete repair and protection systems and build-ups according to their life expectancy. In summary, it can be shown that in this particular environment: cement based systems (either pure or polymer modified) have a relatively short life expectancy (<7.5 years); epoxy modified cement based systems have a medium life expectancy (~10 years) whilst system build-ups with a combination of epoxy modified cement based pore sealers and reactive epoxy materials have a long life expectancy (>17 years). 1. Introduction Waste water treatment plants receive sewage and dirty water from the sewerage system, plus waste water from the storm water drainage system. All of his dirty water goes through a complex series of treatment processes before it can safely be reused or returned to the natural environment. During many of these processes, the dirty water is held and treated in different tanks and structures, which are generally made of reinforced concrete. This concrete is therefore subjected to varying degrees of attack dependent on the stages of the process and the level of aggressive materials in the water. The walls of these concrete structures are generally coated with different protective systems of varying performance and characteristics; indeed their durability also varies quite significantly. In 1991, the owner of the ARA Altenrhein sewage treatment plant allowed Sika Switzerland to conduct in-situ testing and evaluation of the different types of materials, by applying different protective system build-ups in an aeration tank. Periodic inspections and testing were then carried out (in 1999, 2001 and finally 2008) 2. Plant overview 1 The ARA Altenrhein in St Gallen is one of the largest sewage treatment plants in Europe. It was first opened and went into service in 1975, with subsequent expansion over the years. The latest large extension to the plant was added between 1996 and Source: Figure 1: Aerial view of the plant Phone: +44 (0) / Fax: +44 (0) /12

4 The inflow of sewage and waste water comes directly from the City of St Gallen and the Old Rhine. After treatment, the clean water is discharged into Lake Constance, which is also a fresh drinking water source for much of South West Germany The yearly production of Bio-Gas at the ARA plant is around 1.4 Mio m 3. The average dirty inflow during dry weather periods is around 400 l/sec, whilst during rainy periods this can increase to a maximum of around l/sec. 3. In-Situ Tests Inside the aeration tanks at the plant, following normal mechanical concrete surface preparation work, the different protective system build-ups were applied. This was carried out in September 1991, by the Technical Department of Sika Switzerland AG. Some sections of the application area are normally always submerged in the dirty water, some sections are normally in the water level zone and a section is above the water levels. 4. Inspection and Testing This article contains a summary of the inspection and testing reports carried out in 1999 by H. Bänziger, in 2001 by the Sika Diagnostic Center (Report B by M. Dietrich & F. Marty) and in 2008 by the Sika Diagnostic Center (Report B /0H by M. Dietrich & O. Haase) 4.1. Systems Tested Product Evolution No. Product / System Name (when applied in 1991) Current Product System Name / Status (at time of testing in 2008) Testing in Sikadur -31 No change 2 SikaTop -Seal Sika -101a grey Modified in Switzerland after New name Sika MonoTop-107 Seal Remains as SikaTop Seal-107 in many countries Modified in Switzerland pre New name Sika -101 HD 4 SikaTop Modified in Armatec 110 EpoCem Available under the same name 5 SikaTop Sika MonoTop SikaTop -123 Sikafloor -89 No longer in the product range in Switzerland Still available in some countries Modified. New name Sika MonoTop -723 N Both no longer in the range. Figure 2: View of the various systems right after application in September 1991 No No Phone: +44 (0) / Fax: +44 (0) /12

5 No. Product / System Name (when applied in 1991) Current Product System Name / Status (at time of testing in 2008) Testing in SikaTop -123 dark type No longer in the product range No 9 Sikagard Modified before EpoCem New name Sikagard -720 EpoCem Sikagard -75 EpoCem Sika Poxitar F black Sikagard -75 EpoCem Sikagard -64 red brown Sikagard -75 EpoCem Sikagard -63 olive Sikagard -75 EpoCem Sikagard -62 light grey 4.2. Site Inspection Modified before New name Sikagard -720 EpoCem Product modified. Current name still Sika Poxitar F Modified pre New name Sikagard -720 EpoCem No longer in the product range Modified before New name Sikagard -720 EpoCem Modified. New name Sikagard -63 N Modified pre New name Sikagard -720 EpoCem No longer in the product range In December 2008, the following investigations were carried out directly at the structure: Visual inspection (photography taken of the typical damages) Core sampling (Ø 50 mm) Making good the core sample holes 4.3. Laboratory Testing and Analysis The following laboratory testing and analysis was carried out on the samples taken from site: Tensile adhesion test to DafStb Procedures, Part 3: [German Committee for Structural Concrete] - Ø 50 mm - Adhesive Sikadur 31 - Surface lightly ground Microscopic analysis of cores taken Analysis of the chloride, nitrite, nitrate & sulphate contents by ion chromatography after hot water extraction 4.4. Definition of Terminology To avoid any misunderstanding and to ensure a clear definition of the terminology, the definitions are listed below: The surface is intact, no blisters or eruptions, no detectable embrittlement. No No Phone: +44 (0) / Fax: +44 (0) /12

6 Mortar is softened The strength of the mortar is somewhat reduced and it can be removed by hand using a steel rod with considerable force. Mortar can easily be scraped off The strength of the mortar is further reduced and it can be removed by hand using a steel rod with normal force. Mortar can easily be scraped off (with slight pressure) / is soft The strength of the mortar is so much reduced that it can be removed by hand using a steel rod with slight pressure. Mortar can easily be scraped off without using force / is very soft The strength of the mortar is so much reduced that it can be removed by hand using a steel rod without any force. The matrix is totally destroyed / completely soft The mortar has completely lost strength, even cleaning the core sample with tap water and a sponge removes a large part of the coating. Powdering surface (cement) / embrittled surface (polymer ) Only the surface matrix is affected, there may still be greater strength in deeper layers The 2008 Investigation The non-treated concrete areas show the signs of typical chemical attack, with exposed medium to larger sized aggregates due to the deterioration of the cement paste. Sampling was also carried out for analysis of the aggressive salts and / or pollutants that were present. Figure 4: General view of the test zones in 2008 Figure 5: Close-up view of non-treated concrete areas Phone: +44 (0) / Fax: +44 (0) /12

7 5. Measurements and Results 5.1. Tensile strength of the concrete The tensile bond strength testing was carried out according to the DAfStb guidelines, Part 3. This test was done on 20 mm long core samples. The surfaces were slightly grinded No. 1 Protective Treatment Sikadur -31 Tensile Strength (N/mm²) Failure mode in 2008 (break in concrete, bond or coating layer) % concrete / 60% coating % concrete / 20% coating Mean value Sikagard -75 EC + Sika Poxitar F Concrete Concrete Mean value Sikagard -75 EC Concrete 12 + Sikagard -63 olive Concrete Mean value Unknown material sample area % concrete / 50% coating % concrete / 70% coating Mean value Note: SG-75 EC stands for Sikagard -75 EpoCem 5.2. Summary of the Test Zones Inspection and Condition Condition after 7.5 years Condition after 10 years Condition after 17 years Sikadur 31 1 coat system Area OK but small osmotic blisters SikaTop -Seal coat system Mortar can be scraped off with steel rod, softened Sika -101a grey 1 coat system Mortar can be scraped off with steel rod, softened Blisters at the bottom, otherwise no damage. Mortar can easily be scraped off with steel rod. Powdering surface Mortar is powdering badly. It has already worn off at the bottom. Mortar can easily be scraped off with steel rod. Blisters still present at the bottom, but no new ones. Surface discoloured. Intact after scratch test Mortar can easily be scraped off with steel rod without using force. Very soft throughout. Matrix is completely destroyed Phone: +44 (0) / Fax: +44 (0) /12

8 Condition after 7.5 years Condition after 10 years Condition after 17 years SikaTop -Armatec-110 EpoCem 2 coats with brush SikaTo p coat system Mortar can be scraped off with steel rod, softened Sika MonoTop coat system Mortar can be scraped off with steel rod, softened SikaTop -123 (1 coat )+ Sikafloor-89 (2 coats) A few osmotic blisters, otherwise no damage SikaTop -123 dark type 1 coat system Mortar can be scraped off with steel rod, softened. Mortar can easily be scraped off with steel rod. Powdering Mortar is powdering slightly. It has already worn off at the bottom. Mortar can easily be scraped off with steel rod. Mortar is powdering badly. It has already worn off at the bottom. Mortar can easily be scraped off with steel rod. A few osmotic blisters ca. 2 mm otherwise no damage Mortar is powdering badly. It has already worn off at the bottom. Mortar can easily be scraped off with steel rod. Sikagard -75 EpoCem 2 coats system. Mortar can easily be scraped off with steel rod. Powdering surface Sikagard -75 EpoCem (2 coats) + Sika Poxitar-F (2 coats) Sikagard -75 EpoCem (2 coats) + Sikagard -64 red-brown (2 coats) 2-3 osmotic blisters otherwise no visible damage 2-3 osmotic blisters otherwise no visible damage Sikagard -75 EpoCem (2 coats) + Sikagard -63 Olive (2 coats) Ca. 30 osmotic blisters ca mm in the transition zone 13 Sikagard -75 EpoCem (2 coats) + Sikagard -62 light grey (2 coats) Delamination at the bottom (possible application defect, substrate too wet) When the coating is tapped lightly with a chisel, it pops indicating debonding. (Stresses). Mortar can be scraped off with steel rod using slight pressure). Soft matrix No 2008 test Matrix is completely destroyed No 2008 test No 2008 test. Mortar can easily be scraped off with steel rod using slight pressure. Soft matrix Intact after scratch test No 2008 test, just hundreds of osmotic blisters over the whole area. Intact after scratch test No 2008 test Phone: +44 (0) / Fax: +44 (0) /12

9 5.3. Pollutants Concentration The pollutant content detected by the analysis is given as percentage by weight of the cement content. The calculation is based on the following assumptions: Concrete density: 2.4 (kg/l); Original mix design cement content: 300 kg/m 3. Each of the protective coating systems was removed before the analysis. As % of cement content No. Component 0 10 mm mm mm Chloride content 0 Control sample Control sample Sikagard -75 EpoCem SG-75 EC + Sika Poxitar F SG-75 EC + Sikagard -63 olive Sulphate content 0 Control sample Control sample Sikagard -75 EpoCem SG-75 EC + Sika Poxitar F SG-75 EC + Sikagard -63 olive Nitrite content 0 Control sample 1 not found not found not found 0 Control sample 2 9 Sikagard -75 EpoCem 10 SG-75 EC + Sika Poxitar F 12 SG-75 EC + Sikagard -63 olive Nitrate content 0 Control sample Control sample Sikagard -75 EpoCem SG-75 EC + Sika Poxitar F SG-75 EC + Sikagard -63 olive Note: SG-75 EC stands for Sikagard -75 EpoCem Phone: +44 (0) / Fax: +44 (0) /12

10 6. Assessment and Conclusion The pure cement based and acrylic polymer modified, cement based protective surface levelling mortars (SikaTop -Seal 107 (No. 2), Sika -101a grey (No. 3) and Sika MonoTop -620 (No. 6)), are softened after approximately 7.5 years, worn away in some parts after 10 years and their cement matrix is almost completely destroyed after 17 years. The service life expectancy is therefore lower than 7.5 years. The two modified Cement based Combination (ECC) products (SikaTop -Armatec-110 EpoCem, Sikagard -75 EpoCem ) are more resistant than the pure cement based and acrylic polymer modified systems. It was apparent that their cement matrix had softened after approximately 10 years and the products surfaces were powdering slightly. After 17 years both only have low residual mechanical strengths and are softened throughout. The service life expectancy is therefore around 10 years. The synthetic epoxy based systems (Sikadur -31, Sika Poxitar F black and Sikagard -63 olive) are still resistant to the sewage even after 17 years continuous exposure and have little wear. Sikagard - 63 olive has some osmotic blistering, probably due to inadequate substrate or environmental conditions at the time of the original application. The service life expectancy is therefore longer than 17 years. Fixing Fixing Poxitar F Destroyed matrix of non-polymer modified mortar EpoCem Concrete Concrete Figure 6: Non-polymer modified cement waterproofing Figure 7: Coating and EpoCem technology The alternating water line zone (alternating wet and dry) was also investigated on a small test area. A brief visual inspection showed that all of the products are attacked to some extent. They could not be analysed further due to access problems. The analysis of the pollutants did not produce any more detailed results or conclusions: The chloride content test results are virtually identical for all of the measured samples, which is probably because the chloride contamination is very low in this particular sewage treatment plant. Nitrite pollutants were not detected at all. The sulphate content is constant throughout from a depth of 10 mm at a level around 1.1%. The first depth levels show some sulphate accumulation, which is slightly lower in the areas coated with the epoxy based systems. Because sulphates generally accumulate only in the top 5 Phone: +44 (0) / Fax: +44 (0) /12

11 mm, but the measuring level is 10 mm, the efficiency of the protective coating systems cannot be clearly demonstrated by these sulphate measurements. The nitrate content test results are ca. 0.25% for uncoated concrete, ca. 0.15% for Sikagard -75 EpoCem and 0.12% for the Sikagard -75 EpoCem overcoated with epoxy. The trend shown by this series is that areas with cement based protective systems have slight protection against nitrate penetration and areas coated with epoxy based protective systems have higher protection. Measurements before the coatings were applied would have been necessary for a fully representative result, but these differences and the improvement in performance by use of the different protective systems is clear. 7. Current Situation Since the original materials application was carried out in 1991, Sika has continuously improved its product range through our own significant R&D work, or by adoption of new and improved raw materials and technologies that have become available. Based on this inspection and assessment report, our global expertise and experience, the Sika range of protective surface treatment products and systems for high durability in sewage treatment plants and similar installations now includes: Primary Water Treatment Structures (i.e. Mechanical filtering / cleaning) Primer Top coat Expected servicelife Product type Product name Product type Product name Properties Sikafloor -156 Sikacor -277 Rigid, airless spray applied years Sikafloor -156 Polyurea Sikalastic -841 ST Crack-bridging, 2-component hot spray applied years Secondary Water Treatment Structures (i.e. Biological cleaning) Sikafloor Anthracene Oil combination Sika Poxitar F Slightly flexible, 3 layer top coat, roller or spray applied years Sikafloor -156 Sikagard -63 N Rigid, 3 layer top coat, roller applied years Sikafloor -156 Sikacor -277 Rigid, airless spray applied years Sludge Treatment Facilities - Presence of Biogenic Sulphuric Acid corrosion (BSA) and methane gas Sikafloor -156 Sika Permacor 3326 EG H Rigid, airless spray or roller, 3 layer applied years Sikafloor -156 Polyurea Sikalastic -844 XT Crack bridging, 2-component hot spray applied years Phone: +44 (0) / Fax: +44 (0) /12

12 Note: With all systems designed to protect concrete surfaces against chemical attack, the concrete must first be cleaned, prepared, repaired and levelled as required; in order to provide a surface that is sound, clean and open-textured, with a sandpaper-like finish that is free of any pores, blow holes and other defects. When time is available, we recommend the use of acrylic polymer modified, cement based levelling mortars and pore sealers (e.g. Sika Icoment -520), followed by damp curing to good concrete practice and then allowing a further hardening period of at least 10 days prior to over-coating with the reactive products. For reduced waiting / faster over-coating times, we recommend the use of epoxy modified, cement based pore sealers (e.g. Sikagard -720 EpoCem), at a thickness of minimum 3 mm. This type of material allows application and over-coating with the reactive products in a much short waiting time, in fact as soon as the surface moisture content is below 4% (approx. 24 hours in normal conditions) The information contained herein and any other advice are given in good faith based on Sika's current knowledge and experience of the products when properly stored, handled and applied under normal conditions in accordance with Sika's recommendations. The information only applies to the application(s) and product(s) expressly referred to herein. In case of changes in the parameters of the application, such as changes in substrates etc., or in case of a different application, consult Sika's Technical Service prior to using Sika products. The information contained herein does not relieve the user of the products from testing them for the intended application and purpose. All orders are accepted subject to our current terms of sale and delivery. Users must always refer to the most recent issue of the local Product Data Sheet for the product concerned, copies of which will be supplied on request. Phone: +44 (0) / Fax: +44 (0) /12