Reinforced Concrete Chimneys Sika Technology and Concepts for Repair, Strengthening and Protection

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1 Solutions with Sika Systems Reinforced Concrete Chimneys Sika Technology and Concepts for Repair, Strengthening and Protection Protective coating Corrosion inhibition Strengthening Concrete repair Crack sealing and bonding

2 Exposures and Influences on Reinforced Concrete Chimneys The Different Areas of Chimney Structures Influences from Original Construction Chimneys are relatively high and also relatively slender structures. For this reason, different exposures and influences affect the different levels of the chimney.therefore a subdivision of the structure into different zones relating to the height and proximity of the exhaust outlet is normally recommended. Due to fast track programmes, slipform techniques are normally used for chimney construction. These require relatively low slump concrete which is difficult to compact and the formwork is quickly moved and the exposed surface is difficult to cure correctly. This can lead to: s Honeycombing (from difficulties in compaction) s Excessive pores in the surface (from the difficulties in curing) s Surface cracks and defects (from both compaction and curing difficulties) (* FGDS = Flue Gas Desulphurisation System) Head of the chimney and Main influences: s Exhaust gases (especially SO X, NO X ) s Thermal variations s Condensation s Fuel ashes s Rain, wind s Atmospheric and exhaust CO 2 Middle shaft Main influences: s Exhaust gases s Thermal variations s Condensation s Rain, wind s Exhausts from neighbouring chimneys s Atmospheric CO 2 Lower shaft Main influences: s Industrial atmosphere s Atmospheric CO 2 s Rain H Stand Alone Chimney middle shaft D Several Neighbouring Chimneys s With adjacent chimneys Ü Exposure to its own and also to its neighbours exhaust Note: and 2 are more extensive in these cases middle shaft Stand Alone Chimney with Special Exhaust (i.e. FGDS*) s High speed of gases due to narrow exhaust Note: and 2 are smaller in these cases middle shaft Exhaust Fumes and Gases Fuel Ashes Condensation Thermal Variations sunshine, frost, UV exposure Atmospheric CO 2 General Chimney Zone Classifications lower shaft lower shaft lower shaft Rain These are always measured from the top This is Diameter (D) Wind This is the next of the height (H) This is the remainder of the height to the ground (H) Ground Stability 2 3

3 Repair and Protection of Reinforced Co ncrete Chimneys Exposure Exhaust Fumes and Gases Problems and Typical Damages The Most Important Testing and Proof Statements Requirements for the Repair Necessary and Protection System Fuel Ashes Condensation Increased acid attack Sulphate corrosion Erosion of cement matrix Loss of alkalinity Increased surface permeability Water penetration Discoloration of the surface Prevent water penetration Resistant to acid attack Resistant to condensed water Minimum dirt pick up Initial water absorption Water absorption after accelerated weathering (10,000 hours) Accelerated weathering (wet / dry) to confirm Condensed water resistance (10,000 hours) Acid chemical resistance testing Long term project references with independent testing and assessment of performance after min. 10 years Rain Water penetration / frost damage Cracks due to thermal shocks Thermal Variations sunshine, frost, UV exposure Sunlight Thermal expansion Stress cracking Frost Thermal contraction Stress cracking Freeze thaw attack of the concrete surface Compatible thermal expansion coefficient Allow each way water vapour diffusion Equal or lower modulus Dynamic crack bridging Effectively halt or prevent carbonation Thermal expansion coefficient equivalent concrete (i.e m/m8k) Water vapour diffusion coefficient to allow each way water vapour diffusion (Sd H 2 O 4 m) Frost resistance (degradation test m30: average erosion of dry substance after 30 freeze/thaw cycles, according to Swiss Standard SIA 162/1, Test No. 9) UV light resistance (min. 10,000 hours accelerated UV weathering) Atmospheric CO 2 Carbonation Corrosion of steel reinforcement Rust staining Cracking and spalling over steel reinforcement Ultraviolet light stability Freeze thaw resistance Initial carbon dioxide diffusion (Engelfried process [resistance Sd CO 2 at least 50 m air] ) Carbon dioxide diffusion resistance after 10,000 hours accelerated weathering to confirm continued resistance (equiv. 15 years) Long term project references min.10, pref. 15 years (with independent testing assessment of performance) Wind Ground Stability Formation of cracks due to windload Insufficient quality of concrete surface Pollution with marine chlorides possible Settlement and therefore cracks Dynamic crack bridging Application with minimal curing Structural strengthening Filling and sealing of cracks Structural bonding Ground stabilisation Crack bridging: static and dynamic at minus 20 C static and dynamic after accelerated weathering (10,000 hours equiv.15 years) Long term project references (10 years assessment) Bond strength of resins for injection Proof of ground stabilisation 4 5

4 Repair and Protection of Reinforced Co ncrete Chimneys Sika Concrete Repair and Protection System Application Area Extended Repair Work Partial Concrete Replacement Typical Repair and Reprofiling Levelling and Pore Sealing Protective Sealing and Standard System Crack Bridging System Additional Requirements Head of the chimney and Middle shaft Lower shaft s Conventional concrete High dense concrete technology. with Sikacrete-PP1 as an additive or with Sikament as an admixture High dense and self compacting concrete using the Sika ViscoCrete technology Early strength development using an accelerator, e.g. Sika Rapid-1 s Shotcrete High dense concrete technology with a fine concrete mix design (PC kg/m 3, aggregate max. Ø 8 mm), e.g. with SikaTard as an admixture or Sikacrete-PP1 TU as an additive combined with an alkalifree set accelerator, e.g. Sigunite-49 AF or Sigunite-L50 AF (possible addition of steel fibres) Exposed steel reinforcement: s Corrosion protection Chloride penetration/co 2 diffusion barrier with active corrosion inhibition, e.g. SikaTop Armatec 110 EpoCem or Sika MonoTop-610 s Gunite mortar (dry spray applied) Very high building, large volume micro-concrete, e.g. Sikacem- Gunite-133 or (wet spray applied) Repair mortar reinforced with fibres, e.g. Sika MonoTop-612 s Grouting Polymer modified, self-levelling grouting mortar for concrete repair work, e.g. SikaTop s Repair mortar Light weight and dense high build repair mortar, e.g. Sika MonoTop repair mortar Epoxy modified, high dense repair mortar without curing, e.g. Sikadur-45 EpoCem Without curing Thin layer levelling mortar which is suitable for aggressive environments and needs no additional curing, and which is overpaintable after short time, e.g. Sikagard-720 EpoCem With curing Thin layer levelling mortar for rendering vertical surfaces, e.g. Sika MonoTop levelling Mortars High chemical resistant high building coating, e.g. Icosit 277 (31 2) + Chemical resistant UV protection coating, e.g. Icosit EG 5 (32) Impregnation Chemical resistant transparent epoxy primer, e.g. Icosit 2406 Primer (31) Chemical resistant EP coating, e.g. Icosit Poxicolor (31) + Chemical resistant UV protection coating, e.g. Icosit EG 5 (31) Hydrophobic impregnation Water repellant, e.g. Sikagard-702 W (32) Waterbased acrylic coating, e.g. Sikagard-670 W (32 3) Impregnation Chemical resistant transparent epoxy primer, e.g. Icosit 2406 Primer (31) Chemical resistant PU coating, e.g. Sikafloor-351 Thixo (31 2) + Chemical resistant PU coating, UV protection, e.g. Sikafloor-363 Elastic (32) Impregnation Chemical resistant transparent epoxy primer, e.g. Icosit 2406 Primer (31) Chemical resistant PU coating, UV protection, e.g. Sikafloor-363 Elastic (32 3) Hydrophobic impregnation Water repellant, e.g. Sikagard-702 W (32) Waterbased acrylic coating, e.g. Sikagard-550 W Elastic (32 3) Important Note When there is a steel reinforcement remaining in or near the carbonated zone or when there are residual chlorides present (marine atmosphere) use Sika FerroGard-903 penetrating Corrosion Inhibitor before levelling, sealing and coating. Bonding and filling structural cracks Pure synthetic resins with low viscosity, good chemical resistance and excellent adhesion on dry and damp surfaces, e.g. Sikagard-52 Injection Resin Elastic sealing of joints and moving cracks One component PU sealants with high joint movement capacity, e.g. Sikaflex PRO-2HP sealant Structural strengthening High performance externally applied strengthening system with composite plates and fabrics, e.g. Sika CarboDur System 6 7

5 Repair and Protection of Reinforced Concrete Chimneys: Advanced Sika Technologies Sika Repair Mortar Testing Technology Sika has Developed Mortar Application Performance Testing s Application performance horizontal, vertical and overhead s Crack free hardening in repair spots under different climatic conditions The Bänziger Block and its Practical Relevance Characteristics Solid member of approx. 70 kg Concrete with aggregate of Ø 16 mm and blast cleaned surface Dimensions: filling volume ca. 11 litres Square arrises Differential repair thickness Arrises on three sides Long open side Practical Relevance Concrete substrate Ô No deformation possible Poorly prepared substrate Ô Worst case scenario for adhesion Suitable for single/complete trial batches/units Ô Mix errors are avoided Non-bevelled edge to a repair section Ô Worst case scenario for bond and shrinkage Different thicknesses for repair Ô Worst case scenario for crack resistance of mortar Indented repair area Ô Restricted shrinkage Open edge Ô Worst case scenario for unrestained shrinkage Sika EpoCem Technology The only Cementitious Mortars with no Curing Necessary s Repair and Protection under Exposed Conditions Cementitious pore filling mortars need protection from drying winds and direct sun to prevent excessive evaporation and shrinkage cracking. Sikagard-720 EpoCem can be applied in these situations without protection due to its integral curing properties. Sikagard-720 EpoCem also has the added advantage of not requiring a primer when it is to be overcoated with Sikagard-550 W Elastic for crack-bridging protection. When crack-bridging is not necessary, Sikagard-720 EpoCem may be used as the actual protective coating itself, due to its excellent anti-carbonation properties and chemical resistance. Advantages of Sika EpoCem Mortar Technology No curing Minimized reaction setting and hardening time Minimized waiting time if substrate to be overcoated with Sika Epoxy s Easy application Excellent adhesion on damp substrates High frost and freeze/thaw resistance Excellent pore sealer Good chemical resistance Waterproof but water vapour permeable Bänziger Block Testing Conditions s Wind tunnel storage s Water storage s Thermal shock storage s Freeze/thaw cycle storage Sika EpoCem Technology Sika EpoCem products are essentially cementitious mortars with special epoxy resin as a secondary binder system. This means that two separate and complimentary reactions are taking place during the hardening and curing processes: The polymerisation of the epoxy resin and its hardener The hydration of the cement The interaction of these two different binder systems develops with the formation of a lamellar framework of epoxy resin polymer, into and through the interstices of which the cement crystals grow. Good example Bad example Like Epoxy. Like Cement. 8 9

6 Repair and Protection of Reinforced Concrete Chimneys: Advanced Sika Technologies Sika FerroGard Technology The Impregnating Surface Applied Corrosion Inhibitor Sika CarboDur Technology Structural Strengthening with Composite Plates and Fabrics s With traditional concrete repair and protection systems, Sika FerroGard -903 gives additional cost effective protection against the future development of latent damages; for instance due to steel being in carbonated concrete or to the presence of residual s Multidirectional fabrics: seismic conditions, shear strengthening s Unidirectional fabrics and plates: wind loading, flexural reinforcement In reinforced concrete the steel is normally protected against corrosion by the passivating alkalinity of the cement matrix. Due to the ingress of aggressive environmental influences, the steel can corrode: Carbonation Carbon dioxide ingress causes carbonation of the cement matrix, progressively reducing the passivating alkaline protection of the steel reinforcement to a level where corrosion can occur. Chloride Attack Chloride ions from deicing salts or marine exposure are carried into the concrete in solution with water. At the steel surface, even in alkaline concrete, they attack and break down the passivating layer and then accelerate the steel corrosion process. Advantages Light weight Available in any length, no mechanical joints required Minimal overall thickness Easy to carry and apply Economical application no heavy handling and installation equipment Very high performance characteristics Plates and fabrics to suit any application Chemically resistant Non corroding and no under rusting The System The high performance strengthening system for reinforced concrete. System components: Sikadur adhesive for bonding the CarboDur plates and fabrics Sika CarboDur laminates SikaWrap Hex fabrics As soon as sufficient chloride ions or the carbonation front have reached the steel surface, the passive film is destroyed and corrosion accelerates causing cracking and spalling of the concrete. At this stage all of the damaged concrete over the corroding reinforcement must first be removed and repaired with the appropriate Sika Repair System. The Advantage of Sika FerroGard Technology When the concrete is not yet damaged, but is carbonated, and/or contaminated with chlorides below the relevant threshold limit values (TLV) to initiate corrosion themselves; then the use of Sika FerroGard-903 as a surface applied corrosion inhibiting impregnation, can protect against the development of latent damage. Corrosion protection can also be increased on new construction by applying Sika FerroGard-903 from the beginning, for instance to concrete surfaces with inadequate concrete cover over the reinforcement. Strengthening of a column Moment in vertical direction Tensile and Shear Strengthening Works. Sika CarboDur Composite Strengthening Systems. A Global Alliance between Sika and Hexcel

7 Reinforced Concrete Chimneys Sika Technology and Concepts for Repair, Strengthening and Protection Also Available from Sika Sika Concrete Repair and Protection Series Your Local Sika Company The information, and, in particular, the recommendations relating to the application and end-use of Sika products, 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 practice, the differences in materials, substrates and actual site conditions are such that no warranty in respect of merchantability or of fitness for a particular purpose, nor any liability arising out of any legal relationship whatsoever, can be inferred either from this information, or from any written recommendations, or from any other advice offered. The proprietary rights of third parties must be observed. All orders are accepted subject to our current terms of sale and delivery. Users should always refer to the most recent issue of the Technical Data Sheet for the product concerned, copies of which will be supplied on request. Internet: S&W / 98SIC 6.14 / Sika AG, Switzerland