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Κυριακή, 19 Σεπτεμβρίου 2021

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Crack Evaluation and Repair Principles Chris Rodopoulos Prof. of Structural Integrity at Monash University, Editor in Chief International Journal of Structural IntegrityCracks in the concrete structures are early signs of distress which have to be diagnosed properly otherwise the repair of same crack takes place again and again causing loss of time and money. The structural cracks need more attention than non structural cracks. The repair materials and methodology are different depending upon types of cracks, their locations such as joints, structural members etc. and conditions such as dry or moist.Crack Pattern - Symptom 1.Crack in cover concrete, Rebars exposed, concrete spalls. - Corrosion of rebars (main and secondary)2.Vertical and horizontal cracks at interval - Corrosion of secondary rebars3.Cracks at definite interval - Rebars too near the surface, corrosion of rebars4.Diagonal cracks in beams near the support - Overload inadequate section of beam, inadequate stirrups5.Vertical cracks in beams near mid span - Overload, inadequate section of beam, inadequate longitudinal rebars6.Map pattern - Alkali-Silicate Reaction, early drying out condition, high cement content, excess compaction, poor curing.Crack Stability Active/Moving and Dormant Cracks The difference between an active or working crack and a dormant crack is important. An active crack can open or close and get longer, but a dormant crack has stopped moving. Dormant cracks tend to be caused by a temporary overload. Active cracks are created by repeated overloading or temperature or moisture changes that continually cause the crack to open and close. Also, a crack caused by a temporary overload can turn into a working crack due to changes in temperature. As described in ACI 224.1R the goal of all crack repairs is to achieve one or more objectives such as: restore and increase the strength of cracked components; restore and increase the stiffness of cracked components; improve functional performance of the structural members; prevent liquid penetration; improve the appearance of the concrete surface; improve durability; and prevent development of a corrosive environment at the reinforcement. According to EN 1504-5 concrete cracks are classified depending on: Moisture in cracks. Four degrees of moisture for cracks are defined: dry, damp, wet and water flowing.1 / 16 Activity of cracks. Three types of activity are defined: active (live), passive (dead) and latent (dormant) cracks: passive cracks, i.e. the crack is not moving and the cause of cracking is no longer there, i.e. old shrinkage cracks active (‘live’) cracks, i.e. the crack is still moving and the crack width changes. The cause of cracking still exists, e.g. durability cracks (alkali reaction, rust) and cracks due to fluctuating thermal action (temperature) latent (‘dormant’) cracks, i.e. cracks which appear to be passive but may become active by rehabilitation. It is therefore imperative prior to any repair strategy, the engineering team to identify and classify the crack. Despite the fact that as a process is quite simple, in almost 60% of the repair cases failure to achieve a proper repair was registered. Failure emanates from the fact that the diagnostic phase was either absent or wrongful. In an existing structure, the most difficult issue is to separate cracks prior and after hardening of the concrete. According to Australian Standards HB 84-2006 Handbook, Guide to Concrete Repair and Protection, we have: Before concrete Hardening Cracks 1. Early Frost Damage 2. Plastic 2.1 Plastic shrinkage 2.2. Plastic settlement 3. Constructional Movement 3.1. Formwork Movement 3.2. Sub-grade movement 3.3. Random Event movement (earthquake) After concrete Hardening Cracks 1. Physical Cracks 1.1. Shrinkable aggregates 1.2. Drying shrinkage 1.3. Crazing 2. Chemical 2.1. Corrosion of reinforcement 2.2. Alkali-aggregate reactions 2.3. Cement carbonation shrinkage 3. Thermal 3.1. Freeze/thaw cycles 3.2. External seasonal temperature variation 3.3. Early thermal contraction 3.3.1.External restraint3.3.2.Internal temperature gradients2 / 16 4. Structural 4.1. Accidental overload 4.2. Creep 4.3. Design loads The very first, therefore, the inspection team will have to identify are: a)the type of crackb)the Moisture of crackc)the Activity of crack.d)the electrochemistry of the crackTherefore before designing the repair it is essential to do some tests first. We can use ultrasounds to detect the depth of the crack We can use a crack glass to measure the width We can use a IR camera or a probe to measure the Moisture We can use a Half Cell to get some electrochemical indication Lets start with EN 1504 Before concrete Hardening Cracks Force transmitting filling of cracks, defects and interstices with repair materials able to bond to concrete surfaces in cracks, defects and interstices so that transmission of force is possible. Strict requirements are made for the failure criterion, failure deformation and bonding of the repair materials in the actual temperature and moisture intervals. Often injection materials will be brittle after hardening. Force transmitting injection is typically made with epoxy. It is interesting to note that crack width and depth are parameters that govern viscosity of the epoxy A semi-empirical equation is: V = (2807 W) / (0,224 D) where: V is the viscosity of the resin in mPas W is the width of the crack in mm D is the depth of the crack in mm When the engineering team is about to chose an epoxy resin it is imperative to consider the following: a) Pot life.Typical times shall be given by the manufacturer as a function of temperature. Yet it is extremely important to note the relationship between pot life/temperature and viscosity.b) Repair details. The engineering team shall clearly distinguish orientation (horizontal/vertical), density of cracks, distance between injection nipples.3 / 16 Horizontal repairs are profoundly more difficult and wear out our technical team more easily. At the same time due to gravitational forces requires a higher injection pressure of about 25-30%. In contrast to what most contractor do, horizontal repair requires larger distance between the nipples compare to vertical repairs. Again a semi-empirical equation providing the distance between nipples is DS = (907 W) / (1,05 D) DS is the distance between the nipples in cm W is the width of the crack in mm D is the depth of the crack in mm Injection procedures are critical in safeguarding a sound repair. Field Guide to Concrete Repair Application Procedures Structural Crack Repair by Epoxy Injection ACI RAP Bulletin 1: http://www.concrete.org/general/RAP-1.pdf EN 1504-10 contains similar notions to ACI. After concrete Hardening Cracks Physical Cracks Shrinkable aggregates Drying shrinkage Crazing Shrinkable aggregate Cracking - Definition According to the Portland Cement Association, restraint to shrinkage is the most common cause of concrete cracking. This condition is inherent in continuously-poured concrete slabs. In applications such as concrete slabs and residential foundation walls, cracking is inevitable and expected. As the surface of concrete dries, water evaporates from the spaces between particles. As this water dissipates, the particles move closer together, resulting in shrinkage of the concrete. Because the surface of a concrete slab is exposed to air but the underlying concrete is not, concrete near the surface dries and shrinks at a rate different from that of the underlying concrete. The underlying concrete acts as a restraint to shrinkage, resulting in cracking of the surface layer. The issue is also covered in ACI 224R-01. http://www.concrete.org/General/f224R%2801%29Chap3.pdf Prior to establishing our repair on drying shrinkage cracking it is important to cover the definition and the physics: http://www.oboa.on.ca/events/2009/sessions/files/Slab%20Surface%20Prevention%20Repair.pdf http://www.nrmca.org/aboutconcrete/cips/04p.pdfCrazing Cracking Definition http://www.nrmca.org/aboutconcrete/cips/03p.pdf4 / 16 In order to establish the repair of Physical cracks it is imperative to identify the density. Most likely crazing cracking will exhibit the highest. In most cases the engineering team shall require information related to the soundness of the cracked area. A hammer shall provide a reasonable information. Yet again it is imperative to identify the depth of cracking. In cases of high cracking density, ultrasonic based inspection is not reliable since the noise in the signal will increase beyond the limits of data filtering. Coring is perhaps the most reasonable method. A small core of D 100mm and L 50mm will most likely suffice. Bear in mind that we are not examining strength but the core perimeter for cracks. If the cracks appear not to extend on a plane parallel to the direction of the reinforcement and strictly their depth is not exceeding the cover thickness then shall be considered as repairable. In any other case the issue shall be evaluated as strengthening. In the last 10 years this type of cracking (high density) is tackled by the so called vacuum injection. Herein part of the concrete is subjected to vacuum with subsequent pressurized injection. This method is not included in EN 1504-5 on ‘Concrete injection’. The method covers also strengthening and repair. Vacuum injection is similar to force injection apart from the fact that instead of pressuring the resin into the crack we use the vacuum to "pull" the resin into the crack which is gravitationally being fed. As such vacuum injection increases significantly the "filling volume" while at the same time is forcing the resin into concrete pore diffusion. Of particular importance is that concrete during the process operates in compression and not in tension as in the force injection and hence there are no pressure limitations.Classification of injection products The manufacturer/supplier should classify injection materials according to the performance requirements. EN 1504-5 applies the following classification, e.g. U(F) W(1)(1/2)(5/30) D(1)(0), where: U identifies the group followed by a parenthesis where: F signifies force transmitting injection material D signifies ductile injection material S signifies swelling injection material W signifies conditions for crack and environment followed by three parentheses; where: − allowed min thickness of crack, measured in tenths of mm (0.1, 0.2, 0.3, 0.5 and 0.8 mm); − allowed moisture state at which cracks in concrete are injectable with the injection material concerned (1 for dry, 2 for damp, 3 for wet and 4 for water flowing); − minimum and maximum use temperature of the injection. D denotes durability followed by two parentheses: − In the first parenthesis 1 is stated if the bonding is durable at a water-bearing crack and 0 if not (or not documented) − In the second parenthesis 1 is stated if the injection material is compatible with elastomers and 0 if not (or not documented). An injection material, which is, for example, classified as U(F) W(1)(1/2)(5/30) D(1)(0), signifies that: the product is a force transmitting injection material the product is usable for injecting dry as well as damp cracks the product is usable at use temperatures between 5 °C and 30 ° C the bonding of the product is durable when wet the compatibility of the product with elastomers is not documented.5 / 16 EN 1504-5 has classified the three types of injection materials into the following groups: F: force transmitting injection material F1: bonding for pull-off strength above 2MPa for injection (Table E2.1) F2: bonding for pull-off strength above 0.6MPa for filling of cracks (Table E2.1) D: ductile injection material D1: impermeable at 2 105Pa (Table E2.2) D2: impermeable at 7 105Pa for special uses (Table E2.2) S: swelling injection material S1: impermeable at 2 105Pa (Table E2.3) S2: impermeable at 7 105Pa for special uses (Table E2.3).Table 2.1. points towards several ENs and ISOs. Let us check on the EN 12618-2: Adhesion by tensile bond strength after thermal and wet-drying cycles6 / 16 7 / 16 The actual title of the standard is: Products and systems for the protection and repair of concrete structures - Test methods - Part 2: Determination of the adhesion of injection products, with or without thermal cycling - Adhesion by tensile bond strength Part 2 is of particular importance especially when the repair area is exposed to heat. In other words how many heating cycles the repair will last? Requirements like these are quite complex and with a simple market research you will identify that most manufacturers do not comply to EN 1504-5. A typical legend for products in compliance is: 2032-CPD-10.11 EN 1504-5 Concrete injection product U (F1) W (5) (1/2) (8/35) (1) Force transmitting and filling of cracks: 0,5 mm Dry and damp cracks 8 ° to 35 ° C C Adhesion by tensile bond strength: > 2 N/mm2 Adhesion by slant shear strength: monolithic failure Shrinkage: < 3 % Glass transition temperature: ≥ 40 ° C Workability Crack width from 0,5 mm Moisture state of the crack: dry and damp Durability: Pass Corrosion behaviour: deemed to have no corrosion effect Dangerous substances: comply with 5.4 In this realistic example we can identify two problems: Glass transition temperature: ≥ 40 ° C The parameter is truthful and yet should immediately raise the question of whether my structural member temperature can rise higher than 40 degrees. Bear in mind that in such cases the problem is not to the product but to the repair strategy. Hence, the engineering team shall immediately require additional protection against heat levels. i.e. hear resisting mortar or paint. What I am trying to say with the above example is that EN 1504 is not self-standing per se but could lead to additional measures. Failure to identify the problems is predominately the responsibility of the engineering team and to some extend to National Standards. Adhesion by slant shear strength: monolithic failure Monolithic failure in simple terms means that the injection product will not alter the failure mode of an indicative core. The case however is far from simplistic especially when for example injection is used in the case of crazing cracking underneath the deck of a bridge. The problem has to do with the increased strength of the injected concrete (can increase strength up to 70%) and especially the changes in the coefficient of thermal expansion. Hence the engineering team shall evaluate whether potential increases in concrete strength can lead to insufficient reinforcement.8 / 16 Let us move on the Structural cracks due to: Accidental overload Creep Design loads Herein it is important to note that even though EN 1990 does not considered chemical cracks as structural, in Japan and elsewhere do fall in this category. In engineering/design terms we are talking under the principles of tolerable crack width. Crack spacing and depth are unfortunately not parameters to be evaluated even though play a crucial role in the selection of repair method. A simple paper to refresh structural cracking is here: http://www.inti.gob.ar/cirsoc/pdf/estructuras_hormigon/b95081.pdf Crack spacing is explained here: http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/358.pdf and the ACI 224-2R for a more basic understanding here: http://www.bpesol.com/bachphuong/media/images/book/2242r_92540.pdfRepair of active structural Cracks Doweling Anchor doweling consists of drilling holes and anchoring straight steel dowels across the crack. The straight steel is anchored to solid areas of reinforced concrete. Epoxy Injection Epoxy injection is a rigid, full -depth repair where the injected crack will be stronger than the adjacent concrete. If active cracks are injected, expect other cracks to form next to or far away from the repaired crack unless you have sufficient amounts of reinforcing crossing the crack. Adding Reinforcement Cracked reinforced concrete has been successfully repaired by inserting reinforcing bars. Concrete crack repair by this option is done by drilling holes across the crack plane at about 90 degrees. The reinforcing bars are placed across the crack to fill the drilled holes. This technique can be normally employed in slabs 150 mm thick and greater. Post Tensioning and Compression Post tensioning is a good concrete crack repair solution when a major portion of a member must be strengthened or when cracks must be closed. Pre-stressing steel strands or bars or FRP plates are used to apply compressive force to the ailing member. This calls for adequate anchorage for the prestressing steel,and balancing the effect of the tensioning force and eccentricity on stresses in the structure. Anchor stitches can be engineered for post-tension and compression for concrete crack repair.9 / 16 Anchor Stitching In the past, contractors often glued metal “U” clips or pins (called stitching dogs) around the crack. Often times this method was not successful and the fracture reappeared. Concrete crack repair by anchor stitching restores tensile strength across major cracks. Where there is a water problem, the stitch should be properly coated to prevent corrosion. This method involves drilling holes on both sides of the crack and grouting in engineered anchor stitches that spans the crack. The anchor stitch system works by tightening down the anchor wedge to post-tension the stitch, inhibiting the crack from expanding and getting larger. The system is engineered to transfer load away from the fracture, thus creating a longlasting fix. Anchor stitch ing is considered very effective method of concrete crack repair in slabs. From the above it is easy to realise that crack repair is not covered strictly by the EN 1504-5. Doweling Required EN 1504 Principles for Doweling (EN 1504-6, ΕΝ 1504-4, EN 1504-9, ΕΝ 1504-3) Doweling details: http://ntl.bts.gov/lib/43000/43500/43503/DowelLoadGuide.pdf http://www.wbdg.org/ccb/DOD/UFC/ufc_3_270_04.pdf http://www.dot.ca.gov/hq/maint/MTAGRigidChapter8-FullDepthConcreteRepair.pdf http://www.dot.ca.gov/hq/maint/MTAGRigidChapter8-FullDepthConcreteRepair.pdf Prior to explaining anchor stitching it is imperative to distinguish two different types of active cracks. a) those being the result of insufficient reinforcement under static loading b) those being the result of sufficient reinforcement under tension requirements that are dynamically unstable. Unfortunately most engineers will rely on solving and re-solving the basic design and try to evaluate shortcomings. The process is fundamentally wrong and in most cases could lead to over-engineering without necessarily solving the problem. It is perhaps a natural tendency for engineers to tackle these sort of problems. Dynamically unstable cracking is predominately the effect of random loading effects the nature of which is not always clear. This is because, crack propagation and growth in a nonindustrialized material as concrete creates a vast spectrum of mechanical properties, i.e. local fracture toughness, grazing effects and crack coalescence patterns. Perhaps the best way of identifying and classifying active cracks is by examining their width along a portion of length spanning over a length of similar reinforcement density. If within that length the crack appears to exhibit opening and re-opening of its tip, then is a good realization of major random overloading effects. Otherwise a crack without re-opening events is most likely due to a more static type of dynamic loading.10 / 16 In a recent analysis of repair efficiency performed in Europe it was identified that 85% of repairs in active cracking have failed within 5 years after amendment. The report concluded that 60% of failures was due to wrong classification of the active crack as dynamically sensitive or not (failure to examine the re-opening pattern). In all the above cases the chosen method of repair was the epoxy resin injection. Herein the engineering team failed to identify that RIGID epoxy injection will most certainly increase the brittleness of concrete making it more susceptible to further cracking. Worst case scenario was that after the application of the RIGID epoxy injection, the newly developed cracks were significantly more and with a more detrimental pattern compared to the original in terms of resistance of the member. In other words the report concluded that wrongful selection of a repair method can lead to significant degradation and huge increase of repair cost. Crack depth is as vital as its width since it signifies variations in the strain field. Unfortunately most engineers fail to identify the effect that bond-slip between concrete and reinforcement is having on the load transfer pattern. That is when the crack in the concrete enters the effective zone the reinforcement and even the reinforcement itself.A good work explaining the problem is Chapter II in UCB/SEMM90/14, DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF CALIFORNIA BERKELEY, http://www.ce.berkeley.edu/~filippou/Research/Publications/Reports/semm9014.pdf After reading the above work it is clear that when the crack depth has affected the bond-slip between concrete and reinforcement rigid resin injection shall be immediately prohibited. As a matter of fact the damage can be so severe as to promote internal cracking of concrete and hence negating any visual examination. In other words we can create a time bomb. I am calling it a time bomb since, a quality control analysis using ultrasounds instead of indicating the problem will deliver a catastrophic perception of soundness. Bear in mind that micro-cracks appear in the great majority of commercial ultrasounds as noise during the Fast Fourier Analysis. In other words not only we can enhanced the problem instead of providing a cure but at the same time our choice will exclude any ability of NDT to detect before it is too late. The best method to identify whether our crack affects or has the ability to affect our slip/bond mechanism is to take two cores along the crack length. One core close to the middle section and the second close the crack tip. If both cores exhibit the same crack depth we shall immediately stop any further repair actions and seek further analysis. If the crack depth of the core close to the crack tip is significantly less that that in the first core the damage shows a progressive damage pattern that can be considered repairable. Anchor Stitching Is perhaps one of the oldest and most reliable methods in the repair methodology of active structural cracks. The method relies on the post-compression principle of the crack. To some extend it operates under the principle of crack bridging. Two different types exist: Passive Passive anchor stitching is basically a U shape rebar having two right angle ends. These ends are secured into concrete via hole openings and resins. In reality dormant anchors are initially stress free. Loading of the anchors is achieved when the active crack continues its growth. In other words these anchors operate in second order repair mode. Passive stitching shall be used in cases where the depth of the active crack has not reached the reinforcement or the density of cracks reaching the reinforcement only partially affecting the flexural stiffness. The degree of stiffness degradation is shall be evaluated by the structural engineer. Since passive stitching is second order repair method it can not provide recovery of flexural stiffness. Passive stitching works as a brake to further degradation by propagation of the crack.11 / 16 Active Active stitching are based on the principle of controllable pre-compression and hence has the ability to provide recovery. Typical information: http://slabstitch.com/wp-content/uploads/2013/03/SlabStitch_Presentation_3-17-13.pdfLet us move on the Chemical cracks and try to remember the causes. Cement carbonation shrinkagehttp://www.dot.state.fl.us/research-center/Completed_Proj/Summary_SMO/FDOT_BC354_26_rpt.pdf12 / 16 Alkali-aggregate reactions http://www.inti.gob.ar/cirsoc/pdf/tecnologia_hormigon/alkai_aggregate_reation_of_concrete_structures.pdfhttp://www.devb.gov.hk/filemanager/en/content_795/Topics%20on%20Alkali%20Aggregate %20Reaction.pdf and this one from my personal library (with evaluation equations that can be linked to EC-8(3) and secondly to EN 1504) https://dl.dropboxusercontent.com/u/37242532/ASR%20classification.pdf Keep in mind that the most complex issue is the crack density! Concrete cracking due to corrosion of the reinforcement is perhaps one of the most complex areas for repair. Cracking is perhaps the least of our concerns since the dominant degradation mechanism is the dynamic reduction of the effective reinforcement area. Concrete cracking immediately points towards bond loss. The second most important issue is that once concrete has cracked, the ability of concrete to control the electro-chemistry and hence the rate of degradation goes to zero. A cracked concrete has almost zero resistance to carbonation, chloride ingress, or chemical attack effects while at the same time is exposed to the full power of temperature and wetness. It is widely accepted that corrosion cracking should be avoided at any cost. Reasoning steams from the fact that corrosion can easily reach critical areas not always accessible. Typical examples are joints (beam/column), foundation, retaining walls, culverts, etc. In other words corrosion in general should be avoided at any cost. To some extend EN206-1 and EN 1504 both stand under the same principle. Please bear in mind that EN 1504 is Protection !!!!!!!!!!!!!!!!!!!!!! and Repair. The term protection stands also for new structures. In cases where earthquake resistance is of primary concern it is imperative to note that the failure mechanism from rupture moves into sliding. As such the energy dissipated can be as much as 50% less compared to the un-corroded. Prior to any repair, the engineering team should assess the level of tolerable corrosion damage and compare it the one found via on site measurements. The basic approach of modeling corrosion into structure resistance is via the force-deformation relationship of the plastic hinge http://cdn.intechopen.com/pdfs/38195/InTechSeismic_performance_evaluation_of_corroded_reinforced_concrete_structures _by_using_default_and_user_defined_plastic_hinge_properties.pdf The most important thing is the connection between corrosion damage to some measurement that can be indicative. Herein, corrosion rate is generally recognized as such. In the work: http://www.claisse.info/2013%20papers/data/e149.pdf you will identify that corrosion rate is given an S number which is related to corrosion rate. Its a simplistic approach and yet can be used as a first touch.13 / 16 Approaching the repair - The strategy 1. Cement carbonation shrinkage cracking - Large Scale Repair - No Active CorrosionAs the phenomenon is dynamic and hence we might find ourselves in a spiral of continuous repairs it is imperative to evaluate damage rates. Checking the depth of the crack taking a core and identifying, using a concrete Ph pencil, the distribution of Ph drop provides quite accurate first hand results. Carbonation rate can then be easily determined. It is imperative to note that carbonation shrinkage cracking has nothing to do with corrosion and hence we need to exclude such potential either by checking the surface of the rebar or using a Half-Cell. The second step is to identify our repair depth. Is it what we seen (the unsound portion)? A safe limit herein is a Ph value > 11. In other words our repair depth shall not be limited to a depth of Ph>9 but to Ph>11. The pencil again will give us the indication. Phenol spraying cannot do that. Removal can take place by either hydrodemolition or surface chemical expansion. Both prevent damage to steel cage. Mechanical means can also be used but are slow and contain the potential of increasing cracking depth due to vibrations.14 / 16 If the depth under the principle of Ph>11 increases the volume and hence the cost it is rational to introduce chemical re-alkalisation of the concrete. This is achieved by spaying a calcium hydroxide 2gm/litre + sodium nitrite of 10 gm/litre solution. The process is extremely cheap and in most cases results into a Ph increase between 1-2 units. Another method is the use of lithium silicate impregnators but with neutralization prior to any other action. Most engineers for some unknown reason shall chose a repair mortar with strength several orders higher than the original concrete. It is beyond any further explanation that such action will increase the potential of debonding during the mechanical or thermal application of strain. The interface will fail to maintain equilibrium of iso-strain. A semi-empirical equation is: Fc,r ≤ Fc,c + 0.60 D (in mm) whereQ Fc,r is the crushing strength of the repair mortar in MPa, Fc,c is the crushing strength of the existing concrete and D is the repair thickness in mm. Bear in mind that the above equation stands for repair depths up to 45mm. 2. Cement carbonation shrinkage cracking - Small Scale Repair - No Active Corrosion Prepare the surface according to the principles of resin injection. Prior to resin injection, pressurize a calcium hydroxide 2gm/litre + sodium nitrite of 10 gm/litre solution in a close circuit for 10-15 minutes. Do not expect the solution to dry naturally but use compressed air for 30 minutes. Select a resin according to U(F2) W(depends on the measure width) (2/3)(5/30) D(1)(1)Chemical Cracks Alkali-aggregate reactionsEverything you need is in here: http://www.fhwa.dot.gov/pavement/concrete/pubs/hif09004/hif09004.pdf15 / 16 Most repairs are based on lithium hydroxide http://www.fmclithium.com/Portals/FMCLithiumConstruction/Content/Docs/QS-PDS804%20r0.pdfhttp://www.euclidchemical.com/elit/ci_artical.pdf of course after critical analysis !!!!!!!!!!!!!!!!!!!!!! Another good example is in here http://www.pwri.go.jp/eng/ujnr/tc/g/pdf/27/27-4-3_Moriyama.pdf Corrosion cracks will be in a new section since the issue is vast !!!!!!!!This is my end for repair of cracks.16 / 16
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