1. UNIT: 6 STRENGTHENING OF STRUCTURES

2. 1. Jacketing  primarily applicable to the repair of deteriorated columns, piers and piles  Jacketing consists of restoring or increasing the section of an existing member, principally a compression member, by encasement in new concrete  The form for the jacket should be provided with spacers to assure clearance between it and the existing concrete surface

3.  The form may be temporary or permanent and may consist of timber, wrought iron, precast concrete or gauge metal, depending on the purpose and exposure  Timber, Wrought iron Gauge metal and other temporary forms can be used under certain conditions  Filling up the forms can be done by pumping the grout, by using prepacked concrete, by using a tremie, or, for subaqueous works, by dewatering the form and placing the concrete in the dry

4. Concrete Jacketing

6. Steel Jacketing

8. Strengthening of RC Columns by FRP Composites

12. Grouting Grouting is an important and common method for filling  Cracks  Open joints  Honey comb and  interior voids with a cement grout, epoxies or other chemical grout It can also be used for structural strengthening, arresting water movement etc.

13. Grouting  Grouting is the process of placing a material into cavities in concrete or masonry structure for the purpose of increasing the load bearing capacity of a structure, restoring the monolithic nature of a structural member, filling voids around pre cast connections steel base plates, providing fire stops, stopping leakages, placing adhesives and soil stabilization.

14. Grouting  GROUT is a mixture of water, cement and optional material like sand, water reducing admixtures, expansion agents and pozzolans.  The water to cement ratio is around 0.5.  Fine sand is used to avoid segregation.

15. Grouting  It is necessary to select the proper grout material to meet the predefined grouting repair objective and where appropriate,  Quality checks should include taking cores to verify that proper penetration and bond has been achieved.  Wide cracks, mainly in gravity dams and thick concrete walls, can be repaired by filling portland cement grout.

16. Properties of grout  Fluidity  Minimum bleeding and segregation  Low shrinkage  Adequate strength after hardening  No detrimental compounds  Durable

17. Specification for grout  The sand should pass 150 µm IS sieve  The compressive strength of 100 mm cubes of the grout shall not be less than 17 N/mm² at 7 days

18. Grouting procedure  The procedure consists of the following steps 1. The holes are drilled along the cracks and in an around hollow spots. staggered manner at 500 mm to 1000 mm spacing. 2. Clean the concrete along the crack and install grout nipples at intervals across the crack GI pipes with one end threaded or PVC nozzels are used as nipples

19. Grouting procedure  The procedure consists of the following steps 3. All the cracks are cut open to a V shaped groove, cleaned and sealed between the nipples with rich cement paint or mortar, sealant or other type of grout. 4. All the grout holes should be cleaned with water using the same equipment a day before grouting and then grout the whole area.

21. Precautions to be taken during the work 1. To reduce the material waste, only pre-estimated quantities of material for preparing grout should be used, as can be used within 15 minutes of its mixing. 2. Maintain grout quantity record injected into every hole. 3. During the grouting operation in track or close to it, speed restrictions of stop- dead and proceed at 10 kmph shall be imposed at the site of work and same should be continued for a period of 24 hours. 4. The restriction may then be relaxed to non-stop 30 kmph to be continued for a period of another 2 to 3 days. However, speed restrictions indicated above are only guidelines and appropriate speed restriction at each individual site should be considered.

22. Precautions to be taken during the work 5. Immediately after grouting work, all the grouting equipment including the slurry and mixing drums, pipes, nozzles, etc. Should be thoroughly washed so that set cement does not damage the equipment. 6. After the work has been completed, it should be inspected thoroughly and should be kept under observation for a period of 6 months to 12 months for its b ehaviour after grouting. 7. Observe and inspect after grout behaviour thoroughly for a period of 6 to 12 months.

23. Grouting types and their uses  Cement grouting - mass placement - structural(high strength) - caustic environments - high temperatures  Chemical grouting - control seepage - shut- off seepage - soil stabilization

24. Cement grouting  It contains a grout, which is, a mixture of cementitious material normally Portland cement based and water, with or without fine aggregate or admixtures, proportioned to produce a pumpable consistency without excessive seggregation of the constituents, depending on the width of the crack. It can be injected into an opening from the surface of a structure or through holes drilled to intersect the opening in the interior.

25. Cement grouting  Wide cracks, particularly in mass concrete abutments / piers and masonry substructures can be repaired by filling with portland cement grout.  Thismethod is effective in sealing the crack in concrete, but it will not structurally bond cracked sections.

26. Applications of cement grouting:  i) When cracks are dormant  ii) Cracks are active but cause of cracking has been determined and remedial action has been taken.  iii) When honeycombing is present in concrete structures.  iv) When masonry is hollow.  v) When deep leached mortar joints are present.

27. Materials proportion and pressure of grouting in cracks:  Ordinary Portland cement to IS:269, sand and water are requi red.  Admixtures to impart nonshrinkable properties and to improve flowability of grout may be added.  The method of using admixture may be as per the manufacturer’s recommendations.  The water-cement ratio (by weight) for the grout should be 0.4 to 0.5, the lower ratio being used when crack width exceeds 0.5mm.  In a typical mix proportion for grout, 20 litres of water to be mixed with 50 kg of cement along with 225 gms of nonshrink admixture, such as conbex 100, should be used.  The grouting pressure should be 2 to 4 kg/cm 2

28. Chemical Grouting  Chemical grouting is the one of the most effective solutions of repairing cracks permanently.  These are basically grouts made from different grades of epoxies, sodium silicate, polysters acrylamides, polyurethanes ( i.e. flexible, semi-rigid or rigid) by adding some inert fillers to enhance specific physical properties such as consistency, heat generation, expandability, flexibility and resilience etc. depending upon the application requirement.

29. Chemical Grouting  Chemical grouting have basically two variants Hydrophillic and Hydrophobic These are capable of sealing leaks in all concrete structures Hydrophillic grouts, has high affinity for water. Hence when they are introduced into cracked concrete, they absorb water to expand in volumes and makes its way into pores of wet concrete. Because of its inherent flexibility and resilience after curing, it allows movement in structure resisting propagation of crack or damaging seal/bond with substrate.

30. Chemical Grouting  Hydrophobic chemical grouts have pre blended accelerators in the compound/resin which expands aggressively on activation  When they are introduced into concrete, because of their water repellent properties, they prevent water ingress forming a water tight seal within the structure.

31. Applications of Chemical Grouting Chemical grout finds usage of  Water cut-off  Soil Stabilization  Crack Sealing (moving and non-moving)  Membrane grouting  Manhole Sealing  Earth Retention  Ground water Control  Sink hole Stabilization