Foundation: The methods are explained in section 6.5.19

REHABILITATION AND RETROFITTING METHODS

B. Chloride Removal

6.7 Repair/Rehabilitation Strategies:

6.7.7 Foundation: The methods are explained in section 6.5.19

6.7.6 Protection: Protective measures for preservation and extending the service life of the structure.

They are given below.

l Water Proofing

l Depressed Floor Treatment (The step by step sequence of stages for one of the alternatives of treatments have been given in Annexure-6.2)

l Terrace Treatment(The step by step sequence of stages for treatment of Khurrahs at terrace have been given in Annexure-6.3)

l Sun Shade

l Surface Treatment

l Creation of Barrier

6.7.7 Foundation: The methods are explained in section 6.5.19

6.7.8 Base Isolation: Seismic forces are transmitted to the structure due to ground motion caused by the seismic activity. In this method, structure is isolated from ground motion by inserting elastomeric isolators. Most of the energy input from the earth due to seismic activity is absorbed due to isolators movement and thus the building is protected from damage. This method is of significance where it is not possible to make structural/

architectural alterations in the superstructure heritage value. The essential requirement of this method is availability of sufficient space all-round the building for movement of the superstructure and high cost.

✯ ✯ ✯

SUGGESTEDFURTHERREADING MATERIALAND REFERENCES

1. REMR Technical Note CS-MR-4.5 Suppl 6 (1994) of Repair-Evaluation-Maintenance-Rehabilitation

2. Jerry L Boyd, Gajanan M Sabnis and Josua A Boyd ‘Application of Vacuum Technology to Restore Concrete Structures’ Indian Concrete Journal, Jan, 2001;

Vol 75, No 1 pp 35-40

3. Manjrekar, S K, ‘Polymer Modified Concrete/Mortars for Repair and Rehabilitation Works’ Indian Concrete Journal, Jan, 1995, Vol 69, No 1 pp 41-44 4. Internet site of ‘Civil Engineering Projects, School of Engineering, University of

Adelaide, Australia’

5. Assessment & Repair of concrete Structural methods, problems choice & new development by C.Keshva Murthy, CKM Consultants Pvt. Ltd., 47, Beach Road, 03-03 Khanchin Building, Singapore 0718

6. REMR (Repair, Evaluation, maintenance Rehabilitation Programme ) Technical note NCS – MR – 9.4 prepared - Aggregate concrete

7. REMR Technical note CSMR- 4 spall repair.

8. Technical information service on “Repair Rehabilitation of RCC structures”

Circular no. 1 issued vide CDO/SE(D)-II/Information series/253 dt. 20/12/1996.

9. Fig. 4- Recent advances in Repair and Rehabilitation of RCC Structures with non metallic fibres.

10. Shotcrete Guides and Specifications by D.K. Morgan. Shotcrete magazine fall 2000. (fibre reinforced shotcreted)

11. Recommendations for maintenance of concrete structures (Draft Japan Society of Civil Engineers (JSCE) copy from the Concrete Library International no. 29 published by JSCE June 1999.

Appendix 6.1

Structural Repairs to RCC Columns, Beams and Slabs

CASE-I: Crack Repair and Protective Coating for less damaged structural members like minor/hair cracks or spalling from beams and columns, where carbonation depth in cover concrete has not reached reinforcement level.

Caution: It may be stated that recommended measures are cosmetic measures.

The distress may continue to take place even after repairs, if the protective coating, provided as per step no. 7 below, is damaged or ineffective.

Step-1: Measures shall be taken to ensure that no seepage/leakage etc. affects the RCC columns/beams.

Step-2: The plaster/finishes over the RCC columns/beams shall be removed as per relevant item in sub head 2 of Chapter 8 and relevant specifications in Chapter 9. The concrete surface exposed, spalled and loose cover concrete removed, cracks marked after close examination on the surface of concrete. Whereas the good surface of concrete shall be hacked and roughened for receiving the repair as per relevant item in sub heads 4 &

5 of Chapter 8 and relevant specifications in Chapter 9.

Step-3: Wherever loose/spalled cover concrete is removed, it shall be repaired with polymer modified cement mortar, done up in layers as per nomenclature of items in sub-heads 4 & 5 of Chapter 8 and relevant specifications in Chapter 9.

Step-4: All cracks in RCC columns/beams wherever noticed shall be sealed by injection grouting through nipples fixed along the crack line as per nomenclature of items in sub head 3 of Chapter 8 and relevant specifications in Chapter 9.

Step-5: Over the prepared surface of RCC columns/beams, 6 mm thick 1:3 cement sand plaster shall be applied with polymer modified cement

Fig. 6.15 Crack Sealing with Resin Injection Technique

FOLLOWED BY WATER-JETTED CLEANING CHASE A V-GROOVE ALONG THE CRACKS FAST-SETTING POLYESTER RESIN PUTTY

ENTRY PORT WITH ONE-WAY NIPPLE PRE-DRILLED INJECTION POINT

slurry bond coat (item no. 3.2) within 24 hours of injection grouting as per preceding para.

Step-6: Cement plaster shall be cured strictly as per the nomenclature and of items in subhead 6 of Chapter 8 and relevant specifications in Chapter 9.

Step-7: After RCC columns/beams are cured and completely dried, a protective coating shall be applied over it for protecting the reinforcement and concrete against environmental aggressive chemicals in accordance with items of sub-head 8 in Chapter 8 and relevant specifications in Chapter 9

CASE-II: Repair to Damaged Columns/Beams/Slabs where carbonation depth of concrete has reached reinforcement level:

(i) Shotcreting

Stepwise sequence of methodology to be adopted is given hereunder Step-1: Prop and support the structure in order to relieve the RCC column of

stresses due to load coming over it as per the nomenclature of items in subhead 1 of Chapter 8 and relevant specifications in Chapter 9.

Step-2: Remove plaster and finishes all around the distressed RCC columns.

Thereafter remove loose, cracked and spalled concrete to expose the rusted reinforcement as per the nomenclature and of items in subhead 2 of Chapter 8 and relevant specifications in Chapter 9.

Step-3 Remove concrete all around the reinforcement in order to get average 25 mm air gap all around i/c behind the reinforcement & clean the reinforcement of concrete and rust by appropriate methods as per nomenclature of items in subhead 2 of Chapter 8 and relevant specifications in Chapter 9.

Step-4 Put additional reinforcement wherever the reinforcement diameter has been reduced by more than 15% with the necessary overlap or welding with the existing reinforcement as per the nomenclature and of items in subhead 5 of Chapter 8 and relevant specifications in Chapter 9.

Step-5: Fix shear key bars of appropriate diameter at specified spacings in both directions over the surface to be covered with repair materials as per the nomenclature of items in subhead 2 of Chapter 8 and relevant specifications in Chapter 9.

Step-6 Apply appropriate passivating and bond coat over the reinforcement and prepared RCC surface as per the nomenclature of items in subhead 4 of Chapter 8 and relevant specifications in Chapter 9. Shotcrete the RCC column within the time limit specified as pot life of the epoxy or tacking period of slurry as per the nomenclature and of items in subhead 4 of Chapter 8 and relevant specifications in Chapter 9. The necessary shuttering as specified in specifications of shotcreting shall be used for ensuing the desired thickness and shape of the columns.

Step-7: 6 mm thick finishing coat with cement sand plaster 1:3(1cement:3fine sand) (of least possible thickness) if felt necessary, shall be applied within 48 hours of application of shotcreted repair.

Step-8 Wet curing shall be done over the finished surface of the shotcrete for a minimum period of 7 days as per the nomenclature and of items in subhead 6 of Chapter 8 and relevant specifications in Chapter 9.

Step-9: After RCC columns/beams are cured and completely dried, a protective coating shall be applied over it for protecting the reinforcement and concrete as per the nomenclature and of items in subhead 8 of Chapter 8 and relevant specifications in Chapter 9.

(ii) RCC Jacketting

Step no.1 to 5, same as in (i) above

Step-6: Appropriate passivating and bond coat shall be applied over the prepared surface as per the nomenclature and of items in subhead 4 of Chapter 8 and relevant specifications in Chapter 9.

Step-7: Within the tacky period of bond coat, shuttering and concreting shall be done with specified grade of concrete with minimum cement content as specified and water cement ratio not more than 0.45. The consistency of this concrete shall be flowing and self-compacting which shall be achieved by using super plasticiser. The thickness of RCC jacket shall be as specified.

Step-8: Follow steps no. 6 to 8 as in (i) above.

Case-III: Stages for repairs to RCC Slabs, where carbonation depth has reached reinforcement level.

(i) Repair with polymer modified cement mortar (For patch repairs or repairs over smaller magnitude)

Stepwise sequence of methodology to be adopted is given hereunder

Step-1: Propping and supporting of RCC slab under distress shall be as per the nomenclature of items in subhead 1 of Chapter 8 and relevant specifications in Chapter 9.

Step-2: All loose and spalled cover concrete shall be removed including finishing plaster wherever found loose by tapping as per the nomenclature and of items in subhead 2 of Chapter 8 and relevant specifications in Chapter 9.

Step-3: The rusted reinforcement shall be cleaned of concrete preferably by using sand blasting to give a minimum 15 mm clear air gap all around including behind the reinforcement as per the nomenclature of items in subhead 2 of Chapter 8 and relevant specifications in Chapter 9.

Step-4: Additional reinforcement wherever necessary shall be added and tied to the RCC slab with necessary binding wires and nails.

Step-6: The rusted reinforcement shall be cleaned of rust and passivated and applied bond coating as per the nomenclature and of items in subhead 4 of Chapter 8 and relevant specifications in Chapter 9.

Step-7: The prepared concrete surface shall be covered with appropriate mix of polymer modified cement sand mortar in layers including behind reinforcement over a bond coat with polymer modified cement slurry as per the nomenclature of items in subhead 4 & 5 of Chapter 8 and relevant specifications in Chapter 9. The mortar cover thickness shall be not less than 15 mm over the reinforcement. The maximum thickness shall be not more than 30 mm with each layer not exceeding 10 mm.

Step-8: Water curing shall be carried out for a minimum period of 7 days as per the nomenclature and of items in subhead 6 of Chapter 8 and relevant specifications in Chapter 9.

Step-9: Necessary white washing /painting of the surface may be carried out after the curing period is over and the surface gets dried up.

Fig. 6.16 Typical repair procedure for patch repair and corrosion damaged concrete

PROTECTIVE SURFACE FINISH FOLLOWED WITH DECORATIVE FINISH PARENT CONCRETE REQUIRED OVER-CUT BEYOND REINFORCEMENT

BAR FOR CONCRETE COVER TO REINFORCEMENT CUT AT RIGHT-ANGLE WITH THE

HELP OF DISC TYPE MECHANICAL CUTTER

REMOVE THE CORROSION PRODUCT FROM REINFORCING BARS UNTIL THEY SHINE REMOVE ALL DEFECTIVE CONCRETE AND EXPOSE CORRODED REINFORCING BARS TO THEIR FULL CIRCUMFERENCE

APPLY PROTECTIVE COATING AND FOLLOW UP WITH DECORATIVE PAINTING

(ii) Shotcreting: (For repair jobs covering large areas and/ or large magnitude) Stepwise sequence of methodology to be adopted is given hereunder

Step-1: Step no. 1 to 6 shall be same as in case of no. (i) above.

Step-7: Shotcreting with average thickness of 50 mm shall be done within the tacking period of epoxy bond coat to be applied over the prepared surface of concrete.

Step-8: Finishing plaster if necessary, may be provided within 48 hours of shotcreting without allowing the RCC slab to become dry during the intervening period.

Step-9: Water curing shall be carried out for a minimum period of 7 days as per the nomenclature and of items in subhead 6 of Chapter 8 and relevant specifications in Chapter 9.

Fig. 6.17 Typical Column repair by Guniting

a. REMOVE COVER CONCRETE

STAGE 3

STAGE 1 STAGE 2

(B) COLUMN REPAIR

(A) BEAM REPAIR (TIMBER FORM WORK REMOVED) SHUTTER FINISHED SURFACE

PREVIOUSLY GUNITE/

SHORTCRETE SURFACE GUNITE / SHORTCRETE

FIRST STAGE

CROSS FRAMING TIMBER FORM WORK AND

SECOND STAGE GUNITE / SHORTCRETE FIRST STAGE

GUNITE / SHORTCRETE

GUNITE / SHORTCRETE SHORTCRETE

CROSS FRAMING

SECOND STAGE

APPLY FLASH COAT TO FULL AREA c. SPRAY REMAINING SIDES AND b. FIXED SCREEDS AND SPRAY TWO SIDES

FINISHED GUNITE/

FIRST STAGE

TIMBER FORM WORK AND SHUTTER FINISHED SURFACE (TIMBER FORM WORK REMOVED)

Appendix 6.2

TREATMENT OF DEPRESSED FLOOR IN TOILETS/KITCHEN

In document RCC Rehab-1SOR & Spec (Page 174-181)