Las condiciones del habitar

General

1. Structural and non-structural repair covers repairs with mortars and concretes, possibly used in conjunction with other products and systems, to restore and/or to replace defective concrete and to protect reinforcement, necessary to extend the service life of a concrete structure exhibiting deterioration. The fields of application covered are in accordance with BS EN 1504-9 as follows:

a. Principle 3 - Concrete restoration

• Method 3.1 Applying mortar by hand

• Method 3.2 Recasting with concrete

• Method 3.3 Spraying mortar or concrete b. Principle 4 - Structural strengthening

• Method 4.4 Adding mortar or concrete c. Principle 7 - Preserving or restoring passivity

• Method 7.1 Increasing cover to reinforcement with mortar or concrete

• Method 7.2 Replacing contaminated concrete

2. Repair mortar should generally be used where repairs are less than one square metre in area, or repair depth is less than 30mm, or as otherwise instructed by the Overseeing Organisation.

3. Proprietary high-flow repair concrete should generally be used for repairs greater than one square meter in area and repair depth greater than 30mm or as otherwise instructed by the Overseeing Organisation.

Materials

4. Repair products should have similar properties to the original concrete and be either class R3 or R4 for structural repairs and class R1 or R2 for non-structural as defined in BS EN 1504-3.

5. If water for the Works is not available from a Public Utility Undertaking supply, the Overseeing Organisation's approval shall be obtained regarding the source of supply and manner of its use. When required by the Overseeing Organisation the

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Appendix 1 - Specification - October 2012 Contractor shall arrange for tests of the water to be carried out in accordance with

BS EN 1008. Water from the sea or tidal rivers shall not be used. Recasting with concrete or mortar

6. All formwork, where required, should have an inlet system incorporated into the shutter to allow the concrete to be introduced via an external pipe, either pumped or poured with a suitable head.

Spraying mortar or concrete

7. A detailed method statement shall be submitted to the Overseeing Organisation for approval. The following paragraphs offer an acceptable approach but are not exhaustive.

8. The outline of the finished sprayed concrete shall be defined by screed boards, guide wires or other means accepted by the Overseeing Organisation.

9. Guide wires shall be installed tight and true to line and in such a manner that they may be easily tightened.

10. Sprayed concrete shall be mixed in a batch type mixer complying with the requirements of BS 1305 except that the water shall be delivered direct to the nozzle. The delivery equipment shall be capable of delivering a continuous even stream of uniformly mixed material to the nozzle. Water supply at the nozzle shall be maintained at a uniform pressure sufficient to ensure adequate hydration at all times. The delivery equipment and nozzle shall be thoroughly cleaned and inspected at the end of each day and parts replaced as required.

11. The temperature of water and cement when added to the mix shall not exceed 60°C and 65°C respectively.

12. Where shown on the Service or Scheme Instruction reinforcement fixed to prepared surfaces shall consist of 50mm x 50mm x 2.36 kg/m2

13. Sprayed concrete shall emerge from the nozzle in a steady uninterrupted flow and an uninterrupted supply of compressed air shall be provided to maintain adequate nozzle velocity. Should the flow become intermittent the nozzle shall be directed away from the work until the flow again becomes uniform.

welded steel fabric. It shall be carefully bent to follow the shape of the members, and held in position using concrete anchors spaced at not less than two per square metre. The fabric shall be spaced at not less than 25mm from the surface of the existing concrete. Mesh should be lapped one and one half squares and reinforcement shall be staggered and spaced to allow complete encasement by the concrete. A minimum finished cover of 40mm shall be provided to the steel reinforcing fabric, unless agreed otherwise.

14. Sprayed concrete shall be applied under sufficient pressure so as to give a dense and homogeneous covering to the surface in one or more layers of a thickness

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Appendix 1 - Specification - October 2012 compatible with the mix design, constituents, position of reinforcement, and plane of

application to ensure the placed concrete does not slump or sag.

15. Adequate precautions shall be taken to ensure that sprayed concrete rebound is not incorporated in the finished work and that any previously deposited hardened rebound which may prevent a proper bond or encasement is removed from reinforcement.

16. Adequate protection shall be given to the nozzle and application surface during high winds.

17. Finishing of the surface of the final coat shall be carried out as soon as practicable after spray application. A Class U3 finish shall be achieved in accordance with Clause 1708.4.

18. The nozzleman shall hold a current certificate of competence in spray concrete, issued by the Sprayed Concrete Association.

19. The gun and nozzle shall be electrically earthed.

20. Construction joints in sprayed concrete shall be tapered at approximately 30 degrees from a plane perpendicular to the finished surface or cut back square to the reinforcement and then tapered at 30 degrees, unless otherwise specified by the Overseeing Organisation. The construction joint shall be thoroughly cleaned, all laitance and loose material removed and the surface wetted using a strong blast of air and water, prior to the placement of the adjacent sprayed concrete.

21. Freshly sprayed concrete shall be protected from rain or water until the surface is sufficiently hard to resist damage.

22. Immediately after placing and for 14 days thereafter sprayed concrete shall be protected against harmful effects of weather including rain, rapid temperature changes, frost and from drying out. The methods of protection shall in all cases be subject to the acceptance of the Overseeing Organisation. Curing membranes shall not be used.

23. Alternatively subject to the acceptance of the Overseeing Organisation impregnation in accordance with Clause 1709 may be carried out after 14 days.

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Appendix 1 - Specification - October 2012