PROCEDIMIENTOS PARA APELAR DECISIONES Y PRESENTACIÓN DE RECLAMACIONES
VISITE EL SITIO WEB DE BCBSTX PARA OBTENER LOS FORMULARIOS DE RECLAMACIÓN DEL ASEGURADO PRINCIPAL Y OTRA INFORMACIÓN ÚTIL
a) Shotcrete is mortar or concrete conveyed through a hose and pneumatically impinged at high velocity on to the surface to be treated. The force of the jet impinging on the surface compacts the material. Generally a relatively dry mixture is used so that it supports itself without sagging or sloughing even for vertical and overhead applications. This process is also known as Guniting.
b) Shotcrete or gunite is suitable for repairing spalled concrete surface as well as for strengthening weathered stone or brick masonry. For most applications mortar applied by the dry process (guniting) is adequate. With concrete (shotcrete) the wet process is adopted. In both the cases reinforcement in the form of wire 3mm dia, wire fabric or steel bars upto 16mm dia may be used, as necessary.
c) Equipment required (Annexure 2/9)
i) Guniting machine complying requirements given in IS : 6433. ii) Air Compressor with a capacity of 10 cum/per minute and
which can develop a pressure of upto 7 kg/cm2.
iii) Placing nozzle with hose. d) Specification of materials used :
i) Ordinary Portland cement to IS : 269. (Other special cements can be used for special applications requiring higher strength or early setting)
ii) Sand conforming to IS : 383 and graded evenly from fine to coarse as per Zone II and III with a nominal max. size of 6mm.
iii) Coarse aggregate, when used, should conform to IS : 383, with a maximum nominal size of 10 to 12.5 mm.
iv) water conforming to IS : 456. v) Admixture as recommended.
vi) Reinforcing bars, as per IS : 432 or welded wire fabric conforming to IS : 1566 may be used as required.
vii) Water cement ratio 0.35 to 0.50 by weight.
e) Preparation of surface : All weathered or deteriorated material should be removed until the surface exposed is sound and properly shaped to receive the gunite (Shotcrete). The surface should be cleaned of all loose and foreign materials with an air/water jet. If the joint mortar is weak, the joint should be raked to about 10mm depth and all loose, dry mortar scraped out. Exposed reinforcement should be cleaned free of rust, scale etc. and given a coat of neat cement or any other anti-corrosive material. Porous surface should be kept damp for several hours before guniting.
f) Form work : The forms where required shall be plywood or other suitable material set true to line and dimension. They should be adequately braced and constructed so as to permit the escape of air and rebound during the guniting operation (particularly in the case of thick members).
g) Reinforcement : Depending on the thickness and nature of the work; reinforcement may consist of either round bars, or welded wire fabric 3mm diameter. Sufficient clearance should be provided around the reinforcement. The minimum clearance between the reinforcement and form or other back up material may vary between 12mm for the mortar mix and wire fabric reinforcement to 50mm for the concrete mix and 16mm dia reinforcing bars. However, the minimum cover for reinforcement shall be as per IS : 456. The minimum wire mesh spacing should be 50 mm by 50 mm. Clear spacing between bars should be atleast 65 mm.
For repair work, the reinforcement should be fixed to existing masonry by wiring to nails driven into the masonry and rigidly secured.
h) Preparing the gunite : The cement and sand in specified proportion are premixed and placed in the feeding chamber; the same is then fed into the working chamber through a cone valve controlled from outside. The mixture, after passing through an agitator is then carried in suspension by compressed air through the delivery hose to the nozzle. The mixing time shall not be less than one minute. As the material passes through the nozzle body, it is hydrated with water introduced in the form of a fine needle spray. The amount of water added is adjusted so that the in-place gunite/shotcrete is adequately compacted and it neither sags nor shows excessive rebound. The mix used generally ranges from 1:3 to 1:4.5 and moisture content of the mixture before placing in the machine should be within 3 to 6%.
i) Uniform air pressure is maintained at the nozzle outlet. For lengths of hose upto 30m, the air pressure is 3kg/cm2 or more. For longer lengths the pressure is increased by 0.35kg/cm2 for each additional 15m of hose and by 0.35kg/cm2 for each staging of 7.5m that the nozzle is raised above the gun.
j) Placing : The total thickness of gunite required should be built up in a number of layers with an interval of about 4 hours. Each layer is built up by making several passes or loops of the nozzle over the working area. The distance of the nozzle from the work, usually between 0.5 and 1.5m, should be such as to give the best results. Particular care should be taken when gunning through and encasing reinforcing bars. (For walls, columns and beams, the application should begin at the bottom). In guniting slabs, the nozzle should be held at a slight angle so that the rebound is blown on to the completed portion.
k) Rebound : The rebound is mortar or concrete which bounces off the surface during the application. Rebound should not be worked back into the construction and should be rejected.
l) Before laying additional layer, the first layer should be allowed to take its initial set. Then all laitance, loose material and rebound should be removed. The surface should be tested with a hammer for drummy areas which should be carefully cut out and replaced with the succeeding layer.
m) Curing : The surfaces should be kept continuously wet for at least 7 days.
n) Shotcreting by the wet process requires special equipment and can be used for building up thick layer. For further details reference can be made to IS : 9012 "Recommended Practice for shotcreting''.