What is Shotcrete or Gunite or Spray concrete
Shotcrete and Gunite are one and the same. Indian and American standards term this concrete as shotcrete. European standards term the same as sprayed concrete. IS 9012 defines shotcrete as “mortar or concrete (conveyed through a hose) and pneumatically projected at high velocity onto a surface.
Purpose of this Method Statement
This method statement describes the procedure and resources required to do the work. Use any other resources and methods not referred to in this method statement to suit the project requirement. Always execute the work safely complying with the required standard.
This method statement summarizes suggested method of executing works safely within any constraints. This method statement offers advice and guidance to the personnel involved in this activity to:
a) Carry works in a manner that’s safe at all times;
b) Know the hazards involved in the activity;
c) Ensure controls to steer clear of hazard exposure are in place.
The sequence of activities is a repetitive process and many aspects are common to distinct sites. Include with detail, any crucial aspects specific to the project. Always follow the approved checklists prior to the start of the activity.
What this Method Statement covers
The scope of this document covers:
- Safe work method for carrying the work
- Work procedure
- Materials, equipment, and tools needed to lay shotcrete or gunite
- Applicable standards throughout the execution of the project
IS : 9012: Indian Standard Recommended Practice for Shotcreting
Materials for Shotcrete
- Cement: Portland slag cement or Portland pozzolana cement
- Fine aggregate: Zone II and Zone III grading of IS 383-1970
- Coarse aggregate: 10 mm size
- Water: A water cement ratio of 0.4 to 0.5
- Reinforcement: Reinforcing bars or welded wire fabric
Equipment & Tools for shotcrete
- Batching and mixing equipment
- Delivery equipment like Shotcrete gun, nozzle, pump
- Air supply arrangement
- Water supply arrangement
Health, Safety, and Environment
Execute all activities with due regard to Health, Safety & Environment of all the employees and third parties.
- Perform safety checks on all pressurized lines before usage
- Shotcrete spray from the nozzle is potentially hazardous if not handled cautiously
- Maintain adequate visibility at all times by providing appropriate lighting
- Safety clamp all material hoses and airlines
- The nozzle should not be casually put down until pressure is offline.
- Review Material Safety Data Sheets (MSDS) for all materials in use.
- Carry the work under the strict guidance and supervision
Personal Protective Equipment (PPE)
Below are the suggested PPE for shotcrete works:
Find more details about Personal Protective Equipment (PPE) here.
- Compressive strength: cubes or cores shall be taken from the panel of size 75 x 75 cm. Maintain a thickness same as that of the structure but not less than 7.5cm. Alternatively, cores can be taken having a minimum diameter of 7.5 cm and a length-diameter ratio of at least 1.
- Other materials: Same testing requirements as cast-in-situ concrete testing
- Slump tests
- Maintenance of Batch records with details of contents in each batch
Procedure for shotcrete or gunite
- Thoroughly clean all surfaces to receive shotcrete by removing loose materials and dust and pressure washing. Dampen the surface to a saturated surface dry condition.
- Fix wire mesh to the concrete surface. The steel wire mesh has to be placed in position keeping the mesh within 10-15 mm from the surface. Suitable fixing pins are to be inserted to keep the mesh in proper position and to ensure that the weld mesh is not disturbed during concrete spray.
- Prepare a cement/water mix. Pour this mix into Pump hose for lubrication before starting to pump the production mixture.
- When the pumped mixture reaches the nozzle, turn on the compressed air.
- Apply shotcrete evenly to targeted surfaces. Built-up the desired thickness of shotcrete in layers of about 30 mm thick each. The presence of voids can be found by hollow hammering sound after the shotcrete has attained strength after around 3 days.
- Clean all discharge lines with a through water flush
Shotcrete or gunite item description for repair work
Apply shotcrete including removal of defective concrete; cleaning the surface thoroughly; designing the mix with water cement ratio ranging from 0.35 to 0.50, density of gunite not less than 2000 kg/cum, strength not less than 25 Mpa; preparing the mix comprising of cement, sand, coarse aggregates, water and quick setting compound in the specified proportions; applying the shotcrete mixture mechanically with compressed air under pressure;