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Concepts of Shotcrete Technology
- 1. CONCEPTS OF SHOTCRETE TECHNOLGY Presented By: NADEEM AKHTAR | 17CEB207 |GI6252
- 2. CONTENT 01 Introduction 02 Applications 03 Classification 04 Comparison with conventional concrete 05 Conclusion
- 3. Introduction
- 4. Shotcrete Shotcrete is a mortar or high performance concrete conveyed through a hose and pneumatically projected at high velocity onto a backing surface. It is the force of this spraying action that leads to compaction of the concrete or mortar which then forms layers of concrete to the required thickness .
- 5. Composition High performance concrete- Shotcrete Water Potable water should be used. In this is not available, the proposed water source should be tested. . Plasticizers & Admixtures The use of admixtures in shotcrete is not the same as in conventional concrete because of shotcrete equipment Limitations. Alkali free accelerators are preferred. Portland Cement Cement requirements for shotcrete are similar to those for conventional concrete Aggregate Lightweight aggregate shotcrete is most practical since moisture and aggregate contact is initiated at the nozzle, the severe workability reductions common in conventional lightweight 2 43 1
- 6. Properties Strength In terms of compressive and flexural strength, shotcrete can produce strength generally equivalent to conventional concrete. Compressive strengths of between 30 and 60 N/mm² is generally achievable. Bond Strength Bond strength with other materials is reported to be generally higher than can be achieved with conventional concrete. Shrinkage Drying shrinkage is most influenced by the water content of the mixture. Typical values of unrestrained shrinkage range from 600 to 1,000 millionths. Shrinkage is reduced in coarse aggregate shotcrete and increased in shotcrete without coarse aggregate Toughness The addition of fibers to shotcrete can result in a product displaying significant load carrying capability after the occurrence of the first crack.
- 8. Classification DRY MIX SHOTCRETE WET MIX CONCRETE 01 Pre blended, dry or semi-dampened materials are placed into shotcrete equipment and metered into a hose All ingredients, including water, are thoroughly mixed an introduced into the shotcrete equipment 02 Compressed air conveys materials at high velocity to the nozzle where the water is added Wet material is pumped to the nozzle where compresse air is introduced 03 Then the material is consolidated on receiving surface by high impact velocity. Mostly wet-process shotcreting is done with premixed mortar or small aggregate concrete.
- 9. Fig.1. Simplified sketch of a typical dry mix shotcrete system
- 10. Fig.2. Simplified sketch of a typical wet mix shotcrete machine
- 11. Dry Vs Wet Process Bond Strength Bond strengths of new shotcrete to existing materials are generally higher with dry-mix shotcrete than with wet-mix shotcrete. Both shotcrete mixtures often provide significantly higher bond strengths to existing materials than does conventional concrete. 01 02 03 Rate Typically, dry-mix shotcrete is applied at a much slower rate than wet-mix shotcrete. Rebound Rebound is the shotcrete material that 'bounces' off the shooting surface. Rebound for conventional dry-mix shotcrete, in the best of conditions, canbe expected to be at least 20% of the total material passed through the nozzle. Wet-mix shotcrete rebounds somewhat less than dry-mix shotcrete.
- 12. Applications
- 13. Applications • Restoration and repairing of old building and fire damaged structures. • Stabilized rock slopes and mining purposes. • Waterproofing walls and marine structures. • Construction of curved or folded sections like tunnels, canals, reservoirs, or swimming pools and pre stressed tanks
- 14. Fig.3. Rehabilitation of subway tunnels Fig.4. Construction of domed roof
- 16. Shotcrete vs Conventional Concrete Unlike Conventional concrete which is first placed and then compacted in the second operation, shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. Shotcrete is more dense, homogeneous, strong and waterproof than is possible to obtain any other process Shotcrete is not placed or contained by forms. It can be impacted onto any type or shape of surface, including vertical or overhead areas. Shotcrete forms an excellent bond with substrate and can given a variety of surface finishes.. 01 02 03 04
- 17. Shotcrete vs Conventional Concrete The primary disadvantage of shotcrete compared to poured concrete is the amount of time that it takes when used for large foundations, structural piers and other structures with large cross sectional area. Production cost of shotcrete is very high. Wastage of concrete is very high in case of shotcreting. 05 06 07
- 18. Conclusion
- 19. The use of Shotcrete to build new concrete structures as well as to restore and repair existing structures is well known and documented and it is perhapsthe most diverse method available forconcrete construction. The use of this innovative technology is increasing day by day and procedures for its properperformance are well developed and high quality work is regularly obtained.This technology may be expensive atsome scale as compared to conventionalconcrete, but it is rather important to use recent technology, which is innovative in the field of engineering and proves to be efficient and quick..
- 21. Thank you