Placing of concrete

How conventional concrete is placed on site. Different equipment used in placing of concrete.

1. PROPERTIES OF CONCRETE Lecture No.03 UNIVERSITY OF ENGINEERING & TECHNOLOGY, TAXILA

2. Lecture Contents Placing of Concrete Shotcrete Pneumatic guns Tremie Choosing the Best Method for Placing of Concrete

3. shotcrete What is shotcrete? The term “shotcrete“ is a derivate of two English words “shoot“ and “concrete“. The term “shotcrete“ refers to pneumatic high pressure spraying of concrete or mortar using a spraying jet onto a surface.

4. Shotcrete

5. Shotcrete Shotcrete is concrete (or sometimes mortar) conveyed through a pipe (pneumatic guns) and pneumatically projected at high velocity onto a surface, as a construction technique. Pneumatic guns Pneumatic guns are used where concrete is to be placed in difficult locations and where thin sections and large areas are needed

6. Shotcrete Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted onto any type or shape of surface, including vertical or overhead areas.

7. shotcrete History of shotcrete Shotcrete was invented in the early 1900s by an American citizen. He used the method of blowing dry material out of a pipe with compressed air and then wetting this material as it was released. This was later used to patch weak parts in old buildings.

8. shotcrete History of shotcrete In 1911, his invention was named as "cement gun", because of the equipment used, and this process was named as guniting . In the 1960s, the alternative method for gunning by the dry method was devised with the development of the rotary gun, with an open hopper that could be fed continuously.

9. shotcrete Gunite (dry process) Gunite is a process involving a “mixture of Portland cement and sand thoroughly mixed dry, passed through a cement gun and conveyed by air through a flexible tube, hydrated at a nozzle at the end of such flexible tube and deposited by air at the place of final repose”.

10. shotcrete Difference b/w Shotcrete and Gunite Shotcrete and Gunite both are thought of the same but the difference is: Shotcrete is used for both dry mixture and wet mixture. Gunite is used only for Dry mixture.

11. shotcrete Shotcrete Technologies Dry mix Shotcrete. Wet mix Shotcrete . Steel fiber reinforced micro silica Shotcrete. Mesh reinforced Shotcrete

12. shotcrete Dry Mix Shotcrete Pre-mixed dry or damp materials are placed into the delivery equipment. Compressed air conveys material through a hose at high velocity to the nozzle, where water is added. Material is consolidated on the receiving surface by the high-impact velocity.

13. shotcrete Process of dry mix shotcrete

14. shotcrete Wet Mix Shotcrete All ingredients, including water, are thoroughly mixed and introduced into the delivery equipment. Wet material is pumped to the nozzle where compressed air is added to provide high velocity for placement and consolidation of the material onto the receiving surface.

15. shotcrete Process of wet mix shotcrete

16. shotcrete Steel fiber reinforced micro silica shotcrete Steel fiber reinforced shotcrete was introduced in the 1970s. Silica fume or micro silica is a by product of the ferro silicon metal industry and is an extremely fine. Quantities of 8 to 13% of micro silica by weight of cement, allow shotcrete to achieve compressive strengths , increased resistance to alkali and chemical attack, improved resistance to water .

17. shotcrete Mesh reinforced shotcrete In very poor quality, loose rock masses, where adhesion of the shotcrete to the rock surface is poor, the mesh provides a significant amount of reinforcement for shotcrete.

18. shotcrete Meshes for reinforced shotcrete

19. shotcrete Advantages Perfect adhesion of the sprayed material onto the base. Reliable filling of all cracks and uneven places . High initial strength using suitable hardening agents . High water proofing given by perfect compaction and a low ratio of W/C . Easy selection of the thickness of the sprayed on layer depending on the requirements and situation.

20. shotcrete Advantages Formwork savings of 50 to 100% over conventional cast-in-place construction Complex shapes require very little, if any, formwork. Crane and other equipment savings or elimination. Better bonding to the substrate, which enhances durability.

21. shotcrete Disadvantages Handling dry concrete mixture carries the problem of dust. Due to the high speed of discharge and other factors, the dry technology has a higher impact on the material and results in falling off of the material (up to 30% of the gravel aggregate). The pneumatic transport of the dry concrete mixture places higher demands on a more efficient source of air pressure.

22. shotcrete Disadvantages In wet mix ,Only a limited period of time is available between mixing and application of the wet concrete. In case of any longer delays, the entire system must be emptied, cleaned and filled up again before renewing the work.

23. shotcrete Applications Of Shotcrete Tunnels Channels Seismic reinforcing Dams Pools Grouting Plastering bigger concrete areas

24. shotcrete Applications Of Shotcrete Repairing Shotcrete can be used to repair the damaged surface of concrete. The following examples indicate a few ways in which shotcrete can be used in repairs: Bridges ,buildings, marine structures Underground excavations For the most part, shotcrete is used in underground excavations in rock such as tunnel, basement.

25. Shotcrete In Tunneling shotcrete

26. Shotcrete In Pools shotcrete

27. Conclusions shotcrete is one of the very efficient construction technique It is a time saving and we can get required thickness It is durable as compared to the other techniques We can get more strength in our constructions by using shotcrete. shotcrete

28. Tremie This method is used for placing concrete under- water level. In this method, concrete is placed below water level through a pipe, the lower end of which is kept immersed in fresh concrete so that the rising concrete from the bottom displaces the water without washing out the cement content.

29. Tremie The tremie concrete method is often used in bridges that span bodies of water. It c an be used to funnel concrete down through the water into the foundation or other part of the structure being cast.

30. Tremie

31. Laying of Concrete by using Tremie

32. Laying of Concrete by using Tremie

33. Choosing the Best Method The first thing to look at is the type of job , its physical size and the total amount of concrete to be placed. Studying the job details further will tell how much of the work is below, at, or above ground level. This aids in choosing the concrete handling equipment necessary for placing concrete at the required levels.

34. Choosing the Best Method Work Above Ground Level Conveyor belt, crane and bucket, hoist, pump, or the ultimate sky-hook, the helicopter, can be used for lifting concrete to locations above ground level. The tower crane and pumping boom are the right tools for tall buildings.

35. Choosing the Best Method Work At and Below Ground Level The largest volumes of concrete in a typical job usually are either below or at ground level and, therefore, can be placed by methods different from those employed on the superstructure. Concrete work below ground can vary enormously—from filling large-diameter bored piles or massive mat foundations to the complicated work involved in basement and subbasement walls. A crane can be used to handle formwork, reinforcing steel, and concrete.