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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Rak-82-2121 Production Technology of Concrete Structures (2015)
Special Concrete Works20.11.2015
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Learning Outcomes• To acquaint the student with special casting methods
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Shotcrete• Shotcrete is a special type of concrete containing small aggregates or just sand (mortar) which is sprayed under high pressures onto a surface. The technology was developed already in 1911 and since then the basic principle remained the same. Shotcrete can be applied by dry, wet or semi wet method.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Dry-mix shotcrete• Batch of concrete cement and natural dry aggregates –moisture 2..5%
• Transportation by compressed air
• Addition of water• Advantages: long transportation 250-600 m (h0 50 to 150 m); water to cement ratio 0.4 to 0.45; workability of the dry mass 1,5 hours
• Drawbacks: transportation rebound 15-30%; dust and harmful clouds; continuous spraying - thickness layer less than 40mm
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Half wet-mix shotcrete• Finished got involved dry mix concrete W/C= 0.42…0.48
• Transportation in the hose of compresses air
• Possibly the addition of the fluid accelerator in nozzle
• Benefits: it can be used thick spraying floors; the bulk is got involved in the power mixer; water cement relationship no varying
• Drawbacks: the hose is less than 20 meters; fine aggregate and maximum grain size less than 16mm; cement content less that 350 kg/m3
http://www.shotcretetechnologies.com/graphics/i_ecuador1_lg.jpg
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Wet-mix shotcrete• Plastic concrete w/c = 0.55…0.70; max aggregate size 8 mm; compressed air
• Benefits: small dusting; suitable for thick spraying floors; appropriate for closed and tight places; possibility to use fibre
• Drawbacks: low strength; thin layer less than 20 mm; strength degrading with acceleration
https://www.shotcrete.org/media/images/header-wet-mix.jpg
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Wet-mix shotcrete
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Wet-mix shotcrete• Used additives: accelerators –closing the water leaks; retards - better quality; air entraining agent -cohesion and frost resistance of concrete can be improved; when spraying in wet method
• Reinforcement: welded reinforcement mesh more than 100 mm
• High class of concrete: fast movement 80 to 170 m/s; high stone ingredient decrease of elasticity; efficient vibration and tightening; compressive strength 30 to 70 MPa; splitting strength 3,5 to 4,5 MPa; adhesion and cutting strength 1-3MPa
• Weakness: shrinkage risk; rough and uneven surface; act of the thick structures as floors; dry method –dust; high amount of waste concrete due to splashing; higher price per cubic meter
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Execution of work• Sprayed surface: no dirt, and not grease; no segregation; right moisture content –adhesion; not completely dry and not frozen
• Concrete: aggregate to cement ratio 3...5; moisture content 3...5%
• Spraying of concrete: distance from nozzle to surface 0.5…1,2 meters; perpendicular to surface
• Processing of the surface: timber, steel and sponge grinding; as soon as possible after spraying; moist curing for 7…14 days
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Execution of work• Spraying technique
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Applications of shotcrete and economy
• Rock strengthening and tightening
• Repair and rectification of the concrete structures
• Rectification of the stone structures
• Arcs and shells structures • Suspended concrete ceilings
• Fire and corrosion protection of the steel structures
http://www.conconow.com/wp-content/uploads/2012/06/Solution-sculpted-shotcrete-mural-02-e1338916022216.jpg
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Vacuum processed concretes• Remove excess of water and entrapped from concrete before its hardening
• Additional dehydrating of concrete with the help of vacuum reduces a water to cement ratio and decreases its porosity
• Usually finishing of the surface is possible just after vacuum processing
• Vacuum concrete equipment: pump and compressor 0.8 …0.9 atm; vacuum pads; filters installed on the pipes; concrete equipment and surface grinding apparatus
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Vacuum processed concretes• Vacuum pads: tight nylon filter cloth; tight places synthetic mesh- network suction canalization; withstands vacuum up to 80…90 kN/m2
• Vacuum treatment of concrete: 1…5% of compaction; 20…25% reduction of water; 1% reduction of the cement amount (removed together with water); after processing, to the pores to remain under-pressure
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Vacuum processed concretes• Properties of vacuum processed concretes: enhanced early strength development; shorter formworks circulation time; initial strength 0.1…0.15 MPa; allows light traffic; compression strength increases mainly near the vacuumed surface; increase of flexural strength; enhancement of abrasion resistance; better compaction; reduction of shrinkage; increase of the modulus of elasticity.
• Special requirements for vacuum processed concrete: fine aggregate amount must not be too large; risk of filter blocking; aggregates preferably circular; not too fluid consistency; the segregation can occur already during transportation – 2..3 sVB; usage of fly-ash or blast furnace slag is not recommended
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Vacuum processed concretes• Disadvantages: higher demand for manpower; application of expensive devices
• Applications: slabs (vertical and hollow-core); supports for bridges, columns, walls; massive structures; concrete elements; placing of concrete of the inclined surfaces; water tight structures; repairmen of damaged concrete structures; to the large industrial buildings, stores, parking etc.; seamless floors
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Placing of concrete under water
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Tremies• Concrete properties: slump 1..3; max. aggregate size 32 mm; cement content more than 350kg/m3; concrete can not easy to segregation; in the beginning the extra cement 50kg/m3; normally used plasticizers and retarder; difficult control of the properties; no vibration; reason to make 25% stronger concrete than suggested by the loads
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Tremies• The reinforcement should not be used (not recommended): casting climbing speed is less than 30 cm/h. in general 1m/hour or even 6..10m/hour; casting breaks are under 30 min; the distance of the pipes from the moulds below 2.5 m; distance of the pipes in the case of several pipes is under 5 meter and max 2 times thickness of the cast plate
• Concrete production and transportation capacity must be calculated and be done carefully according to: weather conditions; traffic; breaking equipment
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Pumping• Pumping of concrete needs assistance of scuba divers who does the actual work.
• Furthermore, special equipment and monitoring is needed.
• In general very expensive and
• problematic method used in special circumstances.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Horizontal casting with transportation tube
• Similar to tremie method
ftp://dfi.org/OneMine/Marine%20Foundations%20Book%20-%20individual%20papers/29-5.4%20Underwater%20Concrete%20-%20Mix%20Design%20and%20Construction%20Practices.pdf
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Injection methods (Grouted pre-placed aggregate)
• In this method the formwork is filled with aggregates and injection of cement paste under the water between aggregates is done.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Bag work• In this method cement and aggregates filled fabric bags are immersed in water.
• Used mostly for repairs.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Progressing methods• The method is applicable to maximum depth of 0.5 m.
• In this method new concrete will is dropped to the fresh concrete which is over the water.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Self compacting concrete• Self compacting concrete was developed in the 80s in Japan.
• The most characteristic feature of these types of concretes is its capability flow and no need for any kind of additional vibration.
• The mix design is characterized by increased mounts of fines and application of fillers.
• The most commonly used fillers are fly ash, limestone filler and quartz fillers.
• The strength and durability are comparable with conventional concretes
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Pumped concrete• Concrete pumps; a) mechanical, b) squeezing pump
• Hydraulic concrete pump
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
General• Pumping of concrete is one of the most commonly used transportation methods for concrete at the building site.
• The most common applications are foundation, industrial structures, tunnels and bridges, soil structures, dams and power plants and also small size structures.
• Pumped concrete has to full fill certain requirements concerning workability, cohesiveness which is crucial for this type of transportation.
• There are three types of pumps which are commonly used; mechanical, hydraulic and so called squeezing pump.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
General• Truck and trailer mounted concrete pumps
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
General• One of the main advantages of pumping of concrete is the efficiency.
• Theoretically it is possible to pump 50-60m3/h.
• In practice however, it is usually between 20 and 45 m3/h.
• Normal range is more than 20m vertically and 25 m horizontally.
• The possibility to pump concrete to difficult inaccessible places.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Usage• Initially some of the cement paste is lost to lubricate the pipes.
• Always at the beginning of pumping the range is the biggest and decreases with time.
• The pipes can be cleaned
• using water with rubber balls.
• The particle size distribution of aggregates should be optimized towards the higher packing density; the lowest possible amount of voids between them.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Usage• Cement used for pumped concrete should not be too fine due to increasing cohesiveness of the mix resulting in “sticky” consistence.
• If cement is too coarse there might persist problems with flow ability.
• The optimum amount of cement varies between 250-300 kg/m3
• Due to pumping the amount of air in concrete might drop by up to 25%
• Pumping did not show any influence on mechanical properties however, shrinkage appeared to be slightly higher.
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Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen
Autumn 2015
Learning Summary• Shotcrete• Vacuum processed concretes
• Placing of concrete under water
• Self compacting concrete
• Pumped concrete
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