Rak-82-2121 Production Technology of Concrete Structures ... · Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen Autumn 2015 Shotcrete

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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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Autumn 2015

Learning Outcomes• To acquaint the student with special casting methods

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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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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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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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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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Autumn 2015

Wet-mix shotcrete

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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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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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Autumn 2015

Execution of work• Spraying technique

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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

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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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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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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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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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Autumn 2015

Placing of concrete under water

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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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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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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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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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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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Autumn 2015

Bag work• In this method cement and aggregates filled fabric bags are immersed in water.

• Used mostly for repairs.

http://www.sika.com/content/corp/main/en/concrete-redirect/sika-concrete-technology/concrete-handbook-2013/concrete-types/underwater-concrete/_jcr_content/parCenter/textimage/image.thickbox.jpg/1386583799954.jpg

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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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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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Autumn 2015

Pumped concrete• Concrete pumps; a) mechanical, b) squeezing pump

• Hydraulic concrete pump

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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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Autumn 2015

General• Truck and trailer mounted concrete pumps

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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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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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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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Autumn 2015

Learning Summary• Shotcrete• Vacuum processed concretes

• Placing of concrete under water

• Self compacting concrete

• Pumped concrete

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Documents

Rak-82-2121 Production Technology of Concrete Structures ... · Rak-82.2121 Production Technology of Concrete Structures (4 cr) Fahim Al-Neshawy & Esko Sistonen Autumn 2015 Shotcrete