Strengthening of structures Rak-43.3312 Repair Methods of Structures II (4 cr) Esko Sistonen.

Strengthening of structures

Rak-43.3312 Repair Methods of Structures II (4 cr)

Esko Sistonen

Using Self-compacting concrete in repairing

• The usefulness of using self-compact concrete in repaired structure is investigated in balcony repairs.

• Frames work and concreting methods are examined in field tests.

• Concrete properties and resistance to frost are also investigated.

• Shrinkage and bond strength between old and new concrete are also measured.

f 4 @12 mm f 12 @15 mm

250 mm

25 mm

115 mm

150 mm

50 mm

250 mm

25 mm

115 mm

150 mm

50 mm

Repairing process of the supporting walls, parapet and slab of the balcony using self-compacting concrete. (Batch

1, October 2004, laboratory condition)

• Condition before casting • Moulding work

• Condition after repairing

Repairing process of the parapet and slab of the balcony using self-compacting concrete (Batch 2, November 2004,

outdoors condition)

• Condition before casting • Moulding work

• Condition after repairing

Repairing process of the supporting column and slab of the balcony using self-compacting concrete (Batch 2,

November 2004, outdoors condition)

• Condition before casting • Moulding work

• Condition after repairing

Tensile strength results for drilled specimens from Batch 1, stored in laboratory condition

A) SCC, B) Old concrete

Examples of surface cracks of self-compacting concrete cast in the laboratory conditions (Batch 1).

Drying shrinkage of SCC removes forces from the old layer to the old concrete and in that way strengthens the

structure (composite structure)

The result of freeze-thaw test for drilled concrete samples

SCC layer

Substrate concrete

Number of freezing and thawing cycles during July 2005 and April 2006

2429

77

0

20

40

60

80

100

The barrier layer of oldslab & SCC

The barrier layer of oldcolumn & SCC

Outdoors condition

Nu

mb

er o

f fr

eezi

ng-

thaw

ing

cycl

es d

uri

ng

(07

.200

5 -

04.2

006)

The freezing - thawing cycles are below 0 °C

The relative humidity, temperature and water vapour content of the barrier layer between old concrete and the new 50 mm

of SCC layer

Conclusion 1/2• An objective with the work was to find the minimum cover depth

of the self-compacting concrete (SCC) suitable for the repair method studied. This cover depth thickness was defined as 15 mm.

• Fresh and hardened concrete tests for the self-compacting concrete used showed that the concrete fulfilled the requirements for balcony repairing.

• The results of slab frost resistance tests show the scaling and flexural strength change of self-compacting concrete was very small after 300 cycles and the changes in ultrasound transmission time were small, so there is no sign of inner deterioration.

• Drying shrinkage of self-compacting concrete was higher than the theoretical shrinkage for the normal concrete because self-compacting concrete contained more fine aggregate. Using reinforcement mesh reduces the shrinkage of self-compacting concrete.

Conclusion 2/2• Surface cracks were observed in the concrete surface,

specially the area around the reinforcement mesh supports.• The bond between the old concrete, which has a lower

strength than the repairing self-compacting concrete, is poor specially, when casting concrete in the lower surface of concrete slab.

• The results of relative humidity and temperature monitoring and the number of freezing-thawing cycles for the repaired balcony show that the winter condition is severe for the frost resistance of concrete.

• Based on the laboratory results, air entrained self-compacting concrete; with 5% air content is suitable for the outdoor conditions in Finland and fulfilled the requirements for frost resistance of concrete.

Self-compacting concrete in the repair of pier

Self-compacting concrete in the repair of swimming hall structures

Strengthening / shotcrete

Drying shrinkage cracking

Shotcreting stock

The strengthening of reinforced concrete (RC) structures using advanced fibre-reinforced polymer (FRP) composites = non-metallic

• carbon fiber reinforced (CFRP) bar/laminate• Glass Fiber Reinforced Polymer (GFRP)

Rebar/laminate – The unclear alkali and salt-frost resistance of FRP – Good corrosion resistance and high tensile strength – Good fire resistance of CFRP – The epoxy matrix will soften at temperatures close

to its glass transition temperatures between 65 and 150 °C.

– the bending and shaping of FRP elements must to be done beforehand

http://www.trancels.com/ http://www.savcor.com.au/art/?p=services&s=ss

• Flexural strengthening• Shear strengthening• Confining reinforcement

Strengthening foundations

• Shotcreting• Concrete casting

Ref. www.lemcon.fi

Piling

Temporary supports

Build in1860’s

WeeGee-house; Ref. Betoni 3/2006

Column is hanged from the intermediate floor during mining

intermediate floor supported with steel columns

WeeGee-house; Ref. Betoni 3/2006

Shotcreting

Wet injection methodDry injection method

Strenghtening with shotcreting

Concrete injection

Crack injection

two component epoxies (<0.5 mm)Cement glue (>0.5…1.0 mm)Mortar (>5 mm)

Strengthening concrete structures

Old structure and the addition of a new concrete is made to work as well as possible.

The surface must be transferred the shear strength without the parts slipping in between.

- Roughening the surface of the joint

-Into concrete stages are made a hole with a spike (a recess)

Strengthening slabs

Strengthening the upper and underside of the slab

Shortening the span of the slab with new beam

Strengthening the slab with stressing method

Incresing punching shear capasity of the slab

Bolting through the slab

Strengthening hollow-core slabs

Strengthening beams

Compressed side of the beam is to be increased with the upper side casting

Tensile and/or shear reinforcement will be increased by casting a new beam around the old one

Tensile and/or shear capacity is to be increased by cluing steel sheets / carbon fiber reinforced laminates into a lower and/or side surface of the beam

Reinforced concrete beam is to be strengthened by a form steel

Concrete beam is to be substituted with steel beam

Steel profile is to be fixed into a concrete beam

Steel profile is to be wedged below the beam

Extra supporting of the beam

Beam is to be post-tensioned by external tendons or tended beam is to be casted around the old concrete beam

encasing

Strengthening the column

Entirely or partly encasing

Strengthening the column with the steel form

Increasing cross sectional surface with steel profiles

Substituting the concrete column with the steel column

Important factors in strengthening:

-good bonding between new and old concrete (roughening for instance by making a hole with a spike, or sand blasting

-The base concrete should not be too wet or dry

-New reinforcements should have adequate concrete cover

Too low prestressed ridge beam in which hooks at the top surface are missing

www.fise.fi

Ref.: www.norcure.com