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600g unidirectional carbon fiber cloth

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 Singapore international convention center Reinforcement with 600g unidirectional carbon fiber cloth

 

I. Project overview

Being the largest exhibition hall in Asiaand one of key investment projects of government, Singapore Expo was put into formal use in April 2002 with a total investment of 220 million SGD, standing 25 hectares. It incorporates an exhibition hall of 60,000 sqm and an outdoor saloon of 25,000 sqm, 10 meeting halls of varying sizes and 9 parlors, equipped with advanced translation, communication and transmission facilities.  Besides a parking lot  able to accommodate 2,200 cars and two taxi stations, the expo center also possesses the second largest dining hall inSingaporewhere 10,000 people can have diner, to provide the exhibitors with commercial meal service of different levels. 

Due to frequent use, the exhibition hall was not maintained and reinforced for more than one decade. Considering more exhibitions in future and huge visitors flow rate every day, the building began to be refurbished and reinforced in May 2014. 

II. Reinforcement material

600g unidirectional carbon cloth and carbon fiber glue

Major mechanical property indices

Object name

Normal value for tensile strength (MPa)

Elastic modulus

(MPa)

(%)

Tensibility(%)

(MPa)

Bend strength

(MPa)

Interlaminar shear stress

(MPa)

Normal tensile cementation strength of fiber composite and concrete(MPa)

Carbon cloth (grade)

≥3400

≥2.4×105

≥1.7

≥700

≥45

≥2.5

and is concrete cohesive failure

Design of maintenance and reinforcement work

The general structure inspection shows that the building of exhibition center has problems of varying degrees in structural security and endurance.  To guarantee security and endurance of building structure and restore original functions of each part of building, the building should be immediately maintained and reinforced to hinder the damage from further developing, or the buildings' structure is not secure enough. The design scheme of reinforcement using carbon fiber unidirectional cloth reads as follows: 

After sealing the surface for the crack of building, paste carbon cloth to the beam segment where crack spreads. Define scope of pasting carbon cloth to beam bottom according to the detection conclusion and technical parameters provided by the detection unit. Paste carbon cloth to general column position where the structural crack locates according to the position of structural crack as specified in detection report, with primary load bearing wall in basement pasted with carbon cloth. 

III. Construction process of pasting carbon cloth

1.Measurement engineering: loft on bridge-girder according to the position of pasting carbon fiber defined in construction drawing, draw up area of pasting carbon fiber, process this area, the four corners for pasting area and column all need to be rounded with radius of rounded angle being 20mm. The requirement on accuracy of measurement: the error shall not be greater than ±10mm.   

2Facing treatment: the surface of concrete in the construction operation area shall be burnished using angle grinder with burnished depth not smaller than 0.5mm. The burnished surface layer shall be complete without any adhering laitance layer, loose material, dust, oil or grease. The ash and loose materials shall be removed with air pressure nozzle and brush. After burnishing the facing, the dust on the surface shall be thoroughly cleaned away using forced-draft fan or dust collector and kept dry. The surface smoothness is required to be less than or equal 5mm/m. The sticking place of corner and concrete surface shall be rounded and burnished to be arc-formed, with radius beam of arc not smaller than 20mm. 

3Crack restoration: When pasting carbon fiber to the elastic crack which has been tightly sealed, seal by fully brushing the whole area. 

4Shearing of carbon cloth

(1)Shear carbon cloth strictly according to the size required by design. 

(2) Bevel shearing carbon cloth is strictly prohibited and wire drawing shall be prevented; 

(3)Keep the sheared and shaped carbon cloth clean from pollution. 

5Prepare and brush primer

(1)Prepare base glue strictly according to the process stipulation provided by the manufacturer

(2)Smear evenly priming resin on the surface of concrete using roller brush. After the surface of primer is dry to touch, go to next step as soon as possible.   

6Leveling

(1)Prepare leveling material strictly according to the process stipulation provided by the manufacturer

(2)For repairing surface of concrete, adopt acetone to wipe off the floating dust on surface, use leveling material to fill up the surface depression, the position with offset or corner shall be made into smooth curve surface instead of having edges and corners.   

(3)Use leveling material to restore corner into slick circular arc with radius not smaller than 20mm.   

(4)Use scraper with tool tip width ≥100mm to fill up, repair and level the depression, the leveling degree shall be without obvious trace of scraper blade or scraper and grain being smooth.

(5)After the surface of leveling material is dry to touch, go to next step as soon as possible. 

7Prepare and brush impregnating resin or pasting resin  

(1)Read carefully the working instructions provided by manufacturer before preparing agglomerant

(2)Define the intermixed quantity of resin each time according to actual onsite environment temperature and pasting area to avoid failure and waste.   

(3)Measure and prepare strictly according to proportion by weight

(4)Prepare according to mixing proportion of manufacturer and technological requirements, and arrange special personnel for watching. Oily soil and impurities shall not exist in whipping container and on beater. Whip clockwise unidirectionally till the color becomes uniform without bubble produced, and prevent dust or other impurities from getting in.   

(5)Use up the prepared agglomerant as required within controlled use hours. 

(6)Wipe again the surface of concrete to ensure no ash on pasting area before pasting carbon fiber

(7)Evenly smear the impregnating resin prepared according to the process stipulation provided by manufacturer to pasting area. When brushing structural adhesion to surface of concrete, brushing must be stable, accurate and even, i.e. stable: brush with moderate force without flowing, dropping or falling as far as possible; accurate, brushing is within control line; even: the thickness pasted within brushing scope is even.   

8Paste carbon cloth

(1)Lightly paste carbon cloth to the required position with hands. Pasting carbon cloth is also required to be stable, accurate and even. Unwind with moderate force to make carbon cloth not crinkle or fold and spread smoothly. Adopt dedicated roller to roll along direction of fiber. One must roll from one end to another end, and it is inadvisable to repeatedly roll and knead one position. In rolling, make glue permeate the fiber cloth, to realize plump soakage and make bubble extruded, make impregnating resin fully saturate carbon cloth. Don't damage carbon cloth in rolling. When carbon cloth needs to be lapped, all circumferential lap length shall not be smaller than 200mm.    

(2)Repeat above steps for pasting multilayer, and it is advisable to paste the next layer as soon as possible after the impregnating resin on fiber surface is dry to touch  

(3)Evenly smear impregnating resin on the surface of the last layer of carbon cloth

 9Completion: Maintain for 48 hours, during which time the carbon fiber surface shall be prevented from being scraped or touched by sharp objects and pulled artificially. To facilitate subsequent concealed construction, during 6-12 hours after carbon cloth is pasted, spray sand to carbon cloth to coarsen it to the degree that it is viscid to touch. 

10Construction technique measures and key quality control points

(1)The conformity certificate for leaving factory for raw material of carbon fiber and performance indices in product quality detection report must be inspected and checked when material is delivered to the site.   

(2)Surface treatment of substrate concrete is one of the most critical procedures in reinforcement with carbon cloth, which shall be taken seriously. Remove thoroughly the floated coat to expose concrete structure layer, and weed out the poor concrete such as stripped, loosened, beehive and eroded concrete on the surface of to-be-reinforced member. Level off with epoxy resin mortar. If the member has crack, first conduct crack pouring or joint sealing, then burnish to be leveled, clean impurities off, and keep dry. The base plane is required to be leveled off and continuous without recession, and internal and external corner shall be smooth.   

(3)Prepare the glue used for pasting carbon fiber strictly according to product description. The field environmental conditions shall conform to product requirements.   

(4)Prepare a small amount of adhesive each time, as the remnant adhesive and the adhesive exceeding operable time of glue shall not be reused.   

(5)The lap length of carbon cloth in the impact direction of fiber shall not be smaller than 200mm. 

(6)To guarantee carbon fiber sheet can reliably coordinate with concrete, additional anchorage measures can be taken.   

(7)Blank accurately. The carbon cloth strips with uneven edge and recessed and convex corners are prohibited to be used. 

(8)In pasting carbon fiber, rolling must be done properly in place to guarantee fiber material is fully steeped for effective pasting.   
(9)Enhance inspection and acceptance of pasting work of carbon fiber. The quality of bonding between carbon cloth and concrete shall be inspected using hammer to knock or using hands to press the surface of carbon cloth. The total active area shall not be smaller than 95%.  When the hollow area of carbon cloth is smaller than 10000mm2, one can remedy by injecting glue via needle tube. When the hollow area is greater than 10000mm2, it is advisable to cut off the carbon fiber sheet at hollow area, and re-lap with equivalent carbon fiber sheet with lap length not shorter than 100mm.

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