DOKA Formwork

 Doka System Components

            The various basic components that make up the various DOKA system are as follows:

1. Doka formwork beams
2. Doka formwork sheets
3. Dokadur panels
4. Doka floor props
5. Form ties and suspension cones
6. Multi-trip packaging

1. Doka formwork beams

           

            The core of the system lies in the usage of an Engineered timber component, the  H-Beam.

The H-beams are manufactured in a modern automated plant at Pondicherry under strict quality control the flanges are made of seasoned chemically treated timber. The web is made of boiling water proof ply wood and joined with the flange by the unique finger jointing method. The H-beams thus manufactured are  light, dimensionally stable and retains its structural properties over a period of time even after repeated usage. It is more predictable, easy to design and use, The number of reuses of H-Beams is more than 100 times (8 times that of conventional timber) and it consumes only 40% of timber volume required.

The H-beams are available in two size namely in H-16 - 16 cms  depth &  H-20 - 20 cms  depth,  length varying between 1m to 6m.

Salient Feature

•          Reduction in consumption of timber.

•          Making work at site minimized.

•          No. of reuses more than 8 times that of conventional timber.

•          Dimensionally stable, uniform in size and consistent in strength.

•          Cost ratio per use H-16 beam : conventional timber = 1:3.5

•          Economical and long - lasting.

•          Light weight @ 6kgs per RMT.

Max. Shear Force	Max. Bending Moment	EI
11 KN	4 KN/M	170 x 106 KG.CM2

Doka beam H20

Innovative end reinforcement .

• For less damage to the ends of the beams
• For outstanding durability
• Outstanding production level.

• Ensures uniformly high quality and load-bearing strength for safe and dependable usage
• Is the basis for the reliability of the Doka beam formwork and Dokaflex floor formwork
• From mechanical strenght grading

Practical marks for all standard lengths.

§  As a grid for easy installation and checking of the Dokaflex 1-2-4 system

Doka beam H20 eco

Ends of beams bevelled for more strength but have no end reinforcement.

 Doka formwork sheets

Doka has an extensive range of formwork sheets for the most varied areas of application. All sheets are made of glue-bonded layered wood and are extremely strong and dimensionally stable.

Formwork sheet 3-S Plus

Three-ply concrete-formwork sheet, made of European spruce (picea abies), designed specially for building. Produces a uniform concrete surface.

 Surface: Synthetic melamine resin glue with PU sealant and light corundum sanding on one side

 Bonding: Boilproof and weatherproof

Edges:Impregnating emulsion,
Doka yellow

  Thicknesses: 21 and 27 mm

Formwork sheet 3-SO

Three-ply concrete-formwork sheet, made of European spruce. Produces a uniform concrete surface.

§  Surface: Synthetic melamine resin glue

§  Bonding: Boilproof and weatherproof

§  Edges: Impregnating emulsion,

§  Doka yellow

§  Thicknesses: 21 and 27 mm

Dokaplex Multi-ply sheets

High-grade multi-ply sheet made of Finnish birch hardwood for use again and again. Produces a high-quality, smooth concrete surface.

• Surface: Phenol-resin coating, 120 g/m²
• Bonding: Boil proof and weatherproof phenol-resin glue (BFU 100) to DIN 68705-T3
• Edges: Dispersion
• Thickness: 21 mm

3. Dokadur panels

Dokadur panels are the state of the art for floor-slab panels. All-round edge and surface sealing dependably protects the panel against the wear and tear of everyday construction work.

Maximised number of reuses and best-quality concrete surfaces.

• From special surface sealing by means of PUR varnish and melamine resin coating with precision-metered corundum sanding
• For improved safety at work, because risk of slipping is reduced
• From significantly reduced moisture absorption for much-reduced discolouration, structuring and cracking

Big savings on costs

• From easy cleaning of the surfaces, ready for the next use
• From all-round edge protection made of high-grade PU
• For exact edges with minimal cleaning
• For low costs on account of easy and fast reconditioning of the edge

4. Doka Floor Props.

Doka floor props are the right choice for every application. High load-bearing strength plus many practical details that help to make handling easier.

• The props are available in various sizes viz. CT-250,CT-300,CT-340 & CT-410. The number indicates the extended length of props in cms.

• Carrying capacity is rated from 20 kN to 30 kN.

• The tripods make the props self standing for  easier and faster erection of the shuttering system. The adjustments in height are obtained by operating the prop nut. The required dimension in plan is obtained by side-lapping of the H-Beams in the primary or secondary layer.

• A very accurate and convenient shutter is ready for tying of reinforcement and concreting.

• The system also facilitates re-propping. By adopting the method of repropping it is possible to reduce the total quantity of formwork materials significantly. The system is very well adapted for use along with the L&T-Doka Beam Forming Supporting system.

5. Form ties and suspension cones

Doka has a complete range of tried-and-tested formtie solutions and dependable suspension points for wall formwork, single-sided formwork and climbing formwork in uncompromising quality for maximum safety.

Doka tie rods and anchor accessories

§  Provide safety through superb manufacturing quality

§  Reduce labour costs for installing ties, because a hammer is all that is needed for easy installation

§  Are durable, robust and unaffected by dirt

Robustly dimensioned universal climbing cones

§  ensure firm connections between structure and formwork

§  for safety on high structures

§  for all kinds of climbing formwork

Safe suspension solutions for working and protection platforms

§  With different attachments to suit the application

§  Ideally matched to the carrying capacity of Doka working and protection platforms

§  Easy to install and reusable.

Multi-trip packaging

Multi-trip packaging such as containers, stacking pallets and skeleton transport boxes  keep everything in place on the site, minimise time wasted searching for parts, and streamline the storage and transport of system components, small items and accessories.

Savings on material overheads and labour costs.

• Through faster loading and unloading of system components, small items and accessories
• Through easy relocation to the next point where the parts are needed
• Through safe storage in stacks, particularly when space is at a premium

Stacking pallets 150 and 120 simplify the storage and transport of floor props, removable folding tripods, formwork beams and Dokadur panels. The clamp-on wheels make the stacking pallets mobile, so they can easily be steered through standard door-size openings in residential accommodation projects.

CORROSION PROTECTION OF STEEL REINFORCEMENT IN RB AND RCC CONSTRUCTION

Scope

1.1. This standard (revised) specifies the recommended practice for surface preparation, surface pretreatment and anti-corrosive treatment based on inhibited and sealed cement slurry as an in-situ process for corrosion protection of mild steel reinforcement/HYSD bars in conventional reinforced concrete structures and conventional .reinforced brickwork constructions.  This practice is also applicable for non-prestressing steels (mild steel reinforcement/HYSD bars) used in prestressed concrete structure.

1.2. This standard applies only for in-situ corrosion protection of miId steel reinforcement/ HYSD bars after all bending and shaping operations are completed. However, this does not preclude the possibility of using this practice as a factory process.

 

2. Anticorrosive treatment process sequences - The anticorrosive treatment should necessarily include the following sequential steps

(a) Surface preparation (de-rusting) - Since presence of oil, grease, dirt, heavy scale and rust will adversely affect the performance of any anticorrosive treatment, it is essential to adopt suitable surface preparation technique. Surface preparation can be either by acid pickling or by sand blasting.

(b) Surface pretreatment - Surface preparation should be immediately followed by a surface treatment step to ensure temporary protection during the time lag between the de-rusting and finish coating. This pretreatment should not adversely affect either the adhesion of the finish coal or corrosion performance. (c) Inhibited cement slurry coating - A minimum of 2 coats should be applied to ensure full coverage.  (d) Sealing treatment - Sealing treatment should make the coating harder and less permeable. A typical flow diagram is shown in Fig.1,

 

3. Procedure for surface preparation

3.1. Sand blasting - Sand blasting of the steel surface to SAE 21 /2 if standards cm be done

3.2. De-rusting by picking - The pickling weld should be preferably based on hydrochloric acid and should include an efficient inhibitor to prevent base metal attack.

A typical de-rusting solution should have the following characteristics

(a)   Inhibitor efficiency should not be less than 97 per cent (b) Weight loss of a polished standard mild steel reinforcement / HYSD bars specimen when dipped in the solution for 10 minutes should not be more than 2 g per sq. metre. (c) Specific gravity when tested using a standard specific gravity bottle should be around

(b)    

4. Procedure for surface pre-treatment - De-rusted should be immediately convened by using phosphating treatment. It should be ensured by a suitable rinsing process that no residual acid is remaining on the surface at the time of phosphating. A typical phosphating composition of brushable consistency should have the following characteristics:

(a) Coating weight when tested as per test procedure A given hereunder should be around 4.5 gms./Sq.m.  (b)   Density of the product should be in the range of 1.22 to 1.4 kg/litre. (c)   Presence of fungicide shall be tested by dissolving the jelly in deionized water; the resulting solution shall be yellow in colour. (d)  Presence of phosphating chemical in jelly shall be ensured with ammonia molybdate test.  (e) pH of the composition when tested in a standard specific gravity bottle should be

around 2.5 ±0.1  (f)  Nail scratch tea should clearly leave a mark on the specimen. This indicates ihe

existence of the coating.

 

5. Procedure for inhibited cement slurry coating

5.1. A typical inhibitor admixture used should have the following characteristics:

(i) It should in liquid form ready for mixing with ihe ordinary Portland cement. (ii) Specific gravity when tested using a standard specific gravity bottle should be  1.04 ±0.02  (iii)  pH when tested using pH meter should be 12.75  ±0.25  (iv)  Tolerable limit for chloride in inhibitor- admixture when tested using anodic polarization technique (as per lest procedure B) should be 300 ± 25 ppm

5.2. Ordinary Portland cement - This should conform to IS 269 and should be sieved to pass through 75 microns IS sieve.

5.3. Cement and inhibitor admixture should be mixed in specified proportion to have suitable consistency. Coating should be applied preferably by brushings. However, under specific circumstances spraying dipping is also allowable.

5.4. Sufficient time tag should be allowed in between successive coatings to ensure final setting of the undercoat. A minimum of 6 to 12 hours may be necessary.

5.5. A minimum of two coats with sufficient time lag in between should be applied. 

 

6. Sealing treatment - The sealing treatment should be performed over the coated surface immediately after final selling of the top coat. Sealing treatment can be applied by brushing, spraying or dipping.

6.1. A typical sealing solution should have the following characteristics

(a)   Specific gravity when tested using a standard specific gravity bottle should be 1.09 ±0.02

(b)  pH when measured using a pH meter should be -12.25  ±0.25

(c)  Tolerable limit for chloride in sealing solution using anodic polarization technique should be 450 ± 25 ppm (as per test procedure B).

 

7. SPECIFICATIONS FOR FINISHED END PRODUCT

7.1. Finished coating when visually examined should be fairly uniform in thickness and should be devoid of any defects such as cracks, pinholes, peeling, bulging etc. No surface area should be left uncoated. No rust spot should be visible to the naked eye.

7.2. Thickness of the coating - The minimum thickness of the coating shall be 200 microns. Preferable range is 200 to 400 Microns.

7.3. Bond strength of the coated rebar - The bond strength of the coated rebar and concrete shall not be less than that specified in IS:456-2000 as per clause No. 0,2,5, II and 44.1.2 and tested as per IS;2770(Part-1).

7.4. Hardness of the coating when measured using a pencil hardness tester shall be around 5H to7H.

7.5. Tolerable limit for chloride in 0.04 normal NaOH medium using anodic polarisation technique (as per test procedure B) shall be around 4500 to 5000 ppm.

7.6. No film failure as evidenced by evolution of hydrogen gas at the cathode or appearance of corrosion products at the anode shall lake place during one hour of testing (as per test procedure C).

 

8. General remarks - It is advisable that severely rusted and heavily pitied reinforcements are not accepted for treatment.

 

Test procedure A

Determination of phosphate coating weight.

 7.5 cm x 2.5 cm or 7.5 cm x 5 cm mild steel polished and degreased specimens are to be used for this test. First the blank loss of unphosphated specimen is to be found out. For this, the initial weight (W₁) is accurately weighed. The specimen is kept immersed in the Clark's solution or patented inhibited derusting solution for I minute, The specimen is removed, rinsed in distilled water and dried using hot air blower. The specimen is immediately weighed (W₃). The difference between W, and w, is termed as blank loss. Another specimen (polished and degreased) is brushed with phosphating jelly and kept for 45 minutes.  Then the specimen is washed free of jelly, rinsed in clean water and dried using hot air blower. The phosphated specimen (W₁) is accurately weighed. After weighing, the specimen is kept immersed in Clark's solution or patented inhibited de-rusting solution for one minute. Then the specimen is removed, rinsed in distilled water and dried using hot air blower. The specimen is immediately weighed (W₄). Coating weight = W₃ - W₄ - blank loss.

Fig 1000/1 Flow diagram for anti-corrosive treatment of reinforcement bars

Test procedure B

Anodic polarisation technique.

Mild steel reinforcement / HYSD Bar lest specimens of size 10 mm in dia and 100 mm in length with stems of size 5 mm in dia and 50 mm in length is polished, degreased and sealed at bottom edge and at the stem with suitable sealers like wax, lacquer.  Then test specimen ii kept immersed in test solution and potential is monitored using high impedance multimeter against suitable reference electrode such as saturated calomel electrode/ copper-copper sulphate electrode. After getting stabilised potential using appropriate current regulator (0-100 mA), the lest specimen is anodically polarised at a constant current density of 290 mA cm using a platinum/ stainless steel/TSIA/ polished mild steel reinforcement/HYSD Bar as cathode. Potential with timee is followed for 5 minutes after current is applied. The maximum chloride concentration upto, which the potential remains constant for 5 minutes, is taken as a measure of tolerable limit.                                                                

Test procedure C

Resistance to applied voltage test                                     

Two mild steel reinforcement / HYSD bars of size not less than 10 mm in dia and 800 mm in length shall be given anti-corrosive treatment as per specified procedure.  The end of the rebar's shall be soldered with insulated copper electrical connecting wire (14 gauges) to serve as electrical contact point.  Coated rebus at the two ends shall be sealed with an insulating material to a length of 25 mm at each end. Test area shall be the area between the edge of the bottom sealed end and immersion line which shall not be less than 25 mm in this case.

The coated rebar's shall be suspended vertically in a non-conductive plastic container of size not less than 150 mm X 150 mm square and S50 mm high.  The rebar shall be so suspended as to have a clearance of 25 mm at bottom, 45 mm at the sides and 40 mm in between the rods.  Container shall then be filled to a height of 800 mm with aqueous solution of 7 percent NaCI. A potential of 2 V in between the coated rods shall be impressed for a period of 60 minutes using a high resistance volt meter for direct current having an internal resistance of not less than 10 mega Ohms and having a range upto 5 V (minimum).  Storage batteries may be used for impressing the voltage. During these 60 minutes of testing, there shall not be any coating failure as evidenced by evolution of hydrogen gas at the cathode or by appearance of corrosion products of iron at the anode