FAQ

Frequently asked questions - Hot dip galvanized reinforcement

Details

Category: FAQ

Published on Tuesday, 18 March 2014 08:58

Written by Super User

Hits: 23302

Why are hot dip galvanized reinforcements used in concrete constructions?

The zinc coating on the reinforcement isolates the steel from the cement matrix and corrosion of the underlying steel will only commence once the coating has been completely corroded away. Because of the rate of corrosion of zinc in concrete is usually extremely slow, the loss of the coating in this way is a very long-term process and so corrosion of the steel is significantly delayed. Even if the coating has dissolved or been mechanically damaged such that the underlying steel is exposed, the remaining zinc on the adjacent surface becomes anodic and provides sacrificial cathodic protection to the bare steel. As such, the corrosion of the exposed steel is further delayed.

What are the differences between galvanizing and other coatings for reinforcing steel?

Unlike painting and epoxy coating on steel which are solely barrier-type coatings, galvanizing provides both barrier and sacrificial protection to the underlying steel. In a barrier coating, once the coating is damaged and the underlying steel is exposed, corrosion commences. This often leads to so-called under-film or filiform corrosion in which corrosion proceeds under the adjacent coating resulting in the further decohesion of the coating and continuation of corrosion. When usig galvanized steel, because of the more electronegative potential of the zinc in the surrounding area, it provides sacrificial cathodic protection to the exposed steel.

How long have galvanized steels been used in concrete?

The first reports on the use of zinc coated steel in concrete date to about 1908. Its first regular use as a reinforcing material was in the 1930s in the USA. In the post-WWII period the use of galvanized rebar became more common and by the 1960s and early 1970s a considerable tonnage of steel reinforcement was being galvanized especially for use in bridge and highway construction across the snow-belt states of the USA and Canada. Since this time, and especially over about the last 25-30 years, there has been a steady world-wide use of galvanized reinforcement in a wide variety of types of concrete construction and exposure conditions.

Are there different requirements in designing of reinforced concrete when using galvanized bars?

There are no special requirements for the design of galvanized reinforced concrete beyond that which apply to conventional reinforced concrete.

Can galvanized and black steel reinforcement be used together in concrete?

Because zinc is naturally protective to steel, galvanized reinforcement can be safely mixed with uncoated in concrete, especially if the connection point between the two materials is well embedded and sufficiently deep such that there is no corrosion risk for either material.

Does galvanizing affect the structure and properties of the reinforcing steel?

The microstructure and the mechanical properties of steels are primarily controlled by the temperatures to which they are heated during processing and the subsequent rate of cooling to ambient temperature. As a general rule, steels must be heated for a reasonable period of time above about 650°C for there to be any significant effect on either the microstructure or the mechanical properties of the steel concerned. In hot dip galvanizing, the maximum temperature reached in the zinc bath is about 450°C. This temperature is not sufficiently high to cause any noticeable heat treatment effect in structural steels and exhaustive testing of all types of reinforcing steel has consistently shown this to be the case.

Will concrete have an adequate adherence to the reinforcement if it is galvanized?

There is a vast body of evidence showing that concrete tightly adheres to galvanized reinforcement. In fact, this adhesion is better than is achieved with uncoated steel. The basis of this is the formation of the protective surface layer of calcium hydroxyzincate. This layer is not only tightly adhered to the zinc surface it also interacts with the adjacent cement matrix effectively creating a bridge between the bar and the matrix. There is also evidence to show that the zinc corrosion products released from the surface of the coating in these circumstances migrate (or diffuse) into a narrow interfacial zone between the bar and the concrete resulting in strengthening and densification of this zone.

What is the life extension achieved with galvanized reinforcement?

The delay in the onset of corrosion of galvanized steel compared to black steel is known as the extension of the service life. For galvanized reinforcement in concrete, this extension of life to the onset of corrosion has variously been reported to be 4-5 times longer than that for the corrosion of black steel in equivalent exposure conditions.

Are there special transport, handling or on site storage requirements?

There are no special handling or transport methods necessary when loading/unloading or job site handling of galvanized reinforcement. Regarding the on site storage, galvanized reinforcement (as any other hot dip galvanized product) can be stored directly on the ground without risk of significant damage to the coating. It is recommended that bundles of freshly galvanized products be stored on a slant to allow water drainage and air flow in order to reduce the aspect modifications that can occur.

Frequently asked questions - Grounding components

Details

Category: FAQ

Published on Tuesday, 18 March 2014 08:58

Written by Super User

Hits: 11215

Do you fabricate 6 mm thickness galvanized strip in coils?

We produce galvanized strip in coils with thickness between 2 and 5 mm . The strip with 6 mm thickness is produced in 6 m length bars, this is how we fabricate it and we market it accordingly.

What zinc thickness has the strip that you fabricate?

Typically we produce galvanized strip with an average thickness of zinc coating of 70 microns. At the express request of the customer we also produce galvanized strip with zinc coating of 45-50 microns , but we can also deliver coatings up to 100 microns. The most common coatings are:

What is the weight of the galvanized strip coils?

The standard weight is 50 kg but, on request, we also produce coils of 21 kg, 25 kg, 42 kg, or, on request, any weight between 20 and 100 kg.

What is the wight of the galvanized wire rod coils?

The standard weight is 50 kg but on request we can produce coils of up to 200 kg.

What are the dimensions of galvanized strips that you can produce?

We produce galvanized strip with the following dimensions: 20x2 mm, 30x2 mm, 20x2.5 mm, 20x3 mm, 25x3 mm, 30x3 mm, 40x3 mm, 30x3.5 mm, 25X4 mm, 30x4 mm, 40x4 mm, 50x4 mm, 20x5 mm, 40x5 mm, 50x5 mm, 60x5 mm.

What are the dimensions of galvanized wire rods that you can produce?

We produce galvanized wire rods with the following diameters: 6 mm, 8 mm, 10 mm.

What steel grade do you use for wire rods?

The wire rods are made of SAE 1006 steel grade.

What steel grade dou you use for the strips?

The strips are made of S235JR or DD11 steel grade.

What are the specific masses of the strips that you produce?

Specific masses are listed in the Galvanized Strip Technical Sheet.

What are the specific masses of the wire rods that you produce?

Specific masses are listed in the Wire Rods Technical Sheet

What kind of grounding electrodes do you produce?

We produce 3 types of hot dip galvanized grounding electrodes:

• Electrodes made of 50x50x3 mm cross profile;
• Knurled top electrodes made of 20 mm diameter round pipe;
• Electrodes made of 48.3x2.5 mm round pipe.

For all types of electrodes the standard lengths are: 1 m, 1.5 m, 2 m, 2.5 m and 3 m. We can also produce on request other electrode types or dimensions.

Frequently asked questions - Road steel guardrail

Details

Category: FAQ

Published on Tuesday, 18 March 2014 08:58

Written by Super User

Hits: 21902

What are the weights /ml of the guardrails produced at Betak?

Information about the weight /ml can be found in the Guardrail Technical Sheet.

Can you can also provide the guardail installation in the field?

We provide the guardrail installation through subcontracting.

Can you provide transportation?

Yes, on request, at a fee.

You have the ability to produce curved rails (for curves)?

Betak produces rails with 3.2 and 4.2 ml lengths, particularly for use in curves.

What amount of guardrails in ml (main types) can be transported in a full truck?

A full truck can transport ~1300 ml of semi heavy guardrail or ~900 ml of heavy guardrail respectively ~380 ml of very heavy guardrail.

What are the certifications of the guardrails that you produce?

We are certified according to STAS 1948 and certification according to EN 1317 is ongoing.

What are the packaging delivery conditions for the guardrails?

The rails are delivered in packages of 20 pieces, weight - 1, 3 tons / package, the other components are packaged on europallets, maximum weight 1.4 tons / pallet.

What is the loading method?

The products are loaded by crane and forklift.

Frequently asked questions - Hot dip galvanizing

Details

Category: FAQ

Published on Tuesday, 18 March 2014 08:58

Written by Super User

Hits: 25010

What is hot dip galvanizing?

Galvanizing is a process for corrosion protection of steel that consists of specific surface preparation and dipping it into a bath of alloyed molten zinc at 450 ° C for 3-10 minutes. Following this process, on the steel surface a coating is formed due to the reaction between Fe and Zn having a metallurgical bond with the substrate, consisting of several layers of intermetallic compounds with different concentrations of zinc. This coating has a very good resistance to corrosion, abrasion, impact, thermal shock a.o.

Does hot dip galvanizing need special surface preparation?

Galvanizing requires no special preparation of the surface, this being achieved in the galvanizing process. Welding slag, paint and grease abundance though can not be removed through the specific surface preparation steps and must be removed before being sent to the galvanizer.

What are the usual turnover times from galvanizing?

Most of corrosion protection systems depend on adequate temperature or humidity conditions to be correctly applied. Galvanizing is a process whose aplication does not depend on environmental factors, can be done 24/7, 365 days a year, rain or good weather. Hot dip galvanized steel can be galvanized, delivered on site and installed in the same day but the usual processing times are between 3 and 5 days depending on the quantity and typology of parts.

What is the lifespan of hot dip galvanized products?

Hot dip galvanized steel has good corrosion resistance in most types of atmospheres. Usually the life of hot dip galvanized steel exceeds 70 years depending on the thickness and atmospheric corrosivity.

Does the coating present sufficient adhesion to the substrate and abrasion resistance?

The metallurgical bond that the coating forms with the substrate layer at the immersion in the molten zinc confers an excellent adhesion and abrasion resistance to the coatings obtained by hot dip galvanizing. Zinc intermetallic layers formed during the galvanizing process have a higher hardness than steel substrate.

Do hot dip galvanized parts need special storage and transport precautions?

A hot dip galvanized metal object can be stored, transported and used in any natural weather conditions, in air, in water, in soil or on soil. In any of these circumstances the role of corrosion protection of hot dip galvanization is not affected. Instead, the appearance of coating might change. White spots may appear or different shades, zinc flower, shiny or matte surfaces etc. All these aesthetic changes of the hot dip galvanized surfaces occur due to the triggering of the mechanism by which zinc protects the steel and prevents rusting (oxidation).

Why do shiny areas and matt areas appear on the same product?

The aspect of the hot dip galvanized steel immediately after galvanizing can be bright and shiny, zinc flower, mat gray or a combination of the previous. After a period of exposure in the atmosphere, the surface aspect is uniform. The most common cause that generates a different aspect of the surface is the chemical composition of the steel. For specific concentrations of silicon content thicker coatings are obtained that determine differences in appearance. Suggested silicon content must be either less than 0.04 % or between 0.15 % and 0.25 %. Steels whose silicon content is not in this range are considered reactive steels and will form thicker zinc coatings whose appearance will be dull gray or mottled unlike the bright and shiny appearence obtained in general. Differences in aspect can also appear be due to the difference between the cooling rate of the different sections of products (different thickness) or as a result of the processing of the materials during fabrication.

What is the price difference between galvanizing and painting?

Contrary to preconceived opinions, depending on the type of product and the condition of its surface, the initial cost of hot dip galvanizing is often lower than that of painting. If we consider the cost of the entire product life cycle including maintenance costs, hot dip galvanizing is the most economical method of corrosion protection. Painting requires maintenance and reapplication at regular time intervals, which on long term proves extremely costly.

Why are the air and venting holes necessary?

The main purpose of the air and venting holes is to allow therelease of air and gas retained in the inner hollow sections and to enable solutions used in the surface preparation process and molten zinc to freely circulate on all surfaces of the product both interior and exterior and then drain back into the bath. Due to the high temperatures that occur in the galvanizing process and rapid warming there is a significant risk of explosion at the immersion in the galvanizing bath when liquids remain locked inside parts.

What are the proper sizes for the air and venting holes?

The minimum size of the holes to avoid extended zinc leakage at the withdrawal of the product from the bath or blocking in in the interior is 8mm. For products with larger inner hollow sections, larger holes (12mm +) must be executed. This will ensure a better appearance of the surface, the immersion time in the zinc bath can be better controlled like this.

Why certain parts deform after hot dip galvanizing?

Galvanizing process takes place at a temperature of 450 ⁰ C. This is a temperature at which partial stress relieving of the induced stresses during fabrication can appear that sometimes lead to deformations. Deformations might also occur due to section differences between materials welded together that cause various expansions and contractions in the material at the immersion in zinc.

Can we paint over hot dip galvanizing?

Duplex system, as painting over hot dip galvanized steel is known, is an extremely efficient corrosion protection system. Proper surface preparation is essential to avoid possible adhesion problems. Depending on the age of the zinc layer the required surface preparation is established. Hot dip galvanized steel can be painted successfully in a wide range of colors.