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Sprayed Concrete Repairs - Online Shop

Sprayed Concrete Repairs are also sometimes referred to as - Gunite Concrete Repairs (although purists will say that ‘Gunite’ relates to the original dry spray process of spraying traditional concrete mixes with fine aggregate component (<12mm only). They are also described as - Machine Applied Concrete Repairs.

Sprayed Concrete Repairs according to European Standards EN 1504

In the new European Standard EN 1504 Part 9, Principle 3 defines the application of concrete repair mortars by machine (spray) as well as by hand.

There are two different types of this machine application or ‘sprayed concrete process’ that can be used for Sprayed Concrete Repairs:

• The ‘Dry’ spray process - (also referred to as Gunite repairs)

• The ‘Wet’ spray process

The selection of the best application method and the most appropriate repair material is dependent on the different requirements of each individual project, including the volume of concrete repairs and the volume of concrete repair mortar required, the distance available from the sprayed concrete machine to the repair location, the site location and the protection needed for adjacent areas. These criteria are further discussed below on this page.
Examples of Sprayed Concrete Repairs and Machine Applied Repair Works

Overall Advantages of Concrete Repairs by Machine Application

Hand and machine application of repair mortars can both be used for structural and non-structural concrete repair works.

For long-term durability, one of the key issues for successful concrete repairs is placing the repair materials and ensuring there is adequate compaction, especially around any exposed reinforcing steel.

Hand application is generally used for small scale concrete repair patches of limited damage, or where there is difficult access to the repair site and only for localised patch repairs are required. Hand application relies heavily on the skills of the operatives and the mortars can never be compacted by hand as well as they can by machines.

Machine Application of Concrete repair materials as ‘sprayed concrete’ therefore’ has the following advantages because of the application process:

▪ Higher bond performance
▪ Fewer voids because of better compaction
▪ Faster application

Criteria for Selection of the Most Appropriate Method(s) of Concrete Repair Mortar Application

The evaluation process to decide on the best application method for the concrete repairs on a project, is dependent on the different criteria that can obviously vary greatly on different types of structure and location, and from site to site. The following table givesyou a guide to the most important criteria that should be considered to select the most suitable and efficient application system on your concrete repair project:

Criteria Application Methods
Machine
  «Dry» «Wet» Hand
Economic aspects:      
• Cost efficiency for large repair volumes(> 500 kg/day) *** *** 0
• Cost efficiency for small repair volumes (< 200 kg/day) * * ***
• Installation costs * * ***
Application aspects:      
• Overhead application and extensive thick layer re-profiling *** *** *
• Compaction behind exposed reinforcement *** *** *
• Limited working space on site * ** ***
• Larger transport distance for material *** ** *
Environmental aspects:      
• Repair under dynamic load *** *** *
• Dust, noise 0 * ***
Technical aspects:      
• Bond strength *** *** *
• Possibility for high early strengths *** * **
0 = not suitable; * = possible; ** = good; *** = very good

Machine applied concrete repair can therefore be seen to be ideal on projects with high repair volumes. Their cost efficiency is much better than application by hand when higher volumes are involved and the quality of the hardened repairs is more homogeneous, especially for overhead applications.

Machine application of repair mortars not only brings the benefits of increased output, but it also helps to improve the repair's durability. Machine application should therefore be selected over manual / hand application techniques, whenever the economic and environmental conditions are appropriate.

Successful machine application of concrete repair materials is always achieved as the result of the appropriate equipment combined with the right repair material. ‘Added value’ is therefore created for the client, the engineer and the contractor, meaning a win: win: win approach, and in the following situations:

• Using machine application for placing large volumes of repair mortars
• Using machine application for reduced downtime or closures relating to the structures use

A Summary Comparison of the “Wet” and the “Dry” Spray Machine Application Processes

The “Wet” Spray Process for Concrete Repairs

Advantages
• Better yield
• Minimal rebound
• Minimal site protection required
• Suitable for application in confined spaces
• Easy trowel finishing
• Easier QC-procedures
• Reduced dust generation
• These mortars can also be applied by hand
• Constant mortar consistency

How it works
The mortar is first mixed and fed in a “plastic” consistence and as a ‘wet’ dense stream by pump to the point of application. Air is added at the nozzle, which then dissipates the mortar and propels it onto the substrate.

Accelerators can not be added at the nozzle

Typical wet spray equipment includes machines from: Aliva and Putzmeister.)

The “Dry” Spray Process for Concrete Repairs

Advantages
• Highest output
• Equipment blockages are rare
• Low equipment cleaning costs
• Long equipment life
• No premixing required
• No grout priming required
• Higher early strengths
• Long feed distances are possible
• Frequent stop/start sequences are easy
• Thicker layers in a single operation

How it works
The mortar is put into the pump hopper as a dry powder, which is fed ‘dry’ by compressed air in a thin stream to the point of application. At the back of the nozzle the powder is mixed with water, including accelerator if required, and propelled to the substrate by air at a pressure of about 2 bar.

Typical dry spray equipment includes the Aliva AL-246.5 and AL-252.1

Using Machine Application for Repairs Under Dynamic Load

Repair works often have to be carried out whilst the structure remains in service. Dynamically loaded structures such as bridges, silos, factory buildings etc., are frequently also subject to vibration, this dynamic loading places increased demands on the repair systems.

The European Standard EN 1504 Part 10 (Site application and QC of works) does not yet take this situation into consideration. But we understand that this is under review for a future amendment and update.

Concrete repair products that meet the highest requirement of European Standard EN 1504 Part 3 (class R4/R3) may still fail in terms of their bond behaviour, if and when their application is carried out under such difficult conditions.

Therefore NCC only recommend the use of systems that have undergone specific additional testing to confirm their suitability for application, bonding, curing and their hardened performance characteristics in such dynamically loaded situations.

Important Note:
It is essential to consider this important requirement on all dynamically loaded structures. The majority of repair materials and systems available are only statically tested and therefore their application will be at risk in such conditions.

Any repair systems not adequately tested in these onerous conditions may very well not perform in accordance with their published data whatever the method of application.

A Summary of Typical Situations where Machine Application of the Concrete Repair Materials is the Most Appropriate

High volume structural concrete repair - Much more economic and faster application, with less labour and increased Quality Control

Repair under dynamic loading - Faster application, hardening and curing with tested materials and systems that also achieve better compaction.

Overhead application - Faster application with improved adhesion, compaction and considerably less wastage

Short down times or closures - Faster application and hardening / curing with less labour involved

Additional Information on the Sprayed / Machine Application of Repairs

Do I need to use a Bonding Agent?

- With the “Wet” Spray Process? - For the majority of concrete repair materials bonding agents are recommended for both hand application and the wet spray process. However the latest generation of repair mortars (e.g. Sika MonoTop) do not always need a bonding agent if the substrate is well prepared e.g. minimum roughness of substrate >2 mm, with full saturation of capillary pores, immediately prior to the repair mortars application.

In some circumstances, including application under dynamic load, then a bonding agent such as SikaTop-Armatec 110 EpoCem, is usually recommended to increase the contact area at the interface between the parent concrete and the repair mortar, in order to increase the initial 'tack' and the ultimate final bond strength.

- With the “Dry” Spray Process? - In the dry spray process a bonding agent is not generally required. This is because a proportion of the coarse particles rebound in the first spray phase and this forms a transition layer that is enriched with cement and fines, which then also acts as an integral bonding agent. However, on very highly absorbent substrates, bonding agents are also recommended for dry sprayed mortars as these can prevent suction drawing out the mix water, which the repair material needs for good cement hydration.

A bonding agent, such as SikaTop-Armatec 110 EpoCem, can also be used when a barrier to moisture borne chlorides is required in the repair areas. In this instance, two applications of the bonding bridge material are required – the first being allowed to cure before the application of the second.

Do Machine Applied Repairs Need Curing?

As with all cement based materials, the correct curing is also very important with all types of machine applied concrete repairs, - sprayed concrete or - gunite. This is particularly important with the high performance, low w/c ratio mix designs, in order to ensure that sufficient water for is retained in the material for the complete cement hydration to take place. Excessive absorption into an inadequately pre-dampened substrate, or excess evaporation from the repaired surface, could lead to a weakness in the repair. The best methods of providing this curing to the applied concrete mortars are obviously dependent on the area involved, the immediate environment and the site exposure conditions. They can include covering with damp hessian and plastic sheeting, mist spraying with water of the immediate environment, or the use of a surface applied curing agent (only if the surface is not to receive an additional subsequent treatment, such as a protective surface coating – in which case these can act as barriers or even cause de-bonding of the subsequently applied protective coatings for example.

Most sprayed repair mortar applications require specialist equipment, training and experience, therefore we do not include many concrete repair mortar products that are designed to be exclusively spray applied in our Online Shop, although with the right knowledge and equipment it is possible to wet or dry spray almost any mortar products these days – Please call any of our office for specific advice on any aspect of sprayed concrete repairs.
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