Repairs To Bridges And Viaducts - Solutions From Mapei


When the subject of large-scale maintenance of infrastructure is discussed, we are inclined to think about the new, important projects, which are being installed all over the country. Not everybody realises that there is another important aspect, which relates to maintenance on existing infrastructure. In fact, each year the authority managing the road networks must invest a considerable amount of money into maintenance and repair work for the existing network that is currently in use and many operations are carried out on structures such as bridges and viaducts. The durability of such structures is severely tested by the enormous load cycles from the traffic in circulation, flooding conditions, aggressive atmospheric agents and the gases, which are present in the air. This means that their state of conservation, and in the worst cases their static safety, are put in danger. For example, structures built using what are now considered out-of-date design criteria, such as road and railway bridges built in the 19th Century, and the first structures built using reinforced concrete and pre-stressed reinforced concrete in the 20th Century, are highly subject to problems caused by heavy deterioration. We must also consider the fact that the type and volume of traffic has changed enormously from when the structure was built up to today, and that they were built using materials, which are inadequate for today’s standards, or were built by keeping the costs as low as possible. Therefore, it is quite clear that special attention must be paid to the reliability of these infrastructures, and to intervene where necessary. In many cases, these structures are part of a network that carries heavy volumes of traffic. Apart from the safety issues, when repair work is carried out, there is also the problem of potential traffic congestion when traffic needs to be interrupted to replace or repair the structures. All the structures in the road system must be well conserved to avoid compromising design responsibility, safety when the structures are in use and the implementation of maintenance operations. If the condition of a structure is not well monitored, it will be subject to such a degree of deterioration that normal maintenance operations will no longer be enough, and it will be necessary to carry out a more complex and heavier intervention, at a much higher cost. One way of preventing such problems is to have a detailed inspection programme, which periodically singles out maintenance operations required on the structures, thus guaranteeing, apart from the safety of road-users, lower overall maintenance costs.
One of the most important parts of assessing the state of deterioration is a visual inspection, which also singles out the causes of the deterioration:
- Intensity of circulating traffic
- aggressive environment
- climatic factors
- excessive loads
- occasional impacts
- insufficient drainage system for rainwater
Amongst all the possible causes of deterioration, road decks suffer most from the effects of improper maintenance, atmospheric agents and the presence of water in general. The deterioration of concrete shows up in several ways, with the progressive erosion and crumbling of the surface, corrosion of the metal reinforcement and the formation of rust, swelling of the cortex area of the concrete, etc. Apart from the different causes of deterioration, the problem often shows up at different times, which is why all the structures must be carefully checked on a regular basis to identify both routine maintenance and extra maintenance requirements. Below is a list of methods for the repair of bridges and viaducts:
- Preparation of the substrate;
- Protection of reinforcement rods;
- Positioning new reinforcement;
- Repairing concrete using thixotropic mortar;
- Repairing concrete using castable mortar;
- Repairing concrete using cementitious binders;
- Smoothing off concrete surfaces;
- Protecting and decorating concrete structures.

For further information, contact:
Mapei Construction Products India Pvt. Ltd.,
E: infoindia@mapei.co.in
T: 080 22221820 / 22221840
W: www.mapei.co.in

Each of these methods require different types of products, which are all suitable for achieving the required result, and the choice of which one of these to use depends on the location, the thicknesses to be repaired, on-site organisation, etc. To make sure that repair work is efficient and long-lasting, having the most suitable products available is not always enough. Deterioration to a structure may be due to a multitude of causes, and only if these causes are well known, may we be sure that repair work will be resistant and longlasting. Regarding this issue, the diagnosis of deterioration is a fundamental phase in the list of operations to be carried out. Through a detailed analysis of a structure it is possible, and essential, to define the type of aggression, the penetration depth of polluting agents and the characteristics of the concrete used for the structure. After these operations, it is then possible to carry out the repair work.
Substrate Preparation
Generally, every concrete surface that needs to be repaired requires preparation of the substrate. Which type of demolition technique to use will be evaluated according to the area and type of intervention. Manually, if the repair work is small; mechanically, such as with a pneumatic hammer or grinder; hydroscarifying, if the area to be repaired is large and the substrate must be in perfect condition.
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Protection of Reinforcement Bars
Protecting the reinforcement bars with Mapefer 1K, one-component, anti-corrosion cementitious mortar for protecting reinforcement rods.
Positioning New Reinforcement
Diagnosis of the structure also includes the reinforcement rods, since they are a fundamental part of the concrete. According to the results of the analysis, we can then decide which type of intervention must be carried out. A simple cleaning operation and application of a protective layer of a passivating product could be required. If the reinforcement is seriously compromised, on the other hand, with corrosion, which has reduced its section by more than 30%, it will be necessary to place new reinforcement to strengthen the structure. Where necessary, new reinforcement will be placed for the cast concrete to integrate the structure and will become an integral part of the substrate by inserting a series of connectors. The dimensions and amount of reinforcement will result from the calculation of the reinforcement required for the piles.
Repairing Concrete Using Thixotropic Mortars
1.Repairs using Mapegrout Easy Flow IN
Rebuilding of demolished parts by applying MAPEGROUT EASY FLOW IN on substrates saturated with water, but with a dry surface.
Mapegrout Easy Flow IN is one-component, fibre-reinforced, compensated-shrinkage, thixotropic mortar, particularly suitable for repairing concrete structures with a rendering machine.
Mapegrout Easy Flow IN is particularly suitable for repairing concrete structures when repair mortar is applied by spray,
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where the characteristics of the work (considerable height of the structure under repair, such as viaduct piles), the morphology of the site area (little space available to position mixing and pumping units in the vicinity of the structure under repair) and for site organisation requirements, mortar which is easy to pump over long distances and up to considerable heights is required.
Mapegrout Easy Flow IN may be applied by spray with a suitable wormscrew or piston-type spray rendering machine, such as a Turbosol or a Putzmeister. Mapegrout Easy Flow IN meets the minimum requirements of EN 1504-3 Standards for R4-class structural mortar.
2. Repairs Using Mapegrout SV MAPEGROUT SV is a single component, pre-blended, compensated-shrinkage thixotropic mortar in powder form, made from special hydraulic binders, highstrength cement, graded aggregates and special additives. Mapegrout SV is suitable where large thicknesses need to be applied (up to 5 cm), in specially-prepared areas without the use of formwork.
Thanks to its rapid hardening properties, it may be stepped on and opened to rubber-wheeled traffic after only 2 hours from application at a temperature of +20°C. The special
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composition and the additives contained in the product, the mortar has high mechanical qualities even after a long period of time, is waterproof and is highly resistant to abrasion. Apply the product using a trowel in the preprepared area. Mapegrout SV meets the minimum requirements of EN 1504-3 Standards for R4-class structural mortar.
Repairing Concrete Using Castable Mortars 1. Repairs Using MAPEFILL 06
MAPEFILL 06 is used to repair concrete structures where high thicknesses and special conformations of deterioration require the use of a castable mortar. Apply on substrates saturated with water, but with a dry surface. When mixed with water, Mapefill 06 forms a highly-fluid mortar, suitable for application by casting into formwork with no risk of segregation, including when applied at high thicknesses. To improve expansion in the open air during the first few days of the curing cycle, pour the mortar into the formwork in a continuous flow from one side only, to help
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all air to be expelled. The product meets the minimum requirements of EN 1504-3 Standards for R4-class structural mortar.
Smoothing, Protecting and Waterproofing Concrete Surfaces
Waterproofing and protecting structures using MAPELASTIC. After mixing together the two components, which make up Mapelastic to form a homogenous, lump-free product, apply according to the type of intervention to be carried out. The product may be applied manually using a smooth trowel or, in the case of large surface areas, as in this case, by spray using a rendering machine with a smoothing and levelling fitting.
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Whatever type of the above equipment is used, a fitting for smoothing and levelling fitting must be used with a 10 mm diameter nozzle, with an air compressor with a capacity of 800 l/min. Dampen the surface, spray on a layer of at least 2 mm of Mapelastic within 60 minutes of mixing and finish off with a flat trowel. Due to the high content and quality of the synthetic resins, the hardened layer of the product remains highly flexible under all environmental conditions. Mapelastic meets the minimum requirements of EN 1504-2, coating (C) according to the PI, MC and IR required in the EN 14891, for the protection of concrete.
Protecting and Waterproofing with MAPELASTIC SMART
Protecting new concrete structures and concrete structures repaired using special mortar from the Mapegrout or Planitop
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ranges using Mapelastic Smart. When the two components are mixed together, a blend with a plastic consistency is obtained. It may be applied by trowel or roller, or by spraying with a worm screw rendering machine with a smoothing and levelling fitting, on both horizontal and vertical surfaces at a thickness of approximately 2 mm per layer. Thanks to the high content and quality of the synthetic resins, the hardened layer of Mapelastic Smart remains constantly flexible under all environmental conditions.
Mapelastic Smart meets the minimum requirements of EN 1504-2, coating (C) according to the PI,MC and IR, for the protection of concrete and the requirements EN 14891.
Thus, as the saying goes, “Prevention is better than the cure”, Mapei has many innovative products for the prevention of such deterioration and to repair the deteriorated structures.