Wednesday, July 6th, 2022
CECR

Innovation: Re-Profiling Of Bridge Decks With PMMA Resin Before Waterproofing

 

Paul Guinard
Director of Civil Engineering
SOPREMA

 

As renovations are increasing on civil Engineering structures in most of the countries, the re-profiling of surface bridge decks is becoming common but this is not without risk, especially, for the implementation of the successive waterproofing layer and wearing courses. New PMMA resin-based products offer a quick and effective solution that fulfills both the roles of re-profiling and also as pore filler primer for waterproofing by liquid PMMA resin or by bitumen prefabricated sheets.

Current Re-Profiling Techniques

In order to ensure the safety and comfort of users, infrastructure owners must carry out regular renovation campaigns for bridge structures. In particular, the bridges and structures of major motorway projects built over 30 years ago must be regularly monitored. The work for repairs needs the traffic to be stopped during the intervention period. The duration of this stoppage depends not only on the extent of the work to be carried out but also on the techniques used. In general, as the “time” factor is essential. In particular, for re-profiling the surface of the concrete of the deck after wearing course planer, solutions to limit traffic closure are preferred.

Re-Profiling with PMMA Resin
  During the renovations of the structure, the wearing course in asphalt and the existing waterproofing layers are planned in such a way so as to find the concrete substrate for control, to be able to repair it and/or strengthen it and then to rebuild the waterproofing layers and the wearing course layers. Unlike new structures on which the surface of the concrete is regular and smooth; old supports, very rarely meet the actual specifications and requirements for the implementation of the modern waterproofing systems: planimetry, cohesion, roughness.

 

This can be explained by multiple reasons:
– The concretes implemented in those years were not as good quality as those of today
– The action of the planer alters the surface quite strongly and makes an irregular surface
– The old structures were often designed with no slope, which does not allow water runoff and is nowadays strongly discouraged

As a result, re-profiling and a new surface preparation are often necessary

There are currently three main techniques for surfacing support:

– Pouring a hydraulic mortar thin slab (so-called white re-profiling)
– Adding an asphalt layer (so-called black re-profiling)
– Using of charged resins

The first technique should be used when the concrete is badly damaged and requires extensive repairs with possibly reinforcement. It is suitable to use this solution on the entire surface in order to avoid side effects (small steps, peeling, punctual concrete removing). It can also be used for filling spot holes but a specific treatment of the contours is then necessary. It should be noted that, in the implementation of the superior waterproofing layers, a minimum drying period of 14 days will be required in order to limit the concrete water content.

The black re-profiling is now often used for projects requiring rapid implementation. It consists of placing a 2 to a few centimeters thick layer of concrete asphalt on the entire bridge deck. This operation requires heavy machines but presents the advantage to be carried out at high speed, so it is particularly interesting for large works. For small works, it is often expensive and other solutions are preferred. It should be noted that this technique creates an increase in weight on the structure, weight that must be integrate in the calculation of the structure resistance. As far as waterproofing is concerned, this solution has advantages and disadvantages. The first advantage is to have a bitumen made support on which the bituminous membrane will be easily welded with a very good level of adhesion. The second advantage is that, because the concrete asphalt is porous, the pressure rises of the air contained in the substrate are diffused and the risk of blistering of the membrane is thus greatly reduced. But this advantage can also become a risk.

 If, by accident during the work phases or during exploitation, the bituminous membrane is punctually damaged, the water that will enter by this defect will be able to circulate in the under-asphalt layer over the entire structure limitlessly and without any way of detecting the place of leakage. In many cases, the recovery will then have to be the total surface.

The re-profiling with charged resin technique is, for now, less used around the world because the products offered are mainly epoxy-based and the conditions of their use are quite difficult to meet (especially the temperature). In addition, epoxy and epoxide mortars are, by nature, quite rigid. This feature allows for good resistance to compression but low flexibility (not to forget that a bridge deck is mainly used in bending). Thus, it is not advisable to set up these products on large thicknesses and it is not suitable to re-profile large surface (only local repairs of holes are possible).

Bridge Deck Before Re-Profiling

 

In order to overcome the problems faced by the waterproofing applicators with the quality of the substrates after planers, SOPREMA, a French specialist in waterproofing and insulation, conducted research, carried out numerous tests with different types of products and finally developed an innovative solution that meets most of the requirements of the product needed for a perfect re-profiling: speed, regularity, flexibility, compatibility with bituminous membranes and liquid waterproofing. This solution is based on the use of PMMA resins

PMMA Resin

Methyl Poly Methacrylate or PMMA is a thermoplastic polymer initially known for its use in the development of unbreakable windows (the best-known brand is Plexiglas©). It is also used in paints, waterproofing resins, dental products and lubricants. Thanks to its properties, including its transparency, mechanical resistance and resistance to climatic effects (UV, water presence and temperature changes); it is now used in many industries.

For its application on site, the resin is proposed in a two-component form: resin (liquid) and catalyst (powder). It will be charged with silica added to the mixture in order to increase the volume and to reduce the cost of the final mix while maintaining a good fluidity for its easy application.

Implementation On Site

Prior to application, the substrate must be cleaned from all non-cohesive parts (no oil, no dust) and be dry so that the product can bond properly to it. The application of re-profiling must be implemented with a substrate constant or decreasing temperature (usually in the early morning or in the evening) in order to avoid blistering in the resin. The application under sun is prohibited.

The resin-silica mixture is made cold directly on the site by using a mixer with a ratio of 1/1 in weight. The silica is placed in the resin pot (maximum 10 kg in order to be manually installed) and mixed. Once the mixture is homogeneous, the catalyst is integrated and mixed for about a minute. The amount of catalyst to be incorporated into the mixture depends on the outside temperature:

Temperature between 20°C (68°F) and 35°C (95°F): 1 x 100 g pack for 5 kg of resin

Temperature between 3°C (35°F) and 20°C (68°F): 2 x 100 g packs for 5 kg of resin

Mixing of Resin, Silica and Catalyst

Apart from the minimum and maximum quantity, the exact amount of catalyst does not influence the quality of the result but mainly changes the reaction speed of the resin and thus its possible application time. The introduction of the catalyst causes the start of the reaction for the entire mixture.

The mixture is easily applied on the deck by achieving a “zero pull” with the raclette in order to fill all defaults and holes. The resin must be spread out before hardening. No sand dusting is required on the resin layer

The amount of re-profiling mixture to be implemented is generally between 1 kg (0.5 kg of resin and 0.5 kg of silica) for a low-damaged support and 2.5 kg for a medium with large grooves.To fill a local hole, there is no thickness limit (from a film to about ten centimeters) but the thickness needs to be limited (1 to 2 mm maximum) on large areas to reduce the tension on the substrate.

The reaction is exothermic and gives off a characteristic odor without specific toxicity.

 

Once the resin has reacted, it presents itself as a pale-yellow hard layer. Site traffic is possible directly on the resin about fifteen minutes after implementation. Because the resin is not sensitive to UV (a slight change in colour may still take place), the resin can be left exposed for several days.

Where necessary, the welding of the bituminous membrane (manually or using automatic laying machines) is possible two hours after the installation of the resin without adding any tack coat. High temperature resistance allows its use both under bituminous membranes and under asphalt-based systems.

Where requested, the application of liquid waterproofing (PMMA resin) is possible 30 minutes after implementation.

It is advisable to entrust the resin re-profiling works to the company in charge of the waterproofing application. The use of two-component resins requires know-how and the selected waterproofing systems (liquid or bituminous membranes) must be compatible. It should be noted that the use of PMMA resin for re-profiling a substrate can be also considered as pore filler (strongly limiting the risk of blistering) in the use of bituminous waterproofing membranes.

Implementation
Bituminous Membrane Welding by Machine

The Interests Of This Technique

This innovative re-profiling solution in PMMA resins offers many advantages over traditional techniques:

– The speed of the PMMA reaction saves valuable time while requiring neither heavy machine nor specific contract as it is usually implemented by the waterproofing applicator. Even on local areas treated with a high thickness, the support will be circulating in a few minutes and the waterproofing products can be implemented two hours after application.

– The temperature conditions possible for the implementation of this product (between 3°C (35°F) and 40°C (100°F) allows work to be carried out in any season (the only reservations are that the substrate is not frozen and that it does not rain)

– The PMMA resin allows the result of a very puncture resistant re-profiling while having a good flexibility limiting its surface cracking. It should be noted that there is no edge effect as the product can be placed even with very limited thicknesses. The product can therefore be used by area.

– The SOPREMA resins are compatible to direct welding of the bituminous membranes and acts as a pore filler. Welding does not require any additional tack coat.

This solution has been implemented on several projects carried out in from 2017 in Europe with excellent results promising a bright future for this technique.

SOPREMA has built two production units specific to PMMA resins in order to answer to all requests and to maintain a high level of quality on these products.

Product information (SOPREMA manufacturing): PMMA resin:
ALSAN REKU P70 in 25kg buckets Catalyst:
ALSAN CAT in 100g packs Silica: ALSAN Fine Silica in 25 kg bags
Products available for direct sale

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