Spray-on waterproofing - Finding real application
Spray-on waterproofing - Finding real application Aug 2008
Shani Wallis, Editor
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Applying a spray-on waterproofing membrane is gaining acceptance on a growing number of tunnel projects.

The art of the spray-on membrane technique that creates a composite structure with the membrane sandwiched between the primary support and the final lining.

Neat fix in Lebanon
Water ingress through cracks in the existing concrete lining of the 30-year old Chekka highway tunnel north of Beirut forced Lebanon's Council of Development and Reconstruction to refurbish the parallel 360m and 390m long three-lane tubes. Design was based on casting a new 25cm thick reinforced in-situ concrete lining with a PVC waterproofing membrane behind.
In spring 2006 contractor Est. Antoine Makhlouf of Beirut tendered according to the project design and was awarded the contract. But the challenges of meeting the specifications soon became apparent. "What we needed was a solution that would allow us to retain the existing lining, which was intact, and that would provide the required waterproofing properties without encroaching excessively on the internal dimensions of the tunnels," General Manager Roger Makhlouf explained when he met TunnelTalk at the 2007 BAUMA exhibition in Munich.
An internet search led Makhlouf to the Masterseal©345 spray-on waterproofing system developed by the UGC (Underground Construction) division of BASF. With the assistance of the UGC, a value engineering alternative solution was developed and proposed.
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    Chekka tunnel - before.....

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    ......and after rehabilitation

The alternative was based on first repairing the existing lining then spraying the prepared surface with a 3mm coat of the Masterseal waterproofing membrane. A finish of tiles on the walls would then be applied to the final 4cm thick inner lining of steel fibre reinforced shotcrete to assist future cleaning. While the technique's limited track record was a concern, the advantages were difficult to refute.
1. No need to demolish the existing lining;
2. No need for concrete footings to support a new 25cm cast-in-place concrete lining that would interfere with the existing invert drainage channels;
3. Only minimal 5cm on the radius reduction of the interior tunnel profile as opposed to the 30-35cm profile reduction for the original design without removal of the original lining;
4. Simple repair should leaks appear in the new lining; and most significantly
5. A tremendous time saving from the expected eight months for the original refurbishment design to just six weeks for the alternative.
This last advantage was decisive considering the importance of the country's main six-lane north-south traffic route and the need to minimise the period of diversion and reduced contra-flow capacity through one tunnel while work progressed in the parallel tube.

The alternative was approved and Est. Antoine Makhlouf was given notice to proceed in August 2006.
Precise application
Central to accurate application of the Masterseal membrane is precision, consistency and high capacity spraying. This can only be achieved mechanically and in the case of the Chekka Tunnel, Est. Antoine Makhlouf rented a Meyco Logica Potenza computer controlled robot to apply the material to a uniform 3mm coating. Developed by Meyco (also a division of BASF) for precise spraying of materials including concrete, gunite, passive fire protection mortar, and sprayable waterproofing membranes, the electric-hydraulic Logica Potenza robots provide degrees of freedom from manual to fully automatic.
For automatic operation, the geometry of the surface is first scanned with a laser sensor. An on-board computer then calculates the kinematics of the operation and controls the boom and the spraying nozzle through the cycle and according to preset parameters of distance, speed and angle of the spraying jet to the surface. The maximum membrane-spraying capacity achieved to the required average 3mm thickness was about 1,800m2/shift or about 180m2/hr.
After sealing the cracks with epoxy and polyurethane resin grout injection and inserting a dilatation feature into the construction joints to relieve deformation cracking stresses, the concrete surface was cleaned and abraded using high-pressure water jetting to prepare for application of the Masterseal membrane.
Where in the past, the membrane product was delivered as a liquid material ready for spraying, the latest development of the concept by the UGC is to deliver the product as a powder and apply it using a rotor shotcreting machine and compressed air to feed the dry product through a 32mm diameter hose and introducing water to the stream at the nozzle. Control of the air supply, water and product was a manual operation while distance, speed and manipulation of both the boom and the spaying nozzle was controlled fully automatically according to parameters programmed into the robot’s control computer. The 3mm thick layer of Masterseal membrane was applied in one pass in sections of 4m long across the entire 13m diameter arch.
The contractor's personnel were trained to operate the Logica Potenza robot and achieved a production average of 1,500m2/10h shift or about 150m2/h. The membrane wass applied to each tube in just six working days. The coating then required about 48 hours to achieve the membrane's mechanical properties including the 1-1.2 MPa tensile bonding strength to the substrate surface.
Once both tunnels were completed to installation of the Masterseal membrane, the 4cm thick finish of steel-fibre reinforced shotcrete was applied as a single follow-on operation, again using the Meyco Logica Potenza robot on rent from BASF UGC. Working in full automatic mode, the crew achieved production rates of about 60-70linear meters of tunnel in every 10h shift to complete each tunnel in about seven to eight days.

General Manager Roger Makhlouf

According to Makhlouf, the whole composite liner system for both tunnels, comprising a total 750 linear meter of tunnel and 18,500m2 of arch area, was completed in six weeks, compared to eight months predicted to install a PVC membrane and a 25cm reinforced in-situ concrete liner.
When TunnelTalk asked about working with the Masterseal product Makhlouf said that there was very little rebound during application and only when wind through the short self-ventilating tunnel tubes was blowing particularly hard. "Water on the surface was not an issue because all weeping cracks had been sealed with chemical grouts beforehand so application was to a dry surface throughout. Humidity did affect the application but only in the time taken for the material to cure."
The flat, prepared surface of the original lining was said to have removed any issues of bridging or shadowing that could occur over a more rough or uneven surface and the Potenza robot ensured accurate coverage of every square inch. The steel-fibre reinforced shotcrete final lining was applied directly against the membrane without concerns of piercing or undermining its integrity.
"There was little difference between the estimated cost of the original design and the value engineering alternative", said Makhlouf, "and we did have to invest in developing a convincing proposal for the client and the project designer. But the entire process has been a most satisfying achievement especially in furthering a new industry technique and in cutting so much time and disruption from the anticipated construction programme. Time now will pass judgement on the durability and performance of the finished product."

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