Technical Feature
M-Coating shaft rehabilitation has
stood the test of time In 1982 Rainer Hermes first coated inspection shafts using the centrifugal spray method in Germany. By 1999, M-Coating equipment was coating a large number of shafts in Leipzig. In 2010 two shafts were centrifugally coated in Dortmund: a heavily corroded concrete shaft and a brick-built shaft with leaking joints that was showing its age.
Work on both shafts was monitored by the MPA NRW from Dortmund, Germany. Every step was recorded, although today’s automatic recording of cleaning and coating data was not available then. Both shafts were cleaned using the TSSR. The results were striking in the case of the concrete shaft.
In the case of the brick-built shaft, there was some incrustation and in places the brick had been baked very hard so that the surface was glazed. This called for sand & water blasting with the HDS-jet, which was able to remove the incrustation and roughen the surface of the brickwork.
A non-destructive test of compressive strength was then made using a Schmidt rebound hammer. All values were in the range above 20N/mm2.
It was
not possible to carry out tests of pull-off strength because the surfaces were wet and the concrete shaft was badly corroded. Holes and open joints were filled with ERGELIT-KS1. Now for the coating, mortar samples from the M-Coating continuous mixer were taken at the pump. Flow diameter was measured at around 140mm, using a Hegermann flow table as per DIN EN 1015-3. The concrete shaft was coated to a thickness of 30mm. This thickness was chosen to cope with the 50mm deep corrosion and to cover the coarse aggregate particles, which must be coated with at least 10mm of mortar.
The brick-built shaft was coated with approx 10mm of ERGELIT-KS1. Everything was recorded in the Quality Assurance handbook.
The brick-built shaft was stepped at a sharp angle, and varied from rectangular to oval and round. This posed no problem to the M-Coating equipment.
Mortar prisms of 4x4x16cm were made up on site. These prisms were later tested by the MPA for compressive strength and flexural strength. Flexural strength averaged 8.3 N/mm2 and compressive strength 59.8 N/mm2. Tensile bond strength was tested for both shafts after 28 days. In the concrete shaft we achieved a failure load of 2.11 N/mm2 between the pull-off head and the mortar, and in the brick-built shaft a failure load of 1.9 N/mm2. We may conclude from this that adhesion to the substrate is even higher.
TOP: Concrete shaft before and after cleaning (INSET)
ABOVE: Brick shaft before cleaning.
LEFT: After cleaning
14 drain TRADER | September 2015 |
www.draintraderltd.com
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