Reparation of foundation concrete of VNN 645/646-110 kV power line Albrechtice – Vratimov


Concrete composition:

• aggregate – weathered sandstone and smaller weathered pebbles
• cement rock – the material is carbonized, neutral to slightly acidic. The cement rock is porous with caverns of up to 5 mm size and fissured. The material is vulnerable to absorb water. The original cement rock is altered to carbonate. Weathered layers of the foundation gradually fall apart.

The concrete was of very poor quality. When trying to take a sample for compression strength test performance purposes, the drilling core disintegrated.


Concrete foundation of pole no. 80 affected by strong corrosion of the cement rock

Grouting works were performed above and below the ground level. Polyurethane grouting material was used, which replaced the partly disintegrated cement rock of the foundation. Before grouting a reinforcing wire of 8-10 mm diameter was placed into the drillings. Polyurethane materials used were GEOPUR 082/600 LW and Geopur 082/1000, which start to react after 2 min.

Microscope image of the cement rock after grouting - caverns filled out with polyurethane resin, grains closed within the grouting material

Foundation after grouting with the Geopur material

Compression strength tests were performed after the grouting on collected cores from the drillings.
For polyurethane material it is typical that samples tested for compression strength do not disintegrate. They deform in two steps. The first one is a reversible deformation till 3,25kN and ε = 0,5 mm. After deformation greater than 1 mm a secondary texture is formed with reversible reaction of the matrix. At deformation equaling to approx. 3mm, fissures start to appear within the polyurethane foam and further at deformation of 4,5 mm, the fissures massively develop and the material breaks. The breaking is gradual and is blocked by residual strength of the sides of the foamed polyurethane matrix. The above description proves good binding properties of polyurethane materials.