Cement based high strength grouting mortar - CONCRETE REHABILITATION

In projects where CERS must rehabilitate parts of corroded reinforced concrete and protect the reinforcing rebars from further corrosion, the general application method is the following:

 - Removal of all corroded parts of the concrete via lightweight chiseling.
 - Protection of the exposed rebars by application of a protective coating film, according to the EN-1504 Standards.
 - Geometry Rehabilitation and reformation of the concrete element by a vast number of class R4 cement
    based coatings. The solution is chosen based on the total width of the application and the on site conditions
    of the project. In any case all proposed materials must follow the EN-1504 Standards.

Steel elements / plates

A further rehabilitation action that CERS has rich experience is the addition of steel elements or plates. In these cases, the application is made either by welded or bolted steel sections and the additional use of epoxy resin in order for the surfaces (steel – concrete) to adjust firmly. In the case of welded sections, the low viscosity epoxy resin is applied by injecting in order to avoid burning of the resin.

This section also includes the use of steel plates as a radiation protection shield. The plates are of significant width each and placed with a very sophisticated method so as to avoid any radiation leakage according to the regulations of the Greek Atomic Energy Commission (GAEG).

Shotcrete (dry mix  /wet mix)

The most conventional today method for structural rehabilitation / strengthening of reinforced concrete or masonry made constructions remains the dry or wet mix reinforced shotcrete. In general, the steel reinforcement consists of rebar addition to the desired direction, the addition of confinement rebars and at last the shearing cooperation of the shotcrete with the reinforced element through steel dowels or bolts.
The application of shotcrete varies from the final width to the mixing of the concrete (dry mix / wet mix shotcrete).
In each project, apart from the structural design details, the mix design of the material according to the specific needs is the key factor that combined with the necessary experience and know-how provide CERS with the ability to successfully complete any assigned project.
All the shotcreting works are conducted according to the Greek Technical Procedures  (ELOT ΤP 1501-14-01-14-00:2009 ¨Rehabilitation-Strengthening of concrete made constructions with reinforced shotcrete¨) and wherever project that does not cover, according to the American Standard  ACI 506R-05.

On site tests that CERS conducts to the shotcrete:

1. Compressive Strength measurements of three cylindrical shotcrete speciments in collaboration with a
     certified laboratory.
2. Electrical resistivity measurement at a specimen of dimensions 100x40x20 mm.
3. Measurement of the uniformity of the shotcrerte’s compressive strength  through pulse velocity
     (standard deviation < 800 m/sec, velocity > 3000 m/sec.)
4. Adhesion testing according to the EN 1542 (min. 1,70 MPa)
5. Pull out testing before and after 20 days of the shotcrete application (1 measurement per 20 m2).

On site tests that CERS conducts to the steel welding/anchoring
Pull-off testing of at least five anchors according to the ΕΝ 1881 (displacements <0,6mm at load of 70 kN).

Injections (cement – epoxy – PU – grouting mortar)

During a rehabilitation project CERS is often called to repair cracks in concrete elements, to fill cavities in anchoring levels or seal any cavity/crack for waterproofing (with or without ongoing leakage).
In the case of concrete cracks, the sealing is achieved through the low viscosity epoxy resin injecting. The method statement includes the surface cleaning, the placement of plastic injection nipples and surface sealing with 2 component epoxy resin and finally the injection of a low viscosity epoxy resin by pressure with special equipment.
In the cases of cavity sealing, usually in the anchoring level, CERS uses non shrinking grouting mortars of an injectable form that present high premature and final compressive strength (usually about 3 times more than an ordinary concrete casting). The equipment CERS uses differs from the first case and is compatible with the vast majority of the acknowledged materials.
Finally, in the cases of waterproofing injections in concrete made structures, the usual method consists of polyurethane or acrylic resin injecting. The suitable material depends on the volume of the leakage, the kind of the waterproofing and the material active life and maturity. The injections are carried out through metallic or rubber made injection valve – packers placed at a specific formation regarding the crack direction and depending on the wall width. Thus, a possible loss of material, especially in cases of ¨blind¨ concrete walls of the structure (e.g. basements, water tanks containing potable or not water etc.).