When the step irons are directly cemented in by means of plastics-modified mortar, the ground must be thoroughly cleaned and be provided with an adhesive layer.

In all cases it must be made sure that the material, the shape and step height per manhole are standardised and that, from a static point of view, the condition of the manhole wall allows for a replacement.

Measures for the restoration of defective regions in the inside of sewers of concrete, reinforced concrete and pre-stressed concrete have the aim, depending on the selected repair grout, among others of [DAfStBb] :

• The maintaining and replacement of the corrosion protection of the reinforcement;
• Replacing / supplementing the concrete cross section with or without requirements of stability;
• Replacing or increasing the resistance of the concrete surface …

The concretes and grouts, called repair grouts in the following, are constituents of so-called concrete rehabilitation …

Suitable materials for the repair of reinforced and un-reinforced concrete pipes are:

• Cement grout, concrete, spray concrete (Cement Concrete - CC);
• Plastics-modified cement grout (Polymer Cement Grout - PCC);
• Reaction resin grout (Polymer concrete - PC) based on epoxy resins, unsaturated polyester resins, polyurethane or polymethyl-acrilate resins.

An in-between position between cement and reaction resin grouts is occupied by the mineral grouts with water emulsion epoxy resin additives, whose hardening properties depend to a great extent on the exact agreement of the speed of the reaction of both binder materials [BDZ89].

Although the repair grouts are disadvantaged in comparison with concrete due to a lower modulus of elasticity for damage elimination measures that require a static participation, they are normally advantageous due to their greater ability to deform for protective measures for ensuring durability and utility in the near-surface region.

Plastic-modified cement grout (PCC) and reaction resins (PC)

Cement-bound grout
 

For repairs that only affect the …

Concrete surfaces that are to be the foundation for a repair measure must always consist of undamaged concrete, i.e. they must be free from dirt, old paints that cannot carry loads, floury fine grout layers and all other substances that can reduce a bonding effects (e.g. damaging salts such as sulphates, nitrates).

The concrete foundation must be prepared such that a tight and durable bond can be achieved between the repair grout to be applied and the old concrete. If the reinforcement is situated in the carbonised region of the concrete, then it must be exposed and de-rusted in the same manner as already described for reinforcement exposed by corrosion.

The required preparation of reinforcement rods depends on their condition, on the extent of the corrosion and the type of repair measures. For limited repairs of concrete spalling due to corroding reinforcement, the recommended method is conservation by means of anti-corrosion paints in accordance with the rules for steel construction. An anti-corrosion paint can be dispensed with if there is sufficient cover with reference to the rod diameter, …

For a durable bond between old concrete and repair grout, and with reference to the repair process, the concrete foundation must possess the following properties [Grube90] :

• Roughness of the surface;
• Quantity and sizes of cavities and pores;
• Wear resistance;
• Permissible cracks;
• Bearing strength, if necessary, E-Modulus;
• Carbonisation;
• Permissible chloride content;
• Moisture and temperature of the concrete.

The contact between old concrete and repair …

The application of the repair grout must be carried out before the bonding bridge is fully hardened (working "fresh on fresh"), otherwise there is the danger that the bonding bridge becomes a separating layer.

Adhesion bridge:

• Mapei: Mapegrout Primer D
• Keimfarben: Keim Concretal adhesion bridge
• Brillux: PCC Basisschutz 801 (as corrosion protection and adhesion bridge)
• MC-Bauchemie: Nafufill HB-HS
• StoCretec: StoCrete TH 250

Repair mortar:

• Mapei: Mapegrout 50 PCC
• Keimfarben: Keim Concretal mortar
• Brillux: PCC-coarse mortar 802, PCC-filling mortar 803, PCC-…

Repairing bad patches

Local bad patches in the masonry are re-bricked with sewer bricks to DIN 4051 ensuring that they are correct in profile and flush and using corrosion-resistant plastic-modified cement mortar.

Although sewer clinkers in masonry sewers are generally resistant to acids (for exceptions , the cement-bound grout joints are destroyed with corresponding loading .

If these masonry joints are not filled in with an appropriate grout again (pointing), then the result can be leaks, the falling out of one or more sewer bricks from the walls up to collapse of the arching. In this type of damage in the wetted …

Sewer cleaning

Corroded or loose jointing material, blooms, bulges, foreign matter (e.g. greases or oils) growths, dust and other dirt are removed by means of high-pressure jets with a flushing pressure of maximum 150 bar.

Removing loose jointing material

The butt and bed joints in the region of the springing line are cleaned out up to a hard underground but not more than 5 cm deep due to the fact that the joint mortar can soften and parts of it can be scratched out and thus have no real strength properties. This is carried out by means of a pneumatic angle grinder (Flex). Very uneven or small masonry joints are additionally cleaned out.

Cleaning of cleared joints

Then follows the removal of the waste material using the high-pressure jet again.

Re-jointing the previously cleaned-out joints

Ground and cleaned joints are re-filled up to the joint underground cavity with the Sewament 40 corrosion-resistant cement mortar of the Mapei Company making sure that there are no bad parts. The material used is first processed with a manually filled hand cartridge filler. The joints are filled-in from a corrosion depth of 1 cm (after cleaning).