In order to transfer a sufficiently high pressing pressure, the crack should be dammed up, i.e. it should be sealed at the surface, For this purpose, trowelling masses, for instance based on epoxy resin or poly-methacrlylate resin are utilised [Grube90].

Treatment
of base

Boring
 

Cleaning
boring holes

Hammering

In order to prevent damage to concrete structures, the injection pressure according to [Asend88] should be confined to a maximum of 33 % of the cube strength of the concrete.

Huge water infiltrations into concrete and reinforced concrete manholes can be sealed by injections in accordance with [DGEG86b] :

• damming of water infiltrations by means of single-component polyurethane foam
• injection by means of two-component polyurethane resin
• second injection by means of two-component polyurethane resin.

Damming the entry of the water with a single -component polyurethane foam

Due to the rapid foaming of the injection medium on contact with the water, an enclosed blocking layer is created that temporarily prevents the entry of water and thus an uncontrolled flushing away of the subsequent injection medium until the end of the reaction of its components. This step can be left out if there is only a weak flow of water.

Injection with two-component polyurethane resin

This fills the cavity and the previously introduced polyurethane foam, if it was injected, is compressed. A soft elastic resin is formed with a high modulus of expansion, which seals the entry of the water and retains its sealing properties even with later movement of the structure e.g. through temperature and alteration of loading.

Second injection with two-component polyurethane resin

At the contact surface concrete / polyurethane resin there can occur, in the injection at b), in the enclosed water in the concrete pores with the polyurethane, a "foam reaction" and this can impair the local adhesion of the resin to the concrete, which might require a second injection under certain circumstances. For this reason, local pressures of 250 bars must be applied …

The execution of the injections, as well as the events that occur should be recorded in special protocols. For instance, the following should be included:

• Crack figure and position of the crack in the structure;
• Injection points (number of the positioned packers, spacing internally);
• Start and end of the injection for each injection position;
• Injection pressures applied;
• Type and quantity of the inserted injection media;
• Temperature …

A sample of the resin used must be taken daily and the date must be recorded with it [Ruffe81].

An important share of the repairs to manholes is the regulating and exchange of manhole tops because today, as compared to earlier, much greater demands are made on the evenness of the traffic lane and these are subject to higher loads due to the heavier traffic conditions .

According to DIN EN 124 [DINEN124:1994], a manhole top is the upper part of a manhole, namely "that part of a manhole consisting of a frame and a cover and/or a grating".

The following points of damage occur especially often:

• Crack formation at cover, grating or frame;
• Wear of the frame and/or the lid especially on the support surfaces between the lid and frame;
• Positional deviation of the frame of the manhole top ;
• Settling differences between the traffic lane or pavement and the manhole top .

Damages of cover or frame according to DIN EN 13508 [DINEN13508-2] :

• cover broken (A)
• rocking cover (B)
• cover missing (C)…

Consequences of damage:

• traffic hazards (material damages and personal injuries)
• traffic obstruction
• noise disturbance (due to clanging manhole covers or uneven road)

The most common cause for the last two named types of damage is the failure of the grout between the frame of the manhole top and the throat of the manhole or possibly the support ring through a combination of dynamic loading from passing vehicles and chemical / physical stressing caused, for instance, by:

• Effects of thawing salt;
• Temperature differences;
• Differences in moisture content;
• Freezing / thawing change stresses.

Further causes that can …