GB2114640A - Repairing concrete structures - Google Patents

Abstract

A method for repairing the basal portion of a reinforced concrete upright structural member 1 in a building, which method comprises removing unsound concrete from the terminal portion of the member 1 back to sound material, placing a pre-cast concrete plinth member 6 adjacent to an upright structure member 1 which has been cut back to sound material and grouting the plinth 6 in position; the plinth member 6 having a longitudinal aperture 7 therein into which a reinforcing member 8 is inserted into adjacent plinth members 6 to provide a continuous reinforcement to those adjacent plinth members 6. <IMAGE>

Description

SPECIFICATION Repairing concrete structures The present invention relates to a method of repairing concrete structures.

In some forms of houses and other buildings, a main load-bearing structure is constructed from pre-cast concrete columns having steel or other reinforcing. However, with time, the acidity in the air neutralises the alkalinity in the concrete protecting the reinforcing, so that moisture can attack the reinforcing and cause corrosion of the reinforcement, especially where the reinforcement has not been correctly located within the concrete.

This causes the reinforcement to expand, thus cracking the enveloping concrete. Eventually, the structural members become unsound and require to be replaced. This problem is particularly acute at the foot of the concrete columns used in some types of pre-fabricated houses, since moisture occurs not only due to rising damp from the ground, but also due to condensation within the building.

In order to remedy the above defects in such structures, it has been proposed to cast new concrete plinth members encasing the base of the affected columns from which the more adversely affected portions have been cut away.

However, this method is time consuming and costly and can involve evacuation of the building to permit access to the affected areas, the erection of shuttering both inside and outside the building and considerable on-site supervision to ensure that the operations are carried out correctly and that the reinforcement is correctly located in the new plinth. As a result, some local authorities have chosen to demolish affected buildings rather than incurr the cost and disruption of carrying out the repairs.

We have now devised a method for repairing such structure which reduces the above problems.

Accordingly, the present invention provides a method for repairing the basal portion of a reinforced concrete upright structural member in a building, which method comprises removing unsound concrete from the terminal portion of the member back to sound material, placing a pre-cast concrete plinth member adjacent to an upright structural member which has been cut back to sound material and grouting the plinth in position; the plinth member having a longitudinal aperture therein into which a reinforcing member is inserted into adjacent plinth members to provide a continuous reinforcement to those adjacent plinth members.

To aid understanding, the present invention will be described with reference to a preferred form thereof as applied to that type of house structure known as an Airey type house. The invention can be applied to other pre-cast structures, e.g. barns, garages and other sectionally built buildings, in essentially the same manner as described below.

In the accompanying drawings, Figure 1 is a vertical section through the plinth in position, Figure 2 is a horizontal section through the plinth of Figure 1, Figure 3 is a plan view from below of an alternative form of plinth and Figure 4 is a view of yet a further form of plinth from inside a house.

The house is built from a series of generally upright pre-cast concrete columns 1 set on a suitable foundation 2 and damp-proof course. The columns comprise a steel or other reinforcement tube 3 encased in concrete. Whilst a single substantially central tube 3 has been shown, a solid reinforcement rod or rods can also be used.

The columns 1 carry concrete of other external panels 4 to provide the external cladding to the building and usually carry plaster-board or other panels to provide the internal finish.

Uue to the action of water and chemicals, the concrete at the foot of the column 1 becomes unsound. In the process of the invention, this is cut back to sound materia'. With the form of plinth shown in Figure 1, it is necessary to remove sufficient material from the exterior face of the column to enable the reinforcing rod 8 to be put into place as described below. The repair work can often be carried out from the exterior of the house merely hy removing one or more of the panels 4 from the outside of the house and this reduces the need to disrupt the use of the intcrior of the house during the repair period. Where the tube 3 is exposed, it should be cleaned to provide a good surface for the grouting to key onto, e.g. using a wire brush. If desired, the cleaned tube can be given an anti-conosive treatment, e.g. with a phosphate.In some cases it may be necessary to cut away the foot of the tube where this is badly corroded. The foot of the resultant shortened tube should be supported, e.g. by inserting a bolt 11 into the end of the tube and screwing a nut 1 2 on the bolt up hard against the tube, so that the bolt 11 acts as a simple screw jack.

Once the unsound material has been removed from the columns, a precast plinth 6 is positioned at the foot of the column. This plinth 6 can be located between the columns as shown in Figure 2: or can encompass the foot of one column 1 as shown in Figure 3 and extend to either side thereof to co-operate with the plinths to adjacent columns. Also the plinth 6 can extend under part or all of the remainder of the column as shown in Figure 4, in which case the tube 3 can be cut away to permit the piinth to be inserted under the foot of the column and/or plinth 6 can be recessed to accommodate the end of the tube 3 and column 1.

As indicated above, we prefer to remove material from only the outer portion of column 1. We also prefer that plinth 6 has stepped plan shape to its ends so that it lies between adjacent columns and provides a portion extending across the face of column 1 as shown in Figure 2.

The plinth 6 has a longitudinal bore or slot 7 therein which is adapted to receive a reinforcing rod 8. The bores or slots 7 in the adjacent plinths are in register with one another so that a continuous length of rod can be passed through a series of the plinths to tie them together. This bore can have any suitable cross section and this need not be the circular shape shown in Figure 1. The plinth 6 can contain additional bores or slots to those shown in the drawings and each plinth can also be provided with individual reinforcement 10 if desired. A transverse bore or bores 9 is preferably provided linking bore 8 with an outer face, preferably the top face, of the plinth so as to enable grouting medium to be fed to bore 8.

Plinth 6 can be of any suitable size and shape, depending on the structure to be repaired. For an Airey type of house, we prefer that plinth 6 be so dimensioned and shaped that its external face corresponds to and replaces the lowest of the external panels 4.

In addition to plinth 6-and rod 8, other components can be incorporated into the. repair of the structure. For example, an insulation pad 20 can be provided on the inner face of the plinth and this face can also carry a damp-proof membrane 21. The top surface of the plinth 6 is preferably sloped towards the outer face so that any condensation forming on the plinth will drain to the outside. Where a mastic or mortar seal 40 is formed between plinth 6 and the lower lip of the cladding 4, it is preferred that this seal is not continuous so as to permit condensation to drain away.

When the plinth and the reinforcing rod 8 have been put into position, a grouting medium 30, e.g.

cement, is fed into slot or bore 7 via bore 9 and into the gaps between column 1 and plinth 6 to form a unified structure incorporating the foot of column 1, the plinth 6 and the rod 8. Preferably, tube 3 has holes through the wall thereof, notably when it has been shortened and a bolt 11 inserted to support its foot as described above. The holes allow grout to enter the tube and aids formation of a unified structure. Such a structure provides an acceptable repair to the building which can be achieved with preformed components inserted from the outside of the building. This enables the repair to be carried out more rapidly, at a lower cost and with less disruption than when in situ casting techniques are used. The plinth is a precast member, notably of concrete and can benefit from the quality control of dimensions, materials and manufacture which it is possible to achieve in a factory environment but not on site.

Claims (5)

1. A method for repairing the basal portion of a reinforced concrete upright structural member 1 in a building, which method comprises removing unsound concrete from the terminal portion of the member 1 back to sound material, placing a precast concrete plinth member 6 adjacent to an upright structural member 1 which has been cut back to sound material and grouting the plinth 6 in position; the plinth member 6 having a longitudinal aperture 7 therein into which a reinforcing member 8 is inserted into adjacent plinth members 6 to provide a continuous reinforcement to those adjacent plinth members 6.

2. A method as claimed in claim 1 wherein the upright structural member comprises a hollow reinforcing member and this is exposed during removal of unsound material, the basal portion of the reinforcing member is cut away and a bolt carrying a nut is inserted into the reinforcing member and the nut is caused to bear against the foot of the reinforcing member to urge the head of the bolt downward to support the structural member.

3. A method as claimed in either of claims 1 or 2 wherein the building a a prefabricated type house and the repair is carried out at the foot of an external wall.

4. A method as claimed in claim 3 wherein the plinth 6 has an external face corresponding to one of the basal panels 4 of the external wall and when in position replaces that panel 4.

5. A method as claimed in claim 1 substantially as hereinbefore described with respect to and as shown in any one of the accompanying drawings.