1.
Repair
In order to repair or enhance the strength of the column without affecting or spoiling the architectural design, two methods are recommended and should be considered. Reinstate the design strength by demolishing and recasting the failing columns. Enlarge columns section in the longitudinal direction (the direction with the wall)
2.
Method
of Statement of Repair
The following will describe the required material and tools for
reinstating the columns’ strength and the
procedure for repair.
A.
Material
Table A shows a list of materials that shall be used in the repair work. Quantities may vary according to the actual requirement of the work. The table lists the required material for both repair methods.
B. Tools
C.
Repair
Work Methodology for Neck Column and Ground Beam Joint
Repair
method A will incorporate the following steps.
Safety precautions and considerations.
Preconstruction meeting.
Excavation.
Installation of Temporary Vertical Supports for
Column Load Redistribution.
Surface Preparation.
Replacement of Defected Reinforcement Bar.
Reinforcement Bar Moisture Protection Priming.
Bonding Agent Application.
Installation of Column Formworks.
Column Casting.
Installation of Waterproofing Membrane.
Backfilling.
Repair
method A will incorporate the following steps.
Safety precautions and considerations.
Preconstruction meeting.
Excavation.
Installation of Temporary Vertical Supports for
Column Load Redistribution.
Surface Preparation.
Adding longitudinal reinforcement and lateral ties
reinforcement.
Reinforcement Bar Moisture Protection Priming.
Implantation of Anchor Bars.
Bonding Agent Application.
Installation of Column Jacket Formworks.
Column Jacket Casting.
Installation of Waterproofing Membrane.
Backfilling.
The following explains each step in detail, Safety precautions and considerations. Consultant shall hold a safety meeting for all involved parties, led by the prime contractor’s safety manager or the contractor himself, prior to beginning repair operations.
It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use. The user must determine the applicability of all regulatory limitations before applying the described repair procedure and must comply with all applicable laws and regulations and safety standards.
Preconstruction meeting, Prior to proceeding with the repair, a preconstruction meeting is recommended. The meeting should include representatives from all participating parties (owner, engineer, contractor, materials manufacturer, etc.), and specifically address the parameters, means, methods, and materials necessary to achieve the repair objectives. Include the owner’s representative, the project manager, the repair grout manufacturer, and the construction team foreman.
Excavation, With help of the jackhammer and shovels remove the existing ground slab around the column neck and excavate to the depth that exposes the column’s footing. Excavation shall be, at minimum, 0.5 meters wider than the footing to allow for waterproofing installation.
Installation of Temporary Vertical Supports for Column Load Redistribution, Install temporary vertical supports at the sides of each column as temporary vertical supports. Each support shall be well attached to the slab's soffit and foundation top. Consultant shall approve support size and fixation prior to demolishing/repair process commencing. The contractor may propose alternative temporary support works; this shall be subject to Consultant approval.
Surface Preparation, Remove the concrete cover from the required side /s by chipping with a cold chisel or by moderate hand drill chipping to get a rough surface and increase the adhesion of the new concrete. Chipping shall not be exaggerated. Surface preparation shall be inspected and approved in writing by the consultant.
Replacement of Defected Reinforcement Bar, With coordination with the consultant, all damaged reinforcement during the column demolishing process shall be replaced. Cut the damaged portion of the reinforcement bar as directed by the consultant; Consultant approval is vital. Overlap between the replacement reinforcement and the old reinforcement shall not be less than 40 D (bar diameter.
Adding Longitudinal reinforcement and lateral ties reinforcement, For 200mm x 250mm and 200mm x 200mm concrete jackets, 4T20 longitudinal reinforcement shall be added, and T12 @ 200mm transverse tie reinforcement shall be installed to confine the longitudinal bars and connect the new part to the existing one, see figures 9, 10, and 11.
For a 200mm x 600mm concrete jacket, 10T16 longitudinal reinforcement and T12@200mm transverse tie reinforcement shall be added.
Reinforcement Bar Moisture Protection Priming, Moisture protection priming shall be applied to the reinforcement bars as per the material application guide/instruction, in all cases, the minimum drying time shall be 5 hours.
Implantation of Anchor Bars, Holes for lateral anchor ties and vertical additional bar shall be drilled based on the required anchoring size; 20 mm for vertical reinforcement and 12 mm for horizontal tie reinforcement. The hole’s depth shall be as per chemical bond material instruction; however, in no way, the depth of the hole shall be less than 75mm. Mix and apply the chemical anchoring bond as per product instruction, Lokfix, or equivalent.
Bars should be left undisturbed in the required position until the grout is fully hardened.
Bonding Agent Application, For good adhesion between the old and new concrete, a bonding agent shall be used. Use CONREP 412 CRY bonding agent or any equivalent product that could be used. Product instructions shall be followed for mixing and applying. On rough surfaces let the product penetrate all irregularities of the substrate. The bonding must be performed only when the product is tacky. i.e. between I 0 min and 2 hours after application of the product.
Installation of Column / Column’s Jacket Formworks, Formwork shall be prepared in advance according to the jacketing required dimensions shown in Annex 2 and provided Auto CAD drawing.
Install the jacket, Inspect and approve the surface preparation and check the surface for contamination. Saturate the prepared surface. Set forms grout-tight, commonly used grout-head pressure number is 70 kPa. When form joints do not match perfectly against the original concrete, seal with thick mortar, or strong compressible material, figure A.
Grade
the aggregate, PPA requires gap-graded aggregate. This can be provided as
specified in ACI 304.1R, by a supplier, or sieved on-site. Saturate the
aggregate to prevent rapid absorption of water from the grout and thickening of
the grout as it flows.
Place clean/saturated aggregate as the forms are erected. Do not drop aggregate more than 1.5 meters, figure B. Place grout pipes and observation tubes if required (see ACI 304.1R for suggestions concerning placement of grout pipes and observation tubes).
Typical mixing equipment for mixing grout is a
two-tub mixer equipped with a rotor-stator pump and a water meter. Do not use
ball-valve pumps. Consult the manufacturer for mixing recommendations. Check
the grout consistency. Grout should be tested in accordance with ASTM C 939.
This is the flow cone test for consistency. Flow values as recommended by the
manufacturer.
Connect the pump hose to grout inlet openings or pipes.
Start placement at bottom of aggregate placement. External form vibration will
aid in grout consolidation. It is not always necessary with well-graded
aggregates and good-quality grout. When forms appear full, keep light pressure
on from the pump for several minutes to prevent sagging and displace water/air from
forms. Stop if the grout is spilling out
of forms, figure C.
Remove formwork 24 hours after the concrete pouring. Apply to cure compound immediately (CURE Y 40 - SODAMCO). Allow the concrete to cure for 14 days before stripping off the temporary supports.
Installation of Waterproofing Membrane Thoroughly cleans the column footing from dust, dirt loose materials, oil, or grease. Remove debris on the surface and obtain a smooth surface by patching the uneven surface with concrete repair material (CONREP TTX) or equivalent.
Provide cement-sand (1:3) mix cement along corners of the neck column and ground beam, if there, to eliminate 90-degree corners.
Remove sharp concrete edges by grinding the corners
of the column footings as indicated on the drawing.
Apply primer on the surfaces of the footing, neck column,
and ground beam prior to placing the membrane. 24 hours after the primer
application, install the 4 mm thick first layer with a minimum of 100 mm end laps
and 150 mm side laps by torching. Repeat the process till the entire length of
the membrane is bonded firmly to the
surface then lay the second membrane in the same way with an overlap of 150 mm
at the end and 100 mm at the side.
Install a protection board to protect the membranes
from a potential puncture caused by backfilling.
The membrane on the exposed external vertical surfaces shall extend up to 150 mm above the finished ground level and inserted into the provided continuous groove and secured firmly with approved waterproofing sealant/mastic recommended by the manufacturer of the membrane.
Backfilling, After obtaining the approval for the completed repair process, use the excavated material for backfilling, and shall be free of unsuitable material, if any. Backfill shall be done in layers and shall be well compacted.