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7. Insert bond-breaking compressible joint filler( such as expanded polystyrene foam of density 16kg per cubic metre- m 3) into the existing joint against the existing slab to fill the saw cut.
8. Apply an approved wet-to-dry epoxy resin as bonding agent to the entire area, including patch sides.
Bryan Perrie, MD of The Concrete Institute.
If there is adequate load transfer at the joints, the following repair methods are recommended:
1. Conduct a survey to determine the actual repair boundaries: all areas of delamination should be determined using a sounding technique. This may be done by striking the existing concrete surface with a steel rod or by tapping lightly with a hammer: a sharp metallic ring will indicate undamaged concrete, while a dull or hollow sound will indicate delaminated areas.
2. Mark out a rectangular area around the defect at least 100mm wide, parallel to the joint, and extending a minimum of 50mm beyond the defect. Repair areas less than 500mm apart may be combined to improve appearance.
3. Use a concrete saw, saw around the perimeter of the patch area to a minimum depth of 35mm. This provides a vertical face at the patch edges and provide sufficient depth to give integrity to the patch.
4. Provide an additional saw cut in the joint to a depth of 25mm below the bottom of the patch and extending at least 75mm laterally beyond each end of the prepared patch boundaries. The width of the saw cut should be equal to that of the existing joint.
5. Remove the concrete inside the patch area to a minimum depth of 35mm with a hammer and sharp cold chisel or light pneumatic tool until sound and clean concrete is exposed and the patch area is uniform in thickness. It is important that tools of the appropriate size are used. Using a pneumatic hammer which is too large may cause damage and fracture the concrete below. Under no circumstances should heavy jack hammering be used: the maximum allowable pneumatic hammer size should be 12kg.
6. Use compressed air to remove all dust and loose concrete. Partially loose concrete should be removed by wire brushing after which the area should again be cleaned out with compressed air. Then remove all loose particles and dust with an industrial vacuum cleaner.
9. Patch the hole with concrete of appropriate compressive strength and stone size. The concrete mix should be designed by an approved concrete testing laboratory to suit the aggregates available and the desired time of opening to traffic. The required minimum compressive strengths are 30MPa for vehicles with pneumatic tyres, and 40MPa for vehicles with solid tyres. The recommended minimum strengths should be achieved with a cement content not exceeding 500kg / m 3. A water reducer may be used. Preferred stone size is 9.5mm or about a quarter of patch thickness. Where circumstances do not permit a designed concrete mix, trial mix proportions may be used. These proportions will permit opening to traffic with pneumatic tyres after three days, and to traffic with solid tyres after four days, provided that the joints can be sawn and sealed within this time. Advice regarding sealant installation should be obtained from the supplier of the sealant proposed for use. Small poker vibrators( maximum diameter of 25mm) should be used for compaction. The repair area should be slightly over-filled to compensate for compaction.
10. Finish the patch flush with the level of the surrounding slabs. The recommended finishing procedure is to screed from the centre of the patch out to the patch boundaries to promote a good bond with vertical concrete faces.
11. Hand steel trowel to match the finish on the adjacent floor surfaces and carefully round off the edge of the repair area adjacent to the joint to 3mm radius.
12. Cure immediately by covering the patch with polyethylene sheeting sealed at the edges and maintained in place until removal of the polystyrene filler.
13. Remove the polystyrene filler in the joint opposite the patch by sawing.
14. Reseal the joint using liquid or preformed joint sealant and follow the recommendations of the manufacturer of the sealant. Aspects to be observed include the need for clean and dry joint interfaces prior to sealing; priming of joint sides for certain liquid sealants; provision of the proper joint shape factor for liquid sealants; provision of a bondbreaking cord( consisting of closed-cell expanded polyethylene foam); and a bond breaker for liquid sealants, plus the desirability of undersealing joints( usually 3 to 5mm).
For details of the recommended concrete mixes and mixing procedures, consult The Concrete Institute website.
18
MARCH- APRIL 2018
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