FEATURES
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
AFFORDABLE
SA HOUSING