Complete Guide to Repair Cracked Concrete

LOS ANGELES - April 25, 2013 - PRLog -- Procedure and Materials for Comprehensive Crack Repair  

Tools: 4” Masonry Saw, Chipping Hammer, Hammer Drill, 1/2” and 5/8” Masonry Drill Bit, 3/4” Socket Wrench, Shop Vacuum.

Materials: Epoxy Concrete Repair Compound, Hydraulic Cement (see below for materials specification).

Step A: Chase crack with masonry saw 1/4” wide and 2” deep (approx.). Next saw and “V” cut to open crack approximately 3/4” wide. Locate stitch by tracing a rectangle (14 1/2” x 1 3/4”) and marking the holes 12” apart as shown.

Step B: Using 1/2” masonry bit drill both holes into concrete approximately 4” deep.
Step C: To create the box niche, cut and chip approximately 1-1/2" deep rectangular area with masonry saw and chipping hammer. To improve the chipping operation and make cleaner box cuts, the rectangular area can be sliced with the saw as shown prior to chipping. Remove all debris, clean out completely. Open one hole with 5/8” drill and verify holes are 2 1/4” deep below niche bottom. Do not over drill hole depths.

Step D: Place the sleeve anchor through the bottom of the stitch and thread nut onto the topside of the shaft 3-4 turns. Insert sleeve anchor into 5/8” hole and hook into 1/2” hole and tap down the head of the nut until sleeve is fully inserted in the hole and the unit is flush in bottom of niche.

Step E: Using a ratchet and 3/4" socket, tighten the nut on the anchor approximately 3-4 turns up to 50 Ft-Lb torque. Locate each stitch carefully. Mechanical Stitch installation is designed for permanent placement. Once installed and tightened down, the anchor cannot be easily removed or relocated.

Step F: Repeat above procedure with stitches spaced at approx. 1-foot along the length of crack (10 Mechanical Stitches for 10-foot crack).

Step G: Apply epoxy compound along crack by filling material into 1/4" slot at base of “V”. Dab compound at hole at hook end of niche. Wait 30 minutes and fill the niche and “V” with water-stop non-shrink hydraulic cement. For pools, finish with marble-based pool plaster or polymer modified cement for aquatic applications.

*Note: A minimum 5” slab is recommended for Mechanical Stitch installation. For shallower slab thicknesses, drill the anchor hole and install and tighten the nut. Once tightened the threaded shaft may extend upward and can be ground down flush with the top of the nut.

Materials Specification and Quantities

PART 1 – MATERIALS

1)    SlabStitch ST12-10 Mechanical Stitches

2)    Two-Component, High-Solids Epoxy Concrete Repair Compound

3)    Hydraulic Cement High Strength Repair Mortar for Stopping Leaks in Concrete

PART 2 – MATERIALS DESCRIPTION

1)    SlabStitchST12-10 Mechanical Stitches (10-stitch set); When installed properly can restore the tensile strength across the crack, reestablish compression, stabilize the structure, and transfer load away from the fracture. The stitches are fabricated with a machined face and slot, welded to A-706 rebar hook, hot dip galvanized, and installed in a niche below the concrete surface. The mechanical stitches function by tightening down the mechanical wedge to post-tension the rebar stitch, inhibiting the crack from expanding and getting larger. The anchoring mechanism consisting of a threaded stud with an outwardly flared cone-shaped end. Tightening of the nut pulls the cone-shaped stud end into the expander sleeve, wedging it outward and locking the anchor into the concrete base material.

2)    Two-Component, High-Solids Epoxy Concrete Repair Compound; Two-component, high-solids epoxy that chemically bonds with the concrete to provide a structural repair and specially designed and formulated to repair cracks in pool shells and concrete slabs. Dispensed in side-by-side cartridges through a static mixing nozzle and dispensing tool, when properly installed, provides a repair that is both waterproof and high strength (structural).

3)    Hydraulic Cement Rapid Setting, High Strength Repair Mortar for Stopping Leaks in Concrete; a rapid setting, high strength repair material designed to plug leaks instantly in concrete and masonry; designed to block running water or leaks in cracked pool shells and concrete slabs.

PART 3 – MATERIALS NEEDED TO REPAIR 10-FOOT CRACK

- 10-Stitch Set SlabStitch™ ST12-10 Mechanical Stitches (One stitch per foot of crack typical)

- 30 oz Two-Component Epoxy Concrete Repair Compound  AquaBOND Concrete Repair Compound (or equivalent two-component concrete repair epoxy for pool repair)

- Hydraulic Cement ­­­

In Summary
Integrity repair methods restore the tensile strength across the crack. For significant fractures, adequate reinforcing across the crack can inhibit future movement in the slab. Comprehensive Concrete Crack Repair involves a combination of options (adding reinforcement, post tensioning and compression, anchor stitching, doweling, and epoxy injection) and peformed properly, is engineer recommended to restore the structural soundness and integrity of a concrete member. The SlabStitch ST12 Mechanical Stitch method is highly recommended as the cost effective solution to restrain future movement in slabs. For more information, call 754-333-0877 and visit http://SlabStitch.com

About the Author
Mark Weber PE, is a Licensed Professional Engineer that specializes in Mechanical and Civil Engineering. Our Civil Engineering services include design of structural repairs, concrete restoration, and fracture stabilization. Our Mechanical Engineering services include product evaluations, testing, and inspection; and Aquatic services include swimming pool code compliance, design, and structural crack repair. We pride ourselves on high quality, technical expertise, and excellent customer service. For more information, please visit http://MwEngineering.net.

References: ACI 224.1R-93 “Causes, Evaluation and Repair of Cracks in Concrete Structures” reported by ACI Committee 224 in the Journal of the American Concrete Institute, May-June, 1984, (Reapproved 1998), American Concrete Institute, Farmington Hills, MI.