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S-1 A P P E N D I X S AASHTO Quality Assurance Guideline
S-2 AASHTO QUALITY ASSURANCE GUIDELINES FOR MATERIALS AND INSTALLATION OF EPOXY ANCHOR SYSTEMS IN TRANSPORTATION APPLICATIONS ADHESIVE ANCHOR SYSTEMS This guideline addresses the material and installation of adhesive anchor systems in transportation applications. Material Adhesive for adhesive anchor systems can be an epoxy, polyester, vinyl ester, acrylate, or hybrid mortar and consist of two parts (a resin and a hardener) and come in either cartridge or capsule format. Cartridge systems are commonly packaged in two tube cartridges with a dispensing gun and mixing nozzle. Capsule systems have glass or foil packages that are placed directly in the hole and the two parts are mixed during insertion of the anchor. Bulk systems must be approved by ACI 355.4 and have automatically controlled metering and mixing of components. The term âadhesive anchor systemâ includes all the materials and equipment necessary for proper installation. This includes not only the adhesive, but also the anchor, the mixing and delivery systems (dispenser gun, mixing nozzle), equipment for hole cleaning (air nozzles, air pumps, brushes), and the Manufacturerâs Printed Installation Instructions (MPII). Adhesive anchor systems have a shelf life and the expiration date should be checked prior to use and all expired product should be discarded and not used. As most adhesives are sensitive to temperature, the MPII should be consulted for the proper environmental conditions and temperature ranges during storage and installation. INSTALLATION Adhesive anchor systems are approved for use for specific installation conditions and procedures as specified in the Manufacturerâs Printed Installation Instructions (MPII). This quality assurance guideline discusses and explains the common installation conditions and procedures encountered in most MPIIs but should not be viewed as an instruction for installation of adhesive anchor systems. Each adhesive anchor system must be installed in accordance with its specific MPII.
S-3 Per ACI 355.4, adhesive anchors can only be installed in holes drilled in concrete that is at least 21 days old and with a minimum compressive strength of 2500 psi. The concrete should be structurally sound and free of surface cracks. Some products require installation only in dry concrete while others permit damp, saturated, or even submerged installation conditions and the MPII should be consulted for the approved installation conditions. Drilling Most adhesive anchor systems require drilling with a rotary impact drill with carbide bit. Diamond core drilling is not allowed for approved products unless covered in the MPII. Adhesive anchor systems develop their strength partly due to interlock with the roughness of the side of the drilled holes. Due to their violent nature, rotary impact drills create a relatively rough hole while diamond core drills produce a relatively smooth hole â especially in high strength concrete. Holes should be drilled perpendicular to the surface of the concrete. Holes should be drilled to the proper embedment depth as stated in the drawings making sure to observe the minimum and maximum hole depths as stated in the MPII. If reinforcement is encountered during drilling the anchor should be relocated, or, if approved by the Engineer, a diamond core drill can be used to cut the reinforcing steel. Once the reinforcing steel is cut, the drilling should resume with the rotary impact drill. Hole diameters shall be in accordance with the MPII, but typically range from 1.15 to 1.50 times the anchor diameter as this is the range of the adhesive anchor design model found in AASHTO 2010 LRFD Bridge Design Specifications and ACI 318-11. As some adhesive anchor systems are sensitive to the width of the annular gap between the anchor and the side of the hole, manufacturers specify in the MPII the required bit diameter for each anchor type and size which is usually around a 1/8â larger than the anchor. Hole Cleaning One of the most important aspects to ensure adhesive anchor performance is the cleanliness of the hole. Hole cleaning procedures vary by manufacturer and the steps in the MPII should be strictly followed. Most hole cleaning procedures will include a series of blowing, brushing, and blowing cycles.
S-4 Blowing can be accomplished by compressed air or a hand pump with a nozzle that extends to the base of the hole. Manufacturers will typically require several blows of air. The blowing cycle is usually followed by a series of brushing cycles. Brushes can be either metallic or nylon and can be attached to a drill or a hand tool. The type and size of the brush as well as the brushing procedure is specified in the MPII and most manufacturers only allow their proprietary brushes to be used. Brushes should periodically be checked to make sure the diameter is still within the tolerances specified in the MPII. It is common that the brushing cycle be followed by another blowing cycle. If the installation is in a damp, saturated, or submerged condition, the MPII might specify additional hole cleaning and preparation steps, which might include flushing the hole with clean water and vacuuming the water out of the hole. Once the hole has been cleaned per the MPII it is good practice to protect the hole from contamination until the adhesive and anchor are inserted. This can be accomplished by covering the hole with tape. Adhesive Insertion For all adhesive anchor systems, the two parts of the adhesive must be thoroughly mixed at the correct proportions. For cartridge systems, the dispenser gun ensures the proper proportions and the adhesive is thoroughly mixed within the special mixing nozzle. However, most manufacturers require that the first few (typically three) full strokes be discarded until the adhesive is of a consistent color in order to ensure that the adhesive is properly mixed. The adhesive is typically dispensed from the bottom or back of the hole while the nozzle is slowly retracted. The tip of the nozzle should remain submerged in the adhesive to prevent the formation of air pockets which can result in voids that reduce the bond strength of the adhesive anchor system. The hole is filled to roughly 60â75% of the depth of the hole. For capsule systems, the glass or foil capsules are placed directly in the hole and are broken and mixed during the insertion of the anchor. For horizontally or upwardly inclined holes, some manufacturers provide retaining caps to prevent the adhesive from running out of the hole during installation.
S-5 Anchor Installation Each manufacturer will specify approved anchor types for use with their system. Anchors should be free of oil, rust, or other residue that might reduce the adhesive bond. The required embedment depth should be marked on the anchor in order to confirm when the anchor is fully embedded. For cartridge systems, the anchor is inserted by hand and some manufacturers require that the anchor be rotated and jiggled while inserting in the hole to better distribute the adhesive and reduce the chance of voids. For capsule systems, the anchor is most commonly inserted into the hole with a drill but some are also hammered into the hole. The anchor will typically have a chiseled end and will break the capsules and mix the adhesive during the insertion of the anchor. Once inserted to the proper depth, the anchor should be centered in the hole and adjusted for perpendicularity. It is important that this happen immediately upon insertion and within the stated working (or gel) time as specified in the MPII. The working time varies by product and temperature and should be listed in the MPII, but usually is on the order of a few minutes. Anchors installed in overhead and horizontal installations must be installed by ACI/CRSI certified installers and continuously inspected by a qualified inspector. Curing Once the working time has expired, the anchor cannot be disturbed until the cure time has elapsed. As with the working time, the cure time varies by product and temperature and can range from a few minutes to several hours. Information on cure time is provided in the MPII. Torquing Once the adhesive has fully cured, objects can be fixed to the anchor. It is important that the maximum permissible torque for pretension clamping as stated in the MPII not be exceeded. For adhesive anchors used in sustained load applications, the anchor cannot be loaded or torqued until after the manufacturerâs minimum cure time as listed in the MPII plus an additional 24 hours.
S-6 CONCLUSION Correct storage, preparation, installation, and torquing procedures are necessary in order to ensure proper performance of adhesive anchor systems. As these procedures vary by manufacturer and product, it is imperative that the procedures specified in the MPII be strictly followed.
