Product Technical Guides : US-EN Post-Installed Rebar Guide - Page 16

Post-Installed Reinforcing Bar Guide
As with cast-in bars , post-installed reinforcing bars must be provided with sufficient concrete cover to prevent corrosion . If the bar has been properly installed with adhesive surrounding the bar over its entire length , additional protection against corrosion is provided by the adhesive . Qualification of postinstalled reinforcing bar systems under ICC-ES Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements ( AC308 ) includes verification ( through an accelerated aging test ) that the adhesive provides adequate corrosion resistance .
In addition , sufficient distance must be provided from the concrete face to facilitate drilling without splitting and / or spalling the existing concrete , particularly where hammer or rock-drilling equipment is used . Hilti drilling alignment aids can be employed with Hilti hand-held hammer drills to improve drilling accuracy ( Figure 24 ). In the absence of other guidance , and where alignment aids or other techniques to maintain drilling accuracy are not used , equations 2 , 3 & 4 may be used to account for possible deviation of the drilled hole from its intended path 11 :
Hammer-drilled holes :
c min , req
= 1.2 + 0.06 l d ≥ 2d b
( in .)
( Eq . 2 )
Compressed-air ( rock ) drilled holes :
c min , req
= 2.0 + 0.08 l d ≥ 2d b
( in .)
( Eq . 3 )
Drill stand ( e . g ., core-drilled holes ):
c min , req
= 1.2 + 0.02 l d ≥ 2d b
( in .)
( Eq . 4 )
where ,
l d is the hole length in inches ; and
d b is the diameter of the reinforcing bar in inches
c min , req is the distance from the concrete edge to the face of the drill bit ( Figure 23 ).
c min d cmin , req
Figure 23 — c min , reqc is intended to increase the probability that the end of the installed bar will remain within the minimum required concrete cover c min
Figure 24 — Drilling with and without drilling alignment aids .
Clearance requirements for core-drilled holes vary according to the type , diameter and length of core bits being used .
Regardless of the drilling method used , embedded items may cause drill bits to deviate from the intended path .
As a matter of practicality , spacing of adjacent post-installed reinforcing bars should in general be maintained at 4 bar diameters or greater . Where applicable , ACI provisions for cover and bar spacing should be observed .
To satisfy development length requirements , post-installed reinforcing bars are usually associated with deeper embedments , and therefore longer drilled holes , than adhesive anchors . As noted previously , one of the following three drilling methods is typically employed :
• rotary-impact drills ( hammer drills ) equipped with standard or cruciform carbide bits or with Hilti Hollow Drill Bits ( HDB ) 12
• percussive rock drills
• diamond core drills utilizing either wet or dry coring technology
Each method is associated with advantages and disadvantages . See section 3.3 . Hammer drills ( Figure 25 ) are readily available and are the preferred approach for most applications given their portability and ease of use . Hilti hammer drills produce a nonuniform hole surface especially suitable for enhancing bond ( provided correct hole cleaning procedures are used ). For longer holes , hammer drills may not be practical ; they are also not always suitable for drilling through embedded steel where this is required .
The Hilti SafeSet™ system consists of Hollow Drill Bits ( HDB ) used in combination with Hilti Vacuum Cleaners ( VC 40-U or VC 20-U ). Hilti HDBs utilize the same state-of-the-art carbide drilling technology as Hilti TE-CX and Hilti TE-YX bits and they comply
11 ) Source : EOTA Technical Report TR023 [ 7 ] 12 ) Hilti Hollow Drill Bits automatically remove concrete dust during drilling as part of the HIT-HY 200 V3 SafeSet™ System .
14 2021