Types of Anchors for Anchoring to Concrete - Hilti

Bonded systems use a combination of
adhesive bond and micro keying into the
pores of the concrete. Early systems used
polyester resin, epoxies, and later, vinyl
ester resins. In recent years, a larger variety
of resins have been developed that
have individual advantages, such as use
in high temperatures, low temperatures,
damp and wet holes, etc. For two component
epoxy systems, the ratio of hardener
to resin is critical. Prepackaged
cartridge systems assure that the proper
mixing is obtained. While a variety of
installation methods are used, most are
two component resin systems that
anchor threaded rod into predrilled
holes. Most will resist dynamic loads,
both seismic and fatigue, but documentation
in the form of test reports should
be obtained. Bonded or adhesive
anchoring systems are not well suited for
cracked tensile zones of concrete since
about 1/2 the bonding is lost, unless one
uses special anchoring systems developed
for use in cracked concrete. One
should also use the recommended drill
bit size, since many of the adhesives are
sensitive to the size of the gap between
the anchor rod and the concrete.
■ CAPSULE SYSTEMS
The original capsules were made of
glass, with an internal glass capsule that
contained the hardener. Recent versions
use plastic foil instead of the glass capsules.
The capsule is inserted into the
hole. The threaded rod or reinforcing
bar is then rotary-hammered into the
glass capsule, breaking the glass and mixing
the resin and hardener. Capsule
anchors provide very good bonding as
the rotary mixing action wipes and
cleans the surface of the hole, allowing
the adhesive to bond well.
■ CARTRIDGE SYSTEMS
Introduced also about 20 years ago,
cartridge systems are the most popular
delivery method since they are also the
most versatile. The resin and hardener
are packaged in separate but connected
side-by-side plastic or foil tubes. A mixing
nozzle is placed on the end of the tubes
and the resin and hardener dispensed by
a hand operated or a pneumatic dispenser.
Also used for heavy-duty applications,
hole cleaning is very critical since
dust on the concrete hole surface limits
the bond and micro keying.
■ BULK INJECTION SYSTEMS
For high volume applications such as
highway contracts or large building
where repetitive installation of anchors is
required, bulk mechanical and hydraulic
dispensing systems are available. Attention
to the proper mixing ratio for epoxy
resins is critical since bulk equipment
can go “off ratio.”
■ GROUTED SYSTEMS
Predating resin systems are cemetitious
grouts. There are a variety of proprietary
systems available. Non-shrink or
slightly expansive grouts are preferred to
prevent shrinkage and lack of bonding
to the existing concrete.
IN SUMMARY…
A wide variety of anchoring systems
are available. The correct selection
depends on several factors, including
types of loads to be resisted, magnitude
of the load, type of base material (concrete
or masonry), and environment
conditions (damp, wet, dry), among others.
The manufacturers’ literature provides
a good starting place, but also look
for evaluation reports and product listings,
since they may be required under
many building codes. ■
REFERENCES
1. State-of-the-Art Report on Anchorage to
Concrete ACI 355.1R-91, American
Concrete Institute, Detroit, 1991.
2. Fastenings to Concrete and Masonry
Structures; State of the Art Report,
Comité Euro-Intérnational du Béton,
Thomas Telford Services Ltd., London,
1994.
3. ANSI B212.15-1994, American National
Standard for Cutting Tools—Carbide-
Tipped Masonry Drills and Blanks for
Carbide-Tipped Masonry Drills, American
National Standards Institute, New
York, N. Y., 10 pp.
Richard Wollmershauser is Director Technical
Services for Hilti, Inc. of Tulsa,
Oklahoma. He has been active in the concrete
anchor industry for the past 20 years.
He is a registered PE in Ohio and
Oklahoma and a Fellow of the American
Concrete Institute. He currently serves as
Vice-President of CAMA, The Concrete
Anchor Manufactures Association, Chairman
of ASTM Subcommittee E06.13,
Performance of Connections in Building
Construction, and just completed 7 years as
Chairman of the American Concrete
Institute Committee 355, Anchorage to
Concrete. He was editor of the ACI State-ofthe-Report
on Anchorage to Concrete (ACI
355R1-93). He also serves on the Federation
International du Beton Task Group
SAG 4 Fastening to Concrete and Masonry.
He served on three committees of the recent
NEHRP 2000 Seismic Provisions Update
program where he was concerned with the
introduction of anchoring design methods.
Adhesive Capsule
Anchor
Adhesive Cartridge
System
FIGURE 5. Adhesive Bonded Anchor Systems