No. 540 June 2011 

Field-Expedient Shotcrete Adhesion Test System

Objective

To develop a practical method of measuring shotcrete 

adhesion strength in underground mines. A more thorough 

understanding of the in-situ strength properties of shotcrete, 

particularly the bond strength of shotcrete to the rock, will lead 

to improvements in ground support practices, thereby 

preventing groundfalls and reducing mine roof-fall incidents.

Background

When shotcrete is used as an integral part of a mine’s 

ground support system, it is important to know the strength 

properties of the in-place shotcrete. To quantify the bond 

strength of the shotcrete to the rock, a shotcrete adhesion test 

system has been developed for use in underground mines. As 

shown in Figure 1, the test system consists of readily available 

components, primarily a small stand-mounted core drill and a 

pulling unit equipped with a precision pressure gauge. 

 Figure 1. Schematic of direct tensile test system for measuring 

shotcrete adhesion strength.

All of 

these components are rugged and portable, and they can reliably 

be used to measure the adhesion strength of shotcrete applied to 

the surface of an underground mine opening (Figure 2). Figure 2. Shotcrete adhesion test system for underground mines: 

(A) drilling 4-in-diameter hole for the test core and (B) pulling unit 

mounted to mine rib using a three-point safety restraint. 

With this test method, a direct tensile load is applied to a 

core drilled through the shotcrete into the underlying rock. As 

this load is gradually increased, the test core typically breaks or 

fails in tension. This tensile failure can occur in the shotcrete, at 

the bond surface (interface), in the rock, or at some combination 

of these locations. As a result, the tensile-strength values 

derived from these tests provide important information about the 

quality of the applied shotcrete and the competency of the 

underlying rock, as well as the bond strength of the shotcrete to 

the rock. 

Conducting the Shotcrete Adhesion Test

Once a desired test site has been selected, a hand-operated 

rotary percussive drill is used to drill a 16-mm x 51-mm (0.625-

in x 2-in) hole for anchoring the drill stand. After installing a 

13-mm- (0.5-in-) diameter threaded stud and expansion anchor 

in this hole, the drill stand is leveled and secured in position. 

Three holes are then drilled from this drill setup ensuring that all 

of the holes are parallel and concentric (Figure 3). First, an 11.1-

mm- (0.4375-in-) diameter hole is drilled dry into the shotcrete 

using a rotary percussive bit, to a depth of 60 mm (2.375 in), 

assuming a shotcrete thickness of 75 mm (3 in). Next, the hole 

is cleaned, filled with a quick-setting, two-part epoxy adhesive, 

and a 9.5-mm- (0.375-in-) diameter pull anchor is inserted.

After the epoxy has initially set or gelled (about 15 min), a 102-

mm- (4-in-) diameter diamond core bit is used to wet drill a 

second hole through the shotcrete to a depth of about 25 to 50 

mm (1 to 2 in) into the underlying rock. Finally, a 127-mm- (5-

in-) diameter diamond core bit is used to wet drill a shallow kerf 

for seating the base of the pulling fixture (Figure 3).
 Figure 3. Drill hole configuration: (A) plan view and (B) vertical 

cross section.

After the epoxy has fully set (30–60 min), a threaded 

extension rod is connected to the pull anchor with a coupling 

nut; the pulling fixture is then carefully placed over the core 

sample with the base of its reaction ring positioned in the kerf of 

the outer drill hole. Next, a collet and a slip-on, quick-threading 

locknut are connected to the threaded extension rod to serve as a 

mechanical stop for the pulling fixture’s ram. The hydraulic 

hose from the hand pump is then connected to the loading ram, 

and the pressure gauge is zeroed. To conduct a test, an 

increasing tensile load is applied to the core sample through a 

slow and steady movement of the pump handle until the core 

breaks. The adhesion strength of the test core is determined by 

converting the maximum hydraulic pressure value, saved on the 

pressure gauge’s digital display, to the maximum tensile stress 

acting normal to the core’s failure surface. Typical adhesion test 

results comparing tensile strength with shotcrete curing age are 

shown in Figure 4.

 Figure 4. Typical shotcrete adhesion test results. 

Design Features

• Test equipment is portable and easily stored.

• Test system components are easy to set up and operate.

• Test procedures are easily understood and require 

minimal training.

• Test results provide in-situ strength values.

• Power choices: 110-V AC or DC→AC inverter.

Test System Component Specifications

Drilling unit

Drill Hilti DD-130 core drill (wet/dry)

Drive system Three-speed forward/reverse 

Drill stand Hilti DD-ST-130 drill stand 

11-in width x 22-in depth x 43-in height

Diamond 

core bit

Test core Hilti DD-BI, 4 in x 17 in

Kerf Hilti DD-BI, 5 in x 17 in

Drill bit Pulling stud Hilti TE-C3X, 7/16 in x 6 in

Custom

drill chuck

Hilti DD-BI drill bit chuck welded to

Bosch spline to SDS adaptor

Pulling unit

Extension rod

3⁄8-in threaded rod (3⁄8–16 NC x 30 in)

3⁄8-in coupling nut (3⁄8–16 NC x 1 in)

3⁄8-in hex head locknut (3⁄8–16 NC)

3⁄8–16 slip-on quick-threading locknut 

3⁄8-in collet (11⁄4 & 3⁄4-in OD x 1-in height)

Pulling fixture 

Aluminum weldament

6-in OD x 61⁄2-in height x 3⁄8-in wall

Steel-base insert 

53⁄4-in OD x 2-in height x 1⁄2-in wall

Kerf flange

51⁄8-in OD x 5-in ID x 1-in height

Hydraulic 

pump

Enerpac P-142 two-speed

1st stage 200 psi, 2nd stage 10,000 psi

Hydraulic ram Enerpac RCH-123, Holl-O-Ram

10,000 psi, 12 ton

Digital 

pressure gauge

Parker SCJR 8700-2 PD

with min/max display, 0–8,700 psi

Safety restraint

Safety strap 

(3) 

NRS HD 1-in tie-down strap, 3-ft length

heavy-duty 1-in cam buckle

Strap bracket 

Shotcrete

L-shaped (3)

Aluminum

2 in x 2 in x 1⁄4 in

Pull fixture

eyelet (3)

Aluminum

11⁄2 in x 2 in x 1⁄4 in

Anchors

Drill stand 1⁄2-in Hilti Kwik-LOK nut and spindle

1⁄2–13 NC and 5⁄8 rope thread x 71⁄2 in

L-bracket (3) 1⁄2-in hex head bolt (1⁄2–13 NC x 11⁄2 in) 

Shotcrete (3) 1⁄2-in Hilti HDI drop-in (5⁄8 in x 2 in) 

Eyelet bracket (3) 1⁄4-in hex head bolt (1⁄4–20 NC x 1 in) 

Pulling stud 3⁄8-in Hilti HIT-TZ (3⁄8 in x 41⁄2 in) 

Epoxy Hilti HIT-HY 150 MAX

For More Information

For more information on the shotcrete adhesion test system, 

contact Brad Seymour at JSeymour@cdc.gov (509) 354-8019 or 

the Health Communications Coordinator (OMSHR@cdc.gov), 

NIOSH Office of Mine Safety and Health Research, P.O. Box 

18070, Pittsburgh, PA 15236-0070.

To receive NIOSH documents or for more information 

about occupational safety and health topics, contact: 1-800-

CDC-INFO (1-800-232-4636), 1-888-232-6348 (TTY), e-mail: 

cdcinfo@cdc.gov, or visit the NIOSH Web site at 

http://www.cdc.gov/niosh

Mention of any company name or product does not 

constitute endorsement by the National Institute for 

Occupational Safety and Health.

DHHS (NIOSH) Publication No. 2011–185