NATIONAL LNSTITUTE OF STANDARDS &

TECHNOLOGY

Research Moimation Center

Gaithersburg, MD 20899

NISTIR 88>3883

Capita / S

A Method to Measure the

Tensile Bond Strength Between

Two Weakly-Cemented Sand

Grains

Lawrence I. Knab and Nathaniel E. Waters

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

National Engineering Laboratory

Center for Building Technology

Building Materials Division

Gaithersburg, MD 20899

November 1988

Prepared for

US Air Force

AFWUNTES

KIrtland AFB, NM 87117-6008

BUCOPY

C8 NOT REMOyE
,1
NISTIR 88-3883

A Method to Measure the

Tensile Bond Strength Between

Two Weakly-Cemented Sand

Grains

Lawrence I. Knab and Nathaniel E. Waters

U.S. DEPARTMENT OF COMMERCE'

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

National Engineering Laboratory

Center for Building Technology

Building Materials Division

Gaithersburg, MD 20899

November 1988

National Bureau of Standards became the

National Institute of Standards and Technology

on August 23, 1988, when the Omnibus Trade and

Competitiveness Act was signed. NIST retains

all NBS functions. Its new programs will encourage

improved use of technology by U.S. industry.

Prepared for

US Air Force

AFWL7NTES

Kirtland AFB, NM 87117-6008

U.S. DEPARTMENT OF COMMERCE

C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

Ernest Ambler, Director

A Method to Measure the Tensile Bond Strength between Two WeaklyCemented Sand Grains

by Lawrence I. Knab and Nathaniel E. Waters, Center for Building

Technology, National Institute of Standards and Technology

ABSTRACT

A method to measure the tensile bond strength between two weaklycemented sand grains was developed. Special microloading testing

equipment was developed to measure the force required to pull

apart two sand grains. To illustrate the method, bond strengths

were measured in tension for six pairs of cemented sand grains.

A wide range in the bond failure stress occurred and was attributed

primarily to (a) difficulties in identifying and measuring the

actual bond failure surface area and, (b) eccentricity in the

specimens during loading. The method developed is seen as a

starting point and can be used as a basis for further development.

Improved techniques need to be developed to identify and measure

the actual bond failure surface area and to reduce, or at least

measure and account for, the eccentricity introduced.

Keywords: bond; sand grains; strength; tension; test method;

weakly cemented

1
1. INTRODUCTION

A research effort investigating the deformation characteristics

I of weakly-cemented sand grains at the sand-grain level was being

sponsored by the Air Force Scientific Office of Research (AFOSR)

and was being conducted by the Air Force Weapons Laboratory

(AFWL) . An important factor in the investigation is the relationship

! of bond behavior (soil grain/matrix interface) to the macroscopic j response of the overall sample. The determination of the bond

failure mode and bond strength between two weakly-cemented sand

grains tested in tension, compression, and torsion was needed. | The National Institute of Standards and Technology (NIST) was

requested by AFWL to investigate the tensile bond strength and

behavior. Since there was no known test method for measuring the

tensile bond strength of such specimens, a test method had to be

developed.

2. PURPOSE AND APPROACH

The purpose of the NIST research was to develop a method to

measure the tensile bond strength between weakly-cemented sand

grains. ("Weakly-cemented" refers to the use of a cement paste

with a high water/cement ratio) . Special microloading testing

equipment was developed to measure the force required to pull

apart two sand grains. To illustrate the method, preliminary

2
bond strengths were measured in tension for six pairs of cemented

sand grains.

3 . TEST METHOD AND SPECIMENS

3 . 1 Test Frame

A test frame was made as shown in figure 1. It consisted of

upper and lower square stainless steel rods, 1/2 in. on a side,

held together at their ends by threaded rods and spacers. The

rods were spaced 7/8 in. apart. Six sets of holes were drilled

in the stainless steel rods so that the holes were aligned and were

slightly greater in size than the 0.029 in. diameter stainless

steel wire to which the sand grains were attached and the load

applied. The holes provided concentric guides for the wires but

did not prevent the wires from moving freely. One sand grain was

adhered to the end of the upper wire using an epoxy adhesive and

the other similarly adhered to the end of the lower wire. The

two sand grains were then bonded together with cement paste and,

after curing over water, were pulled apart in tension.

3.2 Preparation of Wire and Adhering of Sand Grains to Wire

Stainless steel wire and stainless steel square rod was used to

prevent rusting (during curing over water) which could cause

increased friction between the wire and the walls of the guide

3
holes. The wire was straightened prior to using. The lengths of

the top and bottom pieces of stainless steel wire were 1 1/8 in.

and 2 1/2 in., respectively. Before adhering the sand grains, the

end of the wire to which the sand grain was to be adhered was

sanded until flat and then immersed in hydrochloric acid (labelled

"HCL Approx. 37 %") for two minutes and then dried. The acid

treatment was used to improve the bond of the epoxy to the wire

by cleaning and etching the end of the wire. The wires to which

the sand grains were to be adhered were held vertically in a

holder which could withstand oven-curing temperatures for the

epoxy^'^. Using a sewing needle and a microscope, the epoxy was

applied only to the wire and, using tweezers, the sand grain was

carefully placed on top of the epoxy. The epoxy^ which held the

sand grains to their wires, was then heat cured at about 70*^0 for

two hours (with the wires still in their holder) . The oven used

was not a circulating air type because the air flow could have

blown the sand grains from the wires before the epoxy cured. Use

of the epoxy and the procedures developed were satisfactory and

resulted in no bond failures between (a) the epoxy and the wire

and (b) between the epoxy and the sand grain, in the tests

^ The epoxy was 3M-1838 B/A manufactured by the Adhesives,

Coatings, and Sealers Division of the 3M Company, St. Paul, MN. ^ Certain manufacturers' names, and names of commercial

equipment, instruments, and materials are identified in this

report to adequately specify the experimental procedure. Such an

identification does not imply recommendation or endorsement by

the National Institute of Standards and Technology, nor does it

imply that the equipment, instruments, or materials identified

are necessarily the best available for the purpose.

4
reported in table 1. Use of other procedures and materials

(e.g., quick-setting epoxy) were unsatisfactory in some cases,

where the bond strength between the epoxy and the sand grain, or

the epoxy and the wire, was less than the bond strength of the

sand grains held together by cement paste.

After placing the wire with the adhered (with oven-cured epoxy) sand

grain in the (disassembled) stainless steel frame, an approximate

90° bend was made in the end-most 1/4 in. length of the upper

wire and in the end-most 3/8 in. length of the lower wire to: (i)

cause the end of the upper wire to bear against the stainless

steel rod and not move when loaded, and (ii) serve as a hook for

the loading device for the lower wire (see below) . The stainless

steel frame was then assembled and the sand grains bonded

together with cement paste.

3 . 3 Bonding and Curing of Sand Grains

A cement paste was hand mixed using a water/cement ratio of 2.0

(50 g water to 25 g of a "Type I-II portland cement" provided by

AFWL) . The paste was initially mixed for 3 to 4 minutes but,

because of cement settling to the bottom of the mixing bowl, would

have to be remixed periodically throughout the application of the

paste to the sand grains ("No. 10 Silica sand" used as received

from AFWL) . The stainless steel frame containing the sand grains

was placed over water in a curing pan while the paste was applied

5
so that they would not have to be moved during curing. The paste

was applied using a modified spatula, with a small spoon-shaped

tip with an elliptical-shaped top having long and short dimensions

of about 0.12 in. and 0.06 in., respectively, and an average

depth of about 0.04 in. Using a microscope for viewing, the

paste was applied to both grains and then the grains were butted

together, except for two cases (Specimens 2 and 6, table 1)

where the nearest edges of the two grains were separated about

1/3 of a sand-grain diameter, respectively (sand-grain diameters

used in all six specimens varied from about 0.050 to 0.065 in.).

After applying the cement paste to six pairs of sand grains, the

curing pan was covered without disturbing the stainless-steel

frame and the freshly-bonded sand grains. Prior to being tested,

the cemented sand grains were cured 14 days in a moist environment

over water‘d at room temperature.

3.4 Tensile-Bond Testing of Sand Grains

As shown in figure 1, glass centrifuge tubes were used as loading

devices. Wire was used around the top of the tubes to attach

them to the bent end of the lower wire. The sand-grain specimens

^ Preliminary tests of sand grains bonded together with

cement paste (water/cement = 2.0) showed that (a) curing in air

for 3 days resulted in essentially zero bond strength (failure

load of about 0.2 g, or less), and (b) curing over water for

several days resulted, in some cases, in relatively large failure

loads (e.g., one specimen failed at 227 g at 4 days and another

failed at 211 g at 5 days)

.

6
were loaded by first hanging the lighter centrifuge tube (26.4 g^)

on the bent wire, and then slowly adding water with a syringe.

The 3.66 in.^ (60 ml) syringe had a "Luer-lok" tip fitted with a

reusable 13-gauge, 4 in. long stainless steel, "Luer-lok" needle.

If the tube became filled with water before failure, the tube was

removed, the water emptied, and sufficient 1/4 in. -diameter steel

balls were then put into the tube to approximately equal the

weight of the water. The tube was then rehung on the specimen

and water was added (with a syringe) to the tube and the steel

balls. If the tube again became full of water, the above procedure

was repeated, with more steel balls added to approximately equal

the weight of the water emptied, until failure occurred. When

the load in the lighter centrifuge tube reached the approximate

weight of the empty heavier centrifuge tube (160.6 g) , the

heavier centrifuge tube was substituted and the procedure of

adding water and steel balls was repeated as given above. To

prevent the loss of any water during loading, a beaker was

stationed under the centrifuge tube to catch it when the specimen

failed. Failure load was measured by weighing the centrifuge

tube and its contents. All six specimens were tested at approximately

40 percent relative humidity and within about 2 hours after

removing from their moist curing in water vapor. The order of

testing the specimens is given in table 1.

^ Units of grams are used rather than pounds because the

load was applied and measured in grams.

7
There was, undoubtedly, some eccentricity introduced during

testing of the sands grains. Possible contributing factors

include out-of-straightness of wires, small horizontal movements

of the upper and lower wires relative to each other, sand grains

not centered on the ends of their wires, out-of-roundness of the

sand grains, out-of-alignment of sand grains when they were bonded

together with cement paste, and variations in the volume and

thickness of the paste applied to the sand grains.

4. TEST RESULTS AND DISCUSSION

Table 1 presents the results for the six specimens tested,

including the failure load and very rough estimates of the bond

failure stresses, based on estimated bond failure surface

areas. Each specimen tested consisted of a pair of sand grains.

Table 1 lists the failure stress based on the estimated fracture

surface as observed on the sand grain adhered to the upper wire,

and also on the sand grain adhered to the lower wire.

4.1 Failure Mode

The failure surfaces of all specimens included, to varying degrees,

the paste/sand grain interface. The remaining failure surface

(in addition to the paste/sand grain interface) occurred in the

paste; there was no observed failure of the sand grains (see

figures 2 to 21) . In addition, there was no failure of the

8
interface between: (i) the epoxy and the wire, (ii) the epoxy and

the sand grain, and (iii) the paste and the epoxy (as far as

could be determined, the failure surface of the paste was

confined to the sand grain surface and not to the epoxy bonded to

the sand grain surface). Figures 2, 5 to 7, 9, 12 to 15, 18, 19,

and 21 show the estimated bond surface failures, based on a planar

area and with a 90^-viewing angle (viewed at approximately 90° to

the failure surface) , for the six specimens tested (table 1)

.

The 90°-viewing angle was used to estimate the failure surface

areas in table 1. In addition, a 0°-viewing angle (side view)

and 45° viewing angle (viewed at approximately 45° to the failure

surface) are shown in figures 3, 4, 8, 10, 11, 16, 17 and 20 for

selected specimens.

The failure surface area of specimen 2 as viewed on the upper

wire (figure 7) appeared to contain some relatively large porosity.

4.2 Uncertainty in Estimation of Bond Failure Surface Area

The estimated bond failure surface area was determined as follows.

(i) The perimeter of the failure surface was estimated by viewing

at a 90° angle to the actual failure surface, using a light

microscope. This perimeter was then marked on a photogragh of the

failure surface (see figures showing the 90° viewing angle)

.

9
(ii) The length of a straight line from one side of the perimeter

to the other was measured by viewing the actual failure surface

with a 20-power machinist's microscope. The line length was read

in 0.0001 in. units using a micrometer, mounted to the base of

the microscope. Then the length of a similar line®, at 90® to

the first, was measured. The lengths of the two lines were then

measured on the photograph. The relationships of the two line

lengths on the actual failure surface to the corresponding line

lengths on the photograph were used to obtain an average magnificat!

(see magnification scales on figures showing 90® viewing angle).

(iii) The planar surface area inside the perimeter of the failure

surface, as it appeared on the photograph, was determined by

overlaying the photograph with transparent graph paper (10

squares to the inch) . Using the planar surface area from the

photograph and the magnification^, the planar area inside the

perimeter of the actual failure surface as observed under the

microscope was determined.

The uncertainty in determining the planar surface area inside the

perimeter by using graph paper was considered insignificant

compared to two major sources of uncertainty in estimating the

® The two lines typically intersected near the centroid of

the failure surface.

^ That is, the magnification was used to determine the

relationship between a unit area on the photograph and the

corresponding planar area on the actual failure surface.

10
failure bond surface area:

(1) the assumption that the failure surface was planar, and

(2) the uncertainty in determining the perimeter of the fracture

surface. That is, it was difficult to discern whether exposed

sand-grain surface areas adjacent to evident failure surfaces

were (a) part of the paste which formed the bond between the sand

grains and had resisted the tensile pulling of the sand grains or

(b) the result of paste which originally had coated the sand

grain surface and spalled off during testing but had not participated

in resisting the tensile pulling force. (When applying the

cement paste to the sand grains, it was not possible to prevent

some of the paste from adhering to portions of the sand grains

where the adhered paste was unlikely to participate in resisting

the applied pulling force.)

Because of these two major sources of uncertainty, and the

additional uncertainty of the effects of eccentricity, the calculated

failure stresses are considered very rough estimates of the

actual failure stresses.

4.3 Estimation of Failure Stress

There was a wide range in the estimated failure stress values in

table 1, with values ranging from a failure resulting from

11
placing the 26.4 g loading tube on the specimen (Specimen 4, less

than or equal to 44 psi) to 579 psi (Specimen 2) . The very large

variability in the stress values was attributed primarily to the

effects of eccentricity and the substantial uncertainty in

determining the bond failure surface area (see above) . Ideally,

the two estimated failure stress values for each specimen (one

estimate based on the sand grain adhered to the upper wire and the

other based on the sand grain adhered to the lower wire) should

be the same. However, the ratio of the larger to smaller stress

(equal to the ratio of the larger to smaller planar surface area)

for each specimen ranged from 1.3 to 1.8. This large uncertainty

was attributed to the substantial uncertainty in determining the

bond failure surface area.

With Specimens 1, 3, 4, 6, and possibly 5 (see (ii) below), the

larger of the two estimated stresses for each specimen was

considered to be an upper bound (highest possible stress that

could be obtained for the particular specimen, excluding eccentricit

effects) because:

(i) the assumption of planar failure surfaces (curved surface

would result in more area and less stress) and,

(ii) the higher stresses are based on well-defined failure

surface perimeters which were considered to result in the minimum

possible failure surface areas. That is, if errors were made in

12
identifying the failure surface, they were most likely due to

omission of a portion of the failure surface, giving too high a

stress. With Specimens 1, 3, 4, and 6 (table 1), the smaller

failure surface areas (mostly paste and approximately concave in

shape - figures 2, 9, 13, 19) were better defined than the

corresponding larger failure surface areas (approximately convex

in shape - figures 5, 12, 14, and 21). With Specimen 5, the

failure surface area (figure 15) associated with the higher

stress was well defined but only slightly better defined than the

corresponding larger failure surface area (figure 18)

.

The presence of eccentricity during testing would most likely

decrease the observed failure loads shown in table 1 and thus, if

the effects of eccentricity were eliminated, the failure loads

and the associated failure stresses would most likely increase as

compared to those given in table 1.

5. SUGGESTIONS FOR IMPROVING THE METHOD

The method as developed had a number of experimental difficulties.

The following suggestions are offered to help overcome these

difficulties in future research.

1. Identification of the fraction of the cement paste which

resists the tensile pulling force is needed. High speed photography

probably could be used to capture the failure sequence and to better

13
define the actual failure bond surface.

2. Documentation and quantification is needed of the eccentricityintroduced during pulling apart of the sand grains. Photographic

documentation of the sand grains for the following stages should

help quantify the eccentricity:

(i) prior to their being bonded with cement paste, to show the

eccentricity caused by the out-of-straightness of the wires, and

by the sand grains not having been centered on the ends of the wirej

(ii) prior to pulling apart (after curing) , to show the eccentricity

caused by out-of alignment of the sand grains when they were

bonded together with cement paste, and

(iii) just after testing, with the two sand grains touching each

other, to show the relative orientation of the failure bond

surfaces on the sand grains.

Also, the 7/8 in. spacing between the square stainless steel rods

(Section 3.1) should be decreased, if possible, to reduce the

effects of eccentricity caused by out-of-straightness of the

wires. It is believed that this dimension could be reduced while

still permitting the application of the cement paste, which bonds

the two grains together.

Also, if it can be found, the use of flexible (e.g., braided)

stainless steel wire, instead of the stiff stainless steel wire

14
used, should reduce the eccentricity introduced.

3 . The curvature of the bond failure surfaces should be taken

into account when determining their surface area. Potential

methods include scanning electron microscopy using secondary

electron imaging to depict the topography of the failure bond

surface and image processing to determine the surface area and

porosity of both planar and curved surfaces.

6. CONCLUSION

The method developed for determining the tensile bond strength

between two weakly-cemented sand grains is seen as a starting

point and can be used as a basis for further development. Improved

techniques need to be developed to identify and measure the

actual bond failure surface area and to reduce, or at least

measure and account for, the eccentricity introduced.

15
Table

1.

Failure

Loads

and

Estimated

Bond

Failure

Surface

Areas

and

Stresses

for

Tensile

Bond

Tests^

•H

cn in in a

Q) >—' u in 73

in IT) 04

CO 0)

O o

<u P

rH 'I* 1—1

VI

u Q) CO 3 .. rH 0 -H

•H E-< fO fa T3

u

a) 0) 73

73 x: 0. <N CO CO <7» c o 0. c O rH eg

<0 fO

D •H 04 c—1

iH rH

4->

O o O

O

fC +J <0O o O

O

0) < Q) • • • • u U o o O O < c <

•H

0)

d 0 ^

CJ

U 73 3 C

CO (0 CO •H o in 73 C a

<D 0 

4-) in

fO 73 in o 0^ C\ S 0 <D 0) CO CO VO

•H in

U OJ in rH VI P (C •H 4-) V 1

in P3 CO

fa

0)0 (N 0- CO 04 O'

fa c o* VO 04

•H— 04 iH VO CO 

«H cH o O

rO

OO o O 0 O O o O • • • • < o o o o

CO in CO 73 ov rH in

73 fa 04 VO rH o 0 rH • • • • fa O o o o

Q)U3

fa

•H If) 73 CO VO * • fa CT' CO o CO VO rH CO in 04

VI

fac

Q)

U S Q) •H Si O e rH 04 CO

Q) 3

az

c/3

4J

<U

C

O -H X

CO VO

vy

M

ex' CO ^ 1 04

ther sand

(D

cr> 73 0

4-) <4-1 VO 0

O' in 73

VO 04 0) CO o rH 4-> \ • o O 4-> H C o P -H • • fa 44 o o • p in

0) 0 VO 0 Jh fa o p <D 73 • <a ^ o

0)

in ^ o P C <U 4J

in •H 15 u 73

O

•H ^ in in

<4-1 O' c o

•H • • 73 Q) 73 O

in <D fa

u

VO <u 4-> P C3>4-> in VO 4-> in P

in CO 73 0)

C 0) 0 g p 0) fa fa

•H fa 4-> 73

4-» II 44

in <4-1

g

0) s 73 0 0

rH

C ^

O' O' fa s 73 in <4-4 (N CT> (1) in CO P in 0>73 o o 0 C 73 Q) o o u c •H 0) -H o o •H 73 ^ • • >1 4J Vh 44 73 o o u in CTi in >

0) (1) <U > P 73 3h in C 73 ^

0) <4-1 73 0) 0) u o in C 44

73 0) u fa <u g

CO 0^ in <D 44 fa 73 0^ o in 73 0 44 -H

rg CO <D

U fa 73 • • u 0 0) o o 4J 0 ^ C

in in

p <D tH

<i) fa 73 73 4-> 73 ^ L c 73 (U O'

73 c •H

C7> rH VO 73

CO o 73 •H

a c

CO <1* 0) in a73 73 rH rH U 0) 73 C CO

73 73 73

in

0) V4 73 eg • U Q) ^ 44

73 fa in

u

<4-1

g <U

C 73

U

p 44 (1)

a P c in g 73

in c

73 *H a c; V4

0) a) <D (U u g 44 ifa44 p •H c CO (U LO VO fa 0 <D g

•H 0)

g ^ 73 73 cu (1) 0 -H

fa CO CJ <4-1 73

fO JQU T3

16

Failure

surface

hada

vertical

portion,

with

an

area

of

about

0.000891

in.^

which,

if

added

to

the

horizontal

planar

area

of

0.00168

in.^,

results

in

an

estimated

failure

stress

of

263

psi.

(At

least

part

of

the

vertical

portion

chipped

off

prior

to

when

the

picture

(figure

7)

was

taken)
Figure 1. Test Frame Showing a Failed Specimen with Glass

Centrifuge Loading Tube Containing Steel Balls and Water.

17
Figure 2. Specimen 1, Sand Grain Adhered to Lower Wire, Estimated

Planar Bond Failure Surface Area (Used in Table 1) Shown By

Enclosed Area, 90 “-Viewing Angle.

18
Figure 3. Specimen 1, Sand Grain Adhered to Lower Wire, 45

Viewing Angle (Scale is Approximate)

.

19
Figure 4. Specimen 1, Sand Grain Adhered to Lower Wire, 0°-

Viewing Angle.

20
Figure 5. Specimen 1, Sand Grain Adhered to Upper Wire, Estimated

Planar Failure Bond Surface Area (Used in Table 1) Shown by

Enclosed Area, 90 “-Viewing Angle.

21
Figure 6. Specimen 2 , Sand Grain Adhered to Lower Wire, Estimated

Planar Bond Failure Surface Area (Used in Table 1) Shown by

Enclosed Area, 90° -Viewing Angle.

22
Figure 7. Specimen 2 , Sand Grain Adhered to Upper Wire, Estimated

Planar Bond Failure Surface Area (Used in Table 1) Shown by

Enclosed Area, 90 “-Viewing Angle. See Footnote "d" in Table 1.

23
Figure 8. Specimen 2 , Sand Grains Adhered to Upper Wire, 0°-

Viewing Angle.

24
Figure 9. Specimen 3, Sand Grain Adhered to Lower Wire, Estimated

Planar Bond Failure Surface Area (Used in Table 1) Shown by

Enclosed Area, 90 “-Viewing Angle.

25
Figure 10. Specimen 3 , Viewing Angle.

Sand Grain Adhered to Lower Wire, 45 °-

26
Figure 11. Specimen 3, Sand Grain Adhered to Lower Wire, 0°-

Viewing Angle.

27
Figur© 12. Speciinen 3, Sand Grain Adher©d to Upper Wire,

Estimated Planar Bond Failure Surface Area (Used in Table 1)

Shown by Enclosed Area, 90 “-Viewing Angle.

28
Figure 13. Specimen 4, Sand Grain Adhered to Lower Wire,

Estimated Planar Bond Failure Surface Area (Used in Table 1)

Shown by Enclosed Area, 90° -Viewing Angle.

29
Figure 14. Specimen 4, Sand Grain Adhered to Upper Wire,

Estimated Planar Bond Failure Surface Area (Used in Table 1)

Shown by Enclosed Area, 90 “-Viewing Angle.

30
Figure 15. Specimen 5, Sand Grain Adhered to Lower Wire,

Estimated Planar Bond Failure Surface Area (Used in Table 1)

Shown by Enclosed Area, 90 “-Viewing Angle.

31
Figure 16. Specimen 5, Sand Grain Adhered to Lower Wire, 45 °- Viewing Angle. (Scale is Approximate)

.

32
Figure 17. Specimen 5, Sand Grain Adhered to Lower Wire, 0 °

Viewing Angle.

33
Figure 18. Specimen 5 , Sand Grain Adhered to Upper Wire, Estimated Planar Bond Failure Surface Area (Used in Table 1) Shown by Enclosed Area, 90 “-Viewing Angle.

34
Figure 19. Specimen 6 , Sand Grain Adhered to Lower Wire,

Estimated Planar Bond Failure Surface Area (Used in Table 1)

Shown by enclosed Area, 90 “-Viewing Angle.

35
Figure 20. Specimen 6, Sand Grain Adhered to Lower Wire, 0°-

Viewing Angle.

36
Figure 21 Specimen 6, Sand Grain Adhered to Upper Wire, Estimated

Planar Bond Failure Surface Area (Used in Table 1) Shown by

Enclosed Area, 90 “-Viewing Angle.

37
NBS-n4A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NISTIR 88-3883 NOVEMBER 1988

4. TITLE AND SUBTITLE

A Method to Measure the Tensile Bond Strength between Two Weakly-Cemented Sand Grains

5. AUTHOR(S)

T.awrence I. Knab and Nathaniel E. Waters

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

S. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

US Air Force

AFWL/NTES

Kirtland AFB, NM 87117-6008

10. SUPPLEMENTARY NOTES

I j Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a si gnificant

bi bl io graphy or literature survey, mention it here)

A method to measure the tensile bond strength between two weakly-cemented sand grains ;l was developed. Special microlo'ading testing equipment was developed to measure the

force required to pull apart two sand grains. To illustrate the method, bond strengths

were measured in tension for six pairs of cemented sand grains. A wide range in the

bond failure stress occurred and was attributed primarily to (a) difficulties in

identifying and measuring the actual bond failure surface area and, (b) eccentricity

in the specimens during loading. The method developed is seen as a starting point and

can be used as a basis for further development. Improved techniques need to be

developed to identify and measure the actual bond failure surface area and to reduce,

or at least measure and account for, the eccentricity introduced.

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitali ze only proper names; and separate key words by semicolon s)

bond; sand grains, strength, tension; test method, weakly cemented.

13. availability

[j^ Unl imi ted

I

I For Official Distribution. Do Not Release to NTIS

[ I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

40

15. Price

$11.95

USCOMM-DC 6043-P80 il