Mortar as Grout for Reinforced
Masonry
Phase 1 Report
April 2005
RBA Project 8379
Mortar as Grout for Reinforced
Masonry
Phase 1 Report
Prepared for:
International Masonry Institute
National Lime Association
Bricklayers and Allied Craftworkers Local No.1, New York, NY
National Concrete Masonry Association Research and Education
Foundation
Prepared by:
David T. Biggs, P.E.
Ryan-Biggs Associates, P.C.
291 River Street
Troy, New York 12180
(518) 272-6266
(518) 272-4467 (fax)
dbiggs@ryanbiggs.com
www.ryanbiggs.com
TABLE OF CONTENTS
PAGE
EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Historical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Previous Research Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
TESTING CONCEPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
MATERIAL CHARACTERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mortar Fill and Pourable Mortar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Concrete Masonry Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compressive Strength of Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
13
13
14
16
16
16
TESTING RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pull-Out Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Failure Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bond Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
18
21
23
ANALYSIS OF RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Pull-Out Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Tests of Bond Between Fill Material and CMU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
COMMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
CONCLUSIONS/RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
APPENDIX A
APPENDIX B
APPENDIX C
APPENDIX D
APPENDIX E
APPENDIX F
Sand Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Grout and Mortar Fill Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Concrete Masonry Unit Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pull-Out Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bond Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii
A-1
B-1
C-1
D-1
E-1
F-1
EXECUTIVE SUMMARY
Mortar used as grout for reinforced masonry for grout in commercial construction is a topic of major
interest to many masons that use low-lift grouting techniques. While not specifically allowed by
model codes and standards, it is commonly used on projects. Residential standards in the United
States have allowed Type S and Type M mortar tempered to a “pourable” consistency for grouting
for many years. A pourable consistency has a slump of approximately 6 inches. This report
documents Phase 1 testing of a research program aimed at evaluating mortar as a substitute for
grout for use with vertical reinforcement.
Phase 1 includes a series of pull-out tests and bond shear stress tests performed on prism-sized
samples. This phase was intended to evaluate only vertical reinforcing using small-scale samples
to determine if full-scale testing is recommended and the possible parameters of that testing.
Samples were constructed at facilities of Bricklayer and Allied Craftworkers, Local 2 in Albany, New
York. Testing was performed at commercial laboratories in Watervliet, New York, Scotia, New
York and at the National Concrete Masonry Association.
Several mixes were compared using reinforced CMU:
1. Type N and Type S mortars as commonly mixed for setting units.
2. Type N and Type S mortars that were tempered to a pourable consistency.
3. ASTM C 476 grout.
4. Type S mortar tempered to the consistency of grout.
Type N mortar did not provide acceptable results, primarily due to its low strength.
Type S mortar performed better in the pull-out tests than the “pourable” mortars that are allowed
in residential codes. However, based upon the tests results, Type S and Type M mortar could be
an acceptable substitute for grout provided the mix achieves at least 2000 psi compressive strength
when tested as a grout prism.
Phase 2 full-scale testing is recommended using Type S and Type M mortars in a modified low-lift
application.
The test results suggest some topics for additional consideration. Some of these include:
1.
The strength of the fill material (mortar, pourable mortar, or grout) that encases the
reinforcement affects the development length of the reinforcement. MSJC formulas for lap
splices do not adequately account for the strength of the fill material.
2.
The shrinkage characteristics of the fill material should be evaluated to determine their
importance in achieving adequate bond shear strength.
iii
INTRODUCTION
The Masonry Standards Joint Committee (MSJC)1 requires grout for use in reinforced masonry for
commercial construction. Grout is used to fill cells of hollow masonry and fill cavities of composite
construction. However, the majority of its use is to encase reinforcement. For residential
construction, some model codes allow the use of “pourable” mortars. “Pourable” mortars are
created by adding sufficient water to the mortar so that the mix can be poured into the masonry.
In spite of codes and standards, it is common in some regions of the United States for various
masonry contractors to substitute mortar for grout in commercial construction. The mortar is used
as traditionally mixed without additional water added. Dependent upon the jurisdiction, the mortar
substitution requires the acceptance of the designer as well as the building official. The logic for
the substitution is that mortar and grout have similar constituent materials and therefore should
perform similarly.
Masonry contractors who prefer to use mortar as grout along with the low-lift technique cite the
following reasons:
1. Reduces installation costs for low-lift applications when the masonry is to be grouted.
2. Reduces the number of mixers used since industry standards generally require separate
mixing of mortar and grout.
3. Eliminates contamination of core cells that can occur when using two different materials.
4. Increases the chance of placing consistent material by grouting course by course in walls
when there are numerous mechanical trade penetrations, reduced overhead clearance,
and general access restrictions to the top of the wall.
5. Improves delivery of materials on high-rise buildings for infill walls. Contractor
distribution of different materials is reduced.
For contractors that prefer the high-lift grouting technique, using mortar as grout is generally not
done or limited to filling at openings with embedded hardware such as door jamb anchors.
The material standard in the United States for masonry grout is ASTM C 4762. Within the standard,
there are two types of grout: fine grout and coarse grout. Fine grout has sand aggregate, portland
cement, and lime; coarse grout uses pea gravel in addition to the sand.
The material standard for mortar is ASTM C 2703. The standard allows three cement options for
mixing mortar. These include:
1. Portland cement and lime.
2. Masonry cement.
3. Mortar cement.
In all three options, sand is used as the aggregate.
Page 1
Purpose of this Report
This report documents the research that was initiated to examine the performance of portland
cement and lime-based mortars in reinforced masonry as an alternative for grout to encase vertical
reinforcement. Portland cement and lime-based mortar is evaluated since it most closely replicates
the constituent materials of fine grout. Natural sand was used as the aggregate.
The study is limited to concrete masonry units (CMU) used in a modified low-lift grouting
application.
Page 2
BACKGROUND
Historical
A.
Grouting began in the United States after the 1933 Long Beach California earthquake
damaged many unreinforced brick buildings. The use of reinforcement in the walls made
grout necessary. Initially, all grouting was performed course by course. Six-foot lengths of
reinforcement were used; four feet were grouted each day and two feet were left for a lap
splice. In northern California, masonry contractors wanted to speed up construction and
proposed constructing the masonry full height and then grouting the wall full height. With
limitations, the method was accepted by the State of California 4.
From this beginning, two grouting techniques were developed for the United States: low-lift
and high-lift. Low-lift grouting occurs incrementally with the installation of the masonry.
Standards limit this grouting to a maximum pour of 5 feet.
High-lift grouting allows the masonry to be constructed and grouted in pours greater than 5
feet using lifts that are a function of the grout type and the size of the cell or cavity to be
filled. In the 2005, the MSJC changed its criteria so that the maximum lift heights could
increase from 5 feet to as much as 12 feet 8 inches. Pour heights were not changed.
B.
Amrhein 5 reported that grout slumps for high-lift grouting were determined by the Office of
the State Architect, Structural Safety Section, Circular Number 10, Clay Brick Masonry, High
Lift Grouting Method. The circular stated “The slump of the grout should be varied
depending upon the rate of absorption of the masonry units and temperature and humidity
conditions. The range should be from 8 inches for units with a low rate of absorption (30 to
40 grams per minute) up to 10 inches for units with a high rate of absorption (80 to 90 grams
per minute).” Thus, high-slump grout was developed for high-lift grouting to flow into the
voids of the masonry units and around reinforcement. This became the grout standard for
both low-lift and high-lift grouting.
The absorption rates noted are interesting in that industry recommendations are to pre-wet
bricks before construction whenever the initial rate of absorption (IRA) exceeds 30 grams per
minute per 30 square inches 6. Thus, if the bricks are pre-wetted and the IRA is reduced to
less than 30, the California information would seem to justify lower slump grouts.
C.
Isberner7 reported in 1982 that grout had not been extensively researched. He states “..it is
unfortunate we disallow certain practices and materials on little or no evidence. Some past
and recent research, however, shows there is much to be learned regarding the role of grout
in reinforced masonry”.
Furthermore, “Although many grouted reinforced masonry
structures are now in existence, the specifics of grout design and use are relatively
unfounded.”
Page 3
He suggested that “Grouts be designed, specifically, to develop the specification strength at
the required test age when acceptable test molds and specimens are used.” He also noted
that test data indicates that low water content grouts (2 to 3 inch slump) could develop
compressive strengths in the 2000 psi range. Lastly, Isberner recommended research to
show alternative methods of grouting reinforced masonry.
D.
In many areas of the country, high-lift grouting is not commonly used. Thus, the question
arises as to whether a high-slump grout is necessary for those applications that use low-lift
grouting techniques. If not, is mortar satisfactory for grout for low-lift applications?
There have been no reported incidences found in the literature of structural failures attributed
to mortar being used as grout for vertical reinforcement. Failures associated with grouting
are generally attributed to missing or inadequate filling of masonry. The properties of the
grout were not reported.
Codes and Standards
In the 1982 Uniform Building Code 8, mortar was acceptable as a substitute for grout for chimneys
and fireplaces. This was subsequently deleted in the 1985 edition.
Residential codes from the Council of American Building Officials (CABO)9 allowed Type S or Type
M mortar with water added to be used as grout. CABO became part of the International Code
Council, and its International Residential Code (IRC)10 also allows Type S or Type M mortar with
water added to be used as grout.
Previous Research Work
A.
To support the use of mortars in residential construction, previous research11 was done in
1991 by the National Concrete Masonry Association (NCMA) to evaluate mortar as fine
grout. They used Type S and Type M mortars with sufficient water added to create a
“pourable” mixture that achieved a slump of 7 to 9 inches. The pourable mortars were
compared to three grout mixes with similar slump. The three grout mixes contained only
cement and sand. The aggregate ratios in the grouts were varied to achieve compressive
strengths similar to the mortars.
The test setup was not described; it was noted a No. 5 bar was pulled in tension from the
specimens and tension bond strengths were calculated.
Comparing the data for pourable Type S, PCL (portland cement- lime based) mortar and
ASTM C 476 fine grout:
1. The compressive strength for the grout was 10 percent higher than for the pourable
mortar.
2. The grout only achieved tension bond strengths 6 percent higher than the pourable
Type S mortar.
The report concluded that further research was necessary but that pourable mortars “could
become an effective substitute for grout.”
B.
In 1998, a report prepared by Brown12 at Clemson University reported using mortar as grout
in reinforced hollow clay walls. The tests obtained tension bond strengths between the
Page 4
reinforcement and grout developed from three methods of filling the cell space around
reinforcing in hollow clay units and compared them with each other. The three methods
included grouting with standard grout, “slushing” with mortar, and “souping” with mortar. The
author indicated that “slushing” involved filling the cells of the masonry with mortar as the
walls were laid. “Souping” mortar involved adding sufficient water to produce a slump of
about 10 inches.
Specimens were tested in pull-out mode; some were tested in direct tension, and others were
tested to evaluate lap splices. The direct tension pull-out tests developed flexural tension
cracks in the masonry along the center of the rebar that clearly reduced the pull-out strength.
The report noted that this phenomenon would not be expected in actual walls and was simply
a result of using a test specimen that produced an effect that was not anticipated. They
indicated the results of the pull-out tests should not be considered other than for comparison
with each other.
The mortar used to fill the masonry was a Type S masonry cement mortar. The compressive
strength from mortar cubes was between 1,076 and 1,802 psi for the “slushed” mortar. The
“souped” mortar tested as grout achieved a strength of over 4,500 psi. The grout strengths
were unusually high at over 11,000 psi.
No general conclusions were listed. However, a notable observation was that of the 36 tests
conducted, 35 produced tension bond strengths that developed tensile bar strengths
exceeding the allowable tensile strength of the rebar. The single test that did not achieve
allowable stress was observed after testing to be poorly consolidated.
The “slushed” mortar samples produced results in the pull-out tests slightly less than the
“souped” mortar samples. The grout tests resulted in the highest pull-out results. However,
the ratio of the compressive strength of the grout to the “souped” mortar was approximately
2.44, whereas the ratio of the pull-out strengths was 1.45. Thus, the mortars performed very
well in comparison to the grout.
Page 5
TESTING CONCEPT
Goals
While the compressive strength of masonry is important, the primary concern of this study is how
the masonry, and in particular, the mortar that is used to fill the cells (referred to as mortar fill), is
likely to respond to tension in the reinforcement. The ability of the masonry to develop tension in
the reinforcement is related to the ability of the mortar fill to bond to the CMU and the reinforcement.
This research is intended to study mortar as grout in reinforced masonry by testing the pull-out
strength of vertical reinforcement and the bond strength of the mortar fill to the units.
The study is being performed at an elemental level rather than with full wall tests. The results will
be used to determine if further large-scale testing is appropriate and worthwhile.
Definitions
For the purpose of this research, the following definitions are used.
Mortar fill:
ASTM C 270 mortar used as mixed with no water added.
Pourable mortar: ASTM C 270 mortar with water added to produce a pourable consistency.
Grout:
ASTM C 476 grout with a slump of 8 to 11 inches.
Fill material:
The generic term used for mortar fill, pourable mortar, and grout to make
specimens.
Tests
Two types of tests were performed.
A.
Pull-Out Tests
No specific ASTM test was used for this work. Small scale tests were developed in 1996 by
Ryan-Biggs Associates (RBA) for specific projects to compare the performance of mortar fill
to grout when prism-type samples containing a reinforcing bar are exposed to pull out of the
reinforcement. That testing concept is the basis for this portion of the research and is similar
to the procedure used by Richart 13 to test for tension bond strength.
The tests used were not intended to represent actual wall performance but were selected as
more representative than pure tension tests of lap splices.
A key component of the current study is to create a test that forced a failure in the fill material
under pull out mode. From those results, it would be possible to compare the performance
of the mortar fill and pourable mortar with the grout. It was decided to place the masonry
units in compression rather than use tension samples. While neither the previous tension
tests nor this work adequately represents walls subjected to flexure, it was decided that the
proposed tests would serve to adequately compare mortar fill, pourable mortar, and grout
under similar test conditions. Therefore, from these tests a decision could be made as to
whether further full-scale tests were warranted that represent flexural walls and tension tests
for shear walls.
Page 6
In this portion of the study, the performance of the mortar fill is to be judged based upon its:
1. Capacity to develop tension in the reinforcement.
2. Capacity to develop tension in the reinforcement relative to code requirements.
3. Capacity to develop tension in the reinforcement in comparison to grout.
Testing was performed at Materials Characterization Laboratory, a commercial testing
laboratory in Scotia, New York.
Pull Out Procedure
1. Samples were prepared as shown in Figure 1 with two CMU stack bonded. They were
prepared by a journeyman mason from Bricklayers and Allied Craftworkers (BAC) Local
#2 in Albany, New York. The jacking plate was added prior to the test and was set dry
on the sample.
Figure 1 Pull-Out Test Specimen
Page 7
2. Samples were constructed inside the BAC facilities (Photograph 1). The air temperature
at the time of construction was approximately 75°F, with a relative humidity of
approximately 85 percent.
Photograph 1
For consistency, all samples were made similar to ASTM C101914 prisms by rodding the
fill material 25 times for each lift. Each sample had three lifts.
3. Each sample was created from a sawn half unit of 8-inch CMU; units had either a square
end or a sash block end. Construction was similar to ASTM C 1019 which contains
information related to constructing prisms.
Samples were first constructed two units high and allowed to cure for 21 days. They
were subsequently filled with mortar fill, pourable mortar, or grout and allowed to air dry
for 7 days; no moisture was applied. After 7 days, they were transported to the testing
facility and allowed to continue air curing. Due to the large number of samples and the
presence of reinforcement, the samples were air cured rather than being placed in a
plastic bag as recommended by ASTM. The fill material in the samples were 31days old
when tested.
4. Samples were tested in a tensile testing machine. Photographs 2 and 3 show the test
configuration. The top jacking plate was fitted with spacer bars to allow the bearing of
the steel on the face shells and webs of the CMU and not on the fill material so as not to
restrict slippage of the fill material from the CMU.
Page 8
Photograph 2
Photograph 3
Figure 2 shows the test setup graphically and the free-body diagram of the load application.
Figure 2 - Pull-Out Specimen in Test Frame
5. Test results were recorded for load versus reinforcement slippage and elongation until
maximum load was applied. The test equipment pulled the reinforcement at a constant
rate of 0.2 inches per minute.
6. Samples were photographed and the types of failure categorized.
Page 9
B.
Tests of Bond Between Fill Material and CMU
No specific ASTM test was available to measure this bond property. The test method in this
study followed the procedure outlined in the Department of State Architect of California
requirements in California State Chapter 2405(c)3.C. The test method is described in
Concrete Masonry Association of California and Nevada document, “Recommended
Grouting Procedure for Hollow Concrete Masonry Constructed Under CAC Title 24.”
Prism samples were prepared similar to the
pull-out test samples except without the
reinforcing bar. After approximately 40 days,
prisms were delivered to the National
Concrete Masonry Association in Herndon,
Virginia. Core samples (6-inch nominal)
were taken from the prisms (Photograph 4)
and tested in their laboratory.
The intent was to test for bond shear
strength between the fill material and the
CMU. Theoretically, these results should
correlate with the results of the pull-out tests
that were observed to fail by pull out of the fill
material.
Photograph 4
The test is performed with a guillotine apparatus. Each face shell is sheared off in separate
tests to derive the bond shear strength (Photograph 5). The arrows indicate the shearing
plate elements. The right plate remains stationary; the left plate drops down and shears the
face shell from the core sample.
Photograph 5
Page 10
Variables
Bedding Mortar:
All samples were constructed with mortar mixed according to ASTM C 270, Type S, proportioned
by volume. The proportions were one part portland cement to one-half part lime to four and onehalf parts sand by volume (1:0.5:4.5).
Mortar Fill:
Two variations were used with the Proportions method of ASTM C 270:
Mix N:
Mix S:
Type N mortar mixed by proportions 1:1:6.
Type S mortar mixed by proportions 1:0.5:4.5 (same as bedding mortar).
These mixes were mixed with no additional water. This is similar to the “slushed” mortar in the
Clemson research.
The mortar fill was mixed in a gasoline-powered mortar mixer. Slump measurements were taken
with a concrete slump cone in accordance with ASTM C14315. The mortar fill was placed into the
prisms within 30 minutes of mixing. No retempering was done.
Pourable Mortar:
Two variations were used with the Proportions method of ASTM C 270. These included:
Mix NSL:
Mix SSL:
Type N mortar mixed by proportions 1:1:6 with water added, producing a
slump of 6 inches.
Type S mortar mixed by proportions 1:0.5:4.5 with water added, producing
a slump of 6 1/4 inches.
These mixes had water added to create a pourable consistency. The previous research at NCMA
used a 7 to 9 inch slump; the Clemson work used a 10 inch slump.
The pourable mortar was mixed in a gasoline-powered mortar mixer. Slump measurements were
taken with a concrete slump cone in accordance wtih ASTM C143. The pourable mortar was
placed into the prisms within 30 minutes of mixing.
Grout:
Two variations were used:
Mix G:
Mix ModG:
ASTM C 476 fine grout mixed by proportions 1:0.1:3.3 with a slump of 10 1/4
inches. The proportions are: portland cement, lime, and sand aggregates.
ASTM C476 fine grout modified with extra lime to proportions of 1:0.4:4.2
with a slump of 9 ½ inches. Effectively, this is a Type S mortar with a grout
slump.
Page 11
Mix G is the basis for comparison for the other mixes since grout is currently recommended by
codes and standards for commercial construction. However, recognizing that grout usually
produces much higher strength than is normally associated with mortars, a modified mix (ModG)
was created with increased lime content to produce a mix with a compressive strength close to
2,500 psi, which was anticipated for the Type S mortar mix. Mix ModG does not comply with the
proportions method of ASTM C 476 by virtue of its higher lime content but does conform to the
strength requirements of that standard.
ASTM C 476 specifies a grout slump of between 8 inches and 11 inches. While ASTM allows the
grout to be mixed by proportions, MSJC requires the grout have a minimum strength of 2,000 psi.
Grout was mixed in a gasoline-powered mortar mixer. Slump measurements were taken with a
concrete slump cone in accordance with ASTM C 143. The grout was placed in the prisms within
30 minutes of mixing.
Concrete Masonry Units:
Two types of 8-inch CMUs were used for the pull-out tests and bond shear tests. Both were
manufactured by Zappala Block, Inc., of Rensselaer, New York. One type was a regular (normal
weight) CMU meeting ASTM C 9016. The second type of CMU was the same as the first with the
exception that Block Plus-W10, a liquid integral water-repellent admixture by Addiment
Incorporated, Atlanta, GA, (now a subsidiary of W.R. Grace ) was included in the mix in an attempt
to provide a lower water absorption rate.
There is no ASTM test to evaluate the rate of absorption in CMU, only total absorption. Thus, it is
not possible to quantify the effect of the integral water-repellent on the rate of absorption.
The face shells of the units were tapered with the top 1 7/16 inches thick and the bottom 1 1/4
inches thick. The webs were also tapered with the top 1 1/4 inches thick and the bottom 1 1/2
inches thick.
Page 12
MATERIAL CHARACTERIZATION
Sand
Test samples were prepared using natural sand from the sand pit of William M. Larned and Sons
in Schenectady, New York. The sand is regularly used locally on masonry projects based upon
the ASTM C14417 testing and certification by Construction Technologies Inc. of Schenectady, New
York (Appendix A).
Sieve analyes were performed on two additional samples by Ryan-Biggs Associates and Chemical
Lime Company for conformance with ASTM C 144. Subsequently, the sand tests were compared
to ASTM C 40418. All three analyses indicated a fine-grained sand. The test results by
Construction Technologies Inc. and Ryan-Biggs Associates indicated the sand met C 144, while
the Chemical Lime test indicated it did not. Copies of these analyes are included in Appendix A.
The results are not inconsistent. Two sieve tests indicated the samples were at the high end of the
range for nearly all sieve sizes. The third test indicated that the material exceeded the high end
of the range on two sieve sizes. It is not unreasonable that the one sample would exceed the high
end of the range for a specific sieve size for this material. Based upon the performance of the sand
in the local market and the two passing tests, conformance with ASTM C 144 and its gradation
requirements was assumed.
While the mortar fill sand was tested for compliance with ASTM C 144, grout aggregates are
required to meet ASTM C 404. By comparing standards, natural sands meeting ASTM C 144 also
meet the standards for fine aggregates in accordance with ASTM C 404.
Grout
Grout prisms were made in accordance with ASTM C 1019 to determine compressive strength.
The air temperature was approximately 70°F with a relative humidity of approximately 55 percent
at the time of grout mixing and placement.
Prisms were kept moist with damp paper towels until block molds were removed after two days.
The prisms were then wrapped with damp paper towels and placed in plastic bags, palletized, and
transported to the lab by RBA. At the lab, they were placed in a water storage tank in accordance
with ASTM C 51119 to finish the curing process.
Three samples of each mix were tested at 7, 14, 28, and 90 days. A summary of the results is
shown below in Table 1. Individual test results are in Appendix B.
All mixes achieved approximately 85 percent of their 28-day strength within 7 days. Between 28
and 90 days, the mixes gained less than10 percent greater strength.
Mix G, the typical grout mix, averaged 3,677 psi at 28 days. The modified grout, Mix ModG,
averaged 2,323 psi at 28 days. Both mixes had one unusually low test with the 28-day strengths
that can not be explained. The table gives values denoted with a * that ignore the low values.
These values seem more representative of the actual strength when compared to the 7, 14, and
90 day strengths. At 90 days, the average values (low values) were 4,187 (4,140) and 3,073
(2,940), respectively. Both mixes, G and Mod G, easily surpass the 28-day minimum compressive
strength of 2,000 psi recommended in the MSJC.
The modified grout mix (Mod G) was originally selected to develop a mix that was a high-slump
Page 13
grout with a strength close to 2,500 psi at 28 days. That was achieved.
Mix
7 Days
14 Days
28 Days
90 Days
3080
4050
3010
4200
3160
3460
4180
4220
2790
3950
3840
4140
Mean
3010
3820
3677 (*4010)
4187
Std Deviation
195
316
602
34
COV (%)
6.5
8.3
13.3
1.0
2490
2470
2760
3240
2400
2630
1380
3040
2360
2400
2830
2940
Mean
2416
2500
2323 (*2795)
3073
Std Deviation
67
118
818
153
COV (%)
2.8
4.7
35.2
5.0
G
ModG
Table 1 - Grout Compressive Strengths
Mortar Fill and Pourable Mortar
Since the mortar fill and pourable mortar are being used as grout, samples were also made in
accordance with ASTM C 1019, which is intended for grout and is not the traditional method for
testing mortars. The air temperature was approximately 70°F with a relative humidity of
approximately 55 percent at the time of mortar fill mixing and placement.
Prisms were kept moist with damp paper towels until the block molds were removed after two days.
The prisms were then wrapped with damp paper towels and placed in plastic bags, palletized, and
transported to the lab by RBA. At the lab, they were placed in a water storage tank in accordance
with ASTM C 511 to finish the curing process.
Three samples of each mix were tested at 7, 14, 28, and 90 days. A summary of results are shown
below in Table 2. Individual tests results are in Appendix B.
Page 14
Of the mortar fills, Mix S meets the MSJC minimum compressive strength of 2,000 psi for grout; Mix
N does not. Of the pourable mortars, neither Mix NSL nor Mix SSL meets the MSJC minimum
compressive strength of 2,000 psi for grout.
Mix
7 Days
14 Days
28 Days
90 Days
1190
1450
1550
1460
1240
1460
1220
1360
1320
1320
1530
1620
Mean
1250
1410
1433
1480
Std Deviation
66
78
185
131
COV
5.3
5.5
12.9
8.9
1270
1460
1680
1620
1300
1560
1360
1590
1320
1350
1570
1140
Mean
1297
1457
1537
1450*
Std Deviation
25
105
163
269
COV
1.9
7.2
10.6
18.6
2040
2010
2600
2160
2020
2000
2620
2550
2180
2400
2420
2160
Mean
2080
2137
2547
2290*
Std Deviation
87
228
110
225
COV
4.2
10.7
4.3
9.8
1780
2010
1690
2230
1800
1720
1890
2250
1690
1940
1820
2140
Mean
1757
1890
1800*
2207
Std Deviation
59
151
101
59
COV (%)
3.4
8.0
5.6
2.7
N
(%)
NSL
(%)
S
(%)
SSL
Table 2 - Mortar Fill Compressive Strengths Tested in Accordance with ASTM C 1019
None of the mixes meet the minimum slump requirements of ASTM C 476.
The increase in water content going from a mortar consistency to a pourable mixture had little affect
Page 15
on the strength of the N mix going to the NSL mix. However, the increase in water content reduced
the compressive strength in the SSL mix from the S mix.
Individual results did not conform to the usual strength gain trend for Mix NSL at 90 days, Mix S at
90 days, and Mix SSL at 28 days. These could not be explained and either raised or lowered the
mean values. These values are noted with a * in Table 2.
The mortar used as bedding mortar and mortar fill was also characterized by Chemical Lime
Company. The results are part of Appendix A. They provide mortar cube strengths that will be
discussed later.
Concrete Masonry Units
The units were normal weight and manufactured in accordance with ASTM C 90. Manufacturer’s
data indicates the average net compressive strength is approximately 3,138 psi based upon ASTM
C 14020 testing (Appendix C).
Reinforcement
Twenty-four-inch lengths of No. 5 reinforcement meeting ASTM A 61521 were used for the pull-out
tests. The fabricator reported that the actual yield strength was 61,500 psi and the actual tensile
strength was 98,500 psi. For analysis purposes, the yield capacity was based upon 60,000 psi
yield strength and 90,000 psi tensile strength consistent with ASTM A 615 minimum requirements.
This produces a yield capacity of 18.6 kips and a tensile capacity of 27.9 kips.
Compressive Strength of Masonry
Using the Unit Strength method, Section 1.4B.2.b., Table 2 of the 2002 MSJC Specifications22, the
compressive strength of the masonry was determined based upon Type S mortar in combination
with the CMU unit strength of 3,138 psi. This gives a calculated compressive strength of the
masonry equal to 2,178 psi. While the grout strength is not included in the development of this
value, the MSJC Specification requires that the grout meets either ASTM C 476 or the grout
compressive strength equals or exceeds f'm but not less than 2,000 psi.
Page 16
For this study, the compressive strength of the masonry ( f'm) was taken conservatively as 2,178
psi or the mortar fill strength, whichever is less, as shown in Table 3.
Mix
Compressive Strength (psi) from
Tables 1 and 2
Assumed f'm (psi)
(Compressive
Strength of Masonry)
Mortar fill
N
1,433
1,433
Mortar fill
S
2,547
2,178
Pourable mortar
NSL
1,537
1,537
Pourable mortar
SSL
1,800
1,800
Grout
G
4,010
2,178
Grout
ModG
2,795
Table 3 - Compressive Strength of Masonry
2,178
Page 17
TESTING RESULTS
Pull-Out Tests
Loads
Complete results are provided in Appendix D. Photographs of the tests are included on a disk that
accompanies this report. Figure 3 shows a summary of the test results for the regular CMU with the
various mixes. For reference, the yield strength of the reinforcement is plotted. As previously
noted, the reinforcement has a minimum yield strength of 18.6 kips and a minimum tensile strength
of 27.9 kips.
Figure 3 - Pull-Out Loads versus Mix Type for Regular CMU
Figure 4 shows the summary of the results for the CMU with water-repellent admixture. Individual
test results are in Appendix D.
Page 18
Mix G and Mix ModG gave comparable results.
Figure 4 - Pull-Out Loads versus Mix Type for Water-Repellent CMU
Page 19
Figure 5 superimposes the results for all tests. In all tests, the CMU with water-repellent admixture
gave higher results.
Figure 5 - Pull-Out Loads versus Mix Type for CMU
Page 20
Failure Types
Failure mechanisms took several forms. For the purpose of these descriptions, fill material is either
mortar fill, pourable mortar, or grout. Failures can be classified as:
1.
CMU cracking; fill material cracking (Photograph 6).
Photograph 6
2.
CMU cracking; little or no fill cracking but slippage of the fill material from the core
(Photograph 7).
3.
No CMU cracking;
reinforcement and
Photograph 7
Page 21
spalling around
reinforcement slippage
(Photograph 8).
Photograph 8
Cracking was identified as outwardly visible cracking. In some samples, cracking occurred internal
to the fill material. This was evident in those samples where the face shells broke away exposing
the fill material and the tensile failure of the fill material near the mortar joint level.
Cracking of the CMU is considered a preferred method of failure in that the stress is being
transferred to the units. Referring back to Figure 2, it is noticeable that the CMU has tapered face
shells. For the fill material to be pulled out of the top of the specimen, it is possible some of the
masonry cracking results from the “wedging” action of the fill material as it slips within the tapered
core. Had the sample been constructed upside down, the fill material would have been locked into
the lip created by the overhanging upper unit at the bed joint. In either configuration, there would
have been some mechanical advantage to preventing the fill material from pulling through.
Fill material slippage or slippage of the reinforcement is not a preferable mode of failure. Fill
material slippage was a dominant mode of failure for Mix N with regular CMU (four tests) and also
occurred with Mix SSL (two tests) and Mix ModG (one test). With the water-repellent CMU, Mix N
(one test) and Mix S (one test) also had fill slippage. Fill material slippage is a result of bond failure
between the fill material and the units. Shrinkage of the fill material reduces the bond to the CMU
and increases the possibility of fill material slippage from tension in the reinforcement.
Reinforcement slippage, independent of significant cracking, was the dominant mode of failure for
Mix NSL with water-repellent CMU (six tests) and also occurred with Mix N with water-repellent
CMU (one test).
Visible in Photograph 7 is shrinkage at the interface of the CMU and fill material. This may have
occurred because the samples were initially air dried before being sent to the lab for moist curing
and not covered with a plastic bag as recommended by ASTM C 1019. However, it is more
indicative of how real samples are constructed and may perform.
Page 22
Bond Tests
Six-inch-diameter core samples were taken from the prisms as recommended by the California
standard. The cells of the CMU were narrow and did not have sufficient width to take the 6-inch
cores without coring a portion of the unit. Photograph 9 shows one of the samples after testing; the
embedded portion of the web is visible in the sample.
Photograph 9
Twelve prisms were made, one for each fill material type and CMU type. One core was taken from
each prism. Each core produced two samples. This resulted in 24 bond shear test samples.
Subsequently, two additional tests were taken from the Mix S prism of the water-repellent CMU.
Loads
Table 5 shown later has a summary of test results. Photographs of tests are provided on the disk.
The test results were highly variable. Therefore, it is difficult to draw conclusions with only two
shear values for each type of fill material.
Failure Types
Failure mechanisms took several forms and can be classified as interface or combined. The
specimens exhibiting interface failures sheared at the joint between the fill material and unit. The
surface was generally smooth with little mortar fill, pourable mortar, or grout remaining. This was
the predominant mode of failure.
For the combined failure, the mortar fill, pourable mortar, or grout remained partially intact with the
CMU and the shearing went through both the fill material and the interface. There were combined
failures observed in 5 of the 24 samples.
The initial Mix S samples from the water-repellent CMU tested lower than expected, and a second
set of samples was retested. During the retest, one face shell debonded during the coring
operation and was conservatively recorded as a zero-capacity sample.
Page 23
ANALYSIS OF RESULTS
Pull-Out Tests
2002 MSJC - Allowable Stress Method
Equation 2-8 of the MSJC gives the development length for the reinforcement, l d = 0.0015dbFs ⋅ This
value assumes a minimum grout strength of 2,000 psi. For the No. 5 reinforcing bar, the bar
diameter db = 0.625 inches. For the Grade 60 reinforcement with the allowable stress, Fs = 24,000
psi, the calculated ld = 22.5 inches.
The test specimens had an actual embedment for the reinforcement of 15.6 inches. This length
was selected to try to produce the failure mechanism in the fill material.
There is no MSJC procedure within the Allowable Stress method for calculating the capacity of a
partially developed reinforcing bar. However, we assumed that there is a linear relationship
between embedment length and the stress in the reinforcement. Therefore, using Equation 2-8 with
our reduced actual embedment of 15.6 inches, we solved for the reduced allowable stress, fs =
16,640 psi. This results in a reduced allowable force in the bar of 5,159 lbs. A factor of 2.5 is used
to obtain an anticipated ultimate load of 12,898 lbs.
Figures 7 and 8 replicate the test results shown in Figures 3 and 4 and superimpose the anticipated
ultimate loads that were calculated. Mix S, Mix SSL, and the grout mixes achieved the anticipated
ultimate load. Mix N in water-repellent CMU achieved the anticipated ultimate load also.
Page 24
Figure 7 - Pull-Out Loads versus Mix Type for Regular CMU
Page 25
Figure 8 - Pull-Out Loads versus Mix Type for Water-Repellent CMU
Page 26
2002 MSJC - Strength Design
With the introduction of a Strength Design method in the 2002 edition of the MSJC, a new formula
for development length was produced. It includes factors for the size of the reinforcement (( ) and
cover over the bars (K). Bar diameter (db) and specified compressive strength (f'm) are also
2
variables. The new formula is l d = 0.13db f y γ / φK f' m .
( = 1.0 for a No. 5 bar. K = clear cover or five bar diameters, whichever is less. In this case, the
five bar diameters criteria applies and K = 3.13 inches. The capacity reduction factor, N, equals 0.8.
Figure 9 shows the variation in required development length versus masonry strength for the No.
5 bar. The six mixes are superimposed along with the actual embedment length of the sample.
Since three mixes (Mix S, Mix G, and Mix ModG) had compressive strengths that exceeded the
maximum f'm previously determined by the unit strength method, they are plotted also. However,
by the standard, the development length for those three mixes would be based upon the maximum
f'm value in the figure.
Using the 2002 MSJC - Strength Design criteria, all of the mixes required a development length that
exceeds the actual length used in the test samples. Theoretically, the ultimate load capacity of the
reinforcement should not have been developed and the failure should have occurred in the fill
material.
Page 27
Figure 9 -
Required Development Length versus Compressive Strength of
masonry (f’m) for No. 5 Reinforcement Centered in 8-inch CMU
Based Upon MSJC Strength Design
Page 28
2005 MSJC
Recent developments in the MSJC have again resulted in changes to the development length. The
development length is the same for both Allowable Stress and Strength Design. The new formula
2
is l d = 0.13db f y γ / K f' m . For the No. 5 bar used in the test, the variables are the same as used
in the 2002 Strength Design. The primary changes are that the capacity reduction factor was
dropped and ( was changed to 1.3 for No. 6 and No. 7 bars.
Figure 10 shows the variation in the required development length versus specified compressive
strength for the No. 5 bar. The six mixes are again superimposed along with the actual embedment
length of the sample.
As with the 2002 MSJC - Strength Design criteria, the strengths of three mixes (S, ModG, and G)
exceeded the maximum f'm previously determined by the unit strength method. While all of the
mixes are plotted, the development length for the three mixes (S, ModG, and G) would again be
based upon the maximum f'm value in the figure.
Therefore, using the 2005 MSJC criteria, all of the mixes required a development length that
exceeds the actual length used in the test samples and the ultimate load capacity of the
reinforcement should not have been developed. Using the actual strength of Mix G as the criterion,
it is conceivable that the ultimate load capacity of the reinforcement could be achieved by pull out.
Page 29
Figure 10 -Required Development Length versus Compressive Strength of
masonry (f’m) for no. 5 Reinforcement Centered in 8-inch CMU Based
upon 2005 MSJC
Page 30
CODE SUMMARY
For the No. 5 bar, Table 4 indicates the results for the three versions of the MSJC standard. The
Length column is the required development length for the specific standard. The Load is in kips
and represents the force that would be expected to be developed by the actual embedment. The
masonry compressive strengths from Table 3 were used to calculate the development lengths for
the 2002 MSJC - Strength Design and 2005 MSJC methods.
Mix
2002 MSJC - ASD
2002 MSJC Strength
2005 MSJC
Length
(inches)
Load
(kips)
Length
(inches)
Load
(kips)
Length
(inches)
Load
(kips)
Mortar fill
N
22.5
12.8
32.0
9.1
25.6
11.3
Mortar fill
S
22.5
12.8
26.0
11.2
20.8
14.0
Pourable mortar
NSL
22.5
12.8
30.9
9.4
24.7
11.7
Pourable mortar
SSL
22.5
12.8
28.6
10.2
22.9
12.7
Grout
G
22.5
12.8
26.0
11.2
20.8
14.0
Grout
ModG
22.5
12.8
26.0
11.2
20.8
14.0
Table 4 - Development Lengths
Figure 11 superimposes the tested pull-out values with the calculated values from the three code
criteria. By all criteria, pull-out loads obtained with Mix S, Mix SSL, Mix G, and Mix ModG exceeded
the calculated capacities for all three design methods. In addition, the pull-out loads obtained with
Mix G and Mix ModG exceeded the yield strength of the reinforcement as well.
Mix N with water-repellent units achieved the calculated capacities for the three design methods;
Mix NSL did not.
Page 31
Figure 11 -
Pull-Out Loads versus Mix Types
Page 32
Tests of Bond Between Fill Material and CMU
These test results are provided in Appendix E and are summarized in Table 5. The Average Bond
Shear Stress is calculated from the individual test results on the front and rear face shells. The
Effective Pull-out Capacity is calculated from the Average Bond Shear Stress times the surface
area of the perimeter of the CMU cell for the sample (358.64 in2).
The Tested Pull-out results from Figures 3, 4, and 5 are listed along with the calculated Pull-out
Bond Stresses resulting from the pull-out tests.
Bond
Shear
StressFront
Shell
(psi)
Bond
Shear
Stress Rear
Shell
(psi)
Average
Bond
Shear
Stress
(psi)
Effective
Pull-Out
Capacity
(lbs)
Tested
Pull-out
(lbs)
Pull-out
Bond
Stress
(psi)
Mix
Masonry
Unit
N
Reg
29.6
37.4
33.5
12,015
12,297
34.3
N
WR
28.8
24.9
26.9
9,630
14,257
39.8
S
Reg
144.8
105.9
125.4
44,956
15,261
42.6
S
WR#1
49.1
63.1
56.1
20,120
16,265
45.4
S
WR#2
0
93.1
46.5
16,677
16,265
45.4
NSL
Reg
141.7
9.3
75.5
27,078
9,682
27.0
NSL
WR
17.9
167.4
92.7
33,228
11,402
31.8
SSL
Reg
21.8
197.8
109.8
39,379
14,333
40.0
SSL
WR
191.6
70.9
131.3
47,072
15,816
44.1
G
Reg
204
105.1
154.6
55,428
21,924
61.1
G
WR
206.4
338
272.2
97,623
21,977
61.3
ModG
Reg
199.3
24.9
112.1
40,204
20,665
57.6
ModG
WR
160.4
88.8
124.6
44,687
19,656
54.8
Table 5 - Bond Shear Tests
This testing is not incorporated into ASTM. It is primarily used in California where the
recommendation from the Office of the Architect of the State of California is that 100 psi is an
acceptable bond shear stress.
Overall, the bond shear stress results were highly variable.
The bond shear stress for tests exceeded 100 psi for Mix S with regular units and Mix G with
Page 33
regular and water-repellent units. Mixes NSL, SSL, and ModG with regular and water-repellent units
all had one of the two tests exceed 100 psi. The average bond shear stress of Mix S with regular
units and Mixes SSL, G, and Mod G with regular and water-repellent units exceed 100 psi.
Two sets of samples were tested for Mix S with water-repellent units (WR) because the results of
the first tests appeared to be lower than anticipated. The second test gave one higher result, but
the other test from the front face shell debonded during the coring operation.
In all cases except for Mix N, the average bond shear stress exceeded the calculated bond stresses
from the pull-out tests. That correlated well with the pull-out tests in that most did not fail in bond.
That was interesting because most of the samples when viewed from the top appeared to have
shrinkage around the perimeter of the fill material.
From observations of the pull-out tests, we note that there were fill material pull outs (bond shear
failure with the CMU) for individual samples comprised of N Reg, N WR, S WR, SSL Reg, and
ModG Reg.
Page 34
COMMENTS
General
1.
Pourable mortar Mix SSL is currently allowed by the International Residential Code.
2.
The pull-out tests for Mix S versus Mix SSL indicate that mortar fill performs better than
“pourable” mortars with a 6 inch slump.
3.
The bond tests for Mix S versus Mix SSL indicate that mortar fill performs better than
“pourable” mortars with a 6 inch slump with regular CMU but not the CMU with waterrepellent.
4.
In the Clemson tests, “pourable” mortars had higher compressive strengths than the mortar
fills. As was seen in Table 3, in this study there was little difference in compressive strength
for Mix N as a result of adding water to make it pourable (Mix NSL). In contrast to the
Clemson study, this study produced a significant reduction in the compressive strength of
Mix S by adding water to create a pourable consistency (Mix SSL).
5.
Test results indicate that Mix G performed the best of all mixes. While mortar fill Mix S
achieved 64 percent of the grout strength of Mix G, it had 70 percent of the pull-out strength
for regular CMU and 74 percent of the pull-out strength for the CMU with water-repellent.
6.
Table 6 compares the 28-day strengths of Mix N and Mix S when tested as mortar cubes
versus the grout prisms. The results are included in Appendix A from Chemical Lime
Company. The mortar cubes tested in accordance with ASTM C 78023 overstate the
strength of mortar used as fill material.
Mortar (mixed by
proportions)
Mortar Cubes
(ASTM C 780)
Grout Prisms
(ASTM C 1019)
Ratio
Type N
2421 psi
1433 psi
0.59
Type S
4132 psi
2547 psi
0.61
Table 6 - 28-Day Compressive Strengths for Type N and Type S Mortars
This is not unexpected. ASTM C 780 indicates that mortar samples made as cylinders will
test to approximately 85 percent of the values obtained using cubes due to the variation in
aspect ratio of the samples. In this study, the prisms tested to approximately 60 percent of
the cube samples made in compliance with ASTM C 780. The reduction can generally be
explained as a result of the increased water content of the prisms providing lower
compressive strengths.
Therefore, mortar fill should be evaluated in accordance with ASTM C 1019.
7.
The use of sand meeting ASTM C 144 appears to be acceptable for mortar fill.
Page 35
Based upon the Pull-out Tests:
1.
The mortar fill performed better than the “pourable” mortars with a 6 inch slump that are
allowed by residential codes for the conditions tested in this study.
2.
The mortar fill mixes achieved higher pull-out values when the CMU contained the waterrepellent admixture. The pull-out strengths of the grout mixes were relatively unchanged
by the use of CMU with water-repellent admixture.
3.
The pull-out load results increased with increasing compressive strength of the fill material.
4.
The compressive strengths of Mix N and Mix NSL were less than 1,600 psi when measured
by ASTM C 1019. In general, these mixes did not achieve adequate pull-out values.
5.
The pull-out loads achieved with mortar fill Mix S exceeded the required calculated loads
for all three design methods in the codes. The compressive strength of the mix exceeded
2,000 psi and was closer to 2,500 psi.
6.
The pull-out loads achieved with pourable mortar Mix SSL exceeded the required calculated
loads for all three design methods. The compressive strength of the mix was approximately
1,800 psi.
7.
The pull-out loads achieved with grout mixes Mix G and Mix ModG exceeded the required
calculated loads for all three design methods. The compressive strength of the mixes
exceeded 2,800 psi.
8.
The pull-out loads achieved with the grout mixes (Mix G and Mix ModG) exceeded the yield
strength of the reinforcement. This was well beyond what was anticipated or required
based upon the three MSJC design methods. All three methods had calculated pull-out
loads well below the yield value.
9.
The use of water-repellent admixture in the CMU had little affect on the pull-out test results
for the grout mixes. It appears the grout water content was sufficiently high that the
difference in loss of water through absorption into the units had a negligible effect.
10.
While Type M mortar fill was not tested, it is likely that, based upon the results for mortar
fill Mix S, it too would have produced pull-out loads that exceed the three design methods.
11.
The 2002 and 2005 MSJC formulas produced results for development length that are more
conservative when based upon the compressive strength of the masonry (f'm) as determined
by the unit strength method rather than the fill material strength.
12.
Pull-out strengths for Mix S and Mix SSL were acceptable in spite of the observed shrinkage
of the fill material.
Based upon the Bond Tests:
Page 36
1.
The coring operation to obtain the bond shear samples is highly operator dependent.
Based upon the speed of the coring, the angle of the core relative to the surface, and the
quality of the core drill, it is possible to introduce stress into the sample and, in the extreme
case, to “spin-off” the face shell. The reduction in the tested shear stress due to the
sampling is unknown.
Standard procedure is to take a second sample if one is damaged by the coring operation.
2.
The fill material exhibited shrinkage, but the mortar fill shrinkage seemed greater.
The shrinkage and the coring operation apparently resulted in significant shear stress
differences from one face shell to the other in samples Mix NSL, Mix SSL, Mix G, and Mix
ModG with regular CMU and Mix NSL, Mix S, Mix SSL, Mix G, and Mix ModG with waterrepellent units.
3.
While the California standard does not have a minimum standard for its grout bond test, 100
psi is considered acceptable. The grout mixes developed the highest bond shear stresses.
The other mixes did not give consistent results.
4.
The effect of coring a portion of the web of the CMU was considered insignificant. The
results were not consistently greater due to a portion of the unit in the sample.
5.
With only two bond shear tests for each mix, there was too much variability in the results
to draw any reliable conclusions about the shear bond characteristics of the fill materials.
Page 37
CONCLUSIONS/RECOMMENDATIONS
Overall, the goals of the research were achieved. Mortar fill was evaluated to compare it with
pourable mortar and grout as a means to encase reinforcement in vertical applications. The results
are:
1.
The elemental test results indicate that mortar fill could be an acceptable alternative to fine
grout for modified low-lift applications of reinforced masonry. The specifics of the
modifications for installation techniques need to be developed but could include the lift
height, the method of consolidating the mortar fill, the board life of the mortar, retempering,
and splicing the reinforcement.
2.
While high-slump grout may be necessary for high-lift grouting operations, the high-slump
material may not be required for low-lift grouting applications. Type S and Type M mortar
fill and “pourable” mortars offer an alternative worth further consideration.
Mix N and Mix NSL did not perform adequately. It appears the compressive strength of the
material is too low for use as a fill material. The minimum MSJC value of 2,000 psi for the
grout seems reasonable.
3.
Mortar fill performed better than “pourable” mortar in the pull-out tests.
4.
The development length of reinforcement based upon the MSJC criteria (2002-Strength
Design and 2005) should be based upon the lesser of the compressive strength of the
masonry (from unit strength method or prism test method) or the 28-day mortar fill strength.
The minimum mortar fill strength should be 2,000 psi.
5.
A reduction in the absorption of the concrete masonry units improved the pull-out strength
of the mortar fill. Lower absorption of the units was created by the use of an integral waterrepellent additive. The improved strength is likely due to the higher compressive strength
of the fill due to reduced water loss from the mix. Whereas the grout has excess water to
release to the units, the water retention from the mortar fill is helpful in the hydration of the
mortar. It could also be due to reduced shrinkage.
This is somewhat consistent with Isberner’s statements that low slump material can provide
adequate strengths. However, the mix needs to be appropriately designed.
6.
No definite conclusions can be drawn from the grout bond shear stress tests based upon
the variability of the results and the small sampling.
7.
The sampling process for the bond shear stress test weakens the sample. The results
seem to be affected by the sampling. A test program that compares the bond shear test
method to push-through samples of fill material might provide some insight into the effects
of the coring operation.
Page 38
8.
Full-scale wall tests that evaluate flexural and axial capacity should be performed based
upon the following criteria.
A.
B.
C.
D.
E.
9.
Mortar fill with a minimum compressive strength of 2,000 psi when tested in
accordance with ASTM C 1019. This should be Type S and Type M mortars.
For consistency with this study, the mortar fill would be portland cement and limebased mortar meeting ASTM C 270.
Wall specimens should be constructed in a modified low-lift application.
A procedure should be developed for the installation that should be considered
mandatory if the use of mortar as grout is proposed to MSJC. The procedure should
include lift height, consolidation method, board life of the mortar, retempering, and
reinforcement splicing. Consolidation of the mortar fill must be complete and
consistent.
The results should be compared to those for walls constructed using the low-lift
method using fine grout.
The bond shear strength tests should be repeated with a larger sampling to further
examine the shrinkage characteristics of the mortar fill and its impact on bond shear
stress.
Several additional issues became evident during this research and should be evaluated
further.
A.
B.
C.
D.
E.
The performance of the ModG mix indicates that Type S and Type M portland
cement and lime mortars mixed to a grout consistency could provide a suitable
substitute for ASTM C 476 grout.
The unit strength method for determining the compressive strength of the masonry
is based upon the CMU strength and the mortar type. It does not involve the mortar
fill or grout strength. This study indicates that the development length and lap
lengths for reinforcement should be evaluated using the mortar fill or grout strength.
In this study, the reinforcement always developed in a shorter length than calculated
using the compressive strength of the masonry based upon the unit strength
method. One distinct possibility is that the unit strength underestimates the
compressive strength of the masonry sufficiently to require significantly longer laps
than would be necessary had the compressive strength of the masonry been
determined using the prism test method.
MSJC should reconsider the lap lengths and development lengths for reinforcement.
To avoid overly conservative lap lengths, the compressive strength of the masonry
used in the determination of lap lengths should not be based upon the unit strength
method; it should be based upon grouted prisms.
It is the author’s opinion that research on lap lengths is needed that tests samples
in flexure in comparison to pure tension samples. It would be appropriate to
determine different lap lengths based upon the application.
Shrinkage effects of mortar fill and grout should be evaluated further relative to bond
with regular and low absorption units. Grout aids or other admixtures could be
considered that increase bond.
Page 39
F.
G.
The use of water-repellent additives or other admixtures in mortar fill should be
evaluated for their affect on the material when used as a grout.
The importance of the bond shear strength should be evaluated in light of the
existence of core insulation that has received the acceptance of BOCA Evaluation
Services for grouted masonry. The insulation is U-shaped and debonds the grout
from the face shells and one web leaving the grout only bonded to one web.
Page 40
ACKNOWLEDGMENTS
Peer Review Group
The peer review team for the research program:
John Buck , Bricklayers and Allied Craftworkers Local 2.
Brian Trimble PE, Brick Industry Association (formerly International Masonry Institute - MidAtlantic Region).
Gene Abbate, International Masonry Institute - Empire State Office.
Diane Throop PE, Consultant; Chair of MSJC Construction Practices Subcommitee.
Robert Thomas, National Concrete Masonry Association.
Margaret Thomson, Chemical Lime Co.; MSJC member.
Dr. Arturo Schultz, University of Minnesota; MSJC member.
Tom Murray, Colonie Masonry Corporation of Albany, Inc.
Arthur Del Savio, Del Savio Construction Corp.
Donations
Major funding for this research was provided by:
International Masonry Institute, represented by Mr. Gene Abbate.
National Lime Association, represented by Mr. Eric Males and Ms. Margaret Thomson.
Bricklayers and Allied Craftworkers, Local No.1, New York, New York.
National Concrete Masonry Association Research and Education Foundation represented
by Mr. Robert Thomas, P.E., Vice President of Engineering.
Donated materials and services were provided by:
Dimension Fabricators, Scotia, New York, represented by Mr. Scott Stevens, President reinforcement.
V. Zappala and Co., Rensselaer, New York, represented by Ralph Viloa Jr. - concrete
masonry units.
Glens Falls Lehigh Cement Co., Glens Falls, New York, represented by Mr. Peter Maloney portland cement.
Graymont Dolime (OH), Inc., Genoa, Ohio, - hydrated lime.
Chemical Lime Co., Henderson, Nevada, - mortar characterization represented by Ms.
Margaret Thomson and Mr. Richard Godbey.
Bricklayers and Allied Craftworkers - Local No. 2, Albany, New York, represented by Mr.
John Buck and Mr. Bart McClellan - masonry sand; fabrication of samples.
Subcontractors
Page 41
Evergreen Testing and Environmental Services, Inc., Menands, New York, - compression
testing.
Materials Characterization Laboratory Inc., Scotia, New York, - pull-out tests.
National Concrete Masonry Association, Herndon, VA - grout bond shear tests.
Ryan-Biggs Associates, P.C.
Thanks to Don Trojak for coordinating the testing and assisting with the sample preparation;
Ross Shepherd for graphics; Jill Shorter for report preparation assistance; Jack Healy for
reviewing the report; and Barbara Meagher for editing.
Page 42
APPENDIX A - SAND TEST RESULTS
RYAN-BIGGS ASSOCIATES, P.C.
MATERIAL SOURCE: Mason Sand from Wm. Larned & Sons Inc.
MATERIAL DESCRIPTION: Sand, fine/medium, trace Silt/Clay
MATERIALPROJECT USE: Mortar and Mortar Fill
RBA Project Number: 8379
DATE: October 15, 2004
Sieve Percent
Size Retained
#4
0
#8
0
#16
4
#30
27
#50
67
#100
86
#200
96
C-144 C-144 Percent
Low High Passing
100
100
95
100
100
70
100
96
40
75
73
10
35
33
2
15
14
0
5
4
100
C-144 Low
80
60
C-144 High
40
Percent
Passing
20
#5
0
#1
00
#2
00
#3
0
#1
6
#8
0
#4
Percent Passing
ASTM C144: Size Distribution of Sand:
Sieve Analysis
Sieve Sizes
A-1
A-2
A-3
A-4
A-5
A-6
APPENDIX B - GROUT AND MORTAR FILL TEST RESULTS
B-1
B-2
B-3
B-4
APPENDIX C - CONCRETE MASONRY UNIT TEST RESULTS
C-1
APPENDIX D - PULL-OUT TEST RESULTS
D-1
D-2
D-3
D-4
D-5
D-6
APPENDIX E - BOND TEST RESULTS
E-1
APPENDIX F - REFERENCES
1.
Building Code Requirements for Masonry Structures (ACI 530-02 / ASCE 5-02 / TMS 40202), Masonry Standards Joint Committee, 2002.
2.
ASTM C 476-02, “Standard Specification for Grout for Masonry,” ASTM International, West
Conshohocken, PA.
3.
ASTM C 270-02, “Standard Specification for Mortar for Unit Masonry,” ASTM International,
West Conshohocken, PA.
4.
2005 Personal correspondence from James E. Amrhein, former Executive Director of
Masonry Institute of America, Los Angeles, CA
5.
Grout...The Third Ingredient, James E. Amrhein, MASONRY INDUSTRY magazine, June
1980
6.
Technical Note 9B - Manufacturing, Classification, and Selection of Brick, Part 3 Revised
December 2003, Brick Industry Association, Reston, VA
7.
Grout for Reinforced Masonry, A.W. Isberner, Jr., ASTM STP: Masonry: Materials,
Properties, and Performance, ASTM International, West Conshohocken, PA., 1982
8.
1982 Edition, Uniform Building Code, International Code Council, Falls Church, VA.
9.
One and Two-Family Dwelling Code, Council for American Building Officials, International
Code Council, Falls Church, VA.
10.
2000 International Residential Code, International Code Council, Falls Church, VA, 2000.
11.
Reinforcement Bond Strengths in Portland Cement-Lime Mortars, Masonry Cement Mortars,
and Fine Grout, NCMA research and Development Laboratory, Hedstrom and Thomas,
June 1991.
12.
Feasibility of Using Mortar in Lieu of Grout for Reinforced Hollow Clay Wall Construction,
Russell Brown, Clemson University, 1998. Unpublished, but cited with permission of the
Wall Committee of the National Brick Research Center.
13.
Bond Tests Between Steel and Mortar in Reinforced Brick Masonry, F.E. Richart, Structural
Clay Products Institute, February, 1949.
14.
ASTM C 1019-02, “Standard Test Method for Sampling and Testing Grout,” ASTM
International, West Conshohocken, PA.
15.
ASTM C 143-03, “Standard Test Method for Slump of Hydraulic Cement Concrete,” ASTM
International, West Conshohocken, PA.
16.
ASTM C 90-02, “Standard Specification for Loadbearing Concrete Masonry Units,” ASTM
International, West Conshohocken, PA.
F-1
17.
ASTM C 144-02, “Standard Specification for Aggregate for Masonry Mortar,” ASTM
International, West Conshohocken, PA.
18.
ASTM C 404-97, “Standard Specification for Aggregates for Masonry Grout,” ASTM
International, West Conshohocken, PA.
19.
ASTM C 511-03, “Standard Specification for Mixing Rooms, Moist Cabinets, Moist Rooms,
and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes,” ASTM
International, West Conshohocken, PA.
20.
ASTM C 140-02a, “Standard Test Methods for Sampling and Testing Concrete Masonry
Units and Related Units,” ASTM International, West Conshohocken, PA.
21.
ASTM A 615, “Standard Specification for Deformed and Plain Billet-Steel Bars for Concrete
Reinforcement,” ASTM International, West Conshohocken, PA.
22.
Specifications for Masonry Structures (ACI 530.1-02 / ASCE 6-02 / TMS 602-02), Masonry
Standards Joint Committee, 2002.
23.
ASTM C 780-02, “Standard Test Method for Preconstruction and Construction Evaluation
of Mortars for Plain and Reinforced Unit Masonry,” ASTM International, West
Conshohocken, PA.
F-2