Group 3 performed a test to determine the compressive strength of cement mortar cubes with different water-to-cement ratios. They mixed mortar with a 0.4 ratio and formed 3 cubes. After curing for 7 days, the cubes were tested. The average compressive strength was 6,283 PSI, slightly lower than expected likely due to improper tamping technique introducing air bubbles. Compared to other groups' cubes, the 0.4 ratio cubes did not show as high strength as predicted. Estimates for 14 and 28-day strengths were also calculated using standard equations.

1. CE 3700
Engineering Materials Laboratory
“Determining the Compressive Strength of Hydraulic Cement Mortars”
Performed By:
Group 3
Section 3
Submitted By:
Chase Andrew Bowman
Date Performed: Date Submitted:
September 11th
& 18th
, 2014 September 25th
, 2014
Department of Civil and Environmental Engineering
Louisiana State University and A&M College
Fall 2014

2. Purpose
In accordance with ASTM C 109, Standard Test Method for Compressive
Strength of Hydraulic Cement Mortars, and ASTM C 150-02a, Standard Specification for
Portland Cement, tests were performed on 2” by 2” cubes of mortar fabricated by 3
groups. The purpose of this lab exercise was to understand how different water/cement
ratios affect the compressive strength of a hydraulic cement mortar. By doing this lab
exercise we can better understand the fundamental characteristics of Portland Cement
Concrete mixtures. Portland Cement when mixed with water creates a chemical reaction
called hydration. During hydration the mixture will first display a plastic form before
hardening. The higher the W/C ratio, the higher the workability a mixture will have
during the plastic stage. However with a higher W/C ratio, the compressive strength will
decrease. In a professional setting one might need a certain strength requirement and
choosing a perfect W/C ratio is key to meeting this requirement while still achieving a
high workability. It is important that ASTM C 150-02a sets standard and optional
physical requirements regarding compressive strength because it gives us a reference for
our mixtures.
Please note: certain requirements for ASTM C 109 standards were not meet; this will be explained later in
“Test Procedure.”
Significance and Use
Portland Cement is hydraulic cement that is composed of calcium silicates. Hydraulic
cement undergoes a chemical reaction called Hydration, in which that cement particles
absorb water and create a gel. This gel is what glues individual particles together and
creates Portland Cement Concrete. Different amounts of water added to a mixture affect
its workability and compressive strength. By performing ASTM C 109, we can determine
a W/C ratio to meet certain specifications or requirements required for a mixture. If a
sample of mortar cubes fail at compressive strength lower than required, we would know
to add less water to the next sample. If a mortar cube greatly surpasses the required
compressive strength, we know to add more water to the next sample to increase its
workability.
Equipment
The following devices listed below were used in the fabrication and compressive strength
tests on 2” by 2” Mortar cubes. These Devices are required to comply with ASTM C 109
testing standards.
• Weighing Devices – used for measuring the samples’ weights
• Measuring Cylinder – used for measuring the water needed for the mixture
• Sample Molds – a device made from brass that held 3 2”x2”x2” molds
• Mixing Tray – a plastic tray in which the samples were mixed
• Tamper – a piece of seasoned oak wood that removed air from the molds in two
different stages
• Hammer – used for removing air once the molds have been filled

3. • Trowel – a steel blade with straight edge used for creating a flat/equal top of the
molds
• Moisture Room – a room of high humidity where the samples are kept for 20-72
hours after being molded into cubes.
• Hydraulic Compressor Testing Machine – used for determining the compressive
strength of the molds
Sample Identification
ASTM C 109, Standard Test Method for Compressive Strength of Hydraulic Cement
Mortars, states that for the standard mortar there shall be 1 part cement to 2.75 parts sand.
The lab exercise used a 50/50 sand to cement ratio, therefore it did not meet the standard
mortar ratio requirement. ASTM C 109 also states that a water/cement ratio for all
Portland cement should be .485, however the water/cement ratio for lab was .400. The
following test samples were used for preparing the mortar:
• 907.2 grams of type I Portland cement that is composed of minerals:
1. Lime (CaO) – main component (60-65%)
2. Silica (SiO2)
3. Alumina (Al2O3)
4. Iron Oxide (Fe2O3)
5. Gypsum (CaSO4.2H2O)
• 907.2 grams of course sand
1. 6.1.1 of ASTM C 109, Standard Test Method for Compressive
Strength of Hydraulic Cement Mortars, states, “The sand (Note 4) used
for making test specimens shall be natural silica sand conforming to
the requirements for graded standard sand in Specification C 778.”
2. Being that the sand used for lab was not Graded Standard Sand, it did
not meet the requirements of ASTM C 109 and C 778.
• 362.9 grams of drinkable water
1. Please note that 362.9 grams of water is specific to group 3’s lab
In table 1 you can see the weights and W/C ratios of groups 1,2 and 3.
Table 1. Shows Groups 1,2, and 3’s starting points for preparing the mortar
Group S/C ratio W/C ratio Water Wt. (g) Cement Wt. (g) Sand Wt. (g)
1 50/50 0.5 453.6 907.2 907.2
2 50/50 0.45 408.2 907.2 907.2
3 50/50 0.4 362.9 907.2 907.2
Please note: That all groups had the same sand to cement ratio, (907.2/907.2), but had different water
weights. This gave each group a different W/C ratio. We can predict that group 1’s mortar will have the
lowest compressive strength due to its higher W/C ratio.

4. Test Procedure
The test procedure was in accordance with ASTM C 109, Standard Test Method
for Compressive Strength of Hydraulic Cement Mortars, with a few exceptions. ASTM C
109 states that a 2.75/1 ratio of sand/cement is to be used for a standard mortar, however
a 1/1 ratio was used in lab. The water/cement ratio of .400 that was used for this lab did
not meet the standard of .485 set for Portland cement by 10.1.1 of ASTM C 109. Also
6.1.1 under “Materials” states that a graded standard sand meeting the requirements for
ASTM C 788 is to be used, however course sand was used for this lab exercise. Prior to
our lab session it is assumed that our instructor completed all steps under “Preparation of
Specimen Molds” of ASTM C 109. These steps are 9.1,9.2, and 9.3 and involve properly
preparing the brass molds so that they create a watertight seal and do not expose the
mortar to any unwanted additions that could compromise its strength or dimensions.
Upon arriving to lab we discovered that our lab instructor for time saving reasons
conducted 10.2, (Preparation of Mortar) under “Procedure.” 10.2.1 regards to finding the
proper weights of the cement and the water. It is important to determine if the cement is
air-entrained or not. Performing this step wrong could lead to an inaccurate amount of
water needed for the mixture. After completion of 10.2 our instructor informed us of our
samples’ weights.
Group 3’s first step was 10.4.1 of ASTM C 109. The 907.2 grams of sand and
roughly half of the Portland cement were placed into the mixing tray. The tray was mixed
until a constant mixture was reached. The remaining Portland cement was poured into the
tray and mixed again. Once the mixture reached a consistent spread of both sand and
cement, half of the water was introduced into the tray. After thoroughly mixing by hand,
the remaining water was added and mixed again. Image 1 displays mixing the samples
thoroughly before and after the addition of water.
Image 1: Represents Procedure 10.4.1 in ASTM C 109
The left image shows mixing of the samples without water. The right image shows mixing
after water was introduced. Please note: The samples are thoroughly mixed before and
after the addition of water to achieve maximum consistency.

5. Please note that procedure 10.4.2 of ASTM C 109 was not performed because a
duplicate batch was not needed given that we were only constructing 3 mortar samples.
10.2.1 indicates that this lab exercise involves 6 or 9 mortar samples. After completing
the mixture we began procedure 10.4.3. The plastic mixture was then scooped from the
tray and placed into the brass molds at an interval of 1” deep. After a mold was filled
with mortar up to 1” we began to tamper to remove any possible air bubbles within the
mixture. Each mold was filled to 1” and tampered separately using a 5” long piece of
seasoned oak. Then we filled the brass molds so that they had extra mortar extruding
from the top. They were tampered again using the same method as before. After
tampering, a trowel was used to create an even surface on the top of the mortar. 10.4.3 of
ASTM C 109 states that the mortar needs to be tampered 32 times in 4 rounds making
sure that the tamper is always at a right angle to the adjacent wall. In this lab we did not
meet this requirement being that we only tampered 25 times in a relatively unorganized
manor. This led to air bubbles being present in our final mortar cube and a decrease in
compressive strength. This will be explained later in “Analysis of Results.” After
tampering, a trowel was used to create an even surface on the top of the mortar. Image 2
displays how the mortar extended pass the top of the mold and tampered. Image 3 shows
how the trowel was used to create a flat, even surface.
Image 2: Represents procedure 10.4.3 in ASTM C 109
The image shows tampering using the season oak wood. This was after the molds were
filled over the top with mortar. Please note that improper tampering technique was used,
which caused air bubbles to be present in the cube. This resulted in a decrease of
compressive strength.

6. Image 3: Represents Procedure 10.4.3 of ASTM C 109
After the mortar cubes were set in their mold, a flat surface was placed on top of
them to make sure undesired moisture did not compromise the cubes. In accordance with
procedure 10.5 of ASTM C 109, the mortar cubes were immediately placed in a moisture
closet with high humidity. The mortar cubes would be removed from the high humidity
after a period of 24 hours and were left to harden for another six days.
Upon returning to lab on September 18th
, procedure 10.6.2 of ASTM C 109 was done
prior by the instructor. Please note that procedure 10.6.1 states that each cube once
removed from the moisture closet is kept track of and is to be broken at different times
such as 24 hours, 3 days, 7 days, and 28 days. In this lab exercise all 3 mortar cubes were
broken 7 days following the molding.
The image shows how the trowel was used to define the top edge of the mortar cube. Please
note that extra mortar was added during this set to fill in gaps along the edges of the mold.
Also the lab instructor assisted to confirm that we had an even top.

7. The lab instructor prior to the second lab performed procedure 10.6.3 of ASTM C
109 on two out of the three mortar cubes. He recorded the load at which the cubes failed
using a hydraulic compressor and passed them on to us. Once recording the previous two
cubes’ load at failure we proceeded to perform the compressive strength test on the third.
The third cube was carefully placed under the upper bearing block of the testing machine.
The machine exerted a force on the top mortar until it failed. The third cube’s load at
failure was then recorded. Image 4 displays the cube after if has reached its failing point.
Image 4: Procedure 10.6.3 of ASTM C 109
The image represents the third mortar cube after failing under a load of
24,655 Lbs. please note that the lab instructor performed this test on the first
two mortar cubes.

8. Analysis of results
Table 2 shows the area, load at which the cube failed, compressive strength, the
age of the sample, and Type break. It also includes the average compressive strength of
all samples, standard deviation, and % coefficient of variation. All three samples after
testing displayed an hourglass shape. This tells us that all three mortar cubes were well
dimensioned and that the bearing load during testing was consistent through out the entire
sample. Sample 1 and 2 both showed a similar compressive strength averaging at 6343.25
PSI. The standard deviation for the first and second sample was about 22.5 PSI. This
STD is an expected value for testing. However sample 3 had a compressive strength of
only 6,163.42 PSI and when averaged with the other cubes the STD is raised and the
average strength is decreased. It is assumed that the lower compressive strength of
sample 3 is due to poor tampering technique mentioned previously in “Test Procedure.”
The improper tampering technique allowed air bubbles to reside in the third sample. The
higher standard deviation raises the coefficient of variation %.
Starting with a water/cement ratio of .4, it was expected that the mortar samples
would have a higher average compressive strength. This could have been a human error
related to 10.4.1 of ASTM C 109, which involves mixtures the samples. Even though the
samples had a lower strength than expected, they still achieve standard and optional
physical requirements set by ASTM C 150-02a, Standard Specification for Portland
Cement. ASTM C 150-02a states that a minimum of 4060 PSI is required for optional
physical requirements.
Table 2: Displays Test Results for Group 3
Sample
#
Area
(W x H)
Load at Failure
(LBS)
Compressive Strength
(PSI)
Age at Test
(Days)
Type
Break
1 4" 25,463 6,365.75 7
Hour Glass
2 4" 25,283 6,320.75 7
Hour Glass
3 4" 24,655 6,163.75 7
Hour Glass
Average, PSI 6283.42
Standard Deviation, PSI 106.05
% Coefficient of Variation 1.69%

9. Graph 1 shows the average compressive strengths for each group. It was expected
that the higher the water/cement ratio the more the strength would decrease. Observing
the chart below this is expectation was met, however the difference between .4 W/C and
.45 W/C is noticed. With a W/C ratio of .4, the mortar cubes were expected to have a
much higher compressive strength then the mortar cubes with a .45 W/C ratio. This could
have been a human error involved with mixing the test samples in ASTM C 109
procedure 10.4.1. Group 1’s mortar with a W/C ratio of .5 met expectations being that it
was much lower than the other two groups.
Graph 1: Displays the average CS for each group
Please note: There is an obvious difference between the compressive strength of the Water/Cement
ratio of .5 and .45. This is expected, however the Water/Cement ratio of .4 did not display this large of a
difference. This could be blamed on multiple human errors such as tampering and mixing.

10. Table 3 and Graph 2 illustrate the estimated 14 and 28-day compressive strength
of each group’s samples. The 28-day compressive strength was found by dividing the
average compressive strength at 7 days by .07. The equation for this was f28=f7/.7. The
14-day strength was found by multiplying the estimated 28-day strength by .085. The
equation for this was as follows f14=f28x.085. These equations were developed by
researching different techniques involves converting 7 day strength to 28 day strength.
Most techniques state that the 7 day compressive strength it between .65 and .75 of the 28
day compressive strength. By averaging out the range, .7 was determined to be the best
factor to use to properly estimate.
Table 3: Displays Group’s estimated CS for 14 and 28 Days
Compressive Strength (PSI)
Days Group 1 Group 2 Group 3
7 3926.58 4767.99 5609.4
14 6062.75 7361.91 8661.07
28 6283.42 7629.35 8975.71
Please note: All 9 samples from all three groups met the standard physical requirements set by ASTM C
150-02a. All estimated values of 28-day strength also meet the Optional Physical requirement in Table 4
of ASTM C 150-02a
Graph 2: Represents Table 3 in a visual setting
Please note: Group 1 and 2’s estimated compressive strengths were expected, however Group 3’s
average compressive strength was lower than expected.

11. Findings
After reviewing the results of the lab, it is clear that there were a sign of possible
human error regarding the procedure. These human errors are most likely the improper
tampering techniques. Procedure 10.4.3 of ASTM C 109 was not followed, which likely
let to the presence of air bubbles in the mortar. Also mixing the test samples before and
after the introduction of water maybe has also played a role in this.
Both group 1 and 2 showed expected results, which correctly portrays the known
importance of the water/cement ratio in mortar. Group 1 had the highest W/C ratio and in
turn it showed to have the lowest compressive strength. Group 2 with a W/C ratio of .45
also showed expected results. Groups three’s average compressive strength was noted as
unexpected. Its assumed compressive strength was much lower than the tests results
showed. Not only was the average lower than expected, but the third sample also broke at
a significantly lower bearing load than the others. This was most likely due to a build up
of air bubbles in the mortar cube.
The Lab exercise properly displayed how the Water/Cement ratio affects the
compressive strengths of mortar samples. Even with the factor errors all 9 mortar cubes
of all three groups met Standard and Optional Physical Requirements of ASTM C 150-
02a.