______________________________________________________________________________
Rapid Setting Cement Based Mortars Using Nano Materials
Southeastern Louisiana University
Engineering Technology 494-90I Jordan Perez, Blake McHugh, & Benjamin Boyett
Instructor: Dr. Mohammad Saadeh
Advisor: Dr. Mohamed Zeidan
1
Contents…………………………………………………………………………………………..1
Abstract…………………………………………………………………………………...2
Introduction………………………………………………………………………………………3
Significance………………..……………………………………………………………...3
Additives………………………………………………………………………………….4
Research Design & Methods…………………………………………………………………….6
Flow Table………………………………………………………………………………..6
Compressive Strength……………………………………………………………………7
Normal Consistency……………………………………………………………………...8
Vicat Needle………………………………………………………………………………9
Results……………………………………………………………………………………..…….11
Discussion……………………………………………………………………………….15
Conclusion………………………………………………………………………………………16
References……………………………………………………………………………………….17
Permission Form………………………………...……………………………………………...18
2
Abstract
The objective of this project is to develop a cement-based mortar that will have a reduced
setting time, decreased or unchanged viscosity, and increased compressive strength when
compared to common mortar. Ideally, this mortar design will be capable of being used in 3-D
printing and/or robotic brick laying. Other researchers have found colloidal silica to increase
compressive strength and decrease setting times and flowability in cementitious mixtures by
encouraging early crystallization at Calcium Silica Hydrate (CSH) sites. This study adds to
previous research by testing the properties of hydraulic mortar mixtures with varying amounts of
silica and varying particle size. Additionally, superplasticizer have been added to several
mixtures to improve workability. Compressive tests were taken on those mixtures to determine if
the agent has any negative affect on overall strength. All mixtures have been tested using ASTM
standards for flow table, Vicat needle, and compressive strength. Several mixtures were tested
for “printability” using various methods to ultimately determine if the mixtures were capable of
3-D printing.
3
Introduction:
Mortar has been used for over 200 years as a binding agent in masonry. It can be
composed using a variety of materials, chemical compounds, and additives, but in its basic form,
mortar consists of cement (usually portland type), water, and sand. Evolving technology such as
robotic brick laying and 3D printing have introduced a need for a faster setting mortar.
Traditional mortars are ineffective in new technology due to ranging viscosity, long setting-
times, and low early-compressive strengths. Other research has shown that adding colloidal silica
to various cementitious materials decreases set-time and flowability while increasing the
compressive strength of concrete and mortar. This study has done intensive research involving
the viscosity, setting times, and compressive strengths of mortar mixes containing colloidal silica
particles.
Significance:
Rapid setting mortar can be used for a variety of applications in the construction industry
including 3-D printing and robotic bricklaying. Apis Cor, a construction company based in
Russia, recently 3D printed a 400sqft circular home using a flowable and rapid-setting mortar
(Deamer). Researching this field could potentially lower building costs, improve strength, and/or
decrease construction time of similar projects. Another industry that could benefit from a rapid
setting mortar is the robotic bricklaying industry.
Traditional brick masons set an average of 500 bricks per day and control the setting time
by adding or reducing water. Typical water to cement (W/C) ratios used by brick masons range
from .52-.56. This is because setting bricks by hand requires minute adjustments to square the
structure. Robotic brick laying machines however, do not require these adjustments and can set a
4
staggering 3,000 bricks per day (Curtis). Speeding up the brick laying process requires faster
setting mortar and because the machine cannot determine its own consistency, a standardized one
must be used. Colloidal silica could be a solution to more efficient brick laying machines.
Additives:
Colloidal silica consists of nanoscopic silica (SiO2) particles that have been pre-
suspended in a liquid for easy and consistent mixing. Other researchers have found that the
addition of silica in cementitious mixtures encourage the growth of Calcium Silica Hydrate
(CSH) sites (Figure 1), which directly correlate with the compressive strength of the mix.
Expediting the crystallization at CSH sites result in increased compressive strengths and
decreased set-times, but also decreased flowability. Results obtained last semester support this
claim (Results).
Figure 1. No CS/1% CS (Björnström 2006)
5
The two colloidal silicas that were tested in this study were Cembinder 8™ (C8) and
Cembinder 30™ (C30). Both products of Akzo-Nobel, C8 contains much larger SiO2 particles
and a higher solid to liquid ratio compared to C30 (Figure 2). Smaller silica particles mean a
higher surface area for the SiO2 to react. This generally results in a greater number of CSH sites
compared to larger silica particles. The CSH sites produced by smaller particles are also purer
than those produced by larger ones, but are disadvantaged due to the sheer size of the CSH sites
produced by larger crystals. The increased production of CSH sites when using any size SiO2
particles cause rapid dehydration in the mix, resulting in low workability. To combat this and test
the colloidal silica at higher percentage rates, a superplasticizer was added to some mixtures.
Cembinder 8 Cembinder 30SiO2 (by vol.) 50% SiO2 (by vol.) 30%Avg. SiO2 Size 35 nm Avg. SiO2 Size 6 nmRec. W/C Ratio .3-.5 Rec. W/C Ratio .3-.5Rec. Addition Rate 1-5% Rec. Addition Rate 1-3%
Figure 2: Cembinder Chart
Superplasticizers, also known as High-Range Water Reducers (HRWRs), are polymers
that act as dispersants in cementitious mixes causing particle segregation which improves
flowability. Two common uses of superplasticizers are to reduced W/C ratios while maintaining
workability or to maintain W/C ratios while increasing workability. When HRWRs are used to
decrease W/C ratios, the result is a denser cement product that has a higher corrosion resistance
with a slightly higher compressive strength. When used to increase workability, W/C ratio
remains the same and flowability is drastically improved.
6
Research Design & Methods:
During the first tests, varying amounts of colloidal silica was added to a generic .49 W/C
mortar mix using portland cement and a 2.75 sand to cement ratio. Mortar mixes were tested in
ratios of zero (control), one, two, five, and eight percent colloidal silica by weight using large
and small silica particles (Figure 3). The five and eight percent C8 mixtures were also tested with
1.1% ADVA 190™ superplasticizer (SP) added by weight of cement. Flowability of the samples
were found using the flow table test (ASTM C230/C230M) which determines the mortars
workability. Setting times were found using the normal consistency and Vicat needle tests
(ASTM C187 & C191-13) and compressive strengths were tested and recorded at one, seven,
and twenty-eight day intervals using the ASTM compressive test(ASTM C109-99). Additionally,
the control and C8-5% with SP were also tested for printability.
Mix Design (Figure 3)Mix Cement Sand Water Silica Total W/C
Control 826g 2,273g 401g 0.00g 3,500g 0.49C8-1% 818g 2,273g 393g 16.53g 3,483g 0.49C8-2% 810g 2,273g 384g 33.06g 3,467g 0.49C8-5% 787g 2,273g 362g 78.50g 3,422g 0.49C30-1% 818g 2,273g 382g 27.26g 3,473g 0.49C30-2% 810g 2,273g 362g 55.06g 3,445g 0.49C30-5% 787g 2,273g 309g 131g 3,369g 0.49
Flow Table Test:
The flow table test was the first test conducted. Adhering to ASTM Standard C230M, the
flow mold was placed in the center of the flow table (Figure 4) and filled half way with the test
7
mixture. The mixture was then tamped 25 times using a tamping rod. The mold was then filled
the rest of the way, tamped 25 times again, and the excess mortar was removed using a straight
edge. After the excess mortar was removed; the mix was allowed to rest for 30 seconds before
removing the mold and rotating the handle 25 times within 15 seconds causing the table to
vertically oscillate. The dropping table caused the mix to flatten, forming a disc-like shape on the
table. Four diameter measurements were then taken and averaged to determine the accepted
mortar diameter. Flowability was then calculated using the equation [(MD-ID)/ID]*100% where
MD is the accepted mortar diameter in inches minus the four inch Inner Diameter (ID) of the mold
divided by the Inner Diameter times one hundred, giving flowability represented as a percentage.
Figure 4. Flow Table
Inner Mold
Table
Handle
8
Compressive Strength Test:
Compressive strengths for this study were obtained in accordance with ASTM Standard
C109, which requires the mortar to be formed in two inch by two inch test cubes. The cross-
sectional surface area of the cubes was then measured using digital calipers and taking the
average of six measurements (3 heights and 3 widths). Once the cross-sectional area was
determined, the cubes were crushed using a hydraulic press at 1,7, and 28-day intervals with a
loading rate of 300 lbf/s. Compressive strengths were calculated using the equation ơ=P/A where
compressive strengths (ơ) equals maximum load (P) in pounds divided by the average cross-
sectional area of the cube (A) in square inches, giving the compressive strength (ơ) in units of
psi. Three cubes per mix were tested at each interval and the average of those results were found
and recorded (Compression Strength Results).
Normal Consistency Test:
The normal consistency test is a prequel to the Vicat needle test and is used to determine
the amount of water required to entirely react with the cement. Following ASTM Standard C187,
a paste was prepared using only cement, water, and additives. The paste was then formed into a
ball and compacted by tossing it back and forth six times. The ball was then molded into the
conical ring of the Vicat apparatus and the excess paste was removed with a straight edge (Figure
6). The plunger rod was then zeroed and locked in place on the surface of the paste. When the
plunger rod is released, it must penetrate exactly 10mm into the paste in 30 seconds or the test
must be readmitted. When the rod penetrated more than 10 millimeters; the mixture was too wet
and water had to be reduced for the next trial. When the rod penetrated less than 10 millimeters;
the mixture was too stiff and additional had to be added for the next trial. Once the plunger
penetrated exactly 10 millimeters, the test was complete, and set time testing could resume.
9
Vicat Needle Test:
The Vicat needle test uses the same mix and apparatus as the normal consistency test and
begins as soon as the cement contacts the water. After normal consistency was determined, the
plunger rod was rotated around so that the Vicat needle faced the mix. The needle was then
lowered to the surface of the paste and apparatus was zeroed. The needle would then be dropped
every 15 minutes until a penetration depth of 25mm or less was achieved, giving the initial
setting time. The initial setting time is the elapsed time from when the cement contacted water
until the Vicat needle penetrates 25mm. After the initial set time was determined, the needle
continued to be released until it would no longer penetrates the mix, giving the final setting time.
The final setting time is the elapsed time from when the cement contact water until the needle no
longer penetrates the mix.
Plunger Rod
Vicat Needle
Conical Ring
10
Figure 6. Vicat Needle Apparatus
Printing:
Methods used to test the printing capabilities of the mortars were the mortar gun method,
the jerky gun method, and the mortar bag method. The mortar gun method used the
Quickpoint™ Mortar Gun, which is a drill attachment specifically designed to apply mortar to
brick crevasses. Ideally, this method would provide a steady flow and produce even layers that
would build upon each other, creating a wall of mortar. The jerky gun method used a piston to
force mortar out of a chamber into a steady stream using a hand cranking lever. This would
provide an even layer of mortar, but flow could not be accurately controlled. The mortar bag is
also used to apply mortar to brick, but layer width and flow is strictly controlled by the user.
To obtain a cylindrical shape, a bucket lid was loosely attached to a table allowing it to be
manually rotated with ease. A trial mix was then loaded into a printing device and a bead of
mortar was laid around the circumference of the bucket lid. After each layer was established, 15
minutes were allotted allowing time for the mortar to begin setting before an additional layer was
added.
11
Results:
0 7 14 21 280
1000
2000
3000
4000
5000
6000
7000
8000
9000 Colloidal Silica Strength Table
Control C8-1% C8-2% C8-5% C8-8%Time (Days)
Stre
ngth
(PSI
)
Figure 7: Colloidal Silica Compressive Strength Results
Colloidal Silica Compressive Strength Results1 Day 7 Days 28 Days
Control 2,198 psi 3,953 psi 4,642 psiC8-1% 3,147 psi 6,002 psi 7,222 psiC8-2% 2,794 psi 4,984 psi 5,716 psiC8-5% 2,701 psi 6,226 psi 7,805 psiC8-8% 2,793 psi 4,738 psi 4,653 psi
C30-1% 2,888 psi 4,901 psi 6,427 psiC30-2% 2,815 psi 5,310 psi 5,417 psiC30-5% 2013 psi 5756 psi 6810 psi
12
0 5 10 15 20 250
1000
2000
3000
4000
5000
6000
7000
8000
9000
Colloidal Silica with Superplasticzer Results
C8-8% C8-5% C8-8%-SP C8-5%-SP
Time (Days)
Com
pres
sive
Stre
ngth
(PSI
)
Figure 8: Colloidal Silica with Superplasticizer Results
Colloidal Silica with Superplasticizer Results1 Day 7 Days 28 Days
Control 2,198 psi 3,953 psi 4,642 psiC8-5% 2,701 psi 6,226 psi 7,805 psiC8-8% 2,793 psi 4,738 psi 4,653 psi
C8-5%-SP 1,936 psi 5,918 psi 8,344 psiC8-8%-SP 2,828 psi 6,952 psi 7,330 psi
13
Control C8-1% C8-2% C8-5% C30-1% C30-2% C30-5%0
30
60
90
120
150
180 Set Time(s)
Initial Set Time
Tim
e (m
in)
Figure 9: Setting Times
Setting Times & Flowability (Figure 10)Mix Initial Set Final Set Flowability
Control 125 min 170 min 126.6%C8-1% 115 min 155 min 114.1%C8-2% 107 min 152 min 114.1%C8-5% 84 min 134 min 102.3%C8-8% 105 min 145 min 66.4%C30-1% 106 min 150 min 82.8%C30-2% 95 min 129 min 79.7%
14
Figure 11: Failed Mortar Gun Trial Figure 12: Fractures in the Base (Control)
Figure 13: C8-5%-SP Figure 14: Control Trial
15
Discussion:
The mixture containing five percent Cembinder 8 with superplasticizer (C8-5%-SP)
yielded the best 28-day compressive strength and proved to be the best all-around mixture. This
mix was therefore used in the final printing trial using the bag method (Figure 13). Printing with
the mortar and tamale gun proved unsuccessful due to over-compaction at the condensing point
causing a cease in flow. The mortar gun had a mechanism to combat over-compaction, which
worked for the base layer, but caused the mortar to be very loose and still over-compacted during
the second layer (Figure 11). Using the bag method, the condensing point could be massaged,
and the problem eliminated, but sacrificing consistent flow. This does not nullify results, but
proves the mortar is capable of being printed given the right printing device. An additional
advantage of the C8-5%-SP mix is that it eliminated fractures in the base layer during the
printing process (Figure 12) and produced a much stronger and appeasing finish compared to the
control printing trials (Figure 14). These fractures were most likely caused by the mortar
beginning to set then being crushed under the load from the sequential layer. The addition of
superplasticizer allowed the base layer to absorb the impact of the sequential layers without
losing integrity.
The larger SiO2 particles in the C8 admixtures proved to be far superior in early strength
and flowability than the smaller C30 particles. The increase in early compressive strength can
possibly be attributed to the formation of larger CSH crystals when compared to the C30. The
C30 mixture, however, could yield higher compressive strengths in trials lasting longer than 28
days due to the increased number of CSH sites formed using the smaller silica particles. This is
also the suspected cause for the decreased flowability in the C30 trials. The smaller particles
16
likely formed more, but smaller, CSH sites, which caused both the decrease in flowability and
the decrease in setting time.
Conclusion:
Results from this study agree with similar research. The addition of SiO2 particles in
cementitious mixtures tend to increase compressive strengths up to a certain percentage,
where compaction and air voids become an issue, while decreasing flowability and setting
times. Flowability continually decreased from zero to eight percent silica by weight, with the
smaller particles causing less flowability than larger ones. Setting times also decreased with
the smaller particles having a lower setting time than mixes containing similar percentages of
silica. The mixture that most accurately achieved the goal of the research was the C8-5%-SP,
which had the highest 28-day compressive strength while remaining flowable and rapid
setting. Additional research with that mix could be done, which could possibly result in better
building solutions for 3D printed cementitious structures.
17
References
ASTM Standard C109-99, 2003, "Compressive Strength of Hydraulic Cement Mortars," ASTM
International, West Conshohocken, PA, 2003, www.astm.org.
ASTM Standard C191-13, 2003, "Time of Setting of Hydraulic Cement by Vicat Needle,"
ASTM International, West Conshohocken, PA, 2003, www.astm.org.
ASTM Standard C230/C230M, 2003, "Flow Table for Use in Tests of Hydraulic Cement,"
ASTM International, West Conshohocken, PA, 2003, www.astm.org.
Björnström, J. (Photograph). (2006, March 10). No CS/1% CS [digital image]. Retrieved from
Dr. Joakim Björnström research 2000-2006
Cembinder for the Construction Industry [PDF]. (n.d.). Marietta, GA: AkzoNobel Pulp and
Performance Chemicals.
Curtis, S. (2017, March 27). Bricklaying robots set to replace human builders on hundreds of UK
construction sites. Retrieved February 19, 2018, from
https://www.mirror.co.uk/tech/bricklaying-robots-set-replace-thousands-10107529.
Deamer, K. (2017, March 7). This House was 3D Printed in Less Than 24 Hours. Retrieved
February 19, 2018, from https://www.livescience.com/58156-3d-printed-house-built-in
less-than-a-day.html.
18
