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[SYLWAN., 160(1)]. ISI Indexed 251
Enhancement of thermal efficiency: the effect of polymer microspheres embedded in
mortar for saving energy
Jesús Hernández-Frías1, Rodrigo Velázquez-Castillo2 and Miguel Galván-Ruiz3*
1 Faculty of Engineering, Autonomous University of Queretaro. C.U. Cerro de las Campanas
76010, Querétaro. México. Email: [email protected]
2 Faculty of Engineering, Autonomous University of Queretaro. C.U. Cerro de las Campanas
76010, Querétaro. México. Email: [email protected]
3 Faculty of Engineering, Autonomous University of Queretaro. C.U. Cerro de las Campanas
76010, Querétaro. México; CETIS 105-SEP. Km 3.5 Carretera Tlacote 76138, Querétaro.México. *Corresponding author, Email: [email protected]
Abstract
The aim of this paper is to investigate key aspects related to the thermal conductivity of sand-
cement mortar mixed with polymethylmethacrylate (PMMA) microspheres. The assessment
was done with tests, following ASTM guidelines. Previously, cement particles were bond
permanently to the surface during PMMA microspheres synthesis. The embellishments of
PMMA microspheres increases the resistance of thermal conductivity of the mortar, shown by
this pioneering method substantially.
Keywords: Mortar, PMMA microspheres, saving energy.
1. I ntroduction
Currently, many people noticed the effect on climate change as a result of greenhouse gasses
emissions (Lashof & Ahuja, 1990). A sustainable development satisfies the requirements of
people without committing the capacity of future generations, conserving the environmental
resources using energy, water, and raw materials efficiently (Bruntland, 1987). As a priority,
the generation of new materials increases the productivity of resources and offer a more
efficient use of them (Velázquez-Castillo, Galván-Ruiz and Rivera-Muñoz 2010). Nowadays
is more noticeable the development of a sustainable technology committed to developing new
construction materials. The enhancement of thermal properties offers some advantages for the
common users, such as important savings on the cost of energy consumption. Wellbeing is
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essential in buildings and homes where people spend considerable time (Yeladaqui, 2010).
Comfort in construction depends on factors such as proper lighting, ventilation, and a pleasant
thermal environment. This last one depends primarily on construction materials and
intelligent systems being used (Galván-Ruiz et al. 2009).
The appropriate use of thermal insulation in buildings contributes to reducing energy costs
(Al-Homoud, 2005). The magnitude of saving energy using thermal insulation varies
according to the type of building, climate conditions, building location and insulation
materials (Budaiwi & Abdou, 2013). In general, energy saving has a boundless impact on
environmental quality, use of resources, and human comfort. Hence, the thinking in the
building industry is no longer about should insulation be used or in what way and how much, but to look ahead to new building material for energy saving (Galván-Ruiz and Zaleta, 2013).
Research emphasizes thermal analysis to study various types of inorganic and organic
construction materials (Velázquez-Castillo et al. 2012), more extensively in the examination
of inorganic materials (Ramachandran, Paroli, Beaudoin, & Delgado, 2002).
Alternatively, mortars are broadly construction materials used by a huge number of cultures
disseminated worldwide. With the accelerated technological development, mortars have
evolved until obtaining a well-documented mix by their applicability and physical properties
(Galvan-Ruiz & Velázquez-Castillo, 2011). These spread over for building works as a lining
and final additions to walls (Ohama, 1995). Formerly, development of polymer-modified
mortars resulted in supplies currently used in the construction industry (Afridi, Ohama and
Iqbal 2003). Several studies on different materials were examined for improvement on walls
with compounds containing polymers (MacMullen et al. 2011; Bhutta, Ohama and Tsuruta
2011; Kong et al. 2013), as well for reducing water absorption and improving thermal
insulation saving energy (Saikia & de Brito, 2012). Several polymer additives modify the
properties of mortars (Lanzón and García-Ruiz, 2008; Gadea et al. 2010), or decrease the
density and modify the hydrophobic properties (Zhao et al., 2011; Afridi et al., 1995;
Frattolillo et al., 2005). This research then will be looking at the thermal efficiency – by
studying the effect of polymer microspheres embedded in mortar for saving energy.
2. Materials and M ethods
This research agrees with ASTM guidelines:
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ASTM C-778 Standard Specification for Standard Sand.
ASTM C109/C109M-08 Standard Test Method for Compressive Strength of
Hydraulic Cement Mortars.
ASTM C 1437 Standard Test Method for Flow of Hydraulic Cement Mortar.
ASTM C191-08 Standard Test Methods for Time of Setting of Hydraulic Cement by
Vicat Needle
ASTM C266-08 Standard Test Method for Time of Setting of Hydraulic-Cement Paste
by Gillmore Needles.
ASTM C1403 Standard Test Method for Rate of Water Absorption in Masonry
Mortars.
Workability Test by Abram’s cone.
ASTM C177-10 Standard Test Method for Steady-State Heat Flux Measurements and
Thermal Transmission Properties using the Guarded Hot Plate Apparatus.
2.1 Mortar formulation
The formulation of fresh mortars was 1:2.75 parts of cement CPC 40 and sand according to
ASTM C-778. There is an inclusion of PMMA microspheres from 0% to 40% by volume.
This limit of 40% by volume is about the workability of the mortar because a higher content
produces an inappropriate consistency, and it became unworkable as a layer. Mortar
preparation assures that the aggregate is uniformly mixed, bonding the material and the other
comparatively heavier ingredients of the mortar mix.
Table 1. Percentages of Sand + Cement + PMMA according to the total addition of the
mixture.
PMMA
microspheres
Proportion (m3) volume (m3) weight (kg)
Cement SandPMM
ACement Sand PMMA
Cem
entSand
PMM
A
0% 1 2.750 0.000 0.000850 0.002338 0.000000 2.55 6.194 0.000
10% 1 2.475 0.275 0.000850 0.002104 0.000234 2.55 5.575 0.028
20% 1 2.200 0.550 0.000850 0.001870 0.000468 2.55 4.956 0.056
30% 1 1.925 0.825 0.000850 0.001636 0.000701 2.55 4.337 0.084
40% 1 1.650 1.100 0.000850 0.001403 0.000935 2.55 3.717 0.112
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2.2 Character ization
2.2.1 Scanning Electron Microscopy (SEM)
The morphology and topology of samples were analyzed by scanning electron microscopy
using a JEOL JSM 5600, accelerating voltage 20 kV, and secondary electron images
recorded. A very fine layer of gold was placed on the sample surface, to prevent electrostatic
charge accumulation.
2.2.2 Compressive Strength Test
Standard Test Method for Compressive Strength of Hydraulic Cement Mortars ASTM C109
/C109M-08. This test method agrees with the measurement of the compressive strength ofhydraulic cement mortars using 50 mm cube specimens.
2.2.3 Water Absorption of Masonry Mortars
Standard Test Method for Rate of Water Absorption if Masonry Mortars ASTM C1403. This
test method provides a standardized laboratory procedure for determining the relative water
absorption by capillary uptake (wicking) characteristics of masonry mortars.
2.2.4 Flow of fresh mortar
Standard Test Method for Flow of Hydraulic Cement Mortar ASTM C 1437. This test method
determines the flow of hydraulic cement mortars, and of mortars containing cemented
materials other than hydraulic cement.
2.2.5 Time of setting by Vicat apparatus method
Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle ASTM
C191-08. The test method used in this research is the manually operated standard Vicat
apparatus.
2.2.6 Time of setting by Gillmore Needles method
Standard Test Method for Time of Setting of Hydraulic-Cement Paste by Gillmore Needles
ASTM C266-08. This test method covers the determination of the time of setting of hydraulic
cement paste using the Gillmore needles.
2.2.7 Thermal conductivity
Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission
Properties using the Guarded Hot Plate Apparatus ASTM C177-10. This test method
contributes to the general design requirements necessary to construct and operate a suitable
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Figure 1. SEM Micrographs from PMMA microspheres with cement particles.
Figure 2 shows the mortar matrix appearance obtained after the compression test of the
samples; some microspheres looked broken and deflated and hence collapsed due to this test.
The spreading of the microspheres of various diameters is heterogeneous, contributing to a
more efficient development of the mixture. Dispersion of microspheres is significant
depending on the volume of the sand-cement mixture thus improving the mortar thermal
properties, including air inside.
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Figure 2. Mortar bulk after the compressive test.
3.2 Compressive Strength Test
Samples were prepared according to the established regulation in Standard Test Method for
Compressive Strength of Hydraulic Cement Mortars ASTM C109/C109M-08. PMMA
microspheres added in different percentages from 0% through 40% by volume according to
ASTM compressive strength parameters and using a proportion 1:2.75 of silica sand according
to ASTM C778. Key information about the quality come from the compression tests shown in
Figure 3. The main contribution of this research is the formulation of lightweight mortar
improved by PMMA microspheres with better thermal insulation properties, lengthwise with
the lowest decrement in compressive strength.
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Figure 3. Compression experiment on the test cubes according to guideline ASTM C109,
including PMMA microspheres from 0 to 40%, test age 7 and 28 days.
The results show an inversely proportional relation between the percentage of added
microspheres and the magnitude of the compression strength, for which the final effect will be
the maximum percentage of added PMMA that will allow an appropriate workability and, at
least, the minimum compression strength specified by ASTM directive. The optimal ratio
results at 40% content of PMMA microspheres and 8 Mpa compression strength, at 28 day's
test.
3.3 Water absorption
Water absorption according to regulation ASTM C1403 Standard Test Method for Rate of
Water Absorption in Masonry Mortars.
Water absorption in mortars provides an approximate prediction as to how the material will
respond as mortar. Water absorbing capacity will affect the structure and in some cases the
resistance of the masonry. The results of the absorption tests showed a relation inversely
proportional to PMMA content and water absorption showing in Figure 4. It turned out that the
PMMA microspheres produce certain hydrophobic properties to the mortar. Furthermore, the
water absorption shows an almost linear propensity at small percentages of microspheres, then
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decreasing due to the increment in the fluidity properties, originated by the water reduction
effect of growing of PMMA microspheres content.
Figure 4. Water absorption in mortar samples.
3.4 Flow of f resh mortar
The fluency test analyzes the property that allows mixtures to flow and fill gaps; they can
become self-leveling without the need of vibrating equipment. This material is a new option
for others to fill porosity. A good flow is obtained when no significant segregation occurs,
and the material extends at least 200 mm in diameter. Filling fluids must not have
segregations, exudates or volume shrinkage. When the fresh mixture flows, some have a
slight expansion after hardened. The laboratory data appears in Table 2 and Figure 5. Small
proportions of microspheres increase the flow while decreasing at higher rates.
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Table 2. The flow of fresh mortar by percentage of polymeric microspheres aggregated.
PMMA microspheres
%
Diameter
(flow test) cm
00 20.620
10 22.250
20 24.550
30 23.050
40 22.250
50 19.920
60 18.025
Figure 5. Test flow of fresh mortar mixture according to ASTM C 1437.
3.5 Time of setting by Vicat apparatus method
The assessment consists of preparing a mixture with a previously calculated water content.
The mortar is placed into the mold and using a probe that falls by gravity, the setting time is
then calculated. Curing time may vary depending on the temperature and humidity of the
external environment. The results are shown in Table 3.
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Table 3. Time of setting by Vicat apparatus.
PMMA microspheres
%
Setting time
(minutes)
0 269
10 251
20 244
30 239
40 233
50 228
60 215
3.6 Setting time by Gillmore Needles method
Under the conditions of work, the workability or installation time is shorter than the setting
time obtained in laboratories because it cannot be controlled under environmental conditions.
Indeed, this essay is about finding the time in minutes during which the mortar is pliable
before hardening to a level that makes placing too difficult or impossible. Gillmore needles
support the results obtained using the Vicat apparatus to the final setting time; moreover, the
data also get initial setting time. The results are shown in Table 4.
Table 4. The setting time by Gillmore needles method.
PMMA microspheres
%
Initial setting time
(minutes)
Final setting time
(minutes)
0 140 260
10 130 255
20 130 250
30 125 240
40 125 220
50 120 215
60 120 215
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3.7 Thermal conductivity and thermal resistance
The thermal conductivity accomplished according to ASTM C177 - 10 Standard Test Method
for Steady-State Heat Flux Measurements and Thermal Transmission Properties using the
Guarded Hot Plate Apparatus. Results in Table 5 show an increment of the thermal resistance
of the material. The greatest thermal resistance increment was off about 50% compared to a
material with no PMMA microspheres added. This increment in the thermal resistance is the
key result of this research, and will have a direct impact on the sustainability of construction
where this type of materials is used since this material could contribute to energy saving and a
reduction of 'greenhouse' gas emissions as a cost-effective strategy against the global
warming. Table 5. Thermal measurements.
Results thermal conductivity and thermal resistance
PMMA microspheres % 0 10 20 30 40
Apparent thermal conductivity W/K m 0.580 0.522 0.476 0.415 0.365
Thermal resistance K m2/W 0.033 0.037 0.041 0.045 0.047
Expanded uncertainty (k=2) % 5 5 5 5 5
4. Conclusions
The increase of PMMA microspheres transforms the mortar by decreasing its density while
modifying its mechanical properties, workability, and air content. The material is comparable
to lightweight mortars prepared with other traditional materials. The results obtained by
mixing cement with different ratio of aggregate and PMMA microspheres show noticeable
good thermal properties. On the other hand, decreasing compressive strength of the optimal
formulation proposed to agree with ASTM guidelines that unlock a valuable compatibility in
this research. The microspheres also provide a hydrophobic property to the mortar. The
linkage of cement particles to the surface during microspheres synthesis is a significant aspect
of adhesion to the mortar bulk. The microspheres decrease the density by the inclusion of micro-air
bubbles in the mortar bulk. Therefore, the air inclusion reduces significantly the thermal conductivity
increasing thermal insulation. The enhancement of thermal efficiency by the effect of PMMA
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microspheres embedded in this innovative lightweight mortar maintain more stable room
temperatures and save energy.
Acknowledgements
The authors acknowledge to PROINSA for support this work and to Mr. Rene Plaza for
proofreading.
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