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Study on the phase change cement based materials
Min Li
Southeast University, China 2015.12.14
Southeast University
2015 4th International Conference on Power Science and Engineering
Content Introduction
Experimental
Results and Discussion
Conclusions
Contents
2015 4th International Conference on Power Science and Engineering
Introduction
As a kind of phase change material (PCM) , the PCM microcapsule was used in many fields
2015 4th International Conference on Power Science and Engineering
Introduction
PCMs used in building can improve thermal comfort of indoor environment and conserve energy.
During daytime PCM can absorb heat through the melting process. During night PCM can release heat through the solidification process
[1]S. H. Lee, S. J. Yoon, Y. G. Kim, Y. C. Choi, J. H. Kim, and J. G. Lee, “Development of building materials by using micro-encapsulated phase change material,”Korean Journal of Chemical Engineering, vol. 24, issue 2, pp. 332–335, 2007.[2]D.Rozanna,A. Salmiah,T. G. Chuah,R. Medyan,SC Thomas,M Saari. “A study on thermal characteristics of phase changematerial (PCM) in gypsum board for building application,”Journal of Oil Palm Research, vol.17. pp. 41–6, 2005.[3]]F.Kuznik,J. Virgone. “Experimental assessment of a phase change material for wall building use,”Applied Energy, vol.86, pp. 2038–46. 2009.
2015 4th International Conference on Power Science and Engineering
Introduction
2015 4th International Conference on Power Science and Engineering
Hydrophilic property is an important index of the phase change material.
Good hydrophilic phase change material may be mixed with mortar and mud in any proportion to improve the use efficiency of energy.[4-5]
[4]N Zhang, XM Fang, ZG. Zhang. “Study on the thermal properties of cement boards based on composite phase change material,”New Chemical Materials, vol.40, issue 3, pp.41-42, 2012.[5]X.Liu, HY. Liu, SJ. Wang. “Encapsulation and thermal performance of paraffinshape-stabilized phase change materials,” Fine Chemicals, vol.23, issue 1, pp.8-11, 2006.
mixture
Stirred at 50 ℃water bath for 30min
Added in 20 ml water
Experiment design
Preparation of the modified phase change microcapsules
Experimental
0.05g modifier
5g PCM micro-capsules
Stirred for 1h and then filtrated, dried and grounded
Added in 80 ml water
Modified phase change microcapsules
2015 4th International Conference on Power Science and Engineering
Phase change cement based material
Modified/unmodified PCM microcapsules
cement
cement hydration curve
Mechanical properties
Micro-morphology analysis
Experiment design
0wt%, 3wt%, 5wt%, 8wt%, 10wt% of PCM microcapsules (by the weight of cement) were put into the cement respectively.
The ratio of water to solid was 0.4
Experimental
2015 4th International Conference on Power Science and Engineering
Results and Discussion
Compressive strength
2015 4th International Conference on Power Science and Engineering
0 2 4 6 8 1014
16
18
20
22
24
26
28
30
32
34
36
com
pre
ssiv
e st
ren
gth
/MP
a
the content of PCM microcapsules/%
modified unmodified
The strength of the phase change cement based materials
7d
The compressive strength of the phase change cement based material dropped gradually with an increase of the content of the PCM microcapsules.
Results and Discussion
The reason of the decrease of the compressive strength
2015 4th International Conference on Power Science and Engineering
I. The existence of the PCM microcapsules in the cement paste caused the emergence of the interface defects which leads to the drop of the compressive strength
II. The more the content of the PCM microcapsules, the more the compressive strength of the cement paste drops
The appropriate content should be considered when the phase change cement based material is applied to energy conservation. The strength of the phase change
cement based material
0 2 4 6 8 1014
16
18
20
22
24
26
28
30
32
34
36
com
pre
ssiv
e st
ren
gth
/MP
a
the content of PCM microcapsules/%
modified unmodified
7d
Results and Discussion
2015 4th International Conference on Power Science and Engineering
Compressive strength
28d
The strength of the phase change cement based material
Decreasing degree of the cement paste with unmodified PCM microcapsules was larger than that of the cement paste with modified PCM microcapsules.
This was due to the difference of the hydrophilicity between the two kinds of phase change cement blocks.
The good hydrophilicity is beneficial to form good dispersity and good interface between the cement paste and the PCM microcapsules.
0 2 4 6 8 10
25
30
35
40
45
50
com
pres
sive
str
engt
h/M
Pa
the content of PCM microcapsules/%
modified unmodified
35.6MPa
31.8MPa
Results and Discussion
a) b) c)
The SEM morphology of the cement paste; (a) without PCM microcapsules (b) with 5% of unmodified PCM microcapsules. (c) with 5% of modified PCM microcapsules
Morphology of the phase change cement
2015 4th International Conference on Power Science and Engineering
1.The microstructure of the cement paste was very compact. The interface between cement paste and the PCM microcapsules was good.
2.The dense structure of the cement paste was decreased after PCM microcapsules were mixed into. Therefore, the compressive strength of the phase change cemented material was lower than that of the cement
Results and Discussion
a) b) c)
The SEM morphology of the cement paste; (a) without PCM microcapsules (b) with 5% of unmodified PCM microcapsules. (c) with 5% of modified PCM microcapsules
Morphology of the phase change cement
2015 4th International Conference on Power Science and Engineering
The modified PCM microcapsules dispersed better than the unmodified PCM microcapsules in the cement paste.
The reason is that the hydrophilicity of the unmodified PCM microcapsules is poor and inclined to agglomeration.
Results and Discussion
The cement hydration curve
2015 4th International Conference on Power Science and Engineering
The strength of the phase change cement based material
At around 28 , the ℃phase change occurred when the PCM microcapsules changed the form from the solid state to the liquid state.
The latent heat make the form being changed and can not raise the temperature.
The hydration heat is released and the temperature began to rise from the beginning of the cement hardening for both the cement and the phase change cement.
The curve of the phase change cement has a temperature platform at around 28 .℃
The platform proved the heat storage effect of the phase change cement
Results and Discussion
The cement hydration curve
2015 4th International Conference on Power Science and Engineering
The strength of the phase change cement based material
1.In the elevated temperature phase, the temperature and the peak temperature of the phase change cement is lower and the peak is delayed. 2.The time arriving the peak temperature is delayed for about 60min for phase change cement
5℃. The reason: some hydration heat was used to change the phase from solid to liquid.
Remarkable function of heat storage and decrease the peak temperatureTo some extent, this can solve the cracking phenomenon of massive concrete in the process of hydration.
ConclusionsThe incorporation of microcapsules had a negative impact on the strength of the cement based materials. The compressive strength of the phase change cement based material dropped gradually with an increase of the content of the PCM microcapsules.
.
The peak temperature of the phase change cement is lower than that of the cement for about 5 . Moreover, the time arriving the ℃peak temperature is delayed for about 60min for phase change cement.
The decreasing degree of the cement paste with unmodified PCM microcapsules was larger than that of the cement paste with modified PCM microcapsules.
2015 4th International Conference on Power Science and Engineering
The phase change cement based material that we prepared in this paper had remarkable function of heat storage and decrease the peak temperature.
Thanks for your attentionThanks for your attention
2015 4th International Conference on Power Science and Engineering