Study on the phase change cement based materials Min Li Southeast University, China 2015.12.14...

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


Introduction

As a kind of phase change material (PCM) , the PCM microcapsule was used in many fields


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.


Introduction


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


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



Compressive strength


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.


The reason of the decrease of the compressive strength


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


modified unmodified

7d



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


modified unmodified

35.6MPa

31.8MPa


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


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


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


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.


The cement hydration curve



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


The cement hydration curve



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.


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


Study on the phase change cement based materials Min Li Southeast University, China 2015.12.14...

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