Study on the phase change cement based materials Min Li Southeast University, China Southeast University th International Conference on Power Science and Engineering

Content  Introduction  Experimental  Results and Discussion  Conclusions Contents th International Conference on Power Science and Engineering

Introduction As a kind of phase change material (PCM), the PCM microcapsule was used in many fields th 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, [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, [3]]F.Kuznik,J. Virgone. “Experimental assessment of a phase change material for wall building use,”Applied Energy, vol.86, pp. 2038– th International Conference on Power Science and Engineering

Introduction th 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, [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 th 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 th International Conference on Power Science and Engineering

Results and Discussion Compressive strength th International Conference on Power Science and Engineering 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 th 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 7d

Results and Discussion th 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. 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 th 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 th 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 th 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 th International Conference on Power Science and Engineering The strength of the phase change cement based material 1.In the elevated temperature phase, t he temperature and t he 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℃.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 temperature To some extent, this can solve the cracking phenomenon of massive concrete in the process of hydration.

Conclusions  The 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 th 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 attention th International Conference on Power Science and Engineering