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Cement design should take into account the water confined in the smallest pores

Date:
August 9, 2016
Source:
University of the Basque Country
Summary:
Cement paste has a large amount of water in its structure, and much of it is confined in the smallest pores of the cement which are about one manometer in size. The extreme temperatures in which cement finds itself in certain infrastructures, such as oil wells, lead to changes in water state, which in turn cause internal stresses in the cement. Scientists have characterized the physics of this water in order to contribute towards better cement design.
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At low temperatures, from inside towards the outside, exerted by the water molecules, and at high temperatures from outside towards the inside caused by the absence of the molecules.
Credit: Hegoi Manzano - UPV/EHU

As it is a basic building material used across the world, cement is subjected to a vast range of conditions, both physiological and meteorological, no matter whether they are caused by extreme temperatures and humidity, pressure, etc. It is possible to find conditions ranging from -80 ºC, in places such as the scientific bases in the Antarctic, to several hundreds of degrees in infrastructures close to heat sources or in the case of fires, for example.

These variations in humidity and temperature are translated into physical processes involving evaporation or freezing of the water contained in the cement paste, which often cause stresses and even micro-cracking inside the cement. Characterizing the response to these phenomena affecting the confined water in the smallest pores of the cement "is hugely important as a large proportion of the water, about 30 %, is located in these small spaces, so to a great extent it contributes towards the final properties of the material," explained Hegoi Manzano, a researcher in the UPV/EHU's department of Condensed Matter Physics, and author of the study in collaboration with a research group of the University of Tohoku in Japan.

Given the complexity involved in studying the behaviour of the water located in such tiny pores of approximately 1 nanometre in size by means of experimental channels, the researchers resorted to molecular simulation methods that "imitate" the interactions among the atoms that make up the cement in order to determine how they behave as a whole and the properties that these interactions are translated into," he explained. The temperature range they studied was from -170 ºC to 300 ºC.

Stresses at both extremes

In the results obtained in the simulations they were able to observe that at both extremes of temperature "significant volume changes owing to water physics take place. Through totally opposite effects we arrived at the same consequences," he remarked. At high temperatures the water evaporates and disappears from the pores. In these conditions the pressure brought to bear by the material itself may cause the empty pores to collapse and micro cracking to be created which, in particularly serious cases, could cause the material to collapse.

At the other extreme, at extremely low temperatures, what happens is that the water freezes and therefore expands. "In these conditions it should be highlighted that the frozen water does not manage to form ice because of the small space in which it is located; the water molecules cannot order themselves to form a crystalline ice structure," he stressed. But the expansion it undergoes is enough to create stresses in the cement and likewise cause micro cracking.

The information extracted from this study can be used to "modify the formulation of the cement for infrastructures that are going to be located in environments with extreme temperatures. Let us take for example an oil company: knowing the stresses and forces that may be created in the cement, they would have the chance to change certain design factors, such as the additives added to the cement to compensate for the expansion or collapsing of the material in oil wells. That would be the ideal application of the work," concluded Manzano.


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Materials provided by University of the Basque Country. Note: Content may be edited for style and length.


Journal Reference:

  1. Patrick A. Bonnaud, Hegoi Manzano, Ryuji Miura, Ai Suzuki, Naoto Miyamoto, Nozomu Hatakeyama, Akira Miyamoto. Temperature Dependence of Nanoconfined Water Properties: Application to Cementitious Materials. The Journal of Physical Chemistry C, 2016; 120 (21): 11465 DOI: 10.1021/acs.jpcc.6b00944

Cite This Page:

University of the Basque Country. "Cement design should take into account the water confined in the smallest pores." ScienceDaily. ScienceDaily, 9 August 2016. <www.sciencedaily.com/releases/2016/08/160809122129.htm>.
University of the Basque Country. (2016, August 9). Cement design should take into account the water confined in the smallest pores. ScienceDaily. Retrieved May 29, 2017 from www.sciencedaily.com/releases/2016/08/160809122129.htm
University of the Basque Country. "Cement design should take into account the water confined in the smallest pores." ScienceDaily. www.sciencedaily.com/releases/2016/08/160809122129.htm (accessed May 29, 2017).

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