For longer-lasting, stronger cement, engineers should pay attention to the water found in the smallest pores of the material, researchers from the University of the Basque Country say.
As a basic building material used around the world, cement is subjected to a vast range of conditions. From the coldest places on earth to infrastructures positioned close to heat sources and fires, cement can be subject to extremely low temperatures, or extreme heat, humidity, and pressure.
Cement paste has a large amount of water in its structure, around 30 percent of which is confined in the smallest pores of the cement. These micropores are about one nanometre in size, but the water found inside them contributes to the final properties of the material.
The extreme temperatures that cement finds itself in certain infrastructures, such as oil wells, lead to the water evaporating and freezing, causing massive internal stresses in the cement that can often lead to micro-cracking inside the cement.
In order to improve the performance of cement in these extreme conditions, a Hegoi Manzano, a researcher at the UPV/EHU University of the Basque Country's department of Condensed Matter Physics is working to characterise the physics of this water.
While the researchers are not able to directly study the behaviour of the water located in the nanopores, they utilised 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 how these interactions affect the properties of the cement. Their studies covered temperatures from -170°C to 300°C.
Their simulations showed that at both extremes of temperature, the cement undergoes significant volume changes. At high temperatures, the water evaporates from the pores. The pressure from the material may cause the empty pores to collapse, resulting in micro cracking that undermine the integrity of the material. In serious cases, this could lead to collapse.
At the other extreme, at extremely low temperatures, the water freezes and therefore expands. While the space within the nanopores do not allow the water to form crystalline ice structures, the expansion of water in these circumstances cause stresses in the cement, and also cause micro-cracking.
With the insight from this study, engineers of the future will be able to modify the formulation of the cement that they use in infrastructures that are going to be located in environments with extreme temperatures. By modifying the additives used in cement, oil companies, for example, can engineer cement that is optimised for use in the high pressure, high temperature environments of oil wells.
[Image: FreeImages.com/Ramon Venne]