Using computational modeling techniques, Zhou and Ioannidou calculated how water distributes within a pore and then determined the force that the water exerted on the pore wall. This recent paper drew upon their work to approach these issues. Over the past decade, Ioannidou, along with researchers Roland Pellenq, Franz-Josef Ulm, Sidney Yip, and Emanuela Del Gado of Georgetown University have all worked to advance the modeling of cement at multiple scales. "This means they lost a lot of information on the mesoscale-which is between the atomistic and continuum scales." "In the past, researchers would study the movement of water in pores at either the scale of the atom or on the continuum, or visible, scale," Zhou reports. The second issue is that of multiple scales. Since the pore network is so complex, water becomes unevenly distributed, which makes it difficult to calculate its distribution. To deal with water in cement's messy pore network, Zhou and Katerina Ioannidou, a research scientist with CNRS and the MIT Energy Initiative and a corresponding author of the paper, first wrestled with two issues. But when you have a massive number of grains the water distribution becomes really complicated-the geometry becomes a mess." "In this case, it is easy to measure the water in the pore space and the pressure of this condensation, which we call capillary pressure. "Let's say you only have two grains of calcium silicate hydrate you can imagine there is some water condensation between them," explains Zhou. This poses a problem when trying to study the drying of a pore network. Even ambient humidity can fill these pores." And since they are so small, you don't even need rain to fill them with water. "You have numerous pores of variable sizes that are interconnected," describes Zhou. While this gives cement its strength, the spaces between the cement hydrates create an extensive pore network in the cement paste. "These are the building blocks of cement."ĭuring cement hydration, the cement hydrate's nanograins aggregate with each other, forming a network that glues all constituents together.
student in the Department of Physics and the lead author of the paper. "Cement hydrates are small, on the nanoscale scale," says Tingtao Zhou, a Ph.D. Once the water and the powder mix, they react together and produce compounds known as calcium silicate hydrate (CSH), also known as cement hydrates. This is where the pore network begins to form. From here, this powder is mixed with a certain proportion of water to form cement paste. In a paper published in the Proceedings of the National Academy of Sciences, researchers at the MIT Concrete Sustainability Hub (CSHub), French National Center for Scientific Research (CNRS) and Aix-Marseille University discuss just how the material's porous network absorbs water and propose how drying permanently rearranges the material and leads to potential structural damage.īut to understand how water can change cement's pore structure, one must first look at how it contributes to the formation of this very same structure.Ĭement paste begins as a dry powder composed of carefully blended ingredients including calcium, iron, aluminum, and silicon. And just as the shape of a sponge changes depending on water saturation, so too does that of cement, according to recent work conducted at MIT. A highly porous material, cement tends to absorb water from precipitation and even ambient humidity.
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