<meta name="title" content="Capillary Porosity Depercolation/Repercolation in Hydrating Cement Pastes via Low Temperature Calorimetry Measurements and CEMHYD3D Modeling"> <body> <b>Next:</b> <a href="node2.htm">Experimental Procedure</a> <b>Up: </b><a href="index.html">Main</a> <b>Previous: </b> <a href="index.html">Main</a> <hr> <h2>I. Introduction</h2> <p>Many years ago, Powers, Copeland, and Mann first noted that during the hydration of portland cement, the capillary porosity could become discontinuous.<sup><a href="node13.htm#1.">1</a></sup> This depercolation has many implications for the transport properties and durability of cement-based materials. For example, the permeability of a cement paste with a depercolated pore structure can be more than a factor of 1000 less than an equivalent age [higher water-to-cement mass ratio (<i>w/c</i>)] paste with a pore structure that remains percolated. <sup><a href="node13.htm#2.">2</a></sup> The stability of the depercolated pore structure is of equal importance to its initial depercolation. Powers and his colleagues indicated that the simple slow drying of a cement paste to an equilibrium relative humidity of 79 % could increase its permeability by a factor of about 70.2 While x-ray computed microtomography is now approaching spatial resolutions of better than 1 µm, by which the three-dimensional percolation of the capillary pore structure in hydrating cement paste can be directly observed,<sup><a href="node13.htm#3.">3</a></sup> conventionally, percolation/depercolation has been inferred indirectly from measurements of chemical shrinkage<sup><a href="node13.htm#4.">4</a>, <a href="node13.htm#5.">5</a></sup> or low temperature calorimetry (LTC) scans.<sup><a href="node13.htm#6.">6</a>, <a href="node13.htm#7.">7</a></sup> In addition, capillary porosity percolation has been predicted using the National Institute of Standards and Technology (NIST) CEMHYD3D hydration and microstructure development computer model.<sup><a href="node13.htm#8.">8</a>, <a href="node13.htm#9.">9</a></sup> In this paper, capillary porosity depercolation/repercolation in hydrating cement paste is investigated as a function of <i>w/c</i> (0.25 − 0.45), curing temperature (20 ºC or 40 ºC), and saturation (saturated or sealed curing), from both an experimental and a computer modeling point of view. </p> <hr> <b>Next:</b> <a href="node2.htm">Experimental Procedure</a> <b>Up: </b><a href="index.html">Main</a> <b>Previous: </b> <a href="index.html">Main</a> </body> </html>