ABSTRACT
Portlandite or calcium hydroxide (Ca(OH)2) is considered as a most soluble hydration product, which is formed through the hydration reaction of tricalcium silicate (alite) and dicalcium silicate (belite) with water during curing of concrete. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time of portlandite crystal. First simulations demonstrate far-from-equilibrium dissolution behavior, which encompass 119323 atoms and 26011 initial surface sites. First, the atomistic rate constants of individual Ca dissolution events are computed for three different morphologies of 100 or https://www.w3.org/1998/Math/MathML" display="inline"> 1 ¯ 00 https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_1.tif"/> , 010 or https://www.w3.org/1998/Math/MathML" display="inline"> 0 1 ¯ 0 https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_2.tif"/> , and 001 or https://www.w3.org/1998/Math/MathML" display="inline"> 00 1 ¯ https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_3.tif"/> crystal planes, resulting in a total of 13 different scenarios. We observed that the dissolution process preferentially takes place from edges, sides, and surfaces of 010 or https://www.w3.org/1998/Math/MathML" display="inline"> 0 1 ¯ 0 https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_4.tif"/> crystal plane. Those sites have a significantly higher event probability to be selected, as the event probability is proportional to the atomistic rate constant. On the one hand, the dissolution time of sites follow a liner trend up to 23000, and then the time of site dissolution increases due to the reduction of the surface sites, i.e., the active surface area of the crystal, for the computation of the total rate constant. The steady-state dissolution rates are 0.706 mol/ (s cm2) for 010 or https://www.w3.org/1998/Math/MathML" display="inline"> 0 1 ¯ 0 https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_5.tif"/> , 1.548 × 10−7 mol/ (s cm2) for 001 or https://www.w3.org/1998/Math/MathML" display="inline"> 00 1 ¯ https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_6.tif"/> , and 1.58 × 10−17 mol/ (s cm2) for 100 or https://www.w3.org/1998/Math/MathML" display="inline"> 1 ¯ 00 https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003316404/0adda5cb-1066-4ee6-811c-1171b510a93a/content/inline-math78_7.tif"/> surfaces.
