In this paper we describe the OpenGeoSys (OGS) project, which is a scientific open source initiative for numerical simulation of thermo-hydro-mechanical-chemical (THMC) processes in porous media. The basic concept is to provide a flexible numerical framework (using primarily the Finite Element Method (FEM)) for solving multi-field problems in porous and fractured media for applications in geoscience and hydrology. To this purpose OGS is based on an object-oriented FEM concept including a broad spectrum of interfaces for pre-and post-processing. The OGS idea has been in development since the mid eighties. We provide a short historical note about the continuous process of concept and software development having evolved through Fortran, C, and C++ implementations. The idea behind OGS is to provide an open platform to the community, outfitted with professional software engineering tools such as platform-independent compiling and automated benchmarking. A comprehensive benchmarking book has been prepared for publication. Benchmarking has been proven to be a valuable tool for cooperation between different developer teams, e.g. for code comparison and validation purposes (DEVOVALEX and CO2 BENCH projects). On one hand, object-orientation (OO) provides a suitable framework for distributed code development; however the parallelization of OO codes still lacks efficiency. High-performance-computin (HPC) efficiency of OO codes is subject to future research.

Capillary absorption capacity has an important influence on the durability of concrete and is closely related to pore structure. In this study, the pore structure and capillary water absorption of samples were determined by low-field nuclear magnetic resonance spectroscopy and the gravimetric method, respectively. The test results show that the most probable pore diameter and equivalent pore diameter of cement-based materials increase with increasing water to cement ratio (w/c) and fly ash (FA) content and decrease with increasing curing age and cement to sand ratio (c/s). The porosity of cement-based materials increases with increasing w/c and c/s, decreases with increasing curing age, and first decreases and then increases with increasing FA content. The curves for the amount of capillary water absorption per unit area in specimens with the square root of time for cement-based material under different influence factors are similar and show obvious linear and stable stages.The capillary absorption coefficient is nearly linearly related to w/c or c/s, and nonlinearly related to curing age or FA content, observation that are well correlated with the porosity and square root of the equivalent pore radius. A modified model is proposed for the capillary absorption coefficient with consideration of the pore structure, and the theoretical results of the model are in good agreement with the test results. K E Y W O R D Scapillary absorption coefficient, cement-based materials, equivalent pore radius, low-field nuclear magnetic resonance spectroscopy, modified model, porosity Discussion on this paper must be submitted within two months of the print publication. The discussion will then be published in print, along with the authors' closure, if any, approximately nine months after the print publication.

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