Existing research on the mechanisms affecting the strength of cementitious materials primarily focuses on the composition and properties of cement hydration products, often overlooking the interactions between different products. This study presents a systematic experimental and theoretical investigation into the mechanical properties of cementitious materials, emphasizing the interactions between crystal and gel products driven by crystallization pressure. A new mechanism based on crystallization pressure is proposed to explain the impact of the interactions between hydration products on the strengths of cementitious materials. Experiments were conducted by immersing specimens in solutions with tailored ion concentrations (including water, isopropyl alcohol, ethanol, and solutions of calcium hydroxide and calcium acetate) to vary the crystallization pressure. The flexural and compressive strengths of these specimens were then tested. An analytical model was developed and validated against the experimental data. Both experimental and calculated results demonstrate a negative correlation between crystallization pressure and strength. Specimens subjected to crystallization pressures of 101.7 MPa and 147.8 MPa showed reductions in flexural strength of 19.34 % and 30.65 %, respectively, and decreases in compressive strength of 10.00 % and 14.41 %, compared to control specimens with zero crystallization pressure. These results suggest that ion concentrations in the pore solution alter the crystallization pressure, which in turn affects the interactions between crystal and gel products and strength of cementitious materials. This study provides insights into the mechanisms of strength degradation due to moisture in porous materials.

The Grid computing vision promises to provide the needed platform for a new and more demanding range of applications. For this promise to become true, a number of hurdles, including the design and deployment of adequate resource management and information services, need to be overcome. In this context, understanding the characteristics of real Grid workloads is a crucial step for improving the quality of existing Grid services, and in guiding the design of new solutions. Towards this goal, in this work we present the characteristics of traces of four real Grid environments, namely LCG, Grid3, and TeraGrid, which are among the largest production Grids currently deployed, and the DAS, which is a research Grid. We focus our analysis on virtual organizations, on users, and on individual jobs characteristics. We further attempt to quantify the evolution and the performance of the Grid systems from which our traces originate. Finally, given the scarcity of the information available for analysis purposes, we discuss the requirements of a new format for Grid traces, and we propose the establishment of a virtual center for workload-based Grid benchmarking data: The Grid Workloads Archive.