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Cement paste is the glue that holds concrete together and any improvements in material performance will come from its microstructure. For better understanding and predicting its elastic properties and fracture performance, more and more studies are carried out based on micromechanics simulations. However, the predicted results can be hardly verified experimentally due to the technical limitations. This paper presents a procedure for validating micromechanics simulation by making, testing and modelling deformation and fracture of micro cement paste cube (100 um x 100 um x 100 um). The micro scale specimens were produced by a micro dicing saw which is commonly employed in the semiconductor industry and fractured by a commercialcylindrical wedge tip mounted on a nano-indenter equipment. A combination of X-ray computed tomography technique and a discrete lattice fracture model was applied to simulate the deformation and fracture performance of the micro scale specimen under indentation. Mechanical properties of local phases are the input for this fracture simulation, which are taken from the previous study by the authors, wherein a micro scale experiment is developed to calibrate these values. Load-displacement curve and crack pattern from the simulation show a good agreement with those obtained experimentally. The proposed technique forms the basis for experimental validation of simulation tools that are used in a multi-scale framework at every scale.

Masonry is a composite material, whose behavior is strongly influenced by the presence of vertical and horizontal mortar joints, weak elements along which the shear failure usually occurs. The scope of the present work was to investigate factors that could affect the shear-sliding behavior of masonry, by performing numerical simulations of triplet tests conducted on calcium silicate brick masonry specimens with two different bond patterns. In the numerical analyses, a simplified micro-modeling strategy was adopted. A composite interface model was used, including a tension cut-off, a Coulomb friction criterion and a compressive cap. The numerical models were validated through comparisons with results from experimental tests, in terms of failure load, post-peak behavior and specimen deformability. Moreover, factors that could influence the shear-sliding behavior of masonry were analyzed by performing parametric studies. The simplified-micro modeling confirmed to be a very efficient strategy to capture the nonlinear behavior of masonry.

The ability of Superabsorbent Polymers (SAP) to block water flow along cracks in cement-based materials has become an attractive feature of these admixtures. The diminution of fl w rates in such composites are attributed to the capacity of the SAPs to absorb water and swell in the crack, but no evidence exists in literature that indicates one or the other cause. On the other hand, the SAPs present in the bulk matrix might act as distributed sinks through which water is absorbed (water that otherwise would have continued its path into the matrix). In this paper a preliminary effort is made to numerically model the effect of SAPs on the water absorption by mortar. A lattice-type model is proposed to predict both the bulk water absorption and the resulting penetration depth of water into the cementitious matrix. The results of the simulations point out the mechanisms of water absorption in mortar containing SAPs.

The mechanical response of concrete is complex and as other composite materials, multiscale modelling has the potential for modeling its macroscopic behavior. This paper presents an upscaling methodology for the model-ling of the concrete mechanical properties. The suggested formulation starts from a known chemical and mechanical set of parameters of the cement paste, which are used to evaluate the mechanical properties of the LDPM (Lattice Discrete Particle Model) concrete mechanical parameters. The parameters are divided to groups, which are related to different damage modes such as: pore collapse and material compaction, cohesive behavior, and shear behavior. For each group of parameters, a set of microscopic simulations are performed to complete the up-scaling methodology.

At the previous EURO-C conference, a guideline for nonlinear finite analysis and safety assessment of concrete structures was presented. This guideline is a results of a cooperation between the Delft University of Technology, the University of Parma and the Dutch Ministry of Infrastructure and the Environment. The nonlinear finite element results of a workshop around shear failure, held in Rotterdam in 2007, was the starting point for the development of a guideline for nonlinear finite element analysis. The scatter of the results presented in Rotterdam was considered as too large; knowledge of nonlinear finite element analysis of concrete structures should be controlled better in order to make nonlinear finite element analysis an accepted method. In 2012 the first version of the guideline that focussed on girder structures was published.In 2014, at the concrete structures laboratory of the Delft University of Technology, four almost similar pre-stressed girders were tested till the ultimate limit load level. This was considered as an opportunity to organise a contest to predict this ultimate load level at failure. The participants were asked to make use of the guideline. A workshop at the University of Parma gave the teams the opportunity to pitch their predictions. This paper presents the following topics: an overview of the content of the guideline, the gain of a controlled blind prediction contest and the main outcomes of the contest in Parma.

Due to time constraints on structural design processes, modelling and computational complexityis often a key concern in limit state analysis of reinforced concrete (RC) structures, causing practitioners tochoose efficient but inaccurate methods of analysis over more advanced ones. Recently, a framework usingconvex optimization for elasto-plastic, geometrically linear analysis of RC walls was proposed, enabling analysisof models with more than 10,000 finite elements within minutes on a standard PC. In order to improve theapplicability and relevance of the framework as a design tool, this paper proposes an extension that enablesthe determination of the critical buckling load. Based on the nonlinear solution obtained from the elasto-plasticoptimization problem, the cracked tangent stiffness of the RC sections is determined, and a linearized bucklingproblem is posed and solved as a linear eigenvalue problem. This allows the actual critical buckling load tobe determined by solving a sequence of optimization and eigenvalue problems. The accuracy of the proposedmethod is assessed, and its applicability to practical design scenarios is demonstrated by an analysis of an RCwall with a door hole, showing an average solution time of approximately 30 seconds per load step.

The critical parts of structures are typically discontinuity regions, where abrupt changes in geometry occur or large concentrated loads are applied. In engineering practice the verification of the ultimate limit stage of such discontinuity regions employs strut-and-tie models or stress fields based on the lower bound theorem of plasticity theory. These models are mechanically consistent but they can be prohibitively time consuming and are not directly applicable for serviceability limit state analysis as they do not consider strain compatibility. To overcome these limitations the Compatible Stress Field Method (CSFM) was developed for the design and assessment of discontinuity regions in concrete structures. The CSFM consists of a simplified nonlinear finite element-based stress field analysis procedure.Considering compatibility and equilibrium conditions at stressfree cracks, uniaxial constitutive laws as provided in concrete standards are used. While the concrete tensile strength neglected in terms of strength, the CSFM accounts for tension stiffening to obtain realistic predictions of deflections and crack widths, and cover the deformation capacity aspects. The effective compressive strength of concrete is automatically evaluated based on the transverse strain state. The present work validates the ability of the CSFM to reproduce the observed behaviour of experimentally tested frame corners with an opening moment. A quantitative comparison between the outcomes from the numerical analyses and reported experimental results proves the CSFM to be a reliable tool for assessing the structural behaviour of discontinuity regions. In addition, a numerical study is conducted to investigate the sensitivity of the CSFM to several input and model parameters., Computational Modelling of Concrete and Concrete Structures, ISBN:978-1-003-31640-4, ISBN:978-1-032-32724-2