Heterogeneities in concrete manifest at various scales, from aggregates and its interfacial transition zone (ITZ) at macroscale to various hydration products at the microscale. On the application of load, cracks initiate from ITZ and propagate to the bulk cement paste (BCP), leading to the nonlinear stress-strain behaviour of concrete. This paper proposes a novel multiscale analytical approach to simulate the uniaxial stress-strain behaviour of concrete. Initially, the heterogeneous microstructure of ITZ and BCP is simulated using a cement hydration microstructure model (μic). Considering the gradient of phases in ITZ, aggregate gradation and aggregate volume fraction, stresses in the different phases in the ITZ and BCP are calculated by step-wise stress downscaling using continuum micromechanics. The initiation and propagation of cracks in the ITZ and BCP are modelled using damage mechanics. The efficacy of the current analytical approach is validated by comparing with the experimentally observed stress-strain curve. The current model investigates the relation between the macroscopic strain increment with the distribution of strain and the progression of damage in different ITZ layers. Through a parametric study, the influence of w/c ratio (0.30–0.50), aggregate volume fraction (30% and 50%), and aggregate size distribution on the stress-strain behaviour of concrete are discussed.@en

The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R³ (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R³ heat release test. The effect of the drying step was evaluated to define the R³ bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements.

@en

This paper presents a new approach to model the creep behavior of cement paste at early ages. The creep behavior is simulated by applying a time-varying generalized Maxwell model on the individual elements of a finite-element mesh of a simulated three-dimensional microstructure and compared with results in the literature. All mechanical properties of the constituent phases are taken from literature and Maxwell chain parameters are obtained by fitting the intrinsic creep of calcium silicate hydrate (C-S-H). A reasonable agreement between the simulations and the experimental results are obtained by assuming a constant C-S-H density of 2.0  g/cm3This paper presents a new approach to model the creep behavior of cement paste at early ages. The creep behavior is simulated by applying a time-varying generalized Maxwell model on the individual elements of a finite-element mesh of a simulated three-dimensional microstructure and compared with results in the literature. All mechanical properties of the constituent phases are taken from literature and Maxwell chain parameters are obtained by fitting the intrinsic creep of calcium silicate hydrate (C-S-H). A reasonable agreement between the simulations and the experimental results are obtained by assuming a constant C-S-H density of 2.0  g/cm3 . It was found that better agreements could be obtained at low degree of hydrations, by assuming a loosely packed C-S-H growing in the microstructure. It was also found that the short-term creep characteristics of C-S-H from nanoindentation can be used to reproduce macroscopic creep at least over a few days. The results show how numerical models can be used to upscale phase characteristics to macroscopic properties of composites. @en