دانلود رایگان مقاله مدل سازی رفتار سخت شدن بتن با اندازه گیری غیر مخرب مداوم

Abstract

A recent scientific and industrial interest has been brought to combine multiple supplementary cementitious materials (SCM) in large quantities in concrete binders. The growing use of binary, ternary or quaternary cement binders calls for the development of simple, efficient and accurate experimental and numerical means to characterise and predict the behaviour of such concretes. Continuous non-destructive testing constitutes a major opportunity since it generally consists in simple test setup requiring low human interaction. In this study, isothermal calorimetry and ultrasonic pulse velocity (compression and shear waves) are performed on various concrete compositions with massive incorporation of limestone filler and blast-furnace slag. Indeed, these two additions present interesting complementary effects and positive synergies in terms of fresh properties, mechanical behaviour and durability potential. The setting time, compressive and tensile strength and elastic modulus of these concretes is investigated from the setting time to the hardened state. The existing models linking these properties to the hydration degree, ultrasonic pulse velocity or hydration time are not applicable to these materials, especially during the early age period. New models are proposed and validated for the early age behaviour of concrete with SCMbased binders.

4. Conclusion

From the comparison of destructive measurements and continuous non-destructive measurement of ultrasonic P- and Swave transmission velocity and heat flow of concrete containing various amounts of limestone filler, blast-furnace slag and water/ cement ratio, it is observed that: - Important conceptual adaptations are made to the classical hydration models of concrete mechanical properties. The measurement of fc, ft and Es from the setting time indicates that after the dormant period, all hydration products result in an increase of these mechanical properties. This is in contradiction with the general consensus according to which, before a given degree of hydration, concrete presents no strength or elastic modulus. - Various models are tested for the determination of the evolution of the tensile and compressive strength and of the elastic modulus. It is shown that the effect of w/b ratio and the presence of BFS and/or LMF on these properties can be accurately accounted for by time-based, hydration-based and UPV-based models. This indicates that strength and stiffness of concrete with massive substitution of clinker by limestone filler and/or blast-furnace slag can be modelled with the same equations as Portland cement concrete, only the parameters of these models are modified by the presence of these mineral additions. - Provided that their parameters are accurately determined, these models can be used both for the very early age or hardened concrete behaviour. The UPV-based and time-based models are especially best suited for the early age behaviour, while the hydration-based models can be more accurately used for longer term predictions.