Disorder, pre-stress and non-affinity in polymer 8-chain models

To assess the role of single-chain elasticity, non-affine strain fields and pre-stressed reference states we present and discuss the results of numerical and analytical analyses of modified 8-chain Arruda-Boyce model for cross-linked polymer networks. This class of models has proved highly successful in modeling the finite-strain response of flexible rubbers. We extend it to include the effects of spatial disorder and the associated non-affinity, and use it to assess the validity of replacing the constituent chain's nonlinear elastic response with equivalent linear, Hookean springs. Surprisingly, we find that even in the regime of linear response, the full polymer model gives very different results from its linearized counterpart, even though none of the chains are stretched beyond their linear regime. We demonstrate that this effect is due to the fact that the polymer models are under considerable pre-stress in their ground state. We show that pre-stress strongly suppresses non-affinity in these unit cell models, resulting in a marked stiffening of the bulk response. The effects of pre-stress we discuss may explain why fully affine mechanical models, in many cases, predict the bulk mechanical response of disordered stiff polymer networks so well.Comment: 29 pages, 7 figures. Submitted to J. Mech. Phys. Solid

Durability of ultra-high performance concrete – Experiences from a real-scale application

Ultra-High Strength Concrete or better Ultra-High Performance Concrete (UHPC) is finding increasingly more applications in real construction projects. However, mostly the focus is on the outstanding mechanical properties of this special concrete. But strength is just one side of this multifunctional material. Apart from that, it also comes along with distinguished durability properties which make it attractive to be used in construction projects despite a very high cost price. This paper refers to a real-scale application of UHPC used for the production of two bridge decks. The UHPC was produced in a ready-mixed concrete plant and delivered by concrete mixing trucks to a pre-cast plant. During the production, samples were made and later analysed regarding theirmechanical properties and durability performance. This research is focusing on the latter and shows by means of porosity measurements, freeze-thaw resistance tests, carbonation tests and chloride diffusion and migration tests, that UHPC is a very dense and durable material that will allow for much longer service life periods and low maintenance and repair costs compared to structures made from conventional concrete

Structural ultra-lightweight concrete – from laboratory research to field trials

This article presents the laboratory development and subsequent field trials of a novel structural ultra-lightweight concrete. The concrete is developed aiming at the application in monolithic buildings (i.e. no insulation layer required), which would facilitate the construction and recycling processes, as well as provide new opportunities to architects and structural engineers. The development of the ultra-lightweight concrete presented in this study includes the optimization of its composition (ultra-lightweight aggregates, binders, admixtures) and is targeted on the concrete properties such as the compressive strength, density and thermal conductivity. In order to reduce the risk of an excessive overheating of concrete during its early hydration process caused by its self-insulating properties, the binder composition and amount was further investigated and optimized. Finally, a material of an ultra-low density (< 800 kg/m3), ultra-low thermal conductivity (as low as 0.14 W/(m·K)) and a compressive strength of 10 MPa was developed. Subsequently, several batches of 2 m3 of concrete were produced in a ready-mix concrete plant and a L-shaped test-wall was cast. The temperature development as well as hardened concrete properties were monitored. The field tests show that, although there still are some issues to overcome (e.g. workability), the developed material has a very good potential to enter the concrete market and find new applications

Determination of the chloride diffusion coefficient in mortars with supplementary cementitious materials

The Rapid Chloride Migration (RCM) test, described in the guideline NT Build 492, is one of the most commonly applied accelerated test methods in which chlorides penetrate the concrete at high rates due to the applied electrical field. The output result of the test is the chloride diffusion coefficient DRCM. Literature shows that the RCM test development and experience concerns only ordinary Portland cement. Therefore, a validation of this test method is needed also for other types of binders. This study analyzes the application of the RCM test on mortars prepared with different binder blends: ordinary Portland cement (OPC), ground granulated blast – furnace slag (GGBS), fly ash (FA) and silica fume (SF). The diffusion coefficients are obtained by two approaches: the basic RCM test model and the extended model which considers non-linear chloride binding in non-equilibrium. The analyses presented in this study show that the RCM test can be used for the determination of chloride diffusion coefficient in mortars with supplementary cementitious materials, and the accuracy of AgNO3 colourimetric method is sufficient for the determination of the chloride penetration front in these mortars

Determination of the chloride diffusion coefficient in mortars with supplementary cementitious materials

The Rapid Chloride Migration (RCM) test, described in the guideline NT Build 492, is one of the most commonly applied accelerated test methods in which chlorides penetrate the concrete at high rates due to the applied electrical field. The output result of the test is the chloride diffusion coefficient DRCM. Literature shows that the RCM test development and experience concerns only ordinary Portland cement. Therefore, a validation of this test method is needed also for other types of binders. This study analyzes the application of the RCM test on mortars prepared with different binder blends: ordinary Portland cement (OPC), ground granulated blast – furnace slag (GGBS), fly ash (FA) and silica fume (SF). The diffusion coefficients are obtained by two approaches: the basic RCM test model and the extended model which considers non-linear chloride binding in non-equilibrium. The analyses presented in this study show that the RCM test can be used for the determination of chloride diffusion coefficient in mortars with supplementary cementitious materials, and the accuracy of AgNO3 colourimetric method is sufficient for the determination of the chloride penetration front in these mortars