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

Effects of nano-silica (NS) additions on durability of SCC mixtures

In this study, three different types of nano-silica were applied in self-compacting concrete (SCC), one produced by the controlled dissolution of the olivine mineral and two having similar particle size distributions (PSD), but produced through two different processes: fumed powder nano-silica and precipitated silica in colloidal suspension. The influence of the nano-silica on SCC was investigated with respect to the properties of the concrete in fresh (workability) and hardened state (durability properties). Additionally, the densification of the microstructure of the hardened concrete was analyzed by SEM and EDS techniques. The obtained results demonstrate that an efficient use of nano-silica in SCC can improve its durability properties. Considering the reactivity of the different nano-silica studied, the colloidal type showed a higher reactivity at early age, which influenced the final SCC properties