Pr Przemek Spiesz

Development of an eco-friendly Ultra-High Performance Concrete (UHPC) with efficient cement and mineral admixtures uses

This paper addresses the development of an eco-friendly Ultra-High Performance Concrete (UHPC) with efficient cement and mineral admixtures uses are investigated. The modified Andreasen & Andersen particle packing model is utilized to achieve a densely compacted cementitious matrix. Fly ash (FA), ground granulated blast-furnace slag (GGBS) and limestone powder (LP) are used to replace cement, and their effects on the properties of the designed UHPC are analyzed. The results show that the influence of FA, GGBS or LP on the early hydration kinetics of the UHPC is very similar during the initial five days, while the hydration rate of the blends with GGBS is mostly accelerated afterwards. Moreover, the mechanical properties of the mixture with GGBS are superior, compared to that with FA or LP at both 28 and 91 days. Due to the very low water amount and relatively large superplasticizer dosage in UHPC, the pozzolanic reaction of FA is significantly retarded. Additionally, the calculations of the embedded CO2 emission demonstrate that the cement and mineral admixtures are efficiently used in the developed UHPC, which reduce its environmental impact compared to other UHPCs found in the literature.

Design of ultra-lightweight concrete: towards monolithic concrete structures

This study addresses the development of ultra-lightweight concrete. A moderate strength and an excellent thermal conductivity of the lightweight concrete are set as the design targets. The designed lightweight aggregates concrete is targeted to be used in monolithic concrete facade structure, performing as both load bearing element and thermal insulator. The developed lightweight concrete shows excellent thermal properties, with a low thermal conductivity of about 0.12 W/(m·K); and moderate mechanical properties, with 28-day compressive strengths of about 10-12 N/mm 2. This combination of values exceeds, to the researchers’ knowledge, the performance of all other lightweight building materials. Furthermore, the developed lightweight concrete possesses excellent durability properties.

Study on the chloride diffusion coefficient in concrete obtained in electrically accelerated tests

This study presents an analysis of the chloride diffusion coefficient (D RCM ), obtained in electrically accelerated chloride migration tests. As demonstrated here, the obtained chloride diffusion coefficient does not represent the apparent one, as it is independent of chloride binding. This is accounted for the fact that the D RCM is calculated based on the average chloride penetration depth measured in concrete and binding at the position of the chloride penetration front is very limited. It is also demonstrated in this study that the apparent chloride diffusion coefficient in concrete is not constant within the sample, because it depends upon the local chloride concentrations.

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.

Electrically accelerated transport of chlorides in concrete considering non-linear chloride binding in non-equilibrium conditions

The Rapid Chloride Migration test (NT Build 492) is commonly used in order to determine the chloride diffusion (migration) coefficient in concrete. This coefficient can then be used as the input value for service life design models for concrete structures in marine environment. However, the theoretical background of this test is still raising discussions as the equations describing the transport process of chlorides cannot predict correctly the chloride concentration profiles in concrete.