UPGRADING THE CONCEPT OF UHPFRC FOR HIGH DURABILITY IN THE CRACKED STATE: THE CONCEPT OF ULTRA HIGH DURABILITY CONCRETE (UHDC) IN THE APPROACH OF THE H2020 PROJECT RESHEALIENCE

Current solutions for new concrete constructions in Extremely Aggressive Exposures, as recommended and enforced by design codes, are not taking into account new cement-based construction materials, such as Ultra High Performance Fibre Reinforced Concrete, neither new constituents specifically conceived to improve the concrete durability, because of the lack of standards and technical awareness by most designers and contractors. The H2020 ReSHEALience project will upgrade to the concept of Ultra High Durability Concrete (UHDC), combining nano-scale constituents (nano-cellulose, alumina nanofibers) and self-healing promoters (crystalline admixtures). The paper will present the approach pursued in the project together with a synopsis of the results of ongoing research

Crack sealing capacity in chloride-rich environments of mortars containing different cement substitutes and crystalline admixtures

This paper presents the results of a preliminary study aimed at assessing the crack sealing capacity in chloride environments of different concrete mixtures, incorporating supplementary cementitious materials as well as self-healing enhancing crystalline admixtures. For each addition, also including pulverized fuel ash and silica fume, different contents were taken into consideration. Cylinder specimens were pre-cracked in splitting up to three different crack-opening ranges, simulating different service conditions, and then exposed to different conditioning environments, also containing different concentrations of sodium chloride and including both permanent immersion and wet/dry cycles. Healing conditioning was performed up to three months and crack sealing was visually inspected and quantified via image analysis procedures, monthly. Optimum dosages of each cement substitute/addition were quantified, also considering, besides the healing capacity, also the fresh state performance and compressive strength development. The good performance of mixes with crystalline admixture even under open-air exposure, as well as of other investigated mixes with reference to crack openings and exposure conditions, paves the way to revise the significance of a serviceability design parameter such as the maximum allowable crack width as a function of the exposure with the concept of a sealable crack width

Concept of ultra high durability concrete for improved durability in chemical environments: Preliminary results

Trabajo presentado a la Conference on Durable Concrete for Infrastructure under Severe Conditions, celebrada en Ghent (Belgium) del 10 al 11 de septiembre de 2019.The aim of this work is to analyze the enhanced durability performance of an Ultra High Durability Concrete (UHDC) exposed to chemical attack (XA exposure conditions), with reference to an intended application into infrastructures serving geothermal plants. This study is based on a reference Ultra High Performance Concrete (UHPC) with steel fibers and crystalline admixtures (reference mix) and other two mixes that modify in some aspect the reference one: addition of alumina nanofibers (ANF) and addition of cellulose nanocrystals (CNC). Accelerated and short-term tests, complemented with mineralogical and microstructural characterization, have been employed to measure critical durability indicators according to an XA environment. Based on the monitoring and damage evolution of the UHPC under the intended exposure conditions, a criterion for durability performance assessment is being defined in order to understand the differences due to the incorporation of nanoadditions.The research activity reported in this paper has been performed in the framework of the ReSHEALience project which has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 760824

EFFECT OF AUTOGENOUS SELF-HEALING ON HIGH TEMPERATURE EXPOSED ULTRA HIGH-PERFORMANCE CONCRETE

Mechanical properties of Ultra High-Performance Concrete (UHPC) degrade when exposed to elevated temperatures, even more than ordinary concretes due to its dense microstructure. Concerning, in particular, the special application of nuclear power plants, in which UHPC can find a promising use, concrete can be subjected to moderately high temperature (usually lower than 400 °C) along the working life, this making of interest the study on the influence and persistence of UHPC's innate self-healing capabilities over the thermal degradation. In this context, the paper focuses on an experimental study of UHPC recovery ability by autogenous self-healing after being exposed to high temperatures. The UHPC specimens have been made with hybrid fibers, that is, polypropylene and steel fibers, and have been pre-cracked up to a cumulative crack width of 0.3 mm under 4-point flexural test. The pre-cracked specimens have been exposed to a temperature of 200 °C or 400 °C, with a heating rate of 1 °C / minute from room temperature and kept at the target temperature for two hours, with a following slow cooling at a rate of <1 °C / minute. The specimens have been kept in the lab environment for 24 hours after reaching room temperature. Then they have been tested for residual flexural capacity or allowed to self-heal under water immersion for six months. The damage and healing evolution have been monitored periodically using ultra-sonic pulse velocity survey and digital microscope inspection. In spite of the thermal degradation, during the healing period UHPC showed a significant recovery in terms of strength assessed by ultrasonic pulse velocity tests

An Overview on H2020 Project “ReSHEALience”

Trabajo presentado al International Association for Bridge and Structural Engineering (IABSE): Towards a Resilient Built Environment - Risk and Asset Management, celebrado en Guimarães (Portugal) del 27 al 29 de marzo de 2019.In the framework of H2020, the European Commission recently funded the project ReSHEALience (www.uhdc.eu). The main idea behind the project is that the long-term behaviour of structures under extremely aggressive exposure conditions can highly benefit from the use of high performance materials, in the framework of durability-based design approaches. The project consortium, coordinated by Politecnico di Milano, features 14 partners from 8 different countries, including 6 academic/research institutions and 8 industrial partners, covering the whole value chain from producers of concrete constituents to construction companies to stake-holders and end-users. The main goals of the project are the development (a) of an Ultra High Durability Concrete (UHDC) and (b) a Durability Assessment-based Design (DAD) methodology to improve structure durability and predict long-term performance under Extremely Aggressive Exposures (EAE). The project will tailor the composition of UHDC, by upgrading the UHPC/UHPFRC concept through the incorporation of tailored nanoscale constituents.The ReSHEALience project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 760824.Peer reviewe