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© 2018 The Authors, published by EDP Sciences. Pore structure characterization is a key aspect when studying the durability of cementitious materials. When supplementary cementitious materials (SCMs) are used changes in pore structure are expected, and the complexity of its analysis is increased. The purpose of this paper is to describe the pore structure variation of mortars with two types of SCMs: natural pozzolan from volcanic origin (NP), and limestone powder (LP). We tested mixes with cement replacements (in weight) of 20 % and 40% by NP, and 10 % and 20% by LP. To analyse the pore structure, two widely accepted and complementary techniques were applied: dynamic water vapour sorption (DVS) and mercury intrusion porosimetry (MIP). With the DVS data, the Barret-Joyner-Halenda (BJH) model was used for pore size distribution assessment. Calculations with the Dubinin-Radushkevich (DR) model were also made for the smallest pore size range. Tests were performed at 28 and 90 days. MIP and DVS allowed evaluating the effect of the studied SCMs on different pore size ranges. Both techniques provided comprehensive information over a wide range of pore sizes. The mix with 40 % of NP had the best evolution, showing a significant volume decrease in the mesopore range. ispartof: INTERNATIONAL CONFERENCE ON CONCRETE REPAIR, REHABILITATION AND RETROFITTING (ICCRRR 2018) vol:199 ispartof: 5th International Conference on Concrete Repair, Rehabilitation and Retrofitting (ICCRRR) location:Cape Town, SOUTH AFRICA date:19 Nov - 21 Nov 2018 status: published

Concrete cracking can result in a significant reduction of the durability and the service life due to the ingress of aggressive agents Self-healing concrete is able to heal cracks without external intervention, thereby mitigating the need for manual repair. In the assessment of the healing efficiency of self-healing concrete the to-be-healed crack width is an important parameter and different researchers have emphasised that the variability of the crack width significantly hampers an accurate assessment of the healing efficiency. With two new crack control techniques the variability of the crack width was reduced in order to decrease the variability on the calculated healing efficiency. This paper reports on the application of these techniques for the assessment of self-healing mortar containing encapsulated polyurethane. The healing potential was investigated by looking at the degree of sealing using a water flow test setup. It was observed that by using a crack control technique the variability on the crack width can indeed be reduced. Nonetheless, this does not translate in an equivalent reduction on the variability of the healing efficiency. This indicates that other factors contribute to the variability of the healing efficiency.

Among many different environmental actions causing deterioration of concrete, chlorides are representing one of the most dangerous attacks on the reinforced concrete structure. Numerous chloride analyses were performed on the Krk bridge, which has been exposed to marine environment for more than 30 years. Krk bridge is situated at the Northern part of Adriatic coast, where often very strong winds are blowing which brings sea water to all parts of the structure. Surface chloride concentrations are analysed in relation to the height above sea level and to the orientation of the structural element. In the area of Krk bridge basic value of reference wind speed is 40 m/s, with measured gusts reaching up to 90 m/s. Results show that marine salt deposition at the concrete surface is strongly influenced by wind, its dominant direction and reference wind speed. Based on the analysis of chloride surface concentrations at concrete columns from the Krk bridge, marine chlorides are suggested to be observed as a “loading” in relation to the height above sea level and structural element orientation.

This paper presents experimental study of short-term loss (in time intervals up to 96 hours after initial cooling) of residual mechanical properties of high strength concrete after heating to temperatures 100 – 800°C. Concrete mixture used in the study is specific for the production of hollow core slabs, comprised of standard Portland cement, calcareous aggregate with fraction of 0-8 mm and with 0.33 water/cement ratio. The study comprises residual compressive strength, tensile splitting strength, static and dynamic modulus of elasticity and stress-strain relationship. Experimental results are compared with those obtained from other studies, EN 1994-1-2 and EN 1992-1-2. The results show that compressive strength of concrete has a significant reduction during the first 48 hours, especially at temperatures between 400-800°C. Results of the residual tensile strength show a slight increase at temperatures below 220°C, with a linear reduction at temperatures between 400-600°C. Study of the dynamic and static modulus of elasticity shows that both properties are decreased, but remain constant during the period of 96 hours after cooling. The results presented in this paper were obtained as a part of the ongoing research concerning the behavior of prestressed hollow core concrete slabs in fire.

In the present paper a fully coupled transient three-dimensional thermo-hygro-mechanical model for concrete is discussed. The model is formulated in the framework of continuum mechanics based on the principles of the irreversible thermodynamics. Distribution of moisture, pore pressure, temperature, stresses and strains are calculated by employing a three-dimensional transient finite element analysis of implicit type. The mechanical strain, which is due loading, temperature induced stresses and pore pressure, is calculated by employing temperature dependant microplane model for concrete. To investigate failure mechanism of explosive spalling of high strength concrete under high temperature, the extensive 3D finite element parametric study of concrete wall exposed to high temperature is carried out. In the analysis are varied concrete mechanical properties, permeability, porosity, humidity and heating rate. The results indicate that relatively high pore pressure together with local instabilities (geometrical non-linearity), due to compressive stresses that are generated in direction parallel to the heated concrete surface, are main reasons for explosive spalling. It turns out that permeability is the most sensitive concrete property with respect to the risk of an explosive spalling. The risk significantly increases with decrease of permeability.