Documents published in Scipedia

• Pitfalls in Using Electrical Conductivity to Monitor the Chloride Ingress of Concrete

  L. Huang, L. Tang, Z. Yang

  DBMC 2023.

  
  

  Abstract

  Chloride ingress in the field structure is influenced by many factors. A non-destructive monitoring is a useful tool for assessing the health of reinforced structures. This study used array sensors to measure the temperature and electrical conductivity of concrete at depths from 10 mm to 140 mm. The electrical conductivity in concrete showed a continuous decrease during the exposure to 3% NaCl solution. A numerical modelling of multi-ion species migration in pore solution can explain the evolution of conductivity profile over exposing time. By comparing with several previous investigations, this study identified the pitfalls in using electrical conductivity or resistivity to monitor the chloride ingress in the exposed concrete. To obtain a correct information from the electrical monitoring system, the experimental and analysing process should consider the saturation degree of concrete, the hydration induced structure change, the leaching of ions, the ingress of chloride and composition of binders.

  Abstract
  Chloride ingress in the field structure is influenced by many factors. A non-destructive monitoring is a useful tool for assessing the health of reinforced structures. This [...]

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• Corrosion Mechanisms of Reinforced Alkali-Activated Concrete

  F. Zhang, S. Yang

  DBMC 2023.

  
  

  Abstract

  Alkali-activated concrete (AAC), which exhibits good mechanical strength and chemical resistance properties, has attracted emerging interest from the research perspective considering the sustainable development of construction materials. However, the corrosion mechanism at the steel-AAC interface is not yet well understood including the physical and chemical aspects, which leads to different accumulation and evaluation of corrosion products, compared to ordinary Portland cement (OPC) concrete. In this paper, concrete pull-out test and electrochemical techniques were used to investigate the bond-slip behaviour and the evolution of deterioration of AAC respectively. In addition, the current guidance of corrosion evaluation used for OPC concrete based on ASTM C876 is not suitable for AAC. Five mixed ratios of blended fly ash and slag AAC were investigated under two chloride environments and one non-chloride environment, i.e., (1) 3.5% NaCl salt fog spray in the environmental chamber; (2) 3.5% NaCl saltwater immersion; (3) tap water immersion. Electrochemical techniques include half-cell potential, linear polarization resistance and Tafel extrapolation method were used to determine the corrosion rate. The electrochemical results are validated through the comparison of the gravimetric loss of steel after corrosion and electrochemical loss from calculation.

  Abstract
  Alkali-activated concrete (AAC), which exhibits good mechanical strength and chemical resistance properties, has attracted emerging interest from the research perspective [...]

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• Effect of Moisture History on ASR Expansion and Microstructural Properties

  O. Olajide, M. Nokken, L. Sanchez

  DBMC 2023.

  
  

  Abstract

  Alkali Silica reaction has been a great menace to the durability of concrete infrastructure since its discovery. The mechanism is caused by the reaction between poorly crystallized silica and alkalis in the presence of sufficient amount of water. Just as water plays a critical role in several durability challenges in concrete, the limitation of moisture has been prominently used as a technique for the maintenance of ASR affected structures. The variation in moisture condition to which structures are exposed could lead to alternate wet and dry regimes. Drying aids the mitigation of the reaction, however, the cyclic phenomenon can modify the kinetics of the reaction and exercebate inner damage. This paper focuses on the development of the reaction over an alternate wetting and drying cycle involving aggregates of different levels of reactivity. The influence of the moisture history on the microscopic features were appraised using the damage rating index. The kinetics of the reaction and ASR induced deterioration in specimens undergoing cycles of wet and dry conditions differ when compared to those stored at constant moisture. Furthermore, ASR induced expansion and petrographic features are influenced by the difference in the reactivity level of aggregates.

  Abstract
  Alkali Silica reaction has been a great menace to the durability of concrete infrastructure since its discovery. The mechanism is caused by the reaction between poorly crystallized [...]

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• Comparison Between Parameters of Corrosion, Obtained by Destructive and Non-destructive Electrochemical Techniques

  C. Alves, A. Oliveira, T. Cardoso, O. Cascudo

  DBMC 2023.

  
  

  Abstract

  This research aims to compare corrosion parameters obtained by linear polarization technique and Tafel extrapolation method in steel bars embedded in concrete. It was analyzing the intervention of mineral additions, such as metakaolin (10%) in binary concrete mixtures and silica fume (9% ) and nano silica (1%) in ternary concrete mixtures of water/binder ratio of 0.4 and 0.6 after induction of corrosion by wetting and drying cycles in a solution containing chlorides. Thus, the corrosion potential (Ecorr), polarization resistance (Rp) and corrosion rate (icorr) were measured. As a main result, a good correlation (R² of 0.82 and 0.96) was obtained with the values of polarization resistance (Rp) and corrosion rate (icorr), obtained by Rp and by Tafel slope, respectively. Binary and ternary concretes mixtures showed higher performance than reference concretes. Reference concrete with w/ratio of 0.6 showed a high corrosion rate.

  Abstract
  This research aims to compare corrosion parameters obtained by linear polarization technique and Tafel extrapolation method in steel bars embedded in concrete. It was analyzing [...]

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• Durability of Concrete and Reinforced Concrete Structures Subjected to Temperature Cycles: Insight from Multiscale Thermomechanical Analysis

  B. Pichler

  DBMC 2023.

  
  

  Abstract

  This document refers to thermal expansion of cementitious materials and to related thermal stresses activated in samples of concrete as well as in unreinforced and reinforced concrete structures. It provides an overview of multiscale research which was carried at the Institute for Mechanics of Materials and Structures, TU Wien, Vienna, Austria, in cooperation with Tongji University and Shanghai Jiao Tong University, China. The overview starts with the nanoscopic origin of the thermal expansion behavior of cement paste, which is triggered by the heating-induced release and the cooling-induced uptake of water by calcium-silicate-hydrates (C-S-H). Temperature changes lead to thermal strains. Thermal stresses are activated provided that the thermal strains are constrained. Such constraints prevail at microstructural scales of concrete as well as at cross-sectional and macrostructural scales of unreinforced and reinforced concrete structures such as beams, plates, and frames. Diurnal temperature changes result in daily cycles of self-equilibrated thermal stresses. They represent a considerable loading for interfacial transition zones (ITZs) separating the aggregates from the cement paste matrix. Extreme events such as sudden hail showers or moderate fires are very likely to result in thermal cracking, at least in the microscopic region of the ITZ, but frequently also at the larger scale of concrete.

  Abstract
  This document refers to thermal expansion of cementitious materials and to related thermal stresses activated in samples of concrete as well as in unreinforced and reinforced [...]

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• Influence of Coarse Aggregate Grade on Air Void Structure of Air-entrained Concrete

  Q. Liu, J. Kong

  DBMC 2023.

  
  

  Abstract

  Air void structure has always been a key factor affecting the frost resistance of concrete. The refinement of air void structure mainly comes from the extrusion of slurry and the cutting of aggregates. However, there is no systematic theory on the influence of aggregate on air void structure. In this paper, the effects of different coarse aggregate grades on the concrete air void structure were studied. The fractal dimension D value was used to represent the coarse aggregate gradation. In the range of coarse aggregate particle size between 4.75-26.5 mm, D=2.1, D=2.3, D=2.5, D=2.7 were selected as the experimental group, and single-graded coarse aggregate of 4.75 and 26.5 mm were selected as the control group, with a total of six test groups. By means of an air content tester, Rapid Air, freeze-thaw durability test and other measurements, the air content, air void structure, freeze-thaw durability and other performance parameters were measured. The differences in air void structure parameters of specimens, such as air content, spacing factor and the number of bubbles were compared to obtain the relationship between the coarse aggregate grading and air void structure. Further analysis of its influence on frost resistance can provide a reference for scientific research and engineering application of concrete air void structure.

  Abstract
  Air void structure has always been a key factor affecting the frost resistance of concrete. The refinement of air void structure mainly comes from the extrusion of slurry [...]

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• Efficiency Evaluation of Metakaolins for Use in Concrete

  H. Carasek, P. Passos, O. Cascudo

  DBMC 2023.

  
  

  Abstract

  The use of metakaolins has been shown to be effective in modifying the properties of cementitious materials related to durability, highlighting the very positive impact in terms of increasing the electrical resistivity of concrete and reducing ionic transport in this porous medium. In this sense, the present work aims to evaluate the efficiency of different metakaolins in terms of pozzolanic activity, linking the efficiency to various characteristics of the metakaolin. Five samples of different Brazilian commercial metakaolins were then characterized, using the following methods: BET specific surface area, X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, thermal analysis (TA/DTA), thermogravimetric analysis (TG/DTG) and determination of pozzolanic activity by the modified Chapèlle method. As the main results, it was found that the BET specific surface area and the Al2O3 content, obtained by XRF, better explain the pozzolanic activity of metakaolins (Pearson correlation coefficients equal to 0.89 and 0.94, respectively). The amorphous content (quantified by Rietveld in the XRD) showed only a reasonable correlation with the pozzolanic activity determined by the modified Chapèlle method. In general, the chemical-mineralogical characteristics that indicate purity and amorphism of metakaolin, expressed by the Al2O3 content, Al2O3/SiO2 ratio, SiO2+Al2O3 sum, and amorphous content, represent important performance parameters of metakaolins. The specific surface area compensates for lower purity or chemical reactivity and significantly influences pozzolanic activity.

  Abstract
  The use of metakaolins has been shown to be effective in modifying the properties of cementitious materials related to durability, highlighting the very positive impact in [...]

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• Reinforced Concretes of Tomorrow: Corrosion Behaviour according to Exposure Classes

  V. Bouteiller, E. Marie-Victoire, A. Bonnet, V. Da-Silva, L. Adelaïde, J. Billo, C. Da-Costa, M. Bouichou, J. Ducasse-Lapeyrusse, J. Mai-Nhu, P. Barthélémy, P. Turcry, F. Cussigh, S. Chanut

  DBMC 2023.

  
  

  Abstract

  Reinforced concrete is the most widely used building material but its durability in terms of concrete cover performance and corrosion of steel rebar is still a key point to be studied. To address this topic, within the frame of the national project PERFDUB, two series of eleven reinforced concrete specimens (with metric dimensions) were cast with innovative concrete mixes representative of the French experience, two shapes of rebar and two concrete covers. Then, these specimens were exposed in two natural exposure sites, one in Epernon for carbonation (XC4) and a second one in La Rochelle in the Atlantic Ocean in a tidal zone for chloride ions (XS3m). Their corrosion was carried out using non-destructive testing. In addition, in order to follow the corrosion evolution more accurately in a continuous way, two series of three specimens were casted with embedded sensors and were exposed in two other outdoor sites in Marne-la-Vallée (XC4) and in Eqiom facility (XS3e). The first results of this 20-year project in terms of corrosion of these reinforced concrete specimens obtained with laboratory and field equipment and with monitoring are presented in this paper.

  Abstract
  Reinforced concrete is the most widely used building material but its durability in terms of concrete cover performance and corrosion of steel rebar is still a key point to [...]

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• Hydrophobicity Mechanism of Cementitious Material Containing Carboxylic Acid Ammonium

  H. Zhang, S. Mu, J. Cai, J. Hong

  DBMC 2023.

  
  

  Abstract

  Hydrophobic treatment of cement pastes is most effective way to resist the penetration of water with aggressive ions to improve durability of cement-based materials. In this paper, the mechanism of carboxylic acid ammonium salt integral additionon hydrophobicity of cement-based materials is analyzed. The effects of carboxylic acid ammonium salt on hydrophobicity, moisture diffusion and hydration products are investigated by experimental methods.The results of water vapor sorption isotherm show that the addition of carboxylic acid ammonium salt increases the pore volume. The simplified analytical hydrodynamic model of cone type pore and Young’s relationship is proposed to analyze the relation between characteristic parameters of pore and the permeability of cementitious materials. It can be concluded that the hydrophobicity results from the change of pore structure and the hydrophobic surface of cone region. These results provide the guidance to design the durability and develop the new hydrophobic agent used in cementitious material.

  Abstract
  Hydrophobic treatment of cement pastes is most effective way to resist the penetration of water with aggressive ions to improve durability of cement-based materials. In this [...]

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• Accelerated Degradation of Coating-mortar Interface under UV Radiation in Presence of Water

  Y. Dai, Q. Zeng

  DBMC 2023.

  
  

  Abstract

  The application of organic coatings is one of the most effective and economic methods to protect concrete structures from deterioration. However, organic coatings are prone to degradation under aggressive environmental actions, so the protective function may loss. While ultraviolet (UV) aging is often blamed for the degradation of organic coatings, water may play a more important role on the interfacial adhesion between the coatings and the substrate. To uncover the effect of water on the degradation performance of coating-substrate system, mortar samples coated with water-borne epoxy resin (WER) were exposed to three assigned environments, i.e., UV radiation, UV/water immersion, and UV/dry-wet cycle, up to 60 days. The surface appearance, chemical structure, wettability, and surface micro-morphology of the aged WER coatings were characterized via image process analysis, attenuated total reflectance flourier transform infrared spectroscopy (ATR–FTIR), static water contact angle, and scanning electronic microscopy (SEM). Results show that the UV/water immersion resulted in severest blistering on the WER-mortar interface, while the UV/wet-dry cycle caused the formation of micro-pinholes on the WER surface. In contrast, the UV radiation did not induce such severe aging. The data implied that water can accelerate the aging of WER-mortar system.

  Abstract
  The application of organic coatings is one of the most effective and economic methods to protect concrete structures from deterioration. However, organic coatings are prone [...]

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