Documents published in Scipedia

• 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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• Accelerating Effect of Heating Treatment on the Damage of Cement Paste under Sulfate Attack

  B. Ran, O. Metalssi, T. Fen-Chong, P. Dangla, K. Li

  DBMC 2023.

  
  

  Abstract

  The ettringite (AFt) formation and damage process are investigated for cement paste subjected to external sulfate attack with and without heating treatment during curing. Slice and disc specimens were exposed to 10 g/L Na2SO4 + pH of 13. The evolutions of AFt formation, pore structure, and expansion on slice specimens were characterized through 27Al NMR, MIP, and micrometer. The surface cracks on disc specimens were observed through an optical microscope. The experimental results show that: (1) heating treatment dissolves part of AFt and accelerates the ettringite formation and material expansion; and (2) heating treatment initiates the microcracks, thus promoting the material cracking.

  Abstract
  The ettringite (AFt) formation and damage process are investigated for cement paste subjected to external sulfate attack with and without heating treatment during curing. [...]

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• Degradation of Cement Pastes Subjected to Combined Carbonation and Leaching

  Q. Phung, L. Frederickx, N. Maes

  DBMC 2023.

  
  

  Abstract

  Carbonation and leaching are likely to be the primary concrete degradation mechanisms for concrete utilized in geological repositories when the concrete is fully saturated and in contact with host rock pore water containing increased CO2 content. This work describes the changes in the microstructure and transport properties of cement pastes caused by coupled chemical degradation processes that occur at the cement paste-clay interface. In the laboratory, an experimental program was designed to accelerate the interface interaction under carbonation and leaching by bringing highly porous cement pastes (to mimic backfill materials used in geological disposal) and Boom Clay into contact in either accelerated percolation or batch-type experiments. Mercury intrusion porosimetry (MIP) was used to investigate the microstructural alteration. Inductively coupled plasma optical emission spectrometer (ICP-OES) and permeability, diffusion measurements were used to determine the evolution of chemical and transport properties, respectively. The results of the porosity change at the interface demonstrate an increase in porosity of the cement paste interface due to Ca leaching, which overwhelms the carbonation. As a result, the transport properties increase. This suggests that clogging of the cementitious material side is unlikely.

  Abstract
  Carbonation and leaching are likely to be the primary concrete degradation mechanisms for concrete utilized in geological repositories when the concrete is fully saturated [...]

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• Cement Degradation Caused Risks for Geological Carbon Sequestration Reservoirs

  X. Shi, M. Wu

  DBMC 2023.

  
  

  Abstract

  Geologic carbon sequestration (GCS), a process to capture and store CO2 in deep geologic formations, is considered an essential technique to reduce carbon emissions which are a main cause of global warming and climate change. Depleted oil and gas reservoirs are among the most appealing locations for GCS. However, the success of the strategy relies on the long-term integrity of the reservoirs, which is challenged by the carbonation reactions between the main reservoir sealing material, i.e., cement, and the stored CO2 and then the occurrence of fluid leakage. This work provides a concise review on the degradation of oil well cement and the interface between cement and casing/formation rock, with a special focus on the influence of different factors such as the curing, service conditions and contaminants. The mechanisms and the mitigation methods of the degradation process are also discussed. This work aims to summarise current research progress and identify some remaining challenges for future research.

  Abstract
  Geologic carbon sequestration (GCS), a process to capture and store CO2 in deep geologic formations, is considered an essential technique to reduce carbon emissions which [...]

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• Durability of GFRP and BFRP Bars in Sulfoaluminate Cement Concrete Made with Seawater and Sea Sand

  T. Wang, A. Razaqpur

  DBMC 2023.

  
  

  Abstract

  Due to the large carbon footprint of ordinary Portland cement (OPC) and the rapid corrosion of steel rebars in certain environments, the search for greener, sustainable and more durable reinforced concrete structures is ongoing. In this study, the alkali resistance of basalt- and glass-fibre reinforced polymer (BFRP/GFRP) bars in sulfoaluminate cement (SAC) concrete made with seawater and sea sand is investigated for the first time. Production of SAC involves lower energy consumption and greenhouse gas emission compared to OPC while SAC concrete provides a lower pH environment, which favors the durability of FRP bars. Following ASTM D 7705-D7705M-12 Procedure A, the bars were immersed for three months in simulated pore solution of concrete made with SAC, river sand and fresh water, termed Solution A, and compared their durability to that of companion bars immersed in simulated pore solution of concrete made with SAC, seawater, and sea sand, termed Solution B. Both solutions had the same pH, and their temperature was maintained at 60℃ for the duration of the test. The post-immersion or retained tensile strength of GFRP bars in Solution A and B was 83.0% and 73.6%, respectively, while the corresponding values for the BFRP bars were 52.5% and 67.9%, respectively. It appears that due to the presence of sea salt, Solution B is less damaging to BFRP than Solution A while the opposite is true in the case of GFRP. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results are utilized to explain the damage mechanisms. Based on image analysis, it is shown that the deteriorated zone within the bar cross-section is not a uniform ring, but its cross-sectional area correlates with the reduction in tensile strength.

  Abstract
  Due to the large carbon footprint of ordinary Portland cement (OPC) and the rapid corrosion of steel rebars in certain environments, the search for greener, sustainable and [...]

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• Study of the Chemical Processes of Combined Sulfate-chloride Attack on Low-carbon Cementitious Materials

  F. El Inaty, M. Marchetti, M. Quiertant, O. Omikrine-Metalssi

  DBMC 2023.

  
  

  Abstract

  In marine environments, concrete structures are not only exposed to sulfate ions but also to chloride ones, from an early age. This leads to concrete expansion and cracking as well as steel reinforcements corrosion. However, the coupling effect of sulfate and chloride is still not widely studied. When addressed, some researchers showed that chloride ions mitigate the effect of sulfate while others concluded that it accelerates it and vice versa. Therefore, one of the objectives of this study is to observe both the combined and individual effects of chloride on sulfate attack. The second objective is to perceive the resistance of selected additives (fly ash, blast furnace slag, and metakaolin) to a combined attack. Then, powders of pure cement, binary, ternary, and quaternary blended pastes were immersed in sulfate, chloride, and sulfate-chloride solutions at an early age. Results of the characterization showed that the ettringite formation was delayed due to the presence of chloride. However, the presence of sulfate ions accelerated the chloride effect. The incorporation of more than one additive enhanced the samples’ durability.

  Abstract
  In marine environments, concrete structures are not only exposed to sulfate ions but also to chloride ones, from an early age. This leads to concrete expansion and cracking [...]

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