Documents published in Scipedia

• 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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• Mineralogical Characterization of the Biodegradation of Sewage Cementitious Materials in the Presence of H2S

  J. Ayoub, T. Pons, M. Guéguen Minerbe, M. Oliveira, M. Marchetti

  DBMC 2023.

  
  

  Abstract

  The biodegradation of cementitious materials in sewage systems is mainly due to the biotic oxidation of hydrogen sulfide (H2S) into sulfuric acid. It leads to a local and progressive dissolution of the cementitious matrix as well as the precipitation of some expansive products such as gypsum and ettringite. In such a context, this paper focuses on the characterization of the altered layers present on several types of cementitious materials (CEM I ordinary Portland cement, CEM III blast furnace cement, CEM V composite cement, and CAC: calcium aluminate cement). The studied samples are mortars exposed, to different H2S concentrations, for several years in a local sewage plant managed by the Interdepartmental Syndicate for the Sanitation of the Paris Agglomeration (SIAAP). Transversal crosssections of these mortars were first chemically characterized by energy dispersive spectroscopy (EDS) in order to obtain elemental mapping. Additionally, to better understand the surface degradation and the appearance of mineral phases revealing the process, µ-Raman mappings were performed on the deteriorated zones at different time scales. Gypsum was observed on all samples. The analysis confirmed the greater resistance of CAC materials in such an environment than that of Portland cement-based materials.

  Abstract
  The biodegradation of cementitious materials in sewage systems is mainly due to the biotic oxidation of hydrogen sulfide (H2S) into sulfuric acid. It leads to a local and [...]

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• Hysteretic and Scanning Behaviors of Water Vapor Sorption in Hardened Cement Pastes

  Z. Wang, K. Li

  DBMC 2023.

  
  

  Abstract

  Water in the multiscale porous microstructure of cement-based materials is closely related to multiple deterioration processes, hence significantly influences the durability of concrete structures in atmospheric environment. Water vapor sorption is the key tool for characterizing the hygroscopic properties of cement-based materials, also a promising technique for exploring their nanopore structures. The significant hysteresis between different sorption branches is stemmed from the complexity of interconnecting pore system and concurrence of different physical phenomena. In this study, the hysteretic and scanning behaviors of water vapor sorption in hardened cement pastes are measured with a dynamic vapor sorption instrument, and investigated to provide new insights into the path-dependency of sorption behaviors on humidity history and resolve the overall sorption hysteresis into contributions from different phenomena.

  Abstract
  Water in the multiscale porous microstructure of cement-based materials is closely related to multiple deterioration processes, hence significantly influences the durability [...]

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• Effect of Electric Field on the Degradation Process of Reinforced Mortar under Chloride and Sulfate Attack

  X. Yu, S. Li, X. Chang, Y. Liao, D. Chen

  DBMC 2023.

  
  

  Abstract

  This study investigated the degradation mechanism behind the reinforced mortar exposed to chloride, sulfate and electric field. The steel-mortar samples were exposed to 5% Na2SO4, 5% NaCl + 5% Na2SO4 solutions and deionized water in two regimes (full immersion and direct current electric field). The efficiencies of three current densities were compared as well. The total and free sulfate ion content in the mortar were measured. The microstructural analysis by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were conducted. The results indicated that the electric field drastically increased the ingress of sulfate, as well as the sulfate reaction. Meanwhile, the current attenuated the interaction between chloride and sulfate. The increase in current density decreased the efficiency of degradation acceleration. An acceleration factor (AF) was proposed based on the comparison between the number of ions in the mortar under electric field and immersion. Findings from this study are beneficial to develop a reliable acceleration method for the long-term performance of RC structures under chloride and sulfate attack.

  Abstract
  This study investigated the degradation mechanism behind the reinforced mortar exposed to chloride, sulfate and electric field. The steel-mortar samples were exposed to 5% [...]

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• Dissolution Behaviour of Alkali-activated Fe-rich Non-ferrous Metallurgy Slag in Acetic Acid

  N. Wen, V. Hallet, A. Peys, Y. Pontikes

  DBMC 2023.

  
  

  Abstract

  The application of Fe-rich non-ferrous metallurgy slag (NFS, within a FeOx-SiO2-Al2O3-CaO system) in alkali-activated materials requires detailed information on the durability performance. The present study investigates the durability of alkali activated NFS (AA-NFS) exposed to acetic acid to simulate the attack of a concrete by organic acids present in animal manure or sewage systems. The dissolution behavior of NFS and alkali-activated NFS (AA-NFS) was assessed by immersing NFS and AA-NFS in a 3 wt. % acetic acid solution at a liquid to solid weight ratio of 1000. The dissolved ions in the acetic solution from NFS and AA-NFS were measured at different time intervals over 7 days. Through the comparison of NFS with AA-NFS, the dissolution behavior of unreacted slag and binder in AA-NFS could be evaluated separately, considering a calculated amount of 47.7 wt.% of unreacted slag was present in the AA-NFS. The results demonstrated that the binder dissolves slightly faster than slag in the first 4 hours. Over half of the dissolution rate of the Ca, Fe and Al in AA-NFS was due to binder. While for Si, 41% total dissolution rate in AA-NFS was from binder and the other 59% was from unreacted slag. After 7 days however, the dissolved fraction of slag was higher than binder. About 90% Ca, 79% Fe and 71% Al in slag was ended up in the acetic acid solution, which is higher than that in binder (74%, 62% and 56%, respectively). A significantly higher difference was found for the total dissolved fraction of Si in slag (86%) compared to that in binder (43%). The highly connected silicate network in the binder remains largely intact as silica gel, while due to the low connectivity of the silicate species in the slag the silicate dissolves after the other elements have left the structure. Overall these results suggest that Ca has the lowest dissolution resistance in binder, followed by Fe, Al and Si.

  Abstract
  The application of Fe-rich non-ferrous metallurgy slag (NFS, within a FeOx-SiO2-Al2O3-CaO system) in alkali-activated materials requires detailed information on the durability [...]

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• Thermal-Resistivity Characteristics of Carbon Fabric Reinforced Cementitious Matrix

  Y. Gong, J. Liu, J. Hong, D. Zhang

  DBMC 2023.

  
  

  Abstract

  The thermal-resistivity effect of the carbon fiber reinforced cement (CFRC) has been successfully applied to monitor the temperature of concrete structures. There are insufficient studies on the thermal-resistivity effect of the carbon fabric reinforced cementitious matrix (CFRCM). In this paper, the resistance change of CFRCM from room temperature to 120℃ and the thermal-resistivity characteristics during repeated heating have been studied. It was showed that during the heating process, with the continuous increasement of the carrier concentration, the specimen exhibited obvious negative temperature coefficient (NTC) effect, and a temperature rise of 10℃ lessened relative resistance change by about 0.4%. However, some carriers stayed in the conduction band after the first cooling. Then, the resistance cannot return to the original value, and the curves of subsequent heating processes had a good repeatability.

  Abstract
  The thermal-resistivity effect of the carbon fiber reinforced cement (CFRC) has been successfully applied to monitor the temperature of concrete structures. There are insufficient [...]

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• Study on Shrinkage Properties of Repairing Mortar Modified by Basalt Fiber

  S. Yang, P. Xu

  DBMC 2023.

  
  

  Abstract

  In order to study the shrinkage properties of modified repairing mortar, an orthogonal experiment with four factors and three levels were proceeded. Nine specimens with four factors, i.e., silica powder, sodium silicate, basalt fiber and a U-type expansive agent, were used to measure the length change ratio. The results show that the shrinkage value of modified repairing mortars have been greatly reduced. Compared with the control specimen without any additives, the shrinkage value of the modified repairing mortar with the silica powder of 3 %, the sodium silicate of 1.0 %, the basalt fiber of 0.2 % and the U-type expansive agent of 10 % at 60d drops by 42.5%. Based on experimental results, the shrinkage prediction model of modified repairing mortar has been established. The model can be used to predict the shrinkage value of the modified repairing mortar with similar compositions.

  Abstract
  In order to study the shrinkage properties of modified repairing mortar, an orthogonal experiment with four factors and three levels were proceeded. Nine specimens with four [...]

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