Documents published in Scipedia

• 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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• Experimental Study on Improvement of Interfacial Bond Properties of Carbon Fiber Reinforced Cement Matrix Composites by Nano Silica

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

  DBMC 2023.

  
  

  Abstract

  The fiber reinforcement efficiency of carbon fiber reinforced cement matrix composites (CFRCM) is limited by the low permeability of mortar to internal filaments in the fibers, leading to premature failure of the composites due to low bond strength. In this paper, three kinds of nano-silica materials were used to improve the bond properties of carbon fiber bundles to cement-based matrix by coating and electrophoretic deposition. It is found that different methods have different positive or negative effects on the improvement of bond properties, and the effects are different under different embedded lengths. The modification principle is due to the high impregnation of nano silica particles on the fibers and the reaction of volcanic ash of the particles, which promotes the formation of calcium silicate hydrate gel inside the fibers. Relevant research needs further exploration.

  Abstract
  The fiber reinforcement efficiency of carbon fiber reinforced cement matrix composites (CFRCM) is limited by the low permeability of mortar to internal filaments in the fibers, [...]

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• Electrical Joule Heating and Early Strength of Mineral-impregnated Carbon Fibre Reinforcement (MCF)

  W. Dong, M. Liebscher, B. Yang, J. Zhao, V. Mechtcherine

  DBMC 2023.

  
  

  Abstract

  Mineral-impregnated carbon fibre reinforcement (MCF) has attracted increasing attention due to its low-cost, easy manufacturing, high temperature and chloride resistance, when it replaces traditional steel reinforcement for concrete construction. Considering its excellent electrical conductivity, this paper investigates the effect of electrical Joule heating on the temperature increase, mechanical and microstructural characteristics of MCF. Different duration of electrical heating ranging from 0.5h, 1h, 2h, 4h to 8h had been explored. In addition, the effect of water spray treatment on the electrically heated MCF will be conducted. For the MCF reference without electrical heating, it is not hardened and the early flexural strength can’t be obtained. The temperature of MCF under the voltage of 15 V gradually increases to 100.5 °C and then keeps stable. The highest early flexural strength of MCF immediately tested after heating reached 290.8 MPa when the electrical heating time is 8h, and with the water spray treatment. Interestingly, the water spray treatment seems to benefit the strength development, with the less generated micro pores around the interfaces of carbon fibres to cement matrix. The results indicate that the rapid hardening MCF subjected to electrical heating can work as self-heating elements or rapid production and transportation of MCF for concrete structures.

  Abstract
  Mineral-impregnated carbon fibre reinforcement (MCF) has attracted increasing attention due to its low-cost, easy manufacturing, high temperature and chloride resistance, [...]

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• Developing Multifunctional Ultra-High Performance Concrete via Incorporating Hybrid Steel Wires and Fibers

  S. Dong, X. Wang, B. Han

  DBMC 2023.

  
  

  Abstract

  Stainless steel wires (SSWs) with micro diameter and stainless steel fiber (SFs) with millimeter diameter were incorporated together to develop multifunctional ultra-high performance concrete (UHPC) in this study. The addition of 0.2 vol.% of SSWs can already improve interface between matrix and SFs, reduce the microcracks in UHPC caused by shrinkage and initial load, increase SFs’ distribution and orientation with their high flexibility, thus enhancing the flexural toughness and resulting in the occurrence of multiple cracking flexural failure mode of UHPC with less than 2.0 vol.% SFs. The hybrid SWs and SFs reinforced UHPC possesses low electrical resistivity and can sense its initial cracking, residual flexural loading and cracking development by the measured fractional change in electrical resistivity. This is mainly coming from the inhibition effect of SWs on microcracks and the extensively conductive pathway formed by both SWs and SFs. The multiple cracking failure mode under flexural load and the self-sensing capacity to monitor crack initiation and propagation of UHPC with low content hybrid wires and fibers is important to develop multifunctional UHPC, thus providing a new approach for maintaining sustainable development of infrastructures.

  Abstract
  Stainless steel wires (SSWs) with micro diameter and stainless steel fiber (SFs) with millimeter diameter were incorporated together to develop multifunctional ultra-high [...]

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• Study on Performance of Negative Temperature and High Strength Bed Mortar Material for Wind Power Engineering

  L. Tongwei, Z. Jie, C. Guisheng, W. Linmao, Y. Maoqian

  DBMC 2023.

  
  

  Abstract

  As the development process of affordable wind power projects accelerates, the height of tower hub shows a trend of development to 150m above. The technology of steel and concrete is widely applied. Bed mortar material, as the bonding material between precast concrete rings, is the key material to ensure the lifting speed of steel and concrete tower for wind power. In this study, the basic formula of negative temperature and high strength bed mortar material was explored, and its working performance and strength development under different curing conditions were further studied. The results show that the developed bed mortar material has excellent thixotropy and it is still operable at 50min. Under the condition of negative temperature curing, the early strength of bed mortar material is high, and the late strength develops well. Curing at ultra-low temperature of -15℃, the strength of -1d is 35.4MPa, and the strength of -7+21d is over 90MPa. In the outdoor natural curing environment of alternating positive and negative temperatures, the strength of 1d reaches 51.1MPa, the strength of 60d is 113.2MPa. The performance of bed mortar material far meets the requirements of the strength grade of 80MPa which is used in winter construction of wind power engineering.

  Abstract
  As the development process of affordable wind power projects accelerates, the height of tower hub shows a trend of development to 150m above. The technology of steel and concrete [...]

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