Documents published in Scipedia

• Negative Emission Potentials Using Biogenic Building Materials - A Case Study from Denmark

  R. Torben Valdbjorn, T. Emil Engelund, B. Niclas Scott, N. Thomas, J. Uffe, B. Annette, G. Stefan Christoffer

  DBMC 2023.

  
  

  Abstract

  Significant reductions in carbon footprint can be achieved by increasing the use of biogenic materials in construction. In biogenic materials, carbon is embedded as long as the materials are not biologically degraded, and they consequently act as carbon reservoirs that keep CO2 out of the atmosphere. The reservoirs of carbon are maintained if the biogenic materials during maintenance and renovation are replaced by similar ones. Buildings containing more wood, straw, and other biogenic materials and less concrete, steel, and mineral wool are therefore part of the way forward for a sustainable restructuring of the construction industry. Until now, the main focus has been on reducing energy consumption of buildings, while less focus has been on energy consumption and the climate impact from the production of materials and the construction process itself. This paper examines the potential carbon reservoir in the building stock in Denmark for the next 100 years. In detail the paper describes potential building components made from biogenic resources, outlines the necessary amounts and qualities of biogenic materials, and summarizes the available biogenic resources. The article is based on the conditions for construction in Denmark and the opportunities Denmark has as an industrialized agricultural country with a long coastline, which can be utilized in the production of biogenic resources for manufacturing of building materials.

  Abstract
  Significant reductions in carbon footprint can be achieved by increasing the use of biogenic materials in construction. In biogenic materials, carbon is embedded as long as [...]

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• Molecular Dynamics Study between Amine Solution and Calcium Hydroxide

  T. Pan, R. Kitagaki, Y. Yoda

  DBMC 2023.

  
  

  Abstract

  Carbon dioxide can be captured by amines and carried into calcium hydroxide to generate calcium carbonate. In this study, molecular dynamics simulations were performed to study the interaction energy and structure between amine solution and calcium hydroxide crystal slab at the molecular level. MDEA was chosen as a representative amine. According to the one-dimensional concentration function, it was found that at a low ratio of MDEA, it was preferentially distributed close to the calcium hydroxide. And as the content in the solution increased, MDEA was gradually distributed equally throughout the aqueous solution. Compared to water, the interaction energy between MDEA and calcium hydroxide is greatly reduced and gradually decreases with increasing amine content. This means that the interaction between the two is reduced, and the reaction is more difficult to occur. In addition, the system of carbon dioxide dissolved in a solution of amine and water was simulated. The distribution of carbonate and bicarbonate was found to be relatively uniform at MDEA ratios of 5% and became irregular above 20%.

  Abstract
  Carbon dioxide can be captured by amines and carried into calcium hydroxide to generate calcium carbonate. In this study, molecular dynamics simulations were performed to [...]

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• Laboratory and Pilot Investigation on Properties of precast Engineered Cementitious Composites (ECC) Subjected to Carbonation Curing

  Z. Duo, E. Brian R., L. Victor C.

  DBMC 2023.

  
  

  Abstract

  The concrete industry is facing an increasing challenge for sustainability. Besides the large embodied carbon, the intensive operational carbon associated with repetitive repair becomes the main hurdle for lifecycle emission reduction. In this study, the feasibility of sequestering CO2 into durable engineered cementitious composite (ECC) through early-age carbonation curing was investigated. The goal is to demonstrate a simultaneous reduction of the material’s embodied carbon (by CO2 sequestration) and lifecycle emissions (by ECC’s superior durability). The material was processed at both lab and pilot scales and was demonstrated on precast pedestrian pavement slabs. Results show that ECC was highly reactive to CO2 at lab scale, with 26.5% CO2 uptake by cement mass after 24-hour carbonation. However, the early-age carbonation was subjected to a significant size effect and attained a 4.3% CO2 uptake for pilot-scale specimens with a low specific surface area. Despite this reduction in carbonation efficiency, the calcite precipitation through carbonation curing was found to densify the fiber/matrix interface and improve the composite ultimate tensile and flexural strength by up to 28.8%. Carbonation curing also enhanced ECC’s crack width control, thus mitigating sulfate attack and lowering surface salt scaling on freeze-thaw exposure. It is suggested that producing ECC through carbonation curing is technically viable, and the carbon-sequestered ECC is recommended for small-scale precast components for enhanced durability and sustainability.

  Abstract
  The concrete industry is facing an increasing challenge for sustainability. Besides the large embodied carbon, the intensive operational carbon associated with repetitive [...]

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• Impact of the Thaumasite Sulfate Attack on the Pore Structure and Gas Permeability of Cement Mortar

  R. Bo, H. Tingyu, H. Xiaobin, L. Kefei

  DBMC 2023.

  
  

  Abstract

  In this study, the impact of the thaumasite sulfate attack (TSA) on cement mortar was investigated by comparing it to the ettringite sulfate attack (ESA). Mortar specimens with three binders, corresponding to the blank, ESA, and TSA, were exposed to sulfate solution. The evolutions of thaumasite and ettringite formation, pore structure, and gas permeability on the mortar specimens were characterized through XRD, 1H NMR, and CemBureau device. The experimental results show that: (1) both ettringite and thaumasite were formed in TSA; (2) ESA reduces the capillary pore space, whereas TSA decreases both the capillary pore and interlayer pores; and (3) ESA decreases the gas permeability while TSA significantly increases it.

  Abstract
  In this study, the impact of the thaumasite sulfate attack (TSA) on cement mortar was investigated by comparing it to the ettringite sulfate attack (ESA). Mortar specimens [...]

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• Fracture Process of In-situ Polymerization Modified Cementitious Materials

  X. Chengji, Z. Qiang

  DBMC 2023.

  
  

  Abstract

  By regulating cement hydration reaction and organic monomer polymerization, the strength and deformability of in-situ polymerization modified cement-based materials are greatly improved. However, the fracture processes of this type of organic-inorganic composites have not been systematically investigated. In this work, sodium acrylate (SA) monomer in-situ polymerization modified cementitious composites (iPSA) were fabricated. Three-point bending (TPB) test was conducted with digital image correlation (DIC) technique for characterizing the fracture process zone (FPZ). Microscopic test was conducted to unravel the crosslinked organic-inorganic composite structures in the iPSA matrix. Results showed that an obvious strain concentration region occurred and grew at the notch tip of the iPSA beams with load. The gradually expanding width of FPZ was normally distributed. Microscopic test suggested that the physical interlinks between the cement hydrates and sodium polyacrylate may resist again the FPZ development of iPSA. The findings of this work would deepen the understandings of fracture process of polymer modified cementitious composites with broad engineering applications.

  Abstract
  By regulating cement hydration reaction and organic monomer polymerization, the strength and deformability of in-situ polymerization modified cement-based materials are greatly [...]

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• Evaluation of Carbonation Degree of Hardened Cement Paste with Different Water-Cement Ratio in Wet-Dry Cycle

  Z. Zhao, D. Oh, Y. Wang, R. Kitagaki, T. Masuo

  DBMC 2023.

  
  

  Abstract

  One of the global environmental problems, CO2 emissions from cement production intensifies in these decades. To solve this problem, countermeasures for CO2 emissions using waste concrete, which has ability to absorb CO2 due to contain calcium-silicate-hydrate (C-S-H) and portlandite (Ca(OH)2), are in the spotlight recently. However, considering the limited time before recycling as roadbed materials, it is important to increase CO2 absorption efficiency so that as much CO2 as possible reacts with waste concrete. In this study, hardened cement paste powders (HCPWs) with the water-to-cement ratios of 0.4, 0.5 and 0.6 were evaluated for the degree of carbonation under various humidity conditions. HCPWs were pulverized to a particle size of 0.6 to 1.18mm and put in desiccators keeping constant humidity condition of RH60 and RH80. In addition, desiccators were prepared with RH60-80 cycle (wet-dry cycle) of 30 minutes, 1 hour, 2 hours and 4 hours to determine the degree of carbonation promotion according to periodic humidity changes. The degree of carbonation of HCPWs were measured by thermogravimetric analysis (TGA). The result shows that the degree of carbonation was improved as the water-cement ratio increased, because the higher the water-to-cement ratio, the more open pores were contained. In addition, vaterite and aragonite caused by the decomposition of C-S-H were the most produced under RH60-80 cycle conditions. This is considered to be because the reaction area with CO2 was increased by weakening the C-S-H by repeating drying and wetting.

  Abstract
  One of the global environmental problems, CO2 emissions from cement production intensifies in these decades. To solve this problem, countermeasures for CO2 emissions using [...]

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• Evaluate the Ability to Determine the Carbonation Depth of Concrete by Hyperspectral Imaging

  Y. Wang, D. Oh, R. Kitagaki

  DBMC 2023.

  
  

  Abstract

  In recent years, using concrete to absorb CO2 in the atmosphere has attracted attention as one of the global warming countermeasures. In general, destructive methods have been used to evaluate the amount of CO2 absorption in concrete buildings and civil engineering structures. However, it needs to sample a portion of the concrete, and it is impractical to conduct continuous disruptive sampling of the structures in use. Therefore, it is necessary to develop non-destructive tests to evaluate the amount of CO2 absorption in concrete. In this study, Multi-spectral imaging, which are the methods of non-destructive tests, were used to visualize the presence of calcium carbonate with depth-axis from surface of the concrete specimen which have been the preliminary drilled holes. In addition, moistened cotton swabs were used to extract the pore solution by pressing the inner wall of the hole and to test it for determination of the distribution of pH with depth. The results indicate that Multi-spectral imaging can evaluate different carbonation depths of concrete samples. Moreover, PH of each point examined in the specimens can evaluate as the depth distribution of calcium carbonate. Results were compared and discussed with each other depending on each methodological characteristic.

  Abstract
  In recent years, using concrete to absorb CO2 in the atmosphere has attracted attention as one of the global warming countermeasures. In general, destructive methods have [...]

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• Effects of Multi-scale Siliceous additives on Hydration and Microstructure of Hardened Cement Pastes

  X. Zhang, Y. Zhang, J. Zeng, K. Wu

  DBMC 2023.

  
  

  Abstract

  Siliceous materials are commonly used in concrete with physical filling and higher pozzolanic reactivity, such as silica fume (SF) and nano-silica (NS). Investigations were conducted into the effects of SF, hydrophobic silica fume (HSF), and synthesized NS on the mechanical properties and microscopic characteristics of hardened cement pastes (HCPs). The surface of silica fume was hydrophobically modified using isooctyltriethoxysilane. Fourier infrared spectrometer (FTIR), X-ray diffractometer (XRD), and energy spectrometer (EDS) were used to evaluate the hydration, while mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) were used to analyze the pore structure and microscopic morphology of HCPs. The results demonstrated that HSF has better dispersion in cement pore solution. The addition of HSF exhibits the higher pozzolanic reactivity, weakens CH diffraction peaks, generates higher levels Q3 C-S-H gels, and significantly lowers the Ca/Si ratio of C-S-H gels. Due to the hydrophobicity, HSF increases the volume of micro-pores in range of 10-100 nm, resulting in a decrease in strength. Compounding HSF and NS further weakens the CH diffraction peak, decreases the Ca/Si ratio of C-S-H gels, and reduces the micro-pore volume to refines the pore structure.

  Abstract
  Siliceous materials are commonly used in concrete with physical filling and higher pozzolanic reactivity, such as silica fume (SF) and nano-silica (NS). Investigations were [...]

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• Effect of Sulfate Attack on Compressive Strength of Foamed Cement Paste under Static Cyclic Loading

  Y. Guanbao, X. Yiling, Z. Zhen, S. Honghui

  DBMC 2023.

  
  

  Abstract

  Foamed cement paste has been increasingly used as backfill material in roadways and railway embankments due to its advantages of adjustable density and strength. The embankments constructed by foamed cement paste in coastal regions is subjected to both traffic loading and chemical erosion in service life. This paper conducted a series of durability tests to investigate the reduction of static and dynamic strength of foamed cement paste after the specimens were immersed in sodium sulfate solutions.The specimens were prepared with densities of 800 and 900 kg/m3. The influence factors of specimen density, concentration and cation type of sulfate solution on the strength degradation of the specimens were discussed. The results showed that the corrosion resistant coefficient of the specimens was reduced with the increase of immersion time and concentration of sodium sulfate solution. The degradation of the compressive strength under cyclic loading is more serious than that under static loading. The high density specimens perform better durability than low-density specimens, as the specimens with 900 kg/m3 under 28 and 56 days of sulfate attack had smaller reduction in both dynamic and static strengths than the specimens with 800 kg/m3.

  Abstract
  Foamed cement paste has been increasingly used as backfill material in roadways and railway embankments due to its advantages of adjustable density and strength. The embankments [...]

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• Effect of Endogenous Chloride Ion on Corrosion of Rebar in Sea-sand Ultra-high Performance Concrete

  H. Lian, H. Wei, C. Zhendong, C. Rong, W. Jiangang, C. Baochun

  DBMC 2023.

  
  

  Abstract

  Ultra-high performance concrete (UHPC) is an innovative cement-based composite material characterized by extremely high durability and mechanical properties, which provides a potential possibility of using non-desalted sea-sand as aggregate. However, the long-term steel corrosion behavior in UHPC prepared by simulated sea-sand under different immersion environments remains unclear. In this study, the pore structure of sea-sand UHPC matrix was measured using nitrogen adsorption/desorption method. The corrosion behavior of rebar in sea-sand UHPC with different endogenous chloride ion contents soaking in pure water and NaCl solution was characterized by electrochemical workstation. The experimental results show that the initial UHPC pore structure is refined by incorporation ofsea-sand, and is similar to that of ordinary UHPC at the later hydration. Regardless of the endogenous chloride ion content and immersion environment, the corrosion rate evaluated by corrosion current density (icorr) and polarization resistance (Rp) of reinforcement in UHPC is extremely low. The measurement of EIS shows that UHPC group has higher matrix resistance (Rc) and charge transfer resistance (Rct), while lower electric double layer capacitance (CPEdl) of reinforcement, which indicates that the steel in UHPC made of sea-sand is still in a state ofpassivation. However, the steel bar in comparison specimen OPC soaking in NaCl solution is in the corrosion stage. Furthermore, sea-sand UHPC possesses of excellent ability of anti- pitting corrosion ofreinforcement after 180 days ofimmersion in NaCl solution.

  Abstract
  Ultra-high performance concrete (UHPC) is an innovative cement-based composite material characterized by extremely high durability and mechanical properties, which provides [...]

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