Documents published in Scipedia

• 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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• Carbonation of Concrete Cured Under Different Conditions

  O. Kolawole A., A. Nafisat M.

  DBMC 2023.

  
  

  Abstract

  Concrete is cured under different conditions to preserve the moist state of the concrete matrix for continuous hydration as it is done on most construction sites. In this study, the effect of different curing techniques on the carbonation depth of concrete mix is presented. Concrete matrix of mix ratio 1 :2 :4 with a water-cement ratio of 0.5 was prepared and cast into cubes of sizes 150 mm. After 24 hours, the concrete cubes were removed from moulds and cured using different techniques for 3, 7, 28, 56, and 91 days. Thereafter, the compressive strength of the concrete cubes and carbonation depths were determined for each curing day. The curing techniques investigated were immersion in water (IM), sprinkling (SP), polyethylene membrane (PM), damp sand (DS), indoor (OI), outdoor (OT), and saturated wet covering (SWC). The results indicated that carbonation depth differed with each of the concrete cured in different techniques. It was observed that concrete exposed outside was worst affected by carbonation followed by those cured indoor, while those cured with polythene showed the least carbonation depth. It was concluded that the polythene membrane curing technique was the best curing technique to limit the effect of carbonation of concrete.

  Abstract
  Concrete is cured under different conditions to preserve the moist state of the concrete matrix for continuous hydration as it is done on most construction sites. In this [...]

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• Biomimetic Organic-Inorganic Hybrid Magnesium Oxychloride Cement as Green Adhesive for Biomimetic Organic-Inorganic Hybrid Magnesium Oxychloride Cement as Green Adhesive for Wood Industry

  H. Yufei, K. Xiangming

  DBMC 2023.

  
  

  Abstract

  Benefiting from the negative carbon footprint of wood, wood composites have been considered as eco-friendly alternative building materials. However, adhesives for bonding wood components are mainly formaldehyde-based resins, which are highly combustible and continuously release volatile hazardous substances during service. Therefore, the development of magnesium oxychloride cement (MOC) as wood adhesive is highly compliant with environmental regulations and green material requirements. Unfortunately, the extensive application of MOC adhesive is hindered by poor water resistance and weak interfacial interaction with wood. Herein, an oyster-inspired organic-inorganic hybrid strategy was proposed to develop MOC with high adhesion strength and excellent water resistance. Specifically, the renewable chitosan (CS) and tartaric acid (TA) were selected as organic reinforcing constituents to construct a dense double chelating network in MOC, which induced the structural regulation at the bonding interface, thus enhancing the cohesion strength and interfacial properties. Thanks to the biomimetic organic-inorganic hybrid structure, the dry and wet shear strength of the MOC-CS-TA reached 3.08 MPa and 1.77 MPa, making increases of 27.27% and 53.91% compared to the control sample, respectively. Meanwhile, the MOC-CS-TA adhesive presented excellent flame-retardant properties compared with urea-formaldehyde resin adhesives and soy protein adhesives. The design path presented here provides workable guidance for the preparation of eco-friendly cementitious materials and green wood composites in further applications.

  Abstract
  Benefiting from the negative carbon footprint of wood, wood composites have been considered as eco-friendly alternative building materials. However, adhesives for bonding [...]

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