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المؤلفون: Lianjun Chen, Guoming Liu, Zhaoxia Liu, Guanguo Ma
المصدر: Construction and Building Materials. 225:311-323
مصطلحات موضوعية: Flow resistance, Materials science, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, Shotcrete, 0201 civil engineering, Shock (mechanics), Shear (sheet metal), Slump, Rheology, 021105 building & construction, Air content, General Materials Science, Composite material, Civil and Structural Engineering
الوصف: Wet-mix shotcrete mainly includes two processes: pumping and spraying. In this study, to explore the effects of the pumping and spraying processes on the rheological properties and air content of concrete, a full-scale experimental system of wet-mix shotcrete was developed with the given work parameters of these processes. The rheological parameters, slump, and air content of the fresh concrete were measured before pumping, after pumping, and after spraying, respectively. In general, the air content decreased after pumping, whereas the flow resistance declined after pumping and then increased after spraying. These changes were linked to the shear and shock caused by the pumping or spraying process. Under the interference of the pumping and spraying processes, prediction models of the changes in concrete properties were developed. Finally, a one-way analysis of variance (ANOVA) was conducted to analyze the degree of influence of the pumping and spraying processes on concrete properties. This work could be beneficial for further improvement of the understanding of the overall wet-mix shotcrete material and processes.
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المؤلفون: Marienne do Rocio de Mello Maron da Costa, Laila Valduga Artigas, Carlos Roberto Sanquetta, Leidimara Aparecida Martins, José de Almendra Freitas
المصدر: Construction and Building Materials. 225:496-501
مصطلحات موضوعية: Waste management, Carbonation, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, engineering.material, 0201 civil engineering, law.invention, Portland cement, chemistry.chemical_compound, Construction industry, chemistry, law, Greenhouse gas, 021105 building & construction, engineering, Environmental science, Carbonate, General Materials Science, Mortar, Civil and Structural Engineering, Lime
الوصف: Lime is an aerial binder that requires the absorption of CO2 to harden from the carbonation process. It is difficult to establish how much carbonate and how fast it occurs. Even Portland cement undergoes carbonation after hardening. The best understanding of this reaction is relevant for the construction industry, within the current context of greenhouse gas (GHG) emissions control. This work collaborates with the purpose of evaluating the evolution of the carbonation phenomenon in mixed lime and Portland cement mortars. The correct evaluation of how much CO2 is absorbed will allow a more precise adjustment of the GHG emissions reports.
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المؤلفون: Yu Song, Baoguo Liu, Darui Ren, Jinglai Sun, Bokai Liu, Zhengjie Lin
المصدر: Construction and Building Materials. 224:359-371
مصطلحات موضوعية: Physics, Three point flexural test, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, Fractal dimension, 0201 civil engineering, k-nearest neighbors algorithm, Exponential function, Acoustic emission, 021105 building & construction, Log-normal distribution, Fracture (geology), General Materials Science, Statistical physics, Civil and Structural Engineering, Event (probability theory)
الوصف: Three-point-bending tests on notched concrete beams were performed with real-time AE (acoustic emission) monitoring. Based on the nearest neighbor theory modified from seismology, the minimum interevent distance ηj* for every AE event is calculated. The b-value and space fractal dimension are computed to further explore the parameter ηj*. The experimental results indicate that ηj* values for AE data from three-point-bending tests show a mixed distribution of background and clustered events, similar to earthquakes induced by fluids, and are considered to be due to the formation of a single main fracture under this loading condition. The real-time difference and real-time interval for every nearest event pair are similar to the lognormal and exponential distributions, respectively. According to ηj* combined with the spatial distribution of AE events, ηj* is negatively correlated with the fracture trace, which means that AE events with smaller ηj* values are closer to the trace. Analyses of b-values and spatial fractal dimensions illustrate ηj*’s ability to smooth the variation curves of these two parameters and clarify their change rules. These observations confirm that ηj* is a useful index for illustrating the interevent characteristics of AE data and has significance for analyzing the fracture mechanisms of concrete materials.
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المؤلفون: Bitrus Emmanuel Achara, Mohd Shahir Liew, Bashar S. Mohammed
المصدر: Construction and Building Materials. 224:796-814
مصطلحات موضوعية: Materials science, Bond strength, Engineered cementitious composite, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, engineering.material, Steel bar, 0201 civil engineering, Matrix (mathematics), 021105 building & construction, Nano, engineering, General Materials Science, Response surface methodology, Composite material, Bond energy, Reinforcement, Civil and Structural Engineering
الوصف: This paper analyses the bond behaviour of steel reinforcement bars in the matrix of nano-silica (NS)-modified self-consolidating engineered cementitious composites (SC-ECC). Presented first is the results of pull-out tests performed on three different diameters (12 mm, 16 mm, 20 mm) sizes of reinforcing steel bar embedded in the matrix. Subsequently, the results of the experiment are used in identifying the bond-slip relationship which explains the interactions between steel bars and matrix. A response surface methodology is applied to develop predictive models which are used to perform multi-objective optimization on bond-slip properties such as bond energy, bond slip and bond strength. Lastly, the experimental and predicted results obtained demonstrate that the developed models are suitable for the interpretation of the bond behaviour of steel bars embedded in the NS-modified cementitious matrix.
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المؤلفون: Antonia Moropoulou, Eleni Aggelakopoulou, Asterios Bakolas
المصدر: Construction and Building Materials. 225:633-641
مصطلحات موضوعية: Materials science, Carbonation, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, engineering.material, 0201 civil engineering, Compressive strength, Putty, 021105 building & construction, engineering, General Materials Science, Composite material, Mortar, Porosity, Curing (chemistry), Civil and Structural Engineering, Shrinkage, Lime
الوصف: The aim of this work is to study the influence of calcium hydrated lime (lime putty or hydrated lime powder) to the chemical and physico-mechanical characteristics of lime mortars. The mortars were designed with the same mixing ratio of lime/aggregates and evaluated till 18 months of curing. The carbonation rate is evaluated via DTA/TG, the pore structure by mercury intrusion porosimetry and the hygric properties via capillary rise and water immersion tests. Mortars’ shrinkage and apparent density were also measured along with mechanical strength and static and dynamic modulus of elasticity that were evaluated by using conventional mechanical tests and ultrasonic technique. The obtained results revealed that lime powder mortars present a higher carbonation rate and higher values of compressive strength compared to lime putty mortars. Lime powder mortars also exhibit a unimodal pore size distribution (while lime putty mortars present a bimodal one) and higher capillary rise coefficient and porosity accessible to water in respect to lime putty mortars.
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المؤلفون: Hassan Baaj, Eskedil Melese, Tim Smith, Steve Zupko, Susan L. Tighe
المصدر: Construction and Building Materials. 226:778-792
مصطلحات موضوعية: 0211 other engineering and technologies, 020101 civil engineering, Young's modulus, 02 engineering and technology, 12. Responsible consumption, 0201 civil engineering, law.invention, symbols.namesake, law, 021105 building & construction, Ultimate tensile strength, medicine, General Materials Science, Geotechnical engineering, Civil and Structural Engineering, Cement, Stiffness, Building and Construction, Durability, 6. Clean water, Portland cement, Compressive strength, symbols, Environmental science, Cementitious, medicine.symptom
الوصف: Hydraulic road binders (HRB) are factory made blends which are composed of a substantial amount of supplementary cementitious materials and portland cement. Previous studies indicated that the use of chemical stabilizers containing supplementary cementious materials is a sustainable approach that can reduce carbon dioxide (CO2) emission by 5−25%. Thus, the use of HRB in full-depth reclamation process could make the practice more sustainable if strength, stiffness, and durability of treated materials are not compromised. The primary objective of this study is to evaluate the mechanical properties of full-depth reclaimed pavement materials treated with hydraulic road binders. The study was conducted in the form of comparative assessment by using full-depth reclaimed pavement materials treated with General Use (GU) cement as a control mix. For this study, three types of full-depth reclaimed pavement materials and four types of cementitious binders, including GU cement, were used to make eleven different types of mixes. Unconfined compressive strength, modulus of elasticity, and indirect tensile strength tests were used to assess the mechanical properties of the eleven mixes. The test results indicated that hydraulic road binders could provide equivalent strength and stiffness as GU cement. The study also revealed the HRB content, required to attain equivalent strength and stiffness as GU mixes, is the same or less than GU cement content. Based on the study findings, hydraulic road binders can be sustainable alternative binders that can replace GU cement in full-depth reclamation process without compromising the structural function of the treated layer.
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المؤلفون: Raed Tawadrous, Eliya Henin, George Morcous
المصدر: Construction and Building Materials. 226:449-458
مصطلحات موضوعية: chemistry.chemical_classification, Materials science, Bond strength, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, Polymer, engineering.material, Reinforced concrete, Durability, Surface conditions, 0201 civil engineering, Flexural strength, chemistry, Coating, Basalt fiber, 021105 building & construction, engineering, General Materials Science, Composite material, Civil and Structural Engineering
الوصف: Basalt fiber reinforced polymer (BFRP) bars are used in reinforced concrete structures as an alternative to conventional mild steel bars due to their excellent strength and durability properties. The bond of BFRP bars with concrete is a critical design criterion for both flexural strength and crack control. In this paper, the effect of two surface conditions (primary sand coating and secondary sand coating) on the bond of BFRP bars is evaluated experimentally in three investigations: first, twelve pull-out specimens (six specimens for each surface condition) are tested to determine the bond strength; second, eleven beams (three beams with primary sand coated BFRP bars, three beams with secondary sand coated BFRP bars, three beams with bundled BFRP bars, and two beams with mild steel bars) are tested to determine the bond-dependent coefficient (kb) of different surface conditions compared to that of deformed steel bars; third, eleven beams are tested in flexure to determine the ultimate flexural strength and failure modes of beams with different surface conditions and reinforcement ratios. It was observed that the surface condition of BFRP bars has significant effect on bond strength, kb, and flexural strength. Test results are compared to those predicted using ACI 440-15 and ISIS 2007, which found to be conservative.
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المؤلفون: Cristina Benavides-Reyes, Rosa Maria García Sánchez, Kerstin Elert, Fátima Linares Ordóñez
المصدر: Construction and Building Materials. 226:625-635
مصطلحات موضوعية: Calcite, Materials science, Carbonation, Metallurgy, 0211 other engineering and technologies, 020101 civil engineering, Weathering, 02 engineering and technology, Building and Construction, Animal glue, engineering.material, complex mixtures, 0201 civil engineering, Matrix (geology), chemistry.chemical_compound, chemistry, Color changes, 021105 building & construction, engineering, Substrate (aquarium), General Materials Science, Civil and Structural Engineering, Lime
الوصف: In order to optimize lime plasters for conservation purposes, the influence of animal glue on the mineralogical evolution, mechanical properties, and weathering resistance was studied. The organic additive caused a decrease in carbonation rate and affected mechanical properties negatively, facilitating the formation of large air bubbles in the plaster matrix. However, the weathering resistance (water spraying/SO2 exposure) improved significantly. The organic additive also reduced crack formation and formed a physical barrier around the calcite crystals, which delayed sulfation. Lime-based composite materials are a valuable alternative to conventional lime plasters, showing improved adherence to the substrate and no significant color changes.
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المؤلفون: Faning Dang, Lin Zhu, Weihua Ding, Yi Xue, Le Zhang
المصدر: Construction and Building Materials. 224:534-550
مصطلحات موضوعية: Materials science, business.industry, Gaussian, Static compression, 0211 other engineering and technologies, 020101 civil engineering, Pattern recognition, 02 engineering and technology, Building and Construction, Laplace distribution, 0201 civil engineering, Gray level, symbols.namesake, X ray computed, 021105 building & construction, Homogeneity (physics), symbols, Grey level, General Materials Science, Tomography, Artificial intelligence, business, Civil and Structural Engineering
الوصف: Concrete CT test is an effective method used to analyze micro-structural damage evolution of concrete under loading condition. In the CT images of different stress states in the same section, gray value changes in the original number matrix of CT image are the key to investigate microscopic damage evolution of concrete. However, the slight changes in the gray value of CT images before peak stress cannot be intuitively observed with the naked eye. This study mainly aims to develop a coupled method based on statistical method and X-ray CT to extract indicators of such subtle changes. Different cross-sectional CT images of concrete at different stress stages were obtained by uniaxial static compression CT test. The theory of the grey level co-occurrence matrices (GLCM) was then adopted to analyze micro-damage evolution and crack properties. That is, the GLCM of the CT images were calculated, and four statistical features including contrast, energy, correlation, and homogeneity were extracted, which can be extended into quantitative analysis of micro-damage hidden in the CT images of concrete. Results exhibited that the damage growth area, concentrating between the 45th and 225th concrete cross-section, could be predicted by the distribution of four statistical features (i.e., contrast, energy, correlation and homogeneity) at the fourth scan, and it is consistent with the crack location in the fifth scan. The contrast, energy and homogeneity follow the Gaussian distribution under five scan stages, and the correlation follows the Laplace distribution. In addition, the changes of bandwidth in color heat map illustrating the GLCM before and after specimen failure show that the bandwidth is positively correlated with micro-structural damage of concrete specimen.
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المؤلفون: Tuan-Kiet Tran, Duy-Liem Nguyen, Tri-Thong Nguyen, Duc-Kien Thai, Tri Thuong Ngo
المصدر: Construction and Building Materials. 226:743-758
مصطلحات موضوعية: Materials science, Weibull modulus, 0211 other engineering and technologies, 020101 civil engineering, 02 engineering and technology, Building and Construction, Fiber-reinforced concrete, Bending, Compression (physics), 0201 civil engineering, law.invention, Brittleness, law, 021105 building & construction, Cylinder, General Materials Science, Fiber, Cube, Composite material, Civil and Structural Engineering
الوصف: The Weibull modulus, a material parameter describing the size effect of brittle material, of high-performance fiber-reinforced concretes (HPFRCs) was investigated under compression and flexure. The compressive specimens were as follows: 70.7 × 70.7 × 70.7 mm (cube), 100 × 100 × 100 mm (cube), 150 × 150 × 150 mm (cube), O100 × 200 mm (cylinder), O150 × 300 mm (cylinder). The bending specimens were as follows: 40 × 40 × 120 mm, 100 × 100 × 300 mm and 150 × 150 × 450 mm. For each size or shape, two HPFRCs having different fiber content were examined as follows: HPFRC1 having no fiber and HPFRC2 containing 1.0% macro hooked fibers blended with 0.5% micro smooth fibers by volume. There was a clear size effect on the compressive and bending parameters for both the investigated HPFRCs. The derived Weibull modulus of the investigated HPFRCs for the mechanical parameters varied from 1.33 to 8.74. Furthermore, the correlation between the bending and compressive strengths of the two HPFRCs and their conversion factors for various sizes and shapes of the compressive specimens were explored.
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