•With a FA/binder of 80%, Grade 45 green concrete for structural use is developed.•Adequate workability is maintained in green concrete for normal construction.•Adding a small amount of SF can ...improve both mechanical and sorptivity performance.•FA replacement level (FA/b ≤80%) has no obvious effect on FA cementing efficiency.•Green concrete shows obvious superiority in environmental impact and material cost.
Using a high dosage of fly ash in concrete is an effective approach to control the heat release rate, reduce the material cost and enhance the sustainability. However, ultrahigh-volume fly ash (UHVFA) concrete, with fly ash replacing over 60% of the binder by weight, often exhibits low compressive strength at an early stage, which limits the material to non-structural or semi-structural applications. Though different approaches have been proposed to increase the strength, the efficacy of some of the methods is debatable, because of the high energy consumption and/or low cost-benefit ratio. This study aims to increase the compressive strength of UHVFA concrete by the simple and practical method of reducing the water/binder ratio while adding super-plasticizers to maintain workability. Mortar samples were used to explore the influence of silica fume, and Portland cement was replaced with fly ash at five different percentages (20%, 40%, 60%, 80% and 98%). Mechanical properties up to 360-day age were recorded, and the cementing efficiency factor of the fly ash was studied. With a suitable mix proportion, even with 80% of the binder replaced by fly ash, the compressive strength of the mortar and concrete can reach over 40MPa at 7-day age, and over 60MPa at 28-day age. Compared to commercial Grade 45 concrete, the proposed green structural concrete shows a reduction in CO2 emission of around 70%, a reduction in embodied energy of more than 60%, and a reduction in material cost of 15%.
This study develops a novel graphene oxide (GO) coated polyethylene (PE) fiber (GO/PE fiber) by simply mixing PE fibers in GO aqueous solution at a certain temperature. The experimental results ...indicate that due to the different thermal expansion behavior, the shrinkage of GO at a higher temperature facilitates the formation of a 3D cover around the surface of PE fiber. This would increase the surface wettability, roughness and chemical reactivity of PE fiber, making it much easier for GO/PE fiber to physically and chemically interact with cement hydrates. Compared with the control strain-hardening cementitious composites (SHCC) with pristine PE fiber (2.0 vol%), the use of GO/PE fiber can improve the tensile strength and strain capacity of SHCC by 46.3% and 70.4%, without compromising the compressive strength, and the average crack opening width can be reduced from 138 μm to 58 μm. The remarkable enhancement in the mechanical properties of SHCC is due to the strengthened PE fiber/matrix bond by adding GO, which is further confirmed by results from the aligned single fiber pull out test, showing the increase of interfacial friction from 2.33 MPa to 3.99 MPa. Finally, a micromechanical model is adopted to explain the mechanism behind the improvement of the strain hardening behavior. In conclusion, the research findings provide an effective strategy to functionalize the surface properties of PE fiber by GO coating and to achieve a stronger bond at the fiber/matrix interface, leading to the development of a novel high strength SHCC with tensile strain capacity up to 6%.
As the cracking mode (tensile or shear) of a crack is related to the underlying physical mechanisms, crack mode classification is a very useful method to identify the damage state of a structure for ...proper maintenance to enhance structural safety and durability. Acoustic Emission (AE) is a passive structural health monitoring technique based on the stress wave generated due to cracking in a structure. A framework has been designed in this study for automated probabilistic classification of the cracks in cementitious components based on the AE signals. With this approach, unlabeled hand designed waveform parameters, i.e. RA values (RA) and Average frequency (AF) are clustered using density dictated unsupervised clustering algorithm. Intersecting clusters in the data were then separated through a hyperplane created using Support Vector Machine (SVM) algorithm. Based on physical insight obtained from labeled data, unlabeled data was classified into events corresponding to different cracking modes. The framework was applied to the analysis of AE data from Steel Fiber Reinforced Concrete (SFRC) beam under bending and Strain Hardening Cementitious Composite (SHCC) samples under direct tension. The cracking modes obtained from the proposed machine learning approach are found to be in good agreement with expectations based on composite theory. With good qualitative prediction, the proposed approach shows promise for the prediction of damage state in structures based on unlabeled data obtained in the field.
•Hybrid-fiber SHCC with PVA/steel fibers at a fixed total fiber fraction were studied.•HySHCC showed improved crack control, elastic modulus, compressive strength and flexural toughness.•Finite ...element analysis satisfactorily reproduced static three-point bending performance.•Partially replacing PVA fiber by steel fiber reduced the material cost but increased the environmental impact.•A new insight on selection of fiber-reinforced cementitious composites for structural applications was offered.
Recently, hybridizing fibers with distinct properties in cementitious materials has gained much attention due to their advantage over single-type fiber reinforcements. However, for Strain-Hardening Cementitious Composites (SHCC), most existing studies only compared hybrid-fiber SHCC (HySHCC) with conventional concrete or introduced additional steel fibers into mono-fiber SHCC, rather than keeping the total fiber dosage constant to show the positive synergetic effect. This study aims to explore the benefits of using hybrid steel/polyvinyl alcohol (PVA) fibers in SHCC with a fixed total fiber dosage of 2.5 vol% by evaluating the mechanical, economic and environmental potentials. The mechanical performance of HySHCC was comprehensively tested under compression, tension, static three-point bending and cyclic four-point bending. The crack pattern under uniaxial tension was digitally captured, and the static three-point bending performance was numerically simulated using a finite element method. While HySHCC generally showed slightly lower ultimate tensile strain and higher environmental impacts than PVA-SHCC, the crack control ability, compressive strength, modulus of elasticity and flexural toughness were superior. The findings of this study offer a new insight on the design and selection of fiber-reinforced cementitious composites for structural applications.
•This study explores using SHCC to repair RC members with severely corroded rebars.•14-Day high-strength SHCC has tensile strength of 10 MPa and strain capacity over 2%.•SHCC patch can fully recover ...the load-carrying capacity of the rebar with reduced area.•The proposed repair method is more efficient and less costly than conventional approach.
Steel corrosion is a major cause of deterioration for reinforced concrete structures, leading to significant area loss of rebars that affects structural safety. The most common repair approach is to splice additional reinforcements to the corroded rebars, which is time consuming and costly, as a large volume of sound concrete beyond the corroded part must be removed to provide sufficient lap lengths. The present study explores a new repair technique using high strength Strain-Hardening Cementitious Composites (SHCC) in the aforementioned situation. With SHCC compensating for the area loss of rebars, splicing additional reinforcements or removing a large amount of concrete is not necessary. In this paper, the design of high strength SHCC was first discussed. Then, rebars with reduced area were embedded inside SHCC blocks and tested under direct tension. Further, beams containing rebars with reduced area and patched with SHCC were tested under four-point bending. The test results at different scales verify the feasibility of the proposed repair technique which is more efficient and less costly. The findings of this study can support future repair applications using SHCC.
Analysis of retinal nerve fiber layer (RNFL) abnormalities with optical coherence tomography in eyes with high myopia has been complicated by high rates of false-positive errors. An understanding of ...whether the application of a myopic normative database can improve the specificity for detection of RNFL abnormalities in eyes with high myopia is relevant.
To evaluate the diagnostic performance of a myopic normative database for detection of RNFL abnormalities in eyes with high myopia (spherical equivalent, -6.0 diopters D or less).
In this cross-sectional study, 180 eyes with high myopia (mean SD spherical equivalent, -8.0 1.8 D) from 180 healthy individuals were included in the myopic normative database. Another 46 eyes with high myopia from healthy individuals (mean SD spherical equivalent, -8.1 1.8 D) and 74 eyes from patients with high myopia and glaucoma (mean SD spherical equivalent, -8.3 1.9 D) were included for evaluation of specificity and sensitivity. The 95th and 99th percentiles of the mean and clock-hour circumpapillary RNFL thicknesses and the individual superpixel thicknesses of the RNFL thickness map measured by spectral-domain optical coherence tomography were calculated from the 180 eyes with high myopia. Participants were recruited from January 2, 2013, to December 30, 2015. The following 6 criteria of RNFL abnormalities were examined: (1) mean circumpapillary RNFL thickness below the lower 95th or (2) the lower 99th percentile; (3) one clock-hour or more for RNFL thickness below the lower 95th or (4) the lower 99th percentile; and (5) twenty contiguous superpixels or more of RNFL thickness in the RNFL thickness map below the lower 95th or (6) the lower 99th percentile.
Specificities and sensitivities for detection of RNFL abnormalities.
Of the 46 healthy eyes and 74 eyes with glaucoma studied (from 39 men and 38 women), the myopic normative database showed a higher specificity (63.0%-100%) than did the built-in normative database of the optical coherence tomography instrument (8.7%-87.0%) for detection of RNFL abnormalities across all the criteria examined (differences in specificities between 13.0% 95% CI, 1.1%-24.9%; P = .01 and 54.3% 95% CI, 37.8%-70.9%; P < .001) except for the criterion of mean RNFL thickness below the lower 99th percentile, in which both normative databases had the same specificities (100%) but the myopic normative database exhibited a higher sensitivity (71.6% vs 86.5%; difference in sensitivities, 14.9% 95% CI, 4.6%-25.1%; P = .002).
The application of a myopic normative database improved the specificity without compromising the sensitivity compared with the optical coherence tomography instrument's built-in normative database for detection of RNFL abnormalities in eyes with high myopia. Inclusion of myopic normative databases should be considered in optical coherence tomography instruments.
•The bonding between PVA fiber and cement can be improved by GO addition.•Mechanical behavior of SHCCs can be improved by a moderate amount of GO.•Excessive GO addition has a negative effect on the ...mechanical behavior of SHCCs.
Graphene oxide (GO) is an attractive nanomaterial in reinforcing cementitious materials due to the excellent mechanical properties. This paper presents the effect of GO on the mechanical behavior of Strain Hardening Cementitious Composites (SHCCs), including mechanical performance under compression, tension and flexure. In this study, GO was firstly synthetized by the modified Hummers’ method, and then the SHCCs with different GO content of 0.05wt%, 0.08wt% and 0.12wt% were fabricated. It was found that compared with normal SHCC, the GO reinforced SHCCs show an obvious improvement in mechanical behavior. The addition of 0.08wt% GO leads to 24.8% increase in compressive strength, 37.7% increase in tensile strength, 80.6% increase in flexural strength and 105% increase in flexural toughness, respectively. The improved mechanical behavior of the GO reinforced SHCCs is attributed to the enhanced matrix strength as well as the chemical bonding between the polyvinyl alcohol (PVA fiber) and the cement matrix by GO addition. However, too much GO will cause PVA fiber rupture before being pulled-out from the matrix and should be avoided in the material design.
Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, ...which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry.
Seawater sea-sand Engineered Cementitious Composites (SS-ECC) is a new version of ECC for marine constructions facing the scarcity of freshwater and river/manufactured sand. This study aims to assess ...and model the crack characteristics of SS-ECC, which are critical for its applications with non-corrosive reinforcements. The influence of sea-sand size, fiber length and fiber dosage on the crack characteristics of SS-ECC was explored. A five-dimensional representation was proposed to assess the overall performance of SS-ECC, by comprehensively considering both the crack characteristics (i.e., crack width and its variation) and the mechanical properties (i.e., compressive and tensile properties). A probabilistic model was also proposed to describe the stochastic nature and evolution of crack width, and it can be used to estimate the critical tensile strain on SS-ECC for a given crack-width limit and cumulative probability. The findings and proposed methods can facilitate the design of SS-ECC in marine and coastal structures.
•A probabilistic model was proposed to model the crack width evolution of SS-ECC at different strain levels.•The Weibull distribution fit the crack width distribution better than the log-normal distribution.•A 5-D representation was proposed to assess the SS-ECC by considering both cracking and mechanical performance.•Larger sea-sand size and lower fiber dosage led to larger crack widths in SS-ECC under the same tensile strain.•18-mm PE fiber led to larger crack widths in SS-ECC at strain >2%, due to a large fraction of fiber rupture.
Polyethylene (PE) fibers are widely used to develop high strength Strain-Hardening Cementitious Composites (SHCC). Unlike Polyvinyl Alcohol (PVA) fiber, which has relatively low tensile strength and ...strong bond with matrix, the high tensile strength of the PE fiber is not fully utilized in the system, due to the hydrophobic nature of the fibers. In this study, a promising fiber treatment method by using ozone and ozone-derived hydroxyl radicals is developed to modify the surface properties of PE fibers, aiming to improve the fiber/matrix interactions and then the tensile performance of resulting SHCC. Firstly, feasibility and mechanism of ozonation are revealed by competition kinetic technology, and the XPS results indicate that only hydroxyl groups can be introduced to the PE fiber by optimizing the ozone (O3) concentration and treating time, and surface roughness of the PE fiber is also increased due to the etch effect from ozonation. For the tensile performance of SHCC, compared to the composites with pristine fibers, PE fibers treated with O3 for 30 and 60 min can improve the ultimate tensile strain of SHCC by 1.3 and 2.5 times, respectively. This significant enhancement in deformation capacity of SHCC is attributed to the increased chemical bond and frictional bond after fiber treatment, as the results from single fiber pullout tests show that the fiber/matrix frictional bond is increased from 2.35 MPa (pristine PE) to 3.13 MPa (O3 (30 min)/PE) and 3.38 MPa (O3 (60 min)/PE). The research outcomes provide a novel way on surface treatment for PE fibers to improve the tensile performance of SHCC.
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