Search

• Effect of three TiO 2 incorporation methods on photocatalytic (PC) efficiency of ECC is studied. • Effect of three TiO 2 incorporation methods on mechanical properties of ECC is studied. • Porous microstructure promotes the PC efficiency by increasing the exposure surface of ECC. • Alkaline environment of ECC consumes nitrate acid and promotes PC reactions. Titanium dioxide (TiO 2) nanoparticles have been incorporated in concrete to impart photocatalytic (PC) properties, such as the self-cleaning and air purification functionalities, which are dependent on PC reactions near the exterior surfaces of the concrete exposed to light. This study experimentally investigates the effect of three TiO 2 incorporation methods and surface patterns on the air-purifying functionality and mechanical properties of PC Engineered Cementitious Composites (PC-ECC). The air-purifying functionality was evaluated by measuring the nitrogen oxides (NO x) concentration change with the presence of PC-ECC plate specimens exposed to ultraviolet (UV) irradiation; uniaxial tensile and four-point bending tests were conducted to evaluate the tensile and flexural properties of the PC-ECC plates; scanning electron microscopy (SEM) was used to characterize the surface morphology of the plates; energy dispersive spectroscopy (EDS) was used to map the element distribution on the surface. Test results indicate that the amount of TiO 2 nanoparticles is reduced by 90% when TiO 2 is incorporated through a thin layer on the exterior surface of the ECC plate, while PC functionality and mechanical properties are retained. Incorporating TiO 2 through polyurethane coating reduces the NO x abatement efficiency by 70–80%, compared with directly mixing the TiO 2 nanoparticles in ECC. The reduced PC efficiency is attributed to the dense microstructure and low alkali content of the coating. This study advances the fundamental knowledge for designing functionally graded PC concrete with optimized PC efficiency and mechanical properties. [ABSTRACT FROM AUTHOR]

Highlights • 5% TiO 2 in ECC saturates air-purification ability while preserving tensile properties. • The optimized TiO 2 -doped ECC sustains a tensile strain capacity of 4.0%. • Alterations in tensile properties of ECC by TiO 2 are understood by micromechanics. • Both site effect and dilution effect are operative in ECC when TiO 2 is added. Abstract Engineered Cementitious Composites (ECC) provides a unique platform to develop high-performance and multifunctional construction materials with strain-hardening properties and exceptional crack control capability. ECC incorporating titanium dioxide (TiO 2) nanoparticles has intrinsically embodied photocatalytic properties, such as air-purifying functionality. However, there remains a lack of fundamental knowledge on how the presence of TiO 2 nanoparticles affects fiber/matrix interface and macro tensile properties of ECC. There is a need to establish a holistic understanding of the role of TiO 2 nanoparticles in ECC at multiple scales. To this end, this study experimentally investigates the effect of TiO 2 content (up to 15% of binder) on the fiber/matrix interface and on the tensile properties of ECC. A micromechanical model is used to link the multiscale material properties and interpret the test data of the TiO 2 -doped ECC. Results show that changes in the macroscopic tensile properties as a result of TiO 2 addition can be traced back to the matrix and fiber/matrix interface properties. The research findings provide insights into the underlying mechanisms of tensile property modifications by TiO 2 nanoparticles, as well as establishing a reference for the design of photocatalytic ECC for balanced functional and mechanical properties. [ABSTRACT FROM AUTHOR]

This paper investigates residual thermal and mechanical properties of high-performance fiber-reinforced cementitious composites (HPFRCCs) proportioned with high-volume fly ash after exposure to 200, 400, 600, and 800 °C. The investigated thermal and mechanical properties include the thermal conductivity, specific heat, compressive strength, tensile strength, tensile ductility, and density. The effects of five mix proportioning variables on the material properties are evaluated, which include the water-to-binder ratio (0.24–0.36 by mass), sand-to-binder ratio (0.36–0.66 by mass), fly ash content (60%–75% by mass), polyvinyl alcohol fiber content (1.5%–2.2% by volume), and superplasticizer content (0.10%–0.15% by mass). Experimental results reveal significant dependence of the residual thermal and mechanical properties on temperature and the mix proportion, which can be attributed to a series of chemical and physical reactions that occur at elevated temperatures. This study can facilitate optimization of mix proportions of HPFRCCs for enhanced thermal and mechanical performance in fire or high temperature applications. [ABSTRACT FROM AUTHOR]

The microstructure, impact resistance, pull-off adhesion strength, and corrosion resistances of duplex epoxy/enamel coating applied on steel plates are investigated experimentally. In comparison with those of individual epoxy and enamel coatings, the duplex coating has lower adhesion strength, higher impact resistance, higher short-term and long-term corrosion resistances both in 3.5 wt% NaCl solution and saturated Ca(OH) 2 solution with various chloride concentrations. This is because the outer epoxy fills the micro pores in the inner enamel. Impact induced damage significantly reduces the corrosion resistances of epoxy and duplex coatings but has little effect on the corrosion resistance of enamel coating. [ABSTRACT FROM AUTHOR]

Traditional methods for designing concrete materials typically rely on labor-intensive laboratory experiments, resulting in time and cost inefficiencies. Recently, designing concrete using artificial intelligence (AI) methods has shown high efficiency, but existing AI methods often rely solely on data, which can lead to violation with scientific principles and result in models lacking reasoning abilities. To overcome these challenges, this paper presents an interpretable knowledge graph-guided data-driven design approach. By integrating advanced computing techniques with domain knowledge via knowledge graphs, this approach enables the interpretation of data-driven models and uncovers the underlying mechanisms behind predictions. This approach is applied to ultra-high-performance concrete (UHPC) involving complex physicochemical reactions. The domain knowledge about UHPC is imparted using a knowledge graph, and UHPC properties are predicted using a machine learning model considering mixing proportions, processing methods, and physiochemical properties of materials via natural language processing. The results show that the knowledge graph displays crucial design variables and their effects on UHPC properties, aiding in selecting variables for machine learning models and interpreting their results. The prediction accuracy of the machine learning model reached 0.95. The research paves the way for more transparent and scientific AI models for material design and AI-enabled discovery of scientific knowledge. [Display omitted] ● An artificial intelligence (AI) approach is presented to design concrete with solid wastes. ● The AI approach achieves interpretability by combining machine learning and knowledge graph. ● Knowledge about the physicochemical reactions and properties of concrete is learned and used. ● The AI approach is applied to low-carbon cost-effective ultra-high-performance concrete. ● The AI approach can interpret the underlying mechanisms and generate new knowledge. [ABSTRACT FROM AUTHOR]

This paper presents a generative artificial intelligence (AI) approach to generate images of strain-hardening cementitious composite (SHCC) with complex crack patterns such as dense microcracks. This approach is developed to address the challenge of lacking data for training deep learning models used to automatically measure cracks in SHCC. The development of the approach is based on a framework which results in a hybrid generative adversarial network (HGAN) that seamlessly integrates a deep convolutional generative adversarial network (DCGAN) for generating images and a conditional generative adversarial network (CGAN) for labelling images. From the results, it was found that this approach provided high-quality labelled images automatically, and using these images significantly improved the accuracy of the deep learning models for measuring cracks in SHCC. The F1 score and Intersection Over Union (IOU) for crack segmentation reached 0.982 and 0.980, respectively. This approach will significantly promote crack measurement for SHCC materials and structures. [Display omitted] • A generative computer vision approach is developed for intelligent characterization of cracks. • Automatic generation and labelling of images with complex cracks are realized. • The artificial images with complex cracks are utilized to improve deep learning models. • The developed approach achieves high accuracy and high efficiency. • Dense microcracks in strain-hardening cementitious composites are successfully assessed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adding 1.0% pre-saturated biochar enhances the mechanical strength of UHPC. • Incorporating pre-saturated biochar efficiently reduces the autogenous shrinkage of UHPC. • Every 1 kg of biochar sequesters 1.30 kg of CO 2 equivalent emissions in UHPC. • Incorporating biochar into UHPC eliminates the heavy metal leaching possibility. This study presents the feasibility of utilizing wasted-derived biochar in ultra-high-performance concrete (UHPC) to alleviate autogenous shrinkage, mitigate environmental effects, and further improve mechanical strengths. Two types of wasted-derived biochar are investigated, including the fresh biochar from pyrolysis process of vetiver grass roots and the used biochar after purifying the contaminated water with heavy metals. The wasted-derived biochar is pre-saturated and then used to substitute the cement in UHPC. Experimental results showed that the 1 % of pre-saturated biochar in UHPC enhanced the mechanical strengths (up to 20 %) and toughness (up to 25 %) as well as reduced the autogenous shrinkage (up to 15 %). The underlying mechanisms of the property enhancement are the improved hydration degree of UHPC due to the internal curing effect. However, as non-negligible micro-defects, the utilization of over 1 % biochar reduced mechanical performance instead. Moreover, the sustainability analysis indicated the use of biochar can significantly reduce carbon emissions of UHPC. Specifically, every 1 kg biochar would reduce 1.30 kg CO 2 -eq emissions. In addition, the incorporation of used biochar in UHPC eliminated the possibility of heavy metal leaching. This study successfully proposed a carbon sequestering admixture and internal curing agent in UHPC production that also provides a new avenue for wasted-derived biochar recycling. [ABSTRACT FROM AUTHOR]

• The mixing kinetics of UHPC refers to the mixing torque evolution with mixing time. • Effects of temperature, volume, and mixing method on UHPC mixing kinetics are investigated. • A multi-batching method is presented to reduce peak mixing torque to facilitate large-scale UHPC production. • A mathematical model is developed and validated to describe mixing kinetics of UHPC. The mixing of ultra-high-performance concrete (UHPC) featuring low water-to-binder ratios involves different evolution of microstructures and mixing torques from conventional concrete. This paper investigates the mixing kinetics of UHPC in the mixing process, presents a mixing kinetics model to predict the mixing torque at an arbitrary time instant, and develops a multi-batching method to reduce the mixing torque for large-volume production of UHPC. The presented mixing kinetics model considers the effects of mixing temperature, mixing volume, and mixing methods. The mixing kinetics model is calibrated using experimental data, and the calibrated model shows high prediction accuracy. The multi-batching method enables large-volume mixing of UHPC by reducing the mixing torque while retaining desired flowability and hardened properties of UHPC. Specifically, when the number of sub-batches is two, the peak mixing torque of the multi-batching method was approximately reduced to half of the peak mixing torque of the mono-batching method. Besides, the differences in workability, compressive strength, and autogenous shrinkage by using the multi-batching method and mono-batching method are within 5%. Finally, the reliability and repeatability of the presented mixing kinetics model are verified through the validation tests with different UHPC mixture designs and mixing methods. This study will advance understandings of the mixing kinetics for UHPC and promote large-volume UHPC production. [ABSTRACT FROM AUTHOR]

The use of recycled plastics as modifiers for asphalt binder have gained attention in recent years. Studies have confirmed the enhancement in the rutting resistance of asphalt binder with the addition of these types of plastics, however there are controversies with regards to their long-term cracking performance. The long-term cracking performance of asphalt binder is directly influenced by their rheological properties. This study evaluated the fatigue performance of recycled High-Density Polyethylene (rHDPE) and recycled Polypropylene (rPP) modified asphalt binders using several rheological indices including the Superpave intermediate-temperature PG (G*sin δ), fatigue life (N f), complex modulus (G*), phase angle (δ), the Glover-Rowe (G-R) parameter, the crossover temperature (T δ =45°), the rheological index (R-value), the peak shear stress, failure strain and the yield energy, as well as a newly developed monotonic cracking index (MCI). Additionally, the influence of the process of mixing plastic with asphalt at high temperatures and shear rate on the cracking performance was also investigated. Results indicated that long term cracking performance were not consistent across all rheological indices. While N f indicated improved overall cracking performance with the addition of rHDPE and rPP, G*sin δ, G-R parameter, R-value, T δ =45°, and MCI indicated susceptibility to cracking with the addition of these recycled plastics. • Recycled HDPE and PP were assesed for their effects on asphalt binder cracking. • Long-term cracking performance varied across rheological indices. • LAS test showed improved fatigue life with rHDPE and rPP. • G*sin δ, G-R parameter, R-value, Tδ =45°, and MCI showed increased cracking susceptibility with these plastics. [ABSTRACT FROM AUTHOR]

With superior mechanical strength and durability, ultra-high-performance concrete (UHPC) is becoming an emerging material for resilient infrastructures. However, due to its high shrinkage, the high early-age cracking potential hinders its promotion. The expansive agent (EA) is therefore intensively used to reduce the shrinkage. However, the insufficient free water and dense microstructure of UHPC limit its expansion effect, thus affecting EA's capacity on shrinkage reduction and cracking control. To achieve the minimum cracking potential of UHPC, the CaO-type EA was prewet with mixing water before concrete batching. Results indicated that, after 45-min premix treatment, the 4% prewet EA compare to the 4% EA without prewet, shown: (1) increase in 3-day and 28-day splitting tensile strengths of UHPC by up to 10% and 5%; (2) reduction in 3-day and 28-day autogenous shrinkage of UHPC by around 20% and up to 30%; (3) reduction in the peak and cumulative cracking potential of UHPC by up to 30% and 25%. The prewet process of CaO-type EA was proven to efficiently increase the content of expansive products in UHPC, which contributes to reducing the autogenous shrinkage and increasing tensile strengths, therefore significantly enhancing the cracking resistance, especially at early ages. • Prewet CaO-type EA method is firstly proposed to minimize shrinkage cracking potentials. • 45-min EA prewet treatment increases splitting tensile strengths of UHPC by up to 10%. • 45-min EA prewet treatment reduces autogenous shrinkage of UHPC by up to 30%. • The EA prewet treatment increases expansive products to minimize cracking potentials. [ABSTRACT FROM AUTHOR]

Engineered cementitious composite (ECC), also known as strain-hardening cementitious composite (SHCC), is attracting increasing interest in the construction industry because ECC has unique mechanical properties, crack resistance, damage tolerance, and durability. The properties of ECC have originated from the unique design philosophy for tuning the cementitious matrix, fibers, and fiber-matrix interface. To facilitate the applications of ECC in the construction industry, this paper aims at clarifying the specification, characterization, and quality control methods for ECC materials. The specification includes raw materials, processing and production methods, and key properties such as the fresh and hardened properties as well as durability. A two-stage quality control approach is presented to elucidate the quality control efforts before and during construction events. The representative ranges of ECC properties are introduced, and the methods for evaluating ECC properties and representative applications are reviewed. This paper provides guidelines for practicing engineers and facilitates the applications of ECC in the construction industry. • The specification, characterization, and quality control methods for ECC materials are reviewed. • The specification includes raw materials, processing and production methods, and key properties. • A two-stage quality control approach is presented for the construction industry. • The processing and production methods largely impact the fresh and hardened properties of ECC. • This review provides guidelines to practicing engineers for applications of ECC in construction. [ABSTRACT FROM AUTHOR]

This paper presents a method to measure the shrinkage and cracks of ultra-high-performance concrete (UHPC) using distributed fiber optic sensors. UHPC prisms and rings were prepared and instrumented with fiber optic cables which served as distributed sensors to assess restrained shrinkage based on the Optical Frequency Domain Reflectometry (OFDR) technology with a 0.65-millimeter resolution. The initiation and development of shrinkage cracks were detected, located, quantified, and visualized from the strain distributions. The effect of steel fibers, lightweight sand, and shrinkage reducing agent on shrinkage distribution and crack pattern was investigated. The results indicate that the restrained shrinkage of UHPC decreased from 809 µɛ to 245 µɛ by using steel fibers, lightweight sand, and shrinkage reduce agent. The maximum crack width decreased from 1.605 mm to 0.065 mm. This research enhances the capability of monitoring shrinkage and cracks and supports the development of low-shrinkage UHPC. • A single fiber optic cable is utilized as a distributed sensor for measuring strain distributions. • Ring specimens are instrumented with distributed sensors to monitor restrained shrinkage. • Early-age shrinkage cracks in UHPC rings are detected, located, quantified, and visualized. • The effect of steel fibers, lightweight sand, and shrinkage reducer on shrinkage is investigated. • The development of low-shrinkage UHPC helps enhance durability of concrete structures. [ABSTRACT FROM AUTHOR]

Highlights • Mixture proportioning variables affect tri-axial compressive properties of HPFRCC. • Tri-axial compressive strength of HPFRCC degrades after exposure to high temperature. • Tri-axial compressive strain limit increases with heating temperature from 600 °C to 800 °C. • Tri-axial compressive strength approximately linearly increases with lateral pressure. • Tri-axial compressive strain limit approximately linearly increases with lateral pressure. Abstract This study experimentally investigates tri-axial compressive properties of high-performance fiber-reinforced cementitious composites after exposure to high temperatures up to 800 °C. First, 16 mixtures were designed and tested to evaluate the effect of mixture proportioning variables on the tri-axial compressive properties. The investigated mixture proportioning variables included the water-to-binder ratio (0.24–0.36), sand-to-binder ratio (0.36–0.66), fly ash content (60–75%), fiber content (1.5–2.2%), and superplasticizer content (0.10–0.25%). Based on the test results, an optimum mixture was presented and tested at five confining pressure levels up to 25 MPa and three loading rates up to 60 με/s before and after exposure to high temperature. The cylinders were exposed to the targeted temperatures and then loaded under combined constant lateral confining pressure and an increasing longitudinal compressive load until failure. The tri-axial compressive strength degraded as the heating temperature increased from 200 °C to 800 °C; the strain limit increased with the heating temperature from 600 °C to 800 °C. As the confining pressure increased from 5 MPa to 25 MPa, the tri-axial compressive strength increased by about 50% at 25 °C and 80% at 800 °C. [ABSTRACT FROM AUTHOR]

• Lightweight granules and fibers are used to develop ultra-high-performance concrete. • Mechanical properties and microstructure are improved while shrinkage is reduced. • Life-cycle unit cost, energy consumption, and CO 2 emission are highly reduced. • Ductility is increased by up to 300% by using polyethylene fibers. • Density is reduced to 2000 kg/m3 while retaining a compressive strength above 125 MPa. Ultra-high-performance concrete (UHPC) has high mechanical strengths and durability, but its density and carbon footprint are usually high. This paper developed a lightweight UHPC with low cost, low carbon footprint, low energy consumption, low thermal conductivity, and high ductility, by using three types of lightweight ingredients: hollow glass microsphere (460 kg/m3), expanded glass aggregate (800 kg/m3), and polyethylene fibers (970 kg/m3). Underlying mechanisms were investigated through thermogravimetry, X-ray diffraction, and mercury intrusion porosimetry analyses. Results showed that the hollow glass microsphere reduced the thermal conductivity of concrete; the expanded glass aggregate mitigated shrinkage while enhancing compressive strengths and flexural properties of concrete through internal curing; and the polyethylene fibers promoted multiple cracks, increasing ductility and toughness of concrete. With 20 % hollow glass microsphere, 1.5 % polyethylene fiber, and 25 % expanded glass, UHPC mixtures were developed to achieve high compressive strength (>127 MPa) and high flexural strength (>21 MPa), while reducing the density by 20 % and carbon footprint by 16 % as well as embodied energy by 27 %. [ABSTRACT FROM AUTHOR]

• Impacts of relative humidity (RH) on tensile properties of ECC is elucidated. • Its mechanism is revealed by the response of matrix and fiber/matrix interface to RH. • It advances the standardization of ECC preparation of property characterization. In recent years, broad interests in ductile Engineered Cementitious Composites (ECC) have been accompanied by increasing amount of laboratory investigations of this material. Both wet and air curing have been applied in the preparation of specimens. However, the effect of curing condition on mechanical properties of ECC has yet to be elucidated. This research attempts to fill this knowledge gap. Specifically, experiments were conducted to investigate property changes at different length scales under three curing relative humidity (RH) levels. Macroscopic properties including composite first crack strength, ultimate tensile strength and strain capacity, and crack pattern of ECC reinforced with PVA fibers were recorded. As well, matrix fracture toughness and fiber/matrix interface properties were measured. Correlation of macro-properties and micromechanical parameters was interpreted using a previously developed micromechanical model. The changes of tensile properties and crack pattern were found traceable to RH effects on the matrix and fiber/matrix interface properties. The findings of this study reveal the underlying mechanisms of property differences in specimens cured under different RH. The knowledge gained provides a better understanding of the effects of curing conditions on ECC specimens used in property characterization, and is particularly relevant to maintaining consistency in standardized testing of ECC. [ABSTRACT FROM AUTHOR]

• This review clarifies the debates on the effects of glass particles on concrete properties. • The effects of glass on concrete properties depend on glass particle size and percentage. • Appropriate use of glass can improve the flowability and mechanical strength of concrete. • Using glass can improve the permeability and freezing-thawing resistance of concrete. • Reducing glass particle size is effective in suppressing ASR expansion. While a large amount of waste glass is annually produced worldwide, a limited percentage of waste glass is recycled. Recycling glass in concrete has shown great promise in solid waste management because there is a high volume of concrete in civil infrastructure. However, a consensus on the effects of waste glass in concrete has not been achieved. Some researchers reported that the use of waste glass improved the properties of concrete, but some researchers reported opposite results. The inconsistent results of the effect of waste glass hinder the acceptance of glass in producing concrete. This review aims to clarify the debates and attempts to elucidate the opposite viewpoints. To this end, this paper reviews different results reported by different research groups and proposes new perspectives based on analyzing underlying mechanisms, considering different types of waste glass, including soda-lime, electric, lead, and borosilicate glass. The reviewed contents include the fresh properties, compressive strength, durability, thermal properties, electrical properties, and microstructure of concrete. This review is expected to advance the knowledge of recycling glass in producing concrete, point out future research needs, and facilitate wider adoption of waste glass concrete in developing sustainable and durable infrastructure. [ABSTRACT FROM AUTHOR]

• TiO 2 in ECC is effective in NO x abatement. • Increasing fly ash content is found to enhance the NO x abatement rate and efficiency. • The improvement in NO x abatement rate and efficiency is related to microstructure modification. • A first-order reaction model can effectively capture the NO x abatement through PC reactions. Titanium dioxide (TiO 2) nanoparticles have been incorporated in cementitious composites to achieve photocatalytic (PC) functions such as self-cleaning and air purifying functions. This study experimentally investigates the effect of TiO 2 nanoparticles and fly ash on the nitrogen oxides (NO x) abatement rate and efficiency of Engineered Cementitious Composites (ECC) that has retained strain-hardening properties and tensile ductility. Emphasis is placed on understanding the fundamental mechanisms through research on the microstructures and chemical environment of the composite material. A first-order chemical reaction model is applied to analyze the PC reaction rate and residual NO x concentration. Test results indicate that the PC reaction rate and efficiency increase with the TiO 2 content from 0 to 5%, and the fly ash to cement ratio from 0 to 2.2. Using the low-calcium fly ash further increases the PC reaction rate and efficiency. The microstructure change originated from different fly ash contents and types are closely related to PC efficiency changes. This study advances the fundamental knowledge for engineering the cementitious composites to achieve the optimal PC functions. [ABSTRACT FROM AUTHOR]