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• 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]

• 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]

• 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]