Influence of mixing methods on the NOx reduction capability and electrical properties of photocatalytic cementitious systems

Nitrogen oxides (NOx), regarded as toxic air pollutants, are a group of highly reactive and hazardous gases encompassing compounds ranging from nitrous to nitric acid. Especially in crowded cities, the release of these gases from the industrial organizations and vehicles has reached serious levels. To eliminate the adverse effects of these gases, titanium dioxide (TiO2) is used worldwide as a photocatalyst due to its high efficiency in oxidization of NOx. Incorporating TiO2 into cement-based composites gives them photocatalytic capability: uniform and stable dispersion of TiO2 throughout the matrix is an undisputable requirement for improved photocatalytic efficiency. The main purpose of this study is to investigate the effects of different mixing techniques and surfactant materials on the dispersion of high dosage nano-TiO2 particles (5% of total weight of binder materials) throughout cement-based materials, with the goal of producing cost-effective cementitious systems, more feasible mixing methods, and ensuring proper dispersion of nano-TiO2. Five different mixing methods were proposed to achieve uniform distribution of the nano-TiO2. They were each implemented using different mixing procedures, equipment and surfactants. The performance of each mixing method was evaluated based on photocatalytic performance, electrical impedance (EI), compressive strength and microstructural analysis. Test results showed evidence of the significantly positive effect of polyacrylic acid (PAA) on the dispersion of nano-TiO2. In general, the highest dispersion occurred with ultrasonication and binary utilization of polycarboxylate ether-based plasticizer (PCE) and PAA. The EI test was a highly effective evaluation method for homogeneous distribution of conductive nano particles throughout the matrix. Results also showed a significant relationship between electrical performance and nitric oxide (NO) degradation of composites, and electrical properties of composites are able to provide a reliable estimate of the photocatalytic efficiency of them. © 2020 Elsevier Lt

Use of spent foundry sand and fly ash for the development of green self-consolidating concrete

In the United States alone, the foundry industry discards up to 10 million tons of sand each year, offering up a plentiful potential resource to replace sand in concrete products. However, because the use of spent foundry sand (SFS) is currently very limited in the concrete industry, this study investigates whether SFS can successfully be used as a sand replacement material in cost-effective, green, self-consolidating concrete (SCC). In the study, SCC mixtures were developed to be even more inexpensive and environmentally friendly by incorporating Portland cement with fly ash (FA). Tests done on SCC mixtures to determine fresh properties (slump flow diameter, slump flow time, V-funnel flow time, yield stress, and relative viscosity), compressive strength, drying shrinkage and transport properties (rapid chloride permeability and volume of permeable pores) show that replacing up to 100% of sand with SFS and up to 70% Portland cement with FA enables the manufacture of green, lower cost SCC mixtures with proper fresh, mechanical and durability properties. The beneficial effects of FA compensate for some possible detrimental effects of SFS.Natural Sciences and Engineering Research Council (NSERC) of Canada, and the Canada Research Chair Progra

Role of inclusion size distribution of titanium dioxide on the nitrogen oxides reduction capability and microstructural characteristics of cementitious systems

This paper explores the effect of the inclusion size of titanium dioxide (TiO2) particles on a variety of performance properties of cementitious systems via experimental studies. In addition to comprehensive microstructural analysis including pore size distribution and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analyses, particular consideration was given to the effect of particle size distribution (PSD) of TiO2 particles on mechanical and photocatalytic properties and hydration kinetics of cementitious systems. Nano-sized, submicron-sized and micron-sized anatase-phase TiO2 powders were utilized as photocatalysts at a dosage of 5% by total weight of powder material. In addition to the single use of TiO2 particles with three different size ranges (nano, submicron and micron), they were also used in combination by adjusting their PSDs with three different PSD moduli (q): 0.1, 0.5, and 0.9. Test results show that techniques for achieving optimal microstructural characteristics of cementitious systems also help design and improve their performance in favor of multifunctionality. As a result of PSD optimization of TiO2 particles with three different size ranges, which was significantly influential on the microstructure of the cementitious systems, superior photocatalytic degradation results were obtained from mixtures containing lower amounts of nano-sized TiO2 particles. Cementitious composites with denser microstructure showed lower performance in terms of being able to maintain photocatalytic degradation capability for a prolonged period, whereas the opposite was the case for compressive strength. © 2021 Elsevier Lt

Self-healing capability of large-scale engineered cementitious composites beams

YesEngineered Cementitious Composites (ECC) is a material which possesses advanced self-healing properties. Although the self-healing performance of ECC has been revealed in numerous studies, only small-scale, laboratory-size specimens have been used to assess it under fixed laboratory conditions and curing techniques. In order to evaluate the effect of intrinsic self-healing ability of ECC on the properties of structural-size, large-scale reinforced-beam members, specimens with four different shear span to effective depth (a/d) ratios, ranging from 1 to 4, were prepared to evaluate the effects of shear and flexural deformation. To ensure a realistic assessment, beams were cured using wet burlap, similar to on-site curing. Each beam was tested for mechanical properties including load-carrying capacity, deflection capacity, ductility ratio, yield stiffness, energy absorption capacity, and the influence of self-healing, by comparing types of failure and cracking. Self-healed test beams showed higher strength, energy absorption capacity and ductility ratio than damaged test beams. In test beams with an a/d ratio of 4 in which flexural behavior was prominent, self-healing application was highly successful; the strength, energy absorption capacity and ductility ratios of these beams achieved the level of undamaged beams. In addition, flexural cracks healed better, helping recover the properties of beams with predominantly flexural cracks rather than shear cracks.The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council (TUBITAK) of Turkey provided under Project: MAG-112M876 and the Turkish Academy of Sciences, Young Scientist Award program. The second author would also like to acknowledge the financial support of TÜBITAK for the 2219 Scholarship

Yüksek hacimde uçucu kül içeren kendiliğinden yerleşen beton

In this investigation, SCCs were prepared by keeping the total mass of cementitious materials (cement and fly ash) constant at 500 kg/m3, in which 30, 40, 50, 60, and 70% of cement, by weight, was replaced by the high-lime and low-lime fly ash. For comparison, a control SCC mixture without any fly ash was also produced. The fresh properties of the SCCs were observed through, slump flow time and diameter, V-funnel flow time, L-box height ratio, U-box height difference, segregation ratio and the rheological parameters (relative yield stress and relative plastic viscosity). Relations between workability and rheological parameters were sought. Setting times and temperature rise of the SCC were also determined. The hardened properties included the compressive strength, split tensile strength, drying shrinkage and permeation properties (absorption, sorptivity and rapid chloride permeability tests) up to 360 days. The results obtained indicated that it is possible to produce SCC with a 70% of cement replacement by both types of fly ash. The use of high volumes of fly ash in SCC not only improved the workability and permeability properties but also made it possible to produce concretes between 33-40 MPa compressive strength at 28 days.Ph.D. - Doctoral Progra

Electrical testing for the assessment of self-healing and self-sensing capability of cementitious composites

Engineered Cementitious Composites (ECC) is regarded as a multifunctional smart material due to its intrinsic autogenous self-healing and self-sensing attributes. Here, recent findings related to the utilization of electrical measurements in analyzing combined effectiveness of autogenous self-healing and self-sensing attributes in ECC are discussed. It is concluded that electrical testing which are already widely used for self-sensing, can also be used successfully in estimating the autogenous self-healing efficiency in ECC. It is believed that further research into developing/understanding methods to rapidly and accurately characterize the multifunctional properties of such smart materials will significantly fasten their development and wider practical adoption. © 2019, Associated Cement Companies Ltd.. All rights reserved

Self-healing capability of cementitious composites incorporating different supplementary cementitious materials

The presence of deleterious substances and their transport are among the most important factors controlling the durability of cementitious composites. The present paper studies the relationship among the applied mechanical deterioration in terms of splitting tensile deformation, curing conditions and chloride ion permeability of Engineered Cementitious Composites (ECCs) that contain different supplementary cementitious materials (SCMs). Three SCMs, representing a wide range of compositions, were used in the study. The splitting tensile deformations are introduced to generate microcracks in ECC specimens, where cylindrical specimens were pre-loaded to different deformation levels. After that, the mechanically pre-cracked and pristine ECC specimens were exposed to three different curing conditions (continuous wet, continuous air, and freeze-thaw cycle) for up to 2 months. Rapid chloride permeability test (RCPT), microscopic observation and microstructural analysis were used to assess the rate and extent of self-healing. Test results indicate that the SCM type greatly affects the self-healing capability of cementitious composites as measured by chloride ion permeability. Although ECC samples with fly ash have more unhydrated cementitious materials, and therefore, expectedly, a higher capacity for self-healing, more evident self-healing product was observed from the ECC mixture incorporating slag. Therefore, in addition to the crack width distribution and curing condition, the reaction products associated with SCMs have a great impact on the self-healing capability of cementitious composites.Scientific and Technical Research Council (TUBITAK) of Turkey (MAG-108M495); Gaziantep University Scientific Research Centre (MF.10.09

Determination of cracking related properties of engineering cementitious composites

Engineered Cementitious Composites (ECC) are relatively new types of fiber reinforced cementitious materials with enhanced mechanical properties such as tensile strain hardening accompanying high tensile strain capacity. This is mainly attributed to close and multiple cracks with widths remaining under 60 µm which contributes to durability of ECC material. These properties are only achievable as a result of a micro-mechanical design that requires special ingredients that make ECC costly to be used alone, however it is possible to use ECC together with other construction materials such as steel and concrete. On the other hand, as a result of abundant binders and low water to binder ratio, ECC shrink more compared to other construction materials. In this paper, shrinkage properties including restrained shrinkage of four different ECC mixtures are determined along with the tensile creep behavior. Furthermore a new setup with the method and procedure to determine the tensile creep is given in details

Nano-tailored TiO2-based photocatalytic cementitious systems for NOx reduction and air cleaning

Air quality is one of the main factors having incontestable effect on the quality of life of every being on earth. In addition to its effect on the public health, low air quality also has an indispensable negative effect on the society, environment, and economy as it requires rigorous efforts to be made for proper reduction and/or elimination. Because of the rapidly increasing urban population and industrial activities, the incremental trend in the air pollution, which is one of the world’s major problems nowadays, will most likely continue in the future since the release of greenhouse gases into the atmosphere is also expected to continue at an increasing pace as a consequence of the progressive man-made activities. Among various air pollutants, toxic nitrogen oxide (NOx) is of special interest recently as the release of NOx from the industrial organizations and vehicles has reached serious levels, especially in crowded cities. In an effort to adequately tackle the increased levels of NOx, researchers have looked into several solutions and realized that light irradiated from different types of sources [ultraviolet (UV), visible, solar light, etc.] activates the photocatalytic reactions reducing the pollutiveness of NOx and large surface areas of building members in contact with different light sources offer a unique opportunity for the elimination of detrimental effects of NOx through stimulation of photocatalytic reactions. Given the widespread utilization of cementitious systems in the construction industry, numerous ongoing and completed studies focusing on the use of various photocatalytic materials (photocatalysts) within the cementitious systems can be found. The main focus of these studies is to develop new-generation multi-functional cementitious composites with air cleaning feature without compromising the mechanical features and cost of production. In order to equip cementitious systems with the air cleaning feature, titanium dioxide (TiO2) is a very commonly used semiconductor photocatalyst. The commonness of utilization of TiO2 in cementitious systems is originated from the material’s high efficiency in oxidization of NOx, chemical/photochemical stability, chemical inertness in the absence of irradiation, safety, comparative cost-effectiveness, and nontoxicity. In this chapter, a comprehensive review about the mechanism/properties/advantages of TiO2-based photocatalytic multi-functional cementitious composites with air purification capability is presented. © 2022 Elsevier Ltd. All rights reserved