Microstructure, characterizations, functionality and compressive strength of cement-based materials using zinc oxide nanoparticles as an additive

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Highlights

  • Nano zinc oxide was used as an additive material.

  • Microstructure and phase characterization of pastes were characterized using SEM and XRD.

  • TGA and FTIR were also used to determine the hydration reaction.

  • Compressive strength of ZnO mixes was found to increase at 28 days.

Abstract

Zinc oxide nanoparticles as a nanophotocatalyst has great potential for self-cleaning applications in concrete structures, its effects on the cement hydration, setting time and compressive strength are also important when using it in practice. This paper reports the effects of zinc oxide nanoparticles, as an additive material, on properties of cement-based materials. Setting time, compressive strength and porosity of mortars were investigated. Microstructure and morphology of pastes were characterized using scanning electron microscope and X-ray diffraction (XRD), respectively. Moreover, thermal gravimetric analysis (TGA) and Fourier-transform infrared spectrometer (FTIR) were also used to determine the hydration reaction. The results show that Portland cement paste with additional ZnO was found to slightly increase the water requirement while the setting time presented prolongation period than the control mix. However, compressive strength of ZnO mixes was found to be higher than that of PC mix up to 15% (at 28 days) via filler effect. Microstructure, XRD and TGA results of ZnO pastes show less hydration products before 28 days but similar at 28 days. In addition, FTIR results confirmed the retardation when ZnO was partially added in Portland cement pastes.

Introduction

Nanomaterials have widely attracted considerable scientific interest due to the new potential uses of particles in nanometer scale (10−9 m). The most active fields of nanomaterials are electronics, mechanics, medicals, biomechanics and coating. Currently, there is an increase in interest on research areas dealing with cement and concrete in understanding the hydration of cement particles and the use of nano-sized constituents. However, application and advance of nanotechnology in the construction and building materials fields have been uneven. Many researchers investigated the effects of sub-micron and nanomaterials such as silica fume, SiO2, Fe2O3, Al2O3, ZnO2, Cr2O3 and TiO2 [1], [2], [3], [4], [5], [6], [7], [8], [9] on properties of Portland cement composite. Moreover, high strength properties of Portland cement and Portland cement–fly ash mortars were achieved by using multi-walled carbon nanotubes [10], [11], [12]. It was revealed that these nanomaterials could improve the strength property of Portland cement due to their ultra-fined particle properties which are not only good for hydration reaction but also its acting as filler. Thus, there are many ongoing researches on the development of a new type of nanomaterials for use with Portland cement as a way to improve its properties.

Zinc oxide nanoparticle (ZnO), a versatile semiconductor material, is an inorganic compound which can be prepared by different methods such as sol–gel method, precipitation method, hydrothermal method and pulse combustion-spray pyrolysis methods [13], [14], [15], [16], [17], [18]. ZnO has been known as a representative of the photocatalyst among semiconductors which has a direct band gap (3.3 eV at room temperature), due to their high photocatalytic activity, photocatalytic degradation of organic compounds and strongly resist microorganisms [19], [20], [21]. It is widely used as an additive into numerous materials and products including plastics, ceramics, paints and glass. Similar to TiO2 as a photocatalyst, the nano ZnO can therefore be used in self-cleaning applications in concrete structures but little is known on the fundamental understanding of nano ZnO hydration and its effect on setting time and strength.

Previous researchers [22], [23], [24], [25], [26], [27] tried to explain the effect of zinc ions on the hydration reaction of cement minerals and on the microstructure of hydration products during the use of industrial wastes in cement manufacture. Moreover, the decrement of heat of hydration was found when zinc oxide was used with Portland cement. They believed that zinc retards cement hydration via the formation of a layer of amorphous Zn(OH)2 and/or crystalline CaZn2(OH)6⋅2H2O around the anhydrous cement grains at the onset of hydration. Nano ZnO nonetheless can be used in concrete for photodegradation of pollutants and microorganisms [28]. Furthermore, Riahi [6] and Nazari [7] reported that zinc peroxide nanoparticles (ZnO2) could improve mechanical and physical properties of concrete. Nevertheless, there are only a few reports on the utilization of ZnO together with Portland cement for structural composite application, especially of its nano size, the effects and the characterizations of this nanomaterial as a cement-based building material. Limited information on the compressive strength and characterization of ZnO nanoparticles in cement were found. Consequently, the aim of this research is to investigate the effect of zinc oxide nanoparticles on properties of cement-based materials. Portland cement–zinc oxide nanoparticles pastes were used for water requirement and setting time tests. Compressive strength and volume of permeable pore space tests were also carried out on mortar specimens. Moreover, phase characterizations and microstructure of setting behavior of Portland cement pastes with ZnO were examined using X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA) and Furrier-transform infrared spectrometer (FTIR).

Section snippets

Materials

Portland cement type I (PC) was used with zinc oxide nanoparticles (ZnO) which purchased from Sigma–Aldrich, Singapore (Purity > 99%), to produce PC-ZnO pastes. Micrographs of raw materials taken from scanning electron microscope (SEM) are shown in Fig. 1a and b. Portland cement particles can be seen to be angular with the particle size of about 1–50 μm while ZnO are also angular with the particle size of approximately 100 nm. X-ray diffraction trace of Portland cement is shown in Fig. 2a. Dominant

Normal consistency and setting time of pastes

The water requirements for normal consistency of Portland cement paste with 0, 1, 2 and 5 wt% of ZnO were tested according to ASTM C187 standard, as given in Table 1. It was found that the water demand of ZnO mixes was slightly increased (up to 28.4%) when compared with PC mix (26.2%), calculated from water to binder ratio. It can be explained that particle size of ZnO was smaller than that of PC particle, therefore water requirement increases with respect to the surface area of the particles.

Conclusions

From the results, the effect of ZnO on the enhancement the physical and mechanical properties of Portland cement can clearly be seen. Portland cement containing ZnO nanoparticles have prolongation setting time both initial and final sets. Although the compressive strength of ZnO mix, at early ages (3 days), was found to be less than that of PC mix but it was found to gain compressive strength after 7 days for the mix with 1–2 wt% of ZnO nanoparticles while the 28 days was higher than that of the

Acknowledgements

The authors would like to thank the Office of the Higher Education Commission, Thailand for supporting the grant fund under the program Strategic Scholarships for Frontier Research Network for the Join Ph.D. Program Thai Doctoral degree for this research. The authors are also grateful to the Thailand Research Fund (TRF) for the research grant given to Assistant Professor Dr. Arnon Chaipanich. Finally, the authors would like to acknowledge Mr. Yosuke Takao and Dr. Koji Tomita for their help in

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