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Highlights • Increase in reinforcing effect of graphene oxide at strain rate up to 1700 s−1. • Graphene oxide increases DIF when the strain rate reaches different thresholds. • Correlation is found between the increase in DIF and the speed of crack development. Abstract The reinforcing effect of graphene oxide on cementitious materials under high strain rate remains largely unknown. Existing studies on microfiber reinforced cementitious composites showed that the dynamic increase factor (DIF) decreases due to these fibres. This study reports that the reinforcing effect of graphene oxide nanosheets can, in contrast, increase with strain rate. Tensile splitting and compression tests were conducted under both static and dynamic loadings. High strain rate, up to 1700 s−1, is achieved using a split Hopkinson pressure bar apparatus. It is found that the DIF of graphene oxide nanocomposite only increase when the DIF is higher than a threshold which is about 780 and 30 s−1 for compression and tensile test respectively. The increased of DIF was correlated with the speed of crack development and pull-out of the graphene oxide nanosheets. Also, the pull-out or fracture of graphene oxide on fragmented sand was also found a possible contributing factor to the increased DIF. The findings of this study indicate the future potential of atomic-thin nanosheets for materials under extreme impact and blast loading. [ABSTRACT FROM AUTHOR]

Porosity is an intrinsic property of many cementitious materials. This study uses a new centrifugation-based low-melting-point metal intrusion technique to characterize and analyze the shape of pores in cementitious materials. Low energy electrons with ultra-long beam dwell time are used to obtain nano meter level resolution of the pore shape. Three descriptors, namely circularity, solidity, and aspect ratio, are proposed to represent the area-perimeter relationship, hydration and packing and 3D shape of the pores, respectively. Circularity is found to hold a consistent power correlation with pore size. Based on this correlation, the Washburn’s equation is modified to correct the biased prediction of pore size using mercury intrusion porosimetry (MIP). Solidity, is found to decrease with increased pore size, denser packing of cement particles and more hydration products. Aspect ratio of the observed pores is found to average at about 2 representing an oblate ellipsoid shape of pore in 3D space. [ABSTRACT FROM AUTHOR]

Lightweight cement composites have been proposed in the literature, fabricated by controlling the cement coating onto 3D-printed polymer scaffolds to form submillimeter thin-shell structures. In this study, we adopted graphene oxide (GO) to reinforce the thin-shell structures and modify the weak interface between polymer scaffold and cement paste to produce high-performance, lightweight cement composites. The results indicated the thickness of thin shells was maintained constant for different GO dosages by controlling the workability of cement paste. GO significantly reduced high-porosity regions between the cement matrix and polymer scaffold, along with the microstructure refinement of the cement matrix and promoted the formation of low-density calcium-silicate-hydrates (from 50% to up to 66%). The GO shows a much higher reinforcing efficiency than traditional bulk cement, where the composites' compressive strength and specific energy absorption were increased significantly by up to 91% and 78%, respectively, with 0.01 wt% dosage. Compared with traditional lightweight concrete, the compressive strength of the GO-reinforced composites was increased by up to 20-fold. This study promoted understanding of the reinforcing mechanism of GO in thin-shell structures and demonstrated the effectiveness of GO for enhancing the performance of novel lightweight cementitious composites with a wide range of applications for load-bearing, energy absorption, decoration, and thermal insulation. [ABSTRACT FROM AUTHOR]

Abstract Nano-engineering cement binder using a hybrid of carbon nanotubes (CNTs) and graphene oxide (GO) combines the superior mechanical properties of CNTs and the good dispersibility and affinity of GO. Ultrasonication is a key process implemented in the dispersion of CNTs and GO. The present study characterizes the effect of ultrasonication on the dispersion and size of the GO/CNT particles by using an ultraviolet spectrophotometer and Zetasizer μV detector, respectively. The mechanical properties of GO/CNT-OPC pastes treated with different ultrasonication time and power levels were tested and their microstructure was investigated using scanning electron microscopy and mercury intrusion porosimetry. The results of this study not only reveal that differences in ultrasonication can cause the mechanical properties of the GO/CNT-OPC composite to vary by −11.7–78.8% but also show that the effect of the amount of ultrasonication energy can vary significantly when different ultrasonication time or power levels are adopted. The porosity of the composite is found to have a nonlinear correlation with the ultrasonication. The findings of this study can promote understanding of GO/CNT-OPC composites and help to guide the implementation of ultrasonication in the future. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is a novel class of two-dimensional nanoscale sheet material due to its excellent dispersibility in water, high aspect ratio and good intrinsic strengths. In order to obtain a well-distributed GO-reinforced cement composites, the dispersion of GO in water, alkali and several ionic species are investigated with the aid of UV–vis spectroscopy. High alkalinity and calcium ions are key factors inducing the agglomeration of GO in cement system. Dispersion of GO in simulated pore solution is the culmination of the alkali and salt experiments. Agglomeration of GO occurred when GO contacted with the simulated pore solution, highlighting the necessity to protect GO against such aggressive media. The test on surfactant compatibility was then carried out to ensure GO was effectively dispersed in polycarboxylate, air-entrainment and Gum Arabic admixtures within the pore solution. Polycarboxylate-based superplasticisers gave the most promising results to disperse GO in cement alkaline environment. Flexural experiments was performed to highlight the importance of fabrication protocol on the mechanical properties of GO-cement composites. The result shows that the amount of 0.03% GO by weight of cement can increase the flexural strength of GO-cement composite up to 67%. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs) are promising nanoreinforcing materials owing to the superior mechanical properties. Dispersion of MWCNTs is the key to achieving a desirable reinforcing effect, especially in cementitious mixtures, where dispersion is challenging due to high ionic strength. In this study, methylcellulose (MC) is used to stabilize the dispersion of MWCNTs with a constant mass concentration of 0.08 wt% in sustainable ternary cementitious blends of OPC, FA and SF. The effect of different MC dosages on MWCNTs dispersion in a simulated alkaline environment is investigated via UV–vis–NIR spectrometry. The influences of MC on fluidity, bleeding rate, density, wave velocity, porosity, compressive strength, elastic modulus of cementitious blends with w/c of 0.6 were studied. The results showed that MC could significantly improve the stability of MWCNT dispersion in alkaline environment via the viscosity effect. It was found that an optimal concentration of 0.18 wt% MC addition in MWCNT suspension performed the best for improvement of MWCNT dispersion. The MC is effective in improving consistency and reducing bleeding in the cement pastes. An appropriate range of MC (0.10 ∼ 0.20 wt%) is required to achieve optimum enhancing effect of MWCNTs and strength properties of MWCNT-cementitious composite. [ABSTRACT FROM AUTHOR]