Issue 45

P. Jinchang et alii, Frattura ed Integrità Strutturale, 45 (2018) 156-163; DOI: 10.3221/IGF-ESIS.45.13 158 The size of graphene oxide nanosheets was detected using SPI3800N/SPA400 atomic force microscope (NSK, Japan). 0.5 % graphene oxide was diluted to 1500 times, and one drop was taken and dried on a monocrystalline silicon piece (10 mm × 10 mm) at 25 °C. Preparation of graphene oxide reinforced cement based composite material It has been found that the addition of a small amount of nanometer material can significantly improve various performances of composite materials [17, 18]. In this study, the mass fraction of graphene oxide was set as 0%, 0.01%, 0.03%, 0.05% and 0.07% to study the effects of the mixing amount of graphene oxide on the mechanical properties of test specimens. Water cement ratio is an important parameter determining the strength, working performance and durability of cement based composite material [19]. Water cement ratio was set as 0.35, 0.4, 0.45 and 0.5 to investigate the variation rules of the mechanical strength of specimens under the same mixing amount of graphene oxide and different water cement ratio. 0.2% polycarboxylate superplasticizer was added to all the specimens to solve the problem of reduced fluidity caused by the addition of graphene oxide [20]. According to the preparation techniques described in Method of testing cements - Determination of strength (GB17671- 1999), cement mortar was put into a mould in a size of 40 mm ×40 mm × 160 mm for curing. Then the test specimens were developed as per the mix proportion shown in Tab. 1 for the compressive and bending strength tests. All the specimens were demoulded after 24 h of maintenance and then maintained in water under standard conditions, i.e. 20 °C and 90% relative humidity, before test. No. of specimen Cement/g Water cement ratio Standard sand/g Graphene oxide/wt% Polycarboxylate superplasticizer/wt % 1 450 0.35 1350 0 0.2 2 0.35 0.01 3 0.35 0.03 4 0.35 0.05 5 0.4 0 6 0.4 0.03 7 0.45 0 8 0.45 0.03 9 0.5 0 10 0.5 0.03 Table 1: The mix proportion of cement mortar specimens. Test on the mechanical properties of cement mortar The test specimens were taken out from water and dried, and then the bending and compressive strength of the specimens were detected under 50 N/s and 2400 N/s following GB17671-1999. In each group, three test specimens were tested, and the average value was taken as the final result. Samples were collected from the crashed fracture surface of the test specimens and immersed in absolute ethyl alcohol to stop hydration, and finally preserved in a vacuum drier. Energy spectrum was analyzed using an American JSM-6360LV scanning electron microscope (SEM) and a spectrometer. T EST RESULTS AND ANALYSIS Analysis of Representation of Graphene Oxide he XRD spectra of graphite powder and graphite oxide sample are shown in Fig. 1. The peak in the curve (a) of Fig. 1 was the characteristic peak of graphite, and the peak in the curve (b) was the characteristic peak of graphene oxide. The results demonstrated that the interlayer spacing of graphene oxide increased from 0.33855 nm to 0.83859 nm, which contributed to the introduction of oxygen-containing groups in graphite nanosheets under oxidation. Oxygen connected with graphene in the form of a covalent bond, leading to the changes of laminated structure and diffraction peak deviation of graphene oxide. T