Issue 45

P. Jinchang et alii, Frattura ed Integrità Strutturale, 45 (2018) 156-163; DOI: 10.3221/IGF-ESIS.45.13 160 No. of test specimen Water cement ratio Mixing amount of graphene oxide/(%) Bending strength/ MPa Growth rate of bending strength/(%) Compressive strength/MPa Growth rate of compressive strength/(%) 1 0.35 0 11.07 65.66 2 0.35 0.01 11.12 0.28 68.07 3.66 3 0.35 0.03 13.73 23.82 72.78 10.86 4 0.35 0.05 9.96 -10.21 55.42 -15.61 Table 2 : The basic mechanical properties of cement mortar under different mixing amount of graphene oxide. No. of test specimen Water cement ratio Mixing amount of graphene oxide/(%) Bending strength/ MPa Growth rate of bending strength/(%) Compressive strength/MPa Growth rate of compressive strength/(%) 1 0.35 0 11.07 65.66 3 0.35 0.03 11.13 23.82 72.78 10.86 5 0.4 0 10.41 63.84 6 0.4 0.03 11.85 10.49 67.95 6.42 7 0.45 0 9.32 60.44 8 0.45 0.03 10.94 17.41 65.66 8.60 9 0.5 0 5.77 30.57 10 0.5 0.03 9.98 73.10 52.66 72.36 Table 3: The basic mechanical properties of cement mortar under different water cement ratios. Figure 4 : The variation of the bending and compressive strength of graphene oxide reinforced cement based composite material with the changes of the mixing amount and water-cement ratio of graphene oxide. Fig. 4(a) described the variation rules of the mechanical properties of graphene oxide reinforced cement based composite material with the variation of the mixing amount of graphene oxide when the water-cement ratio was 0.35. As shown in the figure, the influence of the mixing amount of graphene oxide on the compressive and bending strength of the test specimens was consistent, i.e. increase firstly and then decrease; the compressive and bending strength was maximum when the mixing amount of graphene oxide was 0.03%, and there was a growth rate of 23.83% and 10.85%, indicating that the improvement of the bending strength was more obvious when the mixing amount of graphene oxide was within a certain range; when the mixing amount exceeded 0.03%, the bending and compressive strength had significant decline and even became lower than that of the blank samples. The first reason might be water demand significantly improved after the addition of cement- based materials because of the extremely large surface energy and specific surface area of graphene oxide. Zhu [21] found that the slump of cement paste which contained 0.05% graphene oxide reduced by 41.7%, which revealed that water demand sharply increased with the increase of the content of graphene oxide. The second reason might be graphene oxide was prone to gather because of van der Waals attraction when the content of graphene oxide was high. Moreover, many water molecules around were absorbed, leading to inconsistent water-cement ratio and uneven hydrate formation. Fig. 4(b) shows the variation rules of the mechanical properties of compound cement mortar under different water cement ratio. The mechanical performance of the test specimens which were mixed with graphene oxide was superior to that of the specimens which were not mixed with graphene oxide, and the larger the water-cement ratio, the lower the strength of the