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Nano-Fe3O4 is considered as one of the novel materials that can be used to enhance the mechanical behavior of cement-based materials. Moreover, due to the high surface energy of nano-Fe3O4, the use of PP fiber and acrylic can respectively prevent the micro-cracking and increase the viscosity of cement paste already reinforced by nano-Fe3O4. In this study, first, the compressive strength of cement paste reinforced with nano-Fe3O4 and different contents of PP fiber and acrylic at 7th and 28th day are measured in lab. Then, a developed semi-empirical model based on the Chiadic model is proposed to predict the compressive strength of the cement-based composite. A parametric study is then performed to evaluate the effect of nano-Fe3O4, PP fiber, and acrylic contents on the compressive strength. The trends of the developed model are in agreement with the overall trends of the experimental results measured in the lab. It is obtained that the compressive strength increases by the addition of nano-Fe3O4 and/or PP fibers to cement paste. It is also found that the presented prediction model can predict the compressive strength of the cement composite at 7th and 28th days with the overall coefficients of variation about 7% and 6.3%, respectively, implying the accuracy of the developed model.

In this paper, a comprehensive semi-empirical model is developed to predict the drying shrinkage strain of concrete reinforced by graphene oxide nanosheets (GONs). The model involves various internal and external parameters. The effects of three factors,including the age when drying starts, the GON content and aspect ratio on the drying shrinkage strain of concrete reinforced with GONs are investigated. It is found that the presented results are in good agreement with the experimental data compared to the results obtained from the other models, including CABR, CEB-78, CEB-90, ACI209(92), B3, and GL2000 for plain concrete, and modified ACI209(92) and B3 models for concrete with GONs. Moreover, several sensitivity analyses are done for the drying shrinkage strain of concrete with 0.02, 0.05 and 0.08wt% as functions of the relative environmental humidity, temperature, compressive strength, cement content, aggregate-cement ratio, size and dimensions of the sample, gravel-sand ratio, sand-cement ratio, and water-cement ratio. It is noted that the developed model not only evaluates the drying shrinkage behavior of concrete containing GONs well but it can also be applied to predict the drying shrinkage strain of cement that is reinforced by GONs.

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