Comparative Study Of The Preparation And Piezoresistivity Of Three New Carbon Materials Based Cement Composites

Concrete, as the most important and abundant building material, is developing toward the high performance and multifunction. Multifunctional cement–matrix composites are useful as structural materials that provide functional properties, such as electromagnetic interference shielding, strain sensing, etc. All these potential applications are enabled by the use of electrically conductive admixtures, which result in decrease in the electrical resistivity and enhancement of the strain sensing ability through reversible change of the electrical resistivity with strain/stress- a phenomenon known as piezoresistivity. Carbon materials have been shown to be the most effective admixture for rendering the stress sensing ability. Despite reports of successful preparation of carbon fiber(CF)/ carbon nanotubes(MWCNTs)/ graphene cement composites, controlling the microstructure of such composites to reliably achieve the desired material properties remains a challenge due to the problems of dispersion, preparation technology and testing conditions.The dispersion of CF, MWCNTs and Graphene in the cement matrix and the conductivity and stress sensing ability of cement composites were investigated and the economical efficiency and piezoresistivity of these three types of cement composites were compared in this paper. The conclusions are as follows:1. For carbon fiber reinforced cement composites(CFRC), through the orthogonal experiment, the optimum content of silica fume and dispersing agent is 10 wt% and 0.44 wt%, respectively, and the optimum water/cement ratio is 0.6. With the increase of carbon fiber content, resistivity of CFRC decreased gradually, and the stress sensing effectiveness increased firstly and then decreased. The percolation threshold value of carbon fiber in cement paste is 0.2 %-0.8 % and the best dosage is 0.4 %. With the increase of oxidation time, the surface oxygen-containing functional groups of carbon fiber gradually increased, the resistivity decreased and the stress sensing effectiveness increased firstly and then decreased, and the optimum carbon fiber oxidation time is 12 h. With the increase of carbon fiber length, the conductivity gradually increase, and the stress sensing effectiveness increased firstly and then decreased, and the optimum length of carbon fiber is 5 mm.2. For multi-walled carbon nanotubes-based cement composites(MWCNTs/CC), the effects of different dispersing agent on the dispersion of multi-walled carbon nanotubes were studied. It can be seen that polycarboxylate superplasticizer has the optimum performance of dispersing carbon nanotubes. Furthermore, MWCNTs/CC using polycarboxylate superplasticizer as the dispersing agent had a stable stress sensing effectiveness and the curves obtained is smoothing. With the increase of dosage of carbon nanotubes, resistivity gradually decreased, the polarization time gradually reduced. Through the change of the resistance and stress sensing effectiveness of MWCNTs/CC, it can be obtained that the percolation threshold value of MWCNTs is 0.06 wt%- 0.3 wt% and the optimum dosage is 0.1 wt%.3. For graphene-based cement composites, the effects of different dispersing agent on the dispersion of graphene were studied. It can be obtained that the graphene dispersing in GA solution was the optimum. With the increase of dosage of graphene, the resistivity of cement composites decreased, the stress sensing effectiveness first increased and then decreased. The percolation threshold value of graphene in the cement composites is 0.06 wt%-0.15 wt% and the best dosage is 0.12 wt%.4. Within the scope of this study, with the increase of the rate of the load and loading force, the stress sensing effectiveness in the three kinds of cement-based composites showed the tendency of increase.5. By comparing the stress sensing effectiveness of the CF, MWCNTs and graphene cement-based composites in uniaxial compression load, it was concluded that the stress sensing effectiveness of MWCNTs/CC was the optimum. Economical analysis revealed that carbon fiber and carbon nanotubes are both economical.