| In the context of the large-scale development of underground space and the continuous promotion of intelligent tunnel construction,the emerging demand for functional and smart cement structures is growing.Lots of research has been done to broaden the scope of application of cement-based composites.Among such materials,the cement-based composite with a significant thermoelectric effect is a hot topic of research today.Based on the thermoelectric effect,the cement-based composites can convert thermal energy into electrical energy,which has a promising application in the field of energy harvesting and temperature self-awareness.In addition,thermoelectric cement-based composites are homogeneous and compatible with tunnel lining and pavement structures,which can provide significant energy self-harvesting and temperature self-awareness to the lining and pavement structures while maintaining the mechanical properties of tunnel concrete structures.However,the current research status of thermoelectric cement-based composites shows that the thermoelectric conversion efficiency of cement-based composites is still lower than that of semiconductor materials,and the enhancement effect of functional fillers on the thermoelectric effect of cement-based composites is still insufficient to meet the needs of practical engineering.Therefore,the thermoelectric effect of cement-based materials and its mechanism was researched in this paper,and the main research conducted is as follows.（1）.The ionic thermoelectric effect and mechanism of cement-based materials are studied.It is found that the pure cement paste without any conductive materials also has a significant ionic thermoelectric effect due to the large number of freely moving ions in the pore solution.In addition,the OH-concentration in the pore solution is the key to affect the ionic thermoelectric properties of cement-based materials.OH-is more sensitive to the thermal gradient.When the OH-concentration in the pore solution is higher,the OH-will move to the cold end under the effect of temperature difference,which produces the n-type thermal voltage.When the OH-concentration in the pore solution is low,the cations in the pore solution gradually dominate the thermoelectric effect,which produces a p-type thermal voltage.Based on the ionic thermoelectric effect,the pure cement paste also has a significant thermoelectric conversion efficiency.When the leaching time was 72 h,the PF of the pure cement paste reached a maximum value of 0.042μWm-1℃-2,which exceeded the thermoelectric effect of many cement matrix composites based on electrons or holes as carriers.（2）.The thermoelectric effect of reduced graphene oxide reinforced cement matrix composites（r GO/C）after drying was investigated.The results showed that the r GO/C after drying had a significant electron thermoelectric effect,and shows p-type thermoelectric properties due to the hole move to the cold side.The Seebeck coefficient of r GO/C is increasing with the increase of the content of r GO.The most significant thermoelectric effect is observed for 0.15%r GO/C,and the Seebeck coefficient reaches 159.07μV/℃ at a temperature difference of 56℃.（3）.The cement-based composites with"ionic-electronic"hybrid thermoelectric properties were developed in this study based on the ion thermoelectric effect of the pore solution and the electron thermoelectric effect of r GO.The Seebeck coefficient of r GO/C after ion leaching is significantly improved by the synergistic effect of holes in r GO and cations in the pore solution.The positive peak Seebeck coefficient of cement-based composites reaches 1939.46μV/℃ and the stable value reaches 443.15μV/℃ when the content of r GO reaches 0.15%.In addition,the PF value of the cement-based composites based on the"ion-hole"hybrid thermoelectric effect is significantly improved.The peak value of PF of cement-based composite after leaching reaches 8.24×10-2μWm-1℃-2 when the content of rGO is 0.15%. |
