Research On Mechanics, Physics And Durability Behaviour Of Cement Mortar Modified With Carbon Nanotubes

Carbon Nanotubes (CNTs) have excellent mechanical behavior, electricalconductivity, thermal conductivity. And with its good micro-fiber reinforcing,toughening and nanometer filling characteristics, the carbon nanotubes havegreat potential application prospects on improving mechanical, electrical anddurability behavior of cement-based composite materials. The current researchfield of carbon nanotubes cement-based composites has been mainlyconcentrated on the mechanical and electrical behavior of cement paste.Because cement mortar is closer to the real engineering requirements, it isnecessary to conduct a comprehensive research on properties of cement mortarwith carbon nanotubes. Guided by practical engineering, taking account of theearly development and the long-term durability of cement based compositematerials, and through the combining methods of the macroscopic andmicroscopic experiments, systematic research on the mechanical, physical anddurability properties of cement mortar with carbon nanotubes was carried out,and the modifying mechanism of the carbon nanotubes modified cement mortarwas preliminarily explored. The main work of this dissertation are as following:In the aspect of the mechanical properties of cement mortar with carbonnanotubes, through compressive strength experiments of3d,7d and28d and theflexural strength experiment of28d, a comparative research was done on themechanical properties of0.1%,0.3%and0.5%content of carbon nanotubesmodified cement mortar and normal cement mortar under the same dos age ofwater reducing agent and the same fluidity. Combined with SEM morphologyanalysis, the mechanism of carbon nanotubes modifying the mechanical strengthof cement mortar was preliminarily discussed. The results show that theincorporation of carbon nanotubes can effectively improve the compressivestrength and the flexural strength of the cement mortar, especially in the earlyage; the cement mortar with0.3%carbon nanotubes has the best mechanicalbehavior; the improvement of the macroscopic mechanical properties of thecement mortar is mainly attributed to the carbon nanotubes' bridging effects andthe micro-filling effects. In terms of the physical properties of cement mortar with carbon nanotubes,XRD was used to analyze the relative changes in composition of hydrationreactants and products. In addition, experiments were conducted on the fluidity,hydration heat, water loss and mechanical strength under the conditions ofdifferent curing conditions and early-age shrinkage under drying condition.Comparative study was done on the physical properties including fluidity,hydration process, water retention and shrinkage of carbon nanotube modifiedcement mortar and ordinary cement mortar. The results show that theincorporation of carbon nanotubes can reduce the fluidity of cement mortar,improve the degree of hydration of cement paste and accelerate the hydrationrate. Besides, the cement mortar with carbon nanotubes can effectivelyimprove early shrinkage compared with ordinary cement mortar.The durability of the cement mortar with carbon nanotubes including thesulfate attack resistance and the frost stack resistance was studied by measuringcompressive strength of the cement mortar with the carbon nanotubes and theordinary cement mortar of the age of30d,60d and90d under the standardenvironment and the the harsh environment of dry-wet cycles and thefreeze-thaw cycles, and carbon nanotubes' mechanism of improving deteriorationwas discussed. The results show that under the dry-wet cycles and thefreeze-thaw cycles, the cement mortar with carbon nanotubes has lowercompressive strength loss rate; compared with the ordinary cement mortar, thecement mortar with carbon nanotubes has better abilities of sulfate resistance andfrost resistance which is attributed to the synergistic effect of better porestructure and crack resistance.