Effect Of Carbon Nanotubes On The Mechanical Properties And Microstructure Of Rubber Cement Mortar

Developing crumb rubber cementitious composites(CRCC)where rubber is regenerated from the waste tires can not only improve crack resistance of cement-based materials,but also recycle the waste tire.However,crumb rubber brings negative effects as well.The mechanical strength of CRCC is significantly reduced,which limits its application.As a new one-dimensional nanomaterial,carbon nanotubes(CNT)exhibit remarkable strengthening effects in metals and ceramics while the application of the CNT in CRCC has not been studied.In this paper,CNT reinforced rubber cement mortar(CRM),and the mixing process of CNT incorporation,CNT content and CRM mixing method were determined.On this basis,the effects of CNT on the mechanical strength,impermeability and anti-icing ability of rubber aggregate mortar were studied experimentally.The reinforcement of CNT to rubber aggregate mortar was discussed from the perspective of cement hydration and composites microstructure.The main conclusions are as follows:(1)The addition of CNT decreased the flowability of rubber cement mortar(RM)while the decreasing was slight which could be mitigated by the water reducing agent.CNT also decreased the water absorption ratio which reveals that CNT decreased the pore content of CRM.(2)CNT improved the mechanical properties of RM.When adding CNT at 0.04%,0.08% and 0.12%,the compressive strength,flexural strength,and energy absorption were enhanced by 57.0%,24.0% and 21.3% separately.The increase rate of compressive strength was slow down as the increasing of CNT content and the energy absorption reached maxima when adding CNT at 0.08%.These show that there is a limitation of CNT content in regards of effect on mechanical properties.(3)Thermogravimetric analysis and X-ray diffraction results showed that CNT promote the cement hydration.When addition of CNT at 0.04%,0.08% and 0.12%,the hydration degree was improved by 5.6%,26.9% and 19.1% compared with CRM.It is noticed that the when improving CNT content higher than 0.08%,the hydration degree reduce.As the limitation of current dispersion method,higher CNT content results in larger CNT clusters which further alleviate the seed effect of CNT.This also explains the reduction of energy absorption when adding CNT higher than 0.08%.The field emission electron scanning microscopy observation revealed the denser microstructure of CRM than normal rubber cement mortar.CNT was observed linking the micro and nano-cracks.The “forest” distribution of CNT fills the pores and strengthened the composites.The pull-out CNT was spotted as well,which contributed to the increment of energy absorption.(4)CNT was also beneficial for the impermeability and anti-icing performance.The water-drop penetration speed reduced by 4.3%,7.6% and 8.7% and ice adhesion energy reduced by 6.3%,25.1% and 31.9%,when adding CNT at 0.04%,0.08% and0.12% compared with RM.