Investigation On Static And Dynamic Mechanical Properties Of Cementitious Composites With Carbon Nanotubes

Reactive powder concrete(RPC)is a type of cementitious composites with very dense microstructure,high mechanical strength and excellent durability.Owing to unique physical properties,excellent chemical stability,low denisity and high aspect ratio,carbon nanotubes(CNTs)are superior nanofillers.Composition of RPC and CNTs is a promising approach for developing high mechanical performance and durability,and multifunctional/smart composites.In this paper,the influencing effects of multi-walled CNTs(MWCNTs)type and content as well as curing method on the static mechanical properties of RPC were studied,and the fiber-theoretical calculation and electron microscopic observation were carried out to analyze the reinforcing mechanism of MWCNTs to RPC.And then,the effects of MWCNTs type and content as well as strain rate on the dynamic mechanical properties of RPC were invesitagated.The main research contents and conclusions are as follows:(1)Four types of MWCNTs(i.e.,carboxyl functionalization,hydroxy functionalization,spiral treatment and surface nickel coating)at different contents(0.25% and 0.50%)were incorporated into RPC with water curing or heat curing.The enhancing effects of MWCNT type,content and curing method on mechanical properties of RPC were investigated.Experimental results indicate that adding proper type and content of MWCNTs can effectively improve the flexural strength,fracture energy,compressive strength/toughness and flexural strength to compressive strength ratio of RPC.In general,heat curing can acquire higher mechanical strength of composite materials than water curing,which can be attributed to the fact that heat curing is more beneficial to increase the strength of cementitious material matrix.In most cases,MWCNTs in the matrix will be snapped when damage occurs in RPC.In addition,the reinforcement of MWCNTs to RPC mainly results from crack bridging and pull out effects.The excellent mechanical properties of composite materials can be obtained by selecting suitable type and content of MWCNTs as well as curing method.(2)RPC filled with above-mentioned four types of MWCNTs at two different contents were fabricated,then the dynamic mechanical properties of these composite materials were tested and analyzed at three different strain rates(i.e.,200/s,500/s and 800/s).Experimental results show the addition of proper type and content of MWCNTs can effectively increase the dynamic compressive strength and dynamic compressive strength increase factor of RPC at three strain rates,and the incorporation of MWCNTs can reduce the strain rate threshold of RPC.At strain rates of 200/s and 500/s,the addition of MWCNTs can decrease the peak dynamic compressive strain of RPC,while at strain rates of 500/s and 800/s,the addition of MWCNTs can increase the ultimate dynamic compressive strain of RPC.At strain rates of 200/s and 500/s,the dynamic compressive elastic modulus of MWCNTs filled RPC is bigger than that of control RPC,while at strain rate of 800/s,the opposite law is presented.At three strain rates,the addition of 0.50% hydroxy-functionalized MWCNTs can increase the peak dynamic compressive toughness of RPC by 32.8%,11.3% and 151.8%,respectively,while with the incorporation of 0.25% carboxyl-functionalized MWCNTs,0.25% hydroxy-functionalized MWCNTs and 0.50% hydroxy-functionalized MWCNTs,the ultimate dynamic compressive toughness of RPC can be increased by 99.7%,106.2% and 81.6%,respectively.Therefore,the incorporation of hydroxy-functionalized MWCNTs can effectively improve the dynamic compressive toughness of RPC.