Study On Mechanical Properties And Microstructure Of Ultra-high Performance Concrete Incorporating Graphene Oxide

Ultra-high performance concrete(UHPC)normally exhibits exceptional strengths,high toughness and excellent durability.And It has become one of the most promising new construction materials for sustainable infrastructure.However,UHPC generally needs a high volume of cement content,a high production cost and more environmental impact.This study aims to overcome these drawbacks of UHPC by incorporating different dosages of graphene oxide(GO)and then experimentally investigates the effect of GO on the flowability,compressive strength and flexural strength of UHPC with various contents of steel fibers(STF)under standard curing and under heat curing.The study also look into the strengthening mechanism of GO for such UHPC by carrying out a single fiber pull-out test and performing the microstructures examined by scanning electron microscopy(SEM).The details are described as follows:1.Two types of UHPC mix with high volume supplementary cementitiousmaterials(SCMs)and one type of UHPC with high cement contents were developed,respectively.These UHPC mixes were designed on the basis of the particle packing model,existing literatures and well optimized three types of quartz sand.They were used as reference concrete for present study,separately.2.The GO reinforced UHPC with high volume SCMs and a STF dosage of 1.5% by volume of concrete were prepared and the effect of GO on such UHPC under standard curing and under heat curing.The results indicate that the mini slump flow gradually decreases with increasing GO nanosheet content.The results also confirm that the compressive and flexural strengths of such UHPC are improved with the addition of GO dosage while the optimal content of GO nanosheets are relevant to the curing regime.3.The GO reinforced UHPC with high volume SCMs and STF dosages of 0.0%,0.5%,1.0% and 1.5% by volume of concrete were prepared and the effect of GO on such UHPC under standard curing and under heat curing.The results indicate that the mini slump flow gradually decreases with increasing GO nanosheet content for a given content of STF.The results also confirm that the both compressive and flexural strengths are improved with the latter increased significantly greater than the former.Additionally,the optimal dosage value of GO is affected by both curing regime and the content of STF.4.The Go reinforced UHPC with high cement contents and STF dosages of 0.0%,0.5%,1.0% and 1.5% by volume of concrete were prepared and the effect of GO on such UHPC under standard curing and under heat curing.The results indicate that the mini slump flow gradually decreases with increasing GO nanosheet content for a given content of STF.The results also confirm that the both compressive and flexural strengths are improved with the latter increased significantly greater than the former.Additionally,the optimal dosage value of GO is affected by both curing regime and the content of STF.It is important to note that the flexural strength of UHPC with high cement contents and containing GO is much greater than the one with high volume SCMs for a given dosage of STF.5.The strengthening mechanism of GO for such UHPC was investigated by carrying out a single fiber pull-out test and performing the microstructures which was examined by scanning electron microscopy(SEM).The results from a single fiber pull-out test demonstrate that the bonding strength of interface between steel finer and UHPC matrix with GO is significantly increased compared to that without GO.The SEM results also show the microstructure of both UHPC and the interface between steel finer and UHPC matrix with GO is slightly improved.However,it seems there is not big different on some specimens with and without GO.This may be attributed to the original very dense microstructure of UHPC6.The results also suggest that the STF content can be replaced partly with GO to achieve the comparable flowability,compressive strength and flexural strength.It is therefore demonstrated that the addition of GO can help develop more cost-effective UHPC.