The Mechanical And Autogenous Shrinkage Properties Of Carbon Nanotubes/Mineral Admixture Cement-based Composites

With the increase in the application of mineral admixtures in practical engineering,nanomaterials have carried out research on mineral admixtures cement system.Carbon nanotubes are one of the typical nanomaterials,and it can improve the performance of cement-based materials.However,there is limited knowledge of the performance of carbon nanotubes/mineral admixture cement-based composites.In this paper,multi-walled carbon nanotube?MWCNTs?are blend into two commonly used mineral admixture cement-based composites,so that their mechanical properties and autogenous shrinkage are systematically investigated.Besides,combined with a variety of micro-testing methods,the mechanism of MWCNTs on the fly ash cement-based composites and the blast-furnace slag cement-based composites are discussed.The main results and conclusions are as follows:?1?MWCNTs/fly ash cement-based composites with different dosage and MWCNTs/blast-furnace slag cement-based composites with different dosage were prepared,and the mechanical properties were tested separately.The conclusions are as follows.MWCNTs has a significant effect on improving the flexural strength of fly ash cement-based composites and blast-furnace slag cement-based composites,and can significantly compensate for the low early flexural strength of fly ash cement-based composites.The flexural strength of MWCNTs/mineral admixture cement-based composites increases at first and then decreases with the increase of MWCNTs dosage,and gradually increases with the curing ages;MWCNTs can not significantly improve the compressive strength of mineral admixture cement-based composites;The bending toughness of MWCNTs/mineral admixture cement-based composites is reinforced.The flexural toughness,cracking point displacement and maximum loading of MWCNTs/mineral admixture cement-based composites are higher than mineral admixture cement-based composites without MWCNTs.?2?The autogenous shrinkage properties of MWCNTs/mineral admixture cement-based composites were tested.The conclusions are as follows.The autogenous shrinkage value of MWCNTs/fly ash cement-based composites increases with the curing ages,and the autogenous shrinkage curve can be roughly divided into three stages,namely the rapid shrinkage stage,the slight expansion stage and the smooth shrinkage stage;Fly ash is beneficial to reduce the autogenous shrinkage value of cement-based materials,and the appropriate dosage of MWCNTs is beneficial to further reduce the autogenous shrinkage value of fly ash cement-based composites;The autogenous shrinkage value of MWCNTs/blast-furnace slag cement-based composites increases with the curing ages,and the autogenous shrinkage curve can be roughly divided into two stages,namely the rapid shrinkage stage and the smooth shrinkage stage;Blast-furnace slag increases the autogenous shrinkage value of cement-based materials,and the appropriate dosage of MWCNTs is beneficial to reduce the autogenous shrinkage value of blast-furnace slag cement-based composites;The autogenous shrinkage value of MWCNTs/mineral admixture cement-based composites decreases significantly with the water-cement ratio increases.?3?Micro-testing conclusions are as follows.MWCNTs can not only bridge and block the initial cracks,absorb and transfer load,but also fill pores between the hydration products,refine pore size distribution,relieve capillary stress and compact the matrix,thereby improving its mechanical properties and autogenous shrinkage properties.The incorporation of MWCNTs can not change the type of hydration products of the matrix,but promote the formation of C-S-H gel and reduce the crystallinity of Ca?OH?₂.The hydration heat test shows that MWCNTs can significantly promote the early hydration reaction of the fly ash cement-based composite slurry,but it cannot effectively promote the hydration process of the blast-furnace slag cement-based composite slurry.