Study On Mechanical Properties And Damage Mechanism Of Carbon Nanotube Concrete Under Coupling Of Sulfate Attack And Freeze-thaw Cycles

In the cold areas of northwest China,the soil is rich in sulfate ions,which makes the construction project suffer from the severe test of sulfate attack and freeze-thaw cycle damage for a long time.As a kind of artificial material,the durability of concrete has become the focus of research.It is usually used to add fiber material to change its performance,so as to meet certain durability.As a kind of nanomaterial,carbon nanotubes play the roles of filling and bridging in the process of setting and hardening of gelling materials.Carbon nanotubes play an important role in improving the mechanical properties of concrete materials,increasing the connection between hydration products and optimizing the transition zone,thus improving the durability of concrete materials.At present,the research achievements mainly focus on the improvement of the performance of mortar materials by carbon nanotubes,while the research on the influence of carbon nanotubes on concrete materials after sulfate attack and freeze-thaw coupling is relatively rare.Therefore,this article uses three different concentrations of carbon nanotubes solution was prepared by three kinds of carbon nanotubes reinforced concrete composite materials,studing the different content of carbon nanotubes on the mechanical behavior of concrete material,and with the aid of scanning electron microscope(SEM),X-ray diffraction(XRD),TG and DSC thermal analysis,mercury injection and other ways to improve the durability of concrete material microscopic mechanism were studied.This paper focuses on the study of the properties of carbon nanotube concrete composites under the coupling action of sulfate attack and freeze-thaw cycle,and the influence of carbon nanotube content on the corrosion products under the action,the main work is as follows:(1)the influence of carbon nanotubes on the mechanical properties of concrete materials.The mechanical properties of carbon nanotube concrete composites without sulfate attack and freeze-thaw cycle coupling test were tested.When the content of carbon nanotubes was 0.05wt%,the compressive strength of concrete increased most obviously.(2)influence of carbon nanotubes on hydration products of concrete materials.Through TG-DSC comprehensive thermal analysis of carbon nanotube concrete composites without sulfate attack and freeze-thaw cycle coupling test,it is found that the incorporation of carbon nanotubes can promote the generation of hydration products during the setting and hardening process of concrete materials,and the hydration products gradually increase with the increase of the content of carbon nanotubes.(3)study on corrosion products of carbon nanotube concrete.It is found that there are a lot of corrosion products in the pores and cracks of concrete specimens by SEM.With the increase of the coupling test times of sulfuric acid corrosion and freezing-thawing cycle,the internal corrosion products of concrete specimens gradually increase,and ettringite gradually accumulates and increases by fine needles,and finally forms a large cluster of needles.By means of XRD,the corrosion products of carbon nanotube concrete composites were qualitatively analyzed.Combined with TG-DSC comprehensive thermal analysis,it was found that with the increase of the coupling test time between sulfate attack and freeze-thaw cycle,ettringite-the corrosion product of carbon nanotube concrete composites,increased gradually.By controlling the consistency of other conditions,the concrete materials with different carbon nanotubes content were analyzed,and it was found that the amount of corrosion products was the least when the content of carbon nanotubes was 0.05wt%.(4)The effect of carbon nanotubes on the pore structure of concrete blocks.Through the mercury injection test on the carbon nanotube concrete composite specimens without the coupling test of sulfate attack and freeze-thaw cycle,it was found that the porosity and total pore volume of the concrete specimens increased first and then decreased with the increase of carbon nanotubes,and both of them were larger than CNTs0.(5)The effect of carbon nanotubes on the damage of concrete specimens.The damage relationship between different carbon nanotubes was established.It was found that the incorporation of carbon nanotubes had different promoting effects at different stages of the coupling of sulfate attack and freeze-thaw cycle,and its promoting effects at the peak were unstable.The equations of compressive strength and sulfate attack coupled with freeze-thaw cycle were fitted respectively.A spatial model was established among the carbon nanotubes content,the coupling effect of sulfate attack and freeze-thaw cycle,and the variables of compressive strength.