Study On The Compatibility Of Nano-SiO₂ With Superplasticizers And Its Effect On Concrete Performances

The dispersing method of ultrasonic and admixture was adopted,and the ultrasonic cavitation was used to open the agglomerated nanoparticles,so that NS was evenly and fully dispersed in the superplasticizer solution.On this premise,the compatibility between NS with different superplasticizers was studied.The effect of NS on the microscopic properties of concrete was studied by SEM,XRD and MIP under the condition of maintaining the same workingability of the mixture,so as to explain the mechanism of NS on concrete.The optimum dosage of NS in concrete is discussed from the aspects of mechanical properties and durability.Firstly,fresh concrete was used as the carrier to conduct a macro analysis on the workability of fresh concrete.It was found that when the same slump of 200mm was reached without adding NS,PC consumption was the smallest,followed by SAF,and FDN consumption was the largest.With the increase of NS content,the slump loss rate of fresh concrete with PC was less than that of fresh concrete with SAF.As the NS is gradually increasing dosage of keep the same slump,200 mm PC the least increment,SAF findings and the increment of FDN almost reach the requirement.Then,the cement paste was taken as the research object,and through the microscopic interpretation of the flocculation water film thickness,it was found that the amount of PC in the flocculation was lower than that of SAF,and with the increase of NS content,the water film thickness of flocculation with PC content was greater than that with the corresponding SAF content.At last,the test of classic cement paste fluidity was used to verify it.It was found that with the increase of NS content,whether the cement paste with the same PC content or the cement paste with different PC content,the net pulp fluidity was larger than the corresponding net pulp fluidity using SAF on the whole,and the amount of PC was lower than the amount of SAF.The compatibility between NS and PC was determined to be optimal,followed by compatibility with SAF,and compatibility with SAF was the worst.Under the premise of keeping the workingability of the mixture under the addition of PC,SEM showed that the CH crystal in the cement stone decreased correspondingly and the cracks were improved with the increase of NS.Meanwhile,NS content decreased the thickness of ITZ in concrete and optimized ITZ structure.The XRD pattern showed that the incorporation of NS reduces the amount of CH,and CH reacts with NS to form more C-S-H gels;Meanwhile,according to scheele's formula,the incorporation of NS refines the size of CH grains,indicating that the incorporation of NS reduces the dense distribution and orientation of CH in the test piece,thus improving the corresponding performances of paste and concrete.MIP results showed that the addition of NS reduced the total porosity,the total pore area and the porosity.With the increase of NS addition,the porosity of capillary and gel pores basically decreased gradually,thus improving the pore structure and density.The mechanical properties of nano-SiO₂ concrete were studied by compressive strength,flexural strength,axial compressive strength and elastic modulus test.The results show that the mechanical properties of NS-doped specimens are improved to different extents.When the NS content is 1.0%,the mechanical properties increase basically reaches the maximum value.Thus,for mechanical properties,the optimum amount of NS in the concrete is 1.0%.In terms of durability,the anti-freeze test results show that the mass loss rate has a minimal impact on the nano-sio₂ concrete.However,with the increase of NS content,the decline of relative dynamic elastic modulus slows down,and the failure time of nano-sio₂ concrete is prolonged.The results of long-term immersion test of chloride ion show that NS incorporation can effectively reduce the migration of chloride ion into concrete,and has certain inhibitory effect on chloride ion invasion into concrete.The results of sulfate corrosion resistance test showed that the compressive strength and corrosion resistance of the specimens with NS increased as a whole.In terms of durability,1.0%content is also the optimal NS content in concrete.The thesis has 58 figures,15 tables and 140 references.