Effect Of Nano-materials On Shrinkage Performance Of Concrete

As a new building material,high performance concrete attracts more and more attention in engineering field with the increased application.While improving the performance of building structures,high performance concrete also has a variety of problems,such as the cracking of large-span bridge structures,which seriously affects the safety and durability of the building structure.The shrinkage of concrete is the main reason for the cracking of concrete,and it is also the main factor that affects the durability of the building.As the most promising material in twenty-first century,nanomaterials has a size effect,a high reactive activity and a filling effect.When nanomaterials are added into cement-based materials,They can promote cement hydration and optimize pore structure,it can make up the shortcomings of mineral admixtures in some extent and achieve better improvement effect.However,the incorporation of nanomaterials can increase the shrinkage of cement-based materials,and there are few studies.Therefore,it is necessary to study the shrinkage of nanomaterials.This article focuses on the effect of nano-SiO₂ on the shrinkage and mechanical properties of cement-based materials,improves the shrinkage of cement-based materials by added mineral admixtures?fly ash,slag?and expanding agent.The main results obtained are as follows:.?1?Incorporated a constant amount of nano-SiO₂ cement-based materials,in the early days,the incorporation of fly ash will reduce the compressive strength of the concrete,and the compressive strength of the concrete will gradually decrease with the increase of the addition amount.In the later period?60d age?,the change in compressive strength is not so obvious,even higher than that of concrete without fly ash.Due to the dense packing effect of fly ash on the micro-aggregates,the incorporation of fly ash shows a good compensation for the shrinkage of cement-based materials.When the content of nano SiO₂ is 1.2%,the shrinkage value of cement paste 28d increases by57.5%,and the shrinkage strain of concrete 60d increases by 16.7%.?2?Incorporated a constant amount of nano-SiO₂ cement-based materials.In the early stage,the compressive strength of the concrete was reduced by the addition of fly ash,and the compressive strength of the concrete was gradually reduced with the addition of the fly ash in the early stage of the cement based material added with a constant nano SiO₂ content.Its compressive strength in late stage?60d age?is not obvious,even higher than that of concrete without fly ash.Moreover,due to the dense filling effect of fly ash,it has a good compensation effect on shrinkage of cement based materials containing nano SiO₂.When the fly ash content is 40%,the shrinkage value of cement paste 28d decreases by 35%,and the shrinkage strain of concrete 60d decreases by 9.4%.?3?Incorporated a constant amount of nano-SiO₂ cement-based materials.In the early stage,the incorporation of slag will reduce the compressive strength of concrete,but its effect on compressive strength will gradually decrease with age increases.The incorporation of slag has a certain compensating effect on the shrinkage of cement-based materials containing nano-SiO₂.When the slag content is 40%,the shrinkage value of cement paste 28d decreases by 21.2%,and the shrinkage strain of concrete 60d decreases by 7.9%.?4?Incorporated a constant amount of nano-SiO₂ cement-based materials.The addition of expanding agent to cement based materials has a certain compensation effect on shrinkage.When the content of ettringite type expansive agent is 4%,the shrinkage value of cement paste 28d decreases by 21.1%,and the shrinkage strain of concrete 60d decreases by 14.8%.When the dosage of UEA expansive agent is 0.5%,the shrinkage value of cement paste 28d decreases by 18.9%,and the shrinkage strain of concrete 60d decreases by 14.3%.