Study On The Effect Of Nano-CaCO₃ On Concrete Performance

Nanomaterials are a new type of material and are known as"the most promising materials of the 21st century".With their excellent properties,they have achieved good results in many fields.As the traditional building materials with the largest amount of use,the mechanical properties and durability of concrete have always been the focus of research work in the field of materials.With the development of nanotechnology,the application of nanomaterials in concrete will bring new vitality to the field of building materials..In this paper,the physical and mechanical properties and durability of nano-CaCO₃ concrete are studied.It is proposed that the composite of nano-CaCO₃and fly ash can be used to modify the concrete by complementing each other.Focus on the mechanical properties of nano-CaCO₃ concrete,such as compressive strength,flexural strength,toughness,etc.as well as durability,such as chloride ion permeability,carbonation resistance,frost resistance,systematic research.In this paper,the optimal test plan is determined by orthogonal test.The concrete of the optimal group,the concrete of the reference group and the concrete with fly ash are compared.The microstructure of the concrete is analyzed by means of scanning electron microscopy.Mechanism of nano-CaCO₃ strengthening and toughening of concrete and improvement mechanism of durability.At the same time,the physical and mechanical properties of recycled concrete strengthened by nano-CaCO₃ were also studied.The main research work and test results of this paper are as follows:（1）Based on the orthogonal test,the optimal mixture ratio of A₁B₂C₁ for nano-CaCO₃ concrete was determined by range analysis,variance analysis and comprehensive balance method,namely:water-to-binder ratio of 0.4 and fly ash content of 20%.The nano CaCO₃ content is 1%.（2）The significance of various factors on the 3d compressive strength of concrete is:A（water-binder ratio）>C（nano-CaCO₃）>B（fly ash content）;the significance of the influence on 7d compressive strength is:A>C>B;the significance of the 28d compressive strength is:A>B>C.The significance of various factors on the flexural strength of concrete 28d is:A>C>B.The significance of each factor on the 28d compression ratio of concrete is:B>A>C.（3）The comparison test results of the optimal group show that the compressive strength of 3d,7d and 28d is significantly improved compared with the concrete of the reference group,but the early improvement effect is not as good as that of the later stage;the flexural strength of 28d is increased by 19.00%;28d The folding ratio increased by 4.61%.Compared with the concrete with fly ash alone,the compressive strength of 3d,7d and 28d is improved,and the early strength is more obvious.It can be seen that the incorporation of nano-CaCO₃ can make up for the shortcomings of the early strength development of fly ash concrete.The flexural strength of 28d increased by 8.22%;the compression ratio of 28d increased by 1.86%.The mechanical properties of nano-CaCO₃ on concrete are significantly improved.（4）The durability test results of the optimal group show that the optimal group of concrete is significantly improved compared with the benchmark group for the chloride ion penetration resistance of concrete;for the carbonation resistance of concrete,the carbonation depth of concrete with single fly ash is higher than the benchmark.In the group,the anti-carbonization ability was reduced,and the optimal group had the best anti-carbonization ability.For the concrete anti-freezing performance,the concrete of the reference group and the concrete with single fly ash were destroyed after 125 cycles and 150 freeze-thaw cycles tests.After 175freeze-thaw cycles,the nano-CaCO₃ concrete still showed no failure,and its relative dynamic elastic modulus was 65.79%,which decreased by 49.48%,and the mass loss rate was less than 5%.The addition of nano-CaCO₃ has obvious effect on the durability improvement of concrete,and its combination with fly ash improves the low carbonization resistance of fly ash concrete.（5）Scanning electron microscopy analysis shows that the nano-doped CaCO₃concrete structure is more compact and uniform.The microstructure of concrete is analyzed.It is believed that the improvement mechanism of nano-CaCO₃ on concrete performance is mainly micro-aggregate filling and nucleation.Role,but its chemical activity has little effect.（6）Recycled concrete prepared by recycled aggregates strengthened with 1%nano-CaCO₃ solution.For compressive strength,the compressive strength of RNC-1and RNC-2 concretes at 3d and 7d is only slightly higher than that of NAC group.However,compared with RAC-1 and RAC-2,the strength of RNC-1 group was slightly lower than that of NAC group at 28d,and the result of RAC-2 group was similar,but it was very similar to RAC-1 and RAC-2.Great improvement.The experiment shows that the nano-CaCO₃ solution has obvious strengthening effect on the recycled aggregate,and the early effect is better than the later stage.Compared with the flexural strength and the compression ratio at 28d,the flexural strength of the RNC-1 and RNC-2 groups was significantly improved and the toughness was improved after the same substitution rate.