Effect Of Nano C-S-H-PCE On Hydration And Durability Of Cement-mineral Admixture Paste

As a new type of composite nanomaterials,nano C-S-H-PCE has a broad application and development prospect in the production of low carbon emission and non-autoclaved curing of precast concrete components which are strongly advocated by the state.The early hydration and microstructure formation and evolution of cement directly determine the production efficiency of precast concrete members.Nano C-S-H-PCE,as an additional nucleation site of C-S-H gel--the strength source of cement,can effectively regulate the early hydration process and microstructure formation process of cement,accelerate the mold turnover rate of precast concrete components,promote the application of precast concrete components in prefabricated buildings,and move the construction industry toward green factory production.It has important function and significance.In this paper,the effect of nano C-S-H-PCE on the hydration process of cement-mineral admixture paste was studied.The effects of nano C-S-H-PCE on hydration products,microstructure evolution and mechanical properties of cement-mineral admixture paste were revealed.The influence of nano C-S-H-PCE on the durability of cement-mineral admixture mortar was elucidated.The internal relationship between hydration,microstructure and durability was established,and the test results were as follows:(1)Nano C-S-H-PCE accelerated the hydration process of cement-mineral admixture pasteThe effect of nano C-S-H-PCE on the hydration process of cement-mineral admixture paste was studied by setting time,electrical conductivity,pH test and chemical binding water test.The test results showed that with the increase of nano C-S-H-PCE,the setting time of composite cementification system decreased significantly.Nano C-S-H-PCE accelerated the ion dissolution of cement particles and the fracture of chemical bond of mineral admixture.The hydration degree of cement-mineral admixture is increased.The acceleration mechanism of nano C-S-H-PCE on cement-mineral admixture paste was revealed:The addition of nano C-S-H-PCE provides a large number of nucleation sites.By alternating adsorption of H2SiO42-and Ca2+ dissolved by silicate phase in cement paste and H2SiO42-formed by mineral admixture breaking bonds under the action of CH on its surface,hydration products can be formed faster,and microstructure formation and hydration reaction process can be accelerated.(2)Nano C-S-H-PCE promoted the formation,microstructure and strength of hydration productsThe hydration products were characterized by TG,FTIR and BET tests.The results showed that the formation of C-S-H gel,AFt and CH in the early stage of the composite gel system was accelerated with the increase of nano-C-S-H-PCE content.The influence of nano C-S-H-PCE on pozzolanic reaction of mineral admixtures was characterized by BET and NMR tests.The test results confirmed that nano C-S-H-PCE promotes the fracture of Si-O bond and Al-O bond of metakaolin and fly ash.The pore structure evolution was characterized by ultrasonic,MIP and BET micropore analysis.The results showed that nano C-S-H-PCE increased the inner compactness of cement-mineral admixture paste.The cement-mineral admixture with nano C-S-H-PCE has a smaller pore size,a smaller cumulative pore volume,and a significant increase in gel and intergel pores.Nano C-S-H-PCE significantly improved the 12h compressive strength of cement-mineral admixture mortar,and the later strength was further improved under the action of the pozzolanic reaction of mineral admixtures.(3)Nano C-S-H-PCE improved the durability of cement-mineral admixture pasteWith the increase of nano-C-S-H-PCE content,the cement-mineral admixture mortar’s permeability resistance,chloride ion erosion resistance and freeze-thaw damage resistance have been improved to some extent..(4)The internal relationship between hydration,microstructure and propertiesThe addition of nano C-S-H-PCE reduces the porosity and the optimum pore size of cement-mineral admixture mortar,reduces the ability of water tran sport,and improves the permeability.Nano C-S-H-PCE reduces the porosity,improves the pore size ratio of mortar below 50nm,promotes the formation of hydration products of mortar,is conducive to the adsorption and solidification of chloride ions,and prevents their transmission to the interior.Nano C-S-H-PCE reduces freezable water and shortens migration path,which is beneficial to mortar resistance to freezing-thawing damage.