| With the deepening of national construction industrialization policy,concrete prefabricated products have become an important development trend in the concrete industry,because they have advantages of short production cycle,easy quality control and high construction efficiency.Recently,studies have shown that the nano materials represented by C-S-H nanocomposites can accelerate the early hydration of cement and significantly improve the early strength of concrete and won’t compromise long-term strength of concrete.Three kinds of nano organic and inorganic hybrid C-S-H with different particle size are prepared by co-precipitation method at room temperature.At different temperatures,the changes of particle conformation and particle size of nano organic and inorganic hybrid materials in different solution environments are studied by using dynamic and static light scattering.The impact of nano organic and inorganic hybrid materials on the early strength development of mortar specimens under different curing conditions is studied.After particle size optimization,the influence of admixing nano organic and inorganic hybrid materials on mechanical properties and durability of concrete is systematically studied.Finally,the impact of nano organic and inorganic hybrid materials on the hydration process and hydration products of cement is studied via microcalorimetry,XRD analysis and Scanning electronic microscope.It shows that:（1）Particle size and solution conformation of nano organic and inorganic hybrid materials are significantly affected by temperature and solution environments.The particle size of nano-hybrid materials is monodispersed.With the increase of temperature,the particle size of nano organic and inorganic hybrid materials decreased and affected by complexation and electrostatic shield,the particle size is largest in saturated calcium hydroxide and smallest in simulated pore solution.（2）Under the standard curing condition,adding nano organic and inorganic hybrid materials could significantly improve the early compressive strength and flexural strength of mortar specimens.At same dosage,S2 with an average particle size of78.0nm has the best early strength improvement effect,and compressive strength of 6h with 0.4wt%S2 is 314.0%compared with the blank group.The strength enhancement effect of the nano organic and inorganic hybrid materials decreases with the extension of the curing age,and after curing 7days,the compressive strength with or without S2are nearly the same.Under the steam curing condition,the hydration rate of cement itself is fast,at the same time the nano organic and inorganic hybrid materials further accelerate the hydration and improve the early strength of mortar.The mortar’s compressive strength of 12h is only 28.0%higher than that of blank counterpart.（3）Under the conditions of low temperature（5℃）,normal temperature（20℃）and steam curing temperature（40℃）,0.4wt%S2 could significantly improve the early compressive strength of concrete,and compared with the control group,the compressive strength of concrete with nano organic and inorganic hybrid materials at the 12h age increases to 433.0%,206.0%and 274.0%respectively.The addition of nano organic and inorganic hybrid materials has no effect on the 28d strength of concrete,but could improve the long-term strength under steam curing.The introduction of nano organic and inorganic hybrid materials has no obvious effect on the self-shrinkage of concrete but could improve the drying shrinkage of concrete.Meanwhile,nano organic and inorganic hybrid materials basically have little effect on the resistance to chloride ion permeability of concrete at the age of 28d.（4）The addition of nano organic and inorganic hybrid materials could significantly accelerate the heat release rate of cement hydration.The smaller particle size is and the higher dosage is,the greater acceleration effect will be.With dosage increasing,the acceleration effect has been improved.Both temperature and material particle size have an impact on the early strength improvement.On one hand,the increase of temperature can significantly accelerate the hydration rate of cement,and on the other hand the early hydration of cement could be further accelerated due to the decrease in particle size of nano materials under high temperature.（5）XRD analysis and SEM results show that clinker mineral C3S consume fast,and a large number of amorphous hydrated calcium silicate gels and CH layers are generated on the surface of cement particles. |
