Preparation And Basic Properties Of Alkali-activated Recycled Fine Aggregate Mortar

Cement is an important component of concrete materials.The production of cement requires a lot of resources and energy,and emits large amount of CO₂ and pollutants,which is not conducive to sustainable development.The application of alkali-activated cementitious materials provides a new solution to solve this problem.Alkali-activated cementitious materials are made of industrial by-product slag.The production process of alkali-activated cementitious materials has low energy consumption and emission.It is a green building material with good durability and high strength,and is considered as an effective substitute for cement.A large amount of construction waste is produced every year in China,among which waste concrete accounts for a large proportion.After crushing and screening,waste concrete can be made into recycled aggregate.The research shows that recycled coarse aggregate can partly replace natural stone on the premise of ensuring the mechanical properties of concrete,but the efficient utilization of recycled fine aggregate is a difficult problem.If recycled fine aggregate can be fully utilized,natural resources can be saved and the development of construction waste recycling industry can be promoted.At present,many studies focused on recycled concrete materials and alkali-activated materials,but the application of recycled aggregates,especially recycled fine aggregates,to alkali-activated materials is rare and insufficient.Recycled fine aggregate contains a lot of alkaline substances,and the cementitious properties of slag powder need to be stimulated quickly in alkaline environment.According to these characteristics,the alkaline substance in recycled aggregate may promote the activation of the cementitious properties of mineral powder,which can not only save the amount of activator,but also help to improve the properties of materials.Therefore,it is of great significance to study the application of recycled aggregate in alkali-activated materials.In this paper,mortar is used as research carrier,and the application of recycled fine aggregate in alkali-activated cementitious materials is systematically studied.The main contents are as follows:?1?The influence of recycled fine aggregate on the properties of alkali-activated mortar was studied under different kinds and dosages of activators,and the effect of recycled fine aggregate on the hydration of slag powder was investigated.The results show that the compressive and flexural strength of mortar increases with the increase of replacement rate of recycled fine aggregate under the excitation of liquid sodium silicate and anhydrous sodium silicate,especially at the early stage when the amount of low activator is added.Under the excitation of sodium hydroxide,the compressive strength of mortar decreases with the increase of replacement rate of recycled fine aggregate.The setting time of mortar decreases obviously with the increase of replacement rate of recycled fine aggregate,and the fluidity decreases with the increase of replacement rate of recycled fine aggregate.?2?Mortar with different replacement ratios of recycled fine aggregates was tested for pH value,thermal analysis of slag powder hydration,scanning electron microscopy and EDS.The results of pH value determination and hydration heat analysis show that the addition of recycled fine aggregate increases the alkalinity of the environment,thus accelerating the hydration process of slag powder,leading to the advance of hydration exothermic peak,and the greater the replacement rate of recycled fine aggregate,the more obvious the promotion effect.The results of electron microscopy and energy spectrum analysis show that the hydration products of slag powder become denser with the increase of replacement rate of recycled fine aggregate in the early stage of the specimen.?3?The effects of water-binder ratio and cement-mortar ratio on the basic mechanical properties and construction properties of mortar were investigated.The setting time,consistency and tensile bond strength of mortar were modified.The reference mix ratio of this new type mortar is given,which lays a foundation for its engineering application.