Study On Mechanical Properties And Microscopic Mechanism Of Alkali Activated Fly Ash Stabilized Construction Waste

The purpose of this paper is to study the potential of alkali-activated fly ash geopolymers and construction demolition wastes for reuse in the field of engineering.The geotechnical properties,chemical reaction mechanisms,and microstructure evolution of alkali-activated fly-ash-stabilised construction and demolition waste（C&D）and the main components recycled concrete aggregate（RCA）and clay brick（CB）were investigated in this study.The alkali activator was a composite solution of sodium hydroxide and water glass.XRD,FTIR,SEM,and UCS testing methods were used to analyse the properties and mechanisms of the alkali-activated fly-ash-stabilised C&D and main single-component RCA and CB.On the basis of the previous test,the optimal mixing ratio of construction demolition waste and fly ash is obtained,and then uniaxial and triaxial compression tests are carried out on alkali-activated fly ash stabilized construction waste samples.The deformation and damage evolution characteristics of specimens under different confining pressures are studied.The test results demonstrate that using alkali-activated fly ash in stabilising C&D improves the UCS of the material significantly.When C&D is mixed with fly ash at a mass ratio of 60/40,its UCS reaches 37 MPa at 28 days,which is much higher than the strength requirement of cement-stabilised soil mixture and meets the strength requirements of inorganic binder stable materials for road base and sub-base layers.C-A-S-H and N-A-S-H（where N=Na₂O,A=Al₂O₃,C=Ca O,S=Si O₂,and H=H₂O）generated by the alkaline activation have several similarities with cement hydration products and also show high cementing ability.Alkali-activated fly ash improves the strength and stability of C&D as a roadbed filler and has prospective applications in road engineering.The internal damage evolution of this test material has gone through five stages:elastic recovery,damage start,damage acceleration,damage slowing,and complete damage.The confining pressure has a great influence on the deformation characteristics of the sample.Analogous to the damage evolution model of rock materials,it is verified that the model is also suitable for the description of the deformation characteristics and damage evolution law of alkali-activated fly ash stabilized construction and demolition waste materials,Through the analysis of test data and model parameters,The model is highly consistent and the physical meaning of the parameters is clear.It also has good consistency.By obtaining the deformation characteristics and damage evolution law of the material,it can better provide theoretical support for the combined utilization of the two materials of construction demolition waste and fly ash.