Study On Performance And Mechanism Of Structure-function Integrated Alkali-activated Slag Foam Concrete

The traditional foam concrete has the advantages of lightweight and thermal insulation.However,due to the drawbacks of slow development of early strength,and easy to collapse,the application is limited to some extent.Compared with ordinary Portland cement（OPC）,the advantages of using alkali-activated slag（AAS）to prepare foam concrete are:（1）It owns higher rate of strength growth and higher compressive strength than OPC;（2）Its preparation does not require any cement clinker,only industrial products,so it is energy-saving and environmental-friendly;（3）The use of activators including sodium silicate and sodium hydroxide makes the fresh slurry has a great viscosity and fluidity,which can help slurry better bind the foam and form a large number of small pores.It can make alkali-activated slag foam concrete achieve better mechanical properties.However,when sodium silicate and sodium hydroxide are used as the activator to prepare light and high-strength alkali-activated slag（AAS）foam concrete,the biggest disadvantage is that the setting time of alkali-activated slag foam concrete is too short and the speed of losing liquidity is too fast,which leads to certain difficulties in applying it to actual projects.Therefore,alkali-activated slag is used as cementitious materials in this paper to prepare alkali-activated slag foam concrete,and the properties and the corresponding mechanisms are studied.At first,the effect of different mixing times on the setting time and fluidity of alkali-activated slag foam concrete is studied to solve the problem of too short setting time and fast fluidity loss rate.After effectively prolonging the mixing time,the water-binder ratio,the effects of the modulus of the activator,the content of Na₂O,the content of foam,and the content of OPC on setting time,fluidity,compressive strength,thermal conductivity,drying shrinkage and other macro-performance of the alkali-activated slag foam concrete were studied,and a good mix radio with better overall performance was obtained.By studying the microstructure,the relationship between it and the macroscopic performance is discussed.The main results are as follows:（1）The mixing time is an important parameter in the preparation of AAS foam concrete.During the process of prolonging the mixing time from 4 minutes to 20 minutes,the setting time of the alkali-activated slag foam concrete was gradually prolonged,and the fluidity first decreased and then increased.Meanwhile,its compressive strength at 28d first increased and then decreased,and the thermal conductivity increased gradually.When the mixing time was12 minutes,the setting time was prolonged to 340 minutes,and it is was sufficient to meet the requirements of the actual project.Besides,the maximum compressive strength was obtained at this time.（2）The effects of the modulus of activator,water-binder ratio,Na₂O content,foam content,and OPC content on the performance of AAS foam concrete after prolonged mixing time to 12minutes are as follows:1)As the modulus increased from 1.0 to 1.4,the fluidity of the freshly mixed slurry deteriorated gradually,the strength of the AAS foam concrete decreased gradually,and the thermal conductivity increased gradually.2)As the water-cement ratio increases from0.40 to 0.50,the strength first increased and then decreased,and the fluidity of the alkali-activated foam concrete increased gradually.3)As the Na₂O content increased from 3 wt.%to7 wt.%,the strength of the alkali-excited foam concrete increased first and then decreased,the fluidity of the freshly mixed slurry deteriorated gradually,and the thermal conductivity decreased gradually.4)As the content of OPC increased from 1 wt.%to 10 wt.%,the compressive strength of alkali-activated slag foam concrete increased first and then decreased,and the thermal conductivity decreased gradually,accordingly,the drying shrinkage decreased.（3）Through the analysis of the microstructure of alkali-activated slag foam concrete,the relationship between macroscopic properties and microstructure were established.The analysis showed that the compressive strength of the alkali-activated slag foam concrete was related not only to porosity but also to the average pore size and average roundness in the pore characteristics.When the porosity of the AAS foam concrete of different samples was close,if the average pore size and the average roundness was larger,the compressive strength of AAS foam concrete was lower.Besides,the thermal conductivity of the alkali-activated foam concrete was not only related to the porosity but also the average pore size.When the porosity was close,the smaller the average pore size was,the lower the thermal conductivity was.