Study On Preparation And Performance Of Alkali Slag Foamed Concrete

Foamed concrete is a kind of lightweight material formed by introducing a large number of tiny closed pores into the slurry through physical or chemical foaming.It is widely used in the field of construction engineering due to its advantages such as light weight,heat insulation,good fluidity and environmental protection.In order to improve the strength and specific strength of foamed concrete,achieve light weight and high strength,and reduce the thermal conductivity under the condition of ensuring the strength,improve and expand its application.Alkali slag cementitious material is a new type of cementitious material,which has the characteristics of fast setting and hardening,early strength,high strength and easy access,and conforms to the development concept of new building materials.In this paper,the physical foaming method is adopted to prepare foamed concrete with alkali slag as cementitious material,and the coupling optimization of strength and thermal conductivity is carried out.Firstly,the preparation of alkali slag foamed concrete was studied.Then the effects of water-binder ratio and foam content on the properties of alkali slag foamed concrete were studied.Finally,through hydration heat,XRD,thermogravimetric analysis,SEM and other tests,the performance of ordinary Portland cement foamed concrete and alkali slag foamed concrete is compared and analyzed.The following conclusions were drawn:（1）Physical excitation,alkali excitation and thermal excitation are carried out on the slag to optimize the excitation mode and improve the matrix strength.The results show that the finer the slag fineness is,the better the mechanical properties are.When the sodium silicate content is 2%,3%,4%,5%,and the modulus is 0.8,1.0,1.2,1.4,the influence of the modulus and dosage on the strength of alkali slag foamed concrete is studied.The optimal alkali equivalent is 4%,and the optimal modulus is 1.0.High temperature curing is disadvantageous to mechanical properties;The mechanical properties are the best when the temperature of mixing water is 30℃.（2）Change the water-binder ratio to improve the pore wall strength of foamed concrete,and explore the change rule of thermal performance,deformation performance,frost resistance and pore structure.The results show that with the increase of water-binder ratio,the compressive strength and specific strength first increase and then decrease,and the maximum strength reaches 2.16MPa at 28d when the water-binder ratio is 0.43.The drying shrinkage value increased gradually.The thermal conductivity increases first and then decreases,and the thermal performance is the worst when the water-binder ratio is 0.43.The frost resistance becomes worse first and then becomes better.The porosity and average pore diameter decreased first and then increased.（3）Change the amount of foam to reduce the thermal conductivity of foam concrete,and explore the change rule of mechanical properties,deformation properties,frost resistance and pore structure.The results show that with the increase of foam content,the compressive strength and thermal conductivity decrease gradually.The drying shrinkage value increased gradually.The frost resistance gradually deteriorated;The mathematical fitting of density,compressive strength,thermal conductivity,porosity and average pore diameter with different foam content shows a good correlation.（4）Under the same design density condition,the mechanical properties and thermal properties of alkali slag foamed concrete are better than those of ordinary Portland cement foamed concrete,but the drying shrinkage is larger.The total amount of hydration heat release of alkali slag cementitious material is low.There is a large amount of C-S-H gel in the hydration products of alkali slag foamed concrete,but no Ca（OH）₂ is detected,and there is a lack of crystallizing material to limit shrinkage.The microstructure of alkali slag hydration product is more compact than that of cement hydration product,which makes the test block have higher strength.