| At present,foam concrete（FC）is attracting more and more attention.FC is an economic and environmental friendly green material,which has the characteristics of light weight,good heat preservation and insulation,low elasticity and shock absorption,and good fire resistance.It has been widely used in civil construction,underground engineering,municipal engineering,sports,military and other fields.However,FC also has many shortcomings,low strength and high shrinkage are its main shortcomings,so improving the strength of FC and reducing its shrinkage is of positive significance to broaden the application of FC.In this paper,the mechanical and shrinkage properties of high-strength FC are studied.FC with density of 1600kg/m3 is prepared by using ordinary portland cement（OPC）,sulphoaluminate cement（SAC）,silica fume,nano silica fume,fly ash,lime powder,quartz sand,foaming agent and water reducer.First of all,by changing the four parameters of silica fume,fly ash,lime powder and water binder ratio of FC,the flexural and compressive strength of different specimens is tested by orthogonal test design method,and the best ratio of four admixtures is obtained.Then,on the basis of this optimal ratio,set up single mixing test,change the content of silica fume,nano silica fume,lime powder and SAC,test the flexural and compressive strength,self shrinkage value and dry shrinkage value of the specimens with different ratio,and use scanning electron microscope and non-metallic ultrasonic detector to study the mechanism of the change of strength and shrinkage value,and get the following results:（1）Based on the comprehensive consideration of 28 d flexural and compressive strength,the optimal mix proportion of FC with density of 1600 kg/m3 in this experiment is obtained:water binder ratio is 0.22,silica fume content is 15%,lime powder content is 2%,and fly ash content is 25%.In the case of the optimal mix ratio,the flexural strength of FC is 6.6 Mpa and 8.7 Mpa,the compressive strength is 21.7Mpa and 32.8 Mpa,the self shrinkage value is 741.2×10-6 in 72h,and the drying shrinkage value is 862.5×10-6 in 56d.Among the four factors of water cement ratio,silica fume content,lime powder content and fly ash content,the order of 28 d flexural strength is silica fume,water cement ratio,lime powder and fly ash;the order of 28 d compressive strength is water cement ratio,lime powder,fly ash and silica fume.（2）With the increase of silica fume,nano silica fume,lime powder and SAC,the flexural strength and compressive strength of FC increase first and then decrease.When the content of silica fume,nano silica fume,lime powder and SAC is 15%,4%,2%and10%,respectively,FC has the highest flexural and compressive strength.The results show that adding appropriate amount of silica fume,nano silica fume,lime powder and SAC can effectively improve the flexural and compressive strength of FC.When the flexural and compressive strength of FC with silica fume and nano silica fume reached the maximum,the addition amount of nano silica fume was 73.3%less than that of silica fume,but its strength was higher than that of FC with silica fume.（3）With the increase of silica fume,nano silica fume,lime powder and SAC,the self shrinkage value of FC decreases first and then increases,while the dry shrinkage value increases first and then decreases.When the content of silica fume,nano silica fume,lime powder and SAC were 15%,4%,2%and 10%,respectively,the self shrinkage and drying shrinkage of FC reached the extreme value.The shrinkage of FC with 4%nano silica fume is larger than that with 15%silica fume.（4）the microstructure of FC varies with the addition of silica fume,nano silica fume,lime powder and SAC.The smaller the pore size of FC is,the less the unhydrated particles are.The more C-S-H gel is,the denser the ettringite is,the denser the structure is.When the content of silica fume,nano silica fume,lime powder and SAC is 15%,4%,2%and 10%,respectively,the microstructure of FC is the best.FC with 4%nanometer silica fume has better microstructure than FC with 15%ordinary silica fume.（5）The ultrasonic velocity of FC has a strong correlation with its intensity.The higher the intensity of FC,the higher the ultrasonic velocity.When the content of silica fume,nano silica fume,lime powder and SAC is 15%,4%,2%and 10%,respectively,the ultrasonic velocity of FC is the highest.The ultrasonic velocity of FC with 4%nano silica fume is faster than that of FC with 15%nano silica fume. |
