Investigation On Effect Of Pozzolanic Powder On Foam Concrete Pore Structure And Frost Resistance

Foam concrete is a new kind of green material with porous and light weight.The pore structure parameters such as pore diameter distribution and porosity play a decisive role in the performance of foam concrete.Its low strength and poor frost resistance due to its porosity is an important reason that restricts its further promotion and application.The particle filling effect and the volcanic active properties of silica fume and slag powder could improve the performance of foam concrete.On the other hand,silica fume and slag powder are used as industrial waste insead of partial cement to prepare foam concrete,which has good social and economic value.In this thesis,the influences of water-cement ratio,silica fume and slag powder on the frost resistance of foam concrete were studied.Then the image analysis method was used to illustrate the effect of the forementioned factors on the porosity and the pore size distribution before and after 0 and25 freeze-thaw cycles.Subsequently,the regression analysis on porosity and mass loss rate and strength loss rate were performed.Ultrasonic non-destructive test was applied to analyze the effect of ultrasonic velocity after 0,15,20,and 25 freeze-thaw cycles,where frost resistance of foam concrete was evaluated by damage degree.Finally,the macroscopic pore structure and microscopic hydration products of foam concrete after 0 and25 freeze-thaw cycles were compared by electronic scanning electron microscopy.The research results are showed as follows.(1)The mass loss rate and the strength loss rate decreased first and then increased with the increase of water-cement ratio,the ultrasonic speed increased first and then decreased,and the damage degree decreased first and then increased;when the water-cement ratio was 0.5,after 15 cycles,20 cycles,25 cycles,the mass loss rate and strength loss rate were the lowest,the ultrasonic speed was the largest,and the damage degree was the smallest.(2)The porosity decreased first and then increased with the increase of water-cement ratio.When the water-cement ratio was 0.5,the porosity reached the lowest;the pore size distribution ranging from 0-400?m increased first and then decreased;lager than 800?m decreased first and then increased with the increase of water-cement ratio.(3)The mass loss rate and the strength loss rate increased first and then increased with the increase of the amount of silica fume and slag powder.The ultrasonic speed increased first and then decreased,and the damage degree decreased first and then increased;when the dosage of silica fume was and slag powder were 6% and 30% respectively,the mass loss rate and strength loss rate were the lowest,the ultrasonic speed was the largest,and the damage degree was the smallest,after 15 cycles,20 cycles,25 cycles.(4)Porosity decreased first and then increased with the increase of silica fume content and slag powder content.When the dosage of silica fume and slagl powder were 6% and 30%,respectively,the porosity was the lowest;Loss rate and strength loss rate and porosity were linear proportional regression relationship;the pore size distribution range from0-400?m increased first and then decreased with the increase of silica fume content and slag powder content,and lager than 800?m decreased first and then increased.(5)Incorporation of pozzolanic powder silica fume and slag powder reduced the flaky calcium hydroxide of the foam concrete hydration product of foam concrete,increased the hydrated calcium silicate,made the pore size distribution more uniform,decreased the average pore size and the communication pores,increased the thickness of pore wall.It provides a theoretical basis for the improvement of frost resistance.