The Research On Working And Mechanical Properties Of Slag-Metakaolin Based Geopolymer Paste And Recycled Concrete

In order to give full play to the advantages of resources,the system of new environmental protection building materials in a real sense.In this paper,the mix ratio design of slag-metakaolin base polymer clean slurry and recycled concrete is carried out,and the influencing factors of its working performance and mechanical performance are studied respectively.The main contents and results of the research are as follows:The basic performance indexes of the slag-metakaolin based geopolymer recycled concrete in the preparation of the required raw material were determined,and in accordance with the relevant standard established the slag-metakaolin based geopolymer net pulp and recycled concrete preparation plan,work performance(net pulp setting time,fluidity,the concrete slump,extension,degrees)and mechanical properties(compressive strength,flexural strength)measurement scheme.In the test of paste,a mixture of 40/60%slag and metakaolin was used as raw material.Three factors,including the activator modulus,concentration and liquid-solid ratio,were set.Five gradients were set for each parameter to complete 125 sets of paste specimens.When the activator modulus is less than 1,the final setting time of the generated geopolymer paste exceeds 390min,and the highest final setting time reaches 608min.In actual production,the situation that the activator modulus is less than 1 should be avoided.The concentration and modulus of the activator have no significant effect on the fluidity of the paste,and the liquid-solid ratio is the key factor affecting the fluidity of the alkali-activated slag-metakaolin based geopolymer.The compressive strength at 7d and 28d increased with the increase of the concentration of activator,and decreased with the increase of liquid-solid ratio.The compressive strength at 76.03MPa changed from the lowest 14.37MPa with the change of concentration;The geopolymers with SiO2 content between 49%and 51%,H2O content between 40%and 41%,and Na2O content around 12%in the products have higher mechanical properties,but the Na2O content with the best slurry working performance should not exceed 9%,H2O content should not be less than 50%.According to the results of the test of paste,the activator modulus and the concentration of the concrete test were set as 1.2 and 35%,and the bone-binder ratio was selected as 0.35 and the sand ratio was 30%.The effects of mixing process,fine aggregate type,replacement rate of recycled aggregate and liquid-solid ratio on the performance of the concrete test were investigated.The slag-metakaolin base aggregates recycled concrete made of different kinds of fine aggregates have the following slump and expansion degree from large to small:NR>MR>RR;When the liquid-solid ratio is more than 0.8,the replacement rate of recycled aggregate is more than 60%,and the group using natural sand reaches the optimal fluidity defined in ordinary coagulation,and the slump of recycled concrete is less than 100mm,the fluidity of the mixture is poor.When MR is used as fine aggregate,the compressive strength and flexural strength of slag-metakaolin base polymer concrete are the highest,reaching 68.2MPa and 10.4MPa,respectively,in 28d.In comparison,the strength of NR was slightly decreased,and the strength of RR was the lowest.Under the same liquid-solid ratio and the replacement rate of recycled aggregate,the minimum compressiveand repture strength was only 25.3MPa and 4.6MPa.With the increase of the replacement rate of reclaimed aggregate,the failure mode changes from the interface failure between aggregate and mortar to the failure mode of reclaimed aggregate itself.