Research On Influence Of Admixtures About Properties Of Mortar Mixed With Modified Superfine Powder

At present,dry mixed mortar is widely used in the construction industry.This paper mainly studied the influence of single admixtures or several admixtures on the performance of mortar in order to improve the workability and mechanical properties.It can promote the development of admixtures to some extent.The optimum content of hydroxypropyl methyl cellulose（HPMC）,redispersible latex powder（VAE）,starch ether（SE）,polycarboxylate superplasticizer（PS）and sodium dodecyl benzene sulfonate（SDBS）were determined by comparative test.And the best combination of VAE,SE,PS and SDBS was studied by the orthogonal test of L₉（3⁴）.The results of cement mortar test showed that the modified superfine powder with 15%steel slag powder had the best properties.Such as the specific surface area reached the maximum value of 573cm²/g,and the fluidity ratio reached the maximum value of 100.4%.The flexural strengths of colloidal sand of 3d and 28d reached to4.3MPa and 6.7MPa respectively,and the flexural strengths were relatively high.The compressive strength of 3d reached the maximum number,which was 21.9MPa.The compressive strength of 28 days was 69.3MPa,only less than the compressive strength with a content of 20%.The water-material ratio reached the minimum value of 12.6%,as well as the content of air was high relatively when the dosage of QiGong admixture was0.6‰.And the compressive strength at 7 and 28 days reached to the maximum value of 6.1MPa and 7.6MPa respectively.The compressive strength decreased with the increase of HPMC.It has a bad effect for the mechanical properties of mortar,but its performance of water retention is good.Considering its viscous influence on construction,the content of 0.6‰was selected.The compressive strength reached to the maximum values of 7.8MPa and 10.5MPa respectively,both higher than the benchmark mortar when the amount of VAE was 2%.The water retention effect of SE was poor when used lonely.The compressive strength reached the maximum value of6.5MPa and 8.3MPa respectively,and the bonding strength was 2.1 times of the benchmark mortar when the content of SE was 0.6‰.PS has obvious water reducing effect,which affects the mechanical properties of mortar.And its content of 0.8‰was selected.SDBS mainly affected the gas content of mortar and the gas content reached to the maximum value of 9.5%when its content was 0.6%.The orthogonal test results showed that when the modified ultrafine powder had different specific surface areas,the best combination of admixtures was different.The dosages of SDBS,VAE,SE,PS were 0.6%,2%,0.6‰,0.9‰respectively when the specific surface area was 500cm²/g.The dosages of SDBS,VAE,SE,PS were0.7%,2%,0.6‰,0.8‰respectively when the specific surface area was 600cm²/g.The dosages of SDBS,VAE,SE,PS were 0.6%,2%,0.7‰,0.9‰respectively when the specific surface area was 700cm²/g.By comparing three different specific surface areas,the modified superfine powder of 500cm²/g was selected as the admixture material,and its workability and mechanical properties were better.