Study On Cementitious Properties Of Steel Slag-slag Composite

As a huge amount of industrial waste produced annually in China,steel slag has potential hydraulic properties.However,its activity is difficult to be stimulated,and its stability is poor.Thus its wide applications in the construction field are limited.In this thesis,the activation and stability improvement of steel slag are studied,which lays a foundation for the applications of steel slag in the field of building materials.The main contents of this thesis are as follows:The effect of single activator on the cementitious properties of steel slag-slag system was investigated.The results show that water glass,calcium hydroxide,calcium sulfate dihydrate,sodium metaaluminate and sodium citrate can improve the volume stability and cementitious properties of steel slag-slag.With the increase of sodium silicate,calcium hydroxide,calcium sulfate dihydrate,sodium metaaluminate and sodium citrate,the compressive strength of the samples first increases and then decreases.When the respective content of sodium silicate,calcium hydroxide,calcium sulfate dihydrate,sodium metaaluminate and sodium citrate is 3wt%,5wt%,6wt%,3wt%and 4wt%,the 7d compressive strength reaches the maximum value,which is 10.87MPa,9.45MPa,8.75MPa,10.92MPa and 8.89MPa,respectively.The effect of composite activator on the cementitious properties of steel slag-slag system was studied by orthogonal experiment.The order of the influence on the cementitious performance of the samples is ranked as:calcium sulfate dihydrate>calcium hydroxide>sodium metaaluminate>water glass>sodium citrate.The results show that the optimum composite activator is composed of 1.5wt%sodium citrate,1.0wt%calcium hydroxide,5wt%calcium sulfate dihydrate,1.5wt%sodium silicate and 1.0wt%sodium metaaluminate.The 7d compressive strength of steel slag-slag sample reaches 16.84MPa.The hot stewed steel slag was divided into five particle size ranges:larger than8.0mm,4.0-8.0mm,0.3-4.0mm,0.15-0.3mm,and less than 0.15mm.The graded steel slag was ground into steel slag powder,which was then steam cured for 1h,2h and 3h in 100?steam,respectively.The results show that f-Ca O and RO phases are mainly concentrated in the steel slag with large original particle size,Mg O in 0.3-4mm steel slag powder,and Ca CO₃and Ca(OH)₂in fine particles.The content of f-Ca O in steel slag increases with the increase of original particle size of steel slag;steam curing can effectively promote the digestion of f-Ca O in steel slag,but has no obvious effect on the digestion of Mg O;the larger the original particle size of steel slag powder,the more obvious the effect of steam curing to reduce the content of f-Ca O.After steam curing for 3h,the f-Ca O content of steel slag with original particle size larger than8.0mm decreases from 5.43wt%to 1.61wt%,and that of steel slag with particle size of 0.15-0.30mm decreases from 1.34wt%to 0.73wt%.The non-evaporating water content of steel slag samples decreases with the increase of original particle size of steel slag;for steel slag powder with the same original particle size range,the longer the steam curing time is,the higher the non-evaporating water content of the corresponding samples is.With the decrease of the original size of steel slag,the compressive strength of corresponding steel slag-slag samples increases.For the steel slag powder with original particle size larger than 8.0mm,the proper steam curing time is 3h,and the28d compressive strength of the corresponding steel slag-slag sample is 28.40MPa.For the steel slag powder with original particle size of 4.0-8.0mm,the proper steam curing time is 2h,and the 28d compressive strength of the corresponding steel slag-slag sample is 24.78MPa.As for the steel slag powder with original particle size of 0.3-4.0mm,it is not suitable to be used as the raw material of cementitious materials,because it contains a lot of magnesium oxide.For the steel slag powder with original particle size of 0.15-0.3mm,the proper steam curing time is 1h,and the28d compressive strength of the corresponding steel slag-slag sample is 28.25MPa.For the steel slag powder with original particle size less than 0.15mm,no steam curing is required,and the 28d compressive strength of the corresponding steel slag-slag sample is 26.01MPa.