Research On Active & Cementitious Capacity Of Steel-making Slag And Its Concrete Properties

Our environment is deteriorated by the various industries wastes such as Steel-making slag (SMS). But so far reutilization of SMS is still being limited because of the fluctuation of mineral and chemical components, bad trace elements, difficult pretreatment, worse milling-resistant and so on.Aiming at such difficult problems in high efficient reutilization of SMS, the activity agitated technique of SMS and the industrialization parameter were mainly discussed in this thesis. With the same specific surface, the degree of roundness and the particle morphology of fine SMS particle prepared by polarization milling can be improved greatly and the cementitious property of SMS is improved further. The activity of SMS can be confirmed by the physical quantity correlation which is consisted of the physical filling, physical-chemical absorption, chemical linage and coactions between cement particles. The relationship between components, structure and performance of SMS are studied thoroughly and relationship between composition and cementitious property of SMS is discussed. The results indicate that alkalinity parameter can determine the content of active mineral, but it can not determine cementitious property of SMS, which is determined by its mineral composition calculated from chemical composition and pretreatment method. Then the activity factor is put forward to evaluate the activity of SMS, which can obtain the feasible the specific surface and dosage of SMS.In addition, the effect of single SMS or SMS combining with Blast Furnace Slag (BFS) or Fly Ash (FA) on mechanical and long-term durability property is investigated systematically. The results indicate that SMS is a kind of high activity mineral additive. Excellent flowing concrete of C20-C55 strength grade range with about 20cm initial slump can be obtained by replacing 42.5 OPC with 10-50% SMS. The SMS has the good accommodation with BFS and FA. The workability and rate of latter strength growth of concrete with the compound SMS is better than that of concrete with the single SMS. The compound SMS with BFS and FA can improve the shrinkage of concrete at each age. Its resistant to chloride ion permeability of concrete is superior to the single mineral additive. Basing on the study of the macro-performance, composition feature of hydration products and microstructure characteristic of cementitious materials with SMS are studied by XRD, DTA-TG, SEM and hydration heat. The results indicate that Sequence of activity in early age is SMS> BFS> FA and sequence of activity in later age is BFS>SMS> FA. For filling effect, the BFS is the best, the SMS is the next in order and the FA is the worst. At the hydration age, the filling effect of compound of SMS and BFS is higher than that of the BFS only, i.e. the ultra superposition of them is excellent. Single or compound of these three mineral additives can decrease the hydration heat to some extent. Comparing to SMS and FA, reducing hydration heat of BFS is not very obvious, however reducing hydration heat of SMS is similar to FA. Considering the earlier activity of three mineral additives, it can be believed that the SMS has the advantage on preparing the big volume concrete with higher earlier strength.The percolation theory and sub-cluster statistics theory is put forward in the thesis, which can be showed the interaction between the cement particles during the hydration process and the relationship between the microstructure of cement stone and the macro-performance. The relationship between the microstructure and the performance can be described as the percolation problem of the confirm phase, degradation phase and continuous phase in cement stone interspaces. The pore percolation-strength model is used to study the cement containing SMS firstly in the thesis. The results indicate that the SMS begin hydration at earlier age. But with its low hydration activity, there is the big pore in cement structure, meanwhile, there is the positive effect of unhydrated SMS particles impersonation, which prove that the SMS is a kind of faulty clinker.In addition, the cementing compound material is made of the different kinds and hierarchy sub-cluster from the angle of the powder movement. The property of material is determined to exist the competition of the different sub-cluster. So the relationship between them can be established accordingly. The sub-cluster statistic theory is used to study the hydration process of cement containing SMS firstly in the thesis. The essence of the cement hydration process is that the competition capacity is changed with the time collapse process between cement and hydration productions. After adding water, cement hydration is relied on the competition action between the cohesion and disperse. The influences of any factors on the hydration process are realized by changing its competition ability. This competition action can be demonstrated efficiently by the sub-cluster parameter-cybotaxis scale.The particle diameter of compound material reduces greatly when mixing compound SMS, i.e. disperse ability of compound material is very well. The activity of mineral additives is worse, the cybotaxis scale is smaller, and the competition capacity of cement particles being disperse is high, i.e. the dispersion of cement particles becomes stronger. Basing on the sub-cluster statistic theory, it is necessary to analyze the component and structural characteristic of SMS, optimize the fineness and dosage of the SMS in order to gain the optimized dispersancy, further the excellent performance of the SMS concrete in the most effective usage process of the SMS.