| Solid wastes rich in calcareous and silica compositions are increasingly used in the production of autoclaved silicate materials.The ingredient design,hydrothermal product composition and mechanical properties of autoclaved silicate materials are all affected by hydrothermal activity of solid waste materials.In this work,waste concrete were used as calcareous and silica raw materials to prepare autoclaved silicate materials by calcination-hydrothermal synthesis process;The hydrothermal activity of calcareous compositions in waste concrete was characterized by CaO content and CaO activity in calcined products,so as to study the effect on the properties of autoclaved silicate materials.This research results can provide a theoretical basis for optimizing the calcination pretreatment system of waste concrete and improving the properties of autoclaved silicate materials,as well as a reference for investigating hydrothermal activity of other solid waste materials.The main contents are summarized as follows:The effect of CaO content and CaO activity obtained by different testing methods on compressive strength,phase composition and microstructure of autoclaved silicate materials under different calcination systems were investigated,as to determine the best method for characterizing the hydrothermal activity of waste concrete.The influence mechanisms of the hydrothermal activity of calcareous component on the properties of the autoclaved silicate materials was explored.Taking CaO content as the response target and using the CCD response surface design method to optimize waste concrete calcination regime,and meanwhile the effects of calcination resime on CaO conten,CaO activity and properties of autoclaved silicate materials were comprehensively considered.Finally,the optimal calcination system for waste concrete materials was determined.The main results are summarized as follows:（1）The values of CaO content obtained by different testing methods under different calcination systems:sucrose method>ethylene glycol-EDTA method>ethylene glycol method.The compressive strengths of specimens which use waste concrete calcination products as raw materials was generally higher than that of the analytically pure batching group;under different calcination systems,the compressive strength of specimens of the sucrose method ingredients group was the highest;the actual calcium-silica ratio of the specimens was close to the design calcium-silica ratio of 0.9 for calcination products of waste concrete at 890℃/30min and 890℃/60min and the batching according to the test results of the CaO content of the sucrose method;it was determined that the CaO content of the specimens under this thesis The suitable CaO content test method for waste concrete under the conditions of this study was sucrose method.（2）Taking CaO content as the response value,the significance of each factor on the thermal decomposition of Ca CO3in waste concrete was as follows:calcination temperature>holding time>heating rate;the interaction of each factors was significant;the optimal calcination regime obtained by optimization of CCD response surface experimental design method was 890°C,heating rate 3°C/min,holding time 90 min.The corresponding predicted value of CaO content was 37.03%.（3）Using the oxalic acid method to determine CaO activity,the laws of calcination regime and CaO content on CaO activity and CaO activity on the strength of autoclaved specimens were different from the metallurgical lime activity test method and the temperature rise rate method;using the oxalic acid method,CaO activity showed an overall decreasing trend with the increase of CaO content;with the increase of calcination temperature and the extension of holding time,CaO content increased and activity decreased,i.e.High CaO activity and high CaO content contradict the requirements of calcination regime;the effect of temperature rise rate on CaO activity is related to calcination temperature;the suitable CaO activity test method for waste concrete raw materials under the conditions of this thesis is determined as oxalic acid method.（4）Tobermorite phase and C-S-H gels dominated amorphous phase existed in hydrothermal products of autoclaved specimens;C2SH（A）,CSH（Ⅰ）and C2SH（B）phases were also existed in the hydrothermal products under different calcination regimes of waste concrete;with the increase of calcination temperature,the crystallinity of tobermorite decreased and the order degree and content of dicalcium silicate hydrate increased;when the content of amorphous compositions exceeded 50%,the strength of specimens increased significantly with the increase of amorphous compositions;the strength of specimens decreased when the content of dicalcium silicate hydrate increased.（5）Among the calcination systems,the calcination temperature had the most significant effect on the strength of autoclaved specimens,and there was obvious interactions between the effects of holding time and heating rate on the strength;high temperature calcination,high temperature of calcination for a long time and fast firing at high temperature would all affect the matching degree of hydrothermal activity of raw materials and the composition of hydrothermal products of autoclaved specimens,which led to low strength of the specimens;after considering the effects of calcination system on CaO content,CaO activity and the properties of autoclaved specimens,the optimal calcination regime of waste concrete in this work was determined.And the combination was low calcination temperature+high heating rate+long holding time.Finally,the calcareous component in waste concrete materials had high hydrothermal activity and high strength of specimens. |
