刘燕妮1 ，吴晓荣1 ，王 刚2 ，赵明宇1 ，佟 钰1
1. 沈阳建筑大学 材料科学与工程学院，辽宁 沈阳 110168；2. 中建八局第二建设有限公司，山东 济南 250022
引用格式：
刘燕妮，吴晓荣，王刚，等 . 焙烧过程对再生微粉微观结构和活性指数的影响［J］.中国粉体技术，2024，30（5）：113-120.
LIU Y N， WU X R， WANG G， et al. Influence of calcination processing on the microstructural characteristics and activity index of recycled fine powder［J］.China Powder Science and Technology，2024，30（5）：113−120.
DOI：10.13732/j.issn.1008-5548.2024.05.010
收稿日期：2023-11-14，修回日期：2023-12-26，上线日期：2024-08-26。
基金项目：国家自然科学基金项目，编号：52278266；辽宁省教育厅高等学校基本科研项目，编号：JYTZD2023165。
第一作者简介：刘燕妮（1997—），女，硕士生，研究方向为建筑固废综合利用。E-mail：1027421700@qq. com。
通信作者简介：佟钰（1972—），男，副教授，博士，硕士生导师，研究方向为无机纳米材料的制备与应用。E-mail： tong_yu123@hotmail. com。
摘要：【目的】 解析再生微粉焙烧活化机制，改善废弃混凝土的综合利用效果。【方法】 分析焙烧条件对再生微粉火山灰反应活性的影响规律，结合综合热分析和X射线衍射技术对焙烧过程中再生微粉的物相变化进行分析讨论。【结果】 再生微粉的活性指数随焙烧温度上升或焙烧时间延长而明显提高，但温度不宜高于600 ℃且时间控制在1. 0~1. 5 h，否则会导致再生微粉的活性指数下降；微观结构分析发现，温度为600 ℃、焙烧时间为1. 5 h可使再生微粉中的高岭石等黏土矿物以及水化硅酸钙等水泥水化产物发生脱水分解，从而改善再生微粉的火山灰反应活性，但在更高的温度800~900 ℃下则形成铝硅尖晶石、钙黄长石等低活性物质，导致再生微粉火山灰反应活性下降。【结论】 焙烧处理对再生微粉具有明显的活性激发作用，但焙烧温度和时间应与再生微粉的化学成分及矿物组成相匹配。
关键词：混凝土；再生微粉；焙烧；活性指数；微观结构
Objective Recycled fine powder （RFP） is microscaled granules generated in the preparation of recycled aggregates by a process of crushing of construction or demolition wastes. Some feasible ways have been developed to realize the resourced utilization of RFP， of which with the most adaptable one being as the active admixture for the production of Portland cement or commercial concrete. The higher the pozzolanic activity of RFP is， the greater the utilization rate that can be achieved. The process of calcination at a temperature not exceeding 1 000 ℃ is generally esteemed as one of the most effective ways to enhance the economic and technological results of RFP as concrete admixture. However， the activation mechanism of RFP in the process of high temperature calcination may not consistently explain the experimental results in any cases， since the the efficiency of calcination is apparently depending on the source of RFP material and the temperature regime of the calcination. A strong requirement arises subsequently to clarify the activization mechanism of RFP in the process of high temperature calcination.
Methods In this paper， RFP specimens were calcined at a certain temperature ranging from 600 to 900 ℃， while the calcination time was adjusted in the range of 0. 5 to 3. 0 hours. The as-prepared RFP specimens were used to partly replace the Portland cement at a weight ratio of 30% for the preparation of standard mortar with a water-to-cement （W-C） ratio of 0. 5 by weight and a weight ratio of 3∶1 for the standard sand to Portland cement. Changes in the compressive strength of such mortar blocks after the standard curing of 7 d and 28 d were investigated in details to reveal the effect of high temperature calcination on the pozzolanic activity of RFP， followed by the measurements and discussion of the microstructural characteristics of RFP by means of comprehensive thermal analysis，i. e. thermal gravity （TG） and differential scanning calorimeter （ DSC ）， and X-ray diffraction （XRD） to demonstrate the phase changes of RFP during the high-temperature calcination.
Results and Discussion When the calcination temperature increased from 600 to 900 °C step by step， the activity index of calcined RFP was found to increase evidently with the increasing temperature for calcination， but further elevation of calcination temperature higher than 600 °C was not proposed due to the lowering of the activity index. Similar results was observed from the activity index tests of RFP calcined at 600 °C with different time， in which the activity index of RFP was found to increase apparently when the calcination time was not longer than 1. 5 hours， but further increase of calcination time gave rise of a relative low activity index from the obtained RFP. Therefore， the suggested calcination conditions for RFP were to be 600 °C in temperature and 1. 0~1. 5 h in time， which could bring forth of a maximum activity index of 90. 19% at the age of 28 d. It is also found that the as-prepared RFP resulted in a relative high index of pozzolanic reactivity at the age of 7 d compared to that at 28 d. Furthermore， microstructural characterizaion under TG-DSC and XRD showed that the calcination being carried out at 600 °C brought forth of an appreciable change of microscaled structure in RFP，i. e. the dehydration of clay minerals such as kaolinite， as well as the hydrated products of Portland cement including calcium hydroxide and calcium silicate hydrate （ C-S-H）， which must be helpful to improve the pozzolanic activity of RFP. However， high temperature calcination at 800 to 900 °C resulted in the generation of low-activity products such as spinel （Al2O3 ·SiO2 ） or gehlenite （2CaO·Al2O3 ·SiO2， C2AS）， and thus made a negative effect on the pozzolanic activity of RFP. The calcination of hydrated Portland cement at 900 °C did give rise to the generation of C2S rather than C2AS.
Conclusion The processing of high-temperature calcination is evidently helpful to upgrade the pozzolanic activity of RFP， but the calcination regime must be coordinated with the chemical composition and mineral components of RFP. As a result， the calcination of RFP in laboratory is proposed to be carried out at 600 °C in temperature and 1. 0 to 1. 5 h in time to realize an optimized improvement of its pozzolanic activity， which can be attributed to the dehydration and amorphization of clay minerals， as well as the thermal decomposition of hydrated Portland cement， especially C-S-H.
Keywords：concrete； recycled fine powder； calcination； activity index； microstructural characteristics
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