【作者】 朱洪波； 成轶杰； 李晨； 闫美珠；

【Author】 ZHU Hongbo;CHENG Yijie;LI Chen;YAN Meizhu;

【机构】 同济大学先进土木工程材料教育部重点实验室；

【摘要】 粉煤灰被广泛作为辅助胶凝材料来改善混凝土的流动性、提高后期强度和降低成本,但由于其水化活性、尤其是早期水化活性较低,制约了其在混凝土中的掺量及上述作用的发挥;同时,由于粉煤灰中所含的未燃尽碳(烧失量)颗粒会吸附减水剂,因此在使用减水剂、提别是采用聚羧酸减水剂的混凝土中使用粉煤灰,通常会降低流动性。本研究设计开发流化床气相沉积(FB-VD)试验装置,采用该装置并分别以NaOH、Na2SO4、NaCl溶液为激发材料,以木钙为表面活性材料预处理粉煤灰(FA),通过水泥净浆、砂浆和混凝土试验,与传统直接添加这些材料的方法进行对比,测试与分析其对FA火山灰活性及工作性的影响,通过扫描电镜(SEM)观察粉煤灰颗粒在水泥硬化体中的微观形貌,分析其火山灰反应机理;采用X-射线衍射(XRD)分析水化产物组成。结果显示,采用FB-VD方法能够显著提高粉煤灰的早期火山灰活性并不影响水泥浆体的工作性,可使7d和28d的净浆活性指数均提高10%左右,砂浆7d活性指数提高5%,对60d的净浆、砂浆强度无影响;SEM分析认为,FB-VD方法可将激发材料微粒预先吸附于FA表面,提前使FA颗粒表面局部点的Si-O-Si化学键解聚,从而吸附水泥的水化产物CH晶体生长在该点上,通过镶嵌作用将FA与水泥石结构牢固地结合在一起,最终表现出高强度。XRD分析结果显示,采用FB-VD方法改性粉煤灰的水化产物类型与普通水泥和传统改性粉煤灰的产物一致;通过FB-VD方法可使极少量的木钙微粒沉积于FA颗粒表面或被FA中的碳颗粒吸附,从而明显增加了混凝土的流动性,特别是减少了混凝土的坍落度经时损失,通过增加的减水作用可提高C30混凝土7d强度约3MPa。更多还原

【Abstract】 Fly ash,as a supplementary cementing materials,has been widely used to improve the liquidity of concrete,increase the later strength and reduce the cost.Due to lower hydration activity,especially lower the early hydration activity,its dosage in concrete was restricted and the advantage above was reduced.At the same time,because the unburned carbon particles contented in FA would absorb the Super plasticizer,so FA would reduce the liquidity of concrete with the water reducing agent,especially with the poly carboxylic acid.Fluidized bed chemical vapor deposition(FB-VD) testing device was developed to pre-activate fly ash(FA),using NaOH,Na2SO4 or NaCl liquor as activator,or using lignosulphonate as coating material respectively.The pozzolanicity and the workability of paste and motor with FA,which modified by FB-VD or by adding NaOH,Na2S04 or NaCl into FA directly,were comparative analyzed.Microstructure and hydration production of hardened cement with FA were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD) respectively.Experimental results show that FB-VD could accelerate the early pozzolanic reaction and did nothing to do with the workability of paste,7-day and 28-day activity index of paste could be increase by about 10%respectively,7-day activity index of motor could be increase by about 5%and 60-day compressive strengths of paste and motor were close to that of control sample with original FA.SEM results indicate that FB-VD could absorb the atom of activator on the surface of FA globe and made some chemical bond Si-O-Si of FA depolymerized in advance;therefore the CH crystal was attracted to grown here.FA globe was then fixed in hardened cement firmly by means of besetting action,and lead to higher compressive strength.XRD results infer that the hydration production types of sample with FA modified by FB-VD were similar to that of normal cement or the sample with FA modified by traditional activator.Few lignosulphonate can coat on the surface of FA and was absorbed by unburned carbon,then the fluidized increased significantly.The 7 days strength of C30 concrete can rise by about 3MPa due to the water reducing of modified FA.更多还原