摘要
针对碱矿渣胶凝材料易收缩开裂等问题,采用一种新型微米级纤维——碳酸钙晶须对碱矿渣胶凝材料进行减缩增强,研究了碳酸钙晶须掺量对碱矿渣胶凝材料流变性能、抗压强度和干燥收缩的影响,并探究其显微增强机理.结果表明:微米级碳酸钙晶须的掺入对碱矿渣胶凝材料流动性影响较小,当碳酸钙晶须掺量为3%时,其新拌浆体塑性黏度为12.33 Pa·s,较未掺碳酸钙晶须的对照组仅增长14.48%,其硬化浆体28 d抗压强度可达105.8 MPa;碱矿渣胶凝材料的干燥收缩率随着碳酸钙晶须掺量的增加而降低,当碳酸钙晶须掺量为5%时,其28 d干燥收缩率仅有0.87%,较未掺碳酸钙晶须的对照组降低32.56%;碳酸钙晶须与基体紧密结合,在基体受力破坏时分散其所受应力,提升了碱矿渣胶凝材料的力学性能;碳酸钙晶须在体系内部的桥接作用能够有效延缓碱矿渣胶凝材料微裂纹的形成与扩展,在一定程度上遏制了宏观裂纹的发展.
碱激发胶凝材料是由碱性激发剂与具有火山灰活性或潜在水硬性固废原料反应生成的胶凝材
本文针对收缩率较大的碱矿渣胶凝材料,研究了碳酸钙晶须掺量对其流变性能、抗压强度和干燥收缩的影响,并探究了其显微增强机理,以期为低收缩碱矿渣胶凝材料的设计与制备提供技术支持.
矿粉选用武汉微神科技发展有限公司产V600矿粉,其化学组成(质量分数,文中涉及的组成、激固比等均为质量分数或质量比)见
CaO | SiO2 | Al2O3 | MgO | SO3 | K2O | Na2O | Fe2O3 | MnO | TiO2 | IL |
---|---|---|---|---|---|---|---|---|---|---|
38.42 | 30.01 | 16.50 | 9.56 | 2.53 | 0.38 | 0.35 | 0.49 | 0.25 | 1.10 | 0.06 |
Length/μm | Diameter/μm | Aspect ratio/% | Relative density | Tensile strength/GPa | Elastic modulus/GPa |
---|---|---|---|---|---|
20-30 | 1-2 | 10-30 | 2.8±0.2 | 5.2 | 700 |
本研究采用矿粉和改性水玻璃来制备碱矿渣胶凝材料,激固比为1∶1.将碳酸钙晶须掺量(以矿粉质量计)取为0%、1%、2%、3%、4%和5%,共设计6组配合比,试件编号记为CW0、CW1、CW2、CW3、CW4和CW5.
使用MCR 302型流变仪进行测试.先对新拌碱矿渣胶凝材料进行预剪切;再采用阶梯上升-下降方式测得其扭矩与转速的关
(1) |
式中:τ为剪切应力,Pa;γ为剪切速率,

图1 碳酸钙晶须掺量对碱矿渣胶凝材料屈服应力与塑性黏度的影响
Fig.1 Effect of calcium carbonate whiskers’ content on yield stress and plastic viscosity of alkali‑activated slag cementitious materials

图2 碳酸钙晶须掺量对碱矿渣胶凝材料抗压强度的影响
Fig.2 Effect of calcium carbonate whiskers’ content on compressive strength of alkali‑activated slag cementitious materials

图3 碳酸钙晶须掺量对碱矿渣胶凝材料孔隙率和孔径分布的影响
Fig.3 Effect of calcium carbonate whiskers’ content on porosity and pore size distribution of alkali‑activated slag cementitious materials

图4 碳酸钙晶须掺量对碱矿渣胶凝材料干燥收缩的影响
Fig.4 Effect of calcium carbonate whiskers’ content on drying shrinkage of alkali‑activated slag cementitious materials
碳酸钙晶须掺量对碱矿渣胶凝材料质量损失率的影响如

图5 碳酸钙晶须掺量对碱矿渣胶凝材料质量损失率的影响
Fig.5 Effect of calcium carbonate whiskers’ content on mass loss rate of alkali‑activated slag cementitious materials

图6 不同碳酸钙晶须掺量下碱矿渣胶凝材料的经时变化图
Fig.6 Longitude changes of alkali‑activated slag cementitious materials under different calcium carbonate whiskers’ contents

图7 不同碳酸钙晶须掺量下碱矿渣胶凝材料的SEM照片
Fig.7 SEM images of alkali‑activated slag cementitious material with different calcium carbonate whiskers’ contents

图8 碳酸钙晶须在碱矿渣胶凝材料中的激光共聚焦图像
Fig.8 Laser confocal images of calcium carbonate whisker in alkali‑activated slag cementitious materials
(1)碱矿渣胶凝材料的屈服应力与塑性黏度均随着碳酸钙晶须掺量的增加而增大,但掺入微米级碳酸钙晶须的碱矿渣胶凝材料受“纤维阻塞作用”影响较小,浆体的流动性能依然较好.当碳酸钙晶须掺量为3%时,碱矿渣胶凝材料的塑性黏度仅较未掺碳酸钙晶须的对照组增加14.48%.
(2)碱矿渣胶凝材料3、28 d抗压强度随着碳酸钙晶须掺量的增加呈先增后减趋势.当碳酸钙晶须掺量为3%时,CW3组试件3、28 d抗压强度最高,分别为70.1、105.8 MPa.
(3)碳酸钙晶须对碱矿渣胶凝材料的干燥收缩起到了缓解作用.碱矿渣胶凝材料的干燥收缩率随碳酸钙晶须掺量的增加而降低.未掺碳酸钙晶须的CW0组试件28 d干燥收缩率为1.29%;当碳酸钙晶须掺量为5%时,CW5组试件28 d干燥收缩率仅有0.87%,较未掺晶须的CW0组试件降低32.56%.碳酸钙晶须的裂纹桥接作用不仅有效抑制了微裂纹的萌生和发展,延缓了碱矿渣胶凝材料的初裂时间,且在一定程度上限制了宏观裂纹的产生.
(4)碳酸钙晶须的显微增强机理由晶须桥接、晶须拔出和晶须断裂组成.碳酸钙晶须与基体紧密结合,不仅能够分散基体所受应力,阻碍基体内部裂纹发展,提高碱矿渣胶凝材料的抗压强度,而且晶须与基体结合而产生的内摩擦力抵消了材料内部的部分收缩应力.3种机理协同作用下,碳酸钙晶须在碱矿渣胶凝材料中起到显著的减缩增强作用.
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