摘要
为探明微波养护与不同组分碱激发粉煤灰胶凝材料(AAFA)的适应性,采用掺加偏高岭土或硅灰来调整原材料硅铝比的方法,研究微波养护时不同硅铝比AAFA试件的力学性能发展规律,并分析AAFA的聚合反应产物和微观结构.结果表明:与传统蒸汽养护相比,微波养护后硅铝比大于1.92的AAFA试件早期强度发展更快,但微波养护时间过长会使试件呈现明显的强度倒缩;硅铝比小于1.97的AAFA试件内部可生成较多的富铝水化铝硅酸钠(N‑A‑S‑H)凝胶相,具备更为致密的微结构和更优异的高温稳定性,使其在微波养护阶段的最大抗压强度较高,同时可避免强度倒缩现象出现.
关键词
与硅酸盐水泥相比,碱激发粉煤灰胶凝材料(AAFA)具有高抗压强
然而,受煤种、煤质、煤燃烧状况及锅炉构造等因素的影响,粉煤灰具有硅铝比(摩尔比,下同)不确定、组分差异大的特
因此,本文参考文献[
F级粉煤灰来自河南某电厂;偏高岭土和硅灰由河北某矿产品公司提供.粉煤灰和偏高岭土的主要化学组成(质量分数,文中涉及的组成、水胶比等除特别注明外均为质量分数或质量比)见

图1 原材料的XRD图谱
Fig.1 XRD patterns of raw materials

图2 原材料的粒径分布
Fig.2 Particle size distribution of raw materials
采用氟硅酸钾容量
基于文献[
先根据
微波养护:将制备好的净浆带模放入Moilelab微波材料学工作站中养护,微波炉内的温度通过插入试件中心的热电偶实时反馈,以实现自动调节.本试验采用的多级微波养护制度见

图3 多级微波养护制度
Fig.3 Multi‑stage microwave curing regime
蒸汽养护:将制备好的净浆带模放入85 ℃的蒸汽养护箱中养护24 h.
AAFA试件经微波养护至stage 1时,由于养护时间过短且养护温度低于粉煤灰玻璃相碱激发反应的起始温度65
不同微波养护阶段AAFA试件(M‑stage 2~M‑stage 4‑Ⅱ)与蒸汽养护试件(steam)的抗压强度如

图4 AAFA试件在不同微波养护阶段时的抗压强度
Fig.4 Compressive strength of AAFA specimens under different microwave curing stages
进一步分析各微波养护阶段原材料硅铝比对AAFA试件抗压强度的影响.由
综上可知,硅铝比大于1.92的AAFA更适宜采用微波养护的方式来促进其早期强度发展,但微波养护时间过长会导致强度倒缩.AAFA的硅铝比越低,其热养护阶段的最大抗压强度越高.鉴于以上宏观性能表现,本文选取T‑1.83、T‑2.04、T‑2.53这3组AAFA试件进行后续微观测试,以分析不同硅铝比AAFA试件在微波养护各阶段的微观结构.
研

图5 粉煤灰和试件T‑1.83、T‑2.04、T‑2.53微波养护至stage 4‑Ⅰ的FTIR图谱
Fig.5 FTIR spectra of fly ash and specimen T‑1.83, T‑2.04 and T‑2.53 under microwave curing to stage 4‑Ⅰ
由AAFA试件抗压强度结果可知,微波养护至stage 4‑Ⅰ阶段为AAFA的最佳热养护制度.试件T‑1.83、T‑2.04、T‑2.53养护至stage 4‑Ⅰ阶段的XRD图谱如

图6 T‑1.83、T‑2.04、T‑2.53试件采用微波养护至stage 4‑Ⅰ时的XRD图谱
Fig.6 XRD patterns of specimen T‑1.83, T‑2.04 and T‑2.53 under microwave curing to stage 4‑Ⅰ
T‑1.83、T‑2.04、T‑2.53这3组AAFA试件采用微波养护至stage 4‑Ⅰ、stage 4‑Ⅱ时的孔结构分布特征如
由

图7 试件T‑1.83采用微波养护至不同阶段的SEM照片
Fig.7 SEM images of specimen T‑1.83 under microwave curing to different stages

图8 试件T‑2.53采用微波养护至不同阶段的SEM照片
Fig.8 SEM images of specimen T‑2.53 under microwave curing to different stages
(1)与传统蒸汽养护相比,硅铝比大于1.92的AAFA更适宜采用微波养护方式促进其早期强度发展,但微波养护时间过长会使AAFA大孔径孔隙比例急剧增加,试件内部出现微裂纹,呈现明显的强度倒缩,最高可达32%.
(2)硅铝比较低的AAFA内部可生成较多的富铝N‑A‑S‑H凝胶相.该凝胶相具备更为致密的微结构,从而使其在微波养护阶段的最大抗压强度较高,最高可达67 MPa.
(3)硅铝比小于1.97的AAFA中的富铝N‑A‑S‑H凝胶相热稳定性较好,可有效避免试件因微波养护时间过长而出现的强度倒缩现象.
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