摘要
为了缩短硫氧镁水泥(MOSC)的凝结时间,提高其早期力学性能,以蔗糖为分散剂,用不同水化活性的氧化镁(MgO)粉制备了MOSC,分析了蔗糖对MOSC凝结时间、水化性能、抗压强度、物相组成、微观形貌和孔结构的影响. 结果表明:活性为75.0%的MgO粉较活性为65.5%的MgO粉制备的MOSC凝结时间更短,早期抗压强度更高;蔗糖作为分散剂更适用于活性为75.0%的MgO粉制备的MOSC体系,通过其空间位阻效应的发挥,改善新拌浆体的流动度,延长新拌浆体的初凝时间和终凝时间,还能抑制Mg(OH)2的生长,降低硬化浆体的孔隙率,提高其28 d的抗压强度;蔗糖可促进MOSC吸收大气中的CO2形成MgCO3晶体.
硫氧镁水泥(MOSC)是由氧化镁(MgO)粉与硫酸镁溶液混合拌制而成的胶凝材料,常温常压下,其主要水化产物为3Mg(OH)2·MgSO4·8H2
虽然掺加改性剂在一定程度上改善了MOSC的某些性能,但却延长了新拌浆体的凝结时
活性MgO粉T‑LBM来源于辽宁镁菱有限公司,为利用反射窑在约1 000 ℃下焙烧菱镁矿所得,其比表面积为300.0
Material | MgO | SiO2 | CaO | Fe2O3 | Al2O3 | Other |
---|---|---|---|---|---|---|
T‑LBM | 89.13 | 1.41 | 2.34 | 0.47 | 0.42 | 6.23 |
H‑LBM | 82.88 | 10.35 | 1.68 | 0.68 | 0.92 | 3.49 |

图1 T‑LBM和H‑LBM的激光粒度分布曲线
Fig.1 Laser particle size distribution curves of T‑LBM and H‑LBM
耐久性较好的MOSC,其原料摩尔比的范围通常为n(‑MgO)∶n(MgSO4)∶n(H2O)=(6~10)∶1∶(18~21
参照GB/T 1346—2011《水泥标准稠度用水量、凝结时间、安定性检验方法》测定MOSC的凝结时间.参照GB/T 8077—2012《混凝土外加剂匀质性试验方法》测定MOSC新拌浆体的流动度.用RC‑4HC型温度传感器检测MOSC水化前期(24 h内)的水化放热温度,每组试样取3次测试结果的平均值;用TAM Air C80型水化热测定仪测试MOSC水化72 h内的累积水化放热量,测试仓环境温度为20 ℃.称取1 g 按配合比混合好的MOSC粉末(颗粒尺寸≤ 60 μm)溶于10 mL的超纯水中,用THZ‑82A型双数显旋转水浴振荡器振荡24 h后,取上层清液,用Zetasizer Nano‑SZ型电泳仪和PHS‑3C型pH计分别测试上层清液的Zeta电位和pH值.
测试MOSC养护0.5、1、3、7、28 d时的抗压强度,每组6个试块,取其平均值.
制备28 d龄期的MOSC硬化浆体的粉末样品,用X´Pert powder型X射线衍射仪(Cu Kα,λ=0.154 18 nm)测试其物相组成,扫描范围(2θ)为5~75°,步长为0.02°,扫描速率为0.5 s/步.在粉末样品中掺入15.0%的分析纯ZnO作为内标物,结合Topas 6.0软件,通过内标
从养护至28 d的MOSC硬化浆体中取薄片和粒径约为3~5 mm的立方形试块,在45 ℃的真空干燥箱中干燥至恒重.在薄片样品表面镀金,然后用SIGMA HD型场发射扫描电子显微镜(SEM)观察试样断口处的微观形貌. 用Pore Master 33型压汞仪测试立方形试块的孔结构.

图2 掺入蔗糖前后MOSC的凝结时间和流动度
Fig.2 Setting time and fluidities of MOSC with and without sucrose

图3 掺入蔗糖前后MOSC的早期水化放热温度曲线和累积水化放热量曲线
Fig.3 Temperature evolution curves during early hydration and cumulative heat evolution curves of MOSC with and without sucrose

图4 掺入蔗糖前后MOSC的Zeta电位和pH值
Fig.4 Zeta potentials and pH values of MOSC with and without sucrose
(1) |
(2) |
(3) |
由

图5 掺入蔗糖前后MOSC的抗压强度
Fig.5 Compressive strengths of MOSC with and without sucrose

图6 掺入蔗糖前后28 d 龄期MOSC的XRD图谱及物相含量
Fig.6 XRD patterns and contents of mineral phases of MOSC with and without sucrose at the hydration time of 28 d
由
由

图7 掺入蔗糖前后28 d龄期MOSC的SEM图片
Fig.7 SEM images of MOSC with and without sucrose at the hydration time of 28 d

图8 掺入蔗糖前后28 d龄期MOSC的孔径分布曲线
Fig.8 Pore size distribution curves of MOSC with and without sucrose at the hydration time of 28 d
(1)高活性MgO粉在硫酸镁水溶液中的迅速溶解与水化,缩短了MOSC的凝结时间,提高了MOSC的早期力学性能.与用传统MgO粉制备的MOSC相比,用高活性MgO粉制备的MOSC初、终凝时间分别缩短73.1%和76.0%,1 d龄期硬化浆体的抗压强度提高75.1%.
(2)蔗糖与活性MgO间的吸附配位作用,降低了MOSC体系的水化速率,延长了MOSC的凝结时间. 向高活性MgO粉制备的MOSC体系中掺入0.3%蔗糖后,其初、终凝时间分别延长55.9%和58.8%.
(3)蔗糖通过提高MOSC体系中5·1·7相晶体的生成量和结晶度,降低了MOSC基体的总孔隙率,改善了MOSC 28 d龄期硬化浆体的力学性能. 在传统MgO粉和高活性MgO粉制备的MOSC体系中掺入0.3%蔗糖后,其28 d龄期硬化浆体的总孔隙率分别降低至9.7%和8.0%,此时其抗压强度分别可达75.9 MPa和84.1 MPa. 蔗糖作为分散剂和缓凝剂更适用于高活性MgO粉制备的MOSC体系.
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