摘要
研究了原材料摩尔比(n(MgO)∶n(MgSO4)∶n(H2O))对改性硫氧镁(MMOS)水泥力学性能和变形行为的影响,并采用X射线衍射仪(XRD)、扫描电镜(SEM)、傅里叶变换红外光谱(FTIR)及热重分析(TG)等测试技术对其机理进行分析.结果表明:MMOS水泥的抗压强度和抗折强度随着水硫比和氧硫比的提高均呈提升趋势.其中原材料摩尔比为10∶1∶12时,水泥力学性能最优.不同摩尔比MMOS水泥在56 d龄期内均呈膨胀变形,其中总变形随水硫比和氧硫比的提高呈减小趋势;自收缩变形随水硫比的提高而减小,随氧硫比的提高呈先增后减趋势.这主要是由于硬化后不同摩尔比MMOS水泥中的水化产物Mg(OH)2和5·1·7相(5Mg(OH)2·MgSO4·7H2O)含量各有不同.当Mg(OH)2含量减少,而5·1·7相含量增加时,MMOS水泥的膨胀变形量降低,同时其抗折强度和抗压强度有所提升.
改性硫氧镁(MMOS)水泥作为一种新型绿色镁质胶凝材料,与硅酸盐水泥相比,其制备所需的原材料轻烧MgO煅烧温度仅为600~900
近年来,关于MMOS水泥的研究重点多聚焦于提升其力学性能和耐水
鉴于此,本文深入探讨不同原材料摩尔比MMOS水泥在一定养护龄期内的力学性能、变形行为及机理,以期为MMOS水泥在土木工程结构中的广泛应用提供坚实的技术支持.
试验选用宁波新佳公司产工业级七水硫酸镁(MgSO4·7H2O),化学组成(质量分数,文中涉及的组成、水灰比等除特别注明外均为质量分数或质量比)见
MgSO4 | MgCl2 | NaCl | Na2SO4 | H2O | Other |
---|---|---|---|---|---|
47.85 | 0.50 | 0.50 | 0.50 | 50.24 | 0.41 |
MgO | CaO | Al2O3 | SiO2 | IL |
---|---|---|---|---|
82.71 | 5.87 | 5.50 | 3.62 | 2.30 |

图1 轻烧氧化镁的XRD图谱
Fig.1 XRD pattern of light‑burned magnesium oxide

图2 轻烧氧化镁的粒度分布
Fig.2 Particle size distribution of light‑burned magnesium oxide
原材料摩尔比(n(MgO)∶n(MgSO4·7H2O)∶n(H2O))按照氧化镁的反应活性确定.MMOS水泥净浆配合比如
n(MgO)∶n(MgSO4·7H2O)∶n(H2O) | Mix proportion/(kg· | |||
---|---|---|---|---|
MgO | MgSO4· 7H2O | H2O | CA | |
10∶1∶12 | 1 066.0 | 426.0 | 374.0 | 5.3 |
9∶1∶12 | 995.0 | 442.0 | 388.0 | 5.0 |
8∶1∶12 | 920.0 | 460.0 | 404.0 | 4.6 |
8∶1∶11 | 952.0 | 476.0 | 383.0 | 4.8 |
8∶1∶10 | 987.0 | 493.0 | 361.0 | 4.9 |
按
按
(1) |
式中:为试件的初始长度,mm.
按照
将氧硫比(n(MgO)∶n(MgSO4))固定为8∶1,研究水硫比(n(H2O)∶n(MgSO4))对MMOS水泥试件抗折强度和抗压强度的影响,结果见

图3 水硫比对MMOS水泥试件抗折强度和抗压强度的影响
Fig.3 Effect of water‑sulfur ratio on flexural strength and compressive strength of MMOS cement specimens
将水硫比固定为12∶1,研究氧硫比对MMOS水泥试件抗折强度和抗压强度的影响,结果见

图4 氧硫比对MMOS水泥试件抗折强度和抗压强度的影响
Fig.4 Effect of oxygen‑sulfur ratio on flexural strength and compressive strength of MMOS cement specimens
将氧硫比固定为8∶1,研究水硫比对MMOS水泥试件变形特征的影响,结果见

图5 水硫比对MMOS水泥试件变形特征的影响
Fig.5 Effect of water‑sulfur ratio on deformation characteristic of MMOS cement specimens
将水硫比固定为12∶1,研究氧硫比对MMOS水泥试件变形特征的影响,结果见

图6 氧硫比对MMOS水泥试件变形特征的影响
Fig.6 Effect of oxygen‑sulfur ratio on deformation characteristic of MMOS cement specimens
将氧硫比固定为8∶1,不同水硫比MMOS水泥试样的红外光谱见

图7 不同水硫比MMOS水泥试样的红外光谱
Fig.7 FTIR spectra of MMOS cement samples with different water‑sulfur ratios
将水硫比固定为12∶1,研究氧硫比对MMOS水泥试样物相组成的影响,其红外光谱见

图8 不同氧硫比MMOS水泥试样的红外光谱
Fig.8 FTIR spectra of MMOS cement samples with different oxygen‑sulfur ratios
固定氧硫比为8∶1,对不同水硫比MMOS水泥试样进行热重分析,其TG‑DTG曲线如

图9 不同水硫比MMOS水泥试样的TG‑DTG曲线
Fig.9 TG‑DTG curves of MMOS cement samples with different water‑sulfur ratios
对水化56 d试样在300~450 ℃下的DTG曲线进行分峰拟合,得出其Mg(OH)2和5Mg(OH)2·MgSO4含量,结果见
n(MgO)∶n(MgSO4·7H2O)∶n(H2O) | w(Mg(OH)2)/% | w(5Mg (OH) 2·MgSO4)/% |
---|---|---|
8∶1∶10 | 36.7 | 20.5 |
8∶1∶11 | 20.5 | 22.4 |
8∶1∶12 | 16.9 | 32.5 |
(2) |
(3) |
(4) |
(5) |
固定水硫比为12∶1,对不同氧硫比MMOS水泥试样进行热重分析,其TG‑DTG曲线如

图10 不同氧硫比MMOS水泥试样的TG‑DTG曲线
Fig.10 TG‑DTG curves of MMOS cement samples with different oxygen‑sulfur ratios
n(MgO)∶n(MgSO4·7H2O)∶n(H2O) | w(Mg(OH)2)/% | w(5Mg (OH) 2·MgSO4)/% |
---|---|---|
8∶1∶10 | 26.0 | 17.2 |
8∶1∶11 | 36.1 | 19.2 |
8∶1∶12 | 34.4 | 28.6 |

图11 不同水硫比MMOS水泥试样的XRD图谱
Fig.11 XRD patterns of MMOS cement samples with different water‑sulfur ratios

图12 不同氧硫比MMOS水泥试样的XRD图谱
Fig.12 XRD patterns of MMOS cement samples with different oxygen‑sulfur ratios
综上所述,水硫比和氧硫比的提高对MMOS水泥的水化产物含量和力学性能有显著影响.通过调整水硫比和氧硫比,可以调控水化产物的含量,进而改善MMOS水泥的力学性能和变形行为.
固定氧硫比为8∶1,研究水硫比对养护7 d的MMOS水泥试样微观形貌的影响,其SEM照片见

图13 不同水硫比MMOS水泥试样的SEM照片
Fig.13 SEM images of MMOS cement samples with different water‑sulfur ratios
固定水硫比为12∶1,研究氧硫比对养护7 d的MMOS水泥试样微观形貌的影响,其SEM照片见

图14 不同氧硫比MMOS水泥试样的SEM照片
Fig.14 SEM images of MMOS cement samples with different oxygen‑sulfur ratios
(1)随着养护龄期的延长,不同摩尔比MMOS水泥的力学性能呈显著提升趋势;随着水硫比和氧硫比的提高,水泥的抗折强度和抗压强度也呈现提升趋势.原材料摩尔比(n(MgO)∶n(Mgsou)∶n(H2O))为10∶1∶12的MMOS水泥试件的抗折强度和抗压强度最优.
(2)从浇筑完成到养护56 d龄期时,不同摩尔比MMOS水泥的变形主要为膨胀变形.水泥的总变形随着水硫比和氧硫比的提高呈减小趋势;自收缩变形随着水硫比的提高呈减小趋势,随氧硫比的提高呈先增后减趋势.其中水硫比为12∶1、氧硫比为10∶1的MMOS水泥试件的总膨胀变形量最小.
(3)不同摩尔比MMOS水泥在力学性能和变形特征方面的差异主要是由于硬化后水泥基体中5·1·7相和Mg(OH)2的含量不同所致.其中5·1·7相含量增加有助于提升MMOS水泥的力学性能,并减少其体积变形;而Mg(OH)2含量的增加使MMOS水泥的膨胀变形增大,进而导致其力学性能降低.
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