Effect of nano-SiO2 on negative temperature mechanical properties and microstructure of sulfoaluminate concrete
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摘要: 为保证混凝土在负温环境下的安全可靠，采用力学性能测试、超声波波速测试、扫描电子显微镜(SEM)、X射线衍射(XRD)结合Rietveld精修定量分析等方法，研究了恒负温(−10℃)养护条件下不同纳米SiO2(NS)掺量对硫铝酸盐混凝土性能的影响。结果表明：硫铝酸盐混凝土强度随NS掺量的增加，先升高后降低，在2%NS掺量时强度达到最大；当养护温度从负温变为常温时，超声波波速先降低后升高，掺入NS后再次水化(升高段)的超声波波速上升速率均高于空白组，其中2%NS掺量的混凝土超声波波速上升速率最快；SEM和XRD发现随NS掺量增加，混凝土内部孔隙结构变的更加致密，钙矾石(AFt)相对含量逐渐上升，其中2%NS掺量AFt含量最高，说明NS可以促进负温环境下的硫铝酸盐混凝土的水化。Abstract: To ensure the safety and reliability of concrete in a negative temperature environment, mechanical property testing, ultrasonic wave velocity testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) combined with Rietveld refinement quantitative analysis and other methods were used to study the properties of sulfoaluminate concrete modified with different nanosized SiO2 (NS) admixtures under constant negative temperature (−10°C) curing conditions. The results show that the strength of sulfoaluminate concrete increases and then decreases with the increase of NS dosage and reaches the maximum strength at 2% NS dosage; When the curing temperature changes from negative temperature to room temperature, the ultrasonic wave velocity first decreases and then increases, and the ultrasonic wave velocity increase rate of rehydration (elevated section) after mixing NS is higher than that of the blank group, in which the ultrasonic wave velocity increase rate of the concrete with 2% NS admixture is the fastest; SEM and XRD found that with the increase of NS dosage, the internal pore structure of concrete becomes denser,and the relative content of calcium alumina (AFt) rises gradually,the 2% NS admixture AFt content is the highest, indicating that NS can promote the hydration of sulfoaluminate concrete under negative temperature environment.
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Key words:
- sulphoaluminate cement /
- nano-SiO2 /
- ultrasound wave velocity /
- mechanical properties /
- microstructure
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图 1 纳米SiO2(NS)颗粒(a)及SEM图像(b)
Figure 1. Nano-SiO2 (NS) particles (a) and SEM images (b)
图 2 硫铝酸盐水泥、NS的粒度分布曲线
Figure 2. Particle size distribution curve of sulfoaluminate cement and NS
图 4 NS掺量对硫铝酸盐混凝土抗压强度的影响
Figure 4. Effect of NS admixture on compressive strength of sulfo-aluminate concrete
图 5 NS促进早期硫铝酸盐水泥水化过程
Figure 5. NS promotes the hydration process of early sulfoaluminate cements
图 7 硫铝酸盐混凝土升温过程中超声波速度的变化
Figure 7. Variation of ultrasonic velocity during warming of sulfoaluminate concrete
图 8 不同NS掺量混凝土抗压强度与超声波波速的关系
Figure 8. Relationship between compressive strength of concrete with different NS admixture and ultrasonic wave velocity
图 9 不同NS掺量1 d龄期的微观结构：(a)空白组；(b)1%NS掺量；(c)2%NS掺量
Figure 9. Microstructure at 1 d age with different NS doping: (a)0%NS; (b)1%NS; (c)2%NS
图 10 不同NS掺量3 d龄期的微观结构：(a)空白组；(b)1%NS掺量；(c)2%NS掺量
Figure 10. Microstructure at 3 d age with different NS doping: (a)0%;(b)1%; (c)2%
图 11 1、3 d龄期硫铝酸盐水泥的XRD图谱
Figure 11. XRD patterns of sulphoaluminate cement at 1 and 3 d ages
表 1 硫铝酸盐水泥的技术指标
Table 1. Technical specifications for sulphoaluminate cements
Specific surface
area/(m2·kg−1)Setting time/min Compressive strength/MPa Flexural strength/MPa Initial setting Final setting 1 d 3 d 28 d 1 d 3 d 28 d 368 26 68 36.1 44.3 49.4 6.2 7.2 8.4 
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表 2 NS的物理性能
Table 2. Physical properties of NS
Appearance Average Primary size/nm Apparent density/(g·cm−3) Specific surface area/(m2·g−1) Loss on dry/% White powder 21 0.19 198 4.7
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表 3 硫铝酸盐水泥和NS的主要化学成分
Table 3. Main chemical composition of sulphoaluminate cement and NS
Material Mass fraction/ % SiO2 Al2O3 CaO Fe2O3 MgO SO3 K2O Na2O Sulfoaluminate
cement7.58 30.53 45.38 3.52 2.25 14.37 0.30 0.76 NS 99.98 ﹣ 0.001 0.015 0.004 ﹣ ﹣ ﹣
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表 4 硫铝酸盐混凝土配合比(kg/m3)
Table 4. Sulfoaluminate concrete ratio (kg/m3)
Groups w/c NS/% Li2CO3/% Cement Water Aggregate Fine aggregate NS-0 0.45 0 0.2 433.3 195 1151.6 620.1 NS-1 0.45 1 0.2 429 195 1151.6 620.1 NS-1.5 0.45 1.5 0.2 426.8 195 1151.6 620.1 NS-2 0.45 2 0.2 424.6 195 1151.6 620.1 NS-3 0.45 3 0.2 420.3 195 1151.6 620.1 Note: w/c is the water cement ratio of concrete.
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表 5 回归分析计算误差(%)
Table 5. Calculation error of regression analysis (%)
Groups Linear function Logarithmic function Power function Average relative error RSD Average relative error RSD Average relative error RSD NS-0 1.56 2.04 0.83 1.05 0.74 0.96 NS-1 2.59 3.34 2.49 3.19 3.18 4.12 NS-1.5 3.83 5.09 3.52 4.64 5.31 6.77 NS-2 4.34 5.32 3.56 4.78 5.07 6.83 NS-3 6.67 9.34 3.93 4.80 6.22 7.57 Note: RSD refers to relative standard deviation.
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表 6 硫铝酸盐水泥水化产物晶体结构参数
Table 6. Crystal structure parameters of hydration products of sulfoaluminate cement
Mineral a/Å b/Å c/Å α/(º) β/(º) γ/(º) V/Å3 ICSD Ettringite 9.189 9.189 9.189 90 90 90 779.958 9560 Ye'elimite 11.223 11.223 21.428 90 90 120 2358.532 16045 Anhydite 6.984 6.241 6.986 90 90 90 306.180 16382 Belite 5.496 6.756 10.433 90 116.758 90 343.916 963 Quartz 4.907 4.907 5.408 90 90 120 112.876 62405
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表 7 不同NS掺量硫铝酸盐水泥水化1 d、3 d时的矿物含量
Table 7. Mineral content of sulfoaluminate cement hydrated at 1 d and 3 d with different NS dosage
Groups Relative amount/% Rwp Hydration age Ettringite Ye'elimite Anhydite Belite Quartz NS-0 1 d 26.23 36.38 14.42 21.13 1.84 8.81 3 d 28.66 35.11 13.12 21.02 2.09 9.23 NS-1 1 d 27.77 34.64 13.88 20.86 2.85 9.67 3 d 31.86 31.24 12.45 20.34 4.11 8.63 NS-1.5 1 d 29.63 33.32 12.65 20.64 3.76 8.82 3 d 32.98 29.93 12.05 20.22 4.82 9.87 NS-2 1 d 31.82 31.23 12.28 20.41 4.26 9.56 3 d 33.74 28.44 11.87 20.11 5.84 8.97
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