Influence mechanism of curing temperature on the characteristics of dredged ultrafine mortar from Yangtze River
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摘要: 为了实现长江下游疏浚砂的综合利用，拓展细骨料来源，研究不同养护温度对不同疏浚砂掺量砂浆特性的影响。以疏浚砂为原料，设计了3种不同疏浚砂掺量的砂浆配合比，研究了40、60、80、90℃ 4种养护温度对不同龄期抗压、抗折强度的影响，并结合X射线衍射、热重-差示扫描量热、扫描电镜、压汞测试，分析了不同养护温度及不同疏浚砂掺量砂浆的微观结构。研究结果表明：随着养护温度升高，砂浆内部水化产物分布不均匀，阻碍了后续的水化反应，砂浆的抗压、抗折强度总体上先增大后减小，养护温度越高，蒸养损伤越大；疏浚砂颗粒粒径极小，具有良好的填充效果，适量掺入疏浚砂能提高体系的密实度，同时还能减少有害孔和多害孔的数量，进而提高砂浆的力学性能；蒸养条件下，砂浆孔结构缺陷增多，疏浚砂的优化作用被放大，一定程度上可以抵消蒸养带来的部分不利影响，随养护温度的升高，疏浚砂对抗压强度的提升率逐渐降低，最大能提升31.35%，对抗折强度的提升率先增大后减小，最大能提升14.29%。Abstract: In order to realize the comprehensive utilization of dredged sand in the lower Yangtze River and expand the source of fine aggregate, the effects of different maintenance temperatures on different dredged sand admixtures mortar characteristics were investigated. Using dredged sand as raw material, three mortar mix ratios with different dredged sand admixtures were designed, and the effects of four curing temperatures of 40, 60, 80 and 90℃ on the compressive and flexural strengths at different ages were investigated, The microstructures of specimens with different curing temperatures and different dredged sand admixtures were analyzed by combining X-ray diffraction, thermogravimetric-differential scanning calorimetry, scanning electron microscopy and mercury injection test. The results show that with the increase of curing temperature, the distribution of hydration products in mortar is uneven, which hinder the subsequent hydration reaction. The compressive and flexural strengths of mortar increase first and then decrease. The higher the curing temperature is, the greater the steam curing damage is. The particle size of dredged sand is very small, and it has good filling effect. Appropriate incorporation of dredged sand can improve the compactness of the system, and reduce the number of harmful holes and multiple harmful holes, thereby improving the mechanical properties of mortar. Under the condition of steam curing, the pore structure defects of mortar increase, and the optimization effect of dredged sand is amplified, which can offset some adverse effects of steam curing to a certain extent. The enhancement rate of the dredged sand on the compressive strength gradually decreases with the increase of the curing temperature, and the maximum could enhance 31.35%. The enhancement of the flexural strength increases first and then decreases, and the maximum could enhance 14.29%.
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图 1 不同养护温度下疏浚砂砂浆的抗压强度
Figure 1. Compressive strength of dredged sand mortar at different curing temperatures
t—Dredged sand content
图 2 不同疏浚砂掺量砂浆的90天抗压强度
Figure 2. 90 days compressive strength of mortar with different dredged sand admixtures
图 3 不同疏浚砂掺量砂浆的90天抗压强度提升率
Figure 3. 90 days compressive strength improvement rate of mortar with different dredged sand admixtures
图 4 不同养护温度下疏浚砂砂浆的抗折强度
Figure 4. Flexural strength of dredged sand mortar at different curing temperatures
图 5 不同疏浚砂掺量砂浆的90天抗折强度
Figure 5. 90 days flexural strength of mortar with different dredged sand admixtures
图 7 疏浚砂砂浆气泡滞留示意图
Figure 7. Schematic diagram of air bubble retention in dredged sand mortar
图 8 疏浚砂砂浆水化产物XRD图谱
Figure 8. XRD patterns of dredged sand mortar hydration product
C-S-H—Hydrate calcium silicate
图 9 疏浚砂掺量t=0%的砂浆TG-DSC曲线
Figure 9. TG-DSC curves of mortar with dredged sand admixtures t=0%
图 10 疏浚砂掺量t=50%的砂浆TG-DSC曲线
Figure 10. TG-DSC curves of mortar with dredged sand admixtures t=50%
表 1 粉煤灰化学成分
Table 1. Chemical composition of fly ash
Ingredients CaO SiO2 Al2O3 MgO TiO2 P2O5 MnO K2O Fe2O3 Mass fraction/wt% 1.47 55.78 34.69 0.25 1.74 1.17 0.02 1.32 3.56 
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表 2 矿粉化学成分
Table 2. Chemical composition of mineral powder
Ingredients CaO SiO2 Al2O3 MgO TiO2 SO3 MnO K2O Fe2O3 Mass fraction/wt% 39.19 26.31 16.17 9.99 2.18 3.71 1.04 0.38 1.03
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表 3 疏浚砂与机制砂物理性能参数
Table 3. Physical property parameters of dredged sand and mechanism sand
Sand Apparent density/(kg·m−3) Stacking density/(kg·m−3) Porosity/% Mud content/% Water content/% Fineness modulus Dredged sand 2690 1365 12.3 1.9% 13.5 0.5 Mechanism sand 2591 1484 43 — — 3.2
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表 4 砂浆配合比
Table 4. Mortar mix ratio
kg·m−3 Dredged sand content t/% Cement Fly ash Mineral powder Dredged sand Mechanized sand Water Additives 0 322 264.7 150 0.00 1035.00 279.3 3.3 15 322 264.7 150 155.25 879.75 279.3 3.3 50 322 264.7 150 517.50 517.50 279.3 3.3
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表 5 试件编号
Table 5. Specimen number
Specimen
numberDredged sand content t/% Curing temperature/℃ 0%DS-S 0 S 15%DS-40 15 40 50%DS-60 50 60 0%DS-80 0 80 15%DS-90 15 90 Notes: S—Standard curing; Taking 15%DS-40 as an example, 15%DS represents the dredged sand admixture is 15%, 40 represents the curing method is 40°C steam curing.
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表 6 疏浚砂砂浆质量损失率及Ca(OH)2含量
Table 6. Mass loss rate and Ca(OH)2 content of dredged sand mortar
Specimen number Mass loss rate/% Ca(OH)2 content/wt% 0%DS-60 15.20 5.85 0%DS-90 12.93 3.78 50%DS-60 15.53 4.56 50%DS-90 14.08 3.69
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表 7 疏浚砂砂浆平均孔径与孔径分布
Table 7. Average pore size and pore size distribution of dredged sand mortar
Specimen number Average pore size/nm Pore size distribution/% <20 nm 20-50 nm 50-200 nm >200 nm 0%DS-40 11.19 36.97 13.76 13.08 36.19 0%DS-60 11.86 54.39 15.46 5.09 25.06 0%DS-80 16.36 53.27 8.34 1.63 36.76 0%DS-90 16.98 51.01 8.07 2.51 38.41 0%DS-S 13.71 50.97 17.40 7.97 23.66 50%DS-40 10.60 62.95 6.71 4.87 25.47 50%DS-60 10.77 71.35 9.06 3.67 15.92 50%DS-80 11.66 57.20 11.53 6.89 24.38 50%DS-90 11.95 60.68 9.79 4.73 24.80 50%DS-S 10.93 66.28 12.08 0.84 20.80
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