Effect of nano C-S-H-PCE on the properties of high-strength non-steam-cured concrete
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摘要: 针对蒸汽养护易引起混凝土初始损伤及耐久性差等问题。本文采用纳米水化硅酸钙-聚羧酸醚复合材料(n-C-S-H-PCE)制备免蒸养高强混凝土。通过水化热、低场核磁等试验研究了n-C-S-H-PCE对混凝土抗压强度、水化速率、孔径分布、自收缩及耐久性的影响。结果表明：纳米水化硅酸钙(C-S-H)晶核为水化产物提供了成核位点，降低了成核的临界离子浓度Ksp，诱导期和加速期显著提前，显著提高了混凝土早期抗压强度，1天混凝土抗压强度提高64%，且28天以后混凝土没有发生强度倒缩。掺入n-C-S-H-PCE后，混凝土基体孔径细化，凝胶孔和毛细孔比例均增加，导致混凝土自干燥过程中毛细孔负压增大，增大混凝土自收缩；然而，混凝土基体的最可几孔径和50~100 nm孔隙累计体积降低，提高了混凝土的抗氯离子侵蚀性能；孔径大于14 nm (临界孔径)的孔隙含量降低(由0.0287 mL/g降低到0.0156 mL/g)，从而提高了混凝土的抗冻性能；此外，掺入n-C-S-H-PCE后，混凝土孔隙率降低，且随着矿粉掺量的增加，铝酸钙相和Ca2+的浓度降低，混凝土抗硫酸盐侵蚀能力提高。该研究为免蒸养、低收缩、高耐久、高强混凝土制备与应用提供了理论依据。Abstract: To solve the initial damage, poor durability, and other problems of concrete caused by steam curing, the nano-hydrated calcium silicate polycarboxylate ether composite (n-C-S-H-PCE) was used to prepare high-strength non-steam-cured concrete. The effects of n-C-S-H-PCE on the compressive strength, hydration rate, pore size distribution, autogenous shrinkage and durability of concrete were studied using hydration heat, low-field nuclear magnetic resonance and other methods. Results show that the crystal nucleus of nano-C-S-H provides nucleation sites for the hydration products of cement, reducing the critical ion concentration Ksp of nucleation. And the induction and acceleration periods are advanced significantly. Also, the early compressive strength of concrete is improved considerably. The compressive strength of concrete increases by 64% after 1 day of curing, and the strength of concrete has no regression after 28 days of curing. The addition of the n-C-S-H-PCE refines the pore size of concrete matrix and increases the proportion of gel pores and capillary pores. As a result, the negative capillary pressure increases during the auto-drying process of concrete. Thus, the autogenous shrinkage of concrete increases. However, the most probable pore size of the concrete matrix and the cumulative volume of pores with a diameter of 50-100 nm decrease. This improves the resistance to chloride migration into concrete. The content of pores with a pore diameter larger than 14 nm (the critical pore diameter) decreases (from 0.0287 mL/g to 0.0156 mL/g). As a result, the freeze-thaw resistance of concrete is improved. The addition of n-C-S-H-PCE can reduce the porosity of concrete. In addition, with the increase of slag content, the concentration of calcium aluminate phase and Ca2+ decreases. In this way, the resistance to sulfate attack of concrete increases. The results provide a theoretical basis for the preparation of non-steam-cured, low shrinkage, high durability and high-strength concrete.
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Key words:
- nano early strength agent /
- non-steam-cured concrete /
- pore structure /
- autogenous shrinkage /
- durability /
- C-S-H-PCE
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图 3 不同纳米水化硅酸钙-聚羧酸醚(n-C-S-H-PCE)掺量的混凝土抗压强度
Figure 3. Compressive strength of concrete with different nano-hydrated calcium silicate polycarboxylate ether (n-C-S-H-PCE) contents
图 4 混凝土28天抗压强度与胶凝材料总量(a)和水胶比B/W (b)的关系
Figure 4. Compressive strength of concrete in 28 days as functions of amount of cementitious material (a) and water-to binder ratio B/W (b)
图 5 不同n-C-S-H-PCE掺量的水泥-矿粉净浆的水化速率(a)和累积放热量(b)
Figure 5. Hydration rate (a) and cumulative heat release (b) of cement-slag with different n-C-S-H-PCE contents
图 6 不同n-C-S-H-PCE掺量的混凝土孔径分布
Figure 6. Pore size distribution of concrete with different n-C-S-H-PCE contents
dV/d(lgD)—Pore volume differentiation
图 7 不同矿粉掺量的混凝土孔径分布
Figure 7. Pore size distribution of concrete with different slag contents
图 8 不同n-C-S-H-PCE掺量的混凝土毛细孔负压
Figure 8. Negative capillary pressure of concrete with different n-C-S-H-PCE content
图 9 不同n-C-S-H-PCE掺量的混凝土0~30天的自收缩-湿度曲线
Figure 9. Autogenous shrinkage and relative humidity of concrete with different n-C-S-H-PCE content during 0-30 days
图 10 混凝土自收缩与相对湿度(lnRH)的关系
Figure 10. Relationship between of autogenous shrinkage of concrete and relative humidity (lnRH)
图 11 不同n-C-S-H-PCE掺量的混凝土氯离子扩散系数
Figure 11. Coefficient of chloride diffusion of concrete with different n-C-S-H-PCE contents
图 12 混凝土50~100 nm孔径的孔累计体积
Figure 12. Cumulative volume of pores with diameter of 50-100 nm of concrete
图 13 混凝土28天氯离子扩散系数D28归一化
Figure 13. Normalized 28 days coefficient of chloride diffusion D28 of concrete
图 14 胶凝材料总量、W/B与混凝土D28之间的关系
Figure 14. Relationship among D28 of concrete, the quantity of cementitious material and W/B
图 15 不同n-C-S-H-PCE掺量的混凝土的相对动弹性模量
Figure 15. Relative dynamic modulus of elasticity of concrete with different n-C-S-H-PCE contents
图 16 不同n-C-S-H-PCE掺量的混凝土的质量损失
Figure 16. Mass loss of concrete with different n-C-S-H-PCE content
图 17 混凝土孔径与冻融温度的关系
Figure 17. Relationship between pore diameter of concrete and freezing temperature
图 18 孔径＞14 nm的孔累计体积
Figure 18. Cumulative volume of pores with diameter large than 14 nm
图 19 不同n-C-S-H-PCE掺量的混凝土的相对动弹性模量
Figure 19. Relative dynamic modulus of elasticity of concrete with different n-C-S-H-PCE contents
图 20 不同n-C-S-H-PCE掺量的混凝土的质量损失
Figure 20. Mass loss of concrete with different n-C-S-H-PCE contents
图 21 不同n-C-S-H-PCE掺量的混凝土的相对抗压强度
Figure 21. Relative compressive strength of concrete with different n-C-S-H-PCE contents
表 1 水泥和矿粉的化学组成
Table 1. Chemical composition of cement and slag
Material SiO2/wt% Al2O3/wt% Fe2O3/wt% CaO/wt% TiO2/wt% K2O/wt% MgO/wt% SO3/wt% Na2O/wt% Cement 19.94 4.84 2.93 65.71 0.36 0.81 2.93 2.28 0.23 Slag 30.14 15.53 0.43 41.92 0.84 0.46 7.85 2.26 0.56 
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表 2 混凝土配合比
Table 2. Mix proportion of concrete
Content
of slagSpecimen ID Binder/ (kg·m−3) Cement/ (kg·m−3) Slag/
(kg·m−3)n-C-S-H-PCE/
(kg·m−3)Sand/ (kg·m−3) Aggregate/ (kg·m−3) Water-reducing
agent/(kg·m−3)Water-to binder ratio 20% R-450-20% 450 360 90 0 657 1169 6.75 0.275 R-500-20% 500 400 100 0 637 1133 7.50 0.260 R-550-20% 550 440 110 0 616 1095 8.25 0.252 R-600-20% 600 480 120 0 595 1058 9.00 0.245 30% R-450-30% 450 315 135 0 657 1169 6.75 0.275 R-500-30% 500 350 150 0 637 1133 7.50 0.260 R-550-30% 550 385 165 0 616 1095 8.25 0.252 R-600-30% 600 420 180 0 595 1058 9.00 0.245 20% N-450-20% 450 360 90 18 657 1169 5.40 0.275 N-500-20% 500 400 100 20 637 1133 6.00 0.260 N-550-20% 550 440 110 22 616 1095 6.60 0.252 N-600-20% 600 480 120 24 595 1058 7.20 0.245 30% N-450-30% 450 315 135 18 657 1169 5.40 0.275 N-500-30% 500 350 150 20 637 1133 6.00 0.260 N-550-30% 550 385 165 22 616 1095 6.60 0.252 N-600-30% 600 420 180 24 595 1058 7.20 0.245 Notes: n-C-S-H-PCE—Nano-hydrated calcium silicate polycarboxylate ether; R-450-20% refers to the mix proportion where the amount of cementitious material is 450 kg/m3, the content of slag is 20%, and n-C-S-H-PCE is not added; N-450-30% refers to the mix proportion where the amount of cementitious material is 450 kg/m3, the content of slag is 30%, and 4%n-C-S-H-PCE is added; The representation method of other mix proportion with different the amount of cementitious material is similar to the above.
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表 3 不同n-C-S-H-PCE掺量的混凝土自收缩零点
Table 3. Time zero of autogenous shrinkage of concrete with different n-C-S-H-PCE contents
Specimen ID Time zero R-450-20% 6.4 R-600-20% 7.2 R-450-30% 6.2 R-600-30% 7.6 N-450-20% 4.0 N-600-20% 4.6 N-450-30% 4.8 N-600-30% 6.1
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表 4 不同n-C-S-H-PCE 掺量的混凝土氯离子扩散系数的拟合参数h和相关性参数R2
Table 4. Fitting parameter h and relevance parameter R2 of coefficient of chloride diffusion of concrete with different n-C-S-H-PCE contents
Sample ID h R2 Sample ID h R2 N-450-20% 0.293 0.989 R-450-20% 0.296 0.992 N-500-20% 0.296 0.992 R-500-20% 0.282 0.991 N-550-20% 0.310 0.983 R-550-20% 0.246 0.982 N-600-20% 0.369 0.985 R-600-20% 0.343 0.999 N-450-30% 0.391 0.985 R-450-30% 0.369 0.997 N-500-30% 0.433 0.986 R-500-30% 0.387 0.982 N-550-30% 0.521 0.999 R-550-30% 0.384 0.981 N-600-30% 0.534 0.997 R-600-30% 0.483 0.999
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