Optimization of parameters and mechanical properties of silane-nano SiO2 composite surface modified steel fiber reinforced ultra-high performance concrete
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摘要: 为提升钢纤维增强超高性能混凝土(UHPFRC)的力学性能，提出一种采用氨基丙基三乙氧基硅烷(KH550)和纳米SiO2(Nano-SiO2)对钢纤维表面进行复合改性的新工艺。考虑乙醇和水的质量比(We:Wd)、KH550含量(wt%)、Nano-SiO2含量(wt%)和水浴温度(Twb)共4个参数对配比进行正交设计(L9(34))。首先筛选溶液稳定性较好的4种配比对纤维表面进行改性，然后使用FTIR和SEM分析涂层成分和形貌，最后根据UHPFRC试件28天的抗弯和抗压强度给出最优改性工艺参数。结果表明：(1)最优改性工艺参数为：We:Wd =3，KH550(wt%)=10%，Nano-SiO2(wt%)=0.5% 和Twb =80℃，其中We:Wd是影响溶液稳定性的主要因素；(2) FTIR显示存在Fe-O-Si特征峰，表明KH550和Nano-SiO2成功键合于钢纤维表面；(3) SEM显示最优改性工艺下涂层分布均匀，未见纳米SiO2 颗粒明显团聚；(4)掺入最优改性工艺处理后高强纤维的UHPFRC试件在1%、1.5%和2%纤维体积分数下的抗弯强度(28MPa、30.5MPa和37MPa)比未改性试件分别提升40.4%、28.5%和32.7%，抗压强度(133.3MPa、151.7MPa和163.9MPa)分别提升7.5%、8.3%和13%；(5)复合改性使1.5%和2%纤维体积分数下的试件跨中裂缝形态曲折复杂，显著增强了纤维-基体界面性能。Abstract: To improve the mechanical properties of steel fiber reinforced ultra-high performance concrete (UHPFRC), a new composite modification method of steel fiber surfaces was proposed using silane coupling agent KH550 and nano-SiO2 particles. Four parameters, including the mass ratio of ethanol to water (We:Wd), the content of KH550 (wt%), the content of nano-SiO2 (wt%), and the water bath temperature (Twb), were considered for the orthogonal design of proportions (L9(34)). Firstly, four mixtures with good solution stability were selected for fiber surface modification. The FTIR and SEM were then used to analyze the composition and morphology of the coatings. Finally, the optimal modification process parameters were determined based on the bending and compressive strength of UHPFRC specimens at 28 days. The results show that: (1) the ratio of We:Wd is the main factor affecting the stability of the solution, and the optimal modification parameters are: We:Wd = 3, KH550 (wt%) = 10%, Nano-SiO2 (wt%) = 0.5%, and Twb = 80℃ ; (2) the FTIR results exhibit characteristic peaks of Fe-O-Si, indicating successful bonding of KH550 and Nano-SiO2 on the steel fiber surfaces; (3) the SEM results indicate uniform distributions of composite coatings without aggregation of Nano-SiO2 particles on the fiber surfaces modified by the optimal parameters; (4) for the fiber volume fractions of 1%, 1.5%, and 2%, the bending strength (28MPa, 30.5MPa and 37MPa) and compressive strength (133.3MPa, 151.7MPa and 163.9MPa) of UHPFRC specimens with optimally-modified fibers are increased by 40.4%, 28.5%, 32.7%, and 7.5%, 8.3%, 13%, respectively, compared to the specimens with untreated fibers; (5) the composite modification technique significantly improves the fiber-matrix interfaces, as demonstrated by more tortuous and complex crack morphologies in the specimens with fiber volume fractions of 1.5% and 2%.
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图 5 复合改性化学反应机理图
Figure 5. Chemical reaction mechanism diagram of composite modification
图 7 不同钢纤维含量下抗压试件的抗压强度值及荷载-位移曲线
Figure 7. Load-displacement curve and compressive strength of specimens with different steel fiber volume fraction
图 8 不同钢纤维含量下抗压试件的抗压强度值及荷载-位移曲线
Figure 8. Load-deflection curve and bending strength of bending specimens with different steel fiber volume fraction
图 9 抗弯试件的裂缝形态及局部放大图
Figure 9. Crack morphology and local magnification of bending specimens
表 1 复合改性溶液的正交试验因素水平表
Table 1. Orthogonal test factor and level table of composite modified solution
Level We:Wd KH550/wt% Nano-SiO2/wt% Twb/℃ 1 9:1 8 0.5 50 2 6:1 10 1 65 3 3:1 12 1.5 80 Notes: We:Wd is mass ratio of alcohol to water; The mass fraction of KH550 and nano-SiO2 are both relative to the mass of the composite modified solution; Twb is the temperature of water bath. 
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表 2 复合改性溶液配比编号
Table 2. Name of composite modified solutions
Name We:Wd KH550/wt% Nano-SiO2/wt% Twb/℃ C1 9:1 8 0.5 50 C2 9:1 10 1 65 C3 9:1 12 1.5 80 C4 6:1 8 1 80 C5 6:1 10 1.5 50 C6 6:1 12 0.5 65 C7 3:1 8 1.5 65 C8 3:1 10 0.5 80 C9 3:1 12 1 50
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表 3 纤维增强混凝土的配比
Table 3. Ratio of steel fiber reinforced ultra-high performance concrete
Name Cement/g Silica fume/g Quartz
powder/gQuartz sand/g Water/g Water reducing agent/g Steel fiber
(volume fraction)/g1 1200 134 320 586 290 10 60(1%) 2 1200 134 320 586 290 10 90(1.5%) 3 1200 134 320 586 290 10 120(2%)
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表 4 UHPFRC小梁试件编号及数量
Table 4. Name and quantity of UHPFRC beam specimens
Name Quantity per set Bending test Compression test BF-1 3 6 HF-1 3 6 CaF-1 3 6 BF-1.5 3 6 HF-1.5 3 6 CaF-1.5 3 6 BF-2 3 6 HF-2 3 6 CaF-2 3 6 Notes: The naming rule of specimens: steel fiber type–volume fraction; a=2, 3, 8 and 9 (a is consistent with the subscript number of composite modified solution).
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表 5 复合改性液稳定性正交试验结果
Table 5. Orthogonal test results of stability of composite modified solutions
Test Factor Transition
time/hWe:Wd KH550 Nano-SiO2 Twb C1 1 1 1 1 46 C2 1 2 2 2 96 C3 1 3 3 3 88 C4 2 1 2 3 28 C5 2 2 3 1 2 C6 2 3 1 2 42 C7 3 1 3 2 16 C8 3 2 1 3 128 C9 3 3 2 1 90 K1 avg 76.7 30 72 46 K2 avg 24 75.3 71 51.3 K3 avg 78 73.3 35.3 81.3 Range 54 45.3 35.3 35.3 Optimal mixture A3 B2 C1 D3 Note: Kiavg −Average of level i (i = 1,2,3).
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