Interface shear resistance of precast keyway UHPC and post-cast normal concrete
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摘要: 永久性模板的使用可实现混凝土结构的快速施工，缩短工期，提高整体结构的承载能力和耐久性能。其界面粘结抗剪性能是确保永久性模板与混凝土协同工作的关键。本文设计并制作了3组不同强度混凝土试件和10组键槽式超高性能混凝土(UHPC)-普通混凝土(NC)复合试件，通过单面剪切试验和理论分析，系统研究了键槽密度、键槽间距、混凝土强度、养护条件等对键槽式UHPC-NC结合面抗剪性能的影响。结果表明：整体试件的裂缝与加载中心轴线呈一定角度，UHPC-NC结合面破坏发生于普通混凝土一侧。UHPC-NC荷载-滑移曲线细分为4个近似线性阶段，其极限滑移量均在0.9 mm以内。复合试件UHPC-NC的粘结面总剪切强度由粘结面接触摩擦力、水泥石-骨料相互作用、键槽-骨料互锁机制、剪切膨胀提供。合理的UHPC-NC键槽界面在提高界面粘结抗剪强度的同时，可有效提高界面相对位移。在60℃蒸汽养护条件下，水泥石-骨料界面及UHPC-混凝土界面作用减弱。建立了键槽式UHPC-后浇NC界面抗剪承载力修正公式，其计算值与试验值具有较高的吻合度，大多数结果落在90%置信区间，置信区间之外的点，受试件养护龄期的影响。因此，要准确计算键槽式UHPC-NC复合试件抗剪强度还需要考虑养护龄期的影响，引入养护龄期修正参数。Abstract: Use of permanent formwork can achieve rapid construction, shorten the construction period, and improve the bearing capacity and durability of concrete structure. Interfacial bond shear performance is the key to ensure the collaborative work of permanent formwork and concrete. Three groups of concrete specimens with different compressive strengths and ten groups of keyway ultra-high performance concrete (UHPC)-normal concrete (NC) composite specimens were prepared. The effects of keyway density, spacing, concrete strength, and curing condition on the shear property of keyway UHPC-NC were systematically studied through single-side shear tests and theoretical analysis. Results show that the crack of the concrete specimen is at a certain angle to the loading center axis. And the failure of the UHPC-NC joint surface occurs on the side of concrete. The load-displacement curve of UHPC-NC specimens can be subdivided into four approximately linear stages. And all of the displacements are within 0.9 mm. The total shear strength of the UHPC-NC composite specimen was provided by the contact friction of the bonding surface, matrix-aggregate interaction, keyway-aggregate interlocking mechanism and shear expansion. A reasonable interface of the UHPC-NC keyway can improve both the shear strength and the interface relative displacement of UHPC-NC specimens. After steam curing at 60℃, the interface of matrix-aggregate and the interface UHPC-NC are weakened. According to the results, a modified equation for the shear strength of the keyway UHPC-NC composite specimen was proposed. The calculated values agree well with the experimental results. Most of the calculated values fall within the 90% confidence interval. The values outside the confidence interval are affected by the curing time of the specimens. Therefore, to accurately calculate the shear strength of the keyway UHPC-NC composite specimen, the influence of curing time should also be considered by the curing time factor.
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图 2 单面剪切试件钢模具示意图
Figure 2. Schematic diagram of steel mold of single-side shear specimen
图 4 NC试件剪切破坏形态：混凝土强度等级的影响
Figure 4. Shear failure pattern of NC specimen: Effect of concrete strength
图 5 UHPC-NC试件剪切破坏形态：键槽参数((a)~(c))和NC强度((c)~(e))的影响
Figure 5. Shear failure pattern of UHPC-NC specimen: Effects of keyway parameter ((a)-(c)) and NC strength ((c)-(e))
图 6 UHPC-NC试件剪切破坏形态：养护龄期((a), (b))和养护制度(((a), (c))、((b), (d)))的影响
Figure 6. Shear failure pattern of UHPC-NC specimen: Effects of curing time ((a), (b)) and curing regime (((a), (c)), ((b), (d)))
图 7 NC、UHPC-NC试件荷载-位移曲线：混凝土强度的影响
Figure 7. Load-displacement curves of NC specimen and UHPC-NC specimen: Effect of concrete strength
图 8 UHPC-NC试件荷载-位移曲线：键槽类型的影响
Figure 8. Load-displacement curves of UHPC-NC specimen:Effect of keyway
图 9 UHPC-NC试件荷载-位移曲线：养护条件的影响
Figure 9. Load-displacement curves of UHPC-NC specimen:Effect of curing conditions
图 10 极限荷载下NC试件应变云图：混凝土强度的影响
Figure 10. Strain distribution of NC specimen under ultimate load: Effect of concrete strength
图 11 极限荷载下UHPC-NC试件应变云图：键槽参数的影响
Figure 11. Strain distribution of UHPC-NC specimen under ultimate load: Effect of keyway
图 12 极限荷载下UHPC-NC试件应变云图：后浇混凝土强度的影响
Figure 12. Strain distribution of UHPC-NC specimen under ultimate load: Effect of post-cast concrete strength
图 13 UHPC-NC试件粘结面抗剪强度计算值与试验值
Figure 13. Comparison of calculated values and experimental values for shear strength of UHPC-NC specimen
表 1 超高性能混凝土(UHPC)配合比 (kg/m3)
Table 1. Mix proportion of ultra-high performance concrete (UHPC) (kg/m3)
Cement Silica fume Fly ash Quartz sand Steel fiber Superplasticizer Water 680 144 200 1060 156 30 180 
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表 2 普通混凝土(NC)配合比和材料性能(kg/m3)
Table 2. Mix proportion and mechanical property of normal concrete (NC) (kg/m3)
Cement Sand Aggregate
(10-20 mm)Aggregate
(5-10 mm)Fly ash Slag Water Super-
plasticizer28 d compressive
strength/MPa28 d elastic
modulus/GPaC30 214 704 879 211 71 71 178 5.7 34.6 30.96 C40 279 645 878 207 79 79 175 7.0 44.6 33.69 C50 325 522 922 221 50 125 170 8.0 53.3 35.76
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表 3 剪切试验试件编号
Table 3. Number of specimen for shear test
Specimen type Strength of post-cast concrete Type of the interface Curing time/d Influence parameter N3 C30 Monolithic 7 — N4 C40 Monolithic 7 — N5 C50 Monolithic 7 — UN5-B-7 C50 B 7 Curing time UN5-B-Z7 C50 B 1+6 Curing regime UN5-B-14 C50 B 14 Curing time UN5-B-Z14 C50 B 1+13 Curing regime UN5-A-28 C50 A 28 Type of keyway UN5-B-28 C50 B 28 Type of keyway UN5-C-28 C50 C 28 Type of keyway UN3-B-28 C30 B 28 Strength of concrete UN4-B-28 C40 B 28 Strength of concrete UN5-B-Z28 C50 B 1+27 Curing regime
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表 4 NC试件与UHPC-NC试件的剪切性能参数
Table 4. Shear parameters of NC specimen and UHPC-NC specimen
Specimen type Ultimate
load Pu/kNNominal shear
strength τ/MPaVertical limit
displacement S/mmShear stiffness
K/(kN·mm−1)N3 27.36 2.74 0.185 136.80 N4 32.02 3.20 0.370 68.96 N5 43.08 4.31 0.354 147.10 UN5-B-7 45.51 4.55 0.545 113.98 UN5-BZ-7 45.20 4.53 0.290 211.26 UN5-B-14 60.48 6.05 0.410 134.40 UN5-BZ-14 38.96 3.89 0.400 97.40 UN5-A-28 46.94 4.69 0.684 66.78 UN5-B-28 74.50 7.45 0.985 127.36 UN5-C-28 62.59 6.26 0.800 58.42 UN3-B-28 47.00 4.70 0.540 86.58 UN4-B-28 60.15 6.01 0.650 113.80 UN5-BZ-28 53.99 5.40 0.660 85.90
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表 5 UHPC-NC试件粘结面抗剪强度计算值与试验值(MPa)
Table 5. Calculated values and experimental values for shear strength of UHPC-NC specimen (MPa)
Test value Mohr Coulomb theory[15-16] Eurocode 2[31] AASHTO LRFD[32] ACI 318[33] Fib model code[34] N3 2.74 3.84 1.025 0.3 0.866 0.4 N4 3.20 4.96 1.325 0.3 0.983 0.4 N5 4.31 5.93 1.583 0.3 1.075 0.4 UN5-B-7 4.55 5.93 1.583 0.3 2.150 0.4 UN5-BZ-7 4.53 5.93 1.583 0.3 2.150 0.4 UN5-B-14 6.05 5.93 1.583 0.3 2.150 0.4 UN5-BZ-14 3.89 5.93 1.583 0.3 2.150 0.4 UN5-A-28 4.69 5.93 1.583 0.3 2.150 0.4 UN5-B-28 7.45 5.93 1.583 0.3 2.150 0.4 UN5-C-28 6.26 5.93 1.583 0.3 2.040 0.4 UN3-B-28 4.70 3.84 1.025 0.3 1.732 0.4 UN4-B-28 6.01 4.96 1.325 0.3 1.966 0.4 UN5-BZ-28 5.40 5.93 1.583 0.3 2.150 0.4
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表 6 UHPC-NC试件粘结面抗剪强度(τs)修正模型计算值与试验值(MPa)
Table 6. Calculated values of corrected model and experimental values for shear strength (τs) of UHPC-NC specimens (MPa)
Test
valueRef. [17] Ref. [22] Ref. [23] Ref. [29] Calculated model τs (Test value (Calculated value) ) UN5-B-7 4.55 6.457 (0.705) 7.593 (0.599) 4.351 (1.046) 8.594 (0.529) 5.293 (0.860) UN5-BZ-7 4.53 6.457 (0.702) 7.593 (0.597) 4.351 (1.041) 8.594 (0.527) 5.293 (0.856) UN5-B-14 6.05 6.457 (0.937) 7.593 (0.797) 4.351 (1.390) 8.594 (0.704) 5.293 (1.143) UN5-BZ-14 3.89 6.457 (0.602) 7.593 (0.512) 4.351 (0.894) 8.594 (0.453) 5.293 (0.735) UN5-A-28 4.69 6.457 (0.726) 7.593 (0.618) 4.351 (1.078) 8.594 (0.546) 5.293 (0.886) UN5-B-28 7.45 6.457 (1.154) 7.593 (0.981) 4.351 (1.712) 8.594 (0.867) 5.293 (1.407) UN5-C-28 6.26 6.383 (0.981) 7.593 (0.824) 3.916 (1.599) 8.140 (0.769) 6.223 (1.006) UN3-B-28 4.70 3.374 (1.394) 6.117 (0.768) 4.351 (1.080) 6.777 (0.694) 5.094 (0.923) UN4-B-28 6.01 4.462 (1.347) 6.945 (0.868) 4.351 (1.381) 7.792 (0.771) 5.160 (1.165) UN5-BZ-28 5.40 6.457 (0.836) 7.593 (0.711) 4.351 (1.241) 8.594 (0.628) 5.293 (1.020)
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