低温作用下改性骨料-钢纤维再生混凝土弯曲性能试验

苏骏; 黄福; 王淞波; 许子扬; 杨海鑫; 李扬

doi:10.13801/j.cnki.fhclxb.20230531.002

低温作用下改性骨料-钢纤维再生混凝土弯曲性能试验

doi: 10.13801/j.cnki.fhclxb.20230531.002

湖北工业大学　土木建筑与环境学院，武汉 430068

基金项目: 国家自然科学基金(51508171)；湖北省自然科学基金项目(2020CFB860)

详细信息

通讯作者:
黄福，硕士生，研究方向为纤维再生混凝土　E-mail: 1248089087@qq.com

中图分类号: TB332
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出版历程
- 收稿日期: 2023-04-18
- 修回日期: 2023-05-09
- 录用日期: 2023-05-22
- 网络出版日期: 2023-06-01
- 刊出日期: 2024-02-01

Experimental study on bending properties of modified aggregate-steel fibre recycled concrete under low temperature

School of Civil Engineering, Architecture and Environment, Hubei University of Technology, Wuhan 430068, China

Funds: National Natural Science Foundation of China (51508171); Natural Science Foundation of Hubei Province (2020CFB860)

摘要

摘要: 为探究低温作用对改性骨料-钢纤维再生混凝土弯曲性能的影响，将再生骨料通过水泥净浆改性处理后，分别设置30wt%、60wt%再生骨料取代率，掺入适量钢纤维制成净浆改性再生混凝土(CRAC)，以我国北方寒区温度为背景设置20℃、0℃、−20℃、−40℃、−60℃的温度梯度，将CRAC经低温作用进行抗压强度及四点弯曲性能试验，对其进行等效弯曲强度及弯曲韧性分析，同时结合SEM从微观结构角度揭示其宏观性能改变机制，在此基础上给出了低温作用下再生混凝土的纤维增强效应表达式。结果表明：经低温作用CRAC弯拉强度显著提升，较常温最大可提升约168%；随温度的进一步降低，受冰晶生长作用及改性骨料特性影响，再生骨料取代率为60wt%的CRAC耗能能力较30wt%表现更优；同时低温作用下钢纤维体积掺量为1.5vol%的CRAC强度及韧性性能提升效果最佳，研究结论为低温作用下再生混凝土的性能优化设计及推广应用提供参考。
- 改性骨料 /
- 再生混凝土 /
- 低温作用 /
- 弯曲韧性 /
- 纤维掺量 /
- 微观结构
Abstract: In order to study the effect of low temperature on bending property of modified aggregate-steel fiber recycled aggregate concrete, the replacement rates of 30wt% and 60wt% recycled aggregate were set, mixed with appropriate amount of steel fiber to make cement recycled aggregate concrete (CRAC), temperature gradients of 20℃, 0℃, −20℃, −40℃ and −60℃ were set in the cold area of northern China. CRAC was subjected to compressive strength and four-point bending performance tests by low-temperature action, and its equivalent bending strength and bending toughness were analysed, together with SEM to reveal its macroscopic performance change mechanism from the microstructure perspective, on the basis of which an expression for the fibre reinforcement effect of recycled concrete under low-temperature was proposed. The test results show that after low temperature treatment, the flexural strength of CRAC is significantly increased by 168%, respectively. With the further decrease of temperature, the bending property of 60wt% CRAC is better than that of 30wt% CRAC. At the same time, CRAC with 1.5vol% steel fibres has the best strength and toughness properties at low temperatures. The conclusion of the study is expected to provide reference for the performance design and application of recycled concrete in low temperature environment.
- modified aggregate /
- recycled aggregate concrete /
- low temperature /
- bending property /
- fiber content /
- micro structure

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图 1 水泥净浆改性再生骨料(CRA)制作流程及其形态

RA—Recycled aggregate

Figure 1. Production process and morphology of cement recycled aggregate (CRA)

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图 2 降温及温度传感设备

Figure 2. Cryogenic equipment and temperature sensor

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图 3 加载示意图

Figure 3. Loading diagram

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图 4 韧性指标计算简图

δ—Incipient deflection

Figure 4. Calculation diagram of toughness index

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图 5 不同温度下水泥净浆改性再生混凝土(CRAC)受弯荷载-挠度曲线

Figure 5. Bending load-deflection curves of cement recycledaggregate concrete (CRAC) at different temperatures

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图 6 1.5vol%SF/CRAC(60wt%CRA)试件破坏形态

Figure 6. 1.5vol%SF/CRAC(60wt%CRA) specimen damage pattern

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图 7 温度对CRAC等效弯曲强度的影响

Figure 7. Effect of temperature on equivalent bending strength of CRAC

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图 8 低温作用下孔隙水冰晶生长演化过程

Figure 8. Evolution of pore water ice crystal growth under the effect of low temperature

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图 9 不同影响因素下CRAC弯曲韧性指数

Figure 9. Bending toughness index of CRAC under different influence factors

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图 10 不同温度下钢纤维损伤机制

Figure 10. Steel fiber damage mechanisms at different temperatures

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图 11 不同温度下CRAC破坏机制

Figure 11. CRAC destruction mechanisms at different temperatures

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图 12 CRAC纤维增强效应与温度的关系

Figure 12. Relationship between fiber reinforcement effect of CRAC and temperature

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图 13 CRAC微观结构

ITZ—Interface transition zone; Aft—Ettringite; C-H—Calcium hydroxide; C-S-H—Calcium silicate hydrates

Figure 13. Microstructure of CRAC

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图 14 低温作用对CRAC微观结构影响

Figure 14. Effect of low temperature action on the microstructure of CRAC

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表 1 钢纤维物理性能

Table 1. Physical parameters of steel fiber

Density/(g·cm⁻³)	Diameter/mm	Length/mm	Tensile strength/MPa	Modulus of elasticity/GPa
7.8	0.2	13	2900	200

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表 2 不同骨料物理指标

Table 2. Physical indicators of different aggregates

Aggregate type	Aggregate size/mm	Apparent density/(kg·m⁻³)	Crush index/%	Water absorption/%	Moisture content/%
NA RA CRA	5-20	2750 2652 2638	9.60 18.40 15.30	0.83 6.20 7.10	1.20 2.30 3.70
Note: NA—Natural aggregate.

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表 3 试件编号及配合比

Table 3. Number and mix proportion of specimens

Number	NA/ (kg·m⁻³)	CRA/ (kg·m⁻³)	Steel fibre/ vol%	Additional water/(kg·m⁻³)	Compressive strength/MPa
Number	NA/ (kg·m⁻³)	CRA/ (kg·m⁻³)	Steel fibre/ vol%	Additional water/(kg·m⁻³)	20℃	0℃	−20℃	−40℃	−60℃
0vol%SF/CRAC(30wt%CRA)	824.60	353.40	0	13.17	41.62	44.44	48.94	56.71	62.76
0.5vol%SF/CRAC(30wt%CRA)	824.60	353.40	0.50	13.17	47.02	47.56	50.97	60.21	75.56
1.0vol%SF/CRAC(30wt%CRA)	824.60	353.40	1.00	13.17	48.30	55.54	64.11	71.19	86.83
1.5vol%SF/CRAC(30wt%CRA)	824.60	353.40	1.50	13.17	49.36	56.20	56.13	67.18	85.07
0vol%SF/CRAC(60wt%CRA)	471.20	706.80	0	26.34	39.74	52.52	61.76	69.08	81.64
0.5vol%SF/CRAC(60wt%CRA)	471.20	706.80	0.50	26.34	41.68	47.65	48.08	54.22	81.78
1.0vol%SF/CRAC(60wt%CRA)	471.20	706.80	1.00	26.34	43.54	52.55	47.56	72.29	80.62
1.5vol%SF/CRAC(60wt%CRA)	471.20	706.80	1.50	26.34	46.78	58.33	57.46	68.21	83.92
Note: CRAC—Cement recycled aggregate concrete; SF—Steel fibre.

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表 4 CRAC试件平均弯拉强度试验值

Table 4. Test values of average flexural tensile strength of each group CRAC specimens

Number	Test values of average flexural tensile strength/MPa
Number	20℃	0℃	−20℃	−40℃	−60℃
0vol%SF/CRAC(30wt%CRA)	4.88	5.12	5.62	8.21	10.12
0.5vol%SF/CRAC(30wt%CRA)	4.77	5.24	5.03	11.39	12.00
1.0vol%SF/CRAC(30wt%CRA)	4.81	6.26	5.34	7.54	11.12
1.5vol%SF/CRAC(30wt%CRA)	5.22	5.89	6.02	9.54	10.44
0vol%SF/CRAC(60wt%CRA)	3.47	4.20	3.97	8.25	9.30
0.5vol%SF/CRAC(60wt%CRA)	3.91	4.27	4.35	8.44	9.35
1.0vol%SF/CRAC(60wt%CRA)	5.01	4.95	4.65	8.71	10.54
1.5vol%SF/CRAC(60wt%CRA)	5.17	4.95	5.96	8.95	9.93

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表 5 CRAC强度及韧性指标

Table 5. Strength and toughness index of CRAC

Number	Temperature/℃	Initial crack load/kN	Initial crack deflection/mm	Peak load/kN	Equivalent bending strength/MPa	I₅	I₁₀
0vol%SF/CRAC(30wt%CRA)	20	9.21	0.47	16.27	—	—	—
	0	9.73	0.46	17.08	—	—	—
	−20	10.25	0.44	18.74	—	—	—
	−40	15.66	0.48	27.36	—	—	—
	−60	17.66	0.56	33.72	—	—	—
0.5vol%SF/CRAC(30wt%CRA)	20	10.69	0.39	15.91	2.55	5.68	10.05
	0	9.77	0.38	17.45	2.05	5.38	8.59
	−20	10.19	0.36	16.76	1.76	4.62	6.99
	−40	15.79	0.52	39.95	3.90	6.09	8.48
	−60	16.34	0.55	37.96	4.31	6.51	9.31
1.0vol%SF/CRAC(30wt%CRA)	20	13.97	0.44	16.01	3.50	6.01	11.94
	0	12.80	0.41	20.86	2.89	5.61	9.06
	−20	10.96	0.39	17.80	2.28	5.27	8.38
	−40	17.54	0.62	25.14	4.55	6.15	10.06
	−60	20.93	0.60	37.14	5.38	6.52	10.32
1.5vol%SF/CRAC(30wt%CRA)	20	15.05	0.49	17.40	4.05	6.58	12.26
	0	13.64	0.47	19.62	3.54	6.17	10.62
	−20	13.63	0.49	20.08	3.27	5.74	9.74
	−40	17.10	0.59	31.81	4.53	6.29	10.29
	−60	20.18	0.56	34.78	5.48	6.75	10.04
0vol%SF/CRAC(60wt%CRA)	20	8.80	0.32	10.94	—	—	—
	0	9.34	0.37	14.00	—	—	—
	−20	9.19	0.42	13.24	—	—	—
	−40	15.69	0.58	27.51	—	—	—
	−60	17.15	0.58	30.99	—	—	—
0.5vol%SF/CRAC(60wt%CRA)	20	10.17	0.41	13.03	2.69	5.77	10.94
	0	8.95	0.34	14.23	1.53	4.76	7.18
	−20	9.08	0.35	14.10	1.67	5.06	7.69
	−40	16.22	0.52	31.17	3.57	5.51	8.15
	−60	15.08	0.66	28.12	3.65	5.89	8.44
1.0vol%SF/CRAC(60wt%CRA)	20	13.40	0.47	17.91	3.32	5.94	11.15
	0	11.21	0.40	16.51	2.59	5.58	9.22
	−20	11.02	0.39	15.51	2.72	5.70	9.37
	−40	17.99	0.56	29.02	4.71	6.43	9.58
	−60	24.53	0.63	35.13	5.78	7.00	10.62
1.5vol%SF/CRAC(60wt%CRA)	20	14.98	0.49	15.75	4.06	6.32	11.62
	0	12.03	0.43	16.48	2.85	5.70	9.54
	−20	15.10	0.42	19.87	3.73	6.24	10.28
	−40	19.26	0.53	29.84	5.14	6.55	10.77
	−60	23.29	0.64	33.11	6.01	7.08	10.31
Notes: As the 0vol% fibre doping CRAC exhibits brittle fracture, it is not possible to calculate its equivalent flexural strength and toughness index (I₅, I₁₀).

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表 6 不同温度下CRAC纤维增强效应系数

Table 6. Fiber reinforcement effect coefficients of CRAC at different temperatures

Number	Fiber reinforcement effect coefficients
Number	20℃	0℃	−20℃	−40℃	−60℃
0.5vol%SF/CRAC(30wt%CRA)	5.63	4.09	3.39	3.15	2.78
1.0vol%SF/CRAC(30wt%CRA)	8.93	5.88	4.82	5.18	4.02
1.5vol%SF/CRAC(30wt%CRA)	9.00	7.92	6.52	5.34	3.67
0.5vol%SF/CRAC(60wt%CRA)	13.59	7.15	4.62	3.32	2.83
1.0vol%SF/CRAC(60wt%CRA)	18.05	10.52	8.06	4.25	5.25
1.5vol%SF/CRAC(60wt%CRA)	20.38	13.75	11.29	5.29	4.87

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