Experimental Investigation of Relative Humidity Response in Early-Age Concrete Under Tensile Stress
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摘要:
为系统研究早龄期混凝土内部相对湿度对不同水平拉应力的响应规律，设计恒定轴拉下混凝土内部相对湿度测试方法，试验研究了不同拉应力下的相对湿度响应规律，并基于试验结果和理论分析，给出早龄期混凝土单面干燥条件下相对湿度与拉应力的线性模型. 研究结果表明：拉应力施加会造成混凝土内部相对湿度瞬时下降，当拉应力从0.8 MPa增加到3.2 MPa时，混凝土深度分别为50、75、100 mm处的相对湿度变化值从0.5%、0.4%和0.3%增加到0.8%、0.7%和0.6%；随着拉应力逐渐增大，相对湿度下降值逐渐增大；在相同拉应力下，距离混凝土暴露面近的相对湿度对拉应力的响应更为显著；拉应力持荷状态下相对湿度会逐渐恢复，恢复时间约2.5 h，在压应力持荷状态下也出现了类似现象，恢复时间约20.0 h，拉应力持荷状态下相对湿度恢复时间更短.
Abstract:In order to systematically investigate the response law of the internal relative humidity of concrete at an early age to different tensile stress levels, a test method of the internal relative humidity of the concrete under constant axial tension was developed in this paper, and the response law of the relative humidity under different tensile stresses was studied experimentally. According to the experimental results and theoretical analysis, a linear model of the relative humidity and tensile stress of early-age concrete under one-side drying conditions was presented. The results show that the tensile stress causes the instantaneous decrease in the internal relative humidity of the concrete. When the tensile stress increases from 0.8 MPa to 3.2 MPa, the relative humidity change at the depth of 50, 75, and 100 mm of the concrete increases from 0.5%, 0.4%, and 0.3% to 0.8%, 0.7%, and 0.6%, respectively. At the same time, with the increase in tensile stress, the decrease in the relative humidity gradually increases. Under the same tensile stress, the response of relative humidity of the concrete, close to the exposed surface, to tensile stress which is is more obvious. The relative humidity gradually recovers during the tensile stress loading, and the time is about 2.5 h. A similar phenomenon also occurs during the compressive stress loading, and the time is about 20.0 h. Therefore, the relative humidity recovery time is shorter during the tensile stress loading.
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Key words:
- early age /
- concrete /
- relative humidity /
- tensile stress /
- linear model
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图 1 相对湿度测点位置及端部丝杆对中措施
Figure 1. Location of relative humidity measuring point and alignment method of end screws
图 4 不同拉应力水平下相对湿度曲线
Figure 4. Relative humidity curves under different tensile stress levels
图 6 2.4 MPa拉应力下相对湿度和变形对比曲线
Figure 6. Comparison curves of relative humidity and deformation under tensile stress of 2.4 MPa
图 9 动弹性模量和静弹性模量与龄期的关系
Figure 9. Relationship between age and dynamic and static elastic moduli
图 10 由相对湿度变化以及静、动弹性模量差产生的应变差值
Figure 10. Strain difference caused by static and dynamic modulus difference and relative humidity variation
图 11 相对湿度变化引起应变差值拟合结果
Figure 11. Fitting results of strain difference caused by relative humidity variation
表 1 混凝土配合比
Table 1. Concrete mix proportion
kg/m3 材料名称 水泥 水 细骨料 粗骨料 减水剂 配合比 533.00 160.00 597.00 1110.00 4.33 
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表 2 加载试验方案
Table 2. Loading test scheme
工况 拉（压）应力/
抗拉（压）强度/%施加拉（压）应力/MPa 7 d 抗拉（压）强度/MPa 截面面积/m2 施加荷载/kN 备注 T1 20 0.8 3.95 0.01875 15 拉力 T2 40 1.6 3.95 0.01875 30 拉力 T3 60 2.4 3.95 0.01875 45 拉力 T4 80 3.2 3.95 0.01875 60 拉力 C1 20 12.8 63.7 0.01875 240 压力
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表 3 拉应力加载前后相对湿度和饱和度
Table 3. Relative humidity and saturation before and after tensile stress loading
测点 0.8 MPa 1.6 MPa 2.4 MPa 3.2 MPa H1 /% （S1） H2/% （S2） H1 /% （S1） H2/% （S2） H1 /% （S1） H2/% （S2） H1/% （S1） H2 /% （S2） D100 86.6
（0.7941）86.3
（0.7914）86.2
（0.7905）85.8
（0.7870）86.0
（0.7887）85.5
（0.7844）86.3
（0.7914）85.7
（0.7861）D75 84.9
（0.7794）84.5
（0.7762）84.3
（0.7746）83.8
（0.7708）84.5
（0.7762）83.9
（0.7715）84.6
（0.7770）83.9
（0.7715）D50 83.7
（0.7700）83.2
（0.7663）83.0
（0.7649）82.4
（0.7607）83.2
（0.7663）82.5
（0.7614）83.3
（0.7671）82.5
（0.7614）
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