Journal of Jilin University(Engineering and Technology Edition) ›› 2021, Vol. 51 ›› Issue (5): 1734-1741.doi: 10.13229/j.cnki.jdxbgxb20200599

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Effect of hydration heat temperature and cracking mechanism of beam end in early stage of T⁃beam

Ying-xin HUI1,2,3(),Xiao-rong SUN1,Hong-yu WANG1,Chen GAO1   

  1. 1.School of Civil and Hydraulic Engineering，Ningxia University，Yinchuan 750021，China
    2.Ningxia Communications Construction Co. ，Ltd. ，Yinchuan 750002，China
    3.Ningxia Engineering Technology Research Center for Road Maintenance，Yinchuan 750002，China
  • Received:2020-08-10 Online:2021-09-01 Published:2021-09-16

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Abstract:

In order to avoid high hydration heat of precast concrete T beam during construction and maintenance， early vertical cracks appear at the beam end. Taking a 40-meter prestressed concrete T-beam as the research object， the mechanical properties of the concrete t-beam during the pouring process were monitored and tested. According to the measured results， a refined finite element model considering the early time-varying of the beam segment was established. And based on the above model， the evolution characteristics of hydration heat temperature field and the stress distribution law at the end of the beam during pouring process were studied. The results show that in the initial stage of concrete pouring of the 40-meter-span precast T-beam， the position near the beam end has a higher risk of cracking due to the rapid accumulation of temperature during the hydration process. In the area 2m～4m away from the beam end， the cracks are easy to penetrate through the web near the flange plate. It is recommended to control the mold-in temperature within 20 ℃， and adopt the method of optimizing the mixing ratio， reduce the amount of cement or use low-heat-of-hydration cement to reduce the heat of hydration and prevent cracking.

Key words: prestressed concrete T-beam, crack at the beam end, hydration heat, temperature field, stress field, finite element method

CLC Number: 

  • U441

Fig.1

Site diagram of web crack at prefabricated T beam end"

Fig.2

Layout of measuring points beam end"

Fig.3

Time-history curve of hydration heat temperature at relevant measuring points at 2 m and 4 m sections of prefabricated T beam ends"

Table 1

Temperature peak of prefabricated beam at each measuring point"

测点名称2 m截面峰值/℃4 m截面峰值/℃
测点1、342.940.9
测点4、543.843.0
测点7、946.044.4
测点11、1343.543.9
测点243.542.3
测点650.849.9
测点853.851.9
测点1058.956.2
测点1252.850.5

Table 2

Mechanical properties of prefabricated beam concrete at early ages"

龄期τ/df(cu,τ)/MPaf(t,τ)/MPa
113.51.32
329.32.20
536.62.55
741.42.78
1046.53.00
2861.33.60

Fig.4

Meshed finite element model"

Table 3

Comprehensive heat exchange coefficient of concrete surface"

文献风速/（m·s-1）部位

热交换系数/

（W·m-2·K-1）

［10］v顶板?=10.942+4v
腹板?=9.428+4v
底板?=7.514+4v

Table 4

Mixing proportion and thermal parameters of concrete"

项目水水泥砂石外加剂
比热/［kJ·（kg·℃）-1］4.190.460.700.69－

导热系数/

［kJ·（m·h·℃）-1］

2.164.4511.1310.50－
百分比/%5.7715.6329.6044.400.49

Fig.5

Time-history comparison of measured and calculated temperature at 2 m section of beam end"

Fig.6

Characteristic cross section temperature comparison diagram"

Fig.7

Time-history curve of first principal stress at measuring point 2 m and 4 m at beam end"

Fig.8

Temperature and time history at different temperature of casting concrete"

Table 5

Temperature peaks at different variable parameters"

模型编号入模 温度/℃温度 峰值/℃模型 编号水泥含量/（kg·m-3）温度 峰值/℃
1基准模型54.11#基准模型54.1
21550.42#36051.9
32556.73#37053.3
43058.74#39055.1
－－－5#40056.4
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