Deformation Analysis of Reinforced Concrete using Neutron Imaging Technique-猫眼课题宝

DOI：

10.21741/9781945291678-24

发表时间：

2018

期刊：

影响因子：

通讯作者：

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其他

文献类型：

作者：

T. Koyama;K. Ueno;M. Sekine;Y. Matsumoto;T. Kai;T. Shinohara;H.;Iikura;H. Suzuki;M. Kanematsu

我们提出了一种利用中子透射成像技术观察混凝土内部变形的新方法。为了可视化混凝土的内部变形，将含有Gd2O3粉末的水泥膏体标记物二维分散在钢筋混凝土中铁素体变形钢筋周围。Gd标记物的中子透射图像位移是通过标记物位置的变化作为垂直样品台移动距离的函数来评估的，通过分析具有较高对比度和圆度的标记物，成功地评估了Gd标记物的精度在±0.1 mm左右。此外，以同样的方法评估了混凝土在内嵌钢筋拉拔荷载作用下的变形，并通过分析标记的位移成功地观察了混凝土的压缩变形。本文的研究结果为选择球形标记点和提高标记点的对比度可以提高标记点位移的测量精度提供了有益的认识。钢筋混凝土（RC）被广泛应用于各种建筑和土木工程结构，是一种众所周知的复合结构，在这种结构中，抗拉强度和延性相对较低的混凝土被具有高抗拉强度和延性的钢筋（螺杆钢）等增强物所加强。钢筋混凝土的结构性能一般来源于钢筋与混凝土之间的粘结阻力。在之前的研究中已经证明，中子衍射技术可以作为一种替代传统应变片的方法，通过测量嵌入混凝土中的钢筋的应力分布来评估粘结阻力[1-3]。另一方面，为了探讨钢筋混凝土结构混凝土与钢筋粘结退化的机理，对钢筋混凝土周围混凝土的变形行为进行评价也很重要。然而，由于混凝土内部氢的高背景噪声散射，使得中子衍射技术难以应用于混凝土应变的测量。另外，图像分析技术，如点阵法[4]和数字图像相关（DIC）[5]，通常用于定量评估混凝土的变形。他们可以通过分析高分辨率相机拍摄的图像对比度或标记位移来评估混凝土表面MECA SENS 2017材料研究论坛LLC材料研究进展4 (2018)155-160 doi: http://dx.doi.org/10.21741/9781945291678-24 156变形。因此，在本研究中，我们的目标是开发一种利用中子透射成像技术结合晶格法观察混凝土内部变形的新方法。钢筋混凝土试验规程。图1为本研究中使用的RC试件示意图。在尺寸为50 × 50 × 130 mm的矩形混凝土试件中嵌入标称直径为12.7 mm的铁素体钢变形棒。钢筋的预埋长度为100 mm，并用聚氯乙烯（PVC）管包裹钢筋，人为引入30 mm的非粘结区。为了可视化嵌入钢筋周围混凝土的内部变形，将含有34 wt.% Gd2O3粉末的水泥糊标记物（以下简称“Gd标记物”）二维分散，覆盖A-A截面面积的15%。采用粒径为φ50 × 100 mm，具有特定Gd2O3含量的膏体圆柱体粉碎，将其粒度划分为0.6 ~ 1.7 mm，得到Gd标记物。RC试件放置72小时后脱模，在水中固化7天。为了减少混凝土中水分对氢致中子衰减的影响，将RC试件置于恒温（20±1℃）恒湿（60±5 RH %）室内24小时，然后在60℃下干燥4天后进行中子实验。中子光学系统。图2显示了本研究中使用的光学布局。RC试件安装在日本质子加速器研究中心（J-PARC）材料与生命科学实验设施（MLF）的BL22， RADEN[6]样品台上，加载装置由液压千斤顶和称重传感器组成。RADEN是下一代脉冲中子仪器，能量分辨中子成像设备。本次实验的J-PARC MLF束流功率为150 kW，样品位置的中子通量估计为5.0 ×10 n/cm/sec。L/D比率设置为1000。入射中子被RC试样散射和吸收，经闪烁体转化为可见光后，由冷却CCD相机拍摄。闪烁体与样品边缘的距离设置为200mm，以减小样品散射的影响。使用相同的测量配置，共拍摄了四张曝光时间为15分钟的图像。传输图像的分辨率为2048 × 2048像素（16位），空间分辨率约等于0.2 mm。在钢筋混凝土试件上安装了精度为0.01 mm的位移传感器，用于测量内嵌钢筋在拉拔荷载作用下的边缘位移。实验条件。首先对分析条件进行优化，通过评价Gd标记物图像的位移与样品级移动距离的关系，以准确确定Gd标记物在透射图像上的位置。通过使用开源图像处理程序的图像分析技术，评估了Gd标记物在RC试件中子透射图像中的位置，图1为本研究中使用的RC试件示意图。图2成像实验光学布局示意图。200mm负载闪烁位移传感器

We suggest a novel method to observe internal deformation of concrete using a neutron transmission imaging technique. In order to visualize the internal deformation of concrete, cement paste markers containing Gd2O3 powder were dispersed two-dimensionally around the ferritic deformed rebar in reinforced concrete. Displacement of the neutron transmission image of the Gd marker was evaluated by a change in the position of the marker as a function of the travel distance of the vertical sample stage, and it was successfully evaluated to within approximately ±0.1 mm accuracy by analyzing selected markers with higher contrast and circularity. Furthermore, concrete deformation under pullout loading to the embedded rebar was evaluated in the same way and compressive deformation of concrete was successfully observed by analyzing the displacement of the markers. The results obtained in this study bring beneficial knowledge that the measurement accuracy of the marker displacement can be improved by choosing spherical-shaped markers and by increasing the contrast of markers. Introduction Reinforced concrete (RC), widely utilized for various architectural and civil engineering structures, is well known as a composite structure in which concrete with relatively low tensile strength and ductility is strengthened by reinforcements such as steel rods (rebars) with high tensile strength and ductility. The structural performance of RC is generally derived from the bond resistance between rebar and concrete. It has been demonstrated in previous studies that the neutron diffraction technique can be an alternative method to conventional strain gauges for evaluation of bond resistance by measuring the stress distribution of rebar embedded in concrete [1-3]. On the other hand, it is also important to evaluate the deformation behavior of concrete around the embedded rebar in order to discuss the mechanism of bond degradation between concrete and rebar for the RC structure. However, it is difficult to apply the neutron diffraction technique to the measurement of strain in concrete since high background noise scattering from hydrogen within the concrete makes diffraction measurements in concrete difficult. Alternatively, image analysis techniques such as a lattice method [4] and digital image correlation (DIC) [5], are commonly utilized for evaluating deformation of concrete quantitatively. They can assess concrete surface MECA SENS 2017 Materials Research Forum LLC Materials Research Proceedings 4 (2018) 155-160 doi: http://dx.doi.org/10.21741/9781945291678-24 156 deformation by analyzing image contrast or marker displacement taken by a high resolution camera. In this study, therefore, we aim to develop a novel method to observe internal deformation of concrete using the neutron transmission imaging technique combined with a lattice method. Experimental Procedure Reinforced Concrete Specimen. Fig. 1 shows the schematic illustration of the RC specimen used in this study. A ferritic steel deformed-bar with a nominal 12.7 mm diameter to JIS3112 standard was embedded in a rectangular concrete specimen of size 50 × 50 × 130 mm. The embedded length of rebar was 100 mm, and unbonded region of 30 mm in length was artificially introduced by surrounding the rebar with a polyvinyl chloride (PVC) pipe. In order to visualize the internal deformation of concrete around the embedded rebar, the cement paste markers containing 34 wt.% Gd2O3 powder (hereafter called “Gd marker”) were dispersed two-dimensionally covering 15 % of the area of the A-A’ cross section. The Gd markers were obtained by pulverizing a paste cylinder of φ50 × 100 mm having a specific Gd2O3 content and classifying the particle size into 0.6 to 1.7 mm. The RC specimen was demolded 72 hours after placing and then cured in water for 7 days. In order to reduce water in concrete that causes neutron attenuation by hydrogen, the RC specimen was placed in a constant temperature (20 ±1 C) and humidity (60 ±5 RH %) room for 24 hours, and then was dried at 60 C for 4 days before the neutron experiment. Neutron Optical System. Fig. 2 shows the optical layout utilized in this study. The RC specimen mounted on the loading device, composed of a hydraulic jack and a load cell, was set up on a sample stage of BL22, RADEN [6], in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). RADEN is a next generation pulsed-neutron instrument, energyresolved neutron imaging facility. The beam power of J-PARC MLF for this experiment was 150 kW, and the neutron flux at the sample position was estimated to be 5.0 ×10 n/cm/sec. The L/D ratio was set to 1000. The incident neutrons scattered and absorbed by the RC specimen were taken by a cooled CCD camera after being converted to visible light by a scintillator. The distance between the scintillator and the sample edge was set to 200 mm so as to reduce the influence of scattering from the specimen. A total of four images each with a 15 minute exposure time were taken with the same measurement configuration. The resolution of the transmission image was 2048 × 2048 pixels (16 bit), and the spatial resolution was approximately equivalent to be 0.2 mm. A displacement transducer with an accuracy of 0.01 mm was set up on the RC specimen to measure the displacement of the edge of the embedded rebar under pullout loading. Experimental Condition. The analytical condition was, at first optimized by evaluating the displacement of the Gd marker images as a function of the travel distance of the sample stage in order to determine the position of the Gd marker on the transmission image accurately. The position of the Gd marker in a neutron transmission image of the RC specimen was evaluated by an image analysis technique using an open source image processing program, Fig. 1 Schematic illustration of the RC specimen used in this study. Fig. 2 Schematic optical layout for imaging experiment. 200 mm Load Scintillator Displacement transducer

Deformation Analysis of Reinforced Concrete using Neutron Imaging Technique

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