When measuring, divide the total length of the crack into four equal parts, the central point and the two ends, and the central point and the third point in the middle. To measure the vertical width in the direction of the crack, use a special microscope with a scale, place the scale perpendicular to the crack, measure the width of the crack, record the reading and mark it on the graph.
You can also use the crack card to estimate the crack width through a magnifying glass, but this method has a large error. The length of the crack can be measured with a steel ruler, and there should be a mark at the end of the crack, and the year, month and day should be marked to observe the development of the crack.
When measuring the length and width of cracks, the thickness of the protective layer must be confirmed at the same time. When the concrete thickness of the protective layer is not suitable for chiseling, the steel detector can be used to find out its thickness.
03 Determination of crack depth
Ultrasonic method is usually used to detect the depth of cracks in terrazzo floor tiles, and the depth of cracks can be calculated from the relationship between the measured acoustic time and the probe.
Ultrasonic testing of crack depth should be carried out at a position avoiding steel bars, and it is only suitable for some stressed cracks, because the concrete on both sides of such cracks is generally completely separated. Ultrasonic testing is less accurate if the concrete on both sides is not completely separated.
For components whose cracks are not deep and whose direction is roughly in a straight line, the direct coring method can be used for detection.
The method of prefabricated terrazzo is to drill the concrete core sample along the depth direction at the position where there is a crack, so that the crack depth can be directly measured on the side of the core sample, and the disadvantage is that there is a certain damage to the component.
04 裂缝发展情况观测
对于活动裂缝，应进行定期观测，专用仪器有接触式引伸仪、振弦式应变仪等，最简单的办法是骑缝涂抹石膏饼观察。
在典型裂缝位置处抹50mm左右见方的石膏饼，观察石膏饼是否沿原裂缝开裂，就可确定裂缝是否在继续发展。石膏饼开裂宽度大，说明裂缝增长也大，将裂缝的变化情况亦记于图上。通过以上观测绘制形成的裂缝图，即可作为裂缝分析的依据。
5、裂缝修复措施
裂缝处理的原则：
1）首先应能保证裂缝处理后结构原有的承载能力、整体性以及防水、抗渗性能；
2）其次要考虑温度、收缩应力较长时间的影响，以免处理后再出现新的裂缝；
3）再次应防止进一步的人为损伤结构和构件，尽量避免大动大补，并尽可能保持原结构的外观。
