Harmful Cracks What are the criteria for determining harmless cracks?

Cracks are classified according to their shape into superficial, penetrating, longitudinal and transverse, etc. The crack shape is directly related to the stress state of the structure. Cracks are divided into healing, closing, motility, stabilization, and instability.

For example, the width of the crack, the beginning of some leakage, through the crack water combined with the cement, to form calcium hydroxide.

and C-S-H gel, after a period of time the crack heals and does not seep. Some cracks are closed under compressive stress. Some cracks periodically expand and close under the action of periodic temperature difference and periodic repeated loads, which is called crack motion, but this is a stable motion.

Some cracks produce unstable propagation, and depending on where they propagate, reinforcement measures should be considered.

According to the design specifications at home and abroad and the relevant test data, the control standards of the maximum crack width of concrete are roughly as follows:

There is no erosion medium, no seepage requirements.

Severe erosion, with anti-seepage requirements.

To determine whether a crack is harmful or harmless, it is first judged whether it is harmful to the safety and durability of the structure, and secondly, whether it affects the use function (such as waterproof, moisture-proof). For example, underground and hydraulic engineering.

Smaller than the crack is regarded as a harmless crack, and it can be closed with a simple surface, and then it is safer to make a flexible waterproof layer. Floor cracks are safe for the structure and are regarded as harmless cracks and can not be treated. For stressed beams and columns, structural safety is involved, and cracks should be properly handled.

Since the deformation crack generally does not affect the bearing capacity, but its waterproof problem is worth studying, according to the engineering investigation, among the various adverse consequences caused by the crack, leakage water accounts for 60. Water molecules.

The diameter of the is about, can pass through any cracks visible to the naked eye, theoretically waterproof structures are not allowed cracks, but the actual situation is not so, engineering practice shows that the cracks are wide, the beginning of leakage of 5l h, only 10ml h after a year, which shows that the crack gradually heals itself. Of course, it is not a problem to deal with water seepage cracks in time.

Judging Criteria:First, it depends on whether it is harmful to the safety and durability of the structure, and secondly, whether it affects the use function (such as waterproof, moisture-proof). For example, in underground and hydraulic engineering, smaller cracks are regarded as harmless cracks, and simple surface closure can be done, and then a flexible waterproof layer is more secure.

Floor cracks are safe for the structure and are regarded as harmless cracks and can not be treated. For stressed beams and columns, structural safety is involved, and cracks should be properly handled.

Deformation cracks generally do not affect the bearing capacity, but it is worth studying the waterproof problem, according to the engineering investigation, among the various adverse consequences caused by the cracks, leakage water accounts for 60. The diameter of the water molecule is about and can pass through any crack that is visible to the naked eye, and it is theoretically not allowed to crack in waterproof structures.

There is no erosion medium, no seepage requirements. Slight erosion, no anti-seepage requirements. Severe erosion, with anti-seepage requirements.

Cracks that produce unstable expansion are called harmful cracks Cracks are divided into superficial, penetrating, longitudinal and transverse according to their shape. The crack shape is directly related to the stress state of the structure. Cracks are divided into healing, closing, motility, stabilization, and instability.

For example, the width of the crack begins to leak, and the water combines with the cement through the crack to form calcium hydroxide and c-s-h gel, and the crack heals itself after a period of time. Some cracks are closed under compressive stress.