Analysis on bridge crack detection and treatment measures?

Keywords: bridge crack prevention measures, concrete mix ratio

First, the common methods of concrete bridge crack detection

1, length detection

In general, you can use a common tape measure for length detection. In the field measurement, if it is found that the crack has developed, a line should be drawn at both ends of the crack, and after a period of time, whether there is further development can be judged according to the ruler.

2. Width detection

At present, the crack width measuring instrument is generally used to detect concrete cracks. When installing, we should be very careful to ensure that the dial indicator is perpendicular to the crack and the foot of the meter is firm. To detect whether the crack width is increased, the following methods can also be adopted: sticking the thin glass with a V-shaped groove in the middle perpendicular to the crack with a bonding material to ensure that the notch section is flush with the crack. Because the glass section at the notch is small, the glass is a brittle material with no stretchability. As long as the crack develops, the glass will break.

3. Depth detection

Cracks in concrete bridges are mainly divided into two types. The former is confined to the structural surface, and the cracking depth is not more than 500 mm, and the cracking depth of deep cracks is more than 500 mm. Generally, the shallow surface layer can be treated by roughening. The specific operation steps are: injecting phenolphthalein alcohol solution with the concentration of 1% into the cracks, then carefully roughening to the boundary between discoloration and non-discoloration, and measuring its depth. The reason for the boundary line is that the concrete at the crack has been carbonized. However, this test method should be used with caution to reduce further damage to concrete. At present, we use more ultrasonic nondestructive testing methods.

Second, measures to prevent and treat cracks in concrete bridges

1, control the quality of concrete raw materials and the choice of cement concrete mixture ratio.

1) Select suitable raw materials, such as medium and low heat cement, retarding water reducer, fiber and low heat and high performance concrete. At the same time, we should pay attention to whether its characteristics have adverse effects on the strength, durability and service conditions of concrete structures; The gradation, silt content, needle content, crushing value index and harmful substance content of sand and gravel materials should be controlled within the scope permitted by the specification.

Before the concrete is poured on the pier, the sand, stone, steel bar, cement, fly ash and admixture used shall be prepared according to the design drawings and the construction mixture ratio approved by the headquarters, and can only be put into concrete construction after passing the inspection. During construction, it is adjusted according to the actual water content of sand and gravel aggregate to meet the requirements of concrete strength and workability.

2) Targeted concrete mix design, such as reducing the concrete unit cement dosage, appropriately increasing the dosage of fly ash or ground slag, and appropriately adding high-efficiency retarding water reducing agent, can effectively reduce the total hydration heat of concrete and the peak value of its release, thus reducing the cracks caused by excessive external temperature difference of concrete caused by hydration heat; In construction, the construction unit often only pays attention to the strength of concrete and ignores its deformation characteristics and workability, which is the main reason for concrete cracks.

Strict mix design, first of all, according to the design strength of concrete specified in the design drawings, the theoretical mix proportion of concrete is determined by calculation. Secondly, according to the calculated theoretical mixture ratio, try to match, and according to the measured slump, workability, workability, etc. , adjust the dosage of various materials appropriately, and try to match again until it meets the requirements. Finally, the trial-mixed concrete samples are prepared according to the regulations and maintained by standard methods.

2. Strengthen the protective measures of concrete bridge structure construction under the conditions of high temperature in summer and low temperature in winter.

Bridges are most prone to crack problems in summer and winter construction, so we should actively check and deal with small cracks in time without leaving hidden dangers; In addition, in the summer and winter construction process, we should also study and formulate proper schemes to ensure the smooth construction of the project.

At low temperature, in the construction of large plane concrete, sometimes the concrete poured at night will have cracks on the concrete surface corresponding to the steel mesh in the morning, and the concrete surface between cracks will sink. After concrete pouring is completed, cover the poured concrete surface with geotextile in time after the surface is closed, and keep the concrete in good health as soon as possible. Sprinkler curing should be maintained for at least 7 days or the days instructed by the supervision engineer. Keep the concrete surface moist during curing. When the temperature is lower than +5℃, it should be covered with heat preservation, and water should not be sprayed for health preservation. The pier should not be cracked due to concrete shrinkage.

3, control measures in the process of construction

Corresponding measures should be taken in concrete construction, such as lowering the pouring temperature of concrete, burying stones in unreinforced or less reinforced concrete, taking heat dissipation and cooling measures in the early heating stage of concrete, taking heat preservation measures in the cooling stage of concrete, reasonably setting construction joints, carrying out secondary plastering and strengthening concrete maintenance. Calculate the temperature stress of concrete and reinforce the weak parts. In addition, in order to prevent shrinkage cracks in the process of segmental construction of the main pier, the mixture ratio is repeatedly optimized in materials, the aggregate temperature is reduced as much as possible in technology, the concrete age difference between segments is shortened, and concrete maintenance is strengthened.

3, the treatment of concrete cracks

Common methods for repairing concrete cracks include: painting cement mortar on the surface, painting epoxy mortar on the surface, gouging and repairing the surface, sticking the surface, pressure grouting, slotting and filling, etc. These new materials, new tools and repair methods have been tested in the field for nearly ten years, which proves that their durability is satisfactory. At present, these methods have been widely used in many maintenance, reconstruction and reinforcement projects.

The treatment of construction joints is more complicated, so the concrete joints are strictly chiseled and the concrete joint surface is cleaned, so that the new and old concrete can be closely combined. Before pouring, spread the cement mortar with the same label 1 ~ 2 cm, then pour in layers and vibrate.

Third, the conclusion

The advantage of concrete as a building material is its strong compressive strength, but its tensile strength is always unsatisfactory. Bridge is a century-old project, which is directly related to the safety of people's lives and property. Therefore, we must fully ensure its quality and safety, strictly carry out construction, and ensure that there is a 100% sense of responsibility from design, construction to daily maintenance in the later period. Concrete cracks are common problems in bridge construction and later maintenance. When we encounter this kind of crack, we should first analyze its causes and take effective preventive measures to prevent the crack to the greatest extent and ensure the safety of people's livelihood.

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