Analysis of Structural Cracks in Concrete Tank Bodies During Pig Farm Construction (2)
A Brief Discussion of Structural Cracks in Concrete Tank Bodies During Pig Farm Construction (2)
a. Select cement with low heat of hydration to avoid cracks caused by excessive heat of hydration;
b. Water consumption: generally speaking, the greater the unit water consumption of concrete, the greater the drying shrinkage rate of the concrete. When selecting the concrete mix proportion, the unit water consumption of the concrete must be strictly controlled, ensuring both low water content and consideration of factors such as slump, segregation, bleeding, vibration and construction convenience.
c. For concrete with lower drying shrinkage and higher elastic modulus, the greater the porosity of its coarse aggregate, the greater the drying shrinkage rate. Stones with large particle size and good grading can be given priority, thereby reducing the specific surface area of the aggregate in the concrete and reducing bleeding and drying shrinkage of the concrete.
d. In concrete mix proportion design, selecting a higher sand ratio means the content of coarse aggregate stones is relatively reduced, lowering the crack resistance of the concrete; a reasonable sand proportion reduces the possibility of cracks. At the same time, use sand with low mud content for mixing to reduce the possibility of cracks.
e. Admixtures: the pouring area and length of the slab wall and base slab are relatively large; reasonably select additives with low shrinkage to reduce the possibility of cracks appearing.
⟧ In pig farm construction, the construction party often uses commercial concrete supply, and control of the concrete mix proportion is often not professional enough, so the mixing station must participate in the pre-pouring construction briefing, so that the mixing station fully understands the problems that are likely to occur at the construction location, enabling it to adopt countermeasures in the mix proportion.
3. Construction aspects:
a. Strengthen vibration: insert the vibrating rod every 50cm, insert quickly and withdraw slowly; after a large number of bubbles emerge on the surface, slowly pull out the vibrating rod to ensure the component is solid inside and smooth outside
b. Increase the number of troweling passes on the surface concrete to reduce the appearance of micro-cracks and reduce stress concentration of micro-cracks forming cracks visible to the naked eye
4. Curing aspects:
a. The base slab concrete should be cured by watering and then covering; appropriately adjust the curing plan and curing duration according to air temperature.
b. The slab wall is cured by late formwork removal; remove the formwork after the strength reaches 75% of the design strength. After formwork removal, cure by watering and covering or by applying curing liquid; in non-winter seasons, cure by watering and applying curing liquid.
4) Treatment methods for cracks that have already appeared
After various measures are taken, the appearance of cracks is avoided as much as possible, but some tank bodies may still develop cracks because one or more measures are not in place. Adopting certain post-treatment measures for these cracks causes little harm to use and durability. Because the overall bearing capacity is affected very little by the cracks, the main consideration is to meet functional waterproofing requirements: waterproofing treatment is used on the water-facing side, and micro-expansive mortar treatment is used on the non-water-facing side. There are three commonly used treatment methods: brushing with JS waterproof coating, brushing with polyurethane waterproof coating, and oil-soluble polyurethane crack grouting.
Surface cracks are treated with JS and polyurethane coatings, deep cracks are treated with oil-based polyurethane grouting, and a combination of deep and surface treatment can also be used. Brushing with polyurethane has good waterproofing effect but relatively large color differences; JS waterproofing has relatively good color difference control, crack treatment, waterproofing, ductility and corrosion resistance. The following is a brief introduction to JS waterproofing treatment construction:
1. JS waterproof coating is a two-component waterproof coating compounded from polymer emulsion and inorganic powder (special cement, additives, etc.). Its main features are that it has both the high elasticity of organic materials and the good durability of inorganic materials, and colored coatings can be prepared according to engineering needs. It can be directly applied on a variety of substrates, wet or dry (such as asphalt, rubber, SBS, APP, polyurethane, lightweight board, concrete, etc.). Construction on vertical, sloped and top surfaces is uniform and does not run. By adding some fine sand to the liquid and powder, it can be used as bonding and sealing mortar.
2. Construction process flow: base layer and node treatment -> JS polymer cement waterproof coating flexible waterproof layer -> protective bonding layer -> surface layer
3. Construction preparation and steps
a. Tool preparation: base layer cleaning tools such as hammer, chisel, wire brush, water spray gun, broom, rag, etc. Material taking and mixing tools such as,
b. platform scale, water bucket, material weighing bucket, mixing bucket, electric mixer, scissors, etc. Coating application tools such as roller brush, scraper, brush, etc.
c. Material preparation: waterproof materials must have a quality guarantee certificate and conformity certificate. Materials entering the site should be sampled and inspected according to the specified sampling method, and can only enter the site after passing inspection. The packaging, storage and keeping of waterproof materials used shall comply with the specified requirements.
d. Construction site environment: the air temperature should be above zero, ventilation conditions should be good, there should be no obvious standing water on the base layer, and lighting should be sufficient.
4. Main construction methods
a. The base layer must be flat and solid; residual and protruding foreign matter on the surface must be thoroughly removed, then rinsed clean with clear water. Then use sealing material for sealing treatment, fill, tamp and trowel smooth.
b. Preparation of JS polymer cement waterproof coating: according to the specified proportion, take materials with material-taking tools, then fully and evenly stir with a mixer until there are no solid materials in the mixture. During construction, prepare strictly according to the mix proportion, separately preparing the primer layer, middle coating layer and surface layer.
c. Additional layers should be made at irregular parts: internal and external corners, junctions between wall surface and wall surface, junctions between wall surface and ground surface, etc.
d. Water storage test: after the waterproof layer construction is completed and has dried hard, carry out the water storage test.
5. Finished product protection:
a. Waterproofing construction personnel should wear soft-soled shoes; during construction, stepping on the undried waterproof layer is strictly prohibited.
b. Designate dedicated construction operators to strictly protect and watch over the completed waterproof layer.
c. After the waterproof layer construction is completed, the surface layer should be made promptly.