I. Basis of Preparation

1.1 Code for Quality Acceptance of Concrete Structure Engineering Construction (GB50204-2015)

1.2 Standard for Concrete Quality Control (GB50164-2011)

II. Causes of Honeycomb, Rough Surface, Exposed Reinforcement, and Holes in Concrete

① Leakage of grout from cracks during concrete pouring.

② Insufficient compaction of concrete, air bubbles not discharged, some air bubbles remaining on the surface of the formwork.

③ Failure to follow operating procedures by vibrating from low to high, resulting in stone concentration, inability to vibrate out cement slurry, causing concrete segregation.

④ Insufficient compaction or poor coordination between material placement and compaction.

III. Treatment Measures

To ensure project quality and concrete appearance, and to repair minor exposed reinforcement, honeycomb, and holes in the concrete, the following treatment plan is proposed:

① Rough Surface: Rough surfaces mainly affect the appearance of concrete. For larger areas, repair involves washing the rough surface with clean water, thoroughly wetting it for one day, and then repairing and compacting it with high-strength, non-shrinkage grouting material.

② Honeycomb: Small honeycombs in the concrete can be opened using a water impact drill or a chisel, then repaired and compacted with high-strength, non-shrinkage grouting material. For large honeycombs, first remove loose stones, wash with water, thoroughly wet, then repair with high-strength, non-shrinkage grouting material after formwork is installed. After the repaired concrete reaches the design strength, remove the excess concrete), compact, and cure, maintaining a moist condition for at least 7 days.

③ Exposed Reinforcement: Clean with a wire brush or pressure water, apply repair mortar to the surface, fill the exposed reinforcement, smooth, and ensure the protective layer thickness. For deeper exposed reinforcement, remove weak concrete and protruding aggregate particles, clean, fill and compact with high-grade repair mortar. Remove loose stones, clean with a wire brush, rinse, thoroughly wet, apply cement slurry, and repair with high-strength, non-shrinkage grouting material one grade higher than the original concrete strength (formwork protruding cavity more than 3cm, after the repaired grouting material reaches the design strength, remove the excess concrete), compact, and cure, maintaining a moist condition for at least 7 days.

④ Holes: Remove loose stones, clean with a wire brush, rinse, thoroughly wet, apply cement slurry, and then pour micro-expanding fine-stone concrete (expander admixture 8-10%) one grade higher than the original concrete strength (formwork protruding cavity more than 3cm, after the repaired concrete reaches the design strength, remove the excess concrete), compact, and cure, maintaining a moist condition for at least 7 days.

IV. Specific Repair Steps

1. Concrete should be excavated until completely solid. A combination of visual inspection and thin wire detection can be used to identify and completely remove sand holes, air holes, and cracks in the existing concrete. Then clean, rinse with clean water to remove dust and debris, and clean the exposed steel bars with a wire brush to remove cement slurry, for review and inspection by the owner and supervisor.

2. The excavated concrete surface should be roughened, and the shape of the excavated area should be as regular as possible. The bottom should be horizontal and basically flat, the sides should be as vertical and horizontal as possible, and the top can be formed into a slightly higher outer and slightly lower inner slope, with a slope angle not exceeding 20 degrees, so that the repaired concrete can better withstand vertical loads and horizontal shear forces.

3. When excavating concrete, attention must be paid to strengthening the following safety precautions:

1) Operators' eyes, ears, and noses should be protected. Protective measures such as goggles, windproof hats, and masks should be considered to prevent concrete debris from splashing and injuring people.

2) For high positions, a solid operating platform must be set up before excavation. The perimeter of the platform should be equipped with 1.2-meter-high railings, and cantilever boards are strictly prohibited.

3) Multiple people should not excavate at the same operating point or very close operating points simultaneously to prevent splashing concrete debris from injuring each other.

5. The excavated area must be inspected and accepted by the supervision unit and the construction unit before proceeding to the next stage of concrete repair.

6. When installing the formwork, considering the vibration range of the insertion vibrator, a 500mm height limit will be used. Above 500mm, the formwork will be divided into two layers. After the lower layer grouting is poured and compacted, the upper layer formwork will be installed, and then the upper layer concrete will be poured to ensure the compaction effect. The formwork support will use steel pipes for hoops and diagonal supports, reliably supporting the formwork to ensure that the formwork can withstand a certain amount of pressure, so that the concrete can be compacted and tightly connected to the original concrete as a whole.

7. During repair, the grouting must be sufficiently compacted. For larger holes, a Φ30 small vibrator can be used for careful insertion and vibration. For most shallow and small holes, a small iron rod can be carefully inserted and vibrated, supplemented by moderate tapping on the outside of the formwork with a wooden hammer. This serves as auxiliary vibration and can also judge the internal concrete compaction from the degree of dullness of the sound, ensuring that the repaired concrete is qualified in one go and avoiding rework.

8. The top of the repaired concrete should be made into an inclined hopper shape, and the top formwork of the hopper should be more than 150mm higher than the top of the hole, so that the newly built concrete at the top of the hole has a certain pressure to ensure compaction and tight topping.

9. After the concrete repair is poured, it should be fully watered and cured day and night for more than a week to ensure that the concrete is fully cured and expanded in a moist and good environment, ensuring that the newly poured concrete is connected as a whole and subjected to force together.

10. The formwork and hopper concrete should be poured and cured for more than a day before demolding and carefully removing, to ensure that the newly poured concrete is firm and the edges and corners are square.

11. For small defects, such as small holes, honeycombs, and shallow holes limited to the thickness of the concrete protective layer, high-strength, non-shrinkage repair mortar should be used for filling and layered repair. After repair, special personnel should be arranged to water the repaired area for more than three days to ensure firm bonding.

12. The above work should be carried out by a dedicated repair team consisting of experienced workers and managers with a strong sense of responsibility. They should regularly accept approval and inspection from the supervision unit and the construction unit to ensure that 100% of the repair requirements are met, and no further obvious quality defects occur, ensuring the quality of the repair.

V. Post-Repair Inspection

One week after the repair, the concrete should undergo a comprehensive visual inspection and acceptance to check for square edges, smooth surfaces, and initial determination of whether the surface is solid and whether minor defects have occurred. Written records should be kept.

Notes:

Before brushing the cement slurry, the concrete surface should be moist but not dripping. The concrete should be poured approximately 30 minutes after brushing the cement slurry. The interval should not be too long to prevent the formation of an isolation layer.

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