What are some obvious signs of insufficient concrete strength? Here are some obvious signs of insufficient concrete strength:

　　1. Cracks: Insufficient concrete strength may cause cracks in the structure. These cracks may appear on the surface of the concrete or penetrate the entire structure. The presence of cracks may indicate that the tensile strength of the concrete is insufficient, or that the compressive strength of the concrete is not sufficient to withstand the loads applied to it.

　　2. Spalling and wear: Insufficient concrete strength may cause spalling and wear on the surface of the concrete, especially in areas subject to high friction or abrasive forces. This may indicate that the concrete is not sufficiently resistant to wear or impact.

　　3. Deformation: Insufficient concrete strength may cause deformation of the structure, such as bending, twisting, or settling. This may indicate that the flexural strength or compressive strength of the concrete is not sufficient to withstand the loads applied to it.

　　4. Water seepage: Insufficient concrete strength may cause the compactness of the concrete to decrease, resulting in water seepage. This may indicate that the concrete is not sufficiently impermeable.

　　5. Powdering or sanding on the concrete surface: Insufficient concrete strength may cause powdering or sanding on the concrete surface, which may indicate that the concrete has insufficient weathering resistance or durability.

　　6. Reduced bearing capacity of concrete structure: Insufficient concrete strength may cause the bearing capacity of concrete structure to be reduced, unable to bear the designed load, thus affecting the safety and stability of the structure.

　　7. Reduced durability of concrete structure: Insufficient concrete strength may cause the durability of concrete structure to be reduced, unable to resist environmental erosion, such as freeze-thaw cycles, chemical corrosion, etc., thus affecting the service life of the structure.

　　When the above signs are found, concrete strength testing should be carried out immediately to confirm whether the concrete strength meets the design requirements. If the concrete strength is indeed insufficient, measures should be taken immediately to repair or reinforce it to prevent further damage. Before repair or reinforcement, necessary evaluation and analysis should be carried out to determine the necessity and feasibility of repair or reinforcement. Repair or reinforcement should be carried out by experienced professionals in a safe environment to ensure the repair or reinforcement effect and construction safety.