In concrete, stones usually account for about 75% of the volume of concrete, and the quality of sand and gravel directly affects the quality of concrete. When reactive sand and gravel are mixed in concrete, it can cause damage and cracks in concrete components. The following are several common concrete cracks caused by reactive sand and gravel and their treatment methods:

1️⃣Cracks caused by expansive substances: sand and gravel mixed with expansive substances such as montmorillonite, illite, kaolinite, and chlorite, which expand in volume after absorbing water and shrink and harden after losing water, leading to concrete cracks.

2️⃣Cracks caused by excessive mud content: Excessive mud content in sand and gravel leads to a decrease in concrete strength and the formation of mud shrinkage cracks on the surface.

3️⃣Cracks caused by quicklime blocks: When quicklime blocks are mixed in sand and gravel, the volume of the quicklime blocks increases by about 1.98 times after concrete pouring, leading to concrete cracking.

4️⃣Cracks caused by sulfate reaction: Substances such as sulfides or sulfates in sand and gravel react with calcium ions to produce calcium sulfate or calcium sulfoaluminate, while the volume expands, leading to concrete cracks.

The following measures can be taken to address the concrete cracks caused by reactive sand and gravel:

1️⃣Rework and redo: If the strength grade of the concrete is lower than the design requirements and the reactive sand and gravel have severe cracking, and there is a trend of further development, rework and redo must be carried out.

2️⃣Surface treatment: If the fine cracks on the concrete surface are only caused by excessive mud content and the concrete strength grade meets the design requirements, and do not affect the aesthetics or consider aesthetics, no treatment is required. If considering aesthetics, a mortar with a mix ratio of "HQG-4: P.O42.5 ordinary silicon cement=100kg: 10kg" can be used to apply a wet to wet wetting spray/brush on the entire surface 2-3 times to cover cracks.

3️⃣Partial repair: If the concrete strength grade meets the design requirements, a comprehensive inspection and evaluation of the scope, quantity, and degree of damage of cracks should be carried out. Sand and gravel samples should be taken from the severely cracked areas, and tested according to JGJ53-1992 "Quality Standards and Testing Methods for Crushed Stone or Pebble for Ordinary Concrete".

-If the test results are qualified, first excavate the cracked area, clean it with a brush, and then use a quick repair mortar with a mix ratio of "P.O42.5 ordinary silicon cement: fine sand: HQS-Super200 Huaqiansu: water=400kg: 600kg: 15-25kg: 155-165kg" for filling and repair.

-If the test results are not qualified, they must be reworked and redone