11. The key rule
of curing is that it must be covered and kept wet within 12 hours after pouring. The curing time of ordinary concrete is ≥ 7 days, and that of mineral admixture or high-grade concrete is ≥ 14 days. If the curing is not in place, cracks will easily occur.
12. Strength development rule
Cement hydration is the source of concrete strength. The strength reaches 50% -70% of the design value in 3 days, 70% -90% in 7 days and 100% in 28 days. The higher the ambient temperature, the faster the hydration (heat preservation is required when the temperature is lower than 5 ℃).
13. Crack provention and control principle
: Shrinkage cracks are mostly caused by poor curing, and temperature cracks are mostly caused by large temperature difference between inside and outside of mass concrete, which can be avoided by optimizing mix proportion (adding admixtures), pouring in layers, and setting up post-pouring zones.
14. Test block test method
: 1 group of standard curing test blocks shall be made for each mix proportion, each work shift or every 100m ³. The test blocks shall be vibrated and compacted, and the curing standard shall be adopted, so that the test data can be representative.
15. The core principle
of durability is that the impermeability depends on low water-binder ratio + enough cementitious materials, the frost resistance depends on air entraining agent (air content 3% -5%), and the corrosion resistance depends on special cement or rust inhibitor.
16. The mixing time of uniform
mixing shall be calculated from the completion of all materials. The mixing time of ordinary concrete shall be ≥ 90 seconds, and the mixing time of admixtures or admixtures shall be ≥ 120 seconds. Uneven mixing will easily lead to large dispersion of concrete strength.
17. Pouring height
: the free falling height of concrete shall be ≤ 2 m. If the height is exceeded, the tumbling barrel or chute shall be used for auxiliary pouring, otherwise it is easy to be separated. The layered pouring thickness of vertical components shall be ≤ 500 mm.
18. Moderate
vibration: vibrate until the concrete surface bleeds and no bubbles escape (20-30 seconds/point). Excessive vibration is easy to segregate, and missing vibration is easy to empty, affecting the strength and compactness.
19. Raw Material Fluctuation Response Rule
When the cement strength fluctuation exceeds ± 3MPa, the water-binder ratio shall be adjusted. When the water content of sand changes by 1%, the water consumption shall be adjusted by ± 8 kg/m ³. When the aggregate gradation changes, the sand ratio shall be adjusted synchronously.
20. Practical priority rule
book knowledge should be combined with the actual site, focusing on the quality of raw materials, mix execution, construction details and maintenance, which is the core of controlling the quality of concrete.
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