What are the differences in the effects of polypropylene fibers and expanding agents?

Both adding expanding agents and adding fibers to concrete can achieve the purpose of crack resistance and seepage prevention. However, their mechanisms of action and effects differ somewhat.

1. Mechanism: Expanding agents generate ettringite or calcium hydroxide crystals through a chemical reaction, causing the concrete to expand to compensate for its shrinkage, thereby reducing or preventing the formation of concrete cracks. Fibers reduce the formation of concrete cracks through physical action.

2. Effect: Expanding agents only achieve good crack resistance and seepage prevention effects in humid environments. In dry environments, they may be ineffective or even have the opposite effect; while fibers achieve good crack resistance and seepage prevention effects in both humid and dry environments.

3. Construction Conditions: Expanding agents have very demanding curing conditions, requiring water curing for more than 14 days, while fibers have no special curing requirements.