Final answer:
Not all exterior concrete must be air-entrained, but it is highly recommended for surfaces exposed to freeze-thaw cycles to prevent damage.
Step-by-step explanation:
The question whether all exterior concrete has to be air-entrained brings us to the study of construction techniques and concrete technology in engineering. Air-entrainment is the process of incorporating small air bubbles into concrete, which provides several benefits especially for concrete exposed to freezing and thawing cycles. Air-entrained concrete is often used for exterior surfaces to improve durability and resist against freeze-thaw damage.
Air-entrainment adds durability to concrete by creating small air pockets that help manage the expansion of water when it freezes. Innovations like lightweight, fast-drying, and self-healing cement enhance construction techniques.
When concrete is used in outdoor applications where temperatures may drop below freezing, the inclusion of these air pockets is crucial because they allow space for water to expand when it freezes. This process helps to prevent cracking and spalling that is common in non-air-entrained concrete. While it's not mandatory for all exterior concrete to be air-entrained, it is highly recommended for areas subjected to freeze-thaw cycles.
Other innovations in concrete technology, as mentioned, include lightweight concrete, which can be used to reduce structural load and enhance thermal protection. Alongside, fast-drying and self-healing cement are becoming popular in contemporary architectural designs for their unique properties that contribute to the longevity and sustainability of structures.