What is air-entrained Portland cement concrete quite weak in?

Air-entrained Portland cement concrete is designed primarily to improve the material's resistance to freezing-and-thawing cycles by creating microscopic air bubbles that can alleviate tensile stresses when water in the concrete expands during freezing. While this type of concrete performs well under compressive loads, it is inherently weaker in tension.

Concrete, in general, is strong in compression but significantly weaker in tension due to its brittle nature. The addition of air-entraining agents does not enhance the tensile strength of the concrete; instead, it can reduce the materials' overall density, which can further diminish its ability to withstand tensile forces. This means that while air-entrained concrete can be great for enhancing durability and reducing the risk of cracking from freeze-thaw cycles, it is not suitable for applications where tensile strength is critical.

Understanding the specific strengths and weaknesses of various concrete types helps in making informed choices for construction projects, ensuring the right materials are selected for the intended load-bearing requirements.