ASTM C78 is a standard test method developed by the American Society for Testing and Materials to evaluate the flexural strength of concrete. This test measures how much load a concrete beam can withstand before it fails, providing essential data for assessing the material's performance in construction applications. The procedure involves creating a concrete beam sample, which is then subjected to a bending force until it breaks. The results help engineers and builders determine the suitability of concrete mixtures for various structural uses, ensuring safety and durability in construction projects.