Which two factors must be avoided to protect the concrete sample?

To ensure the integrity of a concrete sample, it is essential to avoid both contamination and rapid evaporation. Contamination can introduce foreign substances into the concrete mix, affecting its chemical properties and potentially leading to compromised strength and durability. For instance, the presence of oils, chemicals, or dirt can interfere with the curing process and result in poor bonding and performance characteristics.

Rapid evaporation is equally critical to avoid because it can lead to the formation of cracks and surface defects as the water in the mix evaporates too quickly. This can hinder the hydration process, which is crucial for the concrete's strength development. Proper curing conditions are essential for facilitating the chemical reactions necessary for concrete to achieve its desired structural integrity.

Together, these factors highlight the importance of protecting concrete samples during the initial stages of their setting and curing process to ensure they meet specifications and perform as intended in their final application.