A keyword is a word that, in combination with other keywords, can give a high-level description of the contents of a text document, allowing you to identify its subject matter.
The recommended number is 5-7 keywords.
Please use common terms or indexed keywords. Indexed keywords are those words that are most popular and used on this topic. Using the indexed keywords increases the probability of finding an article in databases and libraries.
Reinforced concrete is a generally accepted term, an indexed keyword.
Concrete with reinforcement - the same meaning as the above term, but not an indexed word, is used in special cases.