Let's say somebody asks me how was your day, is it natural to answer the question with it was normal? What I am trying to say is that the day was as usual. If it is not natural, how would English native seakers respon?
In the U.S at least, I doubt "usual" alone would be common. If the responder's intent to the question of "how was your day" is to indicate that nothing noteworthy happened, the responder might say
It was [routine/ordinary].
It was a [routine/ordinary/normal/usual] day.
I cannot firmly articulate a reason why "normal" or "usual" as an isolated adjective does not sound quite right to me. Perhaps because "How was your day" is phatic language that solicits more than bare information. Conciseness is not a virtue in that kind of conversation.
What is far more likely is a more elaborate answer such as
It was sort of normal, not particularly bad, not particularly good. How was your day?
You are making conversation, establishing a social connection. In this sense, use of "routine" or "ordinary" as isolated adjectives conveys a stronger emotional sense of boredom than do "normal" or "usual" and invites a change of topic.
Phatic language cannot be discussed in isolation from social and cultural expectations. Obviously, "routine," "ordinary," "normal," and "usual" all respresent virtually the same meaning in this context, but the curt response "it was usual" ignores the invitation to start a friendly social interaction.