Blockchain is a concrete, countable noun.

Concrete?

A noun can be concrete or abstract. Concrete nouns represent things that can be interacted with individually.

• You can use software built on a blockchain
• You can't use software built on blockchain
• You can read about blockchains in the news
• You can't read about blockchain in the news
• You can take a course about blockchain technology
• You can't take a course about blockchain

A comparable concrete noun is “cell phone”. Replace “blockchain” with “cell phone” in a sentence. If it sounds wrong you know you've messed up.:

• IBM is investing in blockchain technology
• IBM is investing in cell phone technology

• Wrong: IBM is investing in blockchain
• Wrong: IBM is investing in cell phone

• Blockchains are getting lots of news coverage now
• Cell phones are getting lots of news coverage now

• Wrong: Blockchain is getting lots of news coverage now
• Wrong: Cell phone is getting lots of news coverage new

Countable?

A noun can be countable or uncountable.