C:\test\test-db>gem install bcrypt
Successfully installed bcrypt-3.1.10-x86-mingw32
Parsing documentation for bcrypt-3.1.10-x86-mingw32
Done installing documentation for bcrypt after 0 seconds
1 gem installed

C:\test\test-db>irb
irb(main):001:0> require 'bcrypt'
LoadError: cannot load such file -- bcrypt_ext
        from C:/Ruby/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        from C:/Ruby/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        from C:/Ruby/lib/ruby/gems/2.2.0/gems/bcrypt-3.1.10-x86-mingw32/lib/bcrypt.rb:16:in `rescue in <top (required)>'
        from C:/Ruby/lib/ruby/gems/2.2.0/gems/bcrypt-3.1.10-x86-mingw32/lib/bcrypt.rb:12:in `<top (required)>'
        from C:/Ruby/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:128:in `require'
        from C:/Ruby/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:128:in `rescue in require'
        from C:/Ruby/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:39:in `require'
        from (irb):1
        from C:/Ruby/bin/irb:11:in `<main>'