Tsql to get one of the fields in json format

Transact-SQL
1

Hello,
How is it possible to have field 3 below in json format and the rest of the fields as normal
for example this is the sql I use now to get the data but I would like to have the field4 in jason:
select
field1, field2, field3,
field4 = add1, add2, city
from tblMain

Thank you

2

please help us help you. provide at least DML

declare @noahs_ark table(field1 int,

etc. you are asking for help, so would help if you provide the structure of the table and some sample data/