Hi,
Yes the construction workers are very much eligible for ESI.
When employed for a construction company mostly the employer will directly cover the employees with PF/ESI benefits.
However Laborers ( like who perform the role of shuttering/mason) who work for Contractors will be moving from one construction project to other Project wherein ESI benefits are denied for them as the contractor pays salary on daily /weekly basis. However it is their responsibility to cover workers who work for them under ESI. However when the contractors fail to cover, in such cases it is the responsibility of the Principal employer ( construction companies) who is hiring the services of the contractor to cover workers under ESI.