Bianchi was the team's reserve driver in 2012 and is in contention for a race seat this year.
"My first experience of the new car was very positive and it’s clearly an improvement over last year’s car," he said.
"I spent most of the time on the medium tyres, but I got a chance to run the softs as well and they offered a lot of grip so I enjoyed that. It was also nice to do some long runs, so I’ve felt the car on heavy fuel, which is good for my experience. I’m pleased the team asked me to help out this week and I’m happy with how things went today."
Bianchi finished just 0.027s shy of Raikkonen, before handing over to lead driver Paul di Resta for the final couple of hours.
"Overall it’s been a positive test," said di Resta.
"We’ve worked our way through the programme set by the factory, done some aero mapping, explored the set-up and gathered lots of data. We covered a lot of laps and I’m feeling comfortable with the car. The main challenge at the moment is learning about the tyres, but we have lots of information to help us move in the right direction before the Barcelona test."