The Ferrari driver went out early on in the session to test the new halo head protection system before returning to the track without it.
Raikkonen topped the times with the ultrasoft tyres but the Williams of Felipe Massa was within half a second of the Finn on soft tyres.
A mammoth day of mileage saw almost all the teams cover well north of 100 laps. Haas, which only managed a single installation lap yesterday reached 77, but Romain Grosjean caused all three of the day’s red flags due to stoppages.
Once again Mercedes split the running between its two drivers but Verstappen did one more lap than the pair of them in his STR11.
One more day of testing remains before the season opening Australian Grand Prix in two weeks time.
The Finn said that there was little difference to visibility whilst out on track but not every driver was so neutral.
Nico Hulkenberg critcised the halo saying that danger would always be part of the sport.
However, Nico Rosberg was generally pleased saying that the design would no doubt change before it is finalised.
The designs were tested by the Global Institute for Motor Sport Safety by firing an F1 wheel from a cannon towards the structures at speeds of up to 225kph (139mph).
The Halo successfully guarded the helmet area from the wheel and performed well in other tests.
The halo tested by Ferrari adds around five kilograms to an F1 car.
On day one of the second test, Mercedes showed their hand for the first time so far in 2016 as Nico Rosberg set blistering pace on the soft tyres.
What was all the more impressive was that the German finished more than two tenths ahead of Valtteri Bottas who was on the ultrasoft tyres, two compounds faster than Rosberg’s softs.
Ferrari had a tough day with problems hampering Kimi Raikkonen’s efforts to get used to the new SF16-H.
Fernando Alonso managed a solid day for McLaren after several technical problems hindered them during the first test.
Felipe Nasr had a very productive first day in the new Sauber C35, managing over 100 laps. But Haas suffered a trying day curtailed by a fuel system problem.
Today things didn’t get any better for F1’s newest team with Haas mustering up just one lap.
At the other end of the grid, Bottas took Williams to the top of the time sheets.
It was a high mileage day for most of the teams with Toro Rosso leading the way followed by Mercedes.
And Ferrari were left feeling more confident as Sebastian Vettel completed more than 150 laps following yesterday’s problems.
Marcus Ericsson caused the only red flag of the session after spinning off during his first day in the team’s new C35.