According to Official Guinness Records,
The most concrete blocks broken on the head with a bowling ball dropping from above is 45 and was achieved by John Ferraro (USA) on the set of Lo Show Dei Record, in Milan, Italy, on 14 April 2011.
The participant was on his knees holding stacked concrete blocks on his head. His assistant dropped a bowling ball (weighing 7.3 kg) from above directly on the blocks placed on his head causing them to break.
For a complete list of 2011 records, please visit 2011 Guinness Records in United States.