INDIANAPOLIS (AP) — Two top Republican lawmakers are calling for an independent investigation of asphalt mixes that could be causing Indiana’s roads to break apart easily.

Rep. Ed Soliday of Valparaiso tells The Indianapolis Star that an outside investigation might be the only way to get answers about how the state bought $71 million in possibly defective asphalt.

State Sen. Carlin Yoder of Middlebury says any investigation should be independent of the Indiana Department of Transportation, which hired contractors for the paving jobs in question.

INDOT has investigated 188 roads that might have been paved with asphalt that crumbles and cracks years earlier than it should.

Gov. Mike Pence said in a statement Monday that he has asked INDOT to find the cause of the crumbling pavement.