ROCK sources on Vanua Levu have a high plasticity index (PI) making them vulnerable to moisture, says Fiji Road Authority CEO Neil Cook.
He said this was also the case, although to a lesser extent, for rocks on Viti Levu.
Mr Cook said with such characteristics, such rocks would not make pavements last.
"FRA has been tasked with spending a significant amount of taxpayers money and we need to ensure when the money is spent on something that is going to last," he said.
"If we take the Buca Bay project, between ourselves and the contractors and the consultant, we have slowed progress on that so that we can solve this problem that is just inherent because we need to build something that will last.
"We can solve the high PI issue by modifying the rock and adding cement to the rocks, which may help the situation, but depending on why the PI is high.
"Maybe because of dirt and other impurities in the rock, we might also need to wash the rock and that may solve the defect."
Mr Cook said on Vanua Levu, the high PI was within the rock structure itself so they could not get rid of the situation but to deal with it.
"It has affected road projects here last year and even this year to some extent, but we are getting through to the heart of the problem so that once we know what we can do, we just roll right on.
"We expect road structure to last for a maximum of 20 to 25 years provided that maintenance is done.
"There will be failure here and there within that life span and we might have to do some maintenance during the first few years depending on the amount of traffic accessing the road."
Responding to concerns from members of the public about previous roads that had no problems with local material, Mr Cook said those projects were an example of how companies used local material but relaxed specifications slightly.