Aggregate base for roadway, contractor states it needs to "cure"?
Aggregate base for roadway, contractor states it needs to "cure"?
(OP)
I've recently switched jobs from a private Geotechnical Consultanting firm to a State DOT. Part of my responsibilities with the State DOT is providing pavement designs and reviewing “Value Engineering" proposal when a contractor feels they can save the State money by building the roadway differently than designed.
In one review, a contractor wants to eliminate the aggregate base below the pavement and increase the thickness of the asphalt pavement. In other words they want to construct a thicker asphalt pavement placed directly on a fat clay (LL 60 PI 35) subgrade.
Their reasoning for this is because of traffic control issues and they are stating they do not have the time to wait for the aggregate base to "cure" before being able to place the first lift of hot mix asphalt(HMA).
I believe they are misguided in the use of the term "cure". In our State the aggregate base is crushed limestone with a top size of 3/4" and less than 7% passing the #200. The PI of the fines is usually around 3.
My suspicion is that they are use to placing this material on the wet side of optimum, to help with achieving density, but then they are seeing it pump and rut. However, after a couple days it turns hard. I believe this may be what they are referring to by saying the material needs time to cure. I do not agree with this. First there is no cementitious material in the aggregate base other than the limestone dust from crushing the rock and second, I believe what they are seeing is the excess pore water pressures dissipating and free water evaporating, which is resulting in a hardening of the base.
I think this waiting period could be avoided if they placed the material near the optimum moisture content or no more than 2% above optimum. At these moisture levels I would not expect pumping from a buildup of excess pore water pressure and would be fine with placing the first lift of HMA on top of the base once the proper density for the base had been achieved.
Has anyone else heard of this excuse to wait for a base to cure before placing the first lift of HMA or any thoughts on the subject that an aggregate base needs to cure?
In one review, a contractor wants to eliminate the aggregate base below the pavement and increase the thickness of the asphalt pavement. In other words they want to construct a thicker asphalt pavement placed directly on a fat clay (LL 60 PI 35) subgrade.
Their reasoning for this is because of traffic control issues and they are stating they do not have the time to wait for the aggregate base to "cure" before being able to place the first lift of hot mix asphalt(HMA).
I believe they are misguided in the use of the term "cure". In our State the aggregate base is crushed limestone with a top size of 3/4" and less than 7% passing the #200. The PI of the fines is usually around 3.
My suspicion is that they are use to placing this material on the wet side of optimum, to help with achieving density, but then they are seeing it pump and rut. However, after a couple days it turns hard. I believe this may be what they are referring to by saying the material needs time to cure. I do not agree with this. First there is no cementitious material in the aggregate base other than the limestone dust from crushing the rock and second, I believe what they are seeing is the excess pore water pressures dissipating and free water evaporating, which is resulting in a hardening of the base.
I think this waiting period could be avoided if they placed the material near the optimum moisture content or no more than 2% above optimum. At these moisture levels I would not expect pumping from a buildup of excess pore water pressure and would be fine with placing the first lift of HMA on top of the base once the proper density for the base had been achieved.
Has anyone else heard of this excuse to wait for a base to cure before placing the first lift of HMA or any thoughts on the subject that an aggregate base needs to cure?





RE: Aggregate base for roadway, contractor states it needs to "cure"?
Irrespective of the contractor's claim on "curing" or time, you are the owner of the road, you are spending the peoples' money and you own the long-term maintenance. The contractor does not. Buy what you want.
f-d
¡papá gordo ain’t no madre flaca!
RE: Aggregate base for roadway, contractor states it needs to "cure"?
RE: Aggregate base for roadway, contractor states it needs to "cure"?
With respect to curing, I have seen limestone aggregate base stiffen after a few days. While I haven't explored the effect in detail, it appears to be due to drying (generally placed wet of optimum) and some very weak cementation due to the crushed lime.
Mike Lambert
RE: Aggregate base for roadway, contractor states it needs to "cure"?
f-d
¡papá gordo ain’t no madre flaca!
RE: Aggregate base for roadway, contractor states it needs to "cure"?
RE: Aggregate base for roadway, contractor states it needs to "cure"?
RE: Aggregate base for roadway, contractor states it needs to "cure"?
In regard to the contractors claim that the aggregate base requires time to cure before the first lift of HMS can be placed was also not accepted as a valid claim. Our State has a density requirement for the aggregate base but there is not a moisture requirement. Contractors can place the material at whatever moisture level they feel will be the most effective in helping them achieve density. Some contractors are placing the material too wet of optimum and the material starts to pump during rolling operations. Our inspectors will test the material with a nuclear guage and a lot of the times they will achieve the target density but the material will still pump under wheel loads. Our response to the contractor was to control their moisture levels by coordinating with the quarry and they will not have to wait for the material to become stable.
RE: Aggregate base for roadway, contractor states it needs to "cure"?
RE: Aggregate base for roadway, contractor states it needs to "cure"?
Do you guys look at treating the subgrade with lime or cement as an option?
RE: Aggregate base for roadway, contractor states it needs to "cure"?
RE: Aggregate base for roadway, contractor states it needs to "cure"?