The Complete Package

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TxDOT is still in the process of moving the new special specification for Item 341 Dense-Graded Hot-Mix Asphalt (QC/QA) through the various steps that will lead to its ultimate approval and use by TxDOT and industry.  This may appear to be a slow and deliberate process, but it is a process which helps to insure that TxDOT and industry can ultimately accept and support this special specification.  This is very important not only from a state perspective, since cities and counties look to TxDOT for guidance, but also from a national perspective, since other states are always looking to see what Texas is doing in the highway heavy industry.  In recent discussions with Dale Rand, Director of TxDOT’s Flexible Pavement Branch, he has told TxAPA that barring unforeseen problems with the approval of this new special specification it will probably be ready for statewide use starting with the April or May 2011 lettings.  He also believes that we could see the new draft special specifications for Items 292, 340, 342, 344 and 346 as early as January 2011.  This is exciting news since in my opinion using the new special specification for Item 341 as the boiler plate this group of new special specifications will represent the complete package for TxDOT and industry from an economic, engineering performance and environmental standpoint.

Once all of the various special specifications are approved and in use the benefits contained in Special Provision 341-024 will be available in all of these new special specifications.  The opportunity to use binder substitution, reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), and warm mix asphalt (WMA) in these new special specifications has been a request from industry for a long time.  (Note that the one exception to the ability to take full use of these benefits will be the new special specification for Item 342 Permeable Friction Course (PFC) which does not currently allow the use of RAP or RAS and most likely will not allow the use of these items in the foreseeable future.  WMA will be an available tool for Item 342.)  Other benefits such as the encouragement of the use of the Pave IR-Bar will also be contained in all of these new special specifications once they are complete.

The ability for a contractor to be able to use RAP and RAS in their asphalt pavement mix designs is an obvious economic benefit.  The contractor will not need to use as much virgin material, including virgin binder, in their asphalt pavement mixes.   It is also an economic benefit to use WMA which might not be as apparent.  First the possibility of using less fuel at the hot mix plant to produce the mix is another area in which the contractor can save some money that they can then turn around and pass on to owners such as TxDOT.  WMA has also proven to be a good compaction aid for the contractor which can allow the contractor to achieve required compaction through less effort.  This is not only a drop in physical effort but it is also a drop in man-hours, equipment time, fuel usage, etc. which equates to a cost savings.   Lastly the use of WMA also allows the contractor to extend the paving season which can be an economic benefit to the contractor and the owner.  This also allows projects to be finished more quickly allowing the traveling public the use of these roadways sooner.

The use of WMA has an engineering performance component which is a big benefit to owners such as TxDOT.  The contractor as stated above can get the benefit of WMA being a compaction aid.  The benefit to the owner of this compaction aid is the mix that is placed is more likely to receive the proper densification; therefore, extending the life of the pavement.  The life of the pavement is also extended through the use of lower temperatures to produce the mix.  Asphalt mixes produced at lower temperatures do not initially oxidize the mix as much as mix produced at higher temperatures.  Various studies have also shown that there is less asphalt absorbed by the aggregate at lower temperatures.  This drop in aggregate asphalt absorption leaves more asphalt available in the mix itself which will lead to better overall performance of the mix.  These engineering benefits are extremely attractive to owners such as TxDOT.

The environmental benefit through the use of RAP, RAS, and WMA in asphalt paving mixes is one of those obvious benefits in Special Provision 341-024 that once included in these new special specifications will make the benefits more wide spread across the state.  The use of RAP and RAS as discussed earlier lessens the impact on virgin materials through the use of reclaimed products.  The use of WMA can reduce fuel consumption at the asphalt plant and also at the job site during placement.  This energy savings can be a big environmental benefit and it lessens the need for fuel.  The use of RAP, RAS and WMA individually or in a variety of combinations can reduce carbon dioxide emissions.  It has been shown that if a paving strategy were to use WMA with 15% RAP and 5% RAS carbon emissions could be reduced as much as 23.6% over hot mix asphalt produced without any of these tools.

In conclusion TxDOT and industry are ready to enjoy the benefits contained in Special Provision 341-024 in Items 292, 340, 342, 344 and 346.  These benefits when used together represent the complete package in the asphalt paving industry from an economic, engineering performance and environmental standpoint. The good news is we are getting closer to the day when these benefits can be realized and that day should be within the first half of 2011.