Set Yourself Apart from the Competition with QC/QA Best Practices

How to enhance paving operations, customer satisfaction and pavement life with your best quality control practices.

One of the most critical factors influencing the quality of an asphalt pavement is its density. To improve the quality, durability and life expectancy of asphalt pavement, you can reassess your current quality control (QC) procedures and introduce a plan that includes the monitoring and measurement of the in-place density of asphalt as it’s being laid. When you improve this basic best practice, potential bonus payments can be increased while claims and/or penalties that result from compaction issues can be reduced.

How We Gained Extra Air Voids

Let’s start with some facts our industry acknowledges:

• The normal minimum target in-place density on a “dense” hot-mix asphalt pavement is 92-93% of maximum theoretical specific gravity (Gmm) or 7- 8% air voids, but the preferred in-place compacted mat density value should be between 93 and 94% or 6-7% air voids.
• A potential 35% reduction in pavement service life can be seen from final in-place density values of between 90-92% compared to an in-place density of 93-95%.
• Monitoring the in-place density of the asphalt as it is being laid is one of the most direct and effective measures of compaction.
• A 1% reduction in air voids can potentially increase pavement life by up to 10%.

Let’s look at how that final point affects life cycle costs (LLC) of your project. All things being equal, if you’ve increased the density of the pavement by 1%, you could conservatively see a 10% increase in service life. On a $1 million project, that equates to an 8.8% LLC saving of $88,000. That’s significant for an agency or department of public works (DPW) wishing to extend its pavement maintenance schedule.

One way to improve density is to double-check your numbers. This crew sets the PQI 380 non-nuclear density gauge on the mat directly behind the screed to assess how much compaction they’re starting with before the breakdown roller even touches it. Photo courtesy of TransTech Systems

You might be among the paving contractors who operate in the commercial marketplace where there’s little opportunity to check the compaction and density of your work. You might rely on past projects and performance as a guide for your choice of mix and compaction process for the upcoming job. In most cases, the responsibility falls to the paving contractor to provide a fit-for-purpose finished product that meets the client’s specification on performance and durability, and there are few specification documents in place to give guidance on best practices for commercial paving.

Consider the large number of commercial paving companies serving your local market. You could be in an area with a high level of competition where you need to differentiate your paving crews from your competitors’.

You compete based on your price, timeliness and quality. You can’t really control the weather, base conditions, which mix you get from the FOB plant, the public or the client, but you can control scheduling (such as when materials arrive), communication with the client and public, safety of the crew and public, your equipment, and most importantly your paving process. Your good reputation will lead to repeat business if you manage well the things you can control.

Good Density Equals Smoothness Bonus

One of the critical elements you can control is achieving optimum density numbers through best rolling practices and monitoring the quality. Even if you receive a bad mix to work with, you can overcome that problem because the compaction aspect is so fundamental to the success of the pavement. A bad mix with good density will outperform a good mix with poor density. So, let’s ensure you get good density.

Set your rolling pattern but be flexible enough to change it if you need to. Then test the density behind the rollers.

If you’re working on a state department of transportation (DOT) project, you will likely be required to take cores for compliance testing, but this time-consuming and invasive method of checking density is rarely performed on any commercial projects. If you have rollers with intelligent compaction (IC) systems installed, your operator may be trained in the system’s use to monitor passes and assess pavement stiffness, but typical IC systems do not give a density value of the pavement. A ground penetrating radar (GPR) system also produces a high volume of data which may be better suited to a large project due to both the amount of data and the equipment’s complexity of operation. Another method of density testing is the use of a nuclear density gauge but this comes with a long list of costly licensing and restrictive procedures that any user must adhere to.

The method I propose is using a PQI 380 non-nuclear (electrical impedance) density gauge—as sold by TransTech Systems of Latham, New York—to measure the density of the pavement. The benefits to using this type of gauge include but are not limited to:

• You receive immediate information on the level of compaction as the material is being laid, letting you make adjustments to the rolling train, if necessary.
• Anyone can use the non-nuclear density gauge; it has no restrictions on storage, use or transportation.
• It offers no risk of radiation leak if the gauge is damaged on site and offers less risk of back injury than other, heavier types of non-invasive testing equipment.
• Having on-the-spot density readings will ensure that the specified percent relative compaction can be achieved, reducing the potential for claims or penalties.

The simplest and quickest method to achieve on-site assessment of the asphalt mat’s compaction is as follows:

• Pick a location and measure the density with the non-nuclear density gauge.
• Start the rolling pattern over that location on the mat.
• Roll with one or two passes and take another reading with the device.
• Continue with another two or three passes and take another reading; note the increase in density.
• Continue the rolling and testing process until the density readings do not increase.
• If you see a slight decrease, you’re in danger of over compacting the mix. This is called the break point and is the maximum density you will achieve on this mix with this compaction equipment.

To correlate a core to this location:

• Once the peaked location on the mat cools, mark a spot to cut the core.
• One the same spot, take a set of five readings with the gauge in a clover leaf pattern.
• Take the core from the mat and determine the density by an appropriate ASTM lab test method.
• Compare the core result to the gauge measurements at that location and calculate the difference.
• This difference is called the offset. (The offset may be negative or positive.)
• Input the offset value in the “Edit Mix” menu on the gauge. The device is ow correlated to that specific mix and it should not need to be changed for any future projects involving that mix.

TransTech Systems Model 380 PQI Builds on 25 Years of Non-Nuclear Tech

By using a quality control/quality assurance device like the PQI 380 non-nuclear density gauge, you can monitor and measure the density of the asphalt pavement as you work. You can adjust your rolling pattern if necessary to achieve the optimum density for a long-lasting pavement that meets your customers’ expectations.

This supports your good reputation and puts you on the short list for future bidding opportunities. In other words, your good reputation keeping quality as a priority not only offers long-lasting pavements for our industry, but it also helps you stand out from your competition.

John Lamond is the Sales Manager at TransTech Systems, Latham, New York. He presented this topic at the National Pavement Expo (NPE) 2024 in Tampa. For more information, contact him at jlamond@transtechsys.com.