In the words of the father of modern management, Dr. Peter Drucker says, “What gets measured gets managed”. In the same way we’ll monitor the weight scale to track our progress towards shedding and keeping off those extra holiday pounds, we manage the quality of the pavements we produce by setting targets and then monitoring and measuring our production to ensure we produce a top quality product. In this edition of the RoadReady newsletter, we will examine what Quality Control means, how to manage QC in your business, a little bit about pay factors, and some practical tips.
Who puts the “Quality” in “Quality Control”?
The purpose of a quality control program is to control the level of quality being produced in the end product by setting a target value and minimizing variability. A target value is much as it sounds, it is the value that conforms to (or exceeds) standards and can be achievable. Variability, which describes how much a process varies from the target on any given measurement is also important to a quality control program. If a paving process is highly variable, the pavement may still meet the standard overall, but some sections would be unacceptable.
For example, when constructing an asphalt pavement, a contract may specify a minimum 92% theoretical maximum density, but the contractor may choose to set a higher target value of 93% for production, which is achievable, but also exceeds the standard. In addition, to minimize variability, and achieve that target, a roller pattern may be prescribed so that the contractor is confident in hitting that target since the practices remain consistent.
In making these determinations, quality control actions and considerations should be based on objective evidence and not subjective opinion. Consider the difference between changing a roller pattern based on an inspector’s opinion that compaction is inadequate and that of changing the roller pattern based on consistently low-density test results. This means that while experience and expertise are valuable, they should not be used to improve the process without additional data.
A job mix formula, or JMF is used somewhat like a recipe, in that it sets the targets for the asphalt pavement and production of the resulting mixture of aggregate and asphalt binder. In the cooking world, Martha Stewart has her own “job mix formula” or recipe to follow when mass producing cupcakes…and as you can imagine, not enough sugar in any given batch and the finished product isn’t as sweet. When paving, the JMF prescribes critical information about the mix design and expected qualities of that pavement. How do we measure if we’re hitting the target? By testing, testing, testing. Let’s look at a few common tests that are used to establish quality in the field.
Field samples are taken relatively randomly to ensure good data – data doesn’t stand up to examination if it’s always done from the center of the lane, or every 300 feet. It would be difficult to do true random sampling, as different lots of asphalt would be skipped entirely, while others would be sampled multiple times. Usually, samples are taken randomly, but within predetermined, regular intervals.Click the link below to visit our blog and learn more about how measurements can be used to incentivize top quality construction and some common pavement characteristics that can be measured in the field.
Practical tips to reduce variability and achieve goals consistently
In this section, we’ll share a couple of simple ideas that can help you reduce process variability so you can hit the bulls-eye more often: pre-project planning and laying test strips. These commonsense tips can be reduced to the 6 P’s of pavement performance, “proper prior planning prevents poor performance.” However, it’s worth exploring them in a little greater detail.
Planning ahead of time helps guarantee steady production rates, by examining past projects, looking at project requirements, and keeping an eye on matching production rates to production speeds. This reduces variability and offers predictable production rates and schedule.
Test strips may be laid at the beginning of the project to verify mix design and laydown procedures, and be redone if significant changes are made during the course of the project. If the mix is well known to the contractor, a test strip is not necessary. Test strips can also be helpful for compaction purposes. This kind of testing can help improve equipment utilization by helping the contractor calculate paver and compaction speeds, which lessens the amount of equipment downtime.
A test strip can help establish process control before placing a “for pay” mix, and may be done on the shoulder or other non-critical paving element on the job-site. It helps reduce variation and eliminate start-up issues, helps calibrate the production rate, and can help determine the roller pattern to minimize the number of passes while still achieving the correct density.
Ensuring good quality and performance
Quality control can benefit your organization in several ways: maximizing pavement quality, ensuring efficient performance on the job, and making in-process adjustments to ensure that quality goals are met.
Testing should be done in regular intervals and results communicated in a timely fashion. The driving idea behind the quality control process is to notice trends before they turn into problems…especially if those problems result in a project not meeting specification. This has direct financial impacts on a business as it means an overall reduction in repair or remove-and-replace and in many cases can lead to bonus payments for high quality work.
Often, to ensure that good data is passed on in a timely and easy-to-read fashion, control charts are produced by the tester.