Did you know that traffic jams caused by repair work on roads and highways cost all Americans about 4 billion hours stuck in traffic and 3 billion gallons of gas every year? And that’s just the bigger picture.
If you want to know how much it costs you individually, here it is: traffic congestion alone is estimated to cost the average U.S. driver about $1,400 in fuel. And that’s without taking into account the time you spend commuting that you do not get back.
Shocking, right? Isn’t there a way to solve this or at least minimize it?
The answer is…probably.
A group of researchers at Purdue University developed a groundbreaking piece of technology that addresses the two most common causes of traffic congestion: (1) opening roads to traffic as soon as possible after repair or construction work, and (2) improving the durability of the concrete pavement so it lasts longer.
By resuming traffic quickly and reducing the frequency of repair work, this technology will save millions of taxpayer dollars every year, in addition to the time you’ll save by not being stuck in traffic that much anymore.
And make no mistake; it can be applied to other types of construction work, such as buildings and other structures.
Here’s what this technology is, how it works, where it can be used, and why it’s about to change the construction and transportation industries forever.
Concrete Strength Sensors
Led by Dr. Luna Lu, a Professor of Civil Engineering at Purdue’s Lyles School of Civil Engineering, researchers have developed concrete sensors that can monitor the strength of concrete in real-time and onsite, and then wirelessly transmit that information to civil engineers.
This technology has the potential to significantly reduce spending on infrastructure projects, cut down on repair work, and improve construction safety, as well as speed up construction schedules and be better for the environment.
By replacing the three most used methods of judging concrete’s strength: cylinder testing, maturity curves, and flexural strength testing. All these methods test a specific concrete mix as a proxy for its characteristics on the construction site.
The problem? These methods have their own set of drawbacks, from inaccuracy and quality control issues to user variability and material waste and expense.
In-cylinder testing, concrete is placed in a cylinder and tested to destruction. It can be done in two different ways: field-cured and lab-cured. The first is used to judge the concrete strength in the field while the second is used to verify if the mix can achieve its required and intended strength.
The problem is, no matter which of the two approaches you use, cylinder testing has a low probability of accurately indicating the strength of the in-situ concrete. In fact, most of the time, it gives a strength value that’s lower than what’s in the field, leading to the addition of 10%-15% more cement, increasing the cost of the project and its carbon footprint.
Maturity curves, on the other hand, use a correlation between time and temperature to indicate the strength of the concrete. And even though it’s an effective method with a lot of “pros,” it has two major “cons.”
The first downside is the time required. It takes at least three weeks for a test lab to produce a maturity curve from a trial batch. The second one is the effort. Maturity curves are sometimes not very well understood by mix suppliers and even test labs, which requires ongoing oversight of a competent professional for them to follow ASTM C1074 guidelines and be accurate.
Now, flexural strength testing, an important procedure in the design of concrete pavements, requires workers to cast and place a long and heavy beam onsite and then take it to either a mobile lab on the job site or an offsite facility to test the concrete mix. This risks workers’ safety and is also inaccurate due to the different conditions between the lab and the field.
Finally, and probably even worse, if unexpected events call for changes in the concrete mix, you’ll either have to perform the testing method you're using all over again from the start, which takes time and delays your project schedule, or rely on strength records for the new mix from the supplier you're working with, if they have it.
Therefore, Dr. Lu’s technology is about to change all this. The sensors work onsite, provide real-time information, and don't require expensive and heavy testing setups. And even better, they’re not impacted by the mix design either — meaning the concrete mix can be changed during a project if needed, and the sensors will work just fine with no “calibration” required.
How Do the Sensors Work?
The sensors use electricity to send a mechanical wave into the concrete. By measuring the wave’s propagation through the concrete, you can find out not only how strong the concrete is but also a lot of information about its microstructure and other properties, such as stiffness and hydration.
Just after the pour, the concrete is still kind of “liquid” (it’s not the technical term, but you get the idea). Therefore, it offers little to no resistance to the propagation of such waves. However, as it begins to cure and harden, that resistance grows.
Therefore, using mathematical models, the researchers established the relationship between the opposition of the concrete to the flow of these waves (i.e., wave impedance) and the concrete’s strength.
Each sensor measures only an 11-inch area of concrete, but many sensors can be inexpensively added in different places along a concrete section.
Another important factor is that these sensors live in the concrete forever, allowing data to be collected for years after the concrete has been cured. This makes it possible for engineers to better understand concrete properties after 28 days (the usual time limit of conventional lab test data) and for the concrete to “tell” engineers when it's starting to break down while in use.
The Sensors in Infrastructure Projects
Whenever there’s a Portland Cement Concrete Pavement (PCCP) project, whether it’s construction or repair work, it takes time for the concrete to cure and become strong enough to take on traffic loads and withstand the pavement’s curling and warping.
If the road opens up too early, while the concrete is under-cured and not strong enough, it reduces the lifespan of the pavement, increasing the frequency of repair work, which in turn leads to more frequent traffic jams and more costs.
On the other hand, Department of Transportation guidelines require concrete pavement projects to finish within a specific time frame — for major interstates, that’s usually a 12-hour window. So waiting too long to finish and open up pavements can result in significant penalties for contractors for traffic that’s not opened on time.
In other words, civil engineers face the challenge of having to open up roads and lanes to traffic as fast as possible to meet contractual requirements but not so fast that the concrete pavement is not strong enough to take on the loads.
How to solve this dilemma? Enters Dr. Lu’s concrete strength sensors.
Embedded into the pavement, the sensors provide civil engineers with an accurate method to determine the concrete’s strength in real-time and onsite, allowing them to open up lanes when the concrete is strong enough and within their restricted time periods.
And that’s not all. Since the sensors live in the concrete pavement, they also provide civil engineers with real-time information about the “health” of the pavement after it’s placed. That is, the sensors can communicate the pavement’s strength, weakness, and need for repair throughout its lifespan.
All this can significantly reduce structural failures since the pavement will be able to “talk” when it’s in need of repair. In addition, it can make road repair and construction work a lot more efficient, less frequent, and less costly, preventing unnecessary shutdowns and congestion.
So far, prototypes of the sensors have been embedded into three Indiana highways since 2019. After the test period, the Indiana Department of Transportation (INDOT) plans to adopt the sensors officially, allowing them to live in their highways to keep contractors informed on the pavement’s conditions.
In addition to Indiana, the team has also worked with the Federal Highway Administration to expand the project to other states, and a pooled fund has already made it possible. California, Texas, Kansas, and Missouri were planning to join the study and the testing as well.
The Sensors in Buildings
In addition to their use in infrastructure projects, the concrete strength sensors could also be used in the construction of buildings and other structures. How?
Well, before the construction work can begin on the next floor of a building, the concrete of the previous floor needs to be strong enough to take on the loads it’ll be subjected to. These include workers, equipment, construction materials, other structural elements, etc.
The problem is that traditional methods to estimate the strength of the floor slabs and columns are based on the three most common methods mentioned before. And as you’ve seen, they can have relatively significant drawbacks.
How to solve this? Enters Dr. Lu’s concrete strength sensors…again.
By allowing contractors to accurately check the concrete’s strength directly from the floor slab and columns in real-time and onsite, the sensors eliminate the need for low-accuracy cylinder testing, time-consuming maturity curves, or environment-influenced flexural strength testing.
Not only does it significantly speed up construction schedules and save money and material on in-situ and lab tests, but it also avoids premature failures and constant structural maintenance.
Back in 2020, to test how the sensors work compared to traditional methods, the Purdue team installed 12 of them — six in columns and six in slabs — in the third floor of Purdue’s brand-new five-story Engineering and Polytechnic Gateway Complex. The Complex opened for students in January 2023.
After all the development in Purdue’s SMART lab and real-world testing in highways and buildings, is it possible these sensors will become a real thing and change how civil engineers estimate concrete strength forever?
The answer is…probably. And here’s why.
The technology has received nationwide recognition ever since it started. In 2021, it was named an ASCE Gamechanger, which means an innovation that helps solve the problems identified in the 2021 Infrastructure Report Card.
And there’s more. At the end of 2022, chosen out of 1,400 other groundbreaking technologies already making an impact on a real-world problem, the sensors were named one of the Next Big Things in Tech by Fast Company magazine.
To leverage all this potential and introduce the technology into the AEC market, Dr. Luna Lu founded WaveLogix. The company is a tech startup that will commercialize concrete strength sensors under their Rebel brand.
Wavelogix has received a six-month grant worth more than $250,000 from the National Science Foundation to develop its concrete strength monitoring technology. According to Purdue’s news release, this will help the company speed up its product development phase and get the sensors ready to go to market.
The company plans on conducting beta testing in 2023. After that, they will start the large-scale manufacturing of the sensors, with an initial business focus on infrastructure projects.
There’s no doubt these sensors enable significant savings of both money and time. By providing real-time information on the conditions of different infrastructure assets and structural components of a building, the sensors allow civil engineers to make data-driven decisions for building and maintaining their structures.
If you’re in the construction engineering arena, work in your municipality’s Public Works Department, or if you simply deal a lot with concrete structures, this new piece of technology will truly impact how you do your work on the job site. And probably, that impact will be positive.
Licensed PEs in construction are responsible for making sure the concrete mix meets all the requirements for the project. So if you haven’t gotten that yet, The Ultimate Civil PE Review course is your best choice. Why?
It’s been ranked by Test Prep Insight as the best overall PE exam prep course out there while also being the most affordable option. What does it mean? It gives you the best bang for your buck while giving you the best shot at passing the exam. And it even comes with a CBT exam simulator to give you a realistic feel for the real thing. Check it out!
Author: Allan Cardec
A freelance writer specializing in the civil engineering industry. He helps firms, exam prep companies, professional institutions, trade publications, and other related businesses create engaging content their audience wants. Topics include project highlights, news, academic research, licensure, career development, exam prep, and school.
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