An innovative new sensor that allows concrete to ‘talk’ is increasingly being used to monitor US highways. Embedded directly into a concrete pour, the sensor sends engineers more precise and consistent data about the concrete’s strength and need for repair than is possible with currently used tools and methods.
‘Traffic jams caused by infrastructure repairs have wasted four billion hours and three billion gallons [11 billion litres] of [petrol] on a yearly basis. This is primarily due to insufficient knowledge and understanding of concrete’s strength levels,’ said Luna Lu, the Reilly Professor and acting head of Purdue University’s Lyles School of Civil Engineering, who has been leading development of the sensors since 2017. ‘For instance, we don’t know when concrete will reach the right strength needed to accommodate traffic loads just after construction. The concrete may go through premature failure, leading to frequent repairing.’
According to data from the Federal Highway Administration (FHA), concrete pavement makes up less than two per cent of US roads but about a fifth of the US interstate system. Lu’s research has focused on improving the conditions of concrete pavement first because it’s the most challenging road material to repair. Concrete interstate pavement also must reliably support a large proportion of the nation’s traffic.
More than half of the US states with concrete interstate pavement have signed up to participate in a FHA study to implement the sensors. Two states – Indiana and Texas – have already begun trying out the sensors in highway paving projects.
Lu and her lab started developing the technology in 2017, when the Indiana Department of Transportation requested help in eliminating premature failure of newly repaired concrete pavement by more accurately determining when the pavement is ready to be opened to traffic.
Methods that the industry has used for more than a century call for testing large samples of concrete at a lab or onsite facility. Using those data, engineers estimate the strength level that a particular concrete mix will reach after it has been poured and left to mature at a construction site. Even though these tests are well understood by the industry, discrepancies between lab and outdoor conditions can lead to inaccurate estimates of the concrete’s strength due to the different cement compositions and temperatures of the surrounding area.
With the technology Lu and her team invented, engineers no longer have to rely on concrete samples to estimate when fresh concrete is mature enough. Instead, they can directly monitor the fresh concrete and accurately measure many of its properties at once.
The sensor communicates to engineers via a smartphone app exactly when the pavement is strong enough to handle heavy traffic. The stronger the pavement is before being used by vehicles, the less often it will need to be repaired. The ability to instantly receive information about the concrete’s strength levels also allows roads to open to traffic on time or sooner following a fresh pour.
Construction workers can install the sensors simply by tossing them onto the concrete formwork and covering them with concrete. Next, they plug the sensor cable into a reusable handheld device that automatically starts logging data. Using the app, workers can receive information on real-time changes in the concrete strength for as long as the data is required.
Lu’s startup, WaveLogix, is also developing a way to curb carbon emissions by cutting the amount of cement needed in concrete mixes. The manufacturing of cement is responsible for about eight per cent of global carbon emissions. WaveLogix has made progress on a solution that uses artificial intelligence to optimise the design of concrete mixes based on data that the sensors collect from highways across the country.
Construction codes call for a higher cement content in concrete mixes to ensure that the concrete meets required strength thresholds. However, excess cement can lead to premature cracks in pavement. Based on these code requirements and data from the Global Cement and Concrete Association, Lu estimates that concrete mix overdesign causes more than a billion tonnes of carbon emissions per year.
‘The biggest problem with concrete mixes is that we use more cement to increase the concrete’s strength. That won’t help open the road to traffic any sooner,’ Lu said.
The codes are based on how concrete mixes were made during the early 1900s, before equipment that could grind cement into finer powder was developed during the 1950s. Since concrete mixes use that finer powder today, they should have different water–cement ratios than 100 years ago. The codes also don’t take into consideration the impact that weather in different states has a concrete mix. A concrete pour in the middle of Indiana’s winter, for example, requires different concrete mixes to reach the right strength level than if the concrete were poured during California’s winter.
Lu believes that this new method using artificial intelligence could potentially reduce by 20–25 per cent the amount of the cement used in concrete mixes, while simultaneously making pavement more durable and less expensive.
‘I feel a strong sense of responsibility to make an impact on our infrastructure through developing new types of technology. In the field of civil engineering, if we don’t make an impact on the world, there won’t be a world to worry about,’ Lu said.