The amount of time it takes to construct a building depends largely on the determination process of whether the concrete of each floor is strong enough to take on new loads.
In a bid to speed up that process, engineers from Purdue University have developed sensors that, they say, will safely determine concrete strength on-site and in real time.
Construction sensors for reduced lab time
Today, concrete mix designs require month-long testing before they are implemented on a construction site. Once those mixes have been given the green light, they then cannot be altered without additional offsite testing that can take a long time and delay construction.
The Purdue University solution to this problem would remove the need for extensive offsite testing by allowing construction contractors to test and verify the state of the concrete onsite.
"Our sensors could help make better data-driven decisions to determine the construction schedule and improve the quality of concrete construction," Luna Lu, Purdue’s American Concrete Pavement Association Professor of Civil Engineering, explains in a press release.
"We’re trying to work with contractors to find out how much saving we can do for them in terms of time, cost, and the number of people needed at a site, which reduces risk and improves construction safety," Lu continues.
In the last decade, general contractors have used traditional sensors to make accurate estimates of concrete strength and maturity. These sensors match up temperature measurements from sensors in the field against notes, taken in the lab, on the strength of the concrete mix based on its specific temperature at any time.
Strength values measured by a "maturity curve," help workers decide when the concrete should be strong enough for construction to continue.
If unexpected changes occur, such as weather changes or calls for changing the mix's main ingredients, then a contractor has to generate a maturity curve all over again for the new mix — a process that can take up to a month.
Eliminating the need for a maturity curve
The sensors developed at Purdue University would measure concrete strength from the floor deck in real time, completely eliminating the need for a maturity curve.
"These new sensors are more of a ‘plug and play.’ We could make judgment calls on the fly," says Ryan Decker, Wilhelm’s corporate quality assurance manager.
The sensors would remain in the concrete and provide a direct measurement of strength by using electricity to send an acoustic wave through the concrete.
The way concrete responds to particular wave speeds indicates its strength, Lu says: "a wave propagating through concrete can tell us a lot of information. We can find out not only how strong the concrete is, but also detailed information about the concrete’s microstructure."
Twelve of the team's sensors have been installed into sections of the construction site for Purdue University's five-story Engineering and Polytechnic Gateway Complex to help the team develop the technology. As the site also sports traditional sensors, Lu's team can compare and contrast their new technology to what came before.
All going well, the new technology could save construction sites worldwide months of time that would otherwise be spent in the lab.