TECH

Rowan engineers develop new way to monitor 3D printed concrete during construction

A Rowan University team of engineers has developed a new way to measure how 3D printed concrete deforms during printing and curing, revealing how lower layers respond to the weight and pressure of newly deposited material. The approach could help researchers and manufacturers better understand how printed concrete behaves during construction and what factors affect the quality of finished structures. 

Around the world, concrete additive manufacturing is increasingly used to speed construction. Rather than pouring concrete into forms, builders can use industrial-scale 3D printers to extrude the paste-like material layer by layer to create walls and foundations.  

Researchers have looked for ways to monitor what happens to concrete during the earliest stages of printing, when newly deposited layers are still deforming, curing and bearing the weight of additional material. Understanding that process could advance research aimed at improving the quality, durability and efficiency of 3D printed concrete construction. 

Led by Islam Mantawy, Ph.D., and Behrad Koohbor, Ph.D., researchers in the Henry M. Rowan College of Engineering developed and tested a new method for reconstructing how concrete changes throughout the printing process. That’s important because multiple factors, from temperature and humidity to the material’s chemical composition, can affect how a printed structure behaves as it cures. Understanding those factors and their precise effects could help engineers identify potential problems earlier and improve future concrete printing processes.     

“The idea is we need to avoid any premature failure,” said Mantawy, an assistant professor in the Department of Civil & Environmental Engineering and head of the Additive and Robotic Construction Laboratory. “If you're building an 8-foot-tall wall and the bottom layer starts to crack and collapse, the entire structure can fail before you reach the final layer. What was supposed to be a faster, more efficient construction method becomes slower and less efficient because you have to start over from scratch.”

They started with a long-established imaging technique called digital image correlation (DIC) that measures how materials and structures deform under force. Using a reference image of an existing object, researchers use cameras to take thousands of images as the material and structures respond to external stimuli such as mechanical forces, temperature change and humidity. 

In concrete printing, however, there is no reference image because the structure is being created as the process unfolds.

The team used DIC “in reverse time,” starting with images of the completed structure and working backward through thousands of images captured during printing and curing. With those images, the team was able to construct a mathematical approach to validate the reverse-time DIC method and for explaining what happens as concrete deforms, shrinks and cures, even during the first moments after a layer is printed.  

Published in the journal Experimental Mechanics, the paper demonstrates that images of a fully cured 3D printed structure can be analyzed in reverse order, using the natural surface roughness of the concrete as a tracking pattern, to reveal how the structure deformed throughout printing and curing. 

Beyond concrete printing, the researchers say DIC “in reverse time” could be useful in other additive manufacturing processes where conventional quality control methods are limited because a structure does not yet exist when production begins.

“We are literally writing the history of the process, but we start from the end and go back,” said Koohbor, an associate professor in the Department of Mechanical Engineering and affiliated faculty with Rowan’s Advanced Materials & Manufacturing Institute.  

The researchers see the work as an early step toward smarter, more autonomous forms of additive manufacturing.

“Without knowing what’s happening inside the structure, you won’t be able to achieve self-operating 3D printing,” Mantawy said. “It’s a way to have an eye on the structure as it evolves.”

From conventional construction to digital fabrication...Civil engineering is entering a phase in which construction is no longer defined only by drawings, formwork, manual placement, and conventional sequencing. Digital fabrication and robotic construction introduce a different logic: structures can be designed as data, translated into toolpaths, produced by controlled machines, monitored during fabrication, and verified through a combination of material testing, process control, and structural assessment. 

Three-dimensional concrete printing, often called 3D concrete printing or 3DCP, is one of the most visible examples of this transformation. In many systems, a cementitious material is pumped through a hose and deposited layer by layer by a gantry, robotic arm, or mobile printing platform. The printed object may be a wall, façade element, formwork, shell, bridge component, foundation element, or architectural unit. The attraction is clear: the technology can reduce or eliminate some formwork, allow complex geometries, support material-efficient design, and open new possibilities for automated construction. 

However, 3D concrete printing should not be treated as a simple replacement for conventional casting. It changes the engineering problem. The material must be fluid enough to pump and extrude, but stiff enough to keep its shape and support subsequent layers. The geometry must be printable, not only beautiful. The structure must satisfy load-bearing, durability, reinforcement, connection, fire, tolerance, and inspection requirements. The construction process must therefore be considered as part of the structural system. 

What makes 3D concrete printing different? In conventional reinforced concrete construction, the formwork defines the geometry, reinforcement is placed before casting, and the concrete fills the mould. In 3D concrete printing, the material is deposited directly in its final or near-final geometry. This creates freedom, but also responsibility. Layer geometry, printing speed, extrusion rate, nozzle height, waiting time between layers, ambient temperature, and material thixotropy all influence the final performance of the printed element.

The digital workflow is also different. A printable structure begins as a design model, but it must pass through design-for-additive-manufacturing decisions, toolpath generation, slicing, simulation, robotic control, printing, post-processing, and verification. Recent work on the digital chain in concrete 3D printing emphasizes the need to coordinate parametric design, path planning, numerical simulation, fabrication constraints, and information transfer between platforms. 

For researchers and practitioners, this means that the critical questions are not only “Can we print it?” but also “Can we design it, control it, inspect it, reinforce it, certify it, and maintain it?” A printed element should be judged by the same engineering principles as any other civil infrastructure component, while also accounting for the specific anisotropy, interfaces, geometry, and construction history introduced by layer-wise manufacturing.

The material challenge: printability is a narrow window...The central material challenge in 3D concrete printing is printability. A printable mixture must satisfy several conditions at the same time. It must be pumpable so that it can move through the delivery system without blockage or segregation. It must be extrudable so that the nozzle produces a continuous and stable filament. It must be buildable so that fresh layers can support their own weight and the weight of subsequent layers. It must also provide sufficient interlayer bonding so that the final element behaves as a coherent structural component. 

These requirements can conflict. A highly flowable mixture may be easier to pump but may deform after deposition. A very stiff mixture may keep its shape but may cause pumping problems or weak interfaces. A long delay between layers can reduce interlayer bond, while a short delay can cause excessive deformation if the lower layer has not developed enough stiffness. This is why rheology, thixotropy, setting behavior, admixture compatibility, and early-age mechanical properties are central research topics in printable cementitious materials. 

Environmental conditions matter as well. Temperature, wind, humidity, sun exposure, and moisture loss can affect open time, layer surface condition, bond quality, and dimensional stability. In practice, a printing recipe cannot be separated from the printer, nozzle, hose length, pump, printing speed, layer height, quality-control system, and construction environment.

Structural design, reinforcement, and interfaces...For civil engineering, the largest questions are not only material flow and geometric novelty, but structural reliability. Printed concrete elements can exhibit anisotropic behavior because the interfaces between layers may influence strength, stiffness, fracture behavior, permeability, and durability. The load path must be compatible with the printed geometry and the direction of layers.

Reinforcement remains a key issue. Conventional reinforced concrete depends heavily on steel reinforcement for tensile resistance, crack control, ductility, and robustness. In printed construction, reinforcement may be placed manually, inserted during printing, integrated after printing, combined with printed formwork, or replaced in limited applications by fibers or alternative reinforcement strategies. Each solution has consequences for bond, cover, durability, construction tolerance, and inspection.

Numerical simulation can help engineers understand these problems before printing. FEM-based modelling has been used to simulate fresh-state buildability, layer addition, overhang limits, and print failure modes. These tools are useful because print failure during construction can waste material and time, while validated simulations can help identify safer layer heights, printing speeds, toolpaths, and geometries. 

Quality control: from visual inspection to digital monitoring...Quality control is a major reason why 3D concrete printing should be treated as a digital fabrication process rather than only a new placement method. The printed product is defined by the material, but also by the process history. Layer width, layer height, surface texture, defects, waviness, discontinuities, dimensional deviations, and local instability can all influence performance.

Recent reviews of geometry and surface inspection in 3D concrete printing discuss image-based systems, structured light, laser scanning, point clouds, and other sensing methods for monitoring printed layers and final geometry. These methods can support quality control during printing, after each layer, before assembly, and during assembly of printed components. 

Machine learning is beginning to enter this field. Recent research has explored deep-learning approaches for predicting filament cross-sectional geometry from material properties and process parameters. Such methods point toward future closed-loop systems in which simulations, sensors, and printer control are connected to reduce trial-and-error and adjust printing parameters more intelligently. Still, these tools must be validated carefully and used within the range of the data on which they were developed.

 

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