Researchers have verified an experimental method that separates the cohesive and frictional contributions to the mechanical behavior of early-age concrete. Published in Smart Construction, the study shows that the loss of macroscopic shear strength and stiffness in 3-day concrete is fundamentally linked to the irreversible dissipation of cohesive strength, while frictional effects become increasingly dominant as damage develops.
Concrete is the backbone of modern infrastructure, but its first few days after casting remain a vulnerable period for engineering safety. Before concrete reaches standard curing age, its strength is still developing, making early-age behavior especially important for rapid construction, emergency repair, tunnel lining, foundation support, slope anchoring and other time-sensitive civil engineering projects.
A new study published in Smart Construction provides a clearer way to understand what happens inside early-age concrete as it is loaded and damaged. The research focuses on the combined cohesion-friction mechanical properties of early-age concrete - two mechanisms that are usually intertwined in conventional strength tests.
In concrete, the cementitious matrix provides cohesion, while aggregate interlocking contributes frictional resistance. Traditional tests usually measure the overall macroscopic strength of the material, but they do not clearly show how much of that strength comes from cohesion and how much comes from friction. This makes it difficult to understand why early-age concrete deforms, weakens and ultimately fails under complex stress conditions.
To address this problem, the research team applied a two-stage triaxial loading method to separate the two contributions. In the first loading stage, the stress-strain response reflects the combined effects of cohesion and friction. After the initial loading causes substantial damage and largely consumes the cohesion, the same specimen is loaded again under comparable conditions, allowing the second response to mainly represent frictional behavior.
The team tested 3-day concrete specimens of three strength grades, C30, C40 and C50, under confining pressures of 0, 3, 6 and 9 MPa. By comparing the first and second loading responses, the researchers experimentally decoupled the cohesive and frictional properties of early-age concrete and evaluated how these components evolve during deformation and strength development.
The results show that, under the same confining pressure, differences in macroscopic shear strength among early-age concretes of different strength grades are primarily controlled by cohesive strength. In contrast, their frictional strength remains largely consistent. The findings also show that confining pressure affects shear performance mainly by regulating frictional strength, while cohesive strength is relatively less sensitive to confining pressure within the tested range.
Most importantly, the study reveals that the reduction of macroscopic shear strength and stiffness originates from the irreversible dissipation of cohesive strength. As loading continues, the cohesive properties of early-age concrete are gradually consumed, and frictional behavior becomes more prominent. Eventually, the mechanical behavior of damaged early-age concrete approaches that of a granular material without cohesion.
“Early-age concrete does not simply become weaker in a general sense; our experiments show that the key process is the consumption of cohesion,” says the corresponding author. “By separating cohesion from friction, we can better understand how early-age concrete fails and how its performance can be assessed more accurately.”
The study provides a useful experimental basis for developing concrete strength theory and constitutive models that distinguish between cohesive and frictional mechanisms. This distinction could help engineers better evaluate early-age structural safety and design safer construction or repair procedures when concrete has not yet reached mature strength.
“The method gives engineers a new way to look at concrete strength,” the authors note. “Instead of treating strength as a single number, it becomes possible to track the separate roles of cohesion and friction during damage development.”
The authors also acknowledge that the method can be further refined. Although the second loading response is dominated by frictional behavior, microcracks and damage generated during the first loading may alter aggregate interlocking. Future work will further explore the cohesion-friction mechanism through numerical simulation and additional experimental validation.
Lu D, Guo Z, Cai T, Wang G, Gao Z, et al . Experimental investigation on cohesion-friction mechanical properties for early-age concrete . Smart Constr. 2026(2):0012, https://doi.org/10.55092/sc20260012 .
DOI: 10.55092/sc20260012
Smart Construction
Experimental study
Not applicable
Experimental investigation on cohesion-friction mechanical properties for early-age concrete
22-Jun-2026