Abstract
The mechanical properties of cementitious materials injected by epoxy have seldom been modeled quantitatively, and the atomic origin of the shear strength of polymer/concrete interfaces is still unknown. To understand the main parameters that affect crack filling and interface strength in mode II, we simulated polymethylmethacrylate (PMMA) injection and PMMA/silica interface shear deformation with Molecular Dynamics (MD). Injection simulation results indicate that the notch filling ratio increases with injection pressure (100 MPa–500 MPa) and temperature (200 K–400 K) and decreases with the chain length (4–16). Interface shear strength increases with the strain rate ( s– s). Smooth interfaces have lower shear strengths than polymer alone, and under similar injection conditions, rough interfaces tend to be stronger than smooth ones. The shear strength of rough interfaces increases with the filling ratio and the length of the polymer chains; it is not significantly affected by temperatures under 400 K, but it drops dramatically when the temperature reaches 400 K, which corresponds to the PMMA melting temperature for the range of pressures tested. For the same injection work input, a higher interface shear strength can be achieved with the entanglement of long molecule chains rather than with asperity filling by short molecule chains. Overall, the mechanical work needed to break silica/PMMA interfaces in mode II is mainly contributed by van der Waals forces, but it is noted that interlocking forces play a critical role in interfaces created with long polymer chains, in which less non-bond energy is required to reach failure in comparison to an interface with the same shear strength created with shorter polymer chains. In general, rough interfaces with low filling ratios and long polymer chains perform better than rough interfaces with high filling ratios and short polymer chains, indicating that for the same injection work input, it is more efficient to use polymers with high polymerization.
Highlights
The use of sealants in repairing cracks in reinforced concrete components was originally designed to prevent the exposure of steel reinforcements to the atmosphere and subsequent alkali–silica reactions
We modeled a notched silica/injected PMMA interface system with Molecular Dynamics (MD) to investigate the performance of concrete reparation via PMMA injection
Smooth interfaces were shown to have a lower shear strength than the polymer alone, and under similar injection conditions, rough interfaces tended to be stronger than smooth ones, indicating that concrete reparation via PMMA injection will perform better for crack faces that present asperities
Summary
The use of sealants in repairing cracks in reinforced concrete components was originally designed to prevent the exposure of steel reinforcements to the atmosphere and subsequent alkali–silica reactions. Recent studies (e.g., [2,3]) show that epoxies and polymethylmethacrylates (PMMAs) are the best-performing sealants: epoxies allow flexural strength to be recovered but can only be injected in larger cracks, while PMMAs, and in particular, High-MolecularWeight Methacrylate (HMWM), can efficiently penetrate narrow cracks and reduce the permeability of concrete. The results of PMM3 ofA18 shear deformation tests, MD notch injection tests and silica/PMMA interface shear deformation tests for different fidellpitnh,gtyrpaictaiol osf aNrIeL pdreocsecsrsiinbge.dSeactniodn 2ddisecscurisbseesdtheinMSDemctoidoenl o3f t.heCiontnercflaucesions are summarized in Sbeetcwteioenna4s.ilica substrate with a slit-shaped cavity and PMMA with different chain lengths. Results of PMMA shear deformation tests, MD notch injection tests and silica/. In the third equation above, Enb is the van der Waals energy (Lennard–Jones potential), in which rij is the distance between the ith and jth atoms with charges qi and qj. rc is the cutoff distance, equal to 12 Å in this study [17,39,40]
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