Simulation-Aided Design of Tubular Polymeric Capsules for Self-Healing Concrete

Abstract

Polymeric capsules can have an advantage over glass capsules used up to now as proof-of-concept carriers in self-healing concrete. They allow easier processing and afford the possibility to fine tune their mechanical properties. Out of the multiple requirements for capsules used in this context, the capability of rupturing when crossed by a crack in concrete of a typical size is one of the most relevant, as without it no healing agent is released into the crack. This study assessed the fitness of five types of polymeric capsules to fulfill this requirement by using a numerical model to screen the best performing ones and verifying their fitness with experimental methods. Capsules made of a specific type of poly(methyl methacrylate) (PMMA) were considered fit for the intended application, rupturing at average crack sizes of 69 and 128 μm, respectively for a wall thickness of ~0.3 and ~0.7 mm. Thicker walls were considered unfit, as they ruptured for crack sizes much higher than 100 μm. Other types of PMMA used and polylactic acid were equally unfit for the same reason. There was overall good fitting between model output and experimental results and an elongation at break of 1.5% is recommended regarding polymers for this application.

Research Progress on Numerical Models for Self‐Healing Cementitious Materials

“…Šavija et al used lattice modeling to establish breakage criteria for a range of tubular polymeric capsules embedded in concrete. In the 2D lattice model used for the simulations, the cementitious matrix was represented by brittle beam elements while the capsules were modeled using beam elements governed by a multilinear stress/strain relationship determined directly from experimental data.…”

A review study on encapsulation‐based self‐healing for cementitious materials

“…Capsule material development mainly aims at improving the survival ratio during concrete mixing by introducing different types of polymers, which is summarized in Table . After being heated, the polymer capsules shift from a brittle state to a rubbery state prior to mixing with other components, thus the survivability of capsules considerably increases.…”

“…The capsule fabricated from MMA is the only materials which can release healing agent promptly among all the lactic acid, polystyrene, and MMA. Similarly, a specific type of poly(methyl methacrylate) (PMMA) is considered to be suitable for capsule materials . This kind of capsule is able to rupture at average crack sizes between 69 and 128 μm, when the shell thickness varies from 0.3 to 0.7 mm.…”

Design and testing of tubular polymeric capsules for self-healing of concrete

“…The testing parameters used to determine the crack width at rupture can be found in [7]. Concrete beams: At the age of 14 days, 6 cracks with varying crack widths (0.3 till 0.5 mm) were created in each beam by means of 3-point-bending tests as shown in Fig.1.…”

“…The capsule was connected to the matrix lattice elements by bond beam elements and the bond beam elements were not allowed to break since a perfect bond is seen as a prerequisite for breakage of the capsules. A detailed description of the model used is described in [7]. To verify the model, mortar prisms (40 mm × 40 mm × 160 mm) with a water to cement (CEM I 52.5 N) ratio of 0.5 and a sand to cement ratio of 3 were prepared according to the standard EN 196-1.…”