Groove Agent 4 Crack 18 2021
Groove Agent 4 Crack 18
the effects of crack healing were observed on the dimensions of the crack and the path of crack growth (fig. 8). in this case the crack grows into the matrix and within a few hours cures into a solid zone. healing effectively prevents the crack from widening during subsequent loading cycles. healing occurs mainly in the upper left of the crack. the mean crack width before healing is 2.3mm, and after healing is 2.0mm. the healing effect is most pronounced along the center of the crack axis where the crack width is ~1.4mm before healing and 2.0mm after. the healing zone contains a self-healing gel that is approximately 1mm thick and that has a volume of ~0.3mm3. crack healing is more effective at high strain rates (c). the crack heals more quickly under tensile loading than compressive loading because the plastic flow of the crack front is resisted by the matrix filling the crack. in this case, the crack experiences stresses and strains e and r, respectively, where r=0.13mm (i.e. the width of the crack at the initial crack growth step). the stress e is ~9.6mpa (i. stress at which the crack grows by 0.1mm), whereas the strain r is ~0.093. the direction of crack growth is along z (right to left). the time stated for each step represents the approximate time accumulated since the scan for the initial unloaded step was started.
the amount of solvent release into the crack at each growth step (fig. 9) shows that the bulk of the solvent is released between steps 1 and 2. after step 2 only a small amount of solvent is released into the crack. when the crack is healed after step 2, the crack width increases to ~1.8mm and the crack becomes semi-permeable to the solvent. the amount of solvent that can be released into the crack is related to the amount of solvent remaining in the crack. the solvent remaining in the crack after step 2 is approximately 4 times that after step 1. this indicates that the solvent is pumped back into the crack after step 2. presumably this occurs because the cracks surface is blocked by the capsule fragments filling the crack at step 2. after step 2 the amount of solvent released into the crack is halved, suggesting that the crack has become semipermeable. this is supported by the crack width increasing to ~1.6mm. the crack then heals, increasing its permeability to solvent. the amount of solvent that can be released into the crack after the crack heals is ~1/4 of that before the crack heals, indicating that the crack has lost approximately one-half of its permeability. the healing is incomplete and a layer of gel remains in the crack. this gel has a thickness of ~0.1mm. the crack then heals further, increasing its permeability to solvent. the amount of solvent that can be released into the crack after the crack heals is ~1/3 of that before the crack heals, indicating that the crack has lost approximately one-third of its permeability. the healing process is not complete and a layer of gel remains in the crack. the thickness of this layer is approximately l. the sample will not heal beyond the thickness of this gel.
the problem with an external repair is that it is not as effective as a repair in the concrete itself. external repair joints are prone to cracking because of the many environmental elements that can affect them. a more reliable way to repair concrete cracks is to use an internal, long-term repair. there are two different types: mechanical and chemical.
there is no way to repair concrete that is already cracked. if cracks develop, they will continue to grow, gradually leading to a slab failure. some cracks are repairable, but they take time. the material that can hold cracks closed is called concrete cover-up. concrete cover-up might involve an epoxy resin, a polymer-impregnated fiberglass fabric, or some other material that is applied in a way that keeps water out of the crack. the layer of repair is thin enough to allow water to penetrate through it but thick enough to cause a crack to close. concrete that has been covered is less likely to crack in the future.
the chemistry of concrete is such that it binds well to cement. so in order to create a self-healing concrete, the cement must be changed. the most common way to accomplish this is to incorporate a microencapsulated healing agent.
there are several ways to incorporate the microencapsulated liquid healing agent into concrete. the most common is the addition of a dispersant, which keeps the healing agent well separated from the cement. this allows the healing agent to remain in the microcapsules throughout the curing process.
it is important to keep the microencapsulated liquid healing agent separated from the cement so that it can remain in the microcapsules. the best way to keep the liquid in the microcapsules is by using a dispersant. the dispersant allows the liquid to remain separated from the cement particles.