Concrete structures undergo internal damage; this usually starts at the atomic level with defects that then grow and form cracks, which can propagate through the material. Here, a method of preparation of poly(methyl methacrylate) (PMMA) nanocapsules adhesive system via miniemulsion polymerization technique is reported, where MMA + DMA (resin + accelerator) and BPO (hardener) components are separately encapsulated by PMMA shells. The crack-healing potential of these nanocapsules was then investigated by embedding them into the mortar matrix. The prepared PMMA core–shell self-healing nanostructures survived the mixing and hardening processes, and the hardened mortar alkaline environment. The stress fields associated with propagating cracks (load‐induced cracking) broke the brittle/weak inert shell of these core–shell structures, resulted in releasing the healing agents to bridge the nascent and early-stage fractures (< 10 µm) in a short time. Long-term healing was achieved through the formation of polymorph calcite crystals in the presence of moisture and CO2, which improved the durability of mortar by filling the gaps. Formulation design (addition of chemical admixtures) and process parameters (blade design and mixing speed) were found to directly impact the uniform distribution of nanocapsules, the survival rate of nanocapsules, and the overall strength of the hardened concrete. The stepwise approach to formulate and fabricate a novel high-strength self-healing concrete system unlocks unique opportunities to design nanomaterials that safeguard the integrity of concrete structures.
Concrete is an essential building material used in the majority of structures. The demand for concrete-based infrastructures rises each year in line with population growth. (ABS 2018; BCI_Economic 2018) Concrete structures undergo internal and external damages; degradation of concrete over time increases the life-cycle cost of an asset by an estimated annual cost of billions of dollars to national economies.(Pacheco-Torgal et al. 2017) One problem among many that can endanger the durability and the reliability of concrete structures is cracking (Danish et al. 2020; Taheri 2019; Frosch and Jeffrey 2007); this usually starts at the atomic level with defects that then grow and form cracks which can propagate through a structure and can lead to more serious problems such as accelerated penetration of aggressive agents and subsequent corrosion of embedded reinforcing steel, weakening of the structure, and spalling of concrete cover. Furthermore, the majority of cracks occur deep within the concrete in inaccessible areas that are invisible to normal inspection, causing a major serviceability problem. Controlling and stopping crack propagation and enlargement is thus key to protecting concrete structures, enhancing their performance and reliability, and prolonging their service life. Self-healing of cracked concrete, therefore, can be an answer for sustainable infrastructures, as it can inhibit the development of early age microcracks into larger cracks. Self-healing materials spontaneously heal damage without the need for detection by human or any type of manual intervention (Wool 2008).
Over the past few years, scientists have developed promising technologies for internal healing of concrete cracks using encapsulated spores of limestone-producing bacteria.(Van Tittelboom and Belie 2013; Souradeep and Kua 2016; Tziviloglou et al. 2016) Bacterial spores lie dormant until moisture penetrates through the crack lines, triggering the spores to germinate and produce limestone that eventually seals the crack. Although this green approach is quite appealing and plausible, bacteria self-healing is a low-speed approach (> days), ideal for surface-only fractures and structures located in areas with high levels of relative humidity or in direct contact with a lot of water, such as marine structures or sewer pipes. In addition, a deteriorated structure loses its strength and integrity as a result of crack formation, and these might not be repaired by limestone filler on its own.(Gupta et al. 2017; Tziviloglou et al. 2016) The chemical healing approach is thus more consistent and applicable. Adhesives such as epoxies, acrylates or a hybrid of the two are ideal for bonding most common construction materials such as metal and are popular in filling gaps and repairing cracks (especially dormant cracks) in concrete. Moreover, they can be formulated into fast curing systems with around a few minutes work-life (the time needed before an adhesive harden and dry). The adhesive builds up the strength shortly after curing and, when custom-designed, without the need for external elements such as moisture.
Concrete sidewalks can vary in shapes, colors and be formed into any shape you can imagine. Before starting on this project, look around at other homes and businesses to see what can be done but don't be limited by what you see. Use your imagination. Las Vegas concrete contractors
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