Dosage optimization and seismic retrofitting applications of uhpfrc
- Autores: Joaquín Abellán García
- Directores de la Tesis: Jaime Fernández Gómez (dir. tes.), Nancy Torres Castellanos (codir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
Several structures and constructions situated in earthquake-prone areas were designed and built following old earthquake-resistant building codes and do not obey current seismic regulations. Furthermore, in developing nations located in earthquake-prone areas, this situation is aggravated by the existence of a very widespread informal construction. These circumstances require effective seismic retrofitting interventions by means of solutions of the acceptable cost that allow the widest application.
Colombia, where this Ph.D. thesis was developed, is a clear example of the latter. Colombia is a seismically active country and has a large seismic risk in many areas of its territory due to its location at the boundaries of several tectonic plates. Moreover, according to different researches, it is estimated that about 80% of the buildings in the city of Bogotá were built without meeting any seismic regulation. If this happens in the capital of the country, it is easy to extrapolate that it also happens in the rest of Colombia.
On the other hand, ultra-high-performance fiber reinforced concrete (UHPFRC) is an advanced construction material that provides new opportunities in the construction industry around the world. Among those new applications, rehabilitation, and seismic retrofitting of existing damaged or non-ductile concrete structures can be highlighted. The main objective of this Ph.D. is to optimize a UHPFRC mixture, developed with the highest proportion of Colombian raw materials and under minimum cost criteria, to achieve the ductility requirements for seismic retrofitting applications in the country.
The research thesis is developed in different phases. First, the UHPC without fibers is optimized, selecting the components under the criteria of minimum cement content, without using quartz powder and with a silica fume content limited to 100 kg/m3, reaching resistance at 28 days equal to or greater than 150 MPa and keeping the concrete in the self-compacting range. In the second phase, once the UHPC is mixture optimized, the objective consisted of determine the binary mixture of fibers, from among steel (normal and high-strength) and polymeric fibers available in the local market, that allow achieving the necessary characteristics for the application of seismic reinforcement material at a lower cost. Energy capacity absorption (g) and strain capacity at maximum tensile strength (εpc) were the parameters used to verify the ductility properties necessary for the seismic retrofitting applications of UHPFRC.
Several statistical and computational tools such as Design of Experiments, artificial neural networks, response surface methodology, main effect plots, and multi-objective optimization were used to reduce the number of trials needed in the optimization and perform effective analysis.
Lower final cost and cement content was achieved when blending micro-limestone powder (d50= 2.1 µm) and recycled glass flour (d50= 28 µm) as partial substitution of cement and silica fume. An optimal mixture was designed to reach a 150 MPa 28-day compressive strength with only 590 kg/m3 of cement and 100 kg/m3 of silica fume, providing an ultra-high-performance concrete which incorporates by-products in its dosage.
Finally, the optimal blending of fibers for achieving the necessary properties for seismic retrofitting applications (i.e., g≥50 kJ/m3 and εpc≥0.3%), when using the previously optimized UPHC mixture, was 0.34% of high-strength steel straight (lf/df =65) fibers in addition to 1.36% of normal strength hooked end steel fibers (lf/df =80). Totalizing a total volume fiber fraction on 1.7%. This mixture outperforms the ductility parameters obtained by other authors with successful applications in seismic retrofitting of reinforced concrete structures, which reaffirms its value for the desired application.
