Applied Fundamental Research Of Phase Change Stored Energy Material In The Fire Resistance Of Concrete Structure

In order to improve the fire resistance of concrete structures, we prepared form-stable polyethylene glycol （PEG）/silicon dioxide （SiO₂） composite as thermal energy storage materials by sol-gel methods, using polysilicon byproduct, then the shape-stabilized phase change materials （PCMs） were joined concrete, expected to increase the concrete specific heat with the phase change material to achieve the purpose of concrete structural fire resistance from the view of material. In this paper, preparation and characterization of form-stable phase change material, phase change energy storage concrete preparation and performance testing, finite element analysis on temperature and stress field of energy-storage concrete members were carried out.The main work of this thesis can be summarized as follows:1. With the silicon tetrachloride a new shape-stabilized PCM was simply prepared by sol-gel methods, and the modified form-stable phase change material to be coated is made with cement. Then the performance of form-stable phase change materials were investigated.（1） By SEM it was found that the polyethylene glycol is well dispersed into the network of solid SiO₂due to the effect of capillary and surface tension forces. And the maximum mass percentage of PEG dispersed into the composites was found to be85%. There was no leakage of PEG from the composites up to this mass ratio even when it melts, which solved the mobility and corrosion problems in the solid-liquid phase change transition.（2） The chemical properties of the form-stable PCMs were studied by FTIR. No significant new peaks were observed, in another word, the main peaks are not changed but just a little shift, which proved that the reaction was physical.（3） The thermal analysis on the form-stable PCMs with different PEG content by DSC. The results showed that the energy density of composites with80%PEG was close to the theoretical value, up to133J/g, and the higher content of the polyethylene glycol, the higher the energy density of the form-stable PCMs.（4） TG was used to evaluated the thermal stability of form-stable PCMs. It showed the prepared PCMs had good heat resistant performance below150℃.2. Phase-change energy storage concrete were prepared with the form-stable PCMs, and the mixture workability, the mechanical properties and thermal performance were studied.（1） Different kinds of phase-change energy storage concrete were prepared using form-stable PCMs and modified PCMs. It showed that the mixture workability of energy storage concrete is superior to the ordinary one. It took too long to cure the energy storage concrete made by form-stable PCMs, but the curing cycle of modified one was almost the same with the ordinary concrete.（2） The compressive strength of phase-change energy storage concrete with different energy density were carried out. The results showed the concrete strength were low when the modified PCMs replaced sand completely, the strength was greatly enhanced when partly replaced. Moreover, the concrete strength rised with the increase of the PEG content. The current strength of phase-change energy storage concrete was up to1OMPa, which met the minimum requirements for plain concrete when the PEG content is1.5%.（3） The thermal performance of the energy storage concrete was tested. It showed that both the energy storage density and the specific heat of the concrete increased with the increase of PEG content, but the thermal conductivity reduced obviously.3. The general computation program （ANSYS） was utilized to make finite element analysis on the fire behavior of phase-change energy storage concrete members.（1） Analysis for the temperature field of concrete was carried out, it found that the internal temperature of phase-change energy storage concrete was lower than the ordinary one under the same heat load.10min later, the opposite side of the energy storage concrete member only reached30%the ordinary concrete member. The temperature of a certain point of concrete rised over time, and the higher the energy density, the smaller the temperature rising rate.（2） From the results of the stress field analysis we can see30min later the equivalent strain of ordinary concrete slab was close to2times the energy storage one when the load was same, which indicated that the phase-change energy storage concrete showed better constitutive relation.（3） Results showed that with the addition of phase-change energy storage material, the thermal inertia of concrete was improved, slowing the heating rate of concrete members, sothat the concrete structure could ensure integrity, adiabaticity and stability for longer time.