| Intumescent coating contains mechanical components,it is easily degraded and aged under the influence of complex environment,and the thermal insulation performance will decrease.After several years of use,the steel structure will not meet the initial fire resistance design requirements.In engineering applications,the hydrothermal aging resistance of intumescent coating is improved by the physical method of applying a topcoat to the surface.What effect does the topcoat have on the hygrothermal aging properties of the fire protection coating? In the event of a fire,what effect will it have on its expansion process? These issues remain to be studied.The main purpose of this paper is to investigate the effect of topcoat on the aging mechanism of fire-retardant coatings for intumescent steel structures,and to quantify the effect of topcoats on the thermal insulation properties of fire-retardant coatings under standard fires.The experimental conclusions can provide reference for practical engineering applications.In this paper,105 samples were tested for hygrothermal aging and thermal insulation properties.In addition,microstructure and chemical composition tests were carried out.Including thermogravimetric analysis,Fourier infrared spectroscopy,photoelectron spectroscopy,viscous detection,and electron microscopy.According to the different type of topcoat,it is divided into 15 uncoated top test pieces,60 coated thermoplastic top coats(indicated by A)and 30 coated thermosetting top coats(indicated by B).The apparent phenomenon of topcoat/coating in the whole process of hydrothermal aging and thermal insulation performance test was observed,The expansion ratio of the carbonized layer was measured to calculate the expansion ratio,The equivalent thermal conductivity of the coating was calculated according to the steel plate temperature measurement result,The effect of topcoat on the hygrothermal aging and thermal insulation properties of the coating was analyzed by microscopic mechanism.The results:(1)The coated A/B topcoats exhibit positive and negative bi-directional effects on the hygrothermal resistance and thermal insulation properties of the intumescent fireproof coating.The so-called positive effect means that the topcoat delays the hygrothermal aging process of the coating,and the rate of decrease of the thermal insulation performance is slowed compared with the uncoated topcoat;Negative action refers to the pressure exerted on the formation of the carbonized layer cell structure during the coating expansion process,which affects the original morphological characteristics of the cell.When the type A topcoat is applied,when the hygrothermal aging time is short(?21 cycles),the negative effect is greater than the positive action,which is manifested by the top coat impeding the expansion of the fireproof coating;After 42 cycles of hygrothermal aging,the test results are not much different,indicating that the negative action and the positive action cancel each other;When the hygrothermal aging time is long(?63 cycles),the negative effect is less than the positive action,and the overall performance is that the top coat promotes the expansion of the fireproof coating.When the B-type topcoat is coated,when the hygrothermal aging time is short(?42 cycles),the negative effect is greater than the positive action,and the damp heat aging time is long(?63 cycles),the negative effect is less than the positive effect.(2)Coating topcoat A/B can improve the hydrothermal aging resistance of fire retardant coating.The hydrothermal aging resistance of B(thermoset)topcoat is better than A(thermoplastic)topcoat,and the ductility of B topcoat is excellent than A.(3)The temperature of the steel plate coated with B topcoat is about 12%higher than that of A topcoat,the expansion ratio is about 17% lower,and the average thermal conductivity of coating is about 10% higher.The results show that:A topcoat has less inhibitory effect on fire retardant coating than B topcoat.(4)Micro-test results show that the effect of topcoat on the hydrothermal aging resistance of fire retardant coatings is as follows: the topcoat isolates the direct contact between the moisture in the air and the fireproof coating,and reduces the migration of hydrophilic substances to the surface of the coating,the amount of effective chemical composition damage in the coating is reduced.The greater thethickness of the topcoat,the less the migration amount,and the more the effective components are retained,which effectively protects the fireproof coating from hydrothermal aging.(5)When the thickness of the A topcoat is greater than 50?m and the thickness of the B topcoat is greater than 25 ? m,the test results are roughly the same.Therefore,when using A topcoat,apply up to 50?m.When using B topcoat,apply up to 25?m.The above conclusions are combined to give appropriate engineering application recommendations. |
PDF Full Text Request