بررسي خواص فيزيكي، مكانيكي و ايمني در برابر آتش براي بلوك‌هاي سقفي پلي‌استايرن منبسط‌شده در سيستم سقف تيرچه- بلوك

Investigation on Physical, Mechanical and Reaction-to-Fire Properties of EPS Blocks in Block and Joist Floor System

خواص و عملكرد بلوك پلي‌استايرن منبسط‌شده در سيستم سقف تيرچه بلوك، با انجام آزمايش‌ها و مطالعات وسيع، شامل آزمون‌هاي آتش، بارگذاري استاتيكي و ديناميكي، مطالعات حرارتي و آكوستيكي بررسي شد. رفتار در برابر آتش به‌وسيله آزمون گرماسنج مخروطي و مطابقت نتايج با روش‌هاي مختلف طبقه‌بندي ارزيابي شد. نتايج آزمايش‌هاي آتش و بررسي‌هاي به‌عمل آمده نشان داد كه انواع خودخاموش‌شو (يا كندسوز شده) پلي‌استايرن منبسط‌شده نيز در برابر حريق رفتار خطرناكي بروز داده و بايد در برابر آتش محافظت شوند. هم‌چنين، استفاده از اتصال مكانيكي پوشش محافظت‌كننده به سيستم سقف ضروري است. مقاومت خمشي بلوك‌ها با چگالي‌ها و ابعاد هندسي مختلف با انجام آزمايش‌هاي بارگذاري استاتيكي و ديناميكي بررسي و شرايط بهينه براي آن تعيين شد. براين اساس رعايت حداقل چگالي kg/m312 براي بلوك‌هاي 25?50 سانتي‌متر و حداقل kg/m314 براي بلوك‌هاي 20?50 سانتي‌متر مي‌تواند معيار پذيرش را برآورده سازد. عرض بهينه لبه‌ي نشيمن بلوك‌ها در محل قاعده 2?27 ميلي‌متر به دست آمد. هم‌چنين، اثر بلوك پلي‌استايرن در مقاومت حرارتي سقف‌هاي تيرچه و بلوك با آرايش‌هاي هندسي مختلف بررسي و رفتار حرارتي سيستم سقف، براساس استاندارد بين‌المللي EN ISO 10211 و با استفاده از نرم‌افزار‌ شبيه‌سازي تِرم1، ارزيابي شد. افزايش ضخامت يا عرض بلوك و درنظر گرفتن يك پاشنه در بخش تحتاني بلوك، به شرط رعايت مسايل ايمني سازه و حريق، باعث بهترشدن عملكرد حرارتي سقف مي‌شود. نتايج آزمايش‌ها نشان داد كه سقف تيرچه و بلوك با بلوك پلي‌استايرن منبسط‌شده رفتار آكوستيكي تقريباً معادل با سقف مشابه با بلوك سفالي دارد.

Abstract: One of the important applications of Expanded Polystyrene (EPS) in Iran is its use as infill block in Block and Joist Reinforced Concrete Floors. The properties and performance of EPS blocks in this floor system, including reaction-to-fire, mechanical properties, thermal resistance and acoustical performance of the system, was studied. Fire behavior of blocks was tested with ISO 5660 cone calorimeter test method. The fire properties of standard and flame retarded types of EPS were measured and discussed, including time to ignition, average and peak values of heat release rate and total heat release. The influence of type of EPS on its fire behavior was investigated. The results showed that the time-to-ignition and total heat release parameters can not be a characteristic value for distinction between standard and fire retarded types of EPS under cone calorimeter test condition. The reason is that both types are flammable and burn completely at fire temperatures. The peak value of heat release rate (PHRR) of EPS is the most important parameter that can be utilized for distinction of Standard and flame retarded types of EPS with cone calorimeter test method. PHRR values higher than 300 kW/m2 were achieved for standard types, but the results for flame retarded ones were less than 250 (and mostly less than 200) kW/m2. The fire risks of specimens were also evaluated using Conecalc software and Richardson method. The results showed that even flame retarded EPS needs to be protected with a thermal barrier in building applications. Moreover, it is required that the protective barrier be mechanically fixed to the structural system, since EPS melts and recedes away heat, once it is exposed to high temperatures. Hence, it is not able to keep barrier, say plaster, in its position. The flexural strength of blocks under static and dynamic loads and its relation with density and dimensions of blocks was evaluated. The results showed that minimum 12 and 14 (kg/m3) density of foam is required respected for 25 and 20 cm of height of blocks with a width of 50 cm. An optimum 27?2 mm was obtained for the width of sitting section of blocks on joists. The influence of different properties and geometry of EPS block (conductivity, width, height and existence of a thermal covering layer under joists) on thermal resistance of floor system was also studied. The THERM software, Enery Efficiency and Renewable Energy Program, was used for evaluation of thermal resistance of the floor. The increase of height and width of blocks caused improvement in thermal resistance of the floor system, but the best result was obtained when a thermal covering layer was considered under the joists. The acoustical results showed that the replace of EPS blocks with hollow clay blocks does not influence importantly the impact sound insulation of the floor system. Neither of them can fulfill the impact sound acoustical requirements and need to be improved with an extra system, like a floating floor or an appropriate elastic floor covering for this purpose.