بررسي مشخصات مكانيكي و منحني تنش- كرنش بتن سبك‌دانه موجود در ايران

Property Improvement of Iranian LWAC: Investigation of Mechanical Properties and Stress-Strain Curve

در اين پژوهش امكان استفاده از سنگدانه‌هاي اسكوريا و ليكاي موجود در كشور براي توليد بتن سبك‌دانه پرمقاومت بررسي شده است. براساس طرح‌هاي گوناگون اختلاط و روش‌هاي مرسوم، توليد بتن سبك‌دانه‌اي با مقاومت فشاري 28 روزه‌ي بيشتر از 40 مگاپاسكال كه بتوان آن‌را در بتن مسلح به‌كار برد، ممكن شد. براي بررسي مشخصات مكانيكي كوتاه‌مدت اين بتن، آزمايش‌هاي مختلفي چون وزن مخصوص بتن، مقاومت فشاري، مدول الاستيسيته استاتيكي و ضريب پواسون انجام شد؛ روابطي نيز براي پيش‌بيني مدول الاستيسيته استاتيكي اين بتن‌ها براساس مقاومت فشاري و وزن مخصوصشان در سن 28 روز ارايه شده است. مشخص شد كه با افزايش وزن بتن با تغيير در بافت دانه‌بندي، مقاومت فشاري و مدول الاستيسيته بتن‌هاي آزمايش‌شده، افزايش يافته است. استفاده از دوده سيليسي نيز در بهبود مقاومت فشاري اين بتن‌ها موثر بوده است. نتايج نشان مي‌دهند كه اسكوريا و ليكا در بهبود مشخصات مكانيكي نمونه‌ها موثر بوده‌ كه اسكوريا به نتايج مناسب‌تري رسيده است. منحني تنش- كرنش بتن‌هاي مطالعه‌شده بررسي شد و توصيه‌هايي براي تخمين اين منحني‌ها ارايه شد. بر اساس نتايج، منحني‌ها در شاخه‌هاي صعودي و نزولي تقريباً خطي بودند.

The potential use of leca and scoria aggregates available in Iran to produce high strength lightweight concrete has been studied. As a result of various concrete mixes with different lightweight aggregate amount, and using normal techniques, it was possible to obtain high quality lightweight concrete which is suitable for application in reinforced and prestressed concrete structures.In order to investigate the mechanical short term properties of this type of high strength concrete, different tests had done. The properties obtained include unit weight, compressive strength, static modulus of elasticity and poissonʹs ratio.Among the 28 day aged tested specimens, we could produce HSLWC containing scoria with 55 MPa compressive strength and 2070 kg/m3 weight.In LWC containing leca, a cube compressive strength of about 41 MPa with a unit weight of 1865 kg/m3 was reported.Static modulus of elasticity in concretes containingleca was between 15 to 19 GPa. It was between 17 to 19.5 GPa forconcretescontainingscoria. Some equations were offered to estimate static modulus of elasticity of these concretes based on their compressive strength and unit weight. The mechanical properties were improved by reducing the amount of lightweight aggregate. The results show that both scoria and leca were effective in improving the mechanical properties, but scoria could reach superior limits.Stress- strain curves of investigated concretes were studied and some recommendations are presented for estimating the curves.Stress-strain curves of investigated concretes are almost linear in ascending and descending branch.According to the observed coefficients, withincrease in concrete strength, the slope of the curve is reducedin comparison with modulus of elasticity. For scoria, the slope of curve is lower than modulus in all three mix designs, because of the higher modulus of elasticity of scoria aggregates, in comparison with leca.