پديد آورندگان :
گنجه خسروي، بنيامين دانشگاه گيلان , قاسم زاده موسوي نژاد، حسين دانشگاه گيلان , رزاقي لنگرودي، جواد دانشگاه گيلان
كليدواژه :
آزمايش break-off , مقاومت بتن , الياف فولادي , آزمايش نيمه مخرب
چكيده فارسي :
در اين مطالعه آزمايش نيمه مخرب break-off براي ارزيابي مقاومت بتن حاوي الياف فولادي در محل مورد بررسي قرار گرفته است. بتن حاوي الياف فولادي بدليل مزاياي آن در افزايش چقرمگي و مقاومت بتن بويژه كششي و خمشي، در اين مطالعه انتخاب شده است. بمنظور فراهم كردن يك پايگاه آماري كامل و جامع، 24 طرح اختلاط با مقادير مختلف عيار سيمان 400، 450 و 500 كيلوگرم بر متر مكعب با نسبت آب به سيمان ثابت 4.0، حداكثر اندازه سنگدانه 5.12 و 25 ميليمتر و الياف فولادي با نسبت هاي حجمي 0، 33.0، 67.0 و 1 درصد در سنين مختلف 14، 28 و 90 روز انتخاب گرديد. سپس، عوامل تاثيرگذار بر خصوصيات بتن حاوي الياف فولادي و همچنين نتايج آزمايش break-off مورد ارزيابي قرار گرفت. بررسي ها نشان مي دهد علاوه بر مشخصات آزمايش، درصد و مشخصات الياف فولادي تاثير بسزايي بر خواص بتن و نتايج آزمايش break-off دارد. نتايج حاكي از آن است كه ارزيابي مقاومت با روش فوق داراي قابليت اعتماد مناسب مي باشد، هر چند تخمين مقاومت بتن براساس يك منحني كاليبراسيون كلي ممكن نيست. از اينرو منحني هاي كاليبراسيون مستقل براي هر بتن با درصدهاي متفاوت الياف بمنظور تفسير واقع گرايانه نتايج ارائه گرديده است.
چكيده لاتين :
Here, the efficiency of the non-destructive Break-Off (BO) test was investigated for assessing the in-place compressive strength of steel fiber reinforced concrete (SFRC). SFRC was studied due to its advantages in increasing toughness and tensile and flexural strength in particular. To provide a through and comprehensive database, 24 mix designs were selected with cement contents of 400, 450 and 500 kg/m3 with constant water/cement ratio of 0.4 for all mixes, two maximum aggregate sizes of 12.5 and 25 mm along with steel fiber volume fractions of 0%, 0.33%, 0.67% and 1% for ages of 14, 28 and 90 days. A total of 360 BO tests and 216 standard cube tests were carried out in this investigation.Then, effective parameters of SFRC and BO test results were evaluated. In the BO method, the force required to break off an in-place concrete cylinder of 55 mm in diameter and 70 mm long, is related to the compressive strength of the concrete from a predetermined calibration curve developed for concrete mix.The studies showed that volumetric percentage and features of steel fibers had a significant influence on concrete properties as well as BO test results. According to the experimental results it could be generally concluded that the influencing factors, namely, SFRC properties due to presence of steel fibers and BO test significantly affect the results as follows: Generally, for a constant W/C ratio, it can be concluded that raising the cement content increase the mean values of BO strength. It can be stated that the maximum aggregate size within the range of 12.5–25 mm has a negligible effect on the BO test results for SFRC with 1% steel fiber volume fractions as the average value of BO strength for 25 mm aggregate concrete was significantly more than the corresponding value for 12.5 mm aggregate size for plain concrete. Moreover, the improving trend the BO strength with age is observed to be similar for all different concretes. Furthermore, increase of BO strength of SFR concretes respect to corresponding plain value is observed as concrete grows older. In addition, results showed that strength estimation based on a single general calibration curve is not feasible. Therefore, a specific calibration curve for each SFRC should be represented for a realistic assessment and interpretation of results. The coefficient of variation of the BO strength was in range of 4– 11%. The higher values are for concretes with higher amounts of fibers, especially at early ages. The reliability of the method seems to be good in which the coefficient of variation for each group of BO tests are below 11%. It should be noted that even under ideal conditions with a specific calibration it is unlikely that 95% confidence limits of better than ±15% can be achieved for an absolute prediction of concrete compressive strength. The findings show that higher values are not only due to the lack of precision of the test procedure, but also due to the intrinsic heterogeneity of granular materials like concrete, particularly in presence of higher amounts of fibers.
