تاثير تراكم وزني و درصد خاكستر بادي در مقاومت بتن خودمتراكم در ترازهاي مختلف

Effect of Weight Compaction and Percentage of Fly-Ash on Self-Compacting Concrete Strength, at Different Levels

با اينكه سال‌ها از كاربرد بتن خودمتراكم مي‌گذرد، هنوز پژوهشي در خصوص تاثير وزن بتن موجود در قسمت بالاي تراز موردنظر در مقاومت آن تراز از بتن انجام نشده است. به همين دليل با به‌كارگيري مخلوط‌هاي مختلف بتن خودمتراكم و با استفاده از روش درجاي "انتقال اصطكاك" با ساخت ستون‌هاي بتني، تاثير وزن قسمت‌هاي بالايي در مقاومت بتن تراز موردنظر مطالعه و نتايج حاصل در اين نوشتار ارايه شده است. نتايج به‌دست‌آمده نشان مي‌دهد كه وزن بتن در قسمت‌هاي بالايي يك تراز، تاثير مثبتي در مقاومت بتن خودمتراكم در آن تراز دارد. علاوه بر مقايسه‌ي نتايج به‌دست‌آمده با نتايج متناظر بتن معمولي، تاثير تغييرات درصد خاكستر بادي و دانه‌بندي در مقاومت‌هاي به‌دست‌آمده در اين نوشتار نيز بررسي شده‌اند.

Despite the fact that self-compacting concrete has been used for many years, until now, no-one has carried out any research on the strengthening effect of the weight of concrete at any level. For this reason, employing concrete columns made out of different mixes of self-compacting concrete, a research is conducted. In order to measure the concrete strength at any level, the in-situ friction-transfer method was used. Having examined over 50 mix designs, nine mixes were proved to be self-compacting concrete and, therefore, were used for this investigation. In order to see the effect of the weight of the concrete above the level considered, concrete columns were cast using self-compacting concrete without giving any form of compaction. At specified ages, the hardened concrete columns were cut at 150 mm height intervals. Using the Friction-transfer method, the strengths of concrete at different levels were obtained. In the friction-transfer method, a 50 mm diameter partial core is made using a diamond tipped coring drill. A metallic gripping device is fixed on top of this partial core by fastening its side bolts, and torsional moment is applied to the partial core via this gripping device by hand. The applied torsional moment is gradually increased until the partial core is failed, and the maximum (failure) torsional moment is recorded. Using the existing calibration graphs, the ultimate (failure) torsion is converted to the compressive strength of the concrete tested. The results show that the weight of the concrete situated above any level has a positive effect on the strength of the concrete at that level. In addition to the comparison of the obtained results with the respective results of ordinary concrete, the effect of changes in the fillers, segregation and aggregate grading, on the strength of self-compacting concrete, is also studied.