بررسی اثر افزودنی کاهنده جمع‌شدگی در بتن مورد استفاده در روسازیهای بتنی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه راه و ترابری، دانشکده مهندسی عمران و محیط زیست، دانشگاه صنعتی امیرکبیر

2 دانشگاه صنعتی امیر کبیر، تهران، ایران

3 دانشگاه صنعتی امیرکبیر، تهران، ایران

4 دانشگاه تهران، تهران، ایران

چکیده

کاهش منابع نفتی و طول عمر نه چندان بالای روسازی‌های آسفالتی، استفاده از روسازی بتنی را در جهان، مورد توجه قرار داده است. یکی از مشکلات اصلی روسازی‌های بتنی، پدیده جمع‌شدگی (مخصوصاً ناشی از خشک شدن) است که در اثر از دست رفتن آب موجود در ساختار بتن ایجاد و سبب ایجاد تنش کششی در سطح المان‌های آن می‌گردد که اگر تنش ایجاد شده از مقاومت کششی بتن بیشتر باشد، ترک‌هایی در سطح بتن پدیدار می‌شود. افزودنی کاهنده جمع‌شدگی از جمله موادی است که به واسطه کاهش کشش سطحی و فشار جداکننده، سبب کاهش تنش کششی ایجاد شده در بتن می‌شود. هدف از انجام این پژوهش، بررسی اثر افزودنی کاهنده جمع‌شدگی بر مشخصات فیزیکی و مکانیکی بتن مورد استفاده در روسازی‌های بتنی می‌باشد. آزمایش‌های اسلامپ، مقاومت فشاری، خمشی، الکتریکی، اصطکاک سطحی، جمع‌شدگی‌های آزاد و مقید بر روی بتن شاهد و بتن حاوی ماده کاهنده جمع‌شدگی (2 درصد وزن سیمان) در دو نسبت آب به سیمان 0/35 و 0/4 انجام شد. نتایج نشان‌دهنده آن است که استفاده از ماده کاهنده جمع‌شدگی تأثیر چندانی بر کارایی بتن نگذاشته است. کاربرد این ماده در بتن سبب کاهش حدود 10 درصدی مقاومت فشاری، خمشی و الکتریکی می‌شود. به علاوه این ماده میزان جمع‌شدگی آزاد، مقید و عرض ترک‌های ایجاد شده را به ترتیب حدود 10، 20 و 40 درصد کاهش می‌دهد و سن ترک‌خوردگی را حدود 7 روز به تأخیر می‌اندازد. با این حال تأثیر این افزودنی بر روی اصطکاک سطحی واضح و مشخص نمی‌باشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The Effect of Shrinkage Reducing Admixture on the Behavior of Concrete used in Concrete Pavements

نویسندگان [English]

  • masood gholami 1
  • Fereidoon Moghadas Nejad 2
  • Aliakbar Ramezanianpor 3
  • Amir mohammad Ramezanianpour 4
1 highway and transportation engineering, department of civil and environmental engineering, amirkabir university of technology
2 Dep. of Civil Engineering, Amirkabir University of Technology, tehran, iran
3 department of civil and environmental engineering, amirkabir university of technology, tehran, iran
4 Tehran university, tehran, iran
چکیده [English]

Concrete pavements are widely used by pavement engineers due to their advantages over flexible pavements such as long lifetime, good performance and durability, etc. However, concrete pavements represent some drawbacks such as shrinkage that increases the tensile stress in concrete, which may lead to cracking, warping, etc. Drying shrinkage is the most important type of shrinkage in concrete pavements. To prevent or reduce the amount of cracking, shrinkage reducing admixture (SRA) can be used. This admixture controls shrinkage by reducing water surface tensile in capillary tubes. In this study, the effect of shrinkage reducing admixture on the behavior of concrete used in concrete pavements was investigated. Slump, compressive strength, third-point flexural strength, electrical resistance, skid resistance, free shrinkage, and restrained shrinkage by ring test were performed. Two water-cement ratios of 0.35 & 0.4 were used for mix design and the percentage of shrinkage reducing admixture used in mixtures was 2% by weight of cement. The results showed that the use of SRA had a negligible effect on workability. Also, the use of SRA caused about a 10% reduction in compressive and flexural strength and electrical resistance. Furthermore, a reduction of 10% and 20% was observed in free and restrained shrinkages, respectively, followed by a 40% reduction in crack width and more than one-week delay in the occurrence of the first crack. Finally, no certain relationship was observed between the usage of SRA and variations of the skid resistance of concrete pavements.

کلیدواژه‌ها [English]

  • concrete pavement
  • Drying shrinkage
  • tensile stress
  • Shrinkage cracks
  • Shrinkage reducing admixture
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