بررسی اثر مقاومت، زمان و مقدار فشار آب و جهت بتن‎ریزی بر نفوذپذیری بتن

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران

چکیده

به دلیل نفوذ عوامل مخرب به داخل بتن و کاهش پایایی آن، اطالع از میزان نفوذپذیری بتن بسیار مهم می باشد. در آیین‌نامه‌ها، نفوذپذیری بر اساس فشار و زمان مشخصی انجام می‌شود. درصورتی‌که مقدار فشار و مدت اعمال آن از عوامل مهم نفوذپذیری می‌باشند. لذا، اثر مقدار فشار، مدت اعمال آن و جهت بتن‌ریزی بر نفوذپذیری نمونه‌های مکعبی بتنی ساخته شده با استفاده از سنگدانه‌های خشک و نسبت‌های آب به سیمان پرتلند نوع 2 برابر با0/4 ،0/5 و 0/6 در سنین 7 ،28 و 91 روز با استفاده از روش “محفظه استوانه‌ای” بررسی شده است. همچنین روش “پیچش” برای تعیین مقاومت نمونه‌ها بکاررفته است. نتایج بدست آمده نشان می‌دهند رابطه خطی بین تنش برشی حاصل از پیچش و مقاومت فشاری وجود داشته و نفوذپذیری در جهت بتن ریزی کمتر از جهت عمود بر آن بوده و مقدار توان به دست آمده در تقریب ً ثابت رابطه بین حجم و عمق نفوذ با مقدار فشار، صرف‌نظر از نسبت آب به سیمان، در یک سن و جهت مشخص تقریبا است. این موضوع در تقریب رابطه بین حجم و عمق نفوذ با مدت اعمال فشار با استفاده از تابع توانی مشاهده نگردید. رابطه معکوسی بین مقاومت فشاری و نفوذپذیری نمونه‌ها نیز مشاهده گردید. همچنین رابطه بین عمق و حجم نفوذ با استفاده از تابع خطی با دقت بسیار بالایی تقریب زده شد. اعداد رینولدز محاسبه شده نیز نشان‌دهنده جریان لایه‌ای نفوذ آب در نمونه‌های بتنی است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Evaluation of the effect of strength, duration, water pressure and casting direction on concrete permeability

نویسندگان [English]

  • Mahmood Naderi
  • Alireza Kaboudan
Department of civil engineering, Faculty of engineering, International Imam Khomeini university, Qazvin, Iran
چکیده [English]

One of the major factors which controls the serviceability life of a concrete structure is 
its durability. Since the durability is dependent mainly on the permeability, some standards such as BS 
EN 12390-8 and DIN 1048-5 are aimed for water permeability assessment of concrete. Based on these 
standard test methods, a constant pressure is applied to the concrete surface, perpendicular to casting 
direction for a specific period of time. Since the applied water pressure, test duration and the direction 
of casting affect the concrete permeability, 150mm concrete cubes with water/cement ratios of 0.4, 0.5 
and 0.6 were prepared and at the ages of 7, 28 and 91 days (after water curing) the permeability of the 
cubes was investigated, using “Cylindrical chamber” method. The results show that the penetration 
depth and volume in the casting direction are lower than the respective values, obtained in the direction, 
perpendicular to casting. It was also observed that, regarding the water/cement ratio, the exponent of 
the power function used to approximate the relation of penetration depth and volume with pressure, 
is approximately constant at a specific age and testing direction. This issue wasn’t observed when 
approximating the relation of penetration depth and volume with test duration, using the power function. 
A linear relationship between the penetration depth and the penetration volume was also observed.

کلیدواژه‌ها [English]

  • Concrete
  • Permeability
  • Cylindrical chamber method
  • Water Pressure
  • Test duration
  • Direction of casting
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