Concrete Fracture_ شکستگی بتن

Concrete Fracture

شکستگی بتن

Fracture mechanics of concrete remains an important topic of research. The material and structures made of concrete are prone to cracking caused by a variety of reasons. Mechanical loading is one important cause, but other physical loadings such as differential drying, temperature gradients, and chemical attack may also lead to severe cracking and deterioration of structures. The inherent reduction of serviceability time is not acceptable, especially in a world where resources are becoming scarce and global warming threatens the living conditions of all creatures on our home planet. During the production of cement a large emission of greenhouse gases is inevitable; roughly one metric ton of CO2 is emitted for the production of one metric ton of cement, reason enough to limit the use of cement as a building material, not only through a direct decrease of the amount of cement used, but also by providing longer service time for new and existing structures. Both for the development of new high-performance cement composites, as for the improvement of the durability of concrete structures, fracture mechanics plays a key role. Concrete cracking is primarily caused by the material’s low tensile resistance. For ordinary concrete with a compressive strength of around 40 MPa, we may expect a tensile strength of no more than 10% of the compressive, thus approximately 4 MPa is the maximum. The imbalance between tensile and compressive strength is traditionally taken care of through the use of steel reinforcement placed at those locations where the highest tensile stresses appear in the considered structure. The main reason the joint venture between steel and concrete is successful is their almost identical thermal expansion coefficient. Moreover, the bond between steel and concrete is sufficiently good to allow for short anchorage length of the rebar. In principle the combination is ideal, yet problems arise owing to the relatively high porosity and often good permeability of the concrete cover of the steel reinforcement.
Bad workmanship may do the rest, and given sufficient amounts of water and oxygen the rebar may start to corrode once the protective oxide layer is passivated, either through the ingress of chlorides, or through carbonation of the cover concrete. Cracks may facilitate the ingress of corrosive media; therefore there is interest in reducing crack widths to a minimum, or to prevent cracking altogether. The swelling of a corroding rebar may lead to substantial increase of cracking, thereby accelerating the corrosion process, depending on the actual climatic conditions. In summary, there is an interest in developing high-tensile strength concrete, which resists higher tensile stresses, and thereby reduces the probability for crack nucleation and growth. High-performance concretes are usually much denser than the aforementioned average quality, and as an additional advantage there is reduced permeability and the protective cover may perform much better leading to substantial improvement of the service lifetime of the structure. Of course there are many influence factors when the durability and service lifetime of concrete structures are considered, but because cracking is the major deterioration mechanism, it seems quite appropriate to give some attention to fracture processes in concrete and concrete structures, investigate causes for cracking, and to develop models that can “predict” the
whereabouts of cracks during any stage of the lifetime of a concrete structure. Since the beginning of the 1970s there has been a steadily increasing interest in developing robust and reliable models that can simulate concrete cracking; much of the development is certainly caused by the introduction of the finite element method and other numerical simulation techniques in science and engineering. One expression that has been heard a lot over the past decades is that
improvements in the said computer models may eventually reduce the role of experiments, if not make experiments completely obsolete.

شکستگی بتن

شکستگی بتن

شکستگی بتن

برای دانلود این کتاب بر روی دانلود کلیک کنید

دانلود

دیدگاهتان را بنویسید لغو پاسخ

بازگشت به بالا

صنایع شیمیایی بتنو

دسترسی سریع

راه‌های ارتباطی

چرا ما

درباره بتنو:

بتنو به عنوان تولید کننده صنایع شیمیایی تاثیرگذار و پر مخاطب در عرصه صنعت بتن آماده و قطعات بتنی پیش ساخته و کلیه صنایع وابسته به بتن (تولید کنندگان سیمان پوزولان، سنگدانه، افزودنی های بتن، ادوات و تجهیزات تولید، حمل نقل و غیره) فرصت های بی نظیری را برای تان فراهم کرده است.

© کپی رایت 2025 | کلیه حقوق مادی و معنوی متعلق به بتنو می باشد