CONCRETE IN HOT ENVIRONMENTS - CHAPTER 8

Creep - Creep có thể được định nghĩa là sự gia tăng biến dạng theo thời gian, không bao gồm co rút, dưới một áp lực duy trì. Như vậy sự biến dạng xảy ra trong các kim loại ở nhiệt độ cao nhưng trong bê tông nó diễn ra ở nhiệt độ phòng. Do đó, tầm quan trọng của hành vi leo trong thực tế hàng ngày. Trong các cuộc thảo luận sau đây một sự phân biệt không phải lúc nào cũng thực hiện giữa dán xi măng và bê tông. Creep hành vi cụ thể về cơ. | Chapter 8 Creep . INTRODUCTION Creep may be defined as the increase in deformation with time excluding shrinkage under a sustained stress. Such a deformation occurs in metals at elevated temperatures but in concrete it takes place at room temperatures as well. Hence the importance of the creep behaviour in daily practice. In the following discussion a distinction is not always made between cement paste and concrete. Creep behaviour of concrete is essentially similar to that of the paste because the aggregate hardly exhibits any creep. Hence in discussing creep qualitatively paste and concrete are interchangeable. On the other hand aggregate properties and concentration affect creep quantitatively and in this context there is a significant difference between creep of the cement paste and that of concrete. This aspect however is dealt with later in the text see section . Finally creep is usually measured by the length changes involved and is expressed quantitatively by the corresponding strains A1 10 or by the corresponding strains per unit stress. The latter is known as specific creep see section . Copyright 1993 E FN Spon Fig. . Schematic description of the deformation with time of concrete under sustained compressive load and undergoing a simultaneous drying shrinkage. . THE PHENOMENA On loading concrete undergoes an instantaneous deformation which is generally regarded as elastic . a deformation which appears and disappears completely immediately on application and removal of the load respectively. If the load is sustained the deformation increases at a gradually decreasing rate and may reach a value which is two to three times greater than the elastic deformation. If the concrete is allowed to dry when under load shrinkage occurs simultaneously. Accordingly creep is the increase in deformation with time under a sustained load excluding drying shrinkage. This is demonstrated in Fig. for a concrete loaded in compression. It may be .

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