CONCRETE IN HOT ENVIRONMENTS - CHAPTER 2

Setting and Hardening - Thiết lập và cứng của xi măng có thể được mô tả và thảo luận từ ba điểm khác nhau xem hiện tượng hóa học, cấu trúc và. Các điểm hiện tượng xem, theo định nghĩa, là có liên quan với những thay đổi trong hệ thống nước xi măng (hoặc bê tông),, chỉ cảm nhận được hoặc chứng minh bằng các giác quan. Các điểm hóa học của xem là có liên quan với các phản ứng hóa học tham gia, tính chất và thành phần của các sản phẩm phản ứng. Cuối cùng,. | Chapter 2 Setting and Hardening . INTRODUCTION Setting and hardening of cement can be described and discussed from three different points of view phenomenological chemical and structural. The phenomenological point of view by definition is concerned with the changes in the cement-water system or the concrete which are only perceptible to or evidenced by the senses. The chemical point of view is concerned with the chemical reactions involved and the nature and composition of the reactions products. Finally the structural point of view is concerned with the structure of the set cement and with the possible changes in this structure with time. Hence the following discussion is presented accordingly. This discussion mainly considers the cement paste . a paste which is produced as a result of mixing cement with water only. Nevertheless it is valid and applicable to mortar and concrete as well because under normal conditions the aggregate is inert in the cement-water system and its presence therefore does not affect the processes involved. . THE PHENOMENA Mixing cement with water produces a plastic and workable mix commonly referred to as a cement paste . These properties of the mix remain unchanged Copyright 1993 E FN Spon Fig. . Schematic description of setting and hardening of the cement paste. Adapted from Ref. . for some time a period which is known as the dormant period . At a certain stage however the paste stiffens to such a degree that it loses its plasticity and becomes brittle and unworkable. This is known as the initial set and the time required for the paste to reach this stage as the initial setting time . A setting period follows during which the paste continues to stiffen until it becomes a rigid solid . final set is reached. Similarly the time required for the paste to reach final set is known as final setting time . The resulting solid is known as the set cement or the hardened cement paste . The hardened paste continues to gain .

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