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CONCRETE IN HOT ENVIRONMENTS - CHAPTER 1

Portland Cement - Xi măng Portland là một chất kết dính thủy lực hoạt động, tức là một "chất kết dính để thiết lập và cứng lại bởi sự tương tác hóa học với nước và có khả năng làm như vậy dưới nước mà không có sự bổ sung của một hoạt hóa như vôi" (BS 6100, phần 6,1, 1984). Đó là thu được bằng cách đốt cháy, ở nhiệt độ clinke (khoảng 1450 ° C), một hỗn hợp đồng nhất định trước của các vật liệu bao gồm vôi (CaO), silic (SiO2), một tỷ lệ nhỏ các. | Chapter 1 Portland Cement 1.1. INTRODUCTION Portland cement is an active hydraulic binder i.e. a binder that sets and hardens by chemical interaction with water and is capable of doing so under water without the addition of an activator such as lime BS 6100 section 6.1 1984 . It is obtained by burning at a clinkering temperature about 1450 C a homogeneous predetermined mixture of materials comprising lime CaO silica SiO2 a small proportion of alumina Al2O3 and generally iron oxide Fe2O3 . The resulting clinker is finely ground i.e. average particle size of 10 pm together with a few percent of gypsum to give what is commonly known as Portland cement. This is however a generic term for various forms types of Portland cement which include in addition to ordinary Portland cement OPC rapid-hardening Portland cement RHPC low-heat Portland cement LHPC sulphate-resisting Portland cement SRPC and several others. It will be shown later that the different forms of the cement are produced by changing the proportions of the raw materials and thereby also the mineralogical composition of the resulting cements see section 1.5 . Copyright 1993 E FN Spon 1.2. MAJOR CONSTITUENTS Cement is a heterogeneous material made up of several fine-grained minerals which are formed during the clinkering process. Four minerals namely Alite Belite Celite and a calcium-aluminate phase make up some 90 of the cement and are collectively known therefore as major constituents . Accordingly the remaining 10 are known as minor constituents . The structure of the cement constituents is not always exactly known and in engineering applications their composition is usually written therefore in a simple way as made up of oxides i.e. in a form which although representing their chemical composition does not imply any specific structure. For example the composition of the Alite which is essentially tricalcium silicate is written as 3CaO.SiO2. Moreover in cement chemistry it is usual to describe each oxide by a