Kết cấu xây dựng phục vụ việc tính toán và thiết kế công trình trong ngành xây dựng. Đó là một công cụ cho việc thiết kế xây dựng và cùng với lý thuyết mô hình hóa và lý thuyết cấu kiện, nó hình thành nên lý thuyết công trình. | Table Moisture movement in different building materials Materials Movement Irreversible Reversible Clay bricks expansion negligible Calcium silicate Metal and glass nil nil Dense concrete and mortar drying shrinkage m intervals as a general rule. However the length of the panel without movement joint should not exceed twice the height. Some indication of reversible or irreversible movement of various building materials is shown in Table . The EC6 gives guidance for the design values of dimensional changes for unreinforced masonry which are given in Chapter 4 section . Soluble salts a Efflorescence All clay bricks contain soluble salts to some extent. The salt can also find its way from mortar or soil or by contamination of brick by foreign agents. In a new building when the brickwork dries out owing to evaporation of water the dissolved salts normally appear as a white deposit termed efflorescence on the surface of bricks. Sometimes the colour may be yellow or pale green because of the presence of vanadium or chromium. The texture may vary from light and fluffy to hard and glassy. Efflorescence is caused by sulphates of sodium potassium magnesium and calcium not all of these may be present in a particular case. Efflorescence can take place on drying out brickwork after construction or subsequently if it is allowed to become very wet. By and large efflorescence does not normally result in decay but in the United Kingdom magnesium sulphate or sodium sulphate may cause disruption due to crystallization. Abnormal amounts of sodium sulphate constituting more than 3 by weight of a brick will cause disruption of its surface. Brick specimens showing efflorescence in the heavy category are not considered to comply with BS 3921. b Sulphate attack Sulphates slowly react in the presence of water with tricalcium aluminate which is one of the constituents of Portland cement and 2004 Taylor Francis hydraulic .
