Precast concrete materials, manufacture, properties and usage - Chapter 1

MOULDS AND MATERIALS - Với ngoại lệ của phụ gia tro bay, tất cả các khuôn mẫu và các tài liệu được thảo luận trong chương này. Không ai trong số các yếu tố được liệt kê có thể được xem xét trong sự cô lập kể từ khi sự thay đổi trong một thường sẽ ảnh hưởng đến người khác. Kết hợp thiết kế cho các hình thức khác nhau của sản xuất bê tông đúc sẵn được xử lý trong Chương 6. Mục đích của chương này là để làm quen người đọc với tất cả các. | 1 MOULDS AND MATERIALS With the exception of admixtures and fly ash all moulds and materials are discussed in this chapter. None of the factors listed can be considered in isolation since variation in one will often affect another. Mix design for various forms of precast manufacture is dealt with in Chapter 6. The purpose of this chapter is to acquaint the reader with all the starting variables. The background picture will then be fully understood before one proceeds to put these variables into a process in order to produce a precast concrete product. MOULDS Moulds are basically means by which a concrete is kept to a required shape until it is strong enough to be demoulded or b concrete is moulded on a machine and retains that shape on virtually instant demoulding or c concrete is shaped immediately after casting using an additional or secondary mould acting on previously un-moulded surfaces. In the sections that follow are outlined the types of moulding materials available and how they should be selected. Due to geographical and or economic reasons one might be forced to a second or third choice and this is acceptable provided that the persons responsible for this choice appreciate the limitations in use. Notwithstanding all other factors the one thing that all moulding techniques and moulds have in common are dimensions. Whether these be critical for structural architectural and or contractual reasons is a matter Copyright Applied Science Publishers Ltd 1982 that causes quite a lot of argument. It is imperative that one appreciates the reasons for dimensions and what tolerances are permissible when combining the two fields of manufacture and installation. The specification for the product should state strictly what is required bearing in mind what is practical and how the product is to fit into the main construction. All too often precast products such as cladding are specified on a dimension such as A -ỉ where A is the target dimension often called the work