tailieunhanh - Precast concrete materials, manufacture, properties and usage - Chapter 3

PIGMENTS - Sắc tố có thể được định nghĩa là một loại bột khô tốt, hoặc đình chỉ dịch nước hoặc bùn bột, trơ với các thành phần của bê tông, và có ý định truyền đạt một màu sắc cụ thể cho sản phẩm. Từ 'dự định truyền đạt "là cơ sở của chương này bao gồm thảo luận về những gì các sắc tố, làm thế nào họ và hiệu suất của chúng có thể được đánh giá và triển khai thực tế của họ. Các chất màu có sẵn trong một hình dạng và kích cỡ. | 3 PIGMENTS A pigment can be defined as a fine dry powder or aqueous suspension or slurry of the powder inert to the ingredients of concrete and intended to impart a specific colour to the product . The words intended to impart are the basis of this chapter which includes discussion on what pigments are how they and their performance can be assessed and their practical deployment. Pigments are available in a variety of particle shapes and sizes but the property they have in common is that they all have a minimum particle size smaller than the finest cement one would use and rely on their smearing power over the cement and fine aggregate fractions to achieve coloration. Obviously the colours of the cement and the fine aggregate play important roles in determining the final colour of the concrete or mortar and are important in the selection of concrete ingredients. Colour is also affected by the type of formwork or mould materials release agent finishing treatment if used and curing conditions. To obtain uniform appearance of the product requires stringent controls of these variables. Other variables associated with colour are discussed in detail later but one general aspect worth mentioning at this stage is fading of pigments. By the definition given above there should be no such thing as fading. The staining power of a pigment can be masked by lime leaching over the pigment as well as by carbonation of that lime. In the cases of open-textured concretes and mortars or when poor quality soft carbon blacks are used pigments can be washed out by the weather. There is also some evidence that at high temperature . 40-60 C and high humidity carbon becomes slowly oxidised. Copyright Applied Science Publishers Ltd 1982 TYPES OF PIGMENT The most common types of pigment are the metallic oxides and hydroxides with those based upon iron furnishing yellow brown black and red colours and mixtures thereof. Chromic oxide and hydroxide give green colours cobaltic oxide blue .