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Designing and Proportioning Normal Concrete Mixtures
This article mainly talk about designing and Proportioning Normal Concrete Mixtures in accordance with concrete mixture features, proportion, application and quality.
According to concrete material characteristics
The process of determining required and specifiable characteristics of a concrete mixture is called mix design. Characteristics can include:
(1)fresh concrete properties;
(2)required mechanical properties of hardened concrete such as strength and durability requirements;
(3) the inclusion, exclusion, or limits on specific ingredients. Mix design leads to the development of a concrete specification.
According to Mixture proportioning
Mixture proportioning refers to the process of determining the quantities of concrete ingredients, using local materials, to achieve the specified characteristics of the concrete. A properly proportioned concrete mix should possess these qualities:
1. Acceptable workability of the freshly mixed concrete
2. Durability, strength, and uniform appearance of the hardened concrete
Understanding the basic principles of mixture design is as important as the actual calculations used to establish mix proportions. Only with proper selection of materials and mixture characteristics can the above qualities be obtained in concrete construction (Abrams 1918, Hover 1998, and Shilstone 1990).
Before a concrete mixture can be proportioned, mixture characteristics are selected based on the intended use of the concrete, the exposure conditions, the size and shape of building elements, and the physical properties of the concrete (such as frost resistance and strength) required for the structure. The characteristics should reflect the needs of the structure; for example, resistance to chloride ions should be verifiable and the appropriate test methods specified.
Once the characteristics are selected, the mixture can be proportioned from field or laboratory data. Since most of the desirable properties of hardened concrete depend primarily upon the quality of the cementitious paste, the first step in proportioning a concrete mixture is the selection of the appropriate water-cementing materials ratio for the durability and strength needed. Concrete mixtures should be kept as simple as possible, as an excessive number of ingredients often make a concrete mixture difficult to control. The concrete technologist should not, however, overlook the opportunities provided by modern concrete technology.
List features and proportion of concrete materials, Designing and Proportioning Normal Concrete Mixtures are also tested in accordance quantity of tests to decide how to mix the concrete materials.
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