Concrete mix ratio is a process of optimizing a number of desirable characteristics based on the requirements of the project.
Features to be customized Economy, Strength, Tolerance, And locality,
The primary reason for systematically determining mix ratios is economy. Maximum economy can usually be achieved by reducing the amount of cement used and where appropriate, by replacing Portland cement with less expensive pozzolana or GGBF slag. Economy is also improved by conforming to the dimensional requirements of the structures on the project and using the largest nominal maximum size aggregate available for the project.
Strength is an important characteristic of concrete but other characteristics such as durability, permeability and wear resistance may be equal or more important. These may be related to power in general but depend on other factors as well.
For a given set of materials, the strength is inversely proportional to Welcome,
Since the materials that make up concrete are complex and variable, an accurate prediction of strength cannot be based solely on the selected w/c, but confirmed with the material used on the project by testing of cylinders made from test batches Should be known The strength at 28 days of age is often used as a parameter for structural design, proportion of concrete, and evaluation of concrete. When concrete is used on a large scale, the design strength is usually required to exceed 28 days, typically 90 days, because the mixture may pozzolana in relatively large quantities to reduce internal heat production. or GGBF are in proportion to the slag. Mass concrete will have lower starting strength than structural concrete; Therefore, the mass of the concrete should be proportional to the sufficient initial strength as may be required to remove the form and create anchorages. A compressive strength of 500 psi at 3 days of age is required to meet form-removal and anchorage requirements.
Concrete must resist deterioration by the environment to which it is exposed, including freezing and thawing, wetting and drying, chemical attack and abrasion. Concrete must meet three requirements before it can be considered immune to frost action. It must be made with non-frost sensitive aggregates and a proper air-voiding system, and it must achieve a reasonable degree of maturity before the concrete is allowed to undergo repeated freezing and thawing when severely saturated. All exposed concrete held by the core must be air-applied unless it is shown to be inappropriate for a specific condition. Suitable maturity occurs when the concrete has a compressive strength of about 3,500 psi. In general, using less w/c also improves durability as it reduces permeability and penetration of aggressive fluids.
Playability, including satisfactory finishing characteristics, encompasses the characteristics described by the terms “functionality” and “consistency”. Workability is the property of freshly mixed concrete that determines the ease and uniformity with which it can be mixed, laid, consolidated and finished. Consistency is the relative mobility or ability of freshly mixed concrete to flow.
Functionality encompasses concepts such as moldability, cohesion, and compactability and is influenced by grading, particle size, and ratio of aggregate; quantity and properties of the cement material used; the presence or absence of air and chemical mixtures; and consistency of the mixture. recession test, ASTM C 143 The term “playability” is the only test commonly available to measure any aspect of the many features included.
Moldability, cohesion, compactness, and finishability are mostly evaluated by visual observation, and therefore, evaluations are somewhat subjective. Typically, the contractor will evaluate these characteristics from a different perspective than the government personnel involved, and within the contractor’s organization, the placement foreman may evaluate the space differently than the finishing foreman. In general, the contractor wants a high-recession mix, while the government wants a closely controlled recession. The main consideration should be a carefully proportioned concrete mix that can be placed at the placement site by conveying and placing equipment used on the project without the addition of water. Simply adjusting the water content of a mix that was proportional to placement by crane and bucket will not assure that it is pumpable or that such adjustments will result in concrete that meets strength and durability requirements. Massive concrete mixes are particularly susceptible to having problems if not proportioned correctly. Care must be taken to ensure that the mortar content of the lean, mass concrete mix is sufficient to provide suitable space and workability. Water-reducing mixtures should not be used to reduce the paste material and the resulting mortar content of these mixtures to a level that makes the mixture hard and unusable.