Classification of Concrete Mix Design

Concrete Mix design stands for the method of choosing proper components of concrete and ascertaining their proportionate amounts in order to develop a concrete by maintaining the necessary strength, longevity, and adaptability as inexpensively as possible.

The ratio of concrete component is managed by the necessary operation of concrete in 2 states alias the plastic and the hardened states. If the plastic concrete is nonfunctional, it becomes difficult to arrange & compact the concrete preciously. Therefore, functionality of concrete is considered as a crucial point.

Factors affecting the concrete mix design

The selection and parting of mix ingredients are dependent on the following factors :

a) The lowest compressive strength is necessary from structural point of view
b) The acceptable workability is required for full compaction with the existing compacting equipment.
c) Extreme water-cement ratio and/or extrene cement content to give acceptable strength for the specific site conditions
d) Maximum cement content to get rid of shrinkage cracking because of temperature cycle in mass concrete.

Types of Mixes

1. Nominal Mixes: Earlier the specifications for concrete set the ratios of cement, fine and coarse aggregates. These mixes of fixed cement-aggregate ratio which guarantee the suitable strength are called nominal mixes. Because of the changeability of mix ingredients, the nominal concrete for a specified workability differs extensively in strength.

2. Standard mixes: The nominal mixes of fixed cement-aggregate ratio (by volume) extensively differ in strength and may lead to under- or over-rich mixes. Consequently, the minimum compressive strength is contained in various specifications. These mixes are called standard mixes.

IS 456-2000 has labeled the concrete mixes into different types of grades as M10, M15, M20, M25, M30, M35 and M40. Here, the letter M stands for mix and N/mm2 stands for the number to the indicated 28 day cube strength of mix. The mixes of grades M10, M15, M20 and M25 relate roughly to the mix proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2) correspondingly.

3. Designed Mixes: In these mixes, the designer indicate the workability of the concrete but the mix proportions are set by the producer of concrete, excepting that the lowest cement content is disposed of. This is most reasonable approach for choosing mix proportions with definite materials in mind retaining relatively unique characteristics. The approach facilitates generating concrete with the perfect properties most inexpensively. But, the calculated mix can’t be considered as a guide as this does not ensure the proper mix proportions for the recommended performance.

Article Source: theconstructor.org