Editing Concrete (section)

===Design mix===
''Design mix'' ratios are decided by an engineer after analyzing the properties of the specific ingredients being used. Instead of using a 'nominal mix' of 1 part cement, 2 parts sand, and 4 parts aggregate, a civil engineer will custom-design a concrete mix to exactly meet the requirements of the site and conditions, setting material ratios and often designing an admixture package to fine-tune the properties or increase the performance envelope of the mix. Design-mix concrete can have very broad specifications that cannot be met with more basic nominal mixes, but the involvement of the engineer often increases the cost of the concrete mix.

Concrete mixes are primarily divided into nominal mix, standard mix and design mix.

Nominal mix ratios are given in volume of <math>\text{Cement : Sand : Aggregate}</math>. Nominal mixes are a simple, fast way of getting a basic idea of the properties of the finished concrete without having to perform testing in advance.

Various governing bodies (such as [[British Standards]]) define nominal mix ratios into a number of grades, usually ranging from lower [[compressive strength]] to higher compressive strength. The grades usually indicate the 28-day cure strength.<ref>{{cite web |url=http://www.civilology.com/grades-of-concrete/ |title=Grades of Concrete with Proportion (Mix Ratio)| date=26 March 2018}}</ref>