Design and Control of concrete mix | ACI Method Mix Design

Design and Control of concrete mix

Design and Control of concrete mix:

method of concrete mix design

1. american concrete institute
2. bureau of Indian standards method is 10262-82
3. road ( grading curve ) method
4. department of environment (doe) method
5. trail and adjustment method
6. fitness modulus method
7. maximum density method
8. Indian road congress

ACI mix design:

the most common method used in north america is that established by ACI method practice 211.1. any mix design procedure will provide a first approximation of the proportions and must be checked by trail batches. local characteristics in materials should be considered.

conventional pcc cement 11% water 16 % air 6% fine aggregate 26% and coarse aggregate 41%

American concrete institute (aci):

• fineness modulus of fine aggregates
• sp.gravity of coarse and fine aggregate
• absorption characteristics of coarse and fine aggregate
• sp.gravity of cement

 ACI method of proportioning concrete mixes :

step1: choice of slump

if slump is not specified, a value appropriate for the work can be selected from concrete

Measuring of slump:

the concrete slump test measures the consistency of fresh concrete before is sets. it is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows, it can also improperly mixed batch.

step2 : choice of maximum size aggregate

one fifth of the narrowest dimension between sides of forms. one third the depth of slabs. 3/4 of the minimum clear spacing between individual reinforcing bars, bundles of bars, or pre-tensioning strands.

step3 : Estimation of mixing Water and Air Content

the quantity of water per unit volume of concrete required to produce a given slump is dependent on

• nominal maximum size of the aggregate
• grading of the aggregate
• amount of entrained air
• concrete temperature

step4: selection of water cement ratio

the most important indicator of strength, lower w/c ratio is the higher the final concrete strength

              pounds per square inch     1psi=6895N/m2

step5 : calculation of cement content

the amount of cement is fixed by the determination made in steps 3 and 4 above

            weight of cement = weight of water / water cement ratio

step6 : Estimation of coarse aggregate content

the percent of coarse aggregate to concrete for a given maximum size and fineness.

step7 : Estimation of fine aggregate content

     specific gravity = weight of substance / weight of equal volume of water

volume of fine aggregates = total concrete volume - ( the volume of cement,water, air and coarse aggregate)

step8 : adjustment for aggregate moisture aggregate weights

aggregate volume are computed based on oven dry unit weights, but aggregate is typically batched based on actual weights

step9 : trail batch adjustments

the ACI method is written on the basics that trail batch of concrete will be prepared in the laboratory and slump.