Design and Control of concrete mix
Design and Control of concrete mix:
method of concrete mix design
- american concrete institute
- bureau of Indian standards method is 10262-82
- road ( grading curve ) method
- department of environment (doe) method
- trail and adjustment method
- fitness modulus method
- maximum density method
- 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.
0 Comments