Concrete Mix Design Manual Rev08-19 - NCDOT

CONCRETE MIX DESIGN TECHNICIAN

STUDY GUIDE

Prepared by:

North Carolina Division of Highways

Materials and Tests Unit

Revised August 2019

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Table of Contents

Table of Contents .......................................................................................................... 2

Section I: Basics of Mix Design ..................................................................................... 3

Section II: Sieve Analysis of Coarse and Fine Aggregate .......................................... 20

Section III: Study Problems Sieve Analysis of Coarse and Fine Aggregate .............. 32

Section IV: Fineness Modulus ..................................................................................... 38

Section V: Study Problems Fineness Modulus ........................................................... 43

Section VI: Weight ¨C Volume Relationships .............................................................. 48

Section VII: Problems Weight / Volume Relationships ............................................ 57

Section VIII: ACI Concrete Mix Design ..................................................................... 66

Section IX: NC DOT Concrete Mix Design Specifications ........................................ 83

Section X: Study Problems ACI Mix Design .............................................................. 92

Section XI: ACI Mix Design Variations ................................................................... 106

Section XII: Quality Concrete and Field Inspection/Control .................................. 120

Appendix A: Frequently Asked Questions .................................................................. 143

Appendix B: Glossary of Terms and Definitions ........................................................ 148

Appendix C: Study Questions .................................................................................... 152

Appendix D: Mathematical Formulas ......................................................................... 163

Appendix E: Mix Design Forms ................................................................................. 164

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Section I

Basics of Mix Design

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Introduction

Concrete is a material made of cement/cementitious materials, water, and aggregates. It

has been used for many years in Earth¡¯s history as a building material for structures such

as bridges, houses, dams, highways, sidewalks, and skyscrapers. Concrete has several

properties such as strength and durability and can be cast into any shape, form and

texture, and be colored for aesthetics. Unfortunately, there are some challenges still faced

today in delivering uniform and high quality concrete products, and therefore, concrete

technologies continue to be developed to modify and improve both properties of fresh

and hardened concrete.

Concrete mix design is the process of selecting suitable ingredients of concrete and

determine the relative proportions to produce concrete with certain performance and

durability requirements. Different concrete mix designs with different materials, even

with the same proportions, can have significantly different properties of strength and

durability. The properties of concrete can also be affected through production, placement,

finishing, and curing practices. It is therefore important that concrete mixes are designed,

produced, placed, cured, and tested by competent individuals.

The learning objectives for this course include:


Understand the ACI Absolute Volume Method of concrete mix design


Know how to design concrete mixes using NCDOT Specifications/Special Provisions


Be able to adjust mixes using 5% ACI Variations


Understand concrete mix design submittal and approval process for NCDOT


Know how to correctly complete NCDOT mix design forms


Understand the NCDOT mix design numbering system

Upon course completion and successfully passing the examination, the technician will be

certified to design and submit concrete mixes for review and approval by the Department.

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Abbreviations

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Specific Gravity = SG

Weight = Wt. or lbs

Cubic Yards = cy or yd?

Cubic Feet = cf or ft?

Pounds per Cubic Feet = pcf

One hundred pounds of cement, or ¡°hundred weight¡± = cwt

Water-Cement Ratio = W/C

Constants

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1 gallon of water = 8.33 lbs

SG of water = 1.00

1 cubic yard (cy) = 27 cubic feet (cf)

Unit weight of water = 62.4 pcf

1 bag of cement = 94 lbs

Significant Places For Rounding

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Pounds ¨C round to whole number

Gallons ¨C round to tenth

Unit Weight ¨C round to hundredth

Water-Cement Ratio ¨C round to thousandths

Conversion Factors

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1 cubic foot = 7.5 gallons

1 gallon of water = 8.33 pounds

1 bag of cement = 1.00 cubic foot ,(loose volume)

bag of cement = 0.48 cubic feet, (absolute volume)

1 cubic foot of water = 62.4 lbs.

4 bags of cement = 1 barrel

1 cubic yard = 27 cubic feet

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