Mix Design Basics CIVL 3137 1 Mix Design Goals adequate - - PowerPoint PPT Presentation

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Nov 01, 2022 549 likes •790 views

Mix Design Basics CIVL 3137 1 Mix Design Goals adequate workability adequate strength adequate durability minimum cost CIVL 3137 2 Cost of Materials crushed stone = $ 12/ton concrete sand = $ 9/ton Type I cement = $126/ton Minimum

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Mix Design Basics

CIVL 3137 1

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Mix Design Goals

adequate workability adequate strength adequate durability minimum cost

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Cost of Materials

crushed stone = $ 12/ton concrete sand = $ 9/ton Type I cement = $126/ton Minimum Cost = Minimum Cement

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Minimizing Cost Cement

minimize the void space between aggregate particles that must be filled with cement paste minimize the surface area of the aggregate particles that must be coated with cement paste

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Minimizing Void Space

Void content = 48% Void content = 41% Use a gravel-sand blend with a dense gradation to minimize the void content of the aggregate

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Minimizing Surface Area

surface area = 11 ft2 surface area = 22 ft2

10"

Use the largest NMAS you are allowed to in order to minimize the surface area per cubic yard of concrete

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Minimizing Surface Area

surface area = 6.0 ft2/ft3 surface area = 4.8 ft2/ft3 Use gravel instead of crushed stone if possible because it has a lower surface area per unit volume occupied

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Obtaining Adequate Workability

To obtain good workability, you need enough mortar to fill the voids between the gravel particles, enough cement paste to fill the voids between sand particles, and enough water to both hydrate and lubricate the cement particles. The main goal of the ACI mix design method is to get the relative volume proportions of the ingredients right in order to ensured good workability.

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Obtaining Adequate Workability

mortar gravel

Need enough mortar to keep all the gravel particles apart.

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Obtaining Adequate Workability

mortar gravel cement paste sand

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Obtaining Adequate Workability

cement paste sand

Need enough cement paste to keep all the sand grains apart

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Obtaining Adequate Workability

cement paste sand water cement

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Obtaining Adequate Workability

water cement

Need enough mixing water to lubricate all the cement grains

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Obtaining Adequate Workability

water cement

Air entrainment adds lubrication without adding additional water

air bubble

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Obtaining Adequate Strength

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Water-Cement Ratio

Water Cement 0% Hydration 100% Hydration Hydration Products Water Air

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Obtaining Adequate Strength

If the structural engineer designs a beam based

n a concrete strength of 4500 psi, you have

to design your concrete mix to have a strength much higher than that.

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WHY?

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 4500psi

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 4500psi

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 4500psi

f   5700psi

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Overdesign Factors

CIVL 3137 28

Required Average Compressive Strength When Data Are Not Available to Establish a Standard Deviation

Adapted from ASTM C94