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Mix Design Basics
CIVL 3137 1
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Mix Design Goals
adequate workabilityadequate strengthadequate durability
minimum cost
Cost of Materials
CIVL 3137 4Source: November 7, 2011 enr.com
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Mix Design Goals
adequate workabilityadequate strengthadequate durability
minimum cost
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Minimizing Cost Cement
minimize the void space betweenthe aggregate particles
minimize the surface area ofthe aggregate particles
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Minimizing Void Space
Void content = 48% Void content = 41%
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Minimizing Surface Area
surface area = 11 ft2 surface area = 22 ft2
10"
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Minimizing Surface Area
surface area = 6.0 ft2/ft3 surface area = 4.8 ft2/ft3
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Obtaining Adequate Workability
mortar
gravel
Need enough mortar to keep all the gravel particles apart.
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Inside Concrete
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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Inside Concrete
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
airbubble
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Figure 7‐14
CIVL 3137 20 4500psicf
CIVL 3137 21 4500psicf
CIVL 3137 22 4500psicf 5700psicrf
Overdesign Factors
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Table 7-12 Overdesign Necessary to Meet Strength RequirementsA
Overdesign Factors
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Required Average Compressive Strength When DataAre Not Available to Establish a Standard Deviation
Adapted from ASTM C94
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Trial Mix Design
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Mix Design Example
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Step 1: Select the slump
Source: Design and Control of Concrete Mixtures (PCA, 2003)
Equivalent to Table 7‐13
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Step 2: Select the NMAS
narrowest dimensionNMAS 5
depth of slabNMAS 3
NMAS 0.75 clear space
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Step 3: Estimate the water and air
Source: Design and Control of Concrete Mixtures (PCA, 2003)
Equivalent to Table 7‐14
Air Content
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40%Cement
Paste
60%Aggregate
Concrete Air Content0.4 7% = 2.8%
Paste Air ContentAssume 7%
SmallerNMAS
Air Content
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30%Cement
Paste
70%Aggregate
Concrete Air Content0.3 7% = 2.1%
Paste Air ContentAssume 7%
LargerNMAS
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Adjust for Aggregate Shape
Source: Design and Control of Concrete Mixtures (PCA, 2003)
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Step 4: Select the w/c ratio
Source: Design and Control of Concrete Mixtures (PCA, 2003)
crf
Equivalent to Table 7‐15
Overdesign Factors
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Required Average Compressive Strength When DataAre Not Available to Establish a Standard Deviation
Adapted from ASTM C94
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Step 4: Select the w/c ratio
Source: Design and Control of Concrete Mixtures (PCA, 2003)
crf
Equivalent to Table 7‐15
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Figure 7‐14
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Step 5: Calculate the cement weight
WW = w/c ratio
watercement
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Step 6: Estimate coarse aggregate
Source: Design and Control of Concrete Mixtures (PCA, 2003)
o
bb
Equivalent to Table 7‐17
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b/bo
b
bo
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Step 6: Estimate coarse aggregate
bulk bulkgravel o concreteV b b V
bulk bulkgravel o concrete gravelW b b V γ
bulk bulkgravel gravel gravelW V γ dry-rodded
unit weight
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Step 7: Estimate fine aggregateEstimated Weight Method
(Section 7‐8.1)
Equivalent to Table 7‐18
NMAS
(in) Non‐Air‐Entrained Concrete Air‐Entrained Concrete
⅜ 142.0 137.5
½ 144.0 139.0
¾ 146.5 141.5
1 148.5 143.5
1½ 151.0 146.0
2 153.0 147.5
3 155.5 150.0
6 157.5 152.0
First Estimate of Concrete Unit Mass (lb/ft3)
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Step 7: Estimate fine aggregate
total cement gravel sand waterW W W W W
sand total cement gravel waterW W W W W
Estimated Weight Method(Section 7‐8.1)
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Step 7: Estimate fine aggregate
total cement gravel sand water airV V V V V V
sand total cement gravel water airV V V V V V
Absolute Volume Method(Section 7‐8.2)
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Step 7: Estimate fine aggregate
sand total cement gravel water airV V V V V V
gravelbulkgravel
cement watersand total air
w
W1 W WV V Vγ 3.1 G5 1.00
sand sabul
ndk
wsandGW V γ
Absolute Volume Method(Section 7‐8.2)
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Step 8: Adjust for Aggregate Moisture
1. Increase Wwater by an amount equal to the weight of water needed to saturate the fine and coarse aggregate.
2. Increase Wsand and Wgravel by an amount equal to the moisture contents of the aggregate stockpiles.
3. Decrease Wwater by the same amount you increased Wsand and Wgravel.
