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MIX DESIGN OF HIGH STRENGTHCONCRETE, SPECIAL CASES IN

MIX DESIGN

Exercise 7

Introduction

The strength of high strength concretes is K70 K100(By50).

Ultra high strength concrete (RPC aka Reactive PowderConcrete) contains: rock powder as aggregate with steel dust and steel fibres which compact the concrete

so that it can reach strengths of up to 800 MPa.

Low water/cement ratio: below 0,35 even below 0,20

Introduction High strength concretes are composed of same

materials as normal strength concretes. the selection of cement and additives is based on:

The desired strength gain and heat development

The used aggregate contains only small amounts offines and silt. Due to the high amount of binder andthat the aggregate grading does not have as biginfluence as in normal strength concrete.

Requires the use of water reducing admixtures(superplasticizers)

Requires careful curing

Mix design of High Strength Concrete1. Define proportioning strength of concrete2. Define the amount of binder and Calculate the amount

of cement and additional binders3. Define the amount of (super)plasticizer4. Define the amount of water5. Calculate the amount of aggregate with the volumetric

equation of concrete6. Combine the aggregate7. Define the components of the batch and make a trial

batch

1. Define proportioning strength of concretefm = fc + ksfm = the target mean strengthfc = the specified characteristic strengths = the standard deviation, andk = a constant

The constant k is derived fromthe mathematics of the normaldistribution and increases asthe proportion of defectives isdecreased, thus:

k for 10% defectives = 1.28k for 5% defectives = 1.64k for 2.5% defectives = 1.96k for 1% defectives = 2.33

BRE - Building Research Establishment, UKDesign of normal concrete mixeshttp://www.cmse.ed.ac.uk/MSE3/Cement/2ED3575-CIS888614800250940.pdf

1. Define proportioning strength of concrete It is generally accepted

that at a given level ofcontrol the standarddeviation increases as thespecified characteristicstrength increases up to aparticular level

the standard deviationbeing independent of thespecified characteristicstrength above 20N/mm2.

BRE - Building Research Establishment, UKDesign of normal concrete mixeshttp://www.cmse.ed.ac.uk/MSE3/Cement/2ED3575-CIS888614800250940.pdf

2. Define the amount of binder and calculate theamount of cement and additional binders

C = cementSi = Silica fumeLt = Fly ashMk = Blastfurnace slag

From the report: Korkealujuuksisten betonien suhteitus; Penttala V. et. al. (1990).

Binder amount (C+2,5Si+0,3Lt+Mk)- use the mineral admixtures proportion of the cement to

calculate the amount of cement, silica, fly ash andblast furnace slag

3. Define the amount of (super)plasticizer

From the report: Korkealujuuksisten betonien suhteitus; Penttala V. et. al. (1990).

The amount of plastizer as proportion of the binder isdefined based on the target mean strength (proportioningstrength)

4. Define the amount of water Curves determine the (water-

admixture air / binder) ratioof high strength concrete

The proportioning strength isK28

The compressive strength isdetermined using 100 mmcubes

The amount of air is assumedto be 10 dm3/m3

Amount of admixture fromSTEP 3 From the report: Korkealujuuksisten betonien suhteitus; Penttala V. et. al. (1990).

5. Calculate the amount of aggregate

Calculate the amount ofaggregate with the volumetricequation of concrete.

The amount of air is assumed tobe 10 dm3/m3

C = cementSi = Silica fumeLt = Fly ashMk =Blastfurnace slagI = air contentNt = PlasticizerW = WaterR = Aggregates

6. Combine the aggregate

7. Define the components of the batch and make a trialbatch

the mix design process

The guidelines of the mix design are drawn upfor 100*100*100 mm cubes

Binders: Cement kcem 1 Blast furnace slag kMK 1 Fly ash kLT 0,3 Silica ksil 2,5

The mix design guidelines are for concretes ofconsistency 2-3 sVB ( S3/S2)

Exersice 1Proportion a K100 concrete (at the age of 28days) with CEM I as binder with 8 % silica fume.

INPUT:K28 = 100 MPaCement type = CEM ISilica amount = 0,08 * cement [kg/m]

1) Proportioning strength

fm = fc + ksfc = 100 MPak for 10% defectives = 1.28s for 100MPa and less than 30 samples = 8 MPafm = 100 + 1.26*8 = fm = 110MPa

Amount of binder is 630 kg/m3

2) Define the amount of binder

2. Calculate the amounts of cement andadditional binders

from the binder amount (in this case theamounts of cement and silica).

Binder amount (C+2,5Si+0,3Lt+Mk)Si = 8% cement, Lt and MK = 0%C+2,50,08C = 630C(1+0,2) = 630C = 525 kg/m3 and Si = 42 kg/m3

Amount of plasticizer is 3,3 % (C+Si)0,033*(525+42) = 18,7 kg/m3

3) Define the amount of (super) plasticizer

Lt and MK = 0%

4) Define the water amount

We get

(W+Nt+I)/S = 0,25

(W+Nt+I)/(C+2,5*Si) = 0,25

(W+18,7+10)/(525+2,5*42)

W = 0,25(630) 18,7 10

W = 128,8 kg/m3

Binder amount(C+2,5Si+0,3Lt+Mk)

5) Calculate the amount of aggregate

+ W + N + Air + + + + =1000

Thus,

,+ 128,8 + 18,7 + 10 +

,+

,= 1000

QAGG = (1000 128,8 18,7 10 169,4 19,1) * 2,68

QAGG = 654 dm3 = 1753 kg/m3

Ex 1 - Mix designingredient kg/m

Cement 525

Silica fume 42

Fly ash --

GGBS --

Water 128,8

Superplasticizer 18,7

Aggregates 1753

W/C = 0,25W/B = 0,23

Exersice 2Proportion concrete for which the referencestrength for 150 mm cubes is 55 MPa at the ageof 1 day. As binder use CEMI, 10 % silica fumeand 30 % fly ash.INPUT:K28 = ????Cement type = CEM ISilica amount = 0,10 * cement [kg/m]Fly ash amount = 0,30 * cement [kg/m]

1) Proportioning strength The guidelines of the mix design are drawn up for

100*100*100 mm cubes. For 100 mm cubes the compressive strengths are

about 5 % greater than for 150 cubes For 100 mm cubes the compressive strengths should

thus be fm = 55*1,05 = 58 MPa The standard deviations of the strength of the 100

mm cubes are higher than that of the 150 mm cubes. The mean standard deviation of the strength of the

150 mm cubes are about 4 MPa fm = 58 + 1.26*4 = 63 MPa 1d strength

The compressive strength at28 days

fs at the age of 28 days is 85MPa

1) Proportioning strength

Amount of binder is 440 kg/m3

2) The amount of binder from figure

INPUT: Silica amount = 0,10 * cement [kg/m]Fly ash amount = 0,30 * cement [kg/m]

The amount of binder (C + 2,5Si + 0,3Lt) = 440Si = 0,1C Lt = 0,3CC (1 + 2,5*0,1 + 0,3*0,3) = 440C = 328,4 kg/m3 Si = 32,8 kg/m3 Lt = 98,5 kg/m3

2) The amount of binder

Amount of plasticizer 2,8 %0,028*(328,4 + 32,8 + 98,5) = 12,9 kg/m3

3) define the amount of plasticizer

4) Define the water amount

We get:

(W+Nt+I)/S = 0,39

(W+12,9+10)/(440) = 0,39

W = 0,39(440) 12,9 10

W = 148,7 kg/m3

5) Calculate the amount of aggregate

+ W + N + I + + + + = 1000

Thus,

,+ 148,7 + 12,9 + 10 + ,

,+ ,

,+ ,

,= 1000

QAGG = (1000 148,7 12,9 10 105,9 14,9 42,8) * 2,68QAGG = 664,8 *2,68 = 1782 kg/m3

Ex 2 - Mix designingredient kg/m

Cement 328.4

Silica fume 32.8

Fly ash 98.5

GGBS --

Water 148.7

Superplasticizer 12.9

Aggregates 1782

W/C = 0,45W/B = 0,34

Exersice 3How would you change the mix design if themeasured consistency of the concrete was 4 sVBand the 1st day strength was 58 MPa?INPUT:K28 = ????Consistency = 4 sVBCement type = CEM ISilica amount = 0,10 * cement [kg/m]Fly ash amount = 0,30 * cement [kg/m]

1) Proportioning strength For 100 mm cubes the compressive strengths are

about 5 % greater than for 150 cubes fm = 58*1,05 = 61 MPa The mean standard deviation of the strength of the

150 mm cubes are about 4 MPa fm = 61 + 1.26*4 = 66 MPa 1d strength

From the chart, we cannotice that: 1 day fs = 66 Mpa fs at the age of 28 days is

90 MPa

1) Proportioning strength

New amount of binder is 460 kg/m3

2) The amount of binder

INPUT: Silica amount = 0,10 * cement [kg/m]Fly ash amount = 0,30 * cement [kg/m]

The amount of binder (C + 2,5Si + 0,3Lt) = 460Si = 0,1C Lt = 0,3CC (1 + 2,5*0,1 + 0,3*0,3) = 460C = 343,3 kg/m3 Si = 34,3 kg/m3 Lt = 103 kg/m3

2) The amount of binder

3) amount of plasticizer

BY 15(old)

BY 50(new)

New plasticizer amount is 3,0 % but because the previousconcrete mix was too stiff, well raise the amount of plasticizerto 3,2 %0,032*(480,6) = 15,4 kg/m3

3) amount of plasticizer

4) water amount :

(W+Nt+I)/S = 0,35

(W+15,4+10)/(460) = 0,35

W = 0,35(460) 15,4 10

W = 135,6 kg/m3

4) Calculate the amount of aggregate

+ W + N + I + + + + = 1000

Thus,

,+ 135,6 + 15,4 + 10 + ,

,+ ,

,+

,= 1000

QAGG = (1000 135,6 15,4 10 110,7 15,6 44,8) * 2,68QAGG = 667,9 *2,68 = 1790 kg/m3

C = 343,3 kg/m3 Si = 34,3 kg/m3 Lt = 103 kg/m3

Ex 3 - Mix designingredient kg/m

Cement 343.3

Silica fume 34.3

Fly ash 103

GGBS --

Water 135.6

Superplasticizer 15.4

Aggregates 1790

W/C = 0,39W/B = 0,29

Exersice 4 Which matters should be taken into

consideration when proportioning pumpableconcrete?

How about concrete with high wear resistance(kulutuskestvyys)?

Pumpable

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