ce 611 module6

Concrete TechnologyProportioning of Concrete MixturesProportioning of Concrete Mixtures

Dr Sonalisa RayDr Sonalisa RayAssistant Professor

Department of Civil EngineeringIndian Institute of Technology, Roorkee

• Selection of materials• Mixture proportioning• Mixture proportioning

– Process of arriving at the right combination of cement, aggregates water and admixturesaggregates, water and admixtures

– Significantly affect cost and properties of concrete

Mix design requirements:

(a) Workability of fresh concreteStrength of harden concreteStrength of harden concrete

Durability under adverse situations(b) Arri e at lo est possible cost(b) Arrive at lowest possible cost

Selection of suitable materials at reasonable price

Cost, Workability, Strength and Durability

CostS ll diff i th i f t ill ff t th fi l• Small difference in the price of aggregates will affect the final cost

• Selection of expensive perhaps unnecessary aggregates would• Selection of expensive perhaps unnecessary aggregates would increase the cost to many folds

• Cement cost is much more than aggregates• Cement cost is much more than aggregates • Suitable replacement of pozzolanic or cementitious by

productsproducts

WorkabilityWorkability

• Affect both cost and quality• Low workability: increases the cost of handling

– Poor strength, durability and appearance

• Segregation and bleeding causes expensive finishYi ld l d bl t– Yield less durable concrete

Note:Note:• Consistency should not be more than necessary

C h i d fi i h bilit f t h ld b i d• Cohesiveness and finishability of concrete should be improved by increasing the sand/coarse aggregate ratio alone

• Water reducing and set retarding admixtures need to be used• Water reducing and set retarding admixtures need to be used when high consistency is required

Strength and DurabilityStrength and Durability

• Strength specified is treated as minimum required strength• Closely dependent on W/C ratio and content of air entrained in

tconcrete• Under normal condition of exposure, mix design ignores

durabilitydurability

Variables in Mix ProportioningVariables in Mix Proportioning

• W/C ratio• Cement content/cement to aggregate ratio• Gradation of aggregates• Consistency

Statistical Quality Control of ConcreteStatistical Quality Control of Concrete

• Variability of test results, results vary from batch to batch– In construction material– In construction method

• Distribution of strength– Normal distribution/Gaussian distribution

21 x 21

2

x

y e

f f k

minmeanf f k

Methods of ProportioningMethods of Proportioning

• ACI committee 211 method• IS recommended method, IS 10262:2009• DOE method• High strength concrete mix design

ACI Committee 211 Method

• Sieve analysis of fine and coarse aggregates; fineness modulus• Dry rodded unit weight of coarse aggregates• Bulk specific gravity of the material• Absorption capacity or free moisture in the aggregate• Air content and grading of the available aggregates• Relationship between strength and W/C ratio for available

combination of cement and aggregate• Job specifications if any; maximum W/C ratio and strength at

l ( ll 28d t th i ifi d)early ages (normally 28day strength is specified)

Mix Design• Step 1: Choice of slump

– Mixtures with stiffest possible consistency which can be easily handled

• Step 2: Choice of maximum size of aggregate– Large max size aggregates produce less void space

Max size of coarse aggregates should be consistent with the dimension– Max size of coarse aggregates should be consistent with the dimension of the structure

– Max aggregate size should not exceed, • 1/5th of the narrowest dimension between the sides of the forms• 1/3rd the depth of the slab• 3/4th of the minimum clear spacing between reinforcing bars

• Step 3: Estimation of the mixing water content and air content– Depends on max particle size of aggregates and entrained air

• Step 4: Selection of W/C ratio– For different aggregates and cement types, the relationship between

t th d W/C ti i ht b diff tstrength and W/C ratio might be different

• Step 5: Calculation of the cement content

• Step 6: Estimation of the coarse aggregate content– Volume can be estimated from its maximum aggregate size

d fi d l f fi tand fineness modulus of fine aggregates• Step 7: Estimation of the fine aggregate content

S 8 Adj f h i• Step 8: Adjustments for the aggregate moisture• Step 9: Trial batch adjustments

• Fresh concrete need to be checked for– Workability– Unit weight– Air content– Harden strength

• If desired criteria does not satisfy, the mix may require grading y y q g gimprovement, by the way of changing CA and FA, change of shape and size of CA.

• Last option is to increase water content, keeping W/C ratio constant.

i h i ld– Might cause yield– To keep yield constant, both FA and CA quantities need to

b i di lbe increases correspondingly

Mix Selection for No Slump ConcreteMix Selection for No-Slump Concrete

• No slump concrete– Extremely dry– Very stiff– Stiff

• Modification need to be made – Modification is made in water requirement

• Concrete of 75-100 mm is taken as reference value

– Modification in the values of bulk volume of coarse taggregates

Flowing ConcreteFlowing Concrete

• Pumpable concrete– The mix under pressure must not segregate and bleed– Must be able to bind all constituent materials together– Must be able to deform while flowing through pipeline at

b d d d ibends and tapered section• ASTM C 1017-07, slump > 190 mm• Commonly a slump of 200 mm or a compacting factor of 0.96

to 0.98

– Increase FA content by 5% above the usual content (with the corresponding reduction in CA): contributes to cohesioncohesion

– Grading of aggregates is also importantHighly angular flaky or elongated coarse aggregates– Highly angular, flaky or elongated coarse aggregates should be avoided (avoid bleeding and segregation)

• Total mass of particles smaller than 300 m in the aggregate +• Total mass of particles smaller than 300 m in the aggregate + mass of cementitious materials > 450 Kg/m3, when maximum aggregate size is 20 mmgg g

• Min quantity of fines is a function of max aggregate size

High Performance Concrete• High workability

– Can be controlled by an appropriate dosage of SP

Hi h h• High strength– Water content need to chosen based on W/C ratio required from strength

considerationconsideration

• High durability– Excessive amount of cementitious material need to be avoided so as

control shrinkage; 500-550 kg/m3 (of which about 10% is silica fume) is desirable maximumPortland cement with high fineness is preferred– Portland cement with high fineness is preferred

• Requirement of high modulus of elasticity– Coarse aggregates of high modulus vauleCoarse aggregates of high modulus vaule– Good interface bonding properties

• NO accepted method of mix proportioning is available (ACI 211.4R-93)

IS Mix ProportioningIS Mix Proportioning

• Characteristics compressive strength• Degree of workability• Type and maximum size of aggregate• Standard deviation for compressive strength• Kind of admixture• Specific gravities of all ingredients

Steps

• Target mean strengthf =f + t x s– ft

=fck

+ t x s

• Selection of W/C ratioKeeping W/C ratio strength is dependent on type of cement max size– Keeping W/C ratio, strength is dependent on type of cement, max size of aggregate, grading, surface texture and other characteristics

– Relationship between strength and W/C ratio need to be established

• Selection of water content– Increase in aggregate size, reduction in W/C ratio, reduction in slump,

f d d d t l t f l ti i R duse of rounded and natural aggregates, use of plasticizers: Reduce water content

– Increase in temperature, increase in cement content, increase in slump, p pincrease in W/C ratio, use of angular aggregates, manufactured sand and large percentage of fines wrt coarse: Increase water requirement

• IS Code: • Up to M35 grade

– For angular CA, natural sand, W/C = 0.6, CF = 0.8• Other conditions of workability, W/C ratio, grading of FA,

d d b l dj d b drounded sub-angular aggregates adjustment needs to be done• Beyond M35 grade

– W/C = 0.35

• Calculation of cement content• Estimation of air content

– Function of max aggregate size

• Calculation of aggregate contentC bi i f diff• Combination of different coarse aggregates– IS 383-1970

• T i l i• Trial mixes

IS 10262: 1982

IS 10262: 1982

IS 10262: 2009

IS 456

Mix Design: High Performance ConcreteMix Design: High Performance Concrete

• Conventional method (strength up to 60 MPa, 180 mm slump) – Good predictive values to design of concrete mixM d t• Modern concrete – W/C or W/B extends towards very low value

C i l l i i i l– Contains several supplementary cementitious materials– Contains silica fume, drastically changes properties of fresh

d h d tand harden concrete– Slump can be altered by SP

Mix Design: High Performance Concrete

Draw backs

• Step 1: Slump - essentially dependent on the amount of mixing d h f l i i dwater and on the amount of superplasticizer used

• Step 2: MSA - No longer advantageous to select as coarse an aggregate as possible to reduce the amount of mixing wateraggregate as possible to reduce the amount of mixing water needed to meet a certain slump– Select the coarse aggregate as small as possible for– Select the coarse aggregate as small as possible for

placeability considerations and also for concrete strength considerations

• Step 3: Water content – Contains supplementary cementitious materials (fly ash, slag, silica fume)– Strength and W/C ratio relationship must be established in

each particular case• Step 4: CA content – No longer dependent on FM of sand

• In HPC many characteristics need to meet simultaneously– Low permeability, high durability, low shrinkage, low creep, high

modulus high strength high and lasting workabilitymodulus, high strength, high and lasting workability

• Large no of mix components – difficult for mix designingLarge no. of mix components difficult for mix designing• Requires large no. trials

DOE MethodDOE Method