20100719 Concrete Ingredients Seg1

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Concrete Methods and principles

Concrete ingredients

By

Moayyad Al Nasra, PhD,PE

.

4/13/2013 1Concrete Methods and Principles,(c) Al Nasra



Concrete Ingredients

• Aggregate

– Fine Aggregate

– Course Aggregate

• Cement

• Water

• Air • Admixture




AGGREGATES

• Types – by source / method of manufacture – The source refers to where obtained

– The method refers to how they are made

•

– Natural Mineral Aggregates (Often Smooth)

• Sand

• Gravel / River Sand

•

– Manufactured Mineral Aggregates (Typically More Angular)

• Crushed Stone (Coarse Aggregate)

• Sand from Crushing Stone / Gravel

• Crushed Concrete or Clay Bricks / Blocks

•




AGGREGATES

• Types - size

– Fine Aggregate: Passing No. 4 (4.75mm) and

predominantly retained on No. 200 (0.075

mm), approximately 0.006” – 3/16”

– Course Aggregate: Predominantly retained on

No. 4 (4.75mm), 3/16” – 3 ½”




AGGREGATES

• Types - Shape

– Round : Disintegration and abrasion of rocks

naturally

– Angular: Usually from crushed stones,

artificial crushing




Aggregates

• Types – Unit Weight• Light weight:

– FA: γ < 70 pcf Concrete: γc =( 120 - 140 pcf )

– CA: γ < 55 pcf

• Two types of Lightweight Aggregates: – Natural (i.e. Pumice, volcanic rock)

– Manufactured (i.e. Fly Ash, blast-furnace slag )

• Normal-weight:

– FA: γ < 105 pcf Concrete: γc = (140 - 150 pcf)

– CA: γ < 95 pcf

• • Heavyweight:

• Variable Agg. Weight Concrete: γc =( 150 - 400 pcf ) – (Heavy Rock / Steel)

– FYI: SGsteel ≈ 7.0




AGGREGATES

• Gradation: The gradual gradation in size

from coarse to fine is a key property of

aggregates. The effects are:

– Workability

– Stability

– Drainage

– Frost resistance

– Others: mix proportioning, economy, porosity,

durability, shrinkage, strength




Types of Aggregate Gradation




Aggregate Gradation

• Normally Graded Aggregate is one that conforms to the

grading limits specified by an agency such as ASTM.

• Open-Graded Aggregate has a particle-size distribution

that results in large voids or void content.

• Dense-Graded Aggregate has a particle-size distribution

that results in the least voids or lowest void content.• Gaped-Grades Aggregate has a particle-size distribution

that results in a missing some particle sizes




AGGREGATES

• Types of Aggregate Mixture – Aggregates with no fines. Its strength from grain-to-

grain contact of aggregate particles. Unstable,excellent drainage, completely non-frost susceptible.

– Fines just filling the voids of aggregate fraction. Itsstrength from grain-to-grain contact of aggregateparticles. Stable base coarse material because of finecontent, adequate drainage and can be non-frostsusceptible.

– Fines overfilling the voids of aggregate fraction.Strength is from grain-to-grain contact of fines rather than the aggregate particles. Reduction in strength,poor drainage, very frost susceptible.




Aggregate Mixture

• Aggregates with no

fines

• Aggregates with just

filling the voids

• Aggregates overfilling

the voids




Angularity and surface texture of

aggregates

angular and roughaggregate smooth aggregateriver gravel




AGGREGATES

• Surface Texture

Property Smooth Rough

___________________________________ Bond Strength Weaker Stronger

Water Demand Less Higher

W/C Less Higher

Overall Strength Almost equal =Workability Good More

Mortar




AGGREGATES

• Freezing and Thawing – Saturated aggregates of low porosity may accommodate pore-water

freezing by simple elastic expansion. Saturated aggregates of moderate

to high porosity may fail because the particle dimension exceeds a

certain critical size or may cause failure in the paste immediatelyadjacent to the aggregate particle because of aggregate pore-water

displacement

Aggregate




AGGREGATES

• Freezing and Thawing – The disruption of concrete by aggregates is a result of hydraulic

pressures. The hydraulic pressure is a result of the degree of saturation (proportional to total void space filled with water) andpermeability and size of the aggregate particles. Upon freezing,

water expands 9 percent, and if the degree of saturation of theaggregate particles, 91.7 percent, water will be expelled into thepaste surrounding the aggregate particle, and potentiallydestructive hydraulic pressure may develop there also. So theproperties of paste, its permeability, air content, and porosity arealso involved in the problem. Three additional factors;

composition, texture, and structure, also play important roles infreezing and thawing of concrete.




Properties of Aggregates

• Properties of aggregate affect the properties of the products made from aggregate

(i.e. Portland cement concrete, asphalt concrete, road subbase, railroad ballast)

• Some important aggregate properties are:

– specific gravity

– bulk density

– porosity – voids

– absorption

– moisture content

– shrinkage

– gradation / fineness modulus (FM)

– Young’s modulus (E)

– compressive strength

– others:

• toughness, hardness, shape, texture, chemical reactivity…




Testing Aggregates

• Sieve Analysis – simplified procedure – Record empty weight of sieves

– Assemble sieve stack

– Place a known weight of aggregate in top sieve

– Shake sample with mechanical shaker – Weigh each sieve with retained aggregate

– Perform calculations to produce gradation curves / fineness modulus

– Compare with ASTM specified grading limits

– Report will contain at least the following:

• 2 semi-log graphs (fine & coarse) – containing ASTM limits and test sample

• 2 Tables (fine & coarse)

• Calculation of FM

• Calculation of % Passing

• Calculation of % Retained

•




Testing Aggregates

• Sieve Analysis – Fineness Modulus – Fineness Modulus (FM) is a factor representative of

the sieve analysis.

– It is a number obtained by adding the values of thepercentages coarser than each sieve in the set and

dividing by 100.

– For use in concrete, the FM ranges between 2.3 –

3.1. – A higher FM means more coarse particles and less

fine particles.

– A lower FM means more fine particles and less

coarse particles.4/13/2013 18Concrete Methods and Principles,(c) Al Nasra



Testing Aggregates

• Sieve Analysis – ExampleSieve

No.

Sieve

Size

(mm)

Wt of

Sieve

(g)

Sieve

+ Mat

(g)

Wt

Ret.

(g)

% Ret. %

Coar.

%

Finer

¾ 19 350 400 50 5 5 95

½ 12.5 350 600 250 25 30 70

3/8 9.5 350 650 300 30 60 40

4 4.75 340 630 290 29 89 11

8 2.36 340 440 100 10 99 1

pan 0 300 400 10 1 100 0




Sieve Analysis – Example

cont’d • Sample weight = 1000 g

• Add all the numbers in the column %

coarser = 283

• FM=283/100 = 2.83




AGGREGATE UNIT WEIGHT

Oven dried condition

• From ASTM C29:

• M = (G-T)/V – where:

– M = unit weight of aggregate (pcf)

– G = mass of aggregate and measure (lb)

– T = mass of measure (lb)

– V = volume of measure (ft3)




AGGREGATE UNIT WEIGHT(SSD Condition)

• SSD = saturated surface dry

• This represents the state of moisture when all the pores of theaggregate are filled with water and the surface of the aggregate isdry.

• It is assumed in this state that neither water absorption nor water contribution to the surroundings (i.e. the concrete mix) occurs.

• From ASTM C29:

– M,SSD = M [1 + (AB / 100)]• where:

– M,SSD = unit weight of aggregate (pcf)

– AB = % absorption (ASTM C127)

• AB = [(B – A) / A] * 100

• where: – A = weight of oven dry sample in air

– B = weight of SSD sample in air

• * Equation also used for Absorption Content *




AGGREGATE MOISTURE

CONDITIONS




AGGREGATE MOISTURECONT’D

• All aggregate has internal pores.• Oven dry = no moisture present

• Air dry = some moisture (water) present in pores

• Saturated surface dry = all pores contain water; surface

of aggregate is dry (no further absorption capacity)• Wet = all pores filled with water and surface moisturepresent

• Moisture Content , MC, (%)

• MC = (WAGG with Moisture) – (WAGG OD) * 100

• WAGG OD

• Surface Moisture (%)

• SM = MC - AB




AGGREGATE SPECIFIC GRAVITY(SG)

• Definition – the ratio of the mass of a unit volume of material to the

mass of the same volume of fresh water.• In equation form, SG =γ,AGG / γ,WATER, with γ,WATER = 62.4 pcf

» OR

• W,AGG / (V,AGG * γ,WATER) = W,AGG / W,WATER

• or

• Bulk SG = A / (B-C) where: – A = weight of OD sample in air – B = weight of SSD sample in air

– C = weight of SSD sample in water

• or

• Bulk SGSSD = B / (B-C)

• or • Apparent SG = A / (A-C)




AGGREGATE SPECIFIC

GRAVITY (SG) CONT’D




AGGREGATE SPECIFIC

GRAVITY (SG) CONT’D

• The difference between B and C is the

weight of water displaced by the solid part

of the sample (= buoyancy force).

• Fb=Buoyancy Force, weight of displaced

water

• B-C=B-(B-Fb)=Fb

• C-B+Fb=0, C=B-Fb




VOID CONTENT

• The space between aggregate particles• % VOIDS = 100 [(S * W) – M] / (S * W)

• where:

– S = dry bulk SG

– W = density of water (62.4 pcf)

– M = unit weight of aggregate (pcf)




CEMENT

• Cement is made from a mixture of clay andcalcareous materials. The essential ingredientsare lime and silica, abundantly found in chalk (or limestone) and clay. The silica- and

calcareous-rich materials are mixed at around1500 C (2732 F), which is one of the sources of carbon dioxide emission. The energy stored at1500 C in cement is frozen in a chemical

equilibrium state into clinkers phases of cement.The stored energy is released upon mixing withwater to form cement paste.




CEMENT

• Cements are materials that exhibit

characteristic properties of setting and

hardening

• Groups

– Hydraulic Cements: Ability to set and harden

under water

– Non-hydraulic: Do not have the ability to setand harden under water, but requires air to

harden




Lime

• Lime is a cementing material. It is produced by burninglimestone ( Calcium Carbonates) with impurities to about1800 F

• CaCO3 Heat CaO + CO2

• Calcium Carbonate Calcium mono-oxide + Carbondi-oxide Quick lime)

• CaO + H2O Ca(OH)2 + Heat

• The setting of lime mortar is the result of the loss of water from the slaked lime Ca(OH)2

• Ca(OH)2 + CO2 CaCO3 + H2O• This results in the formation of calcium carbonatecrystals, which bind the heterogeneous mixture into acoherent mass




Pozzolan Cements

• Siliceous or siliceous and aluminous materialwhich possesses little or no cementitious value,but will react chemically with calcium hydro-oxide at ordinary temperatures to form

compounds possessing cementitious properties

• Artificial pozzolans include fly ash, boiler slag,and by-products from the treatment of bauxiteore. Pozzolan cements are manufactures bydirect grinding of volcanic rocks or by calciningand grinding clays, shale, and diatomaceousearth.




Portland Cements

• Main Compounds of Portland Cement• Name of compound Oxide Composition Abbreviation

• Tricalcium Silicate 3CaO.SiO2 C3S

• Dicalcium Silicate 2CaO.SiO2 C2S

• Tricalcium Aluminates 3CaO.Al2O3 C3A• Tetra calcium Aluminoferrite 4CaO.Al2O3.Fe2O3 C4Af

• Minor compounds such as MgO, TiO2, MnO3, K2O and Na2O

• Raw Materials

– Lime

– Silica – Iron Oxide

– Alumina

– Gypsum (added after burning)




Approximate Composition Limits of

Portland Cement

• Oxide Content, %

• CaO 60-67

• SiO2 17-25• Al2O3 3-8

• FeO3 0.5-6.0

• MgO 0.1-4.0• SO3 1-3




Types of Portland Cement

• Type I: No specific properties required

• Type IA: Air-entraining cement Type I

• Type II: Moderate sulfate resistance, moderate

heat of hydration• Type IIA: Air-entraining type ii cement

• Type III: High early strength

• Type IIIA: Air-entraining type iii cement

• Type IV: Low heat of hydration

• Type V: High sulfate resistance




Special Portland Cements

• White Portland Cement: is used for decorative displays. Low in iron and manganese.• Colored Cements: used for decorative purposes, made by inter-grinding a chemically

inert pigment such as metallic oxide in the amount of 3 to 10 percent to Portlandcement.

• Oil-well Cement: Slow setting cement which are used to seal deep wells.

• Regulated Cement: rapid –setting and –hardening cements. They are used in themanufacture of blocks, pipes, prestressed, and pre-cast concrete, and for patch work.

• Waterproofed Cement: is a portland cement inter-ground with water repelledmaterials, such as calcium stearate.

• Hydrophobic Cement: similar to waterproofed cement, but with the purpose of the lifeof the cement during storage, or being transported to long distances.

• Antibacterial Cement: portland cement inter-ground with an antibacterial agent withthe intention of reducing harmful micro-organisms.

• Barium and Strontium Cement: Portland cement in which the calcium oxide is

replaced completely or in part by barium oxide or strontium oxide. Their purpose is toact as concrete shield in which the barium and strontium absorb x-rays and gammarays.




WATER

• Water containing less than 2000 parts per

million (ppm) of total dissolved solids can

generally be used satisfactorily for making

concrete. Water containing more than2000 ppm of dissolved solids should be

tested for its effect on strength and time of

set.




Impurities in Water

• Alkali Carbonate and Bicarbonate: Different effects onsetting times of different cement.

• Chloride: Possible effect of chloride ions on corrosion of reinforcing steel or pre-stressing strands. Concentrationsof 20,000 ppm of sodium chloride are generally tolerable

in concrete that will be dry in service and has lowpotential for corrosive reactions.

• Sulfate: Possible expansive reactions and deteriorationby sulfate attach. 10,000 ppm is generally tolerable.

• Ion Salt: 40,000 ppm do not usually affect strength

adversely.• Inorganic Salts: Salts of magnesium, tin, zinc, copper,

and lead in mixing water can cause significant reductionin strength and large variations in setting time




Impurities in Mixing water

continued• Seawater: Up to 35,000 ppm of dissolved solids is

generally suitable as mixing water for unreinforced concrete. Sea water is not suitable for use in makingsteel reinforced concrete and should not be used for pre-

stresses concrete.• Acid Water: Acid waters with PH 3.0 or less may createhandling problems and should be avoided.

• Sugar: Small amount of sucrose, as little as 0.03% to0.15% by weight of cement, usually retard the setting of

cement.• Silt or suspended particles: 2000 ppm of suspended clay

of fine rock particles can be tolerated.




Air-Entrained Concrete

Effects• Freeze-Thaw Resistance: Significantly improved by the

use intentionally entrained air.

• Resistance to Deicers and Salts: Deicer scaling isbelieved to be caused by buildup of osmotic and

hydraulic pressures in excess of normal hydraulicpressures produced when water in concrete freezes.

• Sulfate resistance: Improved

• Resistance to Alkali-Silica Reactivity: The reactivity isreduced through the use of air entrainment.

• Workability: Entrained air improves the workability.




Recommended Air Contents

• The amount of air to be used in air

entrained concrete depends on:

– Type of structure

– Climate conditions

– Number of freeze-thaw cycles

– Extent of exposure to deicers

– Extent of exposure to sulfates or other aggressive chemicals in soil or water


ADMIXTURE



ADMIXTURE

Classified by Function• Air-entraining: Improve durability in environment of freeze-thaw,

deicers, sulfate, and alkali reactivity. Also improves workability.Material (salts of wood resin”Vinsol resin”, some synthetic detergents, salts of sulfonated lignin, fatty and resinous acids and their salts, …)

• Water-reducing: Reduce water demand. Material (lignosufonates,Hydroxylated carboxylic acids, carbohydrates, …)

• Retarding: Retard setting time. Material (lignin, borax, sugar, tartaric acid and salts, …)

• Accelerating: Accelerate setting time and early-strengthdevelopment. Material (Calcium cloraide, triethanolamine, sodiumthiocyanate, calcium formate, calcium nitrite, calcium nitrate, …)

4/13/2013 42Concrete Methods and Principles,

(c) Al Nasra



Admixture: Classified by Function

Continued• Superplasticiers: Flowing concrete, reduce water-cement ratio.

Material (sulfonated melamine formaldehyde condensates,sulfonated naphthalene formaldehyde condensate,lignosulfonates…)

• Finely divided mineral: Partial cement replacement, improvesworkability, plasticity, sulfate resistance, reduce alkali reactivity,

permeability, heat of hydration, filler. Material (ground granulated blast-furnace slag, pozzolans “ diatomaceous earth, opaline cherts,clays, shale, volcanic tuffs, pumicites, fly ash, silica fume”, …)

• Miscellaneous admixtures: Bonding, damp-proofing, permeability-reducing, grouting, gas-forming, coloring, corrosion inhibiting, andpumping admixture. Material (bonding – rubber, polyvinyl chloride,

poly vinyl acitate,…, damp-proofing – soaps of calcium or ammonium stearate or oleats, butyl stearate, …, permeability reducer – silica fume, fly ash, …, gas former – aluminum powder,…, coloring – modified carbon black, iron oxide, phthalocyanin,umber, …, …, …)


(c) Al Nasra

M j f i



Major reason for using

admixtures• Reduce the cost of concrete construction

• Achieve certain properties in concrete

• Ensure quality in adverse weather conditions

• Overcome certain emergencies during

concreting operation


Documents

20100719 Concrete Ingredients Seg1