concrete technology 2/10 - aalto · 2015. 11. 24. · concrete technology 2 supplementary binders...

Concrete Technology 2/10

Aalto UniversitySchool of EngineeringDepartment of Civil and Structural EngineeringBuilding Materials Technology

Equilibrium moisture - Hygroscopic properties ofcontent the material

Effects of the drying environment on drying of concrete

Three variables-temperature of air-moisture content of air-velocity and direction of air flow

Fast drying concretes

Concrete Technology 2


Equilibrium moisture content of concrete having different water-cementratios and hydration degrees. =0,50 when w/c=0,30, =0,60 whenw/c=0,40, and =0,80 when w/c=0,50...0,80. (Nilsson 1977, Fagerlund1980).


Traditionaalinen rakentamisprosessiValmiusaste

Perus- Betonirunko Sisävalmistustyöttukset Betonin kuivumisaika A1

Tasoitetyö MattotyötJulkisivu

3krs Betonirungon tuotannon 3nopeuttaminen

2

2krs2 vko/krs

1 krs 1 1,5 vko/krs

Betonin kuivumisaika B1 Aika21 viikkoa

Nopeutettu rakentamisprosessi

ValmiusastePerus- Betonirunko Sisävalmistustyöttukset Betonin

kuivumisaika A2 Rakennusaika lyheneeTasoitetyö Mattotyöt

Julkisivu

3krs 1 vko/krs 3

Kriittiset yhteydet1. Julkisivun asentaminen

2krs 2 2. Tasoitustyön vaatima lämpötila3. Betonin kuivuminen

1,5 vko/krs1 krs 1

Betonin kuivumisaika B2 Aika16 viikkoa


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0 25 50 75 100 125 150 175Rel

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Drying time of concrete (d)

K35

K30A, air-entrained 4%

K50AS, air-entrained 4%

RH 70% T=10o C


75

80

85

90

95

100

0 25 50 75 100 125 150 175 200

Rel

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K35

K50



RH 45% T=20o C


75

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95

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0 25 50 75 100 125 150 175 200

Rel

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K35C

K30AA, air-entrained 8%

K50AS, air-entrained 4%

RH 45% T= 20 °C


Fiber reinforced concretesFiber concrete = composite material in which

-fibers can be distributed randomly or in organized manner-fiber length is commonly 10…50 mm-cement-based matrix

Ferroconcrete (ferrocement) = a thin concrete structure reinforced by amesh of thin bars (thinly spaced steel bars having small diameters)


Aggregates-usually fine washed and dried sand-continuous grading curve-maximum aggregate diameters

-steel fiber concretes 10 mm-premixed glass fiber concrete 1 mm-sprayed glass fiber concrete 0.8 mm-ferrocement 4 mm

-filler content less than 10 %-moisture of aggregates below 2 %

When aggregate maximum size decreases, the mixing of the fibers into theconcrete is improving.

Binders-quite large binder amounts-normal, rapid, and low heat Portland cements are applied-in glass fiber concretes alkalinity of pore water causes defects,therefore, aluminate cements or partial substitution by fly ash


Supplementary binders and other additions-fly ash and GGBS which effect workability, segregation,and bleeding

-plasticizers and superplasticizers-air-entraining agents-use of CrO3 in ferrocement to hinder the reaction

between cement and zinc coated reinforcement nets

Mix compositionwater: cement: aggregates

Steel fiber concretes 0.4…0.6 : 1 : 1.5…2-cement content 350…600 kg/m3

Glass fiber concretes 0.3…0.4 : 1 : 0.4…0.5-cement content 1100…1350 kg/m3

Ferroconcrete 0.4 : 1 : 2…3-cement content 500…700 kg/m3


The fiber volume percentage in concrete vary between 0.5 … 5 %.

Fiber dimensions L > 10

Fiber type Density [kg/m3] E [MPa] t [MPa] Price [€/kg]

Asbestos 2.6 170 000 3 000 0.4

Alkaliresist.glass

2.7 80 000 2 500 1.5

Steel 7.8 200 000 1 100 1

Carbon 2.0 400 000 2 000 70

Polypropylene 0.9 5 000 400 1.5

Nylon 1.2 4 000 900 1.5


Steel fibers- length 5 … 50 mm, thickness 0.15 … 0.5 mm-L / d usually below 80 otherwise handling and mixingdifficult-volume amount of the fibers 0.5 … 2.5 volume% whichdenotes 40 … 200 kg/ concrete m3

-bond strength 5 … 8 MPa, bond can be improved bydissolving the grease and dirt on the fiber surface or bycoating fibers with zinc or brass-fiber types

-round cross section-flat-duoform = flattened at small distances in thedirection of the fiber axis

-corrosion


Properties of steel fiber reinforced concretes

Property Numerical value Compared to normalconcrete

Flexural strength,Limit of proportionality

6 … 12 MPa Over twice as high

Flexural strength,Yield strength

6 … 17 MPa Over 3-times as high

Compressive strength 35 … 84 MPa Remarkably higher

Impact strength 136 J Nearly 3-times as high

Fatigue strength 0.8 … 0.95 Over 70 % higherAbrasion resistance

index, sand blast test2 Double

Freeze-thaw durabilityindex, freeze-thaw test

1.9 90 % higher


Glass fibers

-basic strand is about 10 m thick-200 basic strands form a string, thread or fiber which canconstitute a fabric or mesh-alkali resistant glass fiber (AR-glass fiber)

-strength loss during aging-deterioration of glass fibers during mixing, sometimes glassfibers are covered or stained by resin (additional cost), nocourse aggregates in the mix-abrasive effect of the aggregates can be diminished by

-using aggregates rounded by nature-short mixing times


AR-glass fibers

-modulus of elasticity less than half of steel fibers, however,2 … 3-times the modulus of elasticity of concrete-tensional strength twice as high compared to steel-bond to concrete merely 2 … 3 MPa


Ferroconcrete (ferrocement)-reinforcement mesh having small cross-sections-large Ast/Ac-ratio-reinforcement mesh in several layers-used also in complex shell structures


Direction ofreinforcement

Direction of stress

1-dimensionala) In the direction of

thereinforcementb) of the reinforcement

1

02-dimensionalorthogonal

In the direction of thereinforcement

1/2

2-dimensionalrandom

In arbitrary plane 3/8

3-dimensionalrandom

Arbitrary 1/5

Efficiency coefficient


Compressive strength-depends on the properties of concrete-direction of the fibers could cause buckling-compressive strengths of steel fiber concretes and ferroconcretesvary between 30 and 60 MPa

Shear strength-glass fiber concrete is lamellar-shear strength between lamellae 1.5 … 2.0 MPa-shear strength in the plane of lamella 7 … 10 MPa-punching strength 30 … 40 MPa-shear strengths of steel fiber concretes and ferroconcretes havenot been studied


Impact ductility-usually high impact ductility (hindering of crack formation andpropagation)-cracking energy of the matrix is nearly same as with the mortar-impact ductility of glass fiber concrete decreases remarkably asmoisture of the concrete increases

Fatigue strength-fatigue strength in flexure is with fiber concretes less than 90 %of tensile strength-deflection and crack width grow exponentially during fatigueloading, therefore, design strengths are small


Shrinkage and creep-large binder amount and thin structures increase shrinkage,therefore, extended curing-fibers and denser reinforcement mesh decrease shrinkage-increase in the fiber amount by one volume percent decreasesshrinkage by 5 … 10 % compared to fiberless concrete-forming cracks have small widths and they are distributed atwide area-same thing that applies to shrinkage applies also to creep-usually fiber reinforced concrete is not used in structureswhich carry large permanent loads

Freeze-thaw durability-fibers do not affect concrete porosity-normal air-entrainment


Durability against corrosion-steel fibers rust which is hindered by high alkalinity anddense structure of concrete-large binder amounts which slow down carbonation-wide cracks can decrease the utilization age-steel fibers on the surface do rust-if zinc coated reinforcement is used in ferroconcrete, they donot corrode that fast (concrete surface layer at least 3 mm)-glass fibers are corroded in alkaline environment of the porewater


Application fieldsSteel fiber concretes-road pavement structures and dam refurbishing-shotcreting in tunnels and mines-linings in refractory structures-floors-precast unit products, pipes, tubes

Glass fiber concretes-precast façade units, pipes, small containers-plates, slabs, roof tiles, buoys


Ferroconcretes

-boats, ships-floating docks, buoys, barges-grain silos, containers, roof structures-large span hangars-façade units, pipes, gutters-roof tiles


Polymer concretes

Three production methods-impregnated polymer concretes-whole binder consists of polymer = polymer concrete-monomer or polymer is mixed into fresh concrete mix =cement polymer concretes

Impregnated polymer concretes-first a common concrete structure or product is cast-drying-vacuum treatment-monomer is pressed into concrete at 3.5 atm pressurecaused by nitrogen


Partial impregnation-drying of the surface of the structure at 150 oC , forexample, by infra red heaters-monomer is spread on the surface (5 hours causes 4 cmpenetration)-polymerizing by heat treatment

Most common polymer materials-95 % methyl meth acrylate (MMA)-below 5 % tri methyl propane tri methyl acrylate (TMPTMA)-to excite the polymerization below 1 % iso butyro nitrineThe treatment improves freeze-thaw durability, water tightnessand friction properties of the structure surface


Polymer concretes-aggregates of normal concretes 90-95 %-large number of different monomer variations

-methyl meth acrylate + TMPTMA + benzoilperoxide-polyester resins-vinyl ester resins-epoxy resins

-the hardening time is remarkably shorter compared tonormal concretes-no need for outside heating

Applications-bridges, concrete dams, and repair of corrosion damages

-consistency and color similar as with normal concretes,sometimes color pigments are needed-good bond to normal concrete

Applications

-repair of concrete bridges-precast units-preservation of radioactive waste materials-as frame structures for heavy-duty machine tools-products of mechanical engineering


Cement polymer concretes

Several monomers such as MMA are insoluble into waterand, hence, are not suitableRaw materials

-latex polymers-epoxies-elastomers-polyester and acryl resins

Production methods-addition directly during mixing or after one hour ofthe original mixing time

Applications-repair and coating of concrete structures



Concrete Compressivestrength[MPa]

Tensionalstrength

[MPa]

Ec

[GPa]

Watersuction

%

Freeze-thawCycles/

% w. loss

AciddurabilityImprov./

comparison

AbrasiondurabilityImprov./

comparison

Normalconcrete

20 - 50 2 - 4 20 - 30 5 - 6 700/25 - -

High-str.concrete

50 - 120 4 - 12 30 - 40 1 - 3

Impr. polconcrete

100 -150

9 - 12 35 - 40 0.3 – 0.6 3000/0 - 2

5 - 10 2 - 5

Polymerconcrete

40 - 150 7 - 14 7 - 35 - 1500/0 - 1

8 - 10 5 - 10

Cementpolym. c

20 - 60 4 - 7 10 - 15 - - 1 - 6 10

Castiron

100 -350

100 -350

90 - 130 - -

Steel 200 -500

200 -500

210 - -

concrete technology 2/10 - aalto · 2015. 11. 24. · concrete technology 2 supplementary binders...

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