Filetype PDF | Posted on 13 Sep 2022 | 4 years ago
Authentication
digital resources
303x Filetype PDF File size 1.51 MB Source: pramudiyanto.blogs.uny.ac.id
Chap. 7 (2010).qxd:EB001 (2010) 1/27/11 2:35 PM Page 117
CHAPTER7
Chemical Admixtures for Concrete
Chemicaladmixturesarethoseingredientsinconcrete Themajorreasonsforusingchemicaladmixturesin
other than hydraulic cement, supplementarycementitious concrete mixtures are:
materials (SCMs), water, aggregates, and fiber reinforce- 1. Toachievecertainpropertiesinconcretemoreeffec-
mentthatareaddedtothemixtureimmediatelybeforeor tively than by other means;
duringmixing(Figure7-1).Thereareavarietyofchemical 2. Tomaintainthequalityofconcreteduringthestages
admixturesavailableforuseinconcretemixturestomod- of mixing, transporting, placing, finishing, and
ify fresh and hardened concrete properties. Chemical ad- curing(especially in adverse weather conditions or
mixturescanbeclassifiedbyfunctionasfollows: intricate placements);
1. Air-entraining 3. Toovercomecertainemergenciesduringconcreting
2. Normal,Mid-range,andHigh-rangewater-reducing operations; and
4. Set accelerating 4. Economy.
5. Set retarding Despitetheseconsiderations,noadmixtureofanytypeor
6. Hydration-control amountisasubstituteforgoodconcretingpractice.
7. Rheologymodifying
8. Corrosioninhibitors Theeffectivenessofanadmixturedependsuponfactors
suchasitscomposition,additionrate,timeofaddition;
9. Shrinkagereducers type, brand, and amountofcementingmaterials;water
10. Permeabilityreducingadmixtures content; aggregate shape, gradation, and proportions;
11. Alkali-silica reactivity inhibitors mixingtime;slump;andtemperatureoftheconcrete.
12. Coloringadmixtures Chemicaladmixturesconsideredforuseinconcrete
13. Miscellaneousadmixturessuchasworkability, shouldmeetapplicablespecificationsaspresentedin
bonding,grouting,gas-forming,anti-washout, Table7-1. Trial mixtures should be made with the admix-
foaming,andpumpingadmixtures ture and the other concrete ingredients at the temperature
andrelativehumidityanticipatedduringplacement.Then,
observationscanbemadeonthecompatibilityofthe
admixturewithotheringredients,aswellasitseffectson
the properties of the fresh and hardened concrete. The
amountofadmixturerecommendedbythemanufacturer
shouldbeused,ortheoptimumdosageshouldbeverified
bylaboratorytesting.Formoreinformationonchemical
admixturesforuseinconcreteseeACICommittee212
(2004 and2010),ThomasandWilson(2002),Hewlett
(1998), and Ramachandran(1995).
Figure 7-1. Liquid admixtures, from far left to right: antiwashout
admixture, shrinkage reducer, water reducer, foaming agent, corro-
sion inhibitor, and air-entraining admixture.
117
Chap. 7 (2010).qxd:EB001 (2010) 1/27/11 2:35 PM Page 118
Design and Control of Concrete Mixtures ◆ EB001
Table 7-1. Concrete Admixtures by Classification
Type of admixture Desired effect Material
Accelerators Accelerate setting and early-strength Calcium chloride (ASTM D98 and AASHTO M 144)
(ASTMC494and development Triethanolamine, sodium thiocyanate, calcium formate, calcium
AASHTOM194,TypeC) nitrite, calcium nitrate
Air detrainers Decrease air content Tributyl phosphate, dibutyl phthalate, octyl alcohol, water-
insoluble esters of carbonic and boric acid, silicones
Air-entraining admixtures Improve durability in freeze-thaw, deicer, Salts of wood resins (Vinsol resin), some synthetic detergents,
(ASTMC260and sulfate, and alkali-reactive environments salts of sulfonated lignin, salts of petroleum acids, salts of
AASHTOM154) Improve workability proteinaceous material, fatty and resinous acids and their salts,
alkylbenzene sulfonates, salts of sulfonated hydrocarbons
Alkali-aggregate reactivity Reduce alkali-aggregate reactivity Barium salts, lithium nitrate, lithium carbonate, lithium
inhibitors expansion hydroxide
Antiwashout admixtures Cohesive concrete for underwater Cellulose, acrylic polymer
placements
Bonding admixtures Increase bond strength Polyvinyl chloride, polyvinyl acetate, acrylics, butadiene-styrene
copolymers
Coloring admixtures Colored concrete Modified carbon black, iron oxide, phthalocyanine, umber,
(ASTMC979) chromium oxide, titanium oxide, cobalt blue
Corrosion inhibitors Reduce steel corrosion activity in a Amine carboxylates aminoester organic emulsion, calcium nitrite,
(ASTMC1582) chloride-laden environment organic alkyidicarboxylic, chromates, phosphates, hypophosphites,
alkalis, and fluorides
Dampproofing admixtures Retard moisture penetration into dry Soaps of calcium or ammonium stearate or oleate
concrete Butyl stearate, Petroleum products
Foaming agents Produce lightweight, foamed concrete Cationic and anionic surfactants
with low density Hydrolized protein
Fungicides, germicides, Inhibit or control bacterial and fungal Polyhalogenated phenols
and insecticides growth Dieldrin emulsions, Copper compounds
Gas formers Cause expansion before setting Aluminum powder
Grouting admixtures Adjust grout properties for specific See Air-entraining admixtures, Accelerators, Retarders, and
applications Water reducers
Hydration control Suspend and reactivate cement Carboxylic acids
admixtures hydration with stabilizer and activator Phosphorus-containing organic acid salts
Permeability-reducing Water-repellent surface, reduced water Long-chain fatty acid derivatives (stearic oleic, caprylic capric),
admixture: non-hydrostatic absorption soaps and oils, (tallows, soya-based), petroleum derivatives
conditions (PRAN) (mineral oil, paraffin, bitumen emulsions), and fine particle
fillers (silicates, bentonite, talc)
Permeability reducing Reduced permeability, increased resis- Crystalline hydrophilic polymers (latex, water-soluble, or liquid
admixture: hydrostatic tance to water penetration under polymer)
conditions (PRAH) pressure
Pumping aids Improve pumpability Organic and synthetic polymers
Organic flocculents
Organic emulsions of paraffin, coal tar, asphalt, acrylics
Bentonite and pyrogenic silicas
Hydrated lime (ASTM C141)
Retarding admixtures Retard setting time Lignin, Borax
(ASTMC494and Sugars, Tartaric acid and salts
AASHTOM194,TypeB)
Shrinkage reducers Reduce drying shrinkage Polyoxyalkylene alkyl ether
Propylene glycol
Superplasticizers* Increase flowability of concrete Sulfonated melamine formaldehyde condensates
(ASTMC1017,Type1) Reduce water-cement ratio Sulfonated naphthalene formaldehyde condensates
Lignosulfonates, Polycarboxylates
118
Chap. 7 (2010).qxd:EB001 (2010) 1/27/11 2:35 PM Page 119
Chapter 7 ◆ Chemical Admixtures for Concrete
Table 7-1. Concrete Admixtures by Classification (Continued)
Type of admixture Desired effect Material
Superplasticizer* and Increase flowability with retarded set See superplasticizers and also water reducers
retarder (ASTM C1017, Reduce water–cement ratio
Type 2)
Water reducer Reduce water content at least 5% Lignosulfonates
(ASTM C494 and Hydroxylated carboxylic acids
AASHTOM194,TypeA) Carbohydrates
(Also tend to retard set so accelerator is often added)
Water reducer and Reduce water content (minimum 5%) See water reducer, Type A (accelerator is added)
accelerator (ASTM C494 and accelerate set
and AASHTO M 194,
Type E)
Water reducer and Reduce water content (minimum 5%) See water reducer, Type A (retarder is added)
retarder (ASTM C494 and and retard set
AASHTOM194,TypeD)
Water reducer—high Reduce water content (minimum 12%) See superplasticizers
range (ASTM C494 and
AASHTOM194,TypeF)
Water reducer—high Reduce water content (minimum 12%) See superplasticizers and also water reducers
range—and retarder and retard set
(ASTM C494 and
AASHTOM194,TypeG)
Water reducer—mid Reduce water content (between 6 and Lignosulfonates
range 12%)without retarding Polycarboxylates
* Superplasticizers are also referred to as high-range water reducers or plasticizers. These admixtures often meet both ASTM C494
(AASHTOM194)andASTMC1017specifications.
. Applicable requirements
Air-Entraining Admixtures Air-Entraining Hydraulic Cement
for air-entraining cements are given inASTM C150, Stan-
Oneofthegreatestadvancesinconcretetechnologywas dard Specification for Portland Cement andAASHTOM85.
the developmentofair-entrainedconcreteinthemid- SeeChapter11,Klieger(1966),andWhitingandNagi
1930s.Air-entrainmentdramaticallyimprovesthedur- (1998) for more information.
ability of concrete exposed to cycles of freezing and Air-Entraining Materials
thawinganddeicerchemicals(seeChapter11).Thereare
also other important benefits of entrained air in both Theprimaryingredientsusedinair-entrainingadmix-
freshly mixedandhardenedconcrete(seeChapter9). tures are listed in Table 7-1. Numerous commercial air-
entraining admixtures, manufacturedfromavarietyof
Air-entraining concrete is produced by using either an air- materials, are available. Most air-entraining admixtures
entraining cementorbyaddinganair-entrainingadmix- consist of one or more of the following materials: wood
tureduringbatching,oracombinationoftheseapproaches. resin (Vinsol resin), sulfonated hydrocarbons, fatty and
Air-entraining cement is a portland cement with an air- resinous acids, and synthetic materials. Chemical descrip-
entraining addition interground with the clinker during tions and performancecharacteristics of commonair-
manufacture(seeChapter3).Anair-entrainingadmixture, entraining agents are shown in Table 7-2.Air-entraining
ontheotherhand,isaddeddirectlytotheconcretemate- admixturesareusuallyliquidsandshouldnotbeallowed
rials either before or during mixing. Regardless of the ap- to freeze.Admixturesaddedatthemixershouldconform
proachused,adequatecontrolandmonitoringisrequired toASTMC260(AASHTOM154).
to ensure the proper air content at all times. Air-entraining cements complywithASTMC150and
Specifications and methods of testing air-entraining C595(AASHTOM85andM240).Toproducesuch
admixturesaregiveninASTMC260,StandardSpecification cements,air-entraining additions conforming toASTM
for Air-Entraining Admixtures for Concrete, and C233, Stan- C226areintergroundwiththecementclinkerduring
dard Test Method for Air-Entraining Admixtures for Concrete manufacture.Air-entrainingcementsgenerallyprovidean
(AASHTOM154andT157).Air-entrainingadditionsfor adequateamountofentrainedairtomeetmostjobcondi-
useinthemanufactureofair-entrainingcementsmust tions; however, a specified air content may not necessarily
beobtainedintheconcrete.Ifaninsufficientvolumeof
meetrequirementsofASTMC226,StandardSpecification air is entrained, it may also be necessary to add an air-
for Air-Entraining Additions for Use in the Manufacture of entraining admixtureatthemixer.
119
Chap. 7 (2010).qxd:EB001 (2010) 1/27/11 2:35 PM Page 120
Design and Control of Concrete Mixtures ◆ EB001
Table 7-2. Classification and Performance Characteristics of Common Air-Entraining Admixtures
Classification Chemical description Notes and performance characteristics
Wood derived acid salts Alkali or alkanolamine salt of:
®
Vinsol resin Amixture of tricyclic acids, phenolics, Quick air generation. Minor air gain with initial mixing.
and terpenes. Air loss with prolonged mixing. Mid-sized air bubbles
formed. Compatible with most other admixtures.
Wood rosin Tricyclic acids-major component. Sameasabove.
Tricyclic acids-minor component.
Tall oil Fatty acids-major component. Slower air generation. Air may increase with prolonged
Tricyclic acids-minor component. mixing. Smallest air bubbles of all agents. Compatible
with most other admixtures.
Vegetable oil acids Coconut fatty acids, alkanolamine salt. Slower air generation than wood rosins. Moderate air loss
with mixing. Coarser air bubbles relative to wood rosins.
Compatible with most other admixtures.
Synthetic detergents Alkyl-aryl sulfonates and sulfates (e.g., Quick air generation. Minor air loss with mixing. Coarser
sodium dodecylbenzenesulfonate). bubbles. May be incompatible with some HRWR. Also
applicable to cellular concretes.
Synthetic workability aids Alkyl-aryl ethoxylates. Primarily used in masonry mortars.
Miscellaneous Alkali-alkanolamine acid salts of ligno- All these are rarely used as concrete air-entraining agents
sulfonate. in current practice.
Oxygenated petroleum residues.
Proteinaceous materials.
Animal tallows.
Mechanism of Air Entrainment coalescenceofbubbles(C&D).Thesurfacechargecauses
Air-entraining admixtures are surfactants (surface-active theairbubbletobeadheredtothechargedsurfacesof
agents) whichconcentrateattheair-waterinterfaceand cementandaggregateparticles.Thefineaggregateparti-
reducethesurfacetensionencouragingtheformationof cles also act as a three-dimensional grid to help hold the
microscopicbubblesduringthemixingprocess.Theair- bubblesinthemixture(E).Thisimprovesthecohesionof
entraining admixturestabilizes those bubbles, enhances themixtureandfurtherstabilizestheairbubbles(F).
the incorporation of bubbles of various sizes, impedes Entrainedairbubblesarenotlikeentrappedairvoids,
bubblecoalescence,andanchorsbubblestocementand whichoccurinallconcretesasaresultofmixing,handling,
aggregateparticles. andplacing.Entrappedairvoidsarelargelyafunction
Theair-entrainingadmixtureactsattheair-waterinterface. of aggregate characteristics. Intentionally entrained air
Air-entrainingadmixturestypicallyhaveanegatively bubblesareextremelysmallinsize,between10to1000µm
chargedheadwhichishydrophilicandattractswater,and in diameter, while entrappedvoidsareusually1000µm
ahydrophobictailwhichrepelswater.Asillustratedin (1 mm)orlarger.Themajorityoftheentrainedairvoidsin
Figure7-2;thehydrophobicendisattractedtotheair normalconcretearebetween10µmand100µmindiam-
withinbubblesgeneratedduringthemixingprocess.The eter. As showninFigure7-3,thebubblesarenotintercon-
polarend,whichishydrophilic,orientsitselftowards nected. Theyarewelldispersedandrandomlydistributed.
water(A).Theair-entrainingadmixtureformsatough, Non-air-entrainedconcretewitha25-mm(1-in.)maximum-
water-repellingfilm, similar to a soap film, with sufficient size aggregate has an air content of approximately 1.5%.
strengthandelasticitytocontainandstabilizetheair Thissamemixtureairentrainedforseverefrostexposure
bubbles.Thehydrophobicfilmalsokeepswateroutofthe wouldrequireatotalaircontentofabout6%,madeupof
bubbles(B).Thestirringandkneadingactionofmechan- bothcoarseentrappedairvoidsandfineentrainedair
ical mixing disperses the air bubbles. The charge around voids. However,itisthefinelyentrainedairsystemthatis
eachbubbleleadstorepulsiveforces,thatpreventthe mosteffectiveatprovidingfrostresistance.
120
no reviews yet
Please Login to review.
