cement & concrete basics
TRANSCRIPT
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 15
Cement amp Concrete Basics FAQs
Are there different types of portland cement
Though all portland cement is basically the same eight types of cement aremanufactured to meet different physical and chemical requirements forspecific applications
bull Type I is a general purpose portland cement suitable for most uses
bull Type II is used for structures in water or soil containing moderate
amounts of sulfate or when heat build-up is a concern
bull Type III cement provides high strength at an early state usually in a
week or less
bull Type IV moderates heat generated by hydration that is used for
massive concrete structures such as dams
bull Type V cement resists chemical attack by soil and water high in
sulfates
bull Types I II and III are cements used to make air-entrained
concrete They have the same properties as types I II and III ecept
that they have small quantities of air-entrained materials combined withthem
hite portland cement is made from raw materials containing little or no ironor manganese the substances that give conventional cement its gray color
How can you tell if youre getting the amount of concrete youre
paying for
The real indicator is the yield or the actual volume produced based on theactual batch quantities of cement water and aggregates The unit weight testcan be used to determine the yield of a sample of the ready mied concreteas delivered Its a simple calculation that requires the unit weight of allmaterials batched The total weight information may be shown on the deliveryticket or it can be provided by the producer $any concrete producers actuallyover yield by about percent to make sure they arent short-changing theircustomers amput other producers may not even realie that a mi designed forone cubic yard might only produce () cubic feet or + percent of what theydesigned
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 25
How do you control the strength of concrete
The easiest way to add strength is to add cement The factor that mostpredominantly influences concrete strength is the ratio of water to cement inthe cement paste that binds the aggregates together The higher this ratio is
the weaker the concrete will be and vice versa very desirable physicalproperty that you can measure will be adversely affected by adding morewater
How do you protect a concrete surface from aggressive
materials like acids
$any materials have no effect on concrete owever there are someaggressive materials such as most acids that can have a deteriorating effecton concrete The first line of defense against chemical attack is to use quality
concrete with maimum chemical resistance followed by the application ofprotective treatments to keep corrosive substances from contacting theconcrete rinciples and practices that improve the chemical resistance ofconcrete include using a low water-cement ratio selecting a suitable cementtype 0such as sulfate-resistant cement to prevent sulfate attack1 usingsuitable aggregates water and air entrainment large number of chemicalformulations are available as sealers and coatings to protect concrete from avariety of environments2 detailed recommendations should be requested frommanufacturers formulators or material suppliers
How do you remove stains from concrete
3tains can be removed from concrete with dry or mechanical methods or bywet methods using chemical or water
4ommon dry methods include sandblasting flame cleaning and shotblastinggrinding scabbing planing and scouring 3teel-wire brushes should be usedwith care because they can leave metal particles on the surface that later mayrust and stain the concrete
et methods involve the application of water or specific chemicals according
to the nature of the stain The chemical treatment either dissolves the stainingsubstance so it can be blotted up from the surface of the concrete or bleachesthe staining substance so it will not show
How is portland cement made
4ement manufacturers mine materials such as limestone shale iron ore andclay crushed and screened the rock and place it in a cement kiln fter beingheated to etremely high temperatures these materials form a small ballcalled 5clinker6 that is very finely grounded to produce portland cement
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 35
ime and silica make up aout percent of the ingredients of cement$ther elements include alumina and iron oide The rotating kiln that cooksthe materials resembles a large horiontal pipe with a diameter of 78 to 7feet and a length of 988 feet or more ne end is raised slightly The raw miis placed in the high end and as the kiln rotates the materials move slowly
toward the lower end lame ltets at the lower end heat all the materials in thekiln to high temperatures that range between (=88 and 9888 degreesahrenheit This high heat drives off or calcines the chemically combinedwater and carbon dioide from the raw materials and forms new compounds0tricalcium silicate dicalcium silicate tricalcium aluminate and tetracalciumaluminoferrite1 or each ton of material that goes into the feed end of the kilntwo thirds of a ton comes out the discharge end called clinker This clinker isin the form of marble sied pellets The clinker is very finely ground to produceportland cement $anufacturers often add gypsum andgtor limestone duringthe grinding process
s there a universal international specification for portland
cement
ach country has its own standard for portland cement so there is nouniversal international standard The nited 3tates uses the specificationprepared by the merican 3ociety for Testing and $aterials-3T$ 4-783tandard 3pecification for ortland 4ement There are a few other countriesthat also have adopted this as their standard however there are countlessother specifications nfortunately they do not use the same criteria formeasuring properties and defining physical characteristics so they are virtually
non-translatable The uropean 4ement ssociation located in amprusselsampelgium publishes a book titled 4ement 3tandards of the orld
hat are recommended mi( proportions for good concrete
Aood concrete can be obtained by using a wide variety of mi proportions ifproper mi design procedures are used good general rule to use is the ruleof )s
bull minimum cement content of si bags per cubic yard of concrete
bull maimum water content of ) gallons per bag of cement
bull curing period 0keeping concrete moist1 a minimum of si days and
bull n air content of ) percent 0if concrete will be subltect to freeing and
thawing1
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 45
hat are the decorative finishes that can e applied to concrete
surfaces
4olor may be added to concrete by adding pigments-before or after concreteis place-and using white cement rather than conventional gray cement byusing chemical stains or by eposing colorful aggregates at the surfaceTetured finishes can vary from a smooth polish to the roughness of gravelAeometric patterns can be scored stamped rolled or inlaid into the concreteto resemble stone brick or tile paving ther interesting patterns are obtainedby using divider strips 0commonly redwood1 to form panels of various siesand shapes rectangular square circular or diamond 3pecial techniques areavailable to make concrete slip-resistant and sparkling
hat is )+++ pound concrete
It is concrete that is strong enough to carry a compressive stress of 9888 psiat ( days 4oncrete may be specified at other strengths as well4onventional concrete has strengths of =888 psi or less2 concrete withstrengths between =888 and 7B88 psi is considered high-strengthconcrete
hat is alkalisilica reactivity -A0
lkali-silica reactivity is an epansive reaction between reactive forms of silicain aggregates and potassium and sodium alkalis mostly from cement butalso from aggregates poolans admitures and miing water ternalsources of alkali from soil deicers and industrial processes can alsocontribute to reactivity The reaction forms an alkali-silica gel that swells as itdraws water from the surrounding cement paste thereby inducing pressureepansion and cracking of the aggregate and surrounding paste This oftenresults in map-pattern cracks sometimes referred to as alligator patterncracking 3C can be avoided through 71 proper aggregate selection (1 useof blended cements 91 use of proper poolanic materials and B1contaminant-free miing water
hat is the difference etween cement and concrete
lthough the terms cement and concrete often are used interchangeablycement is actually an ingredient of concrete 4oncrete is a miture ofaggregates and paste The aggregates are sand and gravel or crushed stone2the paste is water and portland cement
4ement comprises from 78 to 7 percent of the concrete mi by volumeThrough a process called hydration the cement and water harden and bindthe aggregates into a rocklike mass This hardening process continues foryears meaning that concrete gets stronger as it gets older
ortland cement is not a brand name but the generic term for the type ofcement used in virtually all concrete ltust as stainless is a type of steel and
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 55
sterling a type of silver Therefore there is no such thing as a cementsidewalk or a cement mier2 the proper terms are concrete sidewalk andconcrete mier
hy do concrete surfaces flake and spall
4oncrete surfaces can flake or spall for one or more of the following reasons
bull In areas of the country that are subltected to freeing and thawing the
concrete should be air-entrained to resist flaking and scaling of thesurface If air-entrained concrete is not used there will be subsequentdamage to the surface
bull The watergtcement ratio should be as low as possible to improve
durability of the surface Too much water in the mi will produce a
weaker less durable concrete that will contribute to early flaking andspalling of the surface
bull The finishing operations should not begin until the water sheen on the
surface is gone and ecess bleed water on the surface has had achance to evaporate If this ecess water is worked into the concretebecause the finishing operations are begun too soon the concrete onthe surface will have too high a water content and will be weaker andless durable
hy does concrete crack
4oncrete like all other materials will slightly change in volume when it driesout In typical concrete this change amounts to about 88 millionthsTranslated into dimensions-this is about 7gt7) of an inch in 78 feet The reasonthat contractors put ltoints in concrete pavements and floors is to allow theconcrete to crack in a neat straight line at the ltoint when the volume of theconcrete changes due to shrinkage
ill concrete harden under water
ortland cement is a hydraulic cement which means that it sets and hardensdue to a chemical reaction with water 4onsequently it will harden underwater
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 25
How do you control the strength of concrete
The easiest way to add strength is to add cement The factor that mostpredominantly influences concrete strength is the ratio of water to cement inthe cement paste that binds the aggregates together The higher this ratio is
the weaker the concrete will be and vice versa very desirable physicalproperty that you can measure will be adversely affected by adding morewater
How do you protect a concrete surface from aggressive
materials like acids
$any materials have no effect on concrete owever there are someaggressive materials such as most acids that can have a deteriorating effecton concrete The first line of defense against chemical attack is to use quality
concrete with maimum chemical resistance followed by the application ofprotective treatments to keep corrosive substances from contacting theconcrete rinciples and practices that improve the chemical resistance ofconcrete include using a low water-cement ratio selecting a suitable cementtype 0such as sulfate-resistant cement to prevent sulfate attack1 usingsuitable aggregates water and air entrainment large number of chemicalformulations are available as sealers and coatings to protect concrete from avariety of environments2 detailed recommendations should be requested frommanufacturers formulators or material suppliers
How do you remove stains from concrete
3tains can be removed from concrete with dry or mechanical methods or bywet methods using chemical or water
4ommon dry methods include sandblasting flame cleaning and shotblastinggrinding scabbing planing and scouring 3teel-wire brushes should be usedwith care because they can leave metal particles on the surface that later mayrust and stain the concrete
et methods involve the application of water or specific chemicals according
to the nature of the stain The chemical treatment either dissolves the stainingsubstance so it can be blotted up from the surface of the concrete or bleachesthe staining substance so it will not show
How is portland cement made
4ement manufacturers mine materials such as limestone shale iron ore andclay crushed and screened the rock and place it in a cement kiln fter beingheated to etremely high temperatures these materials form a small ballcalled 5clinker6 that is very finely grounded to produce portland cement
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 35
ime and silica make up aout percent of the ingredients of cement$ther elements include alumina and iron oide The rotating kiln that cooksthe materials resembles a large horiontal pipe with a diameter of 78 to 7feet and a length of 988 feet or more ne end is raised slightly The raw miis placed in the high end and as the kiln rotates the materials move slowly
toward the lower end lame ltets at the lower end heat all the materials in thekiln to high temperatures that range between (=88 and 9888 degreesahrenheit This high heat drives off or calcines the chemically combinedwater and carbon dioide from the raw materials and forms new compounds0tricalcium silicate dicalcium silicate tricalcium aluminate and tetracalciumaluminoferrite1 or each ton of material that goes into the feed end of the kilntwo thirds of a ton comes out the discharge end called clinker This clinker isin the form of marble sied pellets The clinker is very finely ground to produceportland cement $anufacturers often add gypsum andgtor limestone duringthe grinding process
s there a universal international specification for portland
cement
ach country has its own standard for portland cement so there is nouniversal international standard The nited 3tates uses the specificationprepared by the merican 3ociety for Testing and $aterials-3T$ 4-783tandard 3pecification for ortland 4ement There are a few other countriesthat also have adopted this as their standard however there are countlessother specifications nfortunately they do not use the same criteria formeasuring properties and defining physical characteristics so they are virtually
non-translatable The uropean 4ement ssociation located in amprusselsampelgium publishes a book titled 4ement 3tandards of the orld
hat are recommended mi( proportions for good concrete
Aood concrete can be obtained by using a wide variety of mi proportions ifproper mi design procedures are used good general rule to use is the ruleof )s
bull minimum cement content of si bags per cubic yard of concrete
bull maimum water content of ) gallons per bag of cement
bull curing period 0keeping concrete moist1 a minimum of si days and
bull n air content of ) percent 0if concrete will be subltect to freeing and
thawing1
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 45
hat are the decorative finishes that can e applied to concrete
surfaces
4olor may be added to concrete by adding pigments-before or after concreteis place-and using white cement rather than conventional gray cement byusing chemical stains or by eposing colorful aggregates at the surfaceTetured finishes can vary from a smooth polish to the roughness of gravelAeometric patterns can be scored stamped rolled or inlaid into the concreteto resemble stone brick or tile paving ther interesting patterns are obtainedby using divider strips 0commonly redwood1 to form panels of various siesand shapes rectangular square circular or diamond 3pecial techniques areavailable to make concrete slip-resistant and sparkling
hat is )+++ pound concrete
It is concrete that is strong enough to carry a compressive stress of 9888 psiat ( days 4oncrete may be specified at other strengths as well4onventional concrete has strengths of =888 psi or less2 concrete withstrengths between =888 and 7B88 psi is considered high-strengthconcrete
hat is alkalisilica reactivity -A0
lkali-silica reactivity is an epansive reaction between reactive forms of silicain aggregates and potassium and sodium alkalis mostly from cement butalso from aggregates poolans admitures and miing water ternalsources of alkali from soil deicers and industrial processes can alsocontribute to reactivity The reaction forms an alkali-silica gel that swells as itdraws water from the surrounding cement paste thereby inducing pressureepansion and cracking of the aggregate and surrounding paste This oftenresults in map-pattern cracks sometimes referred to as alligator patterncracking 3C can be avoided through 71 proper aggregate selection (1 useof blended cements 91 use of proper poolanic materials and B1contaminant-free miing water
hat is the difference etween cement and concrete
lthough the terms cement and concrete often are used interchangeablycement is actually an ingredient of concrete 4oncrete is a miture ofaggregates and paste The aggregates are sand and gravel or crushed stone2the paste is water and portland cement
4ement comprises from 78 to 7 percent of the concrete mi by volumeThrough a process called hydration the cement and water harden and bindthe aggregates into a rocklike mass This hardening process continues foryears meaning that concrete gets stronger as it gets older
ortland cement is not a brand name but the generic term for the type ofcement used in virtually all concrete ltust as stainless is a type of steel and
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 55
sterling a type of silver Therefore there is no such thing as a cementsidewalk or a cement mier2 the proper terms are concrete sidewalk andconcrete mier
hy do concrete surfaces flake and spall
4oncrete surfaces can flake or spall for one or more of the following reasons
bull In areas of the country that are subltected to freeing and thawing the
concrete should be air-entrained to resist flaking and scaling of thesurface If air-entrained concrete is not used there will be subsequentdamage to the surface
bull The watergtcement ratio should be as low as possible to improve
durability of the surface Too much water in the mi will produce a
weaker less durable concrete that will contribute to early flaking andspalling of the surface
bull The finishing operations should not begin until the water sheen on the
surface is gone and ecess bleed water on the surface has had achance to evaporate If this ecess water is worked into the concretebecause the finishing operations are begun too soon the concrete onthe surface will have too high a water content and will be weaker andless durable
hy does concrete crack
4oncrete like all other materials will slightly change in volume when it driesout In typical concrete this change amounts to about 88 millionthsTranslated into dimensions-this is about 7gt7) of an inch in 78 feet The reasonthat contractors put ltoints in concrete pavements and floors is to allow theconcrete to crack in a neat straight line at the ltoint when the volume of theconcrete changes due to shrinkage
ill concrete harden under water
ortland cement is a hydraulic cement which means that it sets and hardensdue to a chemical reaction with water 4onsequently it will harden underwater
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 35
ime and silica make up aout percent of the ingredients of cement$ther elements include alumina and iron oide The rotating kiln that cooksthe materials resembles a large horiontal pipe with a diameter of 78 to 7feet and a length of 988 feet or more ne end is raised slightly The raw miis placed in the high end and as the kiln rotates the materials move slowly
toward the lower end lame ltets at the lower end heat all the materials in thekiln to high temperatures that range between (=88 and 9888 degreesahrenheit This high heat drives off or calcines the chemically combinedwater and carbon dioide from the raw materials and forms new compounds0tricalcium silicate dicalcium silicate tricalcium aluminate and tetracalciumaluminoferrite1 or each ton of material that goes into the feed end of the kilntwo thirds of a ton comes out the discharge end called clinker This clinker isin the form of marble sied pellets The clinker is very finely ground to produceportland cement $anufacturers often add gypsum andgtor limestone duringthe grinding process
s there a universal international specification for portland
cement
ach country has its own standard for portland cement so there is nouniversal international standard The nited 3tates uses the specificationprepared by the merican 3ociety for Testing and $aterials-3T$ 4-783tandard 3pecification for ortland 4ement There are a few other countriesthat also have adopted this as their standard however there are countlessother specifications nfortunately they do not use the same criteria formeasuring properties and defining physical characteristics so they are virtually
non-translatable The uropean 4ement ssociation located in amprusselsampelgium publishes a book titled 4ement 3tandards of the orld
hat are recommended mi( proportions for good concrete
Aood concrete can be obtained by using a wide variety of mi proportions ifproper mi design procedures are used good general rule to use is the ruleof )s
bull minimum cement content of si bags per cubic yard of concrete
bull maimum water content of ) gallons per bag of cement
bull curing period 0keeping concrete moist1 a minimum of si days and
bull n air content of ) percent 0if concrete will be subltect to freeing and
thawing1
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 45
hat are the decorative finishes that can e applied to concrete
surfaces
4olor may be added to concrete by adding pigments-before or after concreteis place-and using white cement rather than conventional gray cement byusing chemical stains or by eposing colorful aggregates at the surfaceTetured finishes can vary from a smooth polish to the roughness of gravelAeometric patterns can be scored stamped rolled or inlaid into the concreteto resemble stone brick or tile paving ther interesting patterns are obtainedby using divider strips 0commonly redwood1 to form panels of various siesand shapes rectangular square circular or diamond 3pecial techniques areavailable to make concrete slip-resistant and sparkling
hat is )+++ pound concrete
It is concrete that is strong enough to carry a compressive stress of 9888 psiat ( days 4oncrete may be specified at other strengths as well4onventional concrete has strengths of =888 psi or less2 concrete withstrengths between =888 and 7B88 psi is considered high-strengthconcrete
hat is alkalisilica reactivity -A0
lkali-silica reactivity is an epansive reaction between reactive forms of silicain aggregates and potassium and sodium alkalis mostly from cement butalso from aggregates poolans admitures and miing water ternalsources of alkali from soil deicers and industrial processes can alsocontribute to reactivity The reaction forms an alkali-silica gel that swells as itdraws water from the surrounding cement paste thereby inducing pressureepansion and cracking of the aggregate and surrounding paste This oftenresults in map-pattern cracks sometimes referred to as alligator patterncracking 3C can be avoided through 71 proper aggregate selection (1 useof blended cements 91 use of proper poolanic materials and B1contaminant-free miing water
hat is the difference etween cement and concrete
lthough the terms cement and concrete often are used interchangeablycement is actually an ingredient of concrete 4oncrete is a miture ofaggregates and paste The aggregates are sand and gravel or crushed stone2the paste is water and portland cement
4ement comprises from 78 to 7 percent of the concrete mi by volumeThrough a process called hydration the cement and water harden and bindthe aggregates into a rocklike mass This hardening process continues foryears meaning that concrete gets stronger as it gets older
ortland cement is not a brand name but the generic term for the type ofcement used in virtually all concrete ltust as stainless is a type of steel and
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 55
sterling a type of silver Therefore there is no such thing as a cementsidewalk or a cement mier2 the proper terms are concrete sidewalk andconcrete mier
hy do concrete surfaces flake and spall
4oncrete surfaces can flake or spall for one or more of the following reasons
bull In areas of the country that are subltected to freeing and thawing the
concrete should be air-entrained to resist flaking and scaling of thesurface If air-entrained concrete is not used there will be subsequentdamage to the surface
bull The watergtcement ratio should be as low as possible to improve
durability of the surface Too much water in the mi will produce a
weaker less durable concrete that will contribute to early flaking andspalling of the surface
bull The finishing operations should not begin until the water sheen on the
surface is gone and ecess bleed water on the surface has had achance to evaporate If this ecess water is worked into the concretebecause the finishing operations are begun too soon the concrete onthe surface will have too high a water content and will be weaker andless durable
hy does concrete crack
4oncrete like all other materials will slightly change in volume when it driesout In typical concrete this change amounts to about 88 millionthsTranslated into dimensions-this is about 7gt7) of an inch in 78 feet The reasonthat contractors put ltoints in concrete pavements and floors is to allow theconcrete to crack in a neat straight line at the ltoint when the volume of theconcrete changes due to shrinkage
ill concrete harden under water
ortland cement is a hydraulic cement which means that it sets and hardensdue to a chemical reaction with water 4onsequently it will harden underwater
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 45
hat are the decorative finishes that can e applied to concrete
surfaces
4olor may be added to concrete by adding pigments-before or after concreteis place-and using white cement rather than conventional gray cement byusing chemical stains or by eposing colorful aggregates at the surfaceTetured finishes can vary from a smooth polish to the roughness of gravelAeometric patterns can be scored stamped rolled or inlaid into the concreteto resemble stone brick or tile paving ther interesting patterns are obtainedby using divider strips 0commonly redwood1 to form panels of various siesand shapes rectangular square circular or diamond 3pecial techniques areavailable to make concrete slip-resistant and sparkling
hat is )+++ pound concrete
It is concrete that is strong enough to carry a compressive stress of 9888 psiat ( days 4oncrete may be specified at other strengths as well4onventional concrete has strengths of =888 psi or less2 concrete withstrengths between =888 and 7B88 psi is considered high-strengthconcrete
hat is alkalisilica reactivity -A0
lkali-silica reactivity is an epansive reaction between reactive forms of silicain aggregates and potassium and sodium alkalis mostly from cement butalso from aggregates poolans admitures and miing water ternalsources of alkali from soil deicers and industrial processes can alsocontribute to reactivity The reaction forms an alkali-silica gel that swells as itdraws water from the surrounding cement paste thereby inducing pressureepansion and cracking of the aggregate and surrounding paste This oftenresults in map-pattern cracks sometimes referred to as alligator patterncracking 3C can be avoided through 71 proper aggregate selection (1 useof blended cements 91 use of proper poolanic materials and B1contaminant-free miing water
hat is the difference etween cement and concrete
lthough the terms cement and concrete often are used interchangeablycement is actually an ingredient of concrete 4oncrete is a miture ofaggregates and paste The aggregates are sand and gravel or crushed stone2the paste is water and portland cement
4ement comprises from 78 to 7 percent of the concrete mi by volumeThrough a process called hydration the cement and water harden and bindthe aggregates into a rocklike mass This hardening process continues foryears meaning that concrete gets stronger as it gets older
ortland cement is not a brand name but the generic term for the type ofcement used in virtually all concrete ltust as stainless is a type of steel and
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 55
sterling a type of silver Therefore there is no such thing as a cementsidewalk or a cement mier2 the proper terms are concrete sidewalk andconcrete mier
hy do concrete surfaces flake and spall
4oncrete surfaces can flake or spall for one or more of the following reasons
bull In areas of the country that are subltected to freeing and thawing the
concrete should be air-entrained to resist flaking and scaling of thesurface If air-entrained concrete is not used there will be subsequentdamage to the surface
bull The watergtcement ratio should be as low as possible to improve
durability of the surface Too much water in the mi will produce a
weaker less durable concrete that will contribute to early flaking andspalling of the surface
bull The finishing operations should not begin until the water sheen on the
surface is gone and ecess bleed water on the surface has had achance to evaporate If this ecess water is worked into the concretebecause the finishing operations are begun too soon the concrete onthe surface will have too high a water content and will be weaker andless durable
hy does concrete crack
4oncrete like all other materials will slightly change in volume when it driesout In typical concrete this change amounts to about 88 millionthsTranslated into dimensions-this is about 7gt7) of an inch in 78 feet The reasonthat contractors put ltoints in concrete pavements and floors is to allow theconcrete to crack in a neat straight line at the ltoint when the volume of theconcrete changes due to shrinkage
ill concrete harden under water
ortland cement is a hydraulic cement which means that it sets and hardensdue to a chemical reaction with water 4onsequently it will harden underwater
7262019 Cement amp Concrete Basics
httpslidepdfcomreaderfullcement-concrete-basics 55
sterling a type of silver Therefore there is no such thing as a cementsidewalk or a cement mier2 the proper terms are concrete sidewalk andconcrete mier
hy do concrete surfaces flake and spall
4oncrete surfaces can flake or spall for one or more of the following reasons
bull In areas of the country that are subltected to freeing and thawing the
concrete should be air-entrained to resist flaking and scaling of thesurface If air-entrained concrete is not used there will be subsequentdamage to the surface
bull The watergtcement ratio should be as low as possible to improve
durability of the surface Too much water in the mi will produce a
weaker less durable concrete that will contribute to early flaking andspalling of the surface
bull The finishing operations should not begin until the water sheen on the
surface is gone and ecess bleed water on the surface has had achance to evaporate If this ecess water is worked into the concretebecause the finishing operations are begun too soon the concrete onthe surface will have too high a water content and will be weaker andless durable
hy does concrete crack
4oncrete like all other materials will slightly change in volume when it driesout In typical concrete this change amounts to about 88 millionthsTranslated into dimensions-this is about 7gt7) of an inch in 78 feet The reasonthat contractors put ltoints in concrete pavements and floors is to allow theconcrete to crack in a neat straight line at the ltoint when the volume of theconcrete changes due to shrinkage
ill concrete harden under water
ortland cement is a hydraulic cement which means that it sets and hardensdue to a chemical reaction with water 4onsequently it will harden underwater