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Lecture #18

Masonry Cement and Mortar

MORTAR

• binder = mortar

• Masonry = mortar + masonry units

MORTAR

• definitions

• differences w/ other cementitious mixtures

• classes

• components

• types

• properties

MORTAR

• cementitious materials– lime– portland cement

• sand• water

• used with individual masonry units– bonding– bedding / seating– leveling– sealing irregularities– providing strength– providing aesthetic qualities

MORTAR

• weak link in masonry construction

• thin layer stronger (compression) than thick layer

• lime added– workability– adhesive properties– extensibility

GROUT• cement• fine and coarse

aggregate• sand• water

• high slump• no segregation

• used to bond two masonry wythes together (walls one unit thick)– filling cores and voids

– binding reinforcing steel and wythes

– providing load carrying capability

• ASTM C476

• fine and coarse grouts f’C - less in non-absorbent molds– match with masonry f’C

Differences w/ other cementitious mixtures

• component materials– mortar

• cement, lime, water, fine aggregate

– grout• cement, water, fine aggregate, small-sized coarse aggregate

– portland cement concrete• cement, water, fine aggregate, coarse aggregate

• proportions

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Differences w/ other cementitious mixtures

• structural performance– PCC is structural material, resists mainly compressive

stresses– mortar, grout are binders, develop strong & durable

bond w/ masonry unit

• workability & placement methods– PCC placed in non-absorbent forms, minimum water,

w/c ratio very important to performance– mortar, grout placed in absorptive forms, much more

water, w/c ratio less important

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Classes• lime mortar

– lime, sand, water– slow strength gain– calcium carbonate

formation– seldom used in

permanent construction

• cement/cement-lime mortar– cement, lime, sand, water– most common

• masonry cement mortar– proprietary ingredients– workable– low bond strength, not durable

- most commonly used but least desirable

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Components• portland cement

– durability– high early strength– high compressive strength– bond strength

• sand– filler– strength

• lime– workability– water retentivity– elasticity– bond strength– extensibility

• water– flow– required for hydration

• admixtures

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Components• portland cement

– Type I - general use when special properties not required

– Type II - when moderate sulfate resistance or moderate heat of hydration required

– Type III - when high early strength required

– Air entrained portland cements tend to reduce bond strengths

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Components• hydrated lime [Ca(OH)2]

– chalk or limestone (CaCO3) burned at 900 0C in kiln to produce quicklime (CaO)

– water added to quicklime

– Types (ASTM C207)• N - normal, unhydrated oxides & plasticity not controlled• S - special, commonly used• NA - normal air-entraining, not recommended• SA - special air-entraining, not recommended

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Components• aggregates

– natural or manufactured– gradation (ASTM C144)

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Components• water

– clean– potable– free of deleterious

materials• acids• alkalies• organic materials

• admixtures– color

– workability

– reduced water penetration

– accelerated curing

– use w/ caution

– air-entraining

– chlorides

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Types (MASONWORK)• ASTM C270

– proportion specifications - RECOMMENDED– property specifications

• established with laboratory testing, trial & error

– same letter designations, but

Type N (proportion) = Type N (property)

(proportion - higher compressive strength)

• Type M (paving brick)– high strength– general use– below grade OR in contact w/ ground

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Types (MASONWORK)

• Type S (structural masonry, reinforced brick)– high strength– reinforced masonry– areas subject to high wind

• Type N (normal, common)– high strength– general use– below grade OR in contact w/ ground

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Types (MASONWORK)

• Type O (interior)– low strength– non-bearing applications– not subject to severe weathering

• Type K (restoration)

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Types (MASONWORK)• Proportion Specifications

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Determine quantities and absolute volumes for an N Type Mortar

• Vsand = 1.0 ft3

• Vlime= 0.5 to 1.25 Vc

• Vsand=2.25 to 3 (Vc+Vl)

• 1 ft3 of damp loose sand will yield 1 ft3 of mortar. (due to bulking of wet sand)

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Types (MASONWORK)• Property Specificationsa

a Laboratory prepared mortar onlyb When structural reinforcement is incorporated in cement-lime mortar, the maximum air content shall be 12%c When structural reinforcement is incorporated in masonry cement mortar, the maximum air content shall be 18%.

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Selecting Mortar Types• considerations

– structural requirements

– exposure– wall type– workability

• no single type for all purposes

• DO NOT change mortar types within same structure– uneconomical

• NEVER use mortar stronger in compression than required– shrinkage, debonding

– uneconomical

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Laboratory vs. Field Mortar

• CANNOT COMPARE– field mortar

• more water required (lost in evaporation or to masonry unit)

– laboratory mortar• less water, lower initial flow• different curing conditions

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Properties• plastic properties

– influence hardened properties

– workability– initial flow– flow after suction– water retentivity

• hardened properties– determine performance

– bond strength– durability– extensibilty– compressive strength

• other properties– color

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Workability• easily spread• adhere to vertical surface• difficult to measure directly• no standard test or quantitative measure• indicators include flow, water retentivity, resistance

to segregation• affected by properties of components

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Flow (ASTM C109)• cone formed on flow table• raised & dropped 25 times in 15 seconds• flow = ratio of increase in diameter

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Water Retentivity (ASTM C91)• ability to resist loss of water to absorbent masonry unit• flow after suction (vacuum for 1 min)/ initial flow• low retentivity will bleed moisture unless brick has

high suction (IRA)• high retentivity will create dry surface

• low bond strength for low or high retentivity paired with average masonry unit

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Bond Strength• most important physical property• difficult to measure directly, simulate construction

Bond Strength

Max Bond

• cement: lime

1:1 to 1:1/4

•Type S mortar

Suction (IRA)

Air Content Elapsed Time Mortar Flow Brick Texture rough Retempering

Pressure Movement after set Water Retentivity

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Bond Strength

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Other Hardened Properties

• durability– not significant if

properly prepared– no air-entraining

components

• extensibility– max t at rupture

– elongation before cracking

– lime contributes

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Other Hardened Properties• compressive strength

– f (cement content, w/c)– cubes (ASTM C109)

– cylinders, briquettes

Proportion f’cCement Lime Water Flow

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Other Properties• color

– colored aggregates - PREFERRED– colored pigment