1 Lecture #18 Masonry Cement and Mortar. MORTAR binder = mortar Masonry = mortar + masonry units.
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Transcript of 1 Lecture #18 Masonry Cement and Mortar. MORTAR binder = mortar Masonry = mortar + masonry units.
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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