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Chapter 5Chapter 5Chapter 5Chapter 5
Construction MortarConstruction MortarConstruction MortarConstruction Mortar
Chapter 5Chapter 5
§5. 3 Technical P§5. 3 Technical Propertropertiesies
Mobility (consistency) Water retentivity Strength Durability
StrengthStrength
• In order to assure the strength of whole structure, there is certain requirements for the strength of masonry mortar for foundation, walls, columns etc.
StrengthStrength
• Compressive strength average f2 (design strength)
– The pressure of cube specimen (the length of 70.7), cured in standard condition, aged of 28, has 85% strength guaranty. (Temp=20C±)
Compressive strength average f2(design strength) and strength grade
The standard condition of hydraulicity cementitious material : 24± 5 , Rh>90%curing 28d in humidity, ℃20±3 , humidity Rh=60℃ ~ 80%
StrengthStrength
• Strength Grade• According to
compressive strength average f2,
mortar can be divided into 6 grades:– M2.5– M5– M7.5– M10– M15– M20
MM 5 5
MortarMortar
Compressive Compressive Strength Strength AverageAverage
Strength Grade
Choices of grade, considering moreforce in sizeenvironment importance of project
Usually grades are M2.5~M10M15 , M20 are used in significant
structure
StrengthStrength
Choice of grade
StrengthStrength
• The major differences between the influencing factors of concrete are– Lacking coarse aggregate;– Setting hardening and the process of increasing st
rength are influenced by hygrophanous beds, that is to say, different mortar strengths for different beds.
Strength formula and influencing factors
Dense substrateDense substrate• Dense substrate (Imhygrophanous beds-Stone)• Similar to concrete, strength lies on cement strength and W/C.• Formula
ffmomo=Af=Afcece(C/W(C/W-- B)B)
fce—28d survey compressive strength of cement (MPa)fmo —28 day strength of mortar (N/mm2 or MPa)A,B—empirical coefficient (according to testing statisticdata)C/W—water cement ratio
Strength formula and influencing factors
• Porous substrate (Hygrophanous beds) • Different from concrete, strength lies on cement streng
th and quantity.
• Formula
ffmomo=A·fce·Qc/1000+B=A·fce·Qc/1000+B
Qc—cement quantity in mortar (Kg/m³)
fce—survey cement strength
A,B—empirical coefficient
Strength formula and influencing factors
Porous substratePorous substrate
A B
Cement Mix Mortar 1.50 -4.25
Cement Mortar 1.03 3.5
Empirical coefficient A,B can be chosen from Tab5.3.2
Strength formula and influencing factors
Tab5.3.2 Empirical Coefficient A,B
• Explanation
• Why the strength of mortar in porous substrate lies on cement quantity– porous substrate absorb water for mortar
while construction. – Water remained in substrate depends on
cement quantity.– For the same reason, the actual W/C depends
on cement quantity.– So the strength of mortar in porous substrate
depends on cement quantity, not W/C.
Strength formula and influencing factors