Chapter 5 Construction Mortar. Chapter 5 §5. 3 Technical Properties Mobility (consistency) Water retentivity Strength Durability.

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%

Fig5.3.2 stirring meter of mortar

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

• Mortar strength formula is much immature, changes according to construction materials dosage, material properties in different areas, mixing methods, and can be modified according to local experience and data.

Strength formula and influencing factors

NoteNote