Chapter 3Chapter 3

CementCement

3.2.3 Technical Properties of Portland Cement

• Fineness

• Setting Time

• Soundness of the Portland Cement

• Strength

• Other properties

C:S:W=1:3:0.5C:S:W=1:3:0.5

Standard specimen Standard specimen 40 × 40×16040 × 40×160

CompressiveCompressive strengthstrength

Cured underCured under the standard the standard

conditionconditionBending strengthBending strength

Compressive strength and bending strength Compressive strength and bending strength can be tested by producing standard specimen can be tested by producing standard specimen （ （ 40×40×16040×40×160 ） ） which is made by C:S:W=1:3:0.5which is made by C:S:W=1:3:0.5 and cured in the standard conditionand cured in the standard condition

Fig.3.2.10 Strength testing instrument

bending strength instrument

Fig3.2.10 Strength testing instrument

Compressive strength instrument

抗压强度抗折强度

Strength Grades• According to

– 3 days and 28 days compressive strength

– 3 days and 28 days bending strength

• Portland cement can be classified into 42.5 ， 42.5R, 52.5 ， 52.5R, 62.5, 62.5R grades.

• The strength of every age should not be lower than the required number in GB175-99 table.

• The cement of every grade can be classified into 2 types, high early-strength(R) ones and normal ones.

62.5R

62.5

52.5R

52.5

42.5R

42.5

Strength Grade

Technical Properties Analysis

The technical indexes of the The technical indexes of the cement before using are the 4 cement before using are the 4 items: fineness, setting items: fineness, setting timetime ，， strength and strength and soundness. . Fineness, setting Fineness, setting timetime ，， strength and strength and soundness must be qualified. The cement must be qualified. The cement can be used according to the can be used according to the requirement of the lower grade, requirement of the lower grade, if only the strength is if only the strength is unqualified.unqualified.

If only the strength is unqualified

Cement of the lower grade

Other Properties

• Density– 3.0-3.15g/cm3, commonly 3.1g/cm3

• Bulk Density– 1000-1600kg/m3

• Density of long-kept cement decreases a little. Free CaO combines with H2O, CO2 in the air to form Ca(OH)2 and CaCO3 with low density.

Alkali Content• Alkali content which is donated by

calculated value of Na2O+0.658K2O avoids alkali-aggregate reaction.

• Alkali content of low alkali cement≯;0.6% ，or treat between supply and requisitioning parties.

• Most hydration heat is given out at the initial period of hydration and its quantity depends on chemical compound and fineness of cement, mineral admixture and intrusion aid.

• The higher C3S, C3A, the finer the particle, the bigger hydration heat, the more advantageous to the construction in winter, but more harmful for mass concrete

Hydration HeatHydration Heat