Chapter 3 Cement

3.2.3 Technical Properties of Portland Cement Fineness Setting Time Soundness of the Portland Cement Strength Other properties

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

Fig Strength testing instrument

bending strength instrument Fig 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 GB table. The cement of every grade can be classified into 2 types, high early- strength(R) ones and normal ones. Strength Grade R R R

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

Other Properties Density – g/cm 3, commonly 3.1g/cm 3 Bulk Density – kg/m 3 Density of long-kept cement decreases a little. Free CaO combines with H 2 O, CO 2 in the air to form Ca(OH) 2 and CaCO 3 with low density.

Alkali Content Alkali content which is donated by calculated value of Na 2 O+0.658K 2 O 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 C 3 S, C 3 A, the finer the particle, the bigger hydration heat, the more advantageous to the construction in winter, but more harmful for mass concrete Hydration Heat