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Cementitious Materials

Fly ash can be used in concrete of cementitious nature however; the minimum cement content must be met by considering both the Portland cement and the fly ash together. The replacement rate must be met from proper laboratory test results. It should be noted that fly ash is a partial additive, not a total replacement. The amount of fly ash should only fall between 10 and 20 percent.

Ground blast-furnace slag can be used by itself, or along with fly ash if desired, again as an additive to the aggregate. The amount used should fall between 25 and 55 percent of the total cementitious material by weight. In some cases only 30 percent by weight slag is allowable.

Admixtures

            Any air entraining mixtures should be added to insure uniform distribution throughout the batch. The allowable air content shall be determined by the testing of gravel and stone course aggregate with ASTM C 231 and slag or other highly porous coarse aggregate ASTM C 173.

                                       

RECOMMENDED AIR CONTENT (PERCENT)

 

 

 

 

Exposure Level

Maximum Size Aggregate inches (mm)

 

2(51)

1.5(38)

1(25)

3/4(19)

1/2(13)

 

Mild

2.0

2.5

3.0

3.5

4.0

Moderate

4.0

4.5

4.5

5.0

5.5

Severe

5.0

5.5

6.0

6.0

7.0

 

            Any chemical admixtures such as water-reducing and set-controlling agents should only be used in the amount necessary to comply with the specification requirements. Tests should be conducted to conform to the results of adequacy in accordance with ASTM C 494.