Now-a-days we are worried about waste product and their safe disposal. Like other products concrete also becomes waste like
-serviceable building but owner need to construct better or more storied structure
-they may also come from other concrete structure like pavement made of concrete etc.
Our concern is not the source of concrete as waste; but is recycling them further as concrete constituents like coarse aggregates. We unconsciously use this concrete wastes for land development or other less productive work.
While specifying coarse aggregates ASTM C-33 provides following materials as coarse aggregates
b. Crushed gravel
c. Crushed stone
d. Blast furnace slag cooled in air
e. Crushed hydraulic cement concrete
f. And a combinations of them are also permitted according to specification
We will discuss about classification of coarse aggregate according to same specification in the next posts.
ASTM doesn’t provide specific specification but recommended to take some precautions while using such concrete as coarse aggregate.
Note-6 of ASTM C33-03:
There have some satisfactory application of crushed hydraulic cement, but need additional precautions as follows:
a. Excess water is required as crushed aggregate are harsh in texture
b. May have such constituent that can induce
1. Alkali-aggregate reaction to new concrete
2. Sulfate attack to new concrete
c. Through their pores it may bring
1. Sulfate to new concrete
2. Chloride to new concrete
3. Organic materials to new concrete
d. When aggregate are derived from partially deteriorated concrete it may
1. Reduce freezing-thawing resistance
2. Negative influence on air void properties
3. Degrade or disintegrate during