Aggregates are used in concrete to offer economy in the cost of concrete. Aggregates act as a filler. They usually do not react with water and cement.
But there are some properties of aggregate which determine the properties of resulting concrete mixture.
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Following are its Properties.
Aggregates consisting of stuff that will react with alkalies in cement and cause deterioration, cracking and excessive growth of concrete combination should not be used. In order that it truly is necessary to analyze aggregates to know not or whether there is presence of these components in aggregate.
- SIZE & SHAPE
Shape and the size of the aggregate particles greatly influence the number of cement required in concrete mix and hence ultimately market of concrete. For the preparation of economic concrete mixture, we should use coarse aggregates for the structure.
Remember that the size & shape of aggregate particles determine the properties of freshly mixed concrete compared to those of hardened concrete.
- SURFACE TEXTURE
The development of tough bond strength between aggregate particles and cement paste is dependent upon surface roughness, the top texture and surface porosity of the aggregate particles.
Maximum bond strength grows, in the event if the surface is rough but porous.
- SPECIFIC GRAVITY
The ratio of weight of oven dried aggregates preserved for 24 hours to the weight of equivalent volume of water displaced by saturated dry surface aggregate, in a temperature of 100 to 1100C is recognized as specific gravity of aggregates.
Specific gravities are primarily of two kinds.
(a.) Apparent specific gravity.
(b.) Mass specific gravity.
Weak porous and absorptive stuff are typically indicated by low specific gravity, whereas high specific gravity indicates stuff of top quality. Specific gravity of leading aggregates falls within the range of 2.6 to 2.9.
While designing concrete mix specific gravity values can also be used.
- BULK DENSITYIt is typically expressed in kg/litre.
Bulk density of aggregates depends upon the following 3 variables.
(a.)Amount of compaction
(b.) Grading of aggregates.
(c.) Shape of aggregate particles
The empty spaces in the aggregate particles are known as voids. The volume of void is equals to the difference involving the gross volume of the aggregate mass as well as the volume occupied by the particles.
- POROSITY & ABSORPTION
The tiny holes formed during solidification of the molten magma in stone, because of air bubbles, are known as pores. Rocks featuring pores are called porous stone.
Water absorption may be defined as the difference between the weight of aggregates that were really dry as well as the weight of the aggregates that were soaked with surface dry states
- BULKING OF SAND
It may be defined as in increase in the mass volume of the quantity of sand (i.e. fine aggregate) in a moist condition over the volume of the same amount of dry or fully drenched sand. When dry, is called bulking variable, the ratio of the volume of damp sand as a result of increase in volume of sand.
- Fineness Modulus
Fineness modulus is an empirical factor obtained by adding the cumulative percents of aggregate retained on all the conventional sieves which range from 80 mm to 150 micron and dividing this sum by 100.
Fineness modulus is ordinarily used to get a notion of how rough or fine the aggregate is. Fineness modulus value indicates little value of fineness modulus signals the aggregate is finer and the aggregate is rougher.
- PARTICULAR SURFACE OF AGGREGATE
Special surface increases with all the reduction in the size of aggregate particle.