Perfect sizes of aggregates in concrete works
With adherence to ES (Ethiopian Standard) Concrete and Concrete Products Vol 16, coarse Aggregate is defined as the aggregate that is generally provided on tile 4.75mm sieve; or that section of an aggregate provided on 4.7~ sieve.
Coarse aggregate comprises of the gravel, crushed gravel, or crushed stone. The grading or particle size distribution of coarse aggregate should remain within the limits indicated in the following Table 3.
From the above table, it is found that the sizes of the aggregates vary from 38-5 , 19-5 and 13-5. You have to choose the proper size for concretes to be provided in buildings.
Aggregate size with reference to cover.
A per EBCS 2 -1995: Concrete cover to Reinforcement.
1) The concrete cover means the among the exterior surface of the reinforcement along with links ad stirrups and the adjacent concrete surface.
2) A minimum concrete cover should be arrange for the following purposes :-
A. To transfer the bond forces securely;
B. To check spilling;
C. To provide good resistance capacity against fire;
D. To safeguard the steel against corrosion.
3) To safeguard the reinforcement from corrosion, there should be persistent existence of a adjoining alkaline environment with a sufficient thickness of good quality, well cured concrete. The thickness of cover is based on the exposure conditions and the concrete quality.
4) The minimum concrete cover necessary for the criterion given above should initially be decided. It should be raised with an permissible (∆h) for tolerances on the basis of the type and size of structural component, the type of construction, standards of workmanship and quality control, and detailing practice. The result is the required nominal cover that should be indicated on the drawings.
5) To transfer bond forces securely, and to maintain sufficient compaction, the concrete cover, to the bar or tendon being considered, should not be under the following :
(a) ø or øa( <=40mm), or
(b) ( ø + 5mm) or (øa +5mm) if dg > 32mm
where ø stands for the diameter of the bar
øa stands for the corresponding diameter for a bundle
dg stands for the highest nominal maximum aggregate size