Road Mix Gradations Tips

 Some must know calculations/tricks for road Engineers

Material mechanics is very important part of road engineering and hence gradation becomes very important for mechanical stabilisation, it is not possible that every time we recieve exact gradation mix, we have to achive that required gradation by mixing two or more diffrent gradation materials.Sometimes the index properties need to be modified by mixing two materials. there are some simple methods which can be easily applied on field to achive required gradation and Index properties as mentioned below.

1) Achieve required gradation by mixing

Many times material that we recieved on site is not as per gradation which is very important for mechanical stabilisation of the layer, if we have mixes having two different gradations but not as per norms or required gradation then it is possible to achieve required gradation in some proportion by mixing those two gradations, Mixing Proportion is the key here.It can be find out in following way.

Material A			Reccommended Limits			Material B
Num Diff	% Passing	Sieve Size (mm)	Lower Limits	Upper Limits	Arithmetic mean	% Passing	Num Diff
0	100	40	100	100	100	100	0
-8	98	20	80	100	90	73	17
-26.5	94	10	55	80	67.5	55	12.5
-33	83	4.75	40	60	50	42	8
-32	72	2.36	30	50	40	35	5
-32.5	55	0.6	15	30	22.5	21	1.5
-7	17	0.075	5	15	10	9	1
139							45

 Material A:B = 45 : 139

Material A:B = 1 : 3.08

2) Mixing of Two Material to get required P.I.

Ratio to Required P.I. A:B= (C-B) : (A-C)

A:B = (6-14) : (2-6) 

A:B = 8 : 4 = 2:1

3) Triangular Chart Method

Thgis method is used for aggregate blending, its quite simple method if it can be done on AutoCAD software. 

Steps :- 

i) Make a triangle with course aggregate (30 to 2 mm), Sand (2 to 0.06 mm) and silt and clay (<0.06 mm) on one side each with 0 to 100%.

ii) Mark materials A,B, C and desired gradation D on triangular Chart.

iii) Joint Point D with A, B or C (Say C).

iv) Extend it to meet the line AB at E.

% of A = EB.DC x 100 / AB.EC

%  of B = EA.DC x 100 / AB.EC

% of C = ED/EC x 100