HINDUSTAN COLAS LTD
Technical Note: TKS01/2011
Hot Mix Vs Cold Mix: Economic Comparison
Summary:
In the asphalt industry a lot of energy is consumed to heat up aggregates and sand. Very often, these
materials are wet from contacting with water (rain) or humidity from air. The economic comparison is
evaluated on this aspect since one of the key proposition for Cold Mixes are enhanced working
window.
In asphalt plants, typically aggregates and sand are stored in open areas, which could lead to
contamination with water. The amount of water depends on the size and porosity of the aggregates
as well as climate/season and the influence of geographical locations. The water content can vary
between 0% to 6% for aggregates and for sand it can go up to 10%. The influence of water content is
calculated on extra energy consumption per kg of aggregates using the specific heat capacity of
minerals. The calculations are based on 100% aggregates with water contents of 2, 4 and 6%
respectively.
-
A reduction of energy can be achieved based on the choice of aggregates/sand and their heat
capacities
-
Every percent of water in the aggregates increases the energy consumption of an asphalt plant
by ~13 to 15% depending on the specific heat of the aggregate
-
The cost of construction with emulsion can be cheaper by about 5 - 6 % than the conventional
bitumen
Technical Note: TKS01/2011
1. Specific Heat Capacity of various Aggregates:
There is a great variation of specific heat capacities of minerals. The specific heat capacities
of minerals and non-porous rocks increase substantially at higher temperatures.
Sp Heat Vs Temp - Aggregates
Specific Heat
1500
1300
1100
Granite
900
Basalt
700
Quartz
500
Temp
2.
20
75
125
175
225
Energy Consumption to heat aggregates at varying % moistures:
In asphalt plants, typically aggregates and sand are stored in open areas, which could lead to
“contamination” with rainwater. The amount of water depends on the size and porosity of the
aggregates as well as climate/season and the influence of geographical locations. The water
content can vary between 0% and (in extreme circumstances) 6% for aggregates and for
sand it can go up to 10%. The energy that is needed to evaporate water is normally
independent from the specific heat capacities of the minerals; in the calculations the influence
of particle size, porosity, natural water and chemical reaction is not included. It can be
deduced from below that aggregates with low specific heat capacities need more energy.
This is caused by the lower amount of required energy, which is needed to heat the minerals
with a low Cp; therefore the percentage of extra energy needed to heat up the water is
relatively higher
Cp (J/Kg/C)
Energy required (30C - 160C)
Extra Energy @ 2% Water
Extra Energy @ 4% Water
Extra Energy @ 6% Water
Granite
Basalt
Quartz
950
123500
172921
222342
271764
899
116870
166424
215978
265531
740
96200
146167
196134
246102
Hot Mix Vs Cold Mix: Economic Comparison
2
Technical Note: TKS01/2011
% Increase in Energy
% Increase in Energy (to heat from 30 - 160 C)
200
Extra Energy @ 2%
Water
150
100
Extra Energy @ 4%
Water
50
0
Granite
Basalt
Quartz
Extra Energy @ 6%
Water
3. Cost of Heating
The drying process in an asphalt installation is done in three stages:
o
Aggregate mix (trapped with water) are heated to the water evaporation temperature
o
The moisture is evaporated, starting from as low as perhaps 40-50°C
o
The aggregates mix heated up to the required temperature
Basis:
1 Ton of Asphalt Mix; 30 to 160C
130
930
20
50
@2% Water
930
20
50
20
kg of Aggregates
kg of Lime
kg of Bitumen
KJ
Kcal
Fuel required for
aggregates
Fuel for Bitumen
Total Fuel
Cost of Energy @40 Rs/Kg
kg of Aggregates
kg of Lime
kg of Bitumen
kg of water
KJ
Kcal
Fuel required for
aggregates
Fuel for Bitumen
Total Fuel
Cost of Energy @40 Rs/Kg
Granite
950
114855
2470
Basalt
899
108689.1
2337
Quartz
740
89466
1924
117325
27935
111026.5
26435
91390
21760
4.4
0.4
4.7
189
4.1
0.4
4.5
179
3.4
0.4
3.8
150
114855
2470
108689.1
2337
89466
1924
56073
173398
41285
56073
167100
39786
56073
147463
35110
6.5
0.4
6.8
272
6.2
0.4
6.6
263
5.5
0.4
5.8
234
Hot Mix Vs Cold Mix: Economic Comparison
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Technical Note: TKS01/2011
@4% Water
@6% Water
930
20
50
40
930
20
50
60
kg of Aggregates
kg of Lime
kg of Bitumen
kg of water
KJ
Kcal
Fuel required for
aggregates
Fuel for Bitumen
Total Fuel
Cost of Energy @40 Rs/Kg
114855
2470
108689.1
2337
89466
1924
112146
229471
54636
112146
223173
53136
112146
203536
48461
8.5
0.4
8.9
356
8.3
0.4
8.7
346
7.6
0.4
7.9
317
kg of Aggregates
kg of Lime
kg of Bitumen
kg of water
KJ
Kcal
Fuel required for
aggregates
Fuel for Bitumen
Total Fuel
Cost of Energy @40 Rs/Kg
114855
2470
108689.1
2337
89466
1924
168220
285545
67987
168220
279246
66487
168220
259610
61812
10.6
0.4
11.0
439
10.4
0.4
10.7
430
9.7
0.4
10.0
400
Significant energy is consumed due to presence of moisture in the aggregates. From these
calculations, it is clear that every 1% of water increases the energy consumption of the asphalt plant
by ~13 to 15% depending on the specific heat of the aggregate.
Hot Mix Vs Cold Mix: Economic Comparison
4
Technical Note: TKS01/2011
4. Cost Comparison of Hot Mix Vs Cold Mix
Basis:
31000 Rs/Ton Bitumen
25000 Rs/Ton Emulsion
Cost of energy @ 0% Moisture
Cost of Bitumen
Wastage @ 2%
Cost of aggregates @800Rs/Ton
Cost of Emulsion
Antistripping agent @ 150Rs/Kg at 0.5%
Transportation, Laying and Compaction
Total
% Cost Reduction with Cold Mix
Hot Mix
Cold Mix
Granite
Basalt
Quartz
189
1550
31
744
179
1550
31
744
150
1550
31
744
38
200
2751
200
2704
38
200
2713
Cost of energy @ 2% Moisture
Cost of Bitumen
Wastage @ 2%
Cost of aggregates @800Rs/Ton
Cost of Emulsion
Antistripping agent @ 150Rs/Kg at 0.5%
Transportation, Laying and Compaction
Total
% Cost Reduction with Cold Mix
272
1550
31
744
263
1550
31
744
234
1550
31
744
38
200
2835
200
2788
38
200
2796
Cost of energy @ 4% Moisture
Cost of Bitumen
Wastage @ 2%
Cost of aggregates @800Rs/Ton
Cost of Emulsion
Antistripping agent @ 150Rs/Kg at 0.5%
Transportation, Laying and Compaction
Total
% Cost Reduction with Cold Mix
356
1550
31
744
346
1550
31
744
317
1550
31
744
38
200
2918
200
2871
38
200
2879
Cost of energy @ 6% Moisture
Cost of Bitumen
Wastage @ 2%
Cost of aggregates @800Rs/Ton
Cost of Emulsion
Antistripping agent @ 150Rs/Kg at 0.5%
Transportation, Laying and Compaction
Total
% Cost Reduction with Cold Mix
439
1550
31
744
430
1550
31
744
400
1550
31
744
200
2955
38
200
2963
38
200
3002
Granite
Basalt
Quartz
744
1923
744
1923
744
1923
200
2867
-4
200
2867
-6
200
2867
-6
744
1923
744
1923
744
1923
200
2867
-1
200
2867
-3
200
2867
-3
744
1923
744
1923
744
1923
200
2867
2
200
2867
0
200
2867
0
744
1923
744
1923
744
1923
200
2867
4
200
2867
3
200
2867
3
Hot Mix Vs Cold Mix: Economic Comparison
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Technical Note: TKS01/2011
Benefits of Cold Mix System:
Bituminous road construction using conventional paving grade bitumen (i.e hot mix technology) is
sometimes not technically feasible and logistically in high rainfall areas, as intermittent rains
throughout the year affects the production and laying of these mixes. Similarly, at high altitude and/ or
in snow-bound areas, very low pavement temperatures make laying of hot mixes rather impossible.
Use of Bitumen emulsion eliminates the need to heat bituminous binder and aggregates; coats damp
aggregates, prevents degradation of environment and thus conserves energy. Cold Mixes enable
construction of roads using emulsion based cold mix technologies in wet and inclement weather.
These cold mixes can be produced either by using concrete mixer or in hot mix plant without heating
facility. The paver and other construction machineries, as in normally employed for hot mixes, can be
used for execution of these works.
The field trials have been carried out by HINCOL on Jammu-Srinagar Highway on NH-1A near
Patnitop (J&K) under cold and snow bound areas; Jowai - Badarpur Road on NH-44 near Silchar
(Assam), Mizoram (N.E. region) under heavy rainfall ; and on H-S Road near Hanumangarh
(Rajasthan) under desert climate.
The main advantages of cold mix technologies for construction of roads are given below:

Construction of binder course and wearing course, using bitumen emulsion in various
specifications is feasible in all weather including wet condition. The working window is
enhanced significantly by this.

Environment friendly technology due to elimination of heating process.

Cold Mix performance is not mixing/laying temp dependant. The mix can be transported to longer
distances easily. Failures which are common in case of hot mix due to nonadherence to temp
requirements are eliminated

The requirements for Anti Stripping agents are eliminated in Cold Mixes

The cost of construction with emulsion can be cheaper by about 5 - 6 % than the conventional
bitumen
Hot Mix Vs Cold Mix: Economic Comparison
6