The total length of road network in India is over 48.5 lakh kilometers, which is second largest road network in the world. About 90 percent of the total roads are constructed as flexible pavements because of the ease and faster pace of construction over the rigid.

The flexible pavements are constructed from hot mix technology. This technology is most suitable for better pavement performance, but there have been some drawbacks in this technology like degradation of environment, high energy depletion, low output for mix production and increase in carbon footprint, low laying work in rains and cold weather, limited construction period in a year, health and safety hazard to labour. So, there is a need of a technology which has least harm to the environment and also with the ease of construction.

Hence, the cold mix technology comes into picture where there is less emission of gases and ease of mixing and laying in the field. In the cold mix technology, the aggregates are premixed with water as pre-wetting water, thereafter emulsion is added to it in a predetermined quantity then the mix is produced, and then it is transferred to the mould and acts compacted, all the processes are done at room temperatures. Cold mixes in the field can be produced by using hot mix plants and laid and compacted by similar techniques.

The cold mixes prepared from emulsions work similar to that of a hot mix technology and they are considered inferior because of their less satisfactory performance. The major problems associated with the cold mixes are they do not have early strength because of the pre-wetting water, and also require long time to cure to achieve full strength, and they have higher void contents compared to hot mixes. Cold mixes are pre-wetted with water to get a good coating, but the water inhibits proper compaction.

Cold Mixes are affected by a number of parameters, such as emulsion grade, curing time, void content, curing condition, and additives. Many researchers have tried different curing conditions and worked on many additives to enhance the mechanical properties of cold mix. Researchers have extensively worked out with the cement and found satisfactory results, but the initial gain of strength replacing the filler material with cement is still a problem.

The objectives of the present study are,

• to select the mix parameters and evaluate their effects on properties of Cold Mix Bitumen (CMB) mixtures;
• to determine the optimum dosage of the additive used, and to study the effect on change in the mix parameters;
• to study and analyse the gain in the early strength by adding the additive and also without adding the additive; and
• to check the effect of the additive on the curing of cold mixes.

Chavez-Valencia et al. (2007) had done a study on cold mixes and they also indicated that when a solution of polyvinyl acetate emulsion (PVAC-E) was added to bitumen, the results show increment in the compressive strength of the cold mix. Hence, with the addition of the polyvinyl acetate emulsion, pavement could show improvement in resistance to the rutting and fatigue caused by the heavy traffic loads.

Cao and Luo (2015) carried out the study on the demulsification of the emulsion with the addition of the compound emulsifier. From the study it was seen that the formation mechanism of the compound emulsion was better than that of the single emulsifier. The paper also shows the different factors affecting the breaking mechanism of the bitumen emulsion.

S.F. Brown and Needham (2000) carried out an experiment on cement modified bitumen emulsion mixes, the experimental results show that Cement enhances the mechanical properties of bitumen mixes. The results of tests shows improvements in key mechanical properties of fatigue and resistance to permanent deformations with the addition of cement. The work was further carried out and shown that the ultimate stiffness achieved after curing and the rate of stiffness gain increased with increasing OPC content up to 4% level. In this study, the stiffening effects of hydrated lime and cement was shown by Dynamic Shear Rheometer test and the study also show that the filler had a very little influence. Crystalline structure was studied by Electron microscopy to study the fully cured mixtures with and without cement addition. The experimental study show that by addition of cement in the cold mix, there were improvements in key properties like hydration of cement, emulsion breakdown, and also after compaction there is an improvement in the viscosity of binder.

Fu et al. (2009) carried out a study on curing mechanism of foamed bituminous mixes. They have presented curing procedures that are appropriate for the use in project level mix design. The two curing conditions used in the study were specimens that was extruded from the mould immediately after compaction, and curing for 24 hours at 20 ^oC, and another set of samples were cured for 7 days at 40 ^oC and they are tested for dry indirect stiffness modulus, then soak the stiffness modulus after one day soaking. The study shows that the addition of the cement improved the curing mechanism of foamed asphalt. The presence of water plays an important role in developing the bond between bitumen and aggregate particles, the curing mechanism was related to interface water content.

In the present study, dense graded bituminous concrete grade – 2 cold mixes were prepared to check the physical characteristics. Selection of aggregate gradation is as per MORT&H (2013) specification for BC – 2 and selection of emulsion is as per IS: 8887 for the dense graded mixes. The selection of the mix design procedure is as per Asphalt Institute manual series – 14 (1997) and specifications as per the MORT&H (2013). The mixes were added with cement to check the improvement in the mix properties and NanoTac (A product of M/s Zydex) was added in the dosage of 0.2, 0.4, and 0.6 to check the suitability of the product in the reduction of emulsion content, improvements in the mix properties and reduction in the curing time. The indirect tensile stiffness was tested at two curing conditions. In the first type, the specimens were extruded from the mould immediately after compaction and cured for 24 hours at 20 ^oC and another set of samples were cured for 7 days at 25 ^oC and 40 ^oC and tested for dry indirect stiffness modulus and soaked indirect stiffness modulus after one day soaking at 25 ^oC. The overall methodology is represented in Figure 1.

Figure 1. Methodology

5.1 Aggregates

Aggregates used in the present study were collected from Bangalore region. The aggregates were tested in accordance with the specified test methods for testing physical properties. For preparation of cold mixes, the aggregate gradation was taken as per MORT&H (Table: 500 – 17) for BC – 2. The design gradation for the mix is given in Table 1.

Table 1. Adopted Gradation for the Cold Mix BC–2 [8]

5.2 Filler

In the present study, the filler used was cement of OPC grade – 43. Specific gravity of cement was found out be 3.14.

5.3 Binder

The Binder used for the preparation of mix was slow setting – 2 of cationic type. The emulsion was collected from Tikitar Company. The residual bitumen content of the emulsion was found out to be 62%. The other tests for the emulsion was carried out as per IS: 8887 and are tabulated in Table 2.

Table 2. Physical Properties of Aggregates

5.4 NanoTac

NanoTac is a Nano chemical used for cationic bitumen emulsions introduced by M/s Zydex industries. It forms alkyl siloxane (Si-O-Si) bonds to create bitumen loving aggregate surface. The use of NanoTac is mainly in the tack coats to improve the bond strength at lower bitumen contents, setting time and eliminates debonding due to moisture susceptibility.

The main objective of the Cold mix design is to produce a bituminous mix by proper proportioning of various components to achieve –

• good workability,
• durable Pavements,
• sufficient strength to resist shear deformation under traffic at higher temperature, and
• sufficient flexibility to avoid premature cracking due to repeated loading by traffic.

7.1 Quality Check

• NanoTac sample was taken from fresh bottle and the previously opened bottles were avoided which had been exposed to moisture.
• The NanoTac liquid was a viscous liquid which was difficult to dissolve in the emulsion, so, for the proper mixing of the nanoTac, it was first mixed with water in the ratio 1ml of nanoTac and with 5 ml of water to achieve proper mixing with the emulsion.
• The solution which was whitish or turbid after diluting due to the exposure to atmospheric moisture, was discarded and a fresh sample from an unopened bottle was taken.
• NanoTac was stored between 5 – 45 ^OC in a closed room away from sunlight and heat.

7.2 Apparatus

• A dry and disposable 2 ml syringe is used for adding NanoTac dosage in emulsion.
• Weigh balance should be accurate to 0.001g.
• Mechanical stirrer is capable of adjusting the rotational speed.
• Beaker, mixing, and handling tools.

7.3 Mixing of NanoTac with Emulsion

• Take a 50 ml beaker, add about 20 g of water and 2 g of NanoTac to it and stir it thoroughly with a spatula till the mixture is homogenous.
• Take about 1000 ml of emulsion in another beaker and add the mixture of water and nanotac for different dosages to it.
• The mixture was then subjected to mechanical stirring for a duration of 10 minutes.

8.1 Blending of Aggregate for BC Grade – 2

JMF for the blend is,

• Material A, 20 mm down: 6%
• Material B, 12.5 mm down: 30%
• Material C, 4.75 mm down: 62%
• Filler (Cement): 2%

8.2 Determination of Pre-Wetting Water Content

• Initial Residual Bitumen Content (IRBC) was found out by using the equation 2.1. The value of IRBC was found out to be 4.87 %.
• Initial Emulsion Content (IEC) is determined from the and the value of IEC is 7.86%.
• Initial Emulsion Content was used in the determination of pre-wetting water content.
• The pre-wetting water content was found to be 3% from Figure 2 and is determined in Table 3.

Figure 2. Relation between Water Content and Density

Table 3. Determination of Pre-wetting Water Content

8.3 Marshal Properties

Marshall Properties of cold mixes for BC – II for following variations were determined in the laboratory and results were analyzed.

• Cold mix with cement as filler material.
• Cold mix with 0.02% NanoTac additive.
• Cold mix with 0.04% NanoTac additive.
• Cold mix with 0.06% NanoTac additive.

The above mixes were in agreement with specifications from the MORT&H 5^th revision as given in Tables 6, 8, 10, and 12, except the air voids which were above the limits for all the mixes.

• The cold mix for BC – 2 was prepared by varying emulsion content for constant pre-wetting water content to obtain optimum residual bitumen content. The optimum residual bitumen for the cold mix without additive was found out to be 5.58%.
• The optimum residual bitumen content by addition of additive with 0.02, 0.04, and 0.06% was 5.5 % lesser than the cold mix without additive.
• From Figure 3, stability of the conventional cold mix is 8.86 kN and with 0.02%, 0.04%, and 0.06% NanoTac additive are 11.65 kN, 12.19 kN, and 11.14 kN, respectively.


Figure 3. Comparison of Stability at different NanoTac Dosages

• The stability of the cold mix with 0.04% NanoTac additive was maximum among other mixes which was 27.31% more than the conventional cold mix as shown in Figure 3.
• The density of the mixes with additives were same for all dosages, but the density of the conventional cold mix was 0.8% higher as shown in Figure 4.


Figure 4. Comparison of Density at different NanoTac Dosages

• The water absorption of the mixes reduces with the increased percentage of additive.
• The retained stability of the cold mix with 0.2% additive was 2.43% higher than the cold mix without additive.
• The retained stability of the cold mix with 0.4% additive was 6.8% higher than the cold mix without additive.
• The retained stability of the cold mix with 0.6% additive was 1% higher than the cold mix without additive.

8.4 Indirect Tensile Strength

• Figures 5 and 6 shows the comparison of air voids and water absorption, respectively at different NanoTac Dosages.


Figure 5. Comparison of Air Voids at different NanoTac Dosages



Figure 6. Comparison of Water Absorption at different NanoTac Dosages

• Indirect tensile strength shows increment with the increase in the curing time and curing temperature for all type of cold mixes.
• The indirect tensile strength of the cold mix without additive, increases with increase in the curing time and temperature. The ITS value of one day curing at 25 ^oC, seven day curing at 25 ^oC and also seven day curing at 40 ^oC were 28.90 kPa, 108.38 kPa, and 186.81 kPa, respectively as shown in Figure 7.


Figure 7. Relationship between Indirect Tensile Strength and different Curing Conditions for Conventional Cold Mix

• The indirect tensile strength of the cold mix with 0.02% additive did not see any of much changes in the ITS values for seven days curing conditions, but for a one day curing condition, there was increase in strength by 32.51% as shown in Figure 8.


Figure 8. Relationship between Indirect Tensile Strength and different Curing Conditions for 0.2% of NanoTac Additive

• The indirect tensile strength of the cold mix with 0.04% additive had 69.45% increase in tensile strength with one day curing condition, 49.13% increase in tensile strength with seven day curing at 25 ^oC and 23.41% increase in the tensile strength with seven day curing at 40 ^oC as shown in Figure 9.


Figure 9. Relationship between Indirect Tensile Strength and different Curing Conditions for 0.4% of NanoTac Additive

• The indirect tensile strength of the cold mix with 0.06% additive had 48.40% increase in tensile strength with one day curing condition, 40.47% increase in tensile strength with seven day curing at 25 ^oC and 9.22% increase in the tensile strength with seven day curing at 40 ^oC as shown in Figure 10.


Figure 10. Relationship between Indirect Tensile Strength and different Curing Conditions for 0.6% of NanoTac Additive

• In general with the addition of the additive, the initial strength of the cold mixes gets increased. Tables 4 shows the results.

Table 4. Results of Indirect Tensile Strength Test at Different Curing Temperatures

The experimental results reported in this paper have focused on developing an improved understanding of the role of Nano chemical in enhancing the mechanical properties of bitumen emulsion mixtures for structural layers in roads.

• The stability of the mixes with NanoTac additive had better results than those mixes which were not mixed with additive. But all the mixes were satisfying with minimum stability criteria of MORT&H.
• By the addition of the additive, the was a marginal decrease in the density. It was due to decrease in the binder content.
• With the addition of the additive, the coating of aggregate was improving with every dosage of additives.
• For every increase in dosage of additive, there was a decrease in the optimum bitumen content.
• The mixes with additives were less moisture susceptible.
• From the results obtained from indirect tensile strength, the strength for one day curing condition increases with the addition of additive which in turn implies that the curing of the specimens accelerates with the addition of the chemical as shown in Figures 11 to 13.


Figure 11. Graph Showing Relationship between Indirect Tensile Strength and different NanoTac Additive for 1 Day Curing at 25 ^oC



Figure 12. Relationship between Indirect Tensile Strength and different dosage of NanoTac Additive cured for 7 Days at 25 ^oC



Figure 13. Relationship between Indirect Tensile Strength and different dosage of NanoTac Additive cured for 7 Days at 40 ^oC

• From all the results obtained, the mixes with 0.04% of NanoTac additive showed better results and improvements in most of the properties.
• Cold mix can be laid on low to medium volume road as a green paving mix. Mixture can be produced by using conventional plant. So it can be laid as a surface course, as a trial stretch and the performance of cold mixes have to be studied in different climatic conditions

• The study can be further be extended to different types of mixes and different types of emulsions.
• In the present study only the emulsion content is varied with the mixes with additives, the further study can include with change in water content as well as emulsion content.
• The present study was only restricted to laboratory study, the field suitability of the mixes has to be carried out to check the performance.