Warm Mix Additives In Bituminous Layers Of Pavements

Dr Praveen Kumar, Professor & Coordinator
Dr Rajiv Kumar, Research Scholar
Transportation Engineering Group, Civil Engineering Department,
Indian Institute of Technology, Roorkee.

A bituminous mixture is a combination of bituminous materials (as binders), properly graded aggregates and additives. The bituminous mixtures are divided into four types according to the mixing temperature, as shown in Figure 1. (a) Cold mix: produced at ambient temperature. (b) Half Warm Mix Asphalt: produced at less than the boiling point of water (100°C) but the mix is still heated. (c) Warm Mix Asphalt: produced at atemperature lower than 20° to 30°C of traditional HMA but still the temperature is more than the boiling point of water (100°C). (d) Hot Mix Asphalt: produced at temperature 140° to 163°C depending on many factors but mainly on the grading of bitumen. In the case of modified bitumen (MB) or crumb rubber modified bitumen (CRMB), the production temperature of the mix is higher and can extend up to 180°C.

Warm Mix Asphalt
Warm mix technologies allow significant lowering the production and paving temperature of the conventional hot mix asphalt. Most of the work on WMA has involved dense-graded mixture; however, in principle, WMA technologies are equally applicable to other types of asphalt mixture (e.g., open-graded, and SMA). Warm stone matrix asphalt (WSMA) reduces the mixing and compaction temperature with similar or better strength, durability and performance characteristics as SMA. Warm Mix Asphalt (WMA) refers to asphalt concrete mixture that is produced at alower temperature than Hot Mix Asphalt (HMA). Generally, it has been observed that the Warm Mix Asphalt has temperature 20°C to 30°C less compared to HMA. The main goal of WMA is to reduce the mixing and compaction temperatures with similar or better strength, durability and performance characteristics as HMA.
Generic placeholder image Dr Praveen Kumar
Professor & Coordinator
Transportation Engineering Group,
Civil Engineering Department,
Indian Institute of Technology, Roorkee.
The workability of WMA at low temperature can be improved by reducing the viscosity of binder or decreasing the frictional resistance between binder and aggregate. On this basis, there are three types of warm mix additivesas explained below.
(a) Organic warm mix additive: The additives, which have melting point less than the normal production temperature of HMA can be added to reduce the viscosity of the asphalt. Example –Sasobit, Asphaltan-B, Licomont BS-100.
(b) Chemical warm mix additive: The additives, which reduce the internal friction between the binder and aggregate particles during mixing and compaction but don’t rely on the principles of foaming or viscosity reduction. Example–Evotherm, Rediset, Cecabase etc.
(c) Foaming warm mix additives: These additives are of two types; water bearing additives and water based process. The water bearing additive contains synthetic zeolites, which are composed of alumina silicates and alkali metals. The synthetic zeolites have crystalline water, which is released at more than 100°C that creates the foam in a binder and increases the volume of the binder and reduces the viscosity. Examples are Aspha Min and Advera. The water-based process utilizes water only to generate bubbles when contacting the hot binder. Examples are Double Barrel Green, WAM Foam, Green Machine, LEA.
Worldwide there are around 30 types of warm mix additives and technologies. The present study utilizes three additives namely Sasobit, Evotherm and Rediset.
Benefits of WMA
The advantages of WMA over HMA are:
- Significantly lower mixing and compaction temperature
- Low energy consumption
- Less aging of binder
- Reduced thermal segregation in the mixing
- Decreased emission /odours from mixing plant and during placement
- Extending paving season
- Extended mix haul distance
- Improved working condition
Limitations of WMA
In some of the studies, it has been found that the moisture susceptibility problem occurs since at lower mixing and compaction temperatures the aggregates do not dry completely. Also, researchers are not in agreement on the issue of density. It is not clear whether satisfactory density can be achieved or not at lower temperature. The Foaming WMA technologies need modification in HMA plant. It may result in the high installation or modification cost. Various Warm Mix Additives Some of the warm mix additives are shown in Table 1.
Warm mix asphalt (WMA) was introduced in Europe in 1997 and in the United States in 2002. The first trial of WMA was done publicly in 1999 in Europe and in 2004 in the US. The present study (1) was conducted at IIT Roorkee, and documented the use of non-foaming warm mix technology including Sasobit, Rediset and Evotherm with bituminous binders VG-30, PMB-40 and CRMB-60. The properties of these three additives are given below.
Generic placeholder image Dr Rajiv Kumar
Research Scholar
Transportation Engineering Group,
Civil Engineering Department,
Indian Institute of Technology, Roorkee.
Sasobit is a product of Sasol Wax, South Africa. It is a fine crystalline, long chain aliphatic hydrocarbon produced from coal gasification using the Fischer-Tropsch process It is typically mixed directly with the asphalt binder at 1.5% by weight and can lower plant production temperatures by 10°C–30°C. Sasobit melts at temperatures of 85°C–115°C and is completely soluble in asphalt binders above 115°C. At temperatures below its melting point, Sasobit forms a lattice structure in asphalt binders that is the basis for the stability of asphalts modified with Sasobit.
Evotherm 3G (Evotherm 3rd Generation) is a product of MeadWestvaco Asphalt Innovations, Charleston, South Carolina. Evotherm is a chemical warm mix additive which increases the workability of the mix and reduces the friction resistance between aggregate and asphalt binder. It is a water-free version of Evotherm (MeadWestvaco Asphalt Innovations). It can be added at the terminal of the asphalt binder supplier or at the binder supply line of an asphalt mix plant. It can achieve reductions of up to 50°C in plant temperatures. Asphalt having polyphosphoric acid or any type of phosphate cross linking agent are more compatible with Evotherm R1 or S1. All other asphalt binders can be usedwith Evotherm J1 or M1.
Rediset WMX
RedisetWMX is a pelletized additive from Akzo Nobel, Netherlands, and classified as both a viscosity reducer and surfactant-based WMA technology. This surface activity of the amine surfactant also reduces the viscosity slightly. Rediset is also a chemical warm mix additive which increases the compactibility of the mix and reduces the frictional resistance between aggregate and asphalt binders.
The additives were blended with the asphalt binder using low shear mixer. The basic tests on asphalt binders were conducted according to Indian Standards. Preliminary tests showed that the softening point, penetration value, and absolute viscosity of the VG-30, PMB-40 and CRMB-60 change with warm mix additives. It has been observed that by adding Rediset and Evotherm, the softening point value slightly increases with doses while penetration value decreased with increase of dose of these additives. These changes are significant were quite significant in the case of Sasobit. The mixing and compaction temperature (MACT) of asphalt binder with and without warm mix additives are determined using three different methodologies (traditional approach, high shear rate and zero shear viscosity). The effects of compaction temperature on properties of stone matrix asphalt mixture containing the warm mix additives have also been studied. The results showed that the warm mix processes were effective to improve the volumetric properties of SMA mixes. Among several methods used in this research, Marshall Method provided good estimate of compaction temperature for warm stone matrix asphalt (WSMA). In the case of VG-30 binder, the compaction temperature is reduced by 10°C, 18°C and 20°C when Rediset (VR), Evotherm (VE) and Sasobit (VS) are added respectively to the binder. The reduction in compaction temperature is 18°C, 24°C and 17°C for PMB-40+ Rediset (PR), PMB-40+ Evotherm (PE) and PMB-40+ Sasobit (PS) respectively. For CRMB-60 reduction in compaction temperature is 9°C, 19°C and 18°C respectively for Rediset (CR), Evotherm (CE) and Sasobit (CS). Reduction in compaction temperature obtained through high shear rate method in binders is almost same as obtained by Marshall Method. However, ZSV was found not a good property to determine the compaction temperature of WSMA.
1. Kumar Rajiv, Development of Warm Mix Asphalt, Ph.D. Thesis, Indian Institute of Technology, Roorkee, 2017