The new trend in technology is faster compaction by achieving the required density at a lower operating cost. Also, the latest equipment is designed with features to improve operator safety, comfort and maintainability. Equipment India finds out more?

For over a decade, the road-building sector in India has offered major growth opportunities for the cons?truction equipment industry. With more than 60 per cent of the cargo movement being handled by the road network, the focus will naturally be on road infrastructure. According to Off-Highway Research, the growth rate of compaction equipment from 7.6 per cent in 2009-10 will reach to over 60 per cent by 2014. (The total volume of compaction equipment in 2009 was 2,787 units, which in 2010, crossed 3,000 units (a growth rate of 7.6 per cent) and the forecast is a growth in volume of around 4,800 units by 2014, a growth rate of 60 per cent.

Vibratory compaction today is a must for building any road; however, this is not adhered to in some cases. A contractor in?vo?lved in building roads today has a lot of choice as far as construction equipment is concerned. It?s a competitive market and se?veral world-class products are available off-the-shelf. Of course, there is always scope for improvement, and products will keep getting better with more R&D and technology going into their design and ma?nu?facturing. These machines have been helping build India?s rural and urban roads, and highways. The contractors use these ma??chines at various sites across the country like various yards, access roads, residential streets, car parks, roads, highways and airports.

?The size of the market for compactors is around 3,000 rollers a year but the segment we operate in, which is soil compactors, is 1,500 rollers. We just started this year, and we have been able to achieve seven to eight per cent of the market share. Our target is to reach 40 per cent in the next two years,? says Ramesh Palagiri, Managing Director and CEO, Wirtgen India, which offers Hamm-11T soil com?pactor, 9T asphalt compactors and 24T pneu?matic tyre rollers (PTR) for the Indian market. Hamm compactors come with German design and technology mai?nly featuring excellent operator comf?ort and safety. The equipment is powered by a fuel-efficient and highly durable water-cooled engine.

?JCB offers the finest road compaction equipment through its Vibromax series,? says Amit Gossain, Vice President, Marketing, JCB India. ?The VM115 caters to the soil compaction needs of the sector while the VMT 860 is a master at asphalt compaction. These machines are built specially for Indian roads and are amongst the best at compaction. High productivity and reliability with maximum operating economy are second nature to these machines. Excellent maneuverability and compact designs make these ideal for a wide range of areas,? Amit says. He further explains, ?The VM115 is a proven work horse to compact high volumes of soil to a very large degree of compaction in minimum number of passes. The 11.5 tonne roller has very prominent compaction boosting parameters like very high amplitude of 1.95 mm, best in class centrifugal force, maintenance friendly with a lifetime lubricated centre joint, comfortable operator station with weight adjustable seat, and zero greasing points. The VMT860 is a new generation tandem roller with unmatched productivity and economy. The zero maintenance VMT 860 has exceptional standard features make it cost effective like standard lift pump for filling tanks, hydraulic based anti-vibration pads, 2 rotating operator seats, tiltable steering, which makes it easy to use for the operator.Both these machines are powered by the JCB Engine ecoMAX. Above parameters will give users an edge in achieving compaction at lowest operating cost.?

Says Sunil Sapru, President, LiuGong India, ?The growth potential is good. As far as the projects are concerned that will be another area which needs to be looked into and the area where the customer?s requirement for the latest generation products are really felt. I think we need really innovative products in this segment. We are looking at products which can give value addition to the customers, and we will soon be launching our compactor model specifically designed to suit the site conditions. We have developed road compactors that will be launched in the first quarter of this year. The field tests are already on.?

Sapru adds, ?The technological trends, as compared to conventional grading and compacting methodologies, are apparent in the increased use of GPS guidance and laser control techniques.?

?The first road roller was horse-drawn; this was followed by steam and diesel rollers. For a long period, static compactors of various sizes were used. The introduction of the vibratory compactor in 1946 opened a new era in the construction industry. A few decades ago, grading was done manually or with tractor dozers where operator skill was important for accuracy. Advanced technology has made grading work simple by offering the option of automatic slope and elevation offsets. GPS navigation and machine guidance systems have reduced the amount of external surveying required. Almost every cons?truction project or site preparation requires some kind of grading and compaction. The Indian contracting community extensively uses the graders and compactors for various purposes based on size and extent of projects,? points out SM Roy, Chief Executive Officer, Lanco Infratech.

Improvements

High-technology machines are desi?gned to achieve optimum compaction with a minimum number of passes to reduce the overall operating cost. The new trend is faster compaction by achieving the required density at lower operating cost. Also, the latest equipment are desi?gned with features to improve the operator safety, comfort and maintai?nability, The advanced methods of compaction refer to vibratory compaction of soil/asphalt. In simplest terms, com?paction is the process of mechanically increasing the density of a material by reducing the voids between the particles that make them up. More dense or compacted material is able to support heavier loads without deforming (bending, cracking, moving). The adva?nced methods provide a better compacted road surface thereby leading to a smoother ride, saving in fuel costs and maintenance costs and most important of them all, saving time.

Vibratory soil compactors produce a rapid succession of pressure waves which spread in all directions. The vibratory pre?ssure waves are useful in breaking the bonds between the particles of the mate?rials being compacted. When pressure is applied, the particles tend to re-orient themselves into a more dense (fewer voids) state. In static compaction, weighted loads applied by rollers produce shear stresses in the soil or asphalt that cause the individual particles to slide across each other. Com?paction happens when the applied force causes individual particles to break their natural bonds to one another and move into a more stable position within the material. With vibratory compactors, one is able to achieve a much higher density compared to a static roller.

In the case of static rollers, what matters is only the dead weight of the ro?ller and the compaction is efficient in up?per portion in a given lift. Compaction effi?ciency will be low if the dead weight of the roller is less. This will be one of the pri?me reasons for failure of lower layers. However, in the case of vibratory com?pactors, the compaction is achieved uni?formly over the entire lift. With the help of vibratory rollers, the degree of com?pa?ction is better (95-98 per cent) achieved than with the static ones. It is also possible to increase the lift thickness above 250 mm.

For a usual lift thickness of 250 mm, lower range static compactors provide the compaction density about 80 to 85 per cent. The maximum achievable density is governed by compaction energy, optimum moisture content, and number of passes. The specifications are well defined on the level of compaction required. In case of embankments, the modified proctor den?sity required is 95 per cent while in the case of sub-grade, it is 98 per cent. With vibratory rollers, a hundred per cent density can be achieved using either 10T or 18T rollers. The soil conditions do determine the type of compactors being used. The soil can be clay, gravel, or sandy soil. The cohesive and plasticity nature of soil governs the desired level of compaction. Though the type of soil varies along the length of the project highway, it is usually restricted to have compactor for the predominant soil.

Awards

Hamm is the technology leader in compaction which has been awarded many design prizes for its latest innovations. Recently, it was awarded iF-Gold award 2010 also called the Design Oscar for new HD+ series of asphalt compactor. The GRW 280, rubber-wheeled rollers received the iF Design award 2010. Higher quality level of the components used in Hamm compactors increases the durability of the equipment. Better serviceability and redu?ced maintenance frequency with less fuel consumption results in the lower operating cost of the equipment. Vibratory comp?actors develop dynamic force in addition to the static load and total applied force is the sum of dynamic force and the static weight of the machine. For example, Hamm 11T soil compactor gene?rates 24T dynamic force and with 6.8T static weight at the drum will induce 30.8 tonne load on the ground. The advantage of using 11T vibratory soil compactor versus 30 tonne static compactor is evident from this.

The vibratory compactor with drum vibrating at higher amplitude will result in compacting the higher lift thickness and achie?ving the required density compared with the static roller. In the static roller, the linear load is not uniform over the width of the machine (one front roller and two rear rollers) which results in uneven mat finish. In the vibratory compa?ctors, the linear load is uniform along the width of the drum.

?The ACE range of compactors with a higher total applied force, can achieve the density faster as this is true parameter for achieving maximum dry density,? says Jitendra Sharma, Chief Executive Officer, Action Con?struction Equipment. ACE has a full range of compaction equipment soil, tandem and PTRs; in soil 10T, 12T, standard drum drive and pad foot, all the variants in different capacities are available in our range. In tandem, we have both 9T and 10T and have specific variant for the specific application of pure asphalt and dual application of bituminous and non-bituminous layers including soil. The feature advantages of the Ace range of compaction equipment are top-end aggregates with the best deliverables yet at a most competitive price, features like engine-water-cooled, fuel-efficient and high torque engine, high-pressure close-loop hydraulic, single joystick control, multiple frequency setting, and higher total applied force. With more and more BOT projects, the trend would be for higher capacity equipment which can help in reducing the construction period.

Caterpillar has vibratory soil compa?ctors in the operating weight range of 4.5T?18.5T with drum drive as a standard fitment on all models to increase the machine versatility. The drum drive model has separate hydraulic pumps for the axle drive and the drum drive which helps the machine in achieving high gradients wher?ever required. However, the popular model being offered in India is the CS533E (11T Class) which is required to meet the National Highway Project requirements in India. Speaking about the selection cri?teria, Pankaj Dara, Associate Vice President - Construction, TIPL, says, ?Different factors influence the overall comp?action effort. Vibratory compaction involves a drum which moves up and down (amplitude) rapidly (frequency) and moves forward (working speed) over non-homog?eneous material. All components influe?ncing compaction should be consi?dered as a whole, not as separate entities. It is the combined characteristics of the compactor and the soil or asphalt it atte?mpts to compact which determines the deg?ree of compaction effort. The chara?cteristics of the material to be compacted play a part in the dynamics of compaction. Factors such as soil type, gradation, texture, initial den?sity, moisture content, aggregate strength characteristics, layer thickness, sub soil base and its supporting capability all influ?ence com?paction. For example, granular soils tend to transmit vibratory forces well. Cohesive soils tend to have a damping effect on vibratory forces. Cohesive soil requires a kneading effect to drive out the excessive moisture from the soil. This is best achieved by a pad foot drum.?

He explains further, ?Target densities are established by the specifying agency before the job begins, to ensure that the soil is adequately and consistently com?pacted. Generally, target density is set on the basis of either relative or absolute measures. A relative measure may use a percentage of a laboratory standard. This is done through a standard AASHTO pro?cedure or the modified AASHTO pro?cedure depending upon the desired specifi?cation that needs to be achieved on a specific project. The compaction energy in the modified AASHTO test is 4.5 times larger than the standard AASHTO test and is normally specified on projects where very high axle loads are anticipated. For a given soil sample, either the standard or modified AASHTO is performed five times. The same procedure is used each time the test is run but the moisture co?ntent varied for each.?

The series is begun with the soil in the damp condition somewhat below the probable optimum moisture content. After the first sample is compacted in the mould, the wet weight is measured and the sample is placed in a drying oven. When the sample is completely dry, it is weighed again. The difference between the wet and dry weights yields the moisture content which is expressed as a percentage of the dry weight. A second sample with increased moisture content is compacted and the weighing and drying process is repeated. Additional samples with increasing mois?ture content are processed until the wet weight decreases or the soil becomes too wet to work. Dry density and moisture content va?lues for each sample are then plotted and a smooth curve is for?med. The highest point on the curve represents the maxi?mum dry den?sity and the optimum moisture content for that soil sample. Lab tests determine the moi?sture content at which maxi?mum den?sity can be attained.

Field target dens?ities are specified as a certain per cent of the maximum laboratory dry density. Generally required field den?sities will be 95-98 per cent of the standard AASHTO for emban?kment and up to 100 per cent of modified AASHTO for roadway structures. Likewise, moisture content must be within a range of the laboratory determined optimum moisture content.

In the initial years, compaction using sta?tic rollers, which are about 5T capacity, was the norm. But there?after from the early 90s when the specs got amended from standard proctor density to mo?dified pro?ctor density, static rollers gave way to vibratory compactors of 10T capacity for usual layer thickness of 250 mm.

Globally, the technology was avai?lable but since our government?s policy was to encourage the local manufacturing indu?stry, it took time for us to adopt this technology, but now it has come to stay. Things have improved further and now we are using heavy-duty vib?ra?tory rollers of 18T capacity. Also, the use of a dynamic com?paction analyser fitted to vibratory rollers helps to measure the level of compaction achieved. Similarly in the early days, dozers were most commonly used for grading. But with the advent of motor graders of a heavier capa?city, the quality of surface finish and speed of construction improved drama?tically. There?fore, the contracting frate?rnity has adopted it without much hesitation.