A highway is a public road, especially a major road connecting two or more destinations. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a "highway transportation system”. The history of highway engineering gives us an idea about the roads of ancient times. Roads in Rome were constructed in a large scale and it radiated in many directions helping them in military operations. Thus they are considered to be pioneers in road construction.

The modern roads by and large follow Macadam's construction method, use of bituminous concrete and cement concrete are the most important developments. Various advanced and cost-effective construction technologies are used. Developments of new equipments help in the faster construction of roads. Many easily and locally available materials are tested in the laboratories and then implemented on roads for making economical and durable pavements.

Scope of transportation system has developed very largely. Population of the country is increasing day by. The life style of people began to change. The need for travel to various places at faster speeds also increased. This increasing demand led to the emergence of other modes of transportation like railways and travel by air. While the above development in public transport sector was taking place, the development in

private transport was at a much faster rate mainly because of its advantages like accessibility, privacy, flexibility, convenience and comfort. This led to the increase in vehicular traffic especially in private transport network. Thus road space available was becoming insufficient to meet the growing demand of traffic and congestion started. In addition, chances for accidents also increased. This has led to the increased attention towards control of vehicles so that the transport infrastructure was optimally used. Various control measures like traffic signals, providing Roundabouts and medians, limiting the speed of vehicle at specific zones etc. were implemented.

With the advancement of better roads and efficient control, more and more investments were made in the road sector especially after the World wars. These were large projects requiring large investment. For optimal utilization of funds, one should know the travel pattern and travel behaviour. This has led to the emergence of transportation planning and demand management.

 STABILIZATION WITH CEMENT CTB (CEMENT TREATED BASE)

According to the PCA (Portland Cement Association), CTB (Cement Treated Base) has provided economical, long lasting pavement foundation. These structures have combined soil and/or aggregate with cement and water which compacted to high density. The advantages of cement stabilization are several:

1. Cement stabilization increases the base material strength and stiffness, which reduces deflection due to the traffic loads. This delays surface distresses such as fatigue, cracking and extends pavement structure life.

2. Cement stabilization provides uniform and strong support, which results in reduced stresses to the sub-grade. Testing indicates a thinner cement-stabilized layer can reduce stresses more effectively than a thicker un-stabilized layer of aggregate. This reduces sub-grade failure, pot-hole formation and rough pavement surface.

3. Cement stabilized base has greater moisture resistance to keep water out; this maintains the higher strength of the structure.

4. Cement stabilization reduces the potential for pumping of sub-grade fines

COMPOSITION AND CONSTRUCTION

Cement-Treated Base

The mixture shall be composed of existing sub-grade, base course and surface course materials, and/or an imported soil aggregate, with Portland cement and water added. The mixture shall contain not less than 4% cement by volume of compacted mixture, 1420 kg (94 pounds) of cement being considered as 1 cu m (1 cubic foot). At least 30 days before the beginning of stabilizing operations, adequate quantities of soil and cement shall be supplied to the Materials Division for determination of cement requirements. The Engineer will specify, based on laboratory tests, the exact percentage of cement to be used. Specimens of soil aggregate, cement, and water shall develop a compressive strength of a least 2.7 M Pa (400 psi) in 7 days.

MATERIALS

The materials used shall comply with the following requirements:

(a) WATER

Water used in mixing or curing shall be clean and free from injurious amounts of oil, salt, or other deleterious substances. Where the source of water is relatively shallow, it shall be maintained at such a depth and the intake so enclosed as to exclude grass, vegetable matter, or other foreign materials.

(b) CEMENT

Fly ash may be used as a partial replacement for the cement. Replacement amounts, not exceeding 25% by weight, shall be determined through trial batch investigations using the specific materials proposed for the project. Mixtures with fly ash shall meet the same requirements as mixtures without fly ash. All trial batches required by this specification shall be accomplished by the Contractor, observed by the Engineer, and approved by the Engineer of Materials. Fly ash will not be allowed as a substitute for high early strength or blended cements.

For in-place stabilization, the fly ash and cement shall be blended to form a homogeneous mixture before application on the roadway.

The use of cement salvaged from used or discarded sacks will not be allowed. Cement placed in storage shall be suitably protected. Any loss of quality occurring during the storage period will be cause for rejection. If the cement furnished shows erratic behaviour under the field conditions incident to the mixing and placing of the mixture, or in the time of the initial or final set, the Contractor will at once, without notice from the Engineer, cease the use of that brand of cement and furnish material of such properties as to ensure quality work conforming to these specifications.

CONSTRUCTION REQUIREMENTS

Sufficient equipment shall be available so that the work may proceed in proper sequence to completion without unnecessary delay. Equipment, tools, and machinery used shall be maintained in a satisfactory working condition.

The application of cement and mixing of the cement and soil aggregate will be allowed only on an approved sub-grade, free of excess moisture. No work will be allowed on a frozen sub-grade.

The operations shall be such as to prevent the drifting of cement or dust off the right- of-way.

(a) PREPARATION OF THE ROADBED

Prior to other construction operations, the existing roadbed, including the shoulders, shall be brought to line and grade and shaped to the typical cross section of the completed roadbed and compacted to sufficient density to prevent rutting under normal operations of construction equipment. All soft areas shall be corrected to provide uniform stability.

(b) PULVERIZING

After shaping and compacting the roadbed, the material to be processed shall be scarified and pulverized before application of cement. Pulverizing shall continue during mixing operations until a minimum of 80% by weight of the material, exclusive of coarse aggregate, will pass a 4.75 mm (#4) sieve. Material retained on a 75 mm sieve and other unsuitable material shall be removed.

(c) APPLICATION AND MIXING OF CEMENT

The application and mixing of cement with the aggregate material shall be performed according to one of the following methods:

(1) TRAVEL PLANT METHOD

The specified quantity of cement shall be applied uniformly on the material to be processed, and shall not exceed that which can be processed the same working day. When bulk cement is used the equipment shall be capable of handling and spreading the cement in the required amount. The moisture content of the material to be processed shall be sufficiently low to permit a uniform and intimate mixture of the aggregate material and cement. Mixing shall be accomplished by means of a self-propelled or self-powered

machine equipped with a mechanical rotor or other approved type of mixer that will thoroughly blend the aggregate with the cement. Mixing equipment shall be so constructed as to assure positive depth control.