Abstract:
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.
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.
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.
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.
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:
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