Cement concrete road construction is one of the types of low volume road construction. We know that the construction of the road is mostly dependent upon the factor like amount traffic that is to be handled by the road after its completion. On most of the village roads connecting small villages in the rural areas of the country, the type of vehicular traffic is quite different from the traffic on other highways. The traffic passing on a road can be categorized into three categories as light commercial traffics, medium commercial traffics and heavy commercial traffics, but the frequency of each class of traffic varies with the road.
A design life of 10 years, considered as quality pavements in the case of low volume roads. The average daily traffic flow on cement concrete roads is low and the total equivalent standard axle loads during a design life of 10 years would be less than 1.0 million standard axles. That’s why cement concrete roads are classified as low volume roads. The cement concrete roads are constructed as all-weather roads so that cement concrete roads are not cut off during the monsoon season. The sub-grade of low volume roads like cement concrete roads may be constructed using local soil available along road alignment, provided the specified minimum requirements are fulfilled. The total thickness of the prepared sub-grade is limited to 300 mm.
General Feature of Cement Concrete Road Construction for Low Volume Roads
As we have already discussed earlier that cement concrete roads are a type low volume roads, but among all the types it does have consideration for its implementation. For example, when the ESAL during the design life a road is expected to be between 1,00,000 & 10,00,000 then an appropriate design and construction of a cement concrete road may be considered. The thickness requirement of cement concrete road construction of low volume road is much lesser in comparison with those for the national and state highways, as the expected magnitude of wheel loads and their repetition are much smaller. In general, the thickness of cement concrete roads lies between 160 mm – 190 mm but the thickness of state highways and national highways varies between 250 mm – 330 mm, this may be because the design of cement concrete roads is done for a minimum life of 20 years, after carefully deciding the designing wheel load.
The components of cement concrete road construction
The main components of cement concrete road construction are subgrade, granular sub base course, cement concrete slab, and joints. The sub-grade of total thickness 300 mm is constructed using well graded coarse-grained soil or soil- aggregate mix or stabilized soil. Fixed form method of construction of cement concrete road is adopted. M40 mix may be preferred even for the construction of cement concrete road for low volume roads, as the flexural strength of concrete will be higher resulting in lesser slab thickness and consequent reduction in warping stresses. After the cement concrete pavement, it is joint that follows the list of components.
There are three types of joints namely construction joints, expansion joints and contraction joint. The transverse contraction joints are to be provided in the form of dummy groove joints up to a depth of one-fourth to one-third of slab thickness. The spacing between the contraction joints may preferably be equal to the width of the single lane pavement, i.e. 3.75 m.
The contraction joints may be formed by cutting grooves 6 to 8 hours after laying; the grooves may also be formed by pressing a mild steel T-section into the fresh concrete. At expansion joints and construction joints in cement concrete roads, load transfer dowel bars of 25 mm diameter, 500 m length and 250 mm spacing may be installed. There is no need to provide longitudinal joints, as these roads have single lane pavement; however at a location of cross drainage structure, if the paved width exceeds 4.5 m width, a longitudinal joint has to be provided, similar to the contraction joint. The joints are sealed using rubberized bitumen compound. At expansion joints, joint sealing is done after compressibility synthetic filter board.
Materials for concrete cement road construction
The materials for the cement concrete road construction may be divided into two parts. These are mentioned as follows:-
- Selection of basic component materials
- Mix design and production of pavement quality concrete(PQC) mix required to construct the cement concrete road pavement
The Selection of Component of Materials
The basic component materials for the cement concrete road construction are consists of Portland cement, coarse aggregate, water, admixture and also steel is used at the joints, in the form of dowel bars and tie bars.
The type of cement that may be used for the preparation of PQC and construction of cement concrete road construction pavement are:-
(i) Ordinary Portland cement of 43 Grade.
(ii) Ordinary Portland 53 Grade.
(iii) Portland Pozzolana cement with fly ash content up to 20% by weight.
(iv) Portland slag cement. However most commonly used cement for the cement concrete road construction is ordinary Portland cement of 43 Grade.
Coarse Aggregate Values of Cement Concrete Road
The coarse aggregate that is used for PQC of cement concrete road construction should fulfill the following requirements apart from this the maximum size being limited to 31.5 mm.
|Los angles abrasion value||Less than 35 percent|
|Combined flakiness and elongation index||Less than 35 percent|
|Water absorption||Less than 3.0 percent|
|Soundness test after five cycles: loss with sodium sulphate||Less than 12 percent|
|Loss of magnesium sulphate||Less than 18 percent|
Fine Aggregates Used in Road Construction
Fine aggregate consists of clean natural sand or crushed stone sand or a combination of both; the fine aggregate shall be from clay, coal and lignite. The fine aggregate shall be well graded, with 100 percent passing 10 mm sieve. The IRC has suggested four gradations of fine aggregate for the preparation of the PQC mix.
Water used for mixing of the cement concrete, and also that used for curing of the cement concrete road construction shall be clean and portable. The water should be free from salt, acid, oil and other organic matter.
Admixture in Cement Concrete Road Construction
Commonly used chemical admixture in the cement concrete road construction are:
(i) To improve the workability of the concrete; a suitable air entraining agent may be used.
(ii) To provide an adequate extension of setting time of the concrete mix without adversely affecting the other desirable properties of the concrete; super-plasticizers which retard the setting time may be used. The total quality of chemical admixture used is limited to a maximum of 2.0 %by weight of the cement or used.
Steel dowel bars with yield strength 2400 kg/sq. cm or 240 Mpa is used for the load transfer across in the expansion joints and construction joints of cement concrete roads. Plan or twisted steel bars are used as tie bars at longitudinal joints. All steel rods shall be coated with epoxy paint for protection against corrosion.