DEVELOPING ECONOMICAL ROLLER COMPACTED CONCRETE MIX FOR PAVEMENTS: 2. MATERIAL & PROPERTIES

2.1 Roller Compacted Concrete

Concrete is the most widely used man made material in the world. It is an affordable and reliable material, which is extensively used throughout in the infrastructure of a nation’s construction, industrial, transportation, defense, utility and residential sectors; it has become a huge industry. Slightly more than a tonne of concrete is produced each year for every human being on earth.

The strength, durability and other characteristic of concrete depends upon the properties of its ingredients, on the proportion of mix, the method of compaction and other controls during placing, compaction and curing. The key to producing a strong, durable and uniform concrete lies in the careful control of its basic and process components.

2.2 Constituents of Concrete

Concrete is the universal material of construction. The ingredients of the concrete can be classified into two groups, namely active and inactive. The active group consists of cement and water, whereas inactive group comprises fine and coarse aggregate. The inactive group is also sometimes called the insert matrix.

2.3 Cement

The function of cement is first, to bind the sand and coarse aggregate together, and second, to fill the voids in between sand and coarse aggregate particles to form a compact mass.

2.4 Aggregate

Aggregate are the important constituents in concrete. They give body to the concrete, reduce shrinkage and effect economy. The mere fact that the aggregate occupy 70-80 percent of the volume of concrete, their impact on various characteristics and properties of concrete is undoubtedly considerable. Hence, without the study of the aggregate on depth and range, the study of the concrete in incomplete.

     2.4.1 Cleanliness:

The concrete aggregate should be free from impurities and deleterious aubstance which are likely to interfere with the process of hydration, prevention of effective bond between the aggregates and matrix. The impurities sometimes reduced the durability of the aggregate.

2.5 Crushed Stone Dust:

All along in India, generally we have been using natural sand as fine aggregate. Availability of natural sand is getting depleted and also it is becoming costly. Concrete industry now will have to go for crushed stone dust.

Aggregate content is a factor, which has direct and far-reaching effects on both the quality and cost of concrete. The growing shortage and price rise of the natural sand is a question that a construction industry shall think about. Now looking for viable alternatives to natural sand is a must and not a necessity. Due to short of supply of natural sands and the increased activity in construction sector, the time has come, for manufactured sand to play a significant role as an ingredient in concrete.

     2.5.1 Definition and Function:

The term-manufactured sand is used for aggregate materials having dimensions, less than 4.75mm that are processed from crushed rock or gravel and intended for construction use. The term sand refers to relatively small particles and there are some variations of sand with regard to particle size.

Production of excess amounts of fines and depletion of natural aggregate resources are the main problems for aggregate producers. Crushed/manufactured sand has rough surface texture and the particle size distribution curve can be adjusted in the manufacturing of the material. Another advantage in manufactured sand is quarries can be kept in the near vicinity to its place of end use, therefore shortening transport distances, and increased employment opportunities for the locals. In the future it is expected that manufacturing of sand from rock will increase and production from natural deposits will decrease.

The crushing process caused the manufactured sand to have an irregular particle shape. These fine particles and irregular shape of the aggregate have detrimental effects on the workability and finish of the concrete. These negative effects have given manufactured sands a poor population in the construction industry. However this study reveals that in some other practical areas, these fine particles can be utilized to increase the compressive strength of the concrete.

Table 1. Comparision with natural sand & Crushed Fine Aggregate

S.No. Property Natural Sand Crushed fine Aggregate
1 Shape Spherical Particles Cubical
2 Gradation Cannot be Controlled Can be controlled
3 Particles passing 75 Micron Presence of Silt Should be Less than 3% Presence of Dust Less than 15%
4 Specific Gravity 2.5 to 2.8 2.6.to 2.9
5 Water Absorption 2 to 3 % 3 to 4 %
6 Ability to hold surface moisture Up to 7 % Up to 10 %

Representative APR 391%. Average APR for this type of loans is 391%. Let's say you want to borrow $100 for two week. Lender can charge you $15 for borrowing $100 for two weeks. You will need to return $115 to the lender at the end of 2 weeks. The cost of the $100 loan is a $15 finance charge and an annual percentage rate of 391 percent. If you decide to roll over the loan for another two weeks, lender can charge you another $15. If you roll-over the loan three times, the finance charge would climb to $60 to borrow the $100.

Implications of Non-payment: Some lenders in our network may automatically roll over your existing loan for another two weeks if you don't pay back the loan on time. Fees for renewing the loan range from lender to lender. Most of the time these fees equal the fees you paid to get the initial payday loan. We ask lenders in our network to follow legal and ethical collection practices set by industry associations and government agencies. Non-payment of a payday loan might negatively effect your credit history.

Calculate APR