REINFORCED CEMENT CONCRETE

SPECIFICATIONS AND ESTIMATIONS

INTRODUCTION

Reinforced Cement Concrete in which steel is embedded in such a manner that the two materials act together in resisting forces. The reinforcing steel—rods, bars, or mesh—absorbs the tensile, shear, and sometimes the compressive stresses in a concrete structure. The invention of reinforced concrete in the 19th century revolutionized the construction industry, and concrete became one of the world’s most common building materials.

HISTORYFrançois Coignet was a French industrialist of the nineteenth century, a pioneer in the development of structural, prefabricated and reinforced concrete. Coignet was the first to use iron-reinforced concrete as a technique for constructing building structures.In 1853 Coignet built the first iron reinforced concrete structure, a four story house at 72 rue Charles Michels in the suburbs of Paris.Coignet's descriptions of reinforcing concrete suggests that he did not do it for means of adding strength to the concrete but for keeping walls in monolithic construction from overturning. In 1854, English builder William B. Wilkinson reinforced the concrete roof and floors in the two-storey house he was constructing. His positioning of the reinforcement demonstrated that, unlike his predecessors, he had knowledge of tensile stresses

MATERIALS USED

Cement is the main material used for RCC. It acts as the matrix in which other ingredients are mixed to get the final outcome.

Other than cement, steel reinforcements comprise the RCC. It bears all the tensile load where the compressive load is taken by the concrete.

REINFORCEMENTS

CEMENT

COARSE AGGREGATES

FINE AGGREGATESThe fine aggregates include silt, sand and other binding materials. It holds the concrete and reinforcements together.

Coarse aggregates are slightly bigger than the silt and sand used as binding material.

VARIATION IN GRADIANTS

Aggregates have two types of moisture:1. Absorbed moisture – retained in pores2. Surface moisture – water attached to surface Aggregates have

four moisture states

Oven dry: all moisture removed Air dry: internal pores partially full & surface drySaturated-surface dry: pores full & surface moisture removedWet: pores full and surface film SSD aggregate does not add or subtract water ,not easily obtained in the field

Moisture Absorption -We must determine how much water dry aggregate will consume into its voids This takes water away from the mix and reduces workability & W/C ratio We adjust mix proportions for absorption We want to provide aggregates water for absorption & maintain workability of the mix .

RCC SPECIFICATIONS• Shuttering shall be done using seasoned wooden boards of

thickness not less than 30mm.• Surface contact with concrete shall be free from adhering grout,

nails, splits and other defects.• All the joints are perfectly closed and lined up.• The shuttering and framing is sufficiently braced.• Nowadays timber shuttering is replaced by steel plates.• All the props of approved sizes are supported on double wedges

and when taken out, these wedges are eased and not knocked out.• All the framework is removed after 21 days of curing without any

shocks or vibrations.

• All reinforcement bars conform IS specifications and are free from rust, grease oil etc.

• The steel grills are perfectly as per detailed specifications.• The covers to concrete are perfectly maintained as per code.• Bars of diameter beyond 25mm diameter are bent when red hot.• The materials proportion should be as per the specifications of the

concrete.

NUMBER OF CEMENT BAGS REQUIRED FOR A SPECIFIC CEMENT CONCRETE RATIOS

• For cement concrete of ratio 1:1:2(1 cement:1sand/coarse sand:2graded stone aggregate) require 11no bags of 50kg.

• For cement concrete of ratio 1:1.5:3 require 7.8no bags of 50kg.• For cement concrete of ratio 1:2:4 require 6 no bags of 50kg.• For cement concrete of ratio 1:3:6 require 4.25no bags of 50kg.• For cement concrete of ratio 1:4:8 require 3.2 no bags of 50kg.• For cement concrete of ratio 1:5:10 require 2.50 no bags of 50kg.• For cement concrete of ratio 1:6:12 require 2.25 no bags of 50kg

METHOD OF PREPARATION

CONCRETE PREPARATION:In its simplest form, concrete is a mixture of paste and aggregates, or rocks. The paste, composed of portland cement and water, coats the surface of the fine (small) and coarse (larger) aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete.Within this process lies the key to a remarkable trait of concrete: it's plastic and malleable when newly mixed, strong and durable when hardened.

PROPORTIONING:• The key to achieving a strong, durable concrete rests in the careful

proportioning and mixing of the ingredients. A mixture that does not have enough paste to fill all the voids between the aggregates will be difficult to place and will produce rough surfaces and porous concrete. A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete is not cost-effective and can more easily crack.

• The quality of the paste determines the character of the concrete. The strength of the paste, in turn, depends on the ratio of water to cement. The water-cement ratio is the weight of the mixing water divided by the weight of the cement. High-quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete, allowing it to be properly placed, consolidated, and cured.

• A properly designed mixture possesses the desired workability for the fresh concrete and the required durability and strength for the hardened concrete. Typically, a mix is about 10 to 15 percent cement, 60 to 75 percent aggregate and 15 to 20 percent water. Entrained air in many concrete mixes may also take up another 5 to 8 percent.

OTHER INGREDIENTS: WATER: Almost any natural water that is drinkable and has no

pronounced taste or odor may be used as mixing water for concrete. Excessive impurities in mixing water not only may affect setting time and concrete strength, but can also cause efflorescence, staining, corrosion of reinforcement, volume instability, and reduced durability. Concrete mixture specifications usually set limits on chlorides, sulfates, alkalis, and solids in mixing water unless tests can be performed to determine the effect the impurity has on the final concrete.

• AGGREGATES: Aggregates comprise 60 to 75 percent of the total volume of concrete. The type and size of aggregate used depends on the thickness and purpose of the final concrete product. Relatively thin building sections call for small coarse aggregate, though aggregates up to six inches in diameter have been used in large dams. A continuous gradation of particle sizes is desirable for efficient use of the paste. In addition, aggregates should be clean and free from any matter that might affect the quality of the concrete.

ADVANTAGES• Reinforced concrete has a high compressive strength compared to

other building materials.• Due to the provided reinforcement, reinforced concrete can also

withstand a good amount tensile stress.• Fire and weather resistance of reinforced concrete is fair.• The reinforced concrete building system is more durable than any

other building system.• Reinforced concrete, as a fluid material in the beginning, can be

economically molded into a nearly limitless range of shapes.

• The maintenance cost of reinforced concrete is very low.• In structure like footings, dams, piers etc. reinforced concrete is the

most economical construction material.• It acts like a rigid member with minimum deflection.• As reinforced concrete can be molded to any shape required, it is

widely used in precast structural components. It yields rigid members with minimum apparent deflection.

• Compared to the use of steel in structure, reinforced concrete requires less skilled labor for the erection of structure.

DISADVANTAGES• The tensile strength of reinforced concrete is about one-tenth of its

compressive strength.• The main steps of using reinforced concrete are mixing, casting, and

curing. All of this affect the final strength.• The cost of the forms used for casting RC is relatively higher.• For multi-storied building the RCC column section for is larger than

steel section as the compressive strength is lower in the case of RCC.

• Shrinkage causes crack development and strength loss

PRECAST• Precast concrete is a

construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place. In contrast, standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast concrete by using a fine aggregate in the mixture, so the final product approaches the appearance of naturally occurring rock or stone.

PRECASTED CONCRETE STRUCTURE

• By producing precast concrete in a controlled environment (typically referred to as a precast plant), the precast concrete is afforded the opportunity to properly cure and be closely monitored by plant employees. Utilizing a precast concrete system offers many potential advantages over site casting of concrete. The production process for precast concrete is performed on ground level, which helps with safety throughout a project. There is a greater control of the quality of materials and workmanship in a precast plant rather than on a construction site. Financially, the forms used in a precast plant may be reused hundreds to thousands of times before they have to be replaced, which allow cost of formwork per unit to be lower than for site-cast production.

EXAMPLES OF RCC PRECAST