BUILDING MATERIAL AND

CONSTRUCTIONPRESENTATION

GROUP MEMBERSSHREYA AGRAWAL (Roll no. - 17)

SNEHA SHARMA (Roll no. – 25)SWAPNIL YADAV (Roll no. - 32)

UZMA ZAKI (Roll no. – 36)

READY-MIX CONCRETE

Ready-mix concrete (RMC) is a ready-to-use material, with predetermined mixture of Cement, sand, aggregates and water.

INTRODUCTIONThe first ready mix factory which was built in 1930’s.The consumption of cement in the form of RMC is about

5% in India, where as in developed countries it’s about 70%.

The leading RMC supplier worldwide is the mexican concrete and cement company cemex.

DEFINITIONA concrete which is specially manufactured for the

delivery to the costumer construction site in a freshly mixed, plastic and unhardened state.

BACKGROUND RMC industry is about 12 years old in India, while it was introduced in other countries much earlier - PATENTED IN GERMANY

• 1913- FIRST DELIVERY OF RMC (BALTIMORE)• 1926- BIRTH OF TRANSIT MIXER•1931- ERECTION OF FIRST COMMERCIAL PLANT IN

LONDON• 1950-1974 REMARKABLE GROWTH OF RMC – 31 MILLION

CUBIC METRE OF CONCRETE PER YEAR

MAIN INGREDIANTS OF RMC

CEMENT SAND

COARSE AGGREGATE WATER

INGREDIANTS IN DEPTH..

CEMENTCement is a binder material which sets and hardenindependently, and can bind other materials together.Cement is made up of four main compounds tricalciumsilicate (3CaO SiO2), dicalcium Silicate (2CaO SiO2),tricalcium acuminate (3CaO Al2O3), and tetra-calciumaluminoferrite (4caco Al2O3 Fe2O3).tetra-calciumaluminoferrite (4CaO Al2O3 Fe2O3).

AGGREGATESAggregates are the important constituents in concrete. They give body

to the concrete, reduce shrinkage and effect economy. Earlier, aggregates were considered as chemically inert materials but now it has been recognised that some of the aggregates are chemically active and also that certain aggregates exhibit chemical bond at the interface of aggregate and paste.

Aggregates are divided into two categories from the consideration of size Coarse aggregate Fine aggregate The size of the aggregate bigger than 4.75 mm is considered as coarse aggregate and aggregate whose size is 4.75 mm and less is considered as fine aggregate.

ADMIXTURESA substance added to the basic concrete mixture to alter

one or more properties of the concrete; i.e. fibrous materials for reinforcing, water repellent treatments, and colouring compounds.

Role of Admixture in Ready Mix Concrete: The role of admixture is ready mixed of concrete is same as that in normal concrete. However, admixture used in RMC is modified to meet the requirement of pumpable concrete and other properties of concrete. The types of admixture used in RMC are generally termed as Super plasticizers.

FLY ASHFly ash is a by-product from coal-fired electricity generating power

plants. The coal used in these power plants is mainly composed of combustible elements such as carbon, hydrogen and oxygen (nitrogen and sulphur being minor elements), and non combustible impurities (10 to 40%) usually present in the form of clay, shale, quartz, feldspar and limestone.

Fly ash use improves concrete performance, making it stronger, more durable, and more resistant to chemical attack. Fly ash use also creates significant benefits for our environment. The size of fly ash ranges from 1.0 to 100 micron & the average size is around 20 microns.

WATERThe pH value of water should be

in between 6.0 and 8.0 according to IS 456-2000.

Effect of Mixing Sea Water in Concrete:The sea Water generally contains salinity of about 3.5% in which about 80% is

sodium chloride. Many researchers have been conducted to study the corrosion problem of steel Embedded in concrete where sea water is used as mixing water in concrete nevertheless the Indian standard is adamant & do not permit using sea water for mixing or curing in reinforced Concrete constructions, but allows for using of sea water only for PCC work that too under unavoidable circumstances.

JOURNEY OF RMCReady – mix concrete has cement, aggregates, water and

other ingredients, which are weighed and batched at a centrally located plant.

This is then delivered to the construction site in transit mixers and can be used straightaway without any further treatment.

Ready Mixed Concrete is manufactured under computer-controlled operations and transported and placed at site using sophisticated equipment and methods.

MANUFACTURINGReady mixed concrete is proportioned and mixed off at

the project site and is delivered to the construction area in a freshly mixed and unhardened state. It can be manufactured by any of the following methods:

1. Central – Mixed Concrete2. Truck – Mixed Concrete

READY – MIX

CONCRETE PLANT

CENTRALLY MIXED CONCRETEThe drum carrying the concrete revolves slowly so as to

prevent the mixed concrete from segregation and prevents its stiffening due to initial set

TRUCK MIXED CONCRETEThe batched material(sand,gravl, and cement) are carried and water is added just at the time of mixing. In case the cement remains in contact with wet or moist material and this phase cannot exceed the permissible period, which is normally 90 minutes.

RMC- MAJOR ADVANTAGES• Assured And Uniform Quality Of Concrete• Speedier Construction Through Mechanised Operations • Need For Ordering And Storing Cement, Aggregates And Sand On Site Totally Eliminated • Lower Labour And Supervisory Costs • Minimisation of cement wastage through bulk handling and storage • Cleaner working environment • Eco-friendly product

Factors that Prompted Introduction of RMC•Increasing stakes in the reliability and durability of

construction of emerging users.•Decreasing share of construction cost in overall cost of

the facility.•Increasing awareness on environmental factors and

convenience.• Globalization – adoption of best practices across the

globe.• Bigger size of projects and Time is recognised as a cost

factor.

APPROXIMATE CONSUMPTION OF CONCRETE IN INDIA•Approximately 60% cement used for concrete

• 1 ton Cement is needed to produce 3 m3 of concrete

STATUS OF RMC IN INDIA

Growth of RMC plants Percentage of RMC in Total Concrete consumption

PRESENT MAJOR CONSTRAINTS IN PROMOTION OF RMC•AVAILABILITY OF SUITABLE LAND IN CITIES AT

REASONABLE PRICE•SALES TAX / VAT ON RMC •TRANSPORTATION BOTTLENECKS (RESTRICTED

HOURS) •COST COMPARISON WITH SMC, WHILE TWO

PRODUCTS ARE DIFFERENT. CONSUMER STILL COST CONSCIOUS

• LACK OF CODAL PROVISIONS, SPECIFICATIONS AND REGULATIONS TO SUPPORT RMC.

• QUALIFIED AND TRAINED MANPOWER

PROBLEMS POSED DURING

MANUFACTURING OF CONCRETE

QUALITY Quality problems of various natures which may get reported arelisted below:• Delay in setting of concrete beyond 24 hours.• Development of cracks when the concrete is still in fresh state.• Development of cracks in hardened concrete.• Non-compliance of concrete cube strength (cast at site) to specifications at 7-days.• Non-compliance of concrete cube strength (cast at site) to specifications at 28-days.• Concrete supplied to site either has more slump than specified or has become stiff making it difficult to pump.

THERMAL CRACKS1. Early-age thermal cracking is caused by restraint to contraction on cooling from a

temperature peak, which is associated with the release of the heat of hydration of the binders.

2. Early-age thermal cracking occurs within few days in thin sections, but it may take several weeks to develop in massive sections.

3. Because of fast track constructions taking place to meet demands of infrastructure development, the trend towards large continuous pours of concrete with the requirements of high early strength and shorter striking times and problems of heat of hydration are mainly responsible for early-age cracking in hardened concrete.

4. This type of cracks occurs when the restrained thermal contraction strain exceeds tensile strain capacity of concrete.

REASONS FOR ABOVE PROBLEMS TO OCCUR

AT CONSTRUCTION SITE ARE MANY...

It is necessary to understand the behaviour of each and every constituent of concrete and construction techniques adopted at site before arriving at any conclusion regarding quality problems of RMC.

In many cases, information regarding Concrete Mix Design adopted for the type of material available in the plant may not be available. Properties of the constituents may not be available due to lack of testing facilities at RMC plant

R1. Delay in setting of concrete beyond 24 hours: Delay in setting of concrete is

mainly due to excess dosage of set retarding admixture used to retain pumpable slump for longer durations. These admixtures are used to prolong the plasticity of concrete. Useful to counter the effects of high temperature, eliminate cold joints, and reduce cracking associated with form deflections.

2. Basically, retarding admixtures increase dormant stage in the C3S hydration process. Too large a dose of admixture than specified by the manufacturer will cause the hydration reaction never to proceed resulting in cement that will never set.

3. Remedies: It is important to carryout extensive trials while using set retarding admixture to arrive at optimum dosage without delaying setting of concrete than required. This also establishes the compatibility between cement and admixture.

4. It is important to note that when a particular brand of cement is found to be compatible with a particular admixture, results may not be reproducible when cement is from a factory at a different location even though brand of cement is same. It is necessary to have a good quality control practices as properties of constituent materials vary to a large extent.

Market Survey

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