CECMAT20 FT Cement

Cement

Cement

powder

cement paste

Cement + water

mortar

Cement paste + fine aggregate

concrete

Cement + coarse aggregate + fine aggregate

ADVANTAGES OF CONCRETE

• Durability, longevity, heat storage capability, and chemical inertness. • Ability to be cast • Fire resistant • On-site fabrication • Aesthetic properties • The raw materials used in cement production are widely available in great quantities • Needs little of no finish or final treatments • Chemically inert concrete doesn’t require paint to achieve a given color: natural- mineral pigments and coloring agents can be added at the mixing to provide a rainbow of options • Low maintenance • Can be reused or recycled • Concrete can be reused with bituminous asphalt as road base materials, can be recycled and reused by crushing into aggregates for new concrete or as fill material for road beds or site works.

LIMITATIONS OF CONCRETE

1. Low tensile strength

2. Low ductility

3. Volume instability

4. Low strength-to-weight ratio

proportioning of concrete

The process of relative proportions of cement, sand, coarse aggregate, and water, so as to obtain a concrete of desired quality

design mix concrete

By designing the concrete mix, such concrete shall be called ____________. nominal mix concrete

nominal mixes

The wide use of concrete as construction materials has led to the use of mixes of fixed proportion, which ensures adequate strength. These mixes are called ________.

M5 to M25 (IS standard)

Nominal mix concrete may be used for concrete of grades _________.

very high strength

1 : 1 : 2 and 1 : 1.2 : 2.4 for

normal works

1 : 1.5 : 3 and 1 : 2 : 4 for

foundations and mass concrete works

1 : 3 : 6 and 1 : 4 : 8 for

METHODS OF PROPORTIONING CONCRETE 1. Arbitrary method

The general expression for the proportions of cement, sand and coarse aggregate is 1:n:2n by volume.

concrete slump test

measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. It can also be used as an indicator of an improperly mixed batch. The test is popular due to the simplicity of apparatus used and simple procedure

flow table, or slump-flow test

is used for concrete that is too fluid (workable) to be measured using the standard slump test, because the concrete will not retain its shape when the cone is removed.

mixing

The process of mixing various constituents of concrete in specified proportions is known as ______.

Hand mixing

Mixing concrete by manual labor. It is generally for small works and in special cases where noise is to be avoided.

Machine mixing

This is adopted by big projects where large quantity of concrete is required continuously. The machine mixing requires less quantity of cement than hand mixing. The concrete is produced at a much faster rate.

compaction

The process of eliminating the air voids in the concrete to increase the density of concrete

Hand ramming

For unimportant works, compaction can be carried out by hand methods like ramming, tamping, spading and slicing with suitable tools. Hand methods require use of fairly wet concrete.

Vibrators

The mechanical devices which are used for compaction of concrete in the formwork are depending on the depth of the concrete, and the importance of the work, different types of vibrators are used.

INTERNAL VIBRATORS

These types of vibrators are used for structures such as beams having sufficient depth. These vibrators consist of a metal rod which is inserted in fresh concrete. The rod vibrates while it is being inserted, vibrates the concrete and removes the air. Internal vibrators should be inserted and withdrawn slowly and they should be operated continuously while they are being drawn. These vibrators are more efficient than other types of vibrators. These are also known as needle vibrators.

SURFACE VIBRATORS

These vibrators are mounted on platforms or screeds. They are used for finishing concrete surfaces such as bridge floors, road slabs, station platform and where the thickness of the structure is less.

FORM VIBRATORS

These vibrators are attached to the formwork and the vibrating action is conveyed to concrete through the formwork during vibrations. These are used for structures which are too thin for the use of needle vibrators.

TABLE VIBRATORS

These are in the form of a table and concrete is placed on the table. The vibration of the table increases the compaction of the concrete. These vibrators are widely used for making pre-cast products

curing

plays an important role on strength development and durability of concrete. ________ takes place immediately after concrete placing and finishing, and involves maintenance of desired moisture and temperature conditions, both at depth and near the surface, for extended periods of time.

Slabs on ground and structural concrete

require a minimum curing period of seven days for ambient temperatures above 40 degrees Fahrenheit.

ACI

American Concrete Institute

Ready-mixed concrete

is a type of concrete that is manufactured in a factory of batching plant, according to a set proportion, and then delivered to a work site, by truck mounted transit mixers.

agitator trucks

Proper care during transportation of concrete is also ensured by the use of _______

centrally mixed concrete

mixing is done at a central plant and the mixed concrete is transported, usually in an agitator truck which revolves slowly so as to prevent segregation and undue stiffening of the mix

the transit mixed or truck mixed concrete

Here the materials are batched at a central plant but are mixed in a mixer truck either in transit or site immediately prior to the concrete being discharged.

Shrink-mixed concrete

partially mixed in a stationary mixer and completed in a mixer truck (4 rpm to 16 rpm)

PUMPED CONCRETE

the concrete which is transported to heights be means of pumping using concrete pumps. This method is used where large quantity of concrete work is involved at greater height, where other means of transporting is not easy to do.

PRE-CAST CONCRETE

concrete is manufactured at the factory. It is possible to prepare well- made ________ products by keeping a high standard of finishing. _______ products vary from simple structures such as fencing posts, pipes, paving slabs, etc. To elaborate and complicated artificial concrete blocks.

Admixtures

those ingredients in concrete other than Portland cement, water, and aggregates that are added to the mixture immediately before r during mixing.

Air-entraining admixtures

Purposely used to introduce and stabilize microscopic air bubbles in concrete. Air-entrainment will dramatically improve teh durability f concrete exposed to cycles of freezing and thawing. Entrained air greatly improves concrete’s resistance to surface scaling caused by chemical deicers. Furthermore, the workability of fresh concrete is improved significantly, and segregation and bleeding are reduced or eliminated.

Water-reducing admixtures.

used to reduce the quantity of mixing water required to produce concrete of a certain slump, reduce water-cement ratio, reduce cement content, or increase slump.

Plasticizers

Often called superplasticizers, are essentially high-range water reducers. These admixtures are added to concrete with a low-to-normal slump and w/c ratio to make high-slump flowign concrete. Flowing concrete is highly fluid but workable concrete that can be placed with little or no vibration or compaction hile still remaining essentially free of excessive bleeding or segregation.

Accelerating admixtures

Used to accelerate the rate of hydration (setting) and strength development of concrete at an early age.

Retarding admixtures

Used to delay the rate of setting of concrete. High temperatures of fresh concrete are often teh cause of an increased rate of hardening that makes placing and finishing difficult. One of the most practical methods of counteracting this effect is to reduce the temperature of the concrete by cooling that mixing water and/or aggregates.

Hydration-control admixtures

These admixtures make it possible to reuse concrete returned in a ready-mix truck by suspending setting overnight. The admixture is also useful in maintaining concrete in a stabilized non-hardened state during long hauls. The concrete is reactivated when It arrives at the project.

Corrosion inhibitors

Used in concrete for parking structures, marine structures, and bridges where chloride salts are present. The chlorides can cause corrosion of steel reinforcement in concrete

Shrinkage reducers.

Admixtures which have potential uses in bridge decks, critical floor slabs, and buildings where cracks and curling must be minimized for durability or aesthetic reasons.

Coloring admixtures.

Natural and synthetic materials are used to color concrete for aesthetic and safety reasons. a) Red concrete is used around buried electrical or gas lines as a warning to anyone near these facilities. b) Yellow concrete safety curbs are used in paving applications.

Damp-proofing and waterproofing admixtures.

Reducing the transmission of water vapor through concrete without stopping it entirely, is a desirable feature. Treating concrete to retard, not stop the absorption of water or water vapor by concrete or to retard their transmission through concrete is considered damp-proofing. Treatment of a surface of a structure to prevent the passage of liquid water under hydrostatic pressure is called waterproofing.

Permeability-reducing admixtures.

They reduce the rate at which water under pressure is transmitted through concrete. One of the best methods of decreasing permeability in concrete is to increase the moist-curing period and reduce the w/c ratio. Most admixtures that reduce w/c ratio consequently reduce permeability.

Pumping aids

Admixtures added to concrete mixtures to improve pumpability. They are best used to make marginally pumpable concrete more pumpable although they cannot sure all unpumpable concrete problems. These admixtures increase viscosity or cohesion in concrete to reduce dewatering of the paste while under pressure from the pump

Bonding admixtures and bonding agents.

They are added to Portland cement mixtures to increase the bond strength between old and new concrete. Flexural strength and resistance to chloride-ion ingress are also improved. Bonding agents should not be confused with bonding admixtures. Admixtures are an ingredient in the concrete

bonding agents are applied to existing concrete surfaces immediately before the new concrete is placed. Bonding agents help “glue” the existing and the new materials together. Bonding agents are often used in restoration and repair work.

CONCRETE MASONRY UNITS

It consists of hardened cement and may be completely solid or contain single or multiple hollows. It is made from conventional cement mixes and various types of aggregate.

SOLID CONCRETE BLOCKS

heavy in weight and manufactured from dense aggregate. They are very strong and provides good stability to the structures.

HOLLOW CONCRETE BLOCKS

contains void area greater than 25% of gross area. Solid area of hollow bricks should be more than 50%. The hollow part may be divided into several components based on our requirement. They are manufactured from lightweight aggregates. They are light weight blocks and easy to install.

Concrete stretcher blocks

used to join the corner in the masonry. Stretcher blocks are widely used concrete hollow blocks in construction. They are laid with their length parallel to the face of the wall.

Concrete corner blocks

used at the ends or corners of masonry. The ends may be window or door openings etc. they are arranged in a manner that their plane end visible to the outside and other end is locked with the stretcher block.

Concrete pillar blocks

also called as double corner block. Generally these are used when two ends of the corner are visible. In case of piers or pillars these blocks are widely used.

Jamb concrete blocks

used when there is an elaborated window opening in the wall. They are connected to stretcher and corner blocks. For the provision of double hung windows, jamb blocks are very useful to provide space for the casing members of window.