PART 5

Concrete

A building material that solidifies and hardens after mixing with water and placement due to a chemical process known as hydration.

Hydration

The chemical process in which water reacts with cement in concrete, bonding the other components together and producing a hard stone-like material.

Plain Concrete

A structural concrete with no reinforcement or with less reinforcement than the minimum amount specified for reinforced concrete.

Reinforced Concrete

A structural concrete reinforced with the minimum amounts of reinforcing bars, pre-stressing tendons, or non-pre-stressed reinforcement.

Class AA

A rich concrete mixture used for columns of reinforced concrete buildings and where a very strong and dense concrete is required.

Class A

A good concrete mixture used for reinforced concrete works of all kinds and best suited for general concrete works.

Class AA

(1:1.5:3)

Class A

(1:2:4)

Class B

(1:2.5:5)

Class C

(1:3:6)

Class AA

3500-4000 psi

Class A

2500-3000 psi

Class B

1500-2000 psi

Class C

500-1000 psi

Class B

A medium concrete mixture used for plain concrete foundations, walls, floors, etc., where not much strength or impermeability is required.

Class C

A lean concrete mixture used for heavy masses.

Lime Concrete

A concrete mixture with slaked lime as the main ingredient, used as a binding material.

Special Cement Concrete

Concrete produced to suit a variety of special requirements of environmental conditions.

Reinforced Cement Concrete

Concrete obtained by embedding steel bars in tension zones of the structural member to offset tension weakness of plain cement concrete.

Pre-Stressed Cement Concrete

Concrete obtained with high graded steel wires or tendon wires.

Aerated Concrete

Concrete manufactured from calcareous and siliceous materials.

Heavy Weight Concrete

Concrete produced by using special heavy weight aggregates and compacting well by mechanical means.

Pre-packed Concrete

Concrete obtained by injecting cement sand mortar under pressure to fill voids already packed and fully compact coarse aggregates.

Air Entrained Concrete

Concrete containing billions of microscopic cells per cubic ft and produced by the use of _____________________________.

High-Early Strength Concrete

Concrete produced by using high-early strength cement.

Light weight Concrete

Concrete made from light weight aggregates.

Weight Method

Fairly simple and quick for estimating mix proportion using an assumed or known weight of concrete per unit volume.

Absolute-Volume Method

More accurate method involves use of specific gravity values for all ingredients to calculate the absolute volume and each will occupy in a unit volume of concrete.

Fineness Modulus Method

is used to indicate an index number which is roughly proportional to the average size of the particle in the entire quantity of aggregates.

Arbitrary Standard Method

Ratio of fine aggregates and coarse aggregates to develop a dense mix that lies between 1:1/2 and 1:2/1/2.

Minimum Voids Method

The quantity of fine aggregate used in the mixed is about 10% more than the voids in the coarse aggregates and the quantity of cement is kept about 15% more than the voids in the fine aggregates.

Maximum density Method

In this method a box of fixed volume is filled with varying proportions of fine and coarse aggregates.

Water Cement Ratio.

The amount of water in mixing concrete is the most important factor affecting the strength of a given proportion.

Consistency

The measure of the stiffness, sloppiness, or fluidity of a concrete mix.

Slump Test

A test commonly used to measure the consistency of concrete.

Slump Loss

fresh concrete gradually loses consistency

Workability

The ease with which concrete can be compacted fully without segregation and bleeding.

Segregation

The separation of the coarser particles from the mix, resulting in no homogeneity of the concrete mix.

Bleeding

The appearance of water along the cement particles on the surface of freshly laid concrete on compaction and finishing.

Settlement and Bleeding

Cement and aggregate particles have densities about three times that of water.

Setting

The hardening of concrete before its hydration.

Hydration

The process in which concrete derives its strength by the hydration of cement particles.

Air entrainment

reduces the density of concrete and consequently reduces the strength.

Strength

The compressive strength of concrete, measured in pounds per square inch (psi) or newton per square millimeter (MPa).

Durability

The ability of concrete to maintain satisfactory performance over an extended service life.

Impermeability

The resistance of concrete to the flow of water through its pores.

Dimensional Changes

The shrinkage and creep of concrete caused by drying, chemical changes, and long-term pressure or stress.

Shrinkage

The volume decreases of concrete caused by drying and chemical changes.

Creep

Deformation of concrete structure under sustained load

Modulus of Elasticity

The measure of the stiffness of concrete, dependent on the modulus of elasticity of the concrete ingredients and their mix proportions.

Water Tightness

The property of concrete that relates to its impermeability.

Thermal Conductivity

The measure of how well concrete conducts heat.

Unit Weight

The weight of concrete per unit volume, dependent on the percentage of reinforcement, type of aggregate, and number of voids.

Curing

The method used to maintain a satisfactory moisture content and temperature in concrete for a period of time immediately after placing and finishing to develop the desired properties.

Universal Testing Machine

test mechanical properties of a material such as compressive, tensile, shear and flexural

Universal Testing Machine

This testing machine can make a stress strain diagram that we used to compute yield strength, tensile strength, and others.

1. Loading Unit

2. Control Unit

two main parts of UTM

Loading Unit

Where the test specimen takes place and the load that must be exerted to the material.

Loading unit

Consists of following components:

• load frame

• upper/lower crosshead

• elongation scale

Load Frame

It consists of a table (to place the specimen for compression test), upper crosshead, and lower crosshead.

Upper crosshead

is to clamp the specimen needs to be tested from top or its one end;

Lower crosshead

is the movable crosshead whose screws can be loosened for height adjustment and tightened.

Elongation Scale

The relative movement of the lower and upper table is measured by an elongation scale which is provided along with the loading unit.

Control Unit

Where the load is applied and get the corresponding test result. The load is applied with a control valve and released by a release valve. The load is applied with the help of hydraulic pressure.

Control Unit

Consists of following components:

• Hydraulic Power Unit

• Load Measuring Unit

• Control Devices

Hydraulic Power Unit

This unit consists of an oil pump that provides non-pulsating oil flow into the main cylinder of the load unit. This flow helps in the smooth application of load on the specimen. The oil pump in a hydraulic power unit is run by an electric motor and sump.

Load Measuring Unit

This unit has a pendulum dynamometer unit that has a small cylinder with a piston which moves with the non-pulsating oil flow. The pendulum is connected to the piston by a pivot lever. The pivot deflects based on the load applied to the specimen. This deflection is converted to the load pointer and displayed as the load on the dial. The range of load application can be adjusted by means of a knob in the load measuring unit (0-100 kN; 0-250 kN; 0-500 kN and 0-1000kN). The accuracy of measuring unit controls the overall accuracy of the machine.

Control Devices

It can be electric or hydraulic. Electric control devices make use of switches to move the crossheads and switch on/off the unit. A hydraulic control device consists of two valves, Right Control Valve and Left Control Valve or Release Valve. A right control valve is used to apply load on the specimen. The left control valve is used to release the load application.

Universal Testing Machine

test the mechanical properties of materials

UTM

The following are some standard tests performed by ____:

• Tensile Test

• Compression Test

• Bending Stress

• Peel Test

Tensile Test

Determine the force needed to pull the specimen apart and along with how much the material stretches before it breaks.

Tensile Test

Procedure: Clamp a single piece of anything (re-bar) on each end and pull it apart until it breaks. This measures how strong it is (tensile strength) , how stretchy it is (elongation), and how stiff it is (tensile modulus).

Compression Test

This is opposite of tensile test where you compress an object between two level plates until a certain load or distance has been reached or the product breaks. The compressive strength of a material is calculated as the stress required to rupture the specimen or deform the specimen to a given percentage of its height.

Bending Stress

This is where you support a length of material by spanning it across two supports on each end. There is nothing supporting the middle portion underneath it. Then you press down from above directly in the middle of the span of material until the supported material breaks or reaches a specific distance. This test measures how strong the material in flexure (flexural strength) and how stiff it is (flexural modulus).

Peel Test

This test pulls apart two materials that have been bonded together.

Peel Test

Procedure: One clamp holds one material, and the other clamp holds the other materials. Then you separate them apart for a few inches.