TOPIC 3

CONCRETE WORKS

TOPIC CONTENT: CONCRETE WORKS
3.1 CONCRETE MATERIAL 3.1.1 History of Concrete 3.1.2 Concrete Composition 3.1.3 Concrete Grade 3.1.4 Concrete Types3.2 STRUCTURAL CONCRETE FRAME 3.2.1 Concrete Structural Component 3.2.2 Concrete Reinforcement 3.2.3 Concrete Formwork3.3 CONCRETE DESIGN IDEAS 3.3.1 Concrete Wall 3.3.2 Concrete Column 3.3.3 Concrete Roof 3.3.4 Concrete Finishes & Texture3.4 CONCRETE INNOVATIONS

3.1 CONCRETE MATERIAL

3.1.1 HISTORY OF CONCRETE

Ancient materials were crude cements made by crushing and burning gypsum or limestone. When sand and water were added to these cements, they became mortar, which was a plaster-like material used to adhere stones to each other. Over thousands of years, these materials were improved upon, combined with other materials and, ultimately, morphed into modern concrete.
Cement was first developed when ancient builders found that found that when they coated the outsides of their pounded-clay fortresses and home walls with a thin, damp coating of burned limestone, it reacted chemically with gases in the air to form a hard, protective surface.
Today’s concrete is made using Portland cement, coarse and fine aggregates of stone and sand, and water. Admixtures are chemicals added to the concrete mix to control its setting properties and are used primarily when placing concrete during environmental extremes, such as high or low temperatures, windy conditions, etc.
https://www.bigrentz.com/blog/the-history-of-concrete

3.1.2 CONCRETE COMPOSITION

Concrete is a versatile construction material composed of a mixture of CEMENT, AGGREGATES (such as sand and gravel), WATER, and sometimes additional ADDITIVES or ADMIXTURES, that hardens over time to create a solid, strong substance.

CEMENT
A binding material used in construction that sets, hardens, and adheres to other materials to bind them together.
The characteristics of cement depend on the proportions of the compounds of the raw materials used and the fineness of the grinding of the clinker, produced by burning the raw materials.

1. ORDINARY PORTLAND CEMENT (OPC)

most commonly used in construction
versatile for variety of applications & mixture, from general construction to precast concrete products.
known for its strength, durability, and workability
commonly used in the construction of buildings, bridges, roads, and other structures.

2. PORTLAND POZZOLANO CEMENT

made by blending Portland cement with pozzolanic materials, such as fly ash or silica fume.
Improve the workability and durability of the cement
commonly used in home building construction and mass concrete structures, such as dams and bridges, where durability is a critical factor.

3. RAPID HARDENING CEMENT

specially designed to gain strength quickly.
used in situations where fast-setting concrete is required, such as in the construction of pavements, precast concrete products, and repair work.
has a higher early strength compared to OPC, allowing structures to be put into service faster.

4. EXTRA RAPID HARDENING CEMENT

gaining strength even faster than RHC.
made by grinding OPC clinker with a higher amount of calcium chloride to accelerate the setting time and early strength gain of the cement.
used in situations where fast-setting concrete with high early strength is required, such as in cold weather conditions, emergency repair work, construction of airport runways, industrial floors, and precast concrete products.

5. LOW HEAT CEMENT

specially designed to produce less heat during the hydration process.
made by reducing the amount of tricalcium aluminate by 6% resulting in slower strength gain and lower heat of hydration
for use in large concrete structures that are prone to cracking due to heat buildup like construction of dams, nuclear power plants, and large-mass concrete structures.

6. SUPLHATE RESISTING CEMENT

designed to resist the damaging effects of sulphate salts present in soil and groundwater.
commonly used in construction projects where the soil or groundwater has a high sulphate content, such as in coastal areas, mines, and canal linings, retaining walls.

7. BLAST FURNACE SLAG CEMENT

made by mixing Portland cement clinker with granulated blast furnace slag. The slag is a byproduct of the iron-making process and is ground into a fine powder, which is then mixed with Portland cement.
this combination resulting in a cement with lower heat of hydration, better workability, and improved durability.
commonly used in mass concrete projects, such as dams and bridges, as well as in the construction of high-rise buildings and industrial structures.

8. HIGH ALUMINA CEMENT

made by melting and grinding bauxite and lime together.
has an excellent level of strength and durability.
commonly used in the construction of refractory concrete, chemical plants, furnaces, and kilns which can withstand high temperatures and corrosive chemical environments.

9. WHITE PORTLAND CEMENT

has a high degree of whiteness.
used primarily for decorative purposes, such as in the construction of architectural elements, precast concrete products, and terrazzo flooring.
can also be used in combination with pigments to produce a wide range of coloured concrete finishes. - Coloured Cement

10. AIR ENTRAINING CEMENT

contains air-entraining agents, such as resins, glues and sodium salts, to create microscopic air bubbles within the concrete mix.
requires less water to achieve a specific consistency than ordinary Portland cement.
commonly used in construction projects that require frost resistance, such as concrete pavements, bridges, and buildings located in cold climates.

11. EXPANSIVE CEMENT

designed to expand slightly after setting.
commonly used in construction projects where a tight fit is required, such as precast concrete units and bridge bearings.
also used in grouting and shotcrete applications, where the expansion can help fill voids and gaps.
also be used to compensate for the shrinkage in concrete due to temperature changes or drying.

12. HYDROGRAPHIC CEMENT

designed to set and harden underwater. It's
made by blending Portland cement clinker with special additives that help it hydrate and set even in the presence of water.
commonly used in marine and underwater construction projects, such as building dams, bridges, and underwater tunnels.
also used in the construction of swimming pools, water storage tanks, and sewage treatment plants.

CEMENT GRADE

33 Grade Cement
- general construction work and plastering.
- compressive strength of 33 N/mm² after 28 days of curing.
- use in construction projects where the requirement for high strength is not critical. It is not suitable for concrete mix above M20.
43 Grade cement
- compressive strength of 43 N/mm² after 28 days of curing.
- use in construction projects where moderate to high strength is required, such as plain concrete or plastering works.
- used to make precast items such as tiles, blocks, pipes, etc.
- suitable for medium-scale construction projects. It is suitable for concrete mix up to M30.
53 Grade Cement
- compressive strength of 53 N/mm² after 28 days of curing.
- use in construction projects where high strength is required, such as in the construction of high-rise buildings, dams, and heavy-duty industrial structures.
- more durable and long-lasting. Suitable for concrete mix above M25.

AGGREGATES
Aggregates can be defined as crushed stones used in concrete. Aggregate in concrete occupied about 70 – 80 % of the total volume which provides the main body of concrete. Aggregate makes concrete strong and durable when mixed with cement, sand, and water.
Aggregates can be sourced naturally in river, shores and pit mines, but comes in varying sizes and shapes; while manufactured aggregates can be made to the required size.
Aggregates can be classified into:

Grain Size
Density
Shape

Aggregate classification by GRAIN SIZE

Aggregate classification by DENSITY

Aggregate classification by DENSITY
Ultra Lightweight

Vermiculite, Ceramic
Can be sawed or nailed
Also used for its insulating properties

Lightweight

Expanded perlite, shale, or slate Burned clay Crushed brick
Structural lightweight concrete 1350 to 1850 kg/m3 Masonry units
Also used for its insulating properties

Normal Lightweight

Crushed limestone, Sand, River gravel, Crushed recycled concrete
Used for normal concrete projects
Produce normal-weight concrete 2200 to 2400 kg/m3

Heavyweight

Steel or iron shot Steel or iron pellets
Produce high-density concrete up to 6400 kg/m3
Radiation shielding, counterweights, additional applications where high
the mass-to-volume ratio is desired

Aggregate classification by SHAPE

Aggregate classification by SHAPE
Rounded Aggregates

Due to friction with climatic condition, the aggregates get eroded and they get the round shape.
offer a better workability to concrete on site.
need lesser water cement ratio to form a concrete. But it has rounded surfaces and this why they do not form a good bond in concrete.

Angular Aggregates

even, well defined edges and shape, formed by crushing of rocks.
It gives lesser workability to concrete on site. But form a stronger bond with concrete.
It enhances the compressive strength of concrete by 10-20% in many cases.

Irregular Aggregates

uneven edges and shape, and so that form a very good bond in concrete and gives higher bond strength and mechanical strength to concrete.
It gives lesser workability to concrete on site.

Recycled Aggregates

The flaky aggregates are having a very light thickness, and it can easily crack.
Due to its lower workability, it is not used in concrete, and also it quickly gets broken due to its minor thickness.

ADDITIVES OR ADMIXTURES
Admixtures are additions to a concrete mix that can help control the set time and other aspects of fresh concrete. Common admixtures include accelerating admixtures, retarding admixtures, fly ash, air entraining admixtures, and water-reducing admixtures. Admixtures are used for one purpose: to improve some characteristics of the concrete.
Common admixtures:

Air-Entraining Admixture
- to increase the durability of concrete under freezing and thawing conditions.
- improve the workability of concrete, prevents segregation and bleeding, lower the unit weight and modulus of elasticity of concrete, improves the chemical resistance of concrete and reduction of cement or sand or water content in concrete etc.
Water-Reducing Admixture / Plasticizser
- to minimize the water demand in a concrete mix.
- to increase in workability, improves the strength of concrete, good bond between concrete and steel, prevents cracking, segregation, honeycombing, bleeding etc.
Retarding Admixture
- slow down the rate of hydration of cement in its initial stage and increase the initial setting time of concrete. These are also called as retarders and
- used especially in high temperature zones where concrete will set quickly. The quick setting in some situations may lead to discontinuities in structure, poor bond between the surfaces, creates unnecessary voids in concrete etc.
Accelerating Admixture
- to reduce the initial setting time of concrete.
- improves the strength of concrete in it early stage by increasing the rate of hydration. Earlier hardening of concrete is useful in several situations such as early removal of formwork, less period of curing, emergency repair works, for constructions in low temperature regions etc.
Superplasticizer
- used to produce flowing concrete. Flowing concrete is a highly workable type of concrete that doesn’t sacrifice strength.
- used for thin section placements and areas with closely spaced reinforced steel.
Damp- proofing Admixture - to make the concrete structure impermeable against water and to prevent dampness on concrete surface.
Corrosion Preventing Admixture - To prevent or to slow down the process of corrosion by the steel reinforcement bar within the concrete structure

TEST TO MEASURE CONCRETE'S WORKABILITY

1. SLUMP TEST
Concrete slump value is used to find the workability, which indicates water-cement ratio, but there are various factors including properties of materials, mixing methods, dosage, admixtures etc. also affect the concrete slump value.
The slump test is the most simple workability test for concrete, involves low cost and provides immediate results. Due to this fact, it has been widely used for workability tests since 1922.

True Slump – True slump is the only slump that can be measured in the test. The measurement is taken between the top of the cone and the top of the concrete after the cone has been removed as shown in figure-1.
Zero Slump – Zero slump is the indication of very low water-cement ratio, which results in dry mixes. These type of concrete is generally used for road construction.
Collapsed Slump – This is an indication that the water-cement ratio is too high, i.e. concrete mix is too wet or it is a high workability mix, for which a slump test is not appropriate.
Shear Slump – The shear slump indicates that the result is incomplete, and concrete to be retested.

2. COMPACTION FACTOR TEST

3. FLOW TABLE TEST

3.1.3 CONCRETE GRADES

Strength and composition of the concrete defined the grades of concrete.
Concrete mixes are classified by their grades having specific crushing strength at 28 days as measured in standard conditions with a 150mm x 150mm x 150mm cube, which means the grade of concrete corresponds to its characteristics compressive strength.
The measurement to understand the grade of concrete is MPa, using unit of N/mm2 Here M stands for mix and an MPa shows the overall strength. The imperial Compressive Strength unit is measured using psi (Pounds per square inch)
Example: M-20 shows the crushing strength of that cube having a size of 150mm x 150mm x 150mm at 28 days is 20 N/mm2

COMPRESSIVE STRENGTH OF CONCRETE
The compressive strength of concrete is defined as the maximum crushing stress that the concrete can withstand without undergoing any failure, using a Compression Testing Machine
Various factors can affect the compressive strength of concrete such as water-cement ratio, grade of cement, quality of water used, usage of admixtures, etc.
The concrete samples have to be taken from the concrete batch at the site (highly recommended), if not possible, prepare the concrete mix at the lab using the same proportion. Multiple concrete cubes from the same batch will be needed for varying tests according age of curing.

NORMAL / ORDINARY CONCRETE GRADE
M5, M10 and M15 are used for PCC (Plain cement concrete) work such as levelling course, bedding for footing (Lean Concrete) etc.
M20 is used for RCC (Reinforced Cement Concrete) work such as Slab, beams, columns and footings etc. (for mild exposure)

STANDARD CONCRETE GRADE
M25, M30 and M35 are used for RCC (Reinforced Cement Concrete) like foundations, footings columns, beams, slabs, etc.
M40 grade is used for Pre-stressed concrete work, slabs, beams, columns, footings, etc.
M45 grades are used for RCC, Runways, concrete roads, prestressed concrete friders, RCC columns, prestressed beams etc.
M55 grade is used for Pre-stressed concrete girders and piers etc.

HIGH STRENGTH CONCRETE GRADE
M50 grades are used for RCC, Runways, concrete roads, prestressed concrete friders, RCC columns, prestressed beams etc.
M55 grade is used for Pre-stressed concrete girders and piers etc.
M60, M65 and M70 are used for RCC work where high compressive strength is required such as high rise buildings, long span bridges, ultra-thin white topping and spillways of dams, coastal construction etc.

3.1.4 CONCRETE TYPES

1. REINFORCED CONCRETE (RC)

Steel in various forms is used as reinforcement to give very high tensile strength, while the property of plain concrete resisted the high compressive strength, avoiding cracking or breaking.
The steel reinforcement (REBAR) is cast in the form of rods, bars, meshes, and all conceivable shapes. Some construction have already used fibers as reinforcements in concrete structure.
Great resistance to the actions of fire and water
Very long service life and low-maintenance material

2. PRE-STRESSED CONCRETE

A type of reinforced concrete in which the reinforcement bars are tensioned before being embedded in the concrete.
When the concrete is mixed and placed, these bars are placed at each end of the structural unit where they are used. When the concrete sets, this unit is put into compression.
This compression enhances the strength of the lower section of the unit and improves its resistance against tensile forces. However, this process requires skilled labor and heavy equipment. Normally, prestressed units are created and assembled on-site.
Prestressed concrete is used to build bridges, heavy-loaded structures or roofs that have long spans.

3. PRECAST CONCRETE

refers to numerous types of concrete shapes that are cast into molds either in a factory or at the site, and completely left to cure before transported to the site.
Perfect proportioning of the ingredients of concrete, through thorough mixing of the cement, aggregates, and water to obtain the mix of the desired design and consistency, within a controlled factory environment
The latest trend in the construction industry is to shift more and more to prefabricated concrete units in building construction.

4. FRESH / NORMAL CONCRETE aggregate, concrete and sand — in a 1:2:4 ratio. It takes about 30 to 90 minutes to set. Used for pavements or buildings that don’t need high tensile strength

5. LIGHTWEIGHT CONCRETE has a density of less than 1920kg/m3., created by using lightweight aggregates. It has very low thermal conductivity. Common uses for lightweight concrete include creating long-spanning bridge decks and building blocks. It can also be used to protect steel structures.

6. HIGH DENSITY CONCRETE density varies between 3000-4000 Kg/m3 . Used in the construction of atomic power plants using heavy aggregates that helps the structure resist radiation. Crushed rocks are normally used.

7. STAMPED CONCRETE imprinted or textured concrete, to realistically replicate the look and pattern of natural stones, tiles, brick and granites. Often used to construct patios, pool decks, interior floors and driveways.

8. AIR-ENTRAINED CONCRETE hold billions of microscopic air cells in every cubic foot. These tiny air pockets relieve the internal pressure on the concrete. They provide tiny chambers where water can expand when it freezes.

9. GLASS CONCRETE recycled glass is used as an aggregate in the concrete. They provide better thermal insulation and also have a great appealing look as compared to other types. its

3.2 STRUCTURAL CONCRETE FRAME

Recap from BC1...

3.2.1 CONCRETE STRUCTURAL COMPONENTS

The single most important function of a Structural Concrete Frame is to carry/transfer the load of the building from the top most part, to the soil that it sits on. The loads are:

Dead Loads: the downwards force on the building coming from the weight of the building itself, including the structural elements, walls, facades, and the like.
Live Loads: the downwards force on the building coming from the expected weight of the occupants and their possessions, including furniture, books, and so on.
Dynamic Loads: these occur commonly in bridges and similar infrastructure, and are the loads created by traffic, including braking and accelerating loads.
Wind & Earthquake Loads: especially for tall buildings, or buildings with large surface area. Buildings are designed not to resist the everyday wind conditions or mild earth movement, but extreme conditions that may occur once every 100 years or so.

FOUNDATIONtransfer the overall building load onto the soil that the building is sitting on.

COLUMNS / SHEER WALLSupright pillar or post that is transferring the load vertically from the roof right down to the foundation. Position of columns are most of the time aligned from top to bottom to ensure uniform load transfer. Sheer walls (very large column) counter the lateral/horizontal forces acting on the structure

BEAMScontinuous, long, sturdy piece of squared concrete/timer or steel horizontal member that ties the columns and provides the resting place for the slab above it.

SLABSprovides area for function and loading within each level of the building.

3.2.2 CONCRETE REINFORCEMENT

Structural Concrete Frame of a typical buildings are made using Reinforced Concrete (RC).
Steel reinforcement bars or REBAR are used to improve the tensile strength of the concrete, since concrete is very weak in tension, but is strong in compression. Steel is only used as rebar because elongation of steel due to high temperatures (thermal expansion coefficient) nearly equals to that of concrete.

TENSILE STRENGTH OF CONCRETE
Tensile strength is the ability of concrete to resist breaking or cracking under tension. It affects the size of cracks in concrete structures and the extent to which they occur. Cracks occur when tensile forces exceed the tensile strength of the concrete.
Traditional concrete has a significantly lower tensile strength as compared to compressive strength. This means that concrete structures undergoing tensile stress must be reinforced with materials that have high tensile strength, such as steel. Hence the use of Reinforcement Bar
Tensile strength of Concrete is tested using these 2 methods:

SPLIT TENSILE TEST - a standard cylindrical specimen is laid horizontally, and the force is applied on the cylinder radially on the surface which causes the formation of a vertical crack in the specimen along its diameter https://theconstructor.org/concrete/splitting-tensile-strength-test-cylindrical-concrete-specimen/2116/
FLEXTURAL TEST - tests the ability of unreinforced concrete beam or slab to withstand failure in bending https://theconstructor.org/concrete/flexural-test-concrete-procedure-applications/18576/#google_vignette

TYPES OF REINFORCEMENT BAR (REBAR)

1. MILD STEEL BARsurface of the mild steel bars are plain and round in shape. They are available in various sizes of 6 mm to 50 mm. used as dowels at expansion joints, where bars must slide in a metal or paper sleeve, for contraction joints in roads and runways, and for column spirals. They are easy to cut and bend without damage.

2. DEFORMED STEEL BARDeformed steel bars have ribs, lugs and indentation on the surface of the bar, which reduces the major problem that is faced by mild steel bar due to slippage and good bonding is achieved between concrete and rebar. The tensile properties is higher compared to other rebars. These bars are produced in sections from 6 mm to 50 mm dia.

3. CARBON STEEL REBARmade up of carbon steel and is commonly known as Black Bar due to carbon colour. The main drawback of this rebar is that it corrodes, which adversely effect the concrete and structure. The tensile strength ratio coupled with the value makes black rebar one of the best choices.

4. EPOXY-COATED REBAREpoxy-coated rebar is black rebar with an epoxy coat. It has the same tensile strength, but is 70 to 1,700 times more resistant to corrosion. However, the epoxy coating is incredibly delicate. The greater the damage to the coating, the less resistant to corrosion.

5. GALVANIZED REBARGalvanized rebar is only forty times more resistant to corrosion than black rebar, but it is more difficult to damage the coating of galvanized rebar. In that respect, it has more value than epoxy-coated rebar. However, it is about 40% more expensive than epoxy-coated rebar.

6. GLASS-FIBER REINFORCEMENT POLIMER (GFRP)made up of carbon fibre. As it is made up of fibre, bending is not allowed. It is very resistant to corrosion and is costly when compared to other rebars.

3.2.3 CONCRETE FORMWORK

A formwork is a temporary casing that is designed and constructed to hold the fresh concrete in its place during the process of placing, compacting, and curing till the concrete attains sufficient strength to support its own weight.In addition to the weight of concrete, formwork carries live loads due to the movement of materials, equipment, and workmen.
Considerations for Formwork:

cheap and reusable.
strong enough to withstand all external loads besides the concrete weight.
waterproof so that it should not absorb water from the concrete.
light in weight so that it is easy to transfer.
Swelling and shrinkage should be minimum.
Deflection of formwork should be minimum.
Surface should be smooth and it should afford easy stripping.

Formworks can be made using these materials: Timber, Steel, Aluminum, Plywood, Fabric, Plastic

Foundation Formwork

Staircase Formwork

3.3 CONCRETE DESIGN IDEAS

3.3.4 CONCRETE FINISHES & TEXTURE

3.4 CONCRETE INNOVATION

TOP-MIX PERMEABLE CONCRETE
Top-mix Permeable is widely known as a fast-draining concrete that can ultimately absorb up to 1,500 liters of water each minute per square meter. Usually, road paving materials are typically made from a mix of vast and fine crushed stones. This combination results in the materials being porous enough to accept the enormous amounts of water.

GREEN CONCRETE
The use of recycled or waste materials can be considered sustainable as they can lower costs and raw materials as well as reduce landfills. In a recent project in Malayasia , researchers at Universiti Teknologi MARA introduced an innovative green concrete called “green-mix concrete” that is designed and manufactured using conventional materials but partially replaced with suitable waste and recycled materials to achieve acceptable performance, economics and sustainability.