CAST-IN PLACE CONCRETE

GROUP 2

Topics Preparing concrete

Transportation, handling, and placing of concrete

Finishing concrete

Curing concrete

Formworks

Concrete reinforcing materials

What is Cast-in-place concrete?

Cast-in-place concrete walls are made with ready-mix concrete placed into removable forms erected on site.

It is a concrete that is transported in an unhardened state, primarily as ready-mix, and placed in forms.

Cast-in-place concrete is a common type of building material for commercial structures and residential homes alike.

Most foundations and slabs-on-ground

Walls, beams, columns, floors, roofs

Large portions of bridges, pavements, and other infrastructure.

Uses

If not enough cement is used, then the result is called ''sandcrete'' and the pad will eventually fall apart.

Ingredients of Concrete

ADVANTAGES

Strength

Insulation

Versatility

DISADVANTAGES

Time

Labor Requirements

Advantages and Disadvantages

Preparing Concrete

Cabacungan, Noreen Anne

Components Cement

Sand

Gravel

Water

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.

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.

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.

Soon after the aggregates, water, and the cement are combined, the mixture starts to harden.

Once the concrete is thoroughly mixed and workable it should be placed in forms before the mixture becomes too stiff.

Transporting and Handling Concrete

Catalan, Angelinne

Wheelbarrows and Buggies Used for: Short flat hauls on all types of onsite concrete construction

Advantages: Versatile—ideal inside and on jobsites with changing placing conditions.

Versatile power buggy can move all types of concrete over short distances

Belt Conveyor Used for: Conveying concrete horizontally or higher/lower level.

Advantages: Adjustable reach, traveling diverter, variable speed.

The conveyor belt is an efficient, portable method of handling concrete. A drop chute prevents concrete from segregating as it leaves the belt; a scraper prevents loss of

mortar. Conveyor belts can be operated in series and on extendable booms of hydraulic cranes.

Truck Mounted Conveyors

Used for: Conveying concrete horizontally or higher/lower level.

Advantages: Conveyer arrives with concrete. Adjustable reach and variable speed.

A conveyor belt mounted on a truck mixer places concrete up to about 12 meters (40 feet) without the need for additional handling equipment.

Crane and Buckets Used for: Work above ground level.

Advantages: Can handle concrete, reinforcing steel, formwork, and sundry items.

The tower crane and bucket can easily handle concrete for tall-building construction.

Screw Spreaders Used for: Spreading concrete over large flat areas.

Advantages: Concrete can be quickly spread over a wide area to a uniform depth.

The screw spreader quickly spreads concrete over a wide area to a uniform depth. Screw spreaders are used primarily in pavement construction.

Finishing ConcreteCelino, Cesar

What is finishing? Operation of creating a concrete surface of a desired texture, smoothness

and durability

Can be functional or decorative

Step 1: Pouring the Concrete. After thoroughly mixing the concrete pour it into the forms slightly

overfilling them.

Then take a straight board (a 2x4 piece of lumber works great as long as it isn’t bowed) and simply level off the concrete.

Using a board that is longer than your pour is wide and using a sawing motion work back and forth until the concrete is level.

You really need someone on the other side to help with this part.

This is called “screeding” if you are trying to learn new words with which to impress your friends.

Step 2: Smooth the Concrete Surface If you haven’t done this before or only done it a few times you are likely to

make two mistakes; troweling too soon and troweling too much.

This can lead to a weakened surface, tiny cracks and a white dusty surface.

Then with a wooden trowel or magnesium float if you want to get fancy, smooth off the surface. This step is simply to put a relatively smooth surface on the concrete. Keep an eye on the concrete. The first thing you will notice is that some bleed water will come to the surface. This is a good thing. Allow all of the water to disappear before you do anything else. This can take 20 minutes or 4 hours depending on the temperature, humidity and how hard the wind is blowing.

After the bleed water is all gone you can get out your steel finishing trowel and put on the final touches. You will notice the steel trowel is not perfectly flat. That is done so that when you trowel you will be more prone to lift the leading edge slightly avoiding digging into the concrete.

Step 3: Use a Broom to Finish the Surface Texture of the Concrete

Once you are finished with the trowel, simply take a soft broom and gently drag it across the surface.

Always pull the broom (never push) and always go in the same direction. Just one pass should do the trick.

Broom finish is preferable because it makes the surface slightly rougher.

This is very helpful for those occasions when your sidewalk is wet.

Step 4: Cure the Concrete You need to “cure” the concrete. If the concrete isn’t kept moist for a few

days it may crack. The problem is that the surface will dry out while the bottom is still wet causing tension which basically tears the concrete apart.

There are several ways to cure concrete. The easiest is to simply spray it very lightly with a hose. You can cover it with a wet cloth such as burlap (don’t let the burlap dry out). Or you can use chemical curing agents such as Sakrete Cure `N Seal.

The question of how long to do this and how often is a tough one because it depends on temperature, humidity and air flow. The hotter and dryer and windier it is the more you will have to re apply water.

Why finish concrete? Makes concrete attractive and serviceable

Warehouse or industrial floors need to be flat and level.

Exterior slabs must be sloped to carry away water and must provide a texture that will not be slippery when wet

Curing ConcreteCheong, Janine

Curing

-process of controlling the rate and extent of moisture loss from concrete during hydration

-process in which the concrete is protected from loss of moisture and kept within a reasonable temperature range

Reasons of Concrete Curing

a. Concrete strength gain

b. Improved durability of concrete

c. Enhanced serviceability

d. Improved microstructure

Methods to Cure Concrete

1. Water curing - preventing the moisture loss from the concrete surface by continuously wetting the exposed surface of concrete.

a) Ponding – a ‘dam’ or ‘dike’ is erected around the edge of the slab and water is then added to create a shallow pond.

b) Sprinkling, Fogging, and Mist Curing

Using a fine spray or fog of water can be an efficient method of supplying additional moisture for curing and, during hot weather, helps to reduce the temperature of the concrete.

c) Wet coverings

Water absorbent fabrics such as hessian, burlaps, cotton mats, rugs etc. may be used to maintain water on the concrete surface by completely covering the surface immediately after the concrete has set.

2. Impermeable Membrane Curing

Minimizing moisture loss from the concrete surface by covering it with an impermeable membrane.

a) Formwork - Leaving formwork in place is often an efficient and cost-effective method of curing concrete, particularly during its early stages. In very hot dry weather, it may be desirable to moisten timber formwork, to prevent it drying out during the curing period, thereby increasing the length of time for which it remains effective.

b) Plastic Sheeting

Plastic sheets form an effective barrier to control the moisture losses from the surface of the concrete, provided they are secured in place and are protected from damage.

c) Membrane Curing Compounds

Curing compounds are wax, acrylic and water based liquids which are sprayed over the freshly finished concrete to form an impermeable membrane that minimizes the loss of moisture from the concrete.

3. Steam Curing - keeping the surface moist and raising the temperature of concrete to accelerate the rate of strength gain. This type of system is most commonly used for precast concrete products where standard products are manufactured in the factory and the turnaround time of the formwork is very quick.

Precautionary when Curing during Hot / Cold Weather

Hot Weather-curing materials reflecting sunlight-water curing-framed enclosures of canvas tarpaulins

Cold Weather-heated enclosures-insulating blankets-curing compounds

FORMWORKSCast in Place Concrete

Cunanan, Warren

Definition It is a mould or box into which workable concrete will be poured and

compacted so that it will flow and finally set to the required profile of the mould itself.

It is also acts as a temporary structure that supports: Its own weight

Concrete poured

Live loads during construction process

(materials, labor, logistics)

Characteristics Safe

Cost Effective

Economical

Reusable

High Quality

Easy to use

Design It should be able to support the:

Fresh Concrete until 28 days

Steel Rebars

Formwork Materials

Wind & Lateral Loads

Live Loads

Materials Timber

Steel

Aluminum

Glass Reinforced Plastic

Timber

Timber: Advantages Easy to handle due to its weight

Easy to disassemble

Very flexible

Parts can be easily replaced

Useful for small scale projects

Less in cost

Timber: Disadvantages Cant be used for several times

Limited re-uses only

5-6 times only

It also absorbs water from concrete that results to less strength of concrete

Moisture content of timber will affect the form as it will shrink due to water.

It is also hard to place shoring jacks and supports

Eats up a lot of area

Steel

Steel: Advantages Very String and able to carry heavy loads

Easy to be fixed

Uniformity in size and surface finish

Can be used for a long time

Very rigid

Easy to dismantle

Steel: Disadvantages Limited size and shape of forms

Excessive lose of heat

A very smooth surface will be produced being an advantage to finishing beams and columns but disadvantage to floors and partitions.

Limited fixing only

Weight also adds to transportation problems.

Glass Reinforced Plastic

Glass Reinforced Plastic:Advantages

Very useful in complex shapes

Easy to disassemble

Lightweight

Damages are easily repaired

Glass Reinforced Plastic:Disadvantages

Expensive initial cost.

Requires more skilled workers

Not used world wide due to price and availability.

Board & Steel

Board & Steel: Advantages

Easy to use

Reusable for several times

Flexible

Useable in any type of form or shape

Less shoring used

Board & Steel: Disadvantages

In high rise towers used polyboard are hard to dispose.

Systems on cutting the board for re-useable purposes.

Failures

Improper stripping and shore removal.

Inadequate bracing

Vibration

Unstable soil under mudsills

Inadequate control of concrete pouring

Lack of attention to formwork details

Installation: Foundation

Sheet Piles on foundations vicinity

Excavation and Earthworks

Bored Piles

Rebars

Formworks

Shorings

Concrete Pouring

28 days curing

Installation: Columns

Reinforced bars

Splicing

Stirrups

Ties

Formworks

Side Shorings

7-21 days before removing forms

Columns can be chamfered on a triangular shape.

Installation: Beams

Reinforced bars

Splicing

Stirrups

Ties

Formworks

Side Shorings

48 – 72 hours side forms can be removed

28 days support shoring can be removed

Beams are usually formed with the slab.

Installation: Slabs

Reinforced bars

Splicing

Ties

Formworks

Table Forms usually

Full Shorings at lower level

7 days before some shoring can be removed

28 days support shoring can be removed

Slabs are usually formed with the beams

Pictures

Pictures

Pictures

Pictures

CONCRETE REINFORCING

MATERIALSTupaz, Alyza Krizel

What is Reinforced Concrete?

Concrete, in which steel is embedded in such a manner that they act together in resisting forces.

In reinforced concrete, the tensile strength of steel and the compressive strength of concrete work together to allow the member to sustain these stresses over considerable spans.

High Relative Strength

High toleration of tensile strain

Good bond to the concrete, irrespective of pH, moisture, and similar factors

Thermal compatibility, not causing

unacceptable stresses in response to

changing temperatures

Durability in the concrete

environment, irrespective of

corrosion or sustained stress

Required Properties of Reinforcement

The coefficient of thermal expansion of concrete is similar to steel, eliminating large internal stresses due to differences in thermal expansion and contraction.

Cement paste hardens and conforms to the surface of the steel, thereby transmitting forces efficiently between the two materials.

Hardened cement paste also provides a layer of protection for steel, providing larger resistance against corrosion than in normal conditions.

Key Characteristics of Reinforced Concrete

STEEL

Deformed, Plain, Threaded, Welded Wire Fabric

Deformed steel bars are round steel bars with lugs, or deformations, rolled into the surface of the bar during manufacturing. These deformations create a mechanical bond between concrete and steel.

Deformed Steel Bars

Often rounded in cross section, these steel bars are plain in surface and have diameter ranging from 6 to 50mm

Malleable and can be drilled, cut and welded to suit design needs

Plain Steel Bars

These bars can be spliced with threaded couplers or anchored through steel plates while still providing continuous bond between the bar and concrete.

Used as an alternative to lapping standard deformed bars when long bar lengths are required

Or when bars need to be anchored close to the edge of the member

Threaded Steel Bars

A square or rectangular mesh of wires, factory-welded at all intersections.

Used for may applications such as to resist temperature and shrinkage cracks in slabs.

Often used in concrete slabs

Welded Wire Fabric

Benefits of Steel

Reinforcement

Increases overall strength

Minimum maintenance – Reduces

cracking and

deformation

Allows flexibility in design

Substantial Economy –

Cost efficient in

its constructio

n

FIBER REINFORCED POLYMERS (FRP)

Mainly used in shotcrete ( a type of concrete conveyed through a hose, projected at high velocity)

Mostly used for on-ground floors and pavements, but can also be considered for a wide range of construction parts

Fiber-Reinforced Concrete

Fiber-Reinforced Polymer refers to polymer materials that are reinforced with fiberglass, carbon fiber or aramid fiber

Used where corrosion of steel bars are likely or where sensitive electrical or magnetic equipment might be affected by a large amount of steel reinforcement.

Fiber-Reinforced Polymers

Benefits of Fiber

Reinforcement

Improves durability

to weather cycling

Reduces overall weight

Improves water migration and

thus aids reduction in corrosion for

steel reinforcement

Improves impact

and abrasion

resistance

GLASS REINFORCEDPLASTIC (GRP)

a composite material or fiber-reinforced polymer made of a plastic reinforced by fine fibers made of glass. Like carbon fiber reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass).

Glass-Reinforced Plastic

Benefits of Glass

Reinforcement

Strong lightweig

ht material

Raw materials are much cheaper

Bulk strength and weight are better than

many metals

Can be more readily

molded into complex shapes

Less brittle