Concrete

Concrete

It is an artificial, stone-like building material made by mixing cement and various mineral aggregates with sufficient water to cause the cement to set and bind the entire mass.

Ancient Romans

They were the inventors of concrete construction; discovered mortar which contained all the essential ingredients of modern Portland cement.

John Smeaton

Made the first modern concrete (hydraulic cement) by adding pebbles as a coarse aggregate & mixing powdered brick.

Joseph Aspdin

He patented an artificial cement that he named portland cement, after English Portland limestone.

Frenchman J. L. Lambot

He built several reinforced concrete boats in Paris in 1854

American, Thaddeus Hyatt

He made and tested a number of reinforced concrete beams.

Reinforced Concrete

Concrete in which steel bars are embedded, enhancing strength and durability. Commonly used in construction for its high load-bearing capacity.

Concrete

It is the most widely used material on earth. The raw ingredients for its manufacture are readily available in almost every part of the globe

ASTM, ACI Code, PS

Standards that govern the minimum quality for concrete and concrete construction.

American Society for Testing of Materials

ASTM

American Concrete Institute

ACI Code

Philippine Standards for Materials/Products: Cement/Concrete Products

PS

07:2005

Portland Cement must meet the requirements of PNS ________

63:2006

Blended Hydraulic Cement with Pozzolan must fulfil the requirements of PNS ________

• Has no form of its’ own

• Inherently strong in compression but weak in tension

• Capable of being formed into any shape with variety of surface finishes, textures and patterns

• Relatively low-cost and inherently fire-resistant

• Liability is its own weight (150 lbs/cu.ft)

Physical properties of concrete

compression; tension

Concrete is inherently strong in ________ but weak in ________.

Workability, Weight, Strength, Creep, Fire Resistance, Shrinkage, Hardness, Porosity, Durability

Properties of Concrete

Workability

Property of concrete;

The ease with which concrete can be placed in the formwork and finished. The addition of water makes concrete more workable but decreases its strength.

Weight

Property of concrete;

It depends largely on the display of the coarse aggregate: lightweight aggregates (such as expanded clay) obviously reduce the overall density of the concrete but can also adversely affect its strength.

Strength

Property of concrete;

The ability to withstand applied forces without breaking, measured in pounds per square inch (psi) or megapascals (MPa).

28

The specified strength will be reached after ___ days for ordinary concrete.

cement type, water-cement ratio, curing environment

The concrete will harden at a rate depending on the ______, the ______, and the __________.

Creep

Property of concrete;

The gradual deformation of concrete under a long duration of stress over time.

reinforcement

Creep can be reduced through the use of _________ in the compression zone.

Fire Resistance

Property of concrete;

It is incombustible and somewhat insulative, but long exposure to fire can be damaging.

density; type of aggregate

______ of the concrete and _______ affect fire resistance.

Shrinkage

Property of concrete;

The decrease in volume during curing process.

Hardness

Property of concrete;

A property of the surface which is related to durability as well as to appearance.

Porosity

Property of concrete;

Sizes of pores left during hydration process or created by excessive evaporation and shrinkage cracks affects the watertightness of concrete. Apply compaction techniques.

Durability

Property of concrete;

Ability of concrete to withstand weathering, chemical attacks, abrasion, and other deteriorating factors over time without losing its structural integrity.

Cement

A calcined mixture of clay and limestone, finely pulverized and used as an ingredient in concrete and mortar.

Type I

Normal - Portland cement for general construction (PNS 07:2007)

Type II

Moderate - sulfate resistant, where heat build-up can damage the structure

Type III

High Early Strength (HES) - cures faster (3 - 7 days) and gains earlier strength

Type IV

Low Heat - generates less heat hydration where heat build-up can significantly damage the structure and used for massive concrete structures

Type V

Sulfate Resistant - used where resistance to severe sulfate action is required that damage the structure when it leach out from the soil.

Mortar

cement + sand + water

Plaster

cement + lime + sand + water

Grout

cement + sand + considerable amount of water

Paste

cement + water

Aggregates

Any of various hard, inert, mineral materials, such as sand and gravel, added to cement or mortar. It should be hard, dimensionally stable and free of clay, silt, and organic matter, which can prevent the cementing matrix from binding the particles together.

Aggregates

The strength of a concrete mixture is highly dependent on its’ composition of __________.

60%; 80%

Aggregates represent ___ to ___ of the concrete volume.

Fine aggregates & Coarse aggregates

Types of aggregates

Fine Aggregates

Consisting of sand having a particle size smaller than ¼ in. (6.4mm)

Coarse Aggregates

Consisting of crushed stone, gravel, or blast-furnace slag having particles larger than the ¼ in. (6.4mm)

organic material, clay, salts

The water used in a concrete or mortar mix, exclusive of any absorbed by the aggregate and free of such harmful substance as _________, ____ and _____.

Water-cement ratio

It controls the strength, durability and water tightness of hardened concrete.

Abram’s Law

“the compressive strength of concrete is inversely proportional to the ratio of water to cement”

6 gallons per 40 kg. of cement bag

Average water-cement ratio

weaken

Too much water added to the concrete mixture will _____ concrete.

workability

Little water added to the concrete mixture is dense but causes difficulty in ______ of concrete.

Bleeding

Excess water rising to the surface of freshly placed concrete.

Laitance

Accumulation of fine particles on the surface due to excessive water content.

Pozzolanic Admixture

Used as substitute for cement (35%) for structures in high temperatures and seawater installation or as additives to decrease the weight of a concrete per cubic foot

Water Reducing Admixture

An agent or super plasticizers that improves workability and maintain consistency of concrete

Coloring Agent

Pigments or dyes mixed into topping to render/alter color evenly to concrete surface

Surface Sealing Agents

Liquid waxes sprayed over the surface that is easily removed after curing. Prevents evaporation of water into a new concrete allowing hydration and seal the pores of concrete surface after it has hardened

Set Inhibiting Agent

Inhibits the setting of cement paste avoiding bonding to surface aggregates and left exposed for architectural effect.

Liquid form

Set Inhibiting Agent applied immediately before pouring of concrete

Powder form

Set Inhibiting Agent applied directly after pouring.

Dispersal Agents

Prevents bleeding of concrete from concrete

Bonding Agent

Improves the bond between old and new concrete.

metallic aggregate bonding agent

Bonding through oxidation and expansion

synthetic latex emulsion

Bonding agent that is sprayed or painted to coalesce and bond

Air-Entraining Agent

Enables the concrete to be highly resistant against corrosion.

Gas Forming Agent

Produce microscopic bubbles that increase workability and reduce the weight of the concrete. Develops the potential strength of a concrete.

Non-Skid Surfaces

Use abrasive material in topping to produced unslippery surface for pavement construction.

Hardener

Chemical/fine metallic aggregate improve the density of concrete surface subject to impact and wear

Accelerator

Speeds up the setting of concrete to reduce the whole curing period or for early removal of forms.

Retarder

Delays or extend the setting time of concrete especially during hot weather condition (hydration accelerates curing) allowing more time to place, consolidate and finish the concrete.

AAA

Class of concrete;

Pre-stresses and post-tensioned

AA

Underwater retaining wall, sheer wall, & elevator core walls

A

Class of concrete;

Footings, pier, columns, girders, beams, joists, & slabs

B

Slabs on fill and non-load bearing wall of 4” CHB

C

Concrete plant boxes and parapet walls

D

Plant boxes, footpaths, walkways, & lean concrete

Set the assumption of hard state, Curing Process, Hydration, Shrinkage

Concrete curing process

Curing Process

maintaining the humidity and temperature of freshly placed concrete during some definite period following, placing, casting or finishing to assure satisfactory hydration of cementitious materials and proper hardening of concrete.

7

To maintain newly placed concrete or mortar at the required temperature and humidity for the first __ days following placement, casting or finishing to ensure satisfactory hydration of the cementitious materials and proper handling.

Hydration

Occurs during curing in which, the cement combines chemically with water to form strong crystals that bind the aggregates together.

heat of hydration

During hydration, considerable heat, called ___________, is given off.

drying shrinkage

As excess water evaporates from the concrete shrinks slightly, a phenomenon referred to as __________.

Shrinkage

The end of the concrete curing process. The concrete mixture set on site is expected to shrink due to moisture loss.

Drying Shrinkage

A reduction in volume of concrete, mortar or plaster caused by loss of moisture.

Setting Shrinkage

A reduction in volume of concrete prior to the final set, caused by hydration of the cement paste.

strenght, durability, uniform quality, thoroughly sound

good quality concrete can be determined using these criteria as guidance:

give the 4 criteria being determined.

Strength

this criteria can be achieved by proper selection of materials

Durability

this criteria can be achieved by correct proportion and mixing process

Uniform Quality

this criteria can be achieved by careful transportation and placement

Thoroughly Sound

this criteria can be achieved by timed curing and provision for protection

Slump Test

A method of testing concrete’s strength

to measure the consistency of freshly mixed concrete including mortar and stucco. Where a concrete is placed at a slump cone (12‖ high with a respective top diameter and bottom is 4‖ and 8‖) and tamped in a prescribed manner then lifted to determine the decrease in height expressed by vertical settling in inches

Compressive Cylinder Test

A method of testing concrete’s strength

- a quasi-quality control test based on 7–28 days curing period to determine the compressive strength of a concrete specimen. A metal cast cylinder (12‖ high and 6‖ diameter) is poured with concrete and taken out within 24 hours while still wet and dated. Sent to laboratory check if it can support axial compression before fracturing.

3”

Allowable Slump for Beams & Columns

2”

Allowable Slump for Slabs, Walls, Parapets and Tops

4”

Allowable Slumps for Side Walls and Arches

2”

Allowable Slump for Heavy Mass of Concrete

Manual

Process of mixing concrete

Flat surface with shovels and buggy

Small Power

Process of mixing concrete
Uses a manual mixing rotating drum

Bagger Mixer / Mechanical Mixer

Process of mixing concrete

Equipped with diesel engine and pump operated mechanical mixing drum (1 or 2bags) or rotating mixing drum at the back of a truck.