CONSMAT Midterms: Concrete

Shall be mixed asphalt and mineral

Poured joint fillers

Shall conform to the applicable requirements of item 705

Preformed joint filler

Honeycomb, not desirable for concrete and visible to the eye

Entrapped air

Intentional (0.01 + 0.25mm diameter), desirable for concrete and this soapy materials produced billions of tiny bubbles when scrubbed against the sand when the concrete was mixed

Entrained air

Both entrained and small amount of entrapped will be present

Total air

Materials other than the basic ingredients of concrete cement water and aggregates, used in concrete to improve concrete properties

Admixtures

Item 311

Wearing course

Item 201

Base

Item 200

Subbase

Item 105

Subgrade

Proper selection of materials

Strong

Correct proportion and mixing process

Durable

Careful transportation and placement

Uniform quality

Timed curing and provision for protection

Thoroughly sound

Shovels and buggy

Manual

Mixing rotating drum

Small Power

Equipped with diesel engine and pump

Bagger mixer

Mixed at batch plant for delivery by an agitator

Ready mixed

Partially mixed at the batch plant then mixed completely in a truck

Shrink mixed

Concrete dry batch at a batch plant and mixed at truck mixer

Transit mixed

Pumped through a hose and sprayed at high velocity

Gunite or shotcrete

Workability test for stiff concrete mixes is being evaluated by several organizations

Concrete tests

Measure the consistency of freshly mixed concrete including mortar and stucco

Control of concrete mix

Fit or not fit to drink can be used for mixing to make the concrete paste

Water

AASHTO T23

Making and curing

AASHTO T22

Compressive strength of concrete cylinder (most verified calibration after 12 months)

A quasi-quality control test based on 7-28 day curing period

Compressive cylinder test

Process of eliminating voids other than entrained air

Consolidation of concrete

Separation of coarse aggregate from mortar

Segregation

Separation combined with excessive wetting

Stratification

Concrete deposited, formed, cured and finished

Cast-In place

Can be moved slowly and continuously as concrete is being placed

Slip form

Sequentially lifted into final position

Lift slab construction

Custom pre-casted on site then hoisted into final position

Tilt-up construction

Pre-tensioning and post-tensioning

Pre-stressing

Built covering made of sack

Curing blanket

Staging a temporary platform structure

Scaffolding

Temporary construction to contain wet concrete

Formwork

Maintaining the humidity and temperature freshly placed concrete during some definite period

Curing

Concrete left in natural state

Beton brut

Broom, float, exposed aggregate

Finish

A layer of high quality concrete or mortar placed to form a floor surface

Topping

Design mix

Concrete

Job mix

Asphalt

\[Air voids\]

* Entrapped air
* Entrained air

pH value for water

4\.5 - 8.5

Other types of cement

* Rapid hardening or High Early Strength Cement
* Quick Setting Cement
* High Alumina Cement
* Low Heat Cement
* Air Entraining Cement
* White Cement
* Coloured Cement
* Portland Pozzolan Cement

Paste begin to stiffen

Initial Set

Paste beginning to harden and able to sustain some loads

Final Set

Factors affecting setting time

* Fineness of cement
* Chemical composition
* Amount of water

Added to clinker to retard setting

Gypsum

Rapid development of permanent rigidity

Flash set

Rapid development of rigidity

False set

Most widely used construction material

Concrete

A hard compact building material formed when a mixture if cement, sand, gravel and water undergoes hydration

Concrete

Reasons why concrete is the most widely used material

* Possesses excellent resistance to water
* Can be formed into a variety of shapes and sizes
* One of the cheapest and most readily available materials

Major parts of concrete

* Paste
* Aggregates

Under Paste \[Major parts of concrete\]

* Portland Cement
* Water
* Air voids
* Admixture

Components of Concrete

* Aggregate
* Cement
* Air voids
* Admixture

\[Concrete mixture\] 4 parts calcined limestones plus 1 part clay which are mixed, burned, and pulverized, sold in 40 kgs per bag

Cement

\[Concrete mixture\] fine aggregates, natural sand or crushed stone well-graded

Sand

\[Concrete mixture\] of course aggregates, crushed stone or blast furnace slags

Gravel

\[Concrete mixture\] clean, potable and free from harmful substances

Water

\[Concrete mixture\] additive as required by situations, ingredients added to concrete or mortar modify its properties immediately before or after mixing

Admixture

Low-strength concrete

< 20 MPa (

Moderate-strength concrete

20-40 MPa (3000-6000 psi)

High-strength concrete

>40 MPa (> 6000 psi)

Concrete characteristics

Inherently strong in compression but weak in tension

Concrete characteristics

Capable of being formed into any shape

Concrete characteristics

Low-cost and fire-resistant

Concrete characteristics

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

Controls the strength, durability and water tightness of hardened concrete

Water-cement ratio

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

Abram’s law (D.A. Abrams, 1919)

Too much _____ will weaken concrete after curing

Water

Little water is ________ but causes difficulty in placement and workability of concrete

Dense

Average water-cement ratio

6 gallons per 40 kgs of cement bag

Excessive water causes ( ) and ( )

Bleeding and Laitance

Emergence of excess mixing water of the surface of newly placed concrete cause of settlement of solids within the mass

Bleeding

milky deposit containing cement and fine aggregate on the surface of new concrete combined with bleeding, overworking of mix of improper finishing

Laitance

\[Properties of concrete\] long duration stress produces stress over time and consequently causes permanent deformation

Creep

\[Properties of concrete\] concrete is incombustible and somewhat insulative, but long exposure to fire can be damaging

Fire-resistance

\[Properties of concrete\] ordinary concrete shrinks amount during process

Shrinkage

\[Properties of concrete\] relative to durability and appearance, accomplished through troweled or floated finish to draw more paste to the surface

Hardness

\[Properties of concrete\] sizes of pores left during hydration process or created by excessive evaporation and shrinkage cracks affecting the water-tightness of concrete

Porosity

\[Properties of concrete\] surrogate procedure which measures flow of electrical current; specified on most major bridge and pavements projects

Durability

\[Properties of concrete\] rheological behavior is defined by two characteristics of the concrete, i.e yield stress and plastic viscosity

Workability

Effort needed to initiate movement of the fresh concrete, and correlates well with slump

Yield stress

Flow characteristics of the concrete while moving and for low stiffness concretes can be determined by various rheometers currently available

Plastic viscosity

Provides improvements in strength, density, durability, volume stability, bond and abrasion resistance; useful in confined zones where vibrating compaction is difficult

Self-compacting concrete (SCC)

Steel bars, strands and wires are required to absorb the concrete’s weakness in tensile and shear stress; required to tie the vertical and horizontal elements, reinforce openings, minimize shrinkage cracking and control thermal expansion and contraction

Steel reinforcement

Function of reinforcement

* Tensile strength for bending members
* Resistance to shrinkage
* Ductility

Usually named according to the blinding material used in their preparation; essentially required for masonry work, plastering, painting, etc.

Mortar

cement + sand + water

Mortar

cement + lime + sand + water

Plaster

cement + sand + considerable amount of water

Grout

cement + water

Paste

\[Types of mortar\] paste is prepared by mixing cement and sand in suitable proportions in addition to water

Cement mortar

\[Types of mortar\] general proportion is 1 part of cement to 2-8 parts clean sand

Cement mortar

\[Types of mortar\] must be used within an hour

Cement mortar