Chapter 1: Introduction Flashcards
It is a mixture of sand, gravel, crushed rock, or other aggregates held together in a rocklike mass with a paste of cement and water.
Concrete
Sometimes one or more ______ are added to change certain characteristics of the concrete such as its workability, durability, and time of hardening.
Admixtures
The term _____ indicates all types of concrete used in structural applications.
Structural Concrete
Structural Concrete may be ___, ___, ___, or ____
Plain, reinforced, pre-stressed, or partially pre-stressed
What are the five types of cement?
I - Normal Cement
II - Lower Heat of Hydration (withstand sulfate attacks)
III - High Early Strength cement (higher heat of hydration)
IV - Low Heat (for larger structures)
V - High Sulfate Resistance (to be exposed to high sulfate concentrations)
What are the types of admixtures?
- Air-entraining admixture
- Accelerating admixture
- Retarding admixture
- Superplasticizers
- Waterproofing
It is a combination of concrete and steel wherein the steel reinforcement provides the tensile strength lacking in the concrete.
Reinforced concrete
It is capable of resisting compression forces and is used in columns as well as in other situations, which are described later.
Steel reinforcing
This may be the most important material available for construction. It is used in one form or another for almost all structures, great or small—buildings, bridges, pavements,
dams, retaining walls, tunnels, drainage and irrigation facilities, tanks, and so on.
Reinforced concrete
Advantages of Reinforced Concrete as a Structural Material
- It has considerable compressive strength per unit cost compared with most other materials
- It has great resistance to the actions of fire and water.
- Reinforced concrete structures are very rigid.
- It is a low-maintenance material.
- It has a very long service life.
- It is usually the only economical material available for footings, floor slabs, basement
walls, piers, and similar applications. - Its ability to be cast into an extraordinary variety of
shapes from simple slabs, beams, and columns to great arches and shells. - Concrete takes advantage of inexpensive local materials (sand, gravel, and water) and requires relatively small amounts of cement and reinforcing steel.
- A lower grade of skilled labor is required for erection as compared with other materials
such as structural steel.
Disadvantages of Reinforced Concrete as a Structural Material
- Concrete has a very low tensile strength, requiring the use of tensile reinforcing
- Forms are required to hold the concrete in place until it hardens sufficiently.
- The low strength per unit of weight of concrete leads to heavy members.
- The low strength per unit of volume of concrete means members will be relatively large, an important consideration for tall buildings and long-span structures.
- The properties of concrete vary widely because of variations in its proportioning and mixing.
Properties of Concrete
- Compressive Strength
- Static Modulus of Elasticity
- Dynamic Modulus of Elasticity
- Poisson’s Ratio
- Shrinkage
- Creep
- Tensile Strength
- Shear Strength
It is determined by testing to failure 28-day-old 6-in. diameter by 12-in. concrete cylinders at a specified rate of loading (4-in. diameter by 8-in. cylinders were first permitted in the 2008 code in lieu of the larger cylinders).
Compressive Strength
Its value varies with different concrete
strengths, concrete age, type of loading, and the characteristics and proportions of the cement
and aggregates. Furthermore, there are several different definitions of the modulus:
(a) The initial modulus is the slope of the stress–strain diagram at the origin of the curve.
(b) The tangent modulus is the slope of a tangent to the curve at some point along the
curve—for instance, at 50% of the ultimate strength of the concrete.
(c) The slope of a line drawn from the origin to a point on the curve somewhere between
25% and 50% of its ultimate compressive strength is referred to as a secant modulus.
(d) Another modulus, called the apparent modulus or the long-term modulus, is determined
by using the stresses and strains obtained after the load has been applied for a certain
length of time
Static Modulus of Elasticity
The _____ which corresponds to very small instantaneous strains, is
usually obtained by sonic tests. It is generally 20% to 40% higher than the static modulus and
is approximately equal to the initial modulus. When structures are being analyzed for seismic
or impact loads, the use of the dynamic modulus seems appropriate.
Dynamic Modulus of Elasticity
As a concrete cylinder is subjected to compressive loads, it not only shortens in length but also
expands laterally. The ratio of this lateral expansion to the longitudinal shortening is referred
to as ______
Poisson’s Ratio
When the materials for concrete are mixed, the paste consisting of cement and water fills
the voids between the aggregate and bonds the aggregate together. This mixture needs to be
sufficiently workable or fluid so that it can be made to flow in between the reinforcing bars and
all through the forms. To achieve this desired workability, considerably more water (perhaps
twice as much) is used than is necessary for the cement and water to react (called hydration).
Shrinkage
Under sustained compressive loads, concrete will continue to deform for long periods of time.
After the initial deformation occurs, the additional deformation is called ____, or plastic flow.
Creep
The______ of concrete varies from about 8% to 15% of its compressive strength. A
major reason for this small strength is the fact that concrete is filled with fine cracks. The
cracks have little effect when concrete is subjected to compression loads because the loads
cause the cracks to close and permit compression transfer. Obviously, this is not the case for
tensile loads.
Tensile strength
It is extremely difficult in laboratory testing to obtain pure shear failures unaffected by other
stresses. As a result, the tests of concrete shearing strengths through the years have yielded values all the way from one-third to four-fifths of the ultimate compressive strengths.
Shear Strength
It is granular material, such
as sand, gravel, crushed stone and
iron blast-furnace slag, and when
used with a cementing medium
forms a hydraulic cement concrete
or mortar
Aggregates
Classification of Aggregates by Density
- Lightweight
- Normal-Weight
- Heavyweight
It is more porous than their
heavier counterparts.
They are also used in
mixes for concrete blocks
and pavements, as well as
insulation.
Lightweight
The most commonly used _______ aggregates often have relative densities within a limited range of approximately 2.55–2.75, and therefore all produce concretes with similar densities normally in the range of 2200–2450 kg/m3, depending on the mix proportions.
Normal-weight
They are used for when
high strength, durable
concrete structures are
required - building
foundations or pipework
ballasting
Heavyweight
CLASSIFICATION OF AGGREGATES BY GEOLOGY
- Natural Aggregates
- Processed Aggregates
It came from the nature source such as riverbeds, quarries and mines. Sand, gravel, stone and rock are the most common, and these can be fine or course.
Natural Aggregates
Also called “artificial aggregates” or “by-product” aggregates commonly taken from industrial or engineering waste, then treated to form construction aggregates for high quality concrete. Common ______ aggregates include industrial slag, as well as burnt clay. _____ aggregates are used for both lightweight and high density concrete mixes.
Processed aggregates
CLASSIFICATION OF AGGREGATES BY SHAPE
- Rounded
- Irregular
- Angular
- Flaky
- Elongated
- Flaky and Elongated
Natural aggregates smoothed by weathering, erosion and attrition.
These are the main factor behind work ability
Rounded
These are also shaped by attrition, but are not fully rounded.These
consist of small stone sand gravel, and offer reduced work ability to
rounded aggregates
Irregular
Used for higher strength concrete, _____ aggregates come in the
form of crushed rock and stone. Work ability is low, but this can be
offset by filling voids with rounded or smaller aggregate
Angular
Defined as aggregates that are thin in comparison to length and
width. Increases surface area in a concrete mix
Flaky
Also adds more surface area to a mix – meaning more cement
paste is needed. ______ aggregates are longer than they are
thick or wide.
Elongated
A mix of the previous two – and the least efficient form of aggregate with regards to work ability
Flaky and Elongated
refers to the distribution of particle sizes present in an aggregate. The ____ is determined in accordance with ASTM C 136, “Sieve or Screen Analysis of Fine and Coarse Aggregates.”
Grading
In specifications for aggregates, the
smallest sieve opening through which the entire amount of aggregate is required to pass is called the
Maximum size
The smallest sieve opening through which the entire amount of aggregate is permitted to pass is called the
Nominal Maximum Size
shall consist of natural sand, manufactured sand, or a combination thereof.
Fine aggregate
shall consist of gravel, crushed gravel, crushed stone, air-cooled blast furnace slag, or crushed
hydrauliccement concrete (see Note 5), or a combination thereof, conforming to the requirements of this specification.
Coarse Aggregate
play a pivotal role in engineering, serving as essential components in various
construction applications.
Steel bars
It is an untreated steel rod, lacking any coatings or surface treatements. It is used for construction that does not request high-strength reinforced concrete works widely used on beam and column stirrups, pipeline, roads, small and medium sized projects
Plain Steel Bar
A steel rod with deformations or ribs to enhance its bonding with concrete
Deformed Steel Bar/Reinforcing Bar/Rebar
Testing Methods for Plain Steel Bars
- Compression Test
- Bending Test
- Brinell Hardness Test
- Rockwell Hardness Test
- Impact Test
- Torsion Test
is a prefabricated reinforcement consisting of a series
of parallel longitudinal wires welded to cross wires at
regular intervals.
Welded Wire Fabrics
is the most basic type of welded wire fabric. It is made by welding together wire strands in a simple grid pattern. This type of fabric is strong and durable, making it ideal for use in a wide range of applications.
Plain welded wire fabric
is made by welding together wire strands in a interlocking pattern. This type of fabric is stronger than plain welded wire fabric, making it ideal for use in applications where high levels of strength are required.
Lock crimp welded wire fabric
is made by welding together wire strands in a criss-cross pattern. This type of fabric is even stronger
than lock crimp welded wire fabric, making it ideal for use in applications where extremely
high levels of strength are required.
Intercrimp welded wire fabric
for the reinforcement
in concrete, equipped with a device for the mechanical anchorage of the bar in the concrete.
Headed Steel Bars
Includes deformed and plain
billet steel bars, marked with the
letter S for the type of steel.
ASTM A615
Encompasses low-alloy deformed
and plain bars, marked with the
letter W for the type of steel.
ASTM A706
Covers deformed rail steel
or axle steel bars, identified
by the letter R for the type
of steel.
ASTM A996
This code, which is used primarily for the design of buildings, is followed for the majority of the
numerical examples given in this text. Frequent references are made to this document, and
section numbers are provided.
ACI 318
the purpose of this
code is to provide minimum requirements for the design of
buildings, towers and other vertical structures, and minimum
standards and guidelines to safeguard life or limb, property and
public welfare by regulating and controlling the design,
construction, quality of materials pertaining to the structural
aspects of all buildings and structures within this jurisdiction
NSCP 2015
ASTM REINFORCEMENT BAR (REBAR) MARKINGS:
- Code for manufacturer
- Number code for the size of the bar
- Letter code for the type of steel (S for billet, R
in addition to a rail sign for rail steel, A for axle, and W for low
alloy) - Grade of steel
Minimum Yield Strength: 33,000 psi (pounds per square inch)
This is a relatively low-strength steel often used for low-stress applications or where ease of forming is a primary concern.
Grade 33
Minimum Yield Strength: 40,000 psi
This grade offers a higher strength compared to Grade 33, making it suitable for a wider range of applications that require moderate strength.
Grade 40
Minimum Yield Strength: 60,000 psi
This is a high-strength steel commonly used in construction projects where the structure requires a higher load-bearing capacity
Grade 60
