LECTURE 2 - Material Properties

Material Properties

Lecture #2

References: 1. W. MacGregor, “Reinforced Concrete Mechanics and Design”, 6th Ed 2. ACE 318-11M

Lecture #2 Objectives

Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Objectives

Define strain and its relation to stress

To understand the properties of concrete and steel

2


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Types of Concrete

3

1. Plain

concrete 2. Reinforced

concrete 3. Pre-stressed

concrete


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Definitions

4

ASTM C125 - a composite material that consists essentially of a binding medium within which is embedded particles or fragments of aggregates.

ACI 318 - mixture of portland cement or any other hydraulic cement, fine aggregates, coarse aggregates and water, with or without admixtures.


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

5

Aggregates, Cement, Transition Zone


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

6

Aggregates - comprise from 60% to 80% with an average of 75% of volume Coarse aggregates (4.75 mm - 50 mm, Sieve No.

4 & up) Fine aggregates (< 4.75 mm)

Predominantly responsible for the unit weight, elastic modulus and dimensional stability of concrete


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

7

Aggregates - comprise from 60% to 80% with an average of 75% of volume

light weight (1800 kg/m3)

natural or pyro-processed aggregates having lower bulk density

normal weight (2400 kg/m3) containing natural sand, gravel or crushed rock

heavy weight ( > 3200 kg/m3) high density aggregates for radiation shielding


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

8

Hydrated Cement Paste - usually 10% water and 15% ordinary Portland cement Solids: Calcium-Silicate-Hydrate, Calcium

Hydroxide, Calcium Sulfoluminates, Unhydrated Clinker

Liquid: Capillary water, adsorbed water, interlayer water, chemically combined water (suitable for drinking, do not use saltwater)

Gas (Voids): Interlayer space in C-S-H, capillary voids, air voids Portland Stone


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

9

Hydrated Cement Paste - usually 10% water and 15% ordinary Portland cement

TYPE I Ordinary

TYPE II Moderate Sulfate Resistance and Heat of Hydration

TYPE III High Early Strength

TYPE IV Low Heat of Hydration

TYPE V High Sulfate Resistance


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

10

Hydrated Cement Paste - usually 10% water and 15% ordinary Portland cement


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

11

Transition Zone Thin shell, typically 10 to 50 μm thick Typically weaker thus, it has considerable

influence on the mechanical behavior of concrete

concrete has microcracks in the transition zone even before loading

The reason why concrete behaves non-linear


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

3 Phases

12

Transition Zone

Non

-line

arity

in t

he S

tres

s-St

rain

rel

atio

n of

C

oncr

ete

is d

ue t

o th

e in

terf

acia

l tra

nsiti

on z

one


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Concrete Failure

13


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Properties > Concrete Strength

14

I. Concrete Strength, ’

28th-day compressive strength of a standard 4” by 8” or 6” by 12” cylinder concrete

Minimum ’ 17 MPa (2500 psi) 21 Mpa (3000 psi) – members subject to

seismic forces (NSCP 2010 Section 421.3.4.2) ACI 318 Chapter 4: Durability Requirement


Concrete

Types

Definitions

3 Phases

Properties

′

Steel


Concrete

Types

Definitions

3 Phases

Properties

′

Steel


16

Determining ’ Specimen Average of the strength of at least 2 – 6” x 12” cylinders or 3 – 4” x 8” cylinders

Test Age ACI gives designer freedom to specify age –

usually taken as 28 days For blended cement, due to slower strength gain,

allowed to use more than 28 days fc’(t) = (t/(4+0.85t))fc28’ Curing Conditions Control of humidity and temperature. Specimens should be placed in tanks to keep them

fully saturated at the control temperature


Concrete

Types

Definitions

3 Phases

Properties

′

Steel


17

Normal frequency curves for coefficients of variation of 10, 15, and 20%

V = standard deviation over the mean value fcr' = required average compressive strength

Determining ’


Concrete

Types

Definitions

3 Phases

Properties

′

Steel


18

Determining ’


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Properties > Stress-Strain Relationship

19

Typical concrete stress-strain curves in compression.


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Properties > Stress-Strain Relationship

20

Notes: Max stress, fc’, reached

at a strain between 0.0015 to 0.003 followed descending branch

Initial slope, initial tangent modulus of elasticity increases as fc’ increases –

Rising portion of σ-ε resembles a parabola with its vertex at fc’

Slope of descending branch tends to be less than ascending branch as fc’ becomes smaller

Maximum strain εCU, decreases as fc’ increases


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Properties > Modulus of Elasticity

21

taken as secant modulus to a stress of ≈ 0.5 fc’ (0.45 from ACI)

Varies with age of loading, rate of loading, type and size of specimen


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Reinforcing Steel

22

Reason for using steel as reinforcement: Expansion properties for both steel and

concrete are considered to be approximately the same (compatibility)

steel bonds well with concrete. bond strength is proportional to the contact surface of the steel with the concrete


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Reinforcing Steel

23

Types of Rebar Plain Bars Round in cross section Used for special

purposes such as dowels at expansion joints or construction joints in roads and runways.

Deformed bars Differ from plain bars in

that they have indentations or ridges in them, in a regular pattern


Concrete

Types

Definitions

3 Phases

Properties

′

Steel

Reinforcing Steel

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LECTURE 2 - Material Properties

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