Write introduction Part B:The lab investigation undertaken as part of this module is designed to help you• further understand the basic concept of the fracture properties ofconcrete;• understand the procedure of testing the fracture properties of concrete;• strengthen the ability to design concrete mixes;• develop the ability to numerically calculate the fracture energy of concrete;• develop the ability to analyze test results and make objective judgements.1. TEST SPECIMENSNotched concrete beams are adopted for this lab activity, as shown in the figurebelow, with typical dimensions as follows:Length of the beam L = 500 mmBreadth of the beam B = 100 mmDepth of the beam H = 100 mmDepth of the notch a = 50 mmDepth of the ligament h - a = 50 mmEffective span l = 400 mmHl BFigure 1: Schematic representation of a beam under three-point bending2. MATERIALS FOR MAKING CONCRETEOne concrete grade was used for this laboratory investigation, C50 (50 MPa) at28 days after standard water curing, with main ingredients as follows:Cement Portland cement (OPC) - 52.5N strengthCoarse aggregates 4mm - 20 mm CrushedFine aggregate UncrushedWater Tap waterSlump is required between 30-60 mm and this needs to be monitored duringcasting.Three beams and six cubes are required. The beams are used for obtaining thefracture energy, GF, three cubes for obtaining the cube compressive strength, fcu,and the other three cubes for obtaining the splitting tensile strength, f t'. The testage is fixed at 14 days.All concrete specimens are cured in water for one week and then left in the air toallow the specimens to be dry for further 7 days.The notches are to be prepared using a diamond saw one week before testing.3. TESTING PROCEDUREThe concrete beam is loaded in a three-point bending way at a constantdisplacement rate of 1.5×10-3 mm/s until it is fully broken. The load anddisplacement were recorded using a data logger at a rate of two sets per secondfor future analysis. Each bending test takes 10 to 15 minutes.The concrete cubes are crushed on the same day as the fracture tests and thecorresponding maximum loads under both compression and splitting tension arerecorded for determining the compressive and tensile strengths of concrete.4. DETERMINATION OF MECHANICAL PROPERTIES OF CONCRETEThe fracture energy, GF, defined as the total energy dissipated over a unit areaof the cracked ligament, is obtained on the basis of the work done by the force(the area under a load-displacement curve in three-point bending on a centrallynotched beam) associated with the gravitational work done by the self-weight ofthe beam.The fracture energy, GF, is calculated based on the following formula with somenumerical treatmentG =F00 P() d + m g (L / S ) (2 − L / S) 0B (H − a0 ) whereP load in N; displacement in mm; 0 ultimate displacement in mm when the concrete beam is broken;m mass of the concrete beam between the supports in kg;g acceleration due to gravity and g = 9.81 m/s2;L full length of the beam and L = 500 mm;S effective span of the beam and S = 400 mm;B breadth of the beam and B = 100 mm;H height of the beam and H = 100 mm;a0 notch depth of the beam and a0 = 50 mm.5. Requirement: LAB REPORTYou are asked to prepare a lab report including the following information:1. 2. 3. concrete mix for the C50 concrete used;test description and results of all tests performed;analysis of the test results including the fracture energy, brittleness andstrengths, and potential observed correlations.
Write introduction Part B:
The lab investigation undertaken as part of this module is designed to help you
• further understand the basic concept of the fracture properties of
concrete;
• understand the procedure of testing the fracture properties of concrete;
• strengthen the ability to design concrete mixes;
• develop the ability to numerically calculate the fracture energy of concrete;
• develop the ability to analyze test results and make objective judgements.
1. TEST SPECIMENS
Notched concrete beams are adopted for this lab activity, as shown in the figure
below, with typical dimensions as follows:
Length of the beam L = 500 mm
Breadth of the beam B = 100 mm
Depth of the beam H = 100 mm
Depth of the notch a = 50 mm
Depth of the ligament h - a = 50 mm
Effective span l = 400 mm
H
l B
Figure 1: Schematic representation of a beam under three-point bending2. MATERIALS FOR MAKING CONCRETE
One concrete grade was used for this laboratory investigation, C50 (50 MPa) at
28 days after standard water curing, with main ingredients as follows:
Cement Portland cement (OPC) - 52.5N strength
Coarse aggregates 4mm - 20 mm Crushed
Fine aggregate Uncrushed
Water Tap water
Slump is required between 30-60 mm and this needs to be monitored during
casting.
Three beams and six cubes are required. The beams are used for obtaining the
fracture energy, GF, three cubes for obtaining the cube compressive strength, fcu,
and the other three cubes for obtaining the splitting tensile strength, f t'. The test
age is fixed at 14 days.
All concrete specimens are cured in water for one week and then left in the air to
allow the specimens to be dry for further 7 days.
The notches are to be prepared using a diamond saw one week before testing.
3. TESTING PROCEDURE
The concrete beam is loaded in a three-point bending way at a constant
displacement rate of 1.5×10-3 mm/s until it is fully broken. The load and
displacement were recorded using a data logger at a rate of two sets per second
for future analysis. Each bending test takes 10 to 15 minutes.
The concrete cubes are crushed on the same day as the fracture tests and the
corresponding maximum loads under both compression and splitting tension are
recorded for determining the compressive and tensile strengths of concrete.
4. DETERMINATION OF
The fracture energy, GF, defined as the total energy dissipated over a unit area
of the cracked ligament, is obtained on the basis of the work done by the force
(the area under a load-displacement curve in three-point bending on a centrally
notched beam) associated with the gravitational work done by the self-weight of
the beam.
The fracture energy, GF, is calculated based on the following formula with some
numerical treatment
G =
F
0
0 P() d + m g (L / S ) (2 − L / S) 0
B (H − a0 ) where
P load in N;
displacement in mm;
0 ultimate displacement in mm when the concrete beam is broken;
m mass of the concrete beam between the supports in kg;
g acceleration due to gravity and g = 9.81 m/s2;
L full length of the beam and L = 500 mm;
S effective span of the beam and S = 400 mm;
B breadth of the beam and B = 100 mm;
H height of the beam and H = 100 mm;
a0 notch depth of the beam and a0 = 50 mm.
5. Requirement: LAB REPORT
You are asked to prepare a lab report including the following information:
1. 2. 3. concrete mix for the C50 concrete used;
test description and results of all tests performed;
analysis of the test results including the fracture energy, brittleness and
strengths, and potential observed correlations.
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