LAB 3 - Testing concrete

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29 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Faculty of Architecture BDes
inArch

Design Studies1B


Constructing the Environment


DESA1102 Structures


LAB 3
-

Testing concrete


Before coming to the laboratory, you should have read through these instructions
and be familiar with the general nature of

the work required.

Record the results as the work proceeds, and write
-
up on the report sheets
attached.


Objectives

1.

To teach the students how to do and interpret simple compressive loading tests.

2

To find out the strength of the concrete cylinders mad
e in Experiment 1, and of bricks,
by tests.

3

To give the students an idea of the strength of concrete and brick, and some of the
factors that affect their strength.

PART A:

TESTING CONCRETE CYLINDERS

Apparatus


The equipment to be used is a hydraulic comp
ression machine with a measuring gauge. In
order to obtain consistent test results, the load should be applied at a uniform speed of
about 4kN per second, with the oil pressure being varied as necessary to obtain this speed.

The dial indicates the
force

that the ram applies to materials being tested. This dial
indicates force in kiloNewtons (kN).

˝

Take the cylinders of concrete made in the first experiment. Measure and note their
mass separately. Identify the concrete mix by the colour of the mould t
he cylinder was
cast in and the water/cement ratio.

The cylinders should be fairly consistent in mass. A lightweight cylinder probably means it
was not fully compacted, and has air voids in it.

˝

Place each of the specimens vertically in the testing machi
ne in turn, and load it to
destruction. Note the batch (red, blue or yellow), and the
maximum force
and sketch
the
mode of failure
in each case.

Operating the press


The valve at the bottom of the oil reservoir and the valve behind the dial gauge should

be
closed
finger tight
prior to each test. After each test release the pressure on these valves
slowly.

Attach the safety screen before loading the test pieces. Sometimes a very
strong specimen will shatter on failure.
Most failures will be gradual.

-

From the maximum force, calculate the
crushing stress

of each specimen.

To calculate the crushing stress.


Stress is force per unit area. The force is given directly by the gauge, in kN.

The area of concrete on which it acts is the cross
-
section of the

sp
ecimen. The specimen is
150mm diameter, so the area is πD
2
/4 = 17671 mm
2
.

Therefore

f’
c

= P x 10
3

/ 17671 MPa.,
where

f
’c

is the crushing stress, and P is the force in kiloNewtons (so P x 10
3

is the force in Newtons).
Newtons per mm
2

is the same as M
egaNewtons per m
2

or MegaPascals.

Faculty of Architecture

DESA 1102, Design Studies, Structures

Lab3



-

RECORD ALL THE RELEVANT INFORMATION ABOUT THE DIFFERENT CONCRETES
AND TESTS ON THE ATTACHED
LABORATORY REPORT

SHEETS.

Before filling out the report, make sure you know all the results of your group’s work. Ask
your col
leagues if necessary.


PART B: TESTING BRICKS AND BRICK PIERS

˝

(a) Crushing tests.

The crushing strength of a brick is tested by laying it flat between the plates of the testing
machine, and loading it at a uniform, slow rate.

˝

Carry out

this crushing test:


(i)

on each of two single bricks, and


(ii)

on each of t
wo already
-
made piers, each three bricks high.

-

Record

the maximum crushing force, and observe the mode of failure in each case.
Make sketches showing how the test pieces failed. Compare the results of the bricks
and the “walls”. What can be the reason
for the difference?

-

Determine

the mean crushing strength in megapascals (MPa) in each case.

The crushing strength (compressive strength) is found by dividing the force needed to
cause the brick to fail (P, the maximum force it can resist) by the cross
-
se
ctional area (A)
of the brick
in contact
with the bearing plate of the machine f
b
= P/A.

Note
that the size of the face of the bricks in contact with the bearing plate must be
measured
before
the bricks are tested
.


Before leaving the laboratory, properl
y clean all the equipment. Place the broken
concrete iand brick in the wheelbarrow and bins provided and deposit it in the
industrial waste bin outside.