1. Building
Description
The building
under study is located in --------- on the main road ----- as marked in the
report's cover page photo.
The building
consists of a ground, a mezzanine e, and five typical floors. The ground and
mezzanine floors are used as shops, and the typical floors are used as workers'
accommodation.
The
structure is made of conventional concrete
supported by beams that transfer the loads to the columns, and the latter transfer the loads to the strata through footings. Figures 1 to 3 illustrate the building from different angles.
2. Visual
inspection
During
the physical observation, all floor levels were inspected, and considerable
areas were exposed and checked, and a general assessment was conducted.
Investigation for various signs of deterioration was conducted, such as cracks'
patterns, spalling and delamination of concrete, honeycombs, discoloration,
etc. Also, a check for excessive deflection and distress, such as flexural and
shear cracks, was carried out.
The
physical observations made during the inspection are summarized below, and
figures from 4 to 16 present part of the visual observation.
1.
The structure of the building is extremely
deteriorated
2.
Various temperature and shrinkage cracks were
observed all over the building.
3.
Corrosion cracks were observed. Also, a trail
of corrosion was noticed.
4.
Concrete cover spalling and exposure of
reinforcement was observed in many places
5.
A lot of exposed reinforcement bars have
experienced a size reduction due to corrosion.
6.
Concrete delamination and paint peeling were
observed all over the building.
7.
Vertical cracks between concrete columns and
blockwork were observed in various places.
8.
Horizontal cracks between the staircase roof's
beams and the blockwork were observed.
9.
Diagonal cracks in the blockwork walls were
observed in some places.
10. Noticing
diagonal cracks in some walls
11. Signs of water
leakage were observed in many places
12. Trails of
humidity and mold due to humidity and water leakage were noticed.
13. The roof's
waterproofing system is damaged. No significant cracks in the typical floors
3. Conducted Tests
Tests, mainly,
were conducted on the columns since they are the critical structural element in
the building. The following tests were conducted:
1.
Carry out ultrasonic Pulse velocity test as per
EN 12504-4:2004.
2.
Obtain concrete cores from different locations
of the building to assess the physical and mechanical properties of the
existing concrete, according to EN 12504-1:2009.
3.
Measure the carbonation depth of concrete
elements by using phenolphthalein indicator according to BS 1881-201:1986 and
BS EN 14630.
4.
Extract reinforcement steel sample for a
tensile test following ASTM A370 or ISO 15630-1.
4. Tests
Results
The
following shows the results of the tests conducted. Table 1 summarizes the
conducted tests' results.
4.1
Ultrasonic test
The ultrasonic test was conducted on
several concrete elements to examine the quality of the concrete in general.
Twenty-one columns and five slabs were tested. The results values were varying
between 2765 m/s and 3412 m/s, which means that concrete condition varies
between poor and questionable condition.
4.2
Compressive strength
and carbonation test
Twenty-six
concrete cores were extracted; twenty-one cores were from the columns and five cores were from the slabs.
Core compressive strength test results vary
between 13 MPa and 54 MPa for columns. As for the slab, the compressive
strength varies between 15 MPa and 47 MPa.
4.3 Carbonation
Carbonation was observed in twenty-two of twenty-six of the extracted samples and the carbonation depth varies between 0.3
cm to 1.9 cm.
4.1
Tensile Test
One specimen was extracted from a column to know the
yield strength of the reinforcement steel used in the structural elements. The
yield strength of the deformed bar was found to be 540 MPa
5. Discussion
of the Visual Inspection and the Tests Results
From
the physical investigation conducted, the tests' results obtained, and the
experience with similar buildings, most of the observed cracks are the expected
output due to the bad quality of work, lack of regular and preventive
maintenance, and the effect of variation in temperature and humidity.
By applying standard deviation to the Ultrasound tests'
results, the average ultrasound velocity was 3040 m/s, which means the quality
of concrete is just above the poor category, questionable. This
conclusion was confirmed by the compressive test results obtained, where the
average concrete strength was 24.3 MPa.
Some of the tested columns had shown very low strength values, e.g.,
12.5 MPa. The low compressive strength of the concrete elements combined with
the effect of the numerous cracks in these elements and the reduction in
reinforcement diameter adversely affects the strength of these elements. It
could lead to the redistribution of the stresses within the building, which to
failure or excessive deformation.
Almost 85% of carbonation test for the extracted samples had shown carbonation
depth vary between 0.3cm to 1.9cm which means the alkanity of concrete in these
locations were reduced and the protection of steel bars against corrosion were
reduced by oxidation.
The horizontal crack between the staircase roof's beams and the
blockwork is due to the slab movement due to temperature variation. Also,
vertical cracks between the concrete columns and the blockwork walls are due to
temperature shrinkage.
Some of the observed diagonal cracks are related to the shrinkage
effect. At the same time, some others are related to the deflection in the
supporting elements.
Although the building is not old, the bad quality
control of the work during the construction period had promoted the corrosion
to initiate at an early stage and
propagate.
6. Conclusion
From the preceding observation and tests' results, the structural condition is considered moderate to poor. From the various inspected locations, one can assert that corrosion of the reinforcement steel has been propagating in many places in the building, especially in the roof slabs and the wet areas, and the deterioration is increasing, and spalling of concrete in many places will occur. The structure condition could be considered moderate, and more than 50% of the structural elements in the building require rehabilitation and strengthening.