1. Building Description
The building
under study is located in ------- at the junction of ---- street with ------
street.
The building
consists of the ground floor and four typical floors. The building is abandoned.
The
structure is made of conventional concrete slabs supported by beams that
transfer the loads to the columns, and the latter transfer the loads to the
strata through footings. The building is enveloped with stone. Figure 1 and
figure 2 illustrate the building from different angles
2. Visual
inspection
During
the physical observation, all floor levels were inspected, 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 3 to 9 present part of the visual observation.
1.
The structure of the building is moderately
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 were observed in some 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.
Signs of water leakage were observed in many
places
9.
Trails of humidity and mold due to humidity and
water leakage were noticed.
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 the 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.
Nineteen columns and four slabs were tested. The results values were varying
between 1965 m/s and 2818 m/s, which means that concrete condition varies
between very poor to poor in condition.
4.2
Compressive strength
test
Twenty-three
concrete cores were extracted, thirteen cores from the columns, and three cores
from the slabs.
Core compressive strength test results vary
between 17 MPa and 42 MPa for columns. As for the slab, on average, the
compressive strength was 25 MPa.
4.3
Carbonation Test
Carbonation was
found in 60% of the tested samples. Carbonation's depth varies between 11mm and
44mm.
4.4
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 458 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 2200 m/s, which means the quality of concrete is poor in general. This conclusion was confirmed by the
compressive test results obtained, where the average concrete strength was 22.9
MPa.
Some of the tested columns had shown low
strength values, e.g., 17 MPa. The low compressive strength of the concrete
elements combined with the effect of the cracks in these elements could
adversely affect the strength of these elements. It may lead to the redistribution of the stresses within the building.
About 60% of samples have carbonation,
i.e., the alkalinity of the concrete is decreasing, and protection against
corrosion had gone.
Vertical cracks between the concrete
columns and the blockwork walls are due to temperature shrinkage.
Horizontal cracks between the tiles
finishing layer and the slab are due to temperature variation.
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 poor. From the various inspected locations, and the carbonation in
the concrete and humidity trails, one
can assert that corrosion of the reinforcement steel has been propagating in
many places in the building, and the deterioration is increasing, and spalling
and delamination of the concrete cover will occur in other places. The
structural condition could be considered moderate, and around 20% to 30% of the
structural elements in the building require rehabilitation and strengthening.
The above conclusion was based on the
observed defects during the inspection period, and tests results conducted at
various selected points that could not reveal the condition of not tested
element. Also, to precisely understand the condition and behavior of the
building, the construction drawings should be studied in conjunction with
observation and tests results.