1. Building Description
The building
under study is located in ------- between the main road ------ and 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. Figure 1 and figure 2 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 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 was observed
5.
Some of the exposed reinforcement bars have
experienced a size reduction due to corrosion.
6.
Concrete delamination and paint peeling were
observed in many places.
7.
Vertical cracks between concrete columns and
blockwork were observed in various places.
8.
Horizontal cracks were observed in several
locations
9.
Steps-type cracks were noticed in some walls.
10. Signs of water
leakage were observed in some areas
11. 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.
Twenty-seven columns and two slabs were tested. The results values were varying
between 2662 m/s and 3400 m/s, which means that concrete condition varies
between poor and questionable condition.
4.2
Compressive strength test
Twenty-nine
concrete cores were extracted, Twenty-seven cores from the columns, and two
cores from the slabs.
Core compressive strength test results vary
between 12 MPa and 35.5 MPa for columns. As for the slab, the average
compressive strength was 25 MPa.
4.3 Carbonation test
Carbonation was found in more than 55% of
the tested samples. Carbonation's depth varies between 3mm and 33mm.
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.
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 3061 m/s, which means the quality
of concrete is 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
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.
More than 55% of samples have carbonation, i.e., the alkalinity of the
concrete is decreasing, and protection against corrosion had gone.
Most of the vertical and horizontal cracks between the concrete framing
elements and the blockwork walls are due to temperature shrinkage. Also, the
steps-type crack observed is most probably due to temperature and shrinkage
effect since there is no widening in the crack width along its path.
Although the building is not old, the bad quality
control of the work during the construction period promoted the above-mentioned and observed deterioration to occur.
6. Conclusion
From
the preceding observation and tests results, the structural condition is
considered moderate, and no serious problems were found. From the various
inspected locations, 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.