1. Building
description
The building
under study is located in ------ on the main road ------ and ------- street.
The
building consists of a ground, a mezzanine, and three typical floors. The
ground and mezzanine floors are used as shops. The typical floors are used as
workers' accommodation.
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. 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 9 present part of the visual observation.
1.
There is no sufficient offset between the
building and the building next to it. Also, the building is attached to the
building behind it.
2.
Various temperature and shrinkage cracks were
observed all over the building.
3.
Numerous corrosion cracks were observed. Also,
a trail of corrosion was noticed.
4.
Concrete cover spalling and exposure of
reinforcement were observed in several areas
5.
Joint spalling was observed
6.
A lot of exposed reinforcement bars have
experienced a size reduction due to corrosion.
7.
concrete discoloration was detected in many
places all over the building.
8.
Concrete delamination and paint peeling were
observed all over the building.
9.
Vertical cracks between concrete columns and
blockwork were observed in various places.
10. Signs of water
leakage were observed in many places
11. Trails of
humidity and fungi due to water leakage were noticed.
12. Some occupants had improperly demolished parts of the walls to make openings.
3. Conducted
Tests
Tests, mainly
and mostly, 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 columns to examine the quality of the concrete in general. Sixteen columns and four
slabs were tested. The results values were varying between 1900 m/s and 3235
m/s, which means that concrete condition varies between very poor and questionable
conditions.
4.2
Compressive strength Test
Twenty-Four
concrete cores were extracted from the entire building, twenty cores from the
columns, and four cores from the slabs.
Core compressive strength test results vary
between 5.5 MPa and 18.5 MPa for columns. As for the slabs, the compressive
strength was between 14.5 MPa and 34 MPa. Table 2 present the compressive
strength results by implementing the standard deviation to calculate the
average concrete strength.
4.3
Carbonation Test
Carbonation was observed in all the
twenty–four extracted samples and the carbonation depth vary between 0.3 cm to
3.9 cm.
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 280 Mpa.
5. Discussion of Tests Results and Visual Inspection
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
building's age, lack of regular and preventive maintenance, and the effect of
temperature variation and humidity rate.
Despite the ultrasound tests'
results having shown a few intermediate values, yet, the average velocity was found
2500 m/s, which means poor concrete condition. This conclusion was confirmed by
the compressive test results obtained, where the average concrete strength was
14.3 MPa.
All tested columns had shown low
strength values, and in some tested columns, the values were extremely low,
e.g., 5.5 MPa. The low compressive strength of the concrete columns most
probably led to the load of the blockwork walls and/or redistributing the loads to
stronger elements and causing some cracks to occur. Furthermore, the reduction in
the area of the reinforcing steel, due to corrosion, with the low yield
strength had been adding an adverse effect on the strength of the structural
elements.
One hundred percent of the carbonation
test for the extracted samples had shown carbonation depth vary between 0.3cm
to 3.9cm which means the alkalinity of concrete in these locations was reduced
and the protection of steel bars against corrosion was reduced by oxidation.
Also, the finite space between the
building and the neighboring building allows for water accumulation and a humid
atmosphere during the rainy season, and this adversely affects the concrete
element and expedites the deterioration process.
6. Conclusion
Based on the current condition of the building,
the absence of maintenance, and the obtained tests' results are evidence
that the building keeps undergoing further deterioration. The structural
condition is considered hazardous, and the safety of the occupants is at risk
since the concrete cover in slabs is delaminated in many places and could fall
at any moment. Also, many structural and non-structural elements are loaded
with unconsidered loads; this excessive load could impair their serviceability.
Based on the above, more than 90% of the structural elements require rehabilitation and strengthening.