Wiss, Janney, Elstner Associates, Inc.
2200 Powell Street, Suite 925
Emeryville, California 94608
510.428.2907 tel | 510.428.0456 fax
www.wje.com
SUMMARY OF PRELIMINARY
PETROGRAPHIC STUDIES OF CONCRETE SAMPLES FROM TURKEY
Introduction
Wiss, Janney, Elstner Associates, Inc. (WJE) conducted several reconnaissance surveys of the
regions in Turkey affected by the Magnitude 7.4 Kocaeli earthquake of August 17, 1999. During
one of these surveys, in September 1999, four samples of concrete were collected from buildings
that had collapsed. These fragments were subjected to petrographic evaluations in WJE
laboratories and the findings from the evaluations are contained in this summary report, which
also contains photographic documentation.
General Observations
The dull luster and thick carbonated zones are indicative of a high water to cement ratios for
Samples 1, 3 and 4. The concrete represented by each of the samples was grossly deficient in
coarse aggregate volume.
The pattern of cement paste carbonation for Sample 2 indicated that at least one of the fracture
surfaces was relatively old and was likely present before the recent earthquake occurred.
Textural features detected in Samples 1 and 4 are indicative of incomplete mixing and
incomplete consolidation. Evidence of incomplete consolidation in concrete that does not
contain coarse aggregate is typically due to a deficiency in cement content.
The iron oxide scale on the bottom fracture surfaces of Samples 1 and 4 indicate that the
concrete was reinforced. The thickness of the iron oxide indicated that its deposition during
rusting of the adjacent steel reinforcement was the cause of the fracture plane on which it was
deposited. Iron oxide had also been able to enter the porous cementitious matrix adjacent to
embedded metal. This typically occurs in concrete that has a high water to cement ratio.
The formed surfaces of Samples 1 and 4 had been coated with an air-entrained sand-cement
mortar. Only a remnant of the mortar still adhered to the surface of Sample 1. The mortar layer
that adhered to the surface of Sample 4 was 0.5 inch thick. The composition of the mortar was
similar to the mortar remnant that adhered to the surface of Sample 1.
The cementitious matrix of Sample 4 appeared to contain relatively large unhydrated cement
particles. This suggested that the portland cement was coarsely ground. Additional studies
would be needed to confirm this observation.
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The compressive strength measured for a cube that was cut from Sample 3 was 2560 psi.
Compressive strength measured for a small cube is typically higher than for a proper test
cylinder made from the same material. The equivalent compressive strength of the concrete if
tested as a cylinder is 2230 psi. The unit weight measured for the cube was 127.6 pcf. This
value is low and is consistent with concrete that has a high water to cement ratio and is deficient
in coarse aggregate volume.
Each of the samples represent concrete of generally similar composition. In general, the
concretes had high water to cement ratios, were not air entrained and were deficient in coarse
aggregate. In the case of Sample 1, the gradation of the sand was much finer than in the other
samples. Such fine gradation would be expected to increase the water demand of the plastic
concrete over a similar mix with a coarser sand gradation. The estimated paste content for
Sample 3 was judged to be too low for concrete that does not contain coarse aggregate. The
paste deficiency makes it difficult for the cement paste to adequately coat all the aggregate
surface area. This leads to formation of voids.
The presence of thick iron oxide scale deposits on the bottom of Samples 1 and 4, in combination
with the carbonation pattern for Sample 2 indicate that some of the fracture surfaces were
relatively old and may have been present at the time of the recent earthquakes. Carbonation
extends more deeply and progresses more rapidly in high water to cement ratio concrete, which
will promote rapid steel corrosion and degradation of the concrete. Since porous carbonated
cement paste can not protect embedded metal from corrosion, it is likely that the observed
rusting of the embedded metal may simply be due to the reduction in pH that occurred during
carbonation of cement paste. However, the presence of shell fragments in Sample 1 suggests
that the sand used in this sample may contain chlorides. Chemical studies would be needed to
rule out the presence of excessive chlorides as a contributing cause of the observed corrosion.
The tear-like separation contained in Sample 2 indicated that the concrete was disturbed before it
had achieved initial set. This may indicate that formwork was not rigid, or that autogeneous
shrinkage of concrete that was deficient in coarse aggregate had occurred. In either case, the
separation represents a zone of weakness that was present in the concrete before the recent
earthquake.
Conclusions
Petrographic studies of concrete samples collected from four collapsed buildings subsequent to
the August 17, 1999 earthquake show that the concrete collected was grossly deficient in
numerous respects. Typically, coarse aggregate volume was found to be substandard,
incomplete mixing which resulted in the presence of large lumps of unhydrated cement and
point-to-point contacts of small aggregate particles was noted, and excessively high water to
cement ratios were observed. Such deficiencies, which result in greatly reduced integrity and
durability of the concrete during normal service life and during earthquake events, cannot be
identified without benefit of petrographic analysis, yet need to be considered when assessing the
earthquake resistance of concrete buildings.
TABLE 1 - Summary of Petrographic Observations for Fragments of Concrete From Turkey
Sample
ID
1
Observations
The sample was approximately 2.2 x 3 x 2.5 inches in size and contained remnants of
two formed surfaces that intersected at approximately ninety degrees. Remnants of an
air-entrained sand and cement mortar adhered to the formed surfaces. The sand
contained in the remnant mortar layer was composed primarily of quartz. A 0.05-inch
thick fragment of iron oxide scale was present on the bottom fracture surface (Photo
1). The concrete did not contain coarse aggregate. The fine aggregate was composed
of siliceous and carbonate rocks as well as shell fragments.
The bond between shell fragments contained in the fine aggregate and the
cementitious matrix was judged to be poor. This was due to at least two factors. 1)
The shell fragments are sliver-shaped and would tend to trap rising bleed water
contained in the freshly placed concrete (Photo 2). Concentrations of bleed water that
collect beneath shell fragments would locally increase the water to cement ratio of the
cementitious matrix. The thin "mother of pearl" layer (Photo 3) on the surface of
many of the shell fragments (also called the nacreous structure) consists of very thin,
alternating layers of organic matter and aragonite. Aragonite is of the same chemical
composition as calcite, but it has a different crystal structure. Since Aragonite is
slightly more soluble than calcite, dissolution of aragonite due to movement of water
through the structure could result in removal of the "mother of pearl" surface layers
and contribute to additional weakening of the shell to matrix bond.
The sand contained an excessive amount of relatively fine-sized particles (compare
Photo 2 to Photo 9). The increased amount of fine-sized sand particles would be
expected to increase the water demand compared to concrete with a more proper
gradation. Igneous, metamorphic and sedimentary rock types were present. A few
rhyolite (volcanic igneous rock) particles were detected. Rhyolite is classed as
potentially deleteriously reactive with cement alkalis, but no evidence of such a
reaction was detected.
A tear-like separation that formed before the concrete had achieved initial set was
detected (Photo 4). Separations of this type often form in concrete that suffered from
early settlement. It now represents a plane of weakness. Two cement lumps that had
a conspicuously lower water to cement ratio than the surrounding body of concrete
were detected (Photos 5 and 6). One of the lumps contained numerous fine-sized
spherical air voids. The presence of these voids indicated that the lump was the result
of incomplete mixing and not raw material cement lumps. The cementitious matrix
was soft and friable, and had a dull luster. The water to cement ratio was judged to be
high. Iron oxide that had formed due to rusting of embedded steel had penetrated into
the porous matrix (Photo 7). The cementitious matrix was carbonated from the
formed surfaces to depths of 0.6 to 0.7 inches.
The concrete was judged to be deficient in cementitious matrix. Textural features
indicated that the concrete had been poorly mixed and incompletely consolidated.
Sand particles that were in point-to-point contact were detected in areas of incomplete
consolidation.
TABLE 1 - Summary of Petrographic Observations for Fragments of Concrete From Turkey
Sample
ID
2
3
Observations
The sample was approximately 1 x 3.5 x 3.8 inches in size. A portion of a horizontal
surface that had been struck off but not finished was present. The cementitious matrix
within about 0.2 inches of the horizontal surface was carbonated. The two major
fracture surfaces of the sample intersected the presumed horizontal surface at
approximately a 70-degree angle. The cementitious matrix adjacent to one of the
fractures was not carbonated, but the matrix adjacent to the other fracture surface was
carbonated (Photo 8). This indicated that the fractures were of different ages, and the
one adjacent to the uncarbonated matrix had formed more recently. The concrete was
grossly deficient in coarse aggregate volume. The fine aggregate was a siliceous and
carbonate sand that contained a wide variety of rock types. The composition of the
sand was similar to that described for Sample 1. However, the percentages of the
constituents indicated that the sand was from a different source. In addition, the sand
contained substantially fewer fine-sized particles (Photo 9). The cementitious matrix
was light gray and contained a moderate amount of unhydrated cement. The water to
cement ratio was judged to be moderate and conspicuously lower than that of the
other three samples.
The concrete had been poorly consolidated and sand particles that were in point-topoint contact were common (Photo 10). Irregularly shaped voids that represented
concentrations of bleed water were detected in the underside of aggregate sockets
(Photo 11).
The sample was approximately 3 x 3.5 x 4.5 inches in size and contained remnants of
two formed surfaces. Remnants of a white fibrous layer adhered to the formed
surfaces (Photo 12). Traces of a sand and cement mortar layer that may have been on
the surface were also detected. The concrete was grossly deficient in coarse aggregate
volume. The fine aggregate was a siliceous and carbonate sand that contained a wide
variety of rock types. The source of the sand was different than that described for
Samples 1 and 2. The gradation of the sand was more similar to the sand in Sample 2
than in Sample 1. The cementitious matrix within 1.6 inches of both formed surfaces
was carbonated. The cementitious matrix had a dull luster that is characteristic of an
excessively high water to cement ratio. The estimated water to cement ratio was
judged to be moderately high to very high and a wide variation in the water to cement
ratio was detected. The estimated paste volume of 5 to 5-1/2 bags per cubic yard of
concrete was judged to be deficient for concrete that contained only sand aggregate.
TABLE 1 - Summary of Petrographic Observations for Fragments of Concrete From Turkey
Sample
ID
4
Observations
The sample was approximately 2 x 3.5 x 5 inches in size and was composed of two
distinct layers. The top 0.5-inch layer was composed of an air-entrained sand and
cement mortar that was firmly bonded to the concrete substrate. Remnants of an
orange coating were detected on the exposed surface and on one fracture surface that
was oriented perpendicular to the exposed surface. Remnants of insects or arachnids
were detected on the fracture surfaces. Remnants of a 0.05 to 0.08-inch layer of iron
oxide scale were present on the bottom fracture surface (Photo 13). Some of the iron
oxide had penetrated into the porous adjacent overlying body of the cementitious
matrix. These features all indicated that the fractured edges of the sample were
relatively old. The concrete was grossly deficient in coarse aggregate volume. The
fine aggregate was a combination of siliceous and carbonate sand that contained a
wide variety of rock types. Some of the siliceous sand particles were coated with a
thin white layer (Photo 14) of calcium carbonate (caliche). The body of the
cementitious matrix was buff to tan, porous, friable and had a variable water to
cement ratio that ranged from moderate to high (Photo 15. A number of cement
particles that appeared to be relatively large and may have been composed of belite
nests were detected (Photo 16). This suggested that the cement may have been
coarsely ground. Additional in-depth studies would be needed to confirm this
observation. The cementitious matrix of the base concrete as well as the mortar layer
was fully carbonated.
TABLE 2– Photo Log for Fragments of Concrete From Turkey
Photo #
Description
1
The as-received appearance of the four samples is pictured. Concentrations of iron
oxide scale that were thick enough to have induced cracks in Sample 1 (top left)
and Sample 4 (bottom right) are marked with arrows. Note the deficiency in coarse
aggregate content.
2
Two large elongated shell fragments embedded in Sample 1 are marked with
arrows. Note the large volume of very fine sand particles compared to Sample 2
(Photo 9). The large amount of fine-sized particles would increase the water
requirement of the concrete.
3
A fragment of the "mother of pearl" layer from a shell fragment that still adheres to
the impression of a shell fragment in the cementitious matrix of Sample 1 is
marked with an arrow.
4
A tear-like separation that formed before the concrete had achieved initial set is
marked with an arrow. Such a separation represents a plane of weakness.
5
An irregularly shaped lump of cement that contains numerous small spherical voids
and that has a conspicuously lower water to cement ratio than the surrounding
cementitious matrix is visible.
6
A dark gray lump of cement that doe not contain small spherical voids is marked
with an arrow.
7
The smooth impression of a shell fragment is pictured. A portion of the
cementitious matrix that has been infiltrated by iron oxide is marked with a small
arrow. The larger arrow marks the location of a "mother of pearl" remnant that is
also stained with iron oxide.
8
A cross section oriented at a right angle to the presumed top of Sample 2 is
pictured. The top of the sample is marked with a blue arrow. The surface has been
treated with phenolphthalein indicator in the laboratory. The matrix adjacent to the
fracture surface marked by the green arrow is not carbonated indicating a relatively
young age for the fracture. The matrix adjacent to the fracture surface marked with
the yellow arrow is carbonated, indicating that it is relatively older than the other
fracture.
9
Irregularly shaped voids that are indicative of incomplete consolidation are visible
in Sample 2. A zone where sand particles are in point-to-point contact is outlined
in the blue box.
10
A zone where sand particles are in point-to-point contact is outlined in the blue
box.
11
Irregularly shaped voids located on the underside of an aggregate particle are
visible. These voids are indicative of incomplete consolidation and entrapment of
bleed water.
12
A thin layer of fiber that adhered to the formed surface of Sample 3 is pictured.
Such fibers would be expected to reduce the strength of bond to any mortar layer
that may have been applied to the surface.
13
A thick fragment of iron oxide scale located on the bottom of Sample 4 is marked
with a small arrow. The larger arrow marks the location of porous cementitious
matrix that has been infiltrated by iron oxide
14
A siliceous sand particle that is surrounded by a layer of calcium carbonate
(caliche) is pictured.
15
The variation of water to cement ratio in Sample 4 is apparent by inspection. A
zone with a relatively low water to cement ratio is marked with a small arrow. The
larger arrow marks the location of cement paste with a relatively higher water to
cement ratio.
16
The zone of cementitious matrix that contains a significant amount of relatively
large unhydrated cement particles is outlined in the blue box.
Photo 1: The as-received appearance of the four samples is pictured. Concentrations of iron
oxide scale that was thick enough to have induced cracks in Sample 1 (top left) and Sample 4
(bottom right) are marked with arrows. Note the deficiency in coarse aggregate content.
Photo 2: Two large elongated shell fragments embedded in Sample 1 are marked with arrows.
Note the large volume of very fine sand particles compared to Sample 2 (Photo 9). The large
amount of fine-sized particles would increase the water requirement of the concrete.
Photo 3: A fragment of the "mother of pearl" layer from a shell fragment that still adheres to the
impression of a shell fragment in the cementitious matrix of Sample 1 is marked with an arrow.
Photo 4: A tear-like separation that formed before the concrete had achieved initial set is marked
with an arrow. Such a separation represents a plane of weakness.
Photo 5: An irregular-shaped lump of cement that contains numerous small spherical voids and
that has a conspicuously lower water to cement ratio than the surrounding cementitious matrix is
visible.
Photo 6: A dark gray lump of cement that does not contain small spherical voids is marked with
an arrow.
Photo 7: The smooth impression of a shell fragment is pictured. A portion of the cementitious matrix
that has been infiltrated by iron oxide is marked with a small arrow. The larger arrow marks the location
of a "mother of pearl" remnant that is also stained with iron oxide.
Photo 8: A cross-section oriented at a right angle to the presumed top of Sample 2 is pictured. The top of
the sample is marked with a blue arrow. The surface has been treated with phenolphthalein indicator in
our laboratory. The matrix adjacent to the fracture surface marked by the green arrow is not carbonated
indicating a relatively young age for the fracture. The matrix adjacent to the fracture surface marked with
the yellow arrow is carbonated, indicating that it is relatively older than the other fracture.
Photo 9: Irregularly shaped voids that are indicative of incomplete consolidation are visible in
Sample 2. A zone where sand particles are in point-to-point contact is outlined in the blue box.
Photo 10: A zone where sand particles are in point-to-point contact is outlined in the blue box.
Photo 11: Irregularly shaped voids located on the underside of an aggregate particle are visible.
These voids are indicative of incomplete consolidation and entrapment of bleed water.
Photo 12: A thin layer of fiber that adhered to the formed surface of Sample 3 is pictured. Such
fibers would be expected to reduce the strength of bond to any mortar layer that may have been
applied to the surface.
Photo 13: A thick fragment of iron oxide scale located on the bottom of Sample 4 is marked
with a small arrow. The larger arrow marks the location of porous cementitious matrix that has
been infiltrated by iron oxide.
Photo 14: A siliceous sand particle that is surrounded by a layer of calcium carbonate (caliche)
is pictured.
Photo 15: The variation of water to cement ratio in Sample 4 is apparent by inspection. A zone
with a relatively low water to cement ratio is marked with a small arrow. The larger arrow
marks the location of cement paste with a relatively higher water to cement ratio.
Photo 16: The zone of cementitious matrix that contains a significant amount of relatively large
unhydrated cement particles is outlined in the blue box.