William G. Hime Erlin, Hime Associates 81 1 Skokie Boulevard Northbrook, Ill. 60062
Multitechnique Approach Solves Construction Materials Failure Problems Microscopists and analytical chemists a t the Erlin, Hime Associates Laboratories are regularly confronted with problems involving failures of construction materials: cement, concrete, metals, paints, and coatings. The general approach to the solution of these problems involves initial study of the material by the techniques of petrographic microscopy to discover the mechanism of the failure, followed by the application of analytical techniques to sscertain the causative agents. The techniques typically used and the kinds of information obtained are listed in Table I. It is estimated that over 90% of construction materials failure problems
Technique or method
can be solved by the approach suggested in Table I, provided the microscopist-chemist team is expert enough in the chemistry and behavior of construction materials to know what to look for. For example, the presence of very large quantities of many substances has little effect on the. properties of cement or concrete, but very small quantities of others cause enormously deleterious effects. T o illustrate, silica in the form of quartz can be present as the major concrete component. But silica in the form of opal must be limited to a few percent. Even more powerful in their immediate effect are certain organic substances which at a thousandth of a
Information obtainable
Light microscopy
ure,
classification,
d dispersement of relic cement compounds e“ chemical reactions e such as hardness, Atomic absorption Infrared spectroscopy Wet-chem ica I analysis
X-ray diffractometry
X-ray fluorescence
1230A
dary compounds rtion of elements
A N A L Y T I C A L CHEMISTRY, V O L . 46. NO. 14. DECEMBER 1974
percent level affect the setting, workability, or strength of concrete. The following three examples of “failure analyses” illustrate the approach. “Unset” ConcreteGetting the Lead Out When concrete forms were removed on a large construction project in New York, everyone held their breath. Occasionally, the concrete came pouring out. The uncertainty finally dictated that the multimillion dollar project be halted until the cause for the failureto-set problem was determined and corrected. By the time a sample of the concrete was received in t.he laboratory! the “unset” concrete had already hardened. Microscopical analysis revealed unusual, thin rims on the cement particles, suggesting an excessive amount of a cement set-retarder. Since sabotage had been suspected, the concrete was analyzed for sugara known set-retarder. ( A cup of sugar can delay the set of yards of concrete for weeks.) Colorimetric methods did not detect sugar; therefore, other extracts of the concrete were then analyzed by infrared and ultraviolet spectroscopy for known cement hydration retarders, such as other polysaccharides and lignosulfates. These results also were negative. X-ray fluorescence measurements were then made. Trace quantities of lead and zinc were detected. Since experience has indicated that quantitative analyses of quite varied materials are made more accurately by atomic a hsor p ti o n , A A determinations for lead and zinc were performed, and about 0.03% of each was found. Such quantities, when present as alkali-soluble compounds, are known to delay severely cement hydration. Further work resolved the mystery. A dredged river gravel was being used
___
as t..- ybb.-~lll ”_._ “ ~ c r e t eA. thin hand of the “New Jersey” lead and zinc deposit passed across the river. The dredging operation thus accounted for the sporadic occurrence of these elements in the concrete.
Holey Concrete The quality of concrete is usually monitored by compression tests of samples taken during the “pour.” Unfortunately, a lot of construction may take place before the initial (usually three-day) results become available. Thus, when tests on a large road paving project indicated strengths of 50% below requirements, all work was stopped while the laboratory team worked on the problem. The general approach taken in a problem of this type is illustrated in Figure 1. The microscopists quickly determined the failure mechanism--15% air in the concrete. About 5% air by volume is frequently specified because it provides great protection against freeze-thaw deterioration. Such a quantity does not significantly affect strength, but each additional percent of air leads to a loss of about 5% strength. A photomicrograph of a polished section of the holey concrete is shown in Figure 2. Samples of the concrete were extracted with a number of solutions, and the extracts were prepared for analysis by absorption spectroscopy as detailed in Figure 3. Infrared revealed the presence of two commercially available admixtures, materials added to concrete to produce special properties, One admixture, a triethanolamine salt and tall oil soaps, is added to cause entrainment of air. The other admixture identified (triethanolamine, polysaccharides, and lignosulfonate) is sold to increase the “workability” of plastic concrete. The concentrations of these admixtures were determined by infrared and ultravioletvisible spectrophotometry by comparison of the sample extracts with extracts from “known” concretes containing the identified admixtures. But one admixture singly was known to entrain only 5% air, and the other only 2%. A concrete mix containing both admixtures in the determined
Figure 1. General approach to study of admixture problem
,... . f ’
*’,:.
.
.*
l y concrete. Black Figure 2. Phoroniicroyrapri 0 1 puu~rie‘~ >e-cLIyII I~ ~ n air-entrained “holes” are sectioned microscol
Figure 3. Analytical methods and results for admixture problem ANALYTICAL CHEMISTRY, VOL. 46. N O
14. DECEMBER 1974
*
1231 A
I Less than $500 Completely portable permeation tube calibration system for pollution monitoring.
Mu51 M o d d 821 1 cviibrator
Figure 4. Underside of spalied concrete
“flake” that originally extended across three masonry blocks. Section is about ’l-in. thick. Opposite side is painted
MAST
dosages was prepared, and this particular cornhination proved synergisticover 15%air had been entrained, and 50%loss in strength had resulted. Unfortunately, there was no way to save the mile of concrete pavement (about 10 million Ih) that had been placed, hut succeeding pavement set satisfactorily by controlling the amounts of the admixture in the concrete.
AIR MONITORING DIVISION
DEVELOPMENT CO.
CIRCLE 158 ON READER SERVICE CARD
-_
Concrete Scales
............
. .
1
,.
.
...
1
..
.
ORTEC MAKES YOUR PHOTONS COUNT!
.. .. ...
.
.
.
In physics. optics.. laser systems.. ion experiments.. astronomy . molecular studies luminescence . fluorescence Raman . mass spectroscopy. . wherever critically accurate light measurement is required.
..
The Ortec 5C1 is the most advanced photon-counting system money can buy. And the most practical. It has a dual-channel pulse height analyzer, for example, that provides first-order pile-up correction at high counting rates and window-mode discrimination of high and low pulses. At counting rates where conventional systems “lose” 50% of the counts, the 5C1 linearizes to within 5%. Another unique advantage is spectrum display. Connect the unit to any CRT, and you can visually opti00111EC
1232A
...
.
..
mize high voltage, amplifier gain, and discriminator levels. Then disable the light source and check for rf pickup or spurious signals. You can’t do this with any other photoncounting system. For full technical data, contact your nearby Ortec representative or Ortec Incorporated. 110 Midland Road, Oak Ridge, Tenn. 37830. (615) 482-4411.
&!!EGG
rOM-nNI
CIRCLE 181 ON READER SERVICE CARD
ANALYTiCAL CHEMISTRY, VOL. 46, NO. 14, DECEMBER 1974
5979
Many owners of wood frame houses recognize that the peeling of paint is a major economic headache. Concrete may experience the same distress. But when a concrete block building began losing not only its paint hut also a ‘hin. layer of underlying concrete (Figure 4), consternation really abounded. Microscopic analysis of the received “scales” revealed thin delamination layers within the spalled section received a t our laboratory. This effect is characteristic of freeze-thaw damage to critically saturated concrete. Analysis of the paint by infrared spectroscopy, solvent extraction, and pyrolysis techniques disclosed an alkyd type of paint. Such a paint is classified as “nonbreathing.” With this analytical data, the team speculated that moisture entering the building walls was prevented from escaping by the paint, The concrete near the paint surface became saturated and during winter froze because of its exposure a t outside temperatures. A site visit revealed a flashing detail error that allowed entrance of rain water into the walls. The corrective measures suggested were the elimination of the flashing detail error by properly redoing the flashing and the replacement of the nonhreathing paint with a breathing paint.
