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in the previous paragraph). Because some CLSM specimens Table 3.20. TCLP limits
may suffer significant damage from freeze-thaw cycles, of heavy metals.
shrinkwrap was used to keep the specimens intact, thereby al-
TCLP Limits
lowing for subsequent measurement of water permeability. Element
(ppm)
Porous stones were secured at both ends of the specimens to Arsenic 5.0
facilitate the permeability measurements. After completing Barium 100.0
the freezing and thawing test, water permeability (or hy-
Cadmium 1.0
draulic conductivity) was measured using the falling-head
Chromium 5.0
method. For reference, specimens from each mixture that
Lead 5.0
were not subjected to freeze-thaw testing were also tested for
water permeability. Mercury 0.2
Selenium 1.0
Silver 5.0
Leaching and Environmental Impact
Source: 40 CFR 261.24
Coal combustion products, such as fly ash, and other by-
product materials, such as silica fume and slag, have been
used successfully and safely for years in conventional con- project were found to easily "pass" the TCLP, meaning the
crete. CLSM has proven to be especially well-suited as a con- heavy metal concentrations were very low and not of con-
sumer of various by-product materials; further, by-product cern. However, if the TCLP values exceeded any of those
materials that are not typically allowed in conventional con- listed in Table 3.20, another level of testing would have been
crete, such as fly ash not meeting ASTM C 618, are routinely initiated, specifically the American Nuclear Society leachate
used in CLSM. Therefore, there has been some concern about test (ANS 16.1). This test is a monolith test that measures
the potential for leaching of constituents in by-product ma- the actual leachates from CLSM containing the by-product
terials (e.g., heavy metals, organics) from CLSM and their im- material of interest and is a better indicator of actual leach-
pact on the environment. To address this issue, by-product ing potential.
materials evaluated in this project were tested to determine
their chemical composition and potential for leaching from
Results and Discussion
CLSM.
For each of the by-products included in the initial labo- The main findings from the laboratory study are presented
ratory study (three fly ashes, one bottom ash, and one next, with emphasis on selecting or developing appropriate
foundry sand), the total heavy metal concentration was de- test methods to measure key CLSM properties and building an
termined following EPA Method 610, "Determination of understanding of how specific materials, mixture proportions,
Certain Polynuclear Aromatic Hydrocarbons in Municipal etc. affect CLSM performance.
and Industrial Discharges Using Liquid-Liquid Extraction
and HPLC and/or Gas Chromatography as Provided Under
Fresh Properties
40 CFR 136.1," where nitric acid and hydrogen peroxide
were used to digest the materials. The eight elements ana- An important aspect of this study was the assessment of the
lyzed were arsenic, barium, cadmium, chromium, lead, mer- fresh or plastic properties of CLSM, both in terms of evaluat-
cury, selenium, and silver. Because this testing determines ing candidate test methods and determining the relationship
the total amount of heavy metals, and not the leachable among constituent materials, mixture proportions, and fresh
amount, the extraction values may be 20 times the amount CLSM properties. Tables 3.3 through 3.5 summarize some of
that might be leached in the TCLP limits (a "rule of thumb" the important parameters, including water demand (to obtain
value). If any of the by-products tested in this project the target flow), air content, flow, unit weight, and bleeding
yielded values in excess of the toxicity limits (20 times the (%) for the initial 38 mixtures. The air content, flow, unit
TCLP limit), TCLP was then conducted to assess the type weight, and bleeding tests were found to be effective and user-
and amount of heavy metals that may be leached from the friendly. Clearly, any change in source material, mixture pro-
materials. The TCLP (EPA Method 1311) is one of the most portions, or curing regime would impact each of the relevant
common tests performed on materials to determine their fresh properties of CLSM. For this project, given that the water
potential for leaching. The concentrations of the eight heavy content was adjusted for each mixture to achieve a target flow
metals in the extracts were compared to the TCLP limits (200 to 250 mm), some interesting observations could be
given in EPA publication 40 CFR 261.24 as shown in Table 3.20. made about what factors most affect flow characteristics, as
As described later in this chapter, the materials tested in this discussed next.
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34
Water Demand foundry sand was found to reduce the bleeding significantly,
while the bottom ash was found to significantly increase the
Throughout this study, water (and sometimes AEA) was
bleeding. This finding indicates the importance of the fine ag-
added to CLSM mixtures so that their flow values were be-
gregate on bleeding of water in fresh CLSM mixtures. The fly
tween 200 and 250 mm; this procedure allowed interesting in-
ash type had minimal effect on the bleeding of CLSM mix-
formation and trends to be gleaned from what most affects
tures. Little segregation was found in the five selected CLSM
water demand. The effects of material type and quantity on the
mixtures.
water demand of CLSM were analyzed using a statistical pro-
gram (ECHIP) for the nonair-entrained mixtures; the results
are shown in Figure 3.4. Setting and Hardening
The Pareto graph in Figure 3.4 illustrates the statistically sig-
The setting/hardening behavior of CLSM is important for
nificant variables that affect water demand. In this graph, the ef-
many applications, especially for those where early strengths
fect is the difference between the specified variable level and the
are needed to satisfy construction demands (i.e., timing be-
reference variable level. The reference variable levels are con-
tween lifts or early opening to traffic). Test methods are needed
crete sand (river), Class C fly ash, 180 kg/m3 fly ash content, and
to easily assess the setting of CLSM, both in the laboratory and
30 kg/m3 cement content. The difference was positive for bot-
in the field. This section discusses some of the important find-
tom ash, foundry sand, and high-carbon fly ash. The difference
ings regarding the setting time of CLSM, as measured by the
was negative for 60 kg cement, Class F fly ash, 360 kg fly ash,
needle penetrometer (ASTM C 403), soil pocket penetrometer,
60 kg cement and high-carbon fly ash, 60 kg cement and Class
and pocket vane shear test.
F fly ash, and 60 kg cement and 360 kg fly ash. The figure shows
When the needle penetration of CLSM is measured, a certain
that the fine aggregate type was the most significant factor af-
minimum strength of CLSM is required to obtain meaningful
fecting the water demand of mixtures. The use of high-carbon
test results. Thus, comparing the setting time of CLSM mixtures
fly ash also increased the water demand. There is no significant
to each other at predefined time increments is often not feasible,
difference between the use of the Class C and Class F fly ash. In
but rather, the timing of measurements should be a function of
addition, analysis of variance (ANOVA) calculations identified
constituent materials and mixture proportions. Also, because a
significant variables as fly ash type, fine aggregate type, and the
needle penetrometer penetrates deeper into mixtures than a soil
interactions between cement content and fly ash type.
penetrometer, it is less subject to bleed water effects, as discussed
next. Despite these differences in penetration depth and contact
Bleeding and Segregation angle, there was a fairly reasonable correlation between soil
penetrometer and needle penetrometer values for the 38 mix-
Bleeding and segregation affect the subsidence and the uni-
tures, as shown in Figure 3.5 (with an R2 of approximately 0.75
formity of the placed CLSM mixtures. Using ECHIP, the ef-
for all the CLSM penetration data combined). Figure 3.6 shows
fects of various factors on bleeding were evaluated. The use of
the relationship between the soil pocket penetrometer and the
vane shear device; although a general trend exists, it is not statis-
tically strong.
The walkability time was assessed by preparing large CLSM
boxes that were walked on at various ages. The soil penetrom-
eter values were found to range from 4.32 to 7.35 kPa (average
of 6.14 kPa) when CLSM mixtures were able to support the
weight of an average person with about 6.4 mm indentation.
More comprehensive (and realistic) data were generated in the
Bottom Ash
Foundry Sand field tests on walkability times and how they relate to penetra-
High Carbon Fly Ash
60 kg & High Carbon Fly Ash tion data and other parameters (described in Chapter 4).
60 kg & Type F Fly Ash
60 kg
Class F Fly Ash
60 kg & 360 kg Fly Ash
Fly Ash Content
Subsidence
All of the CLSM mixtures exhibited measurable subsi-
0 20 40 60 80 100 120 140 160 dence, with the exception of mixture 23, which had relatively
Water Demand (kg/m3)
poor flowability. Except for mixture 23, a reasonable correla-
Source: after Du et al. (2004) tion existed between subsidence and bleeding. Mixture 6 had
Figure 3.4. Pareto-effects graph for water demand the highest subsidence of about 2.5 percent of the placement
of nonair-entrained CLSM mixtures. height. Comparison of the results obtained from mixtures 26
