Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 33
33 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.
OCR for page 34
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