These tasks are briefly described in this section; details are provided in the following sections of this chapter. Review of existing specification and testing environment. The literature pertaining to CFA specifications and testing protocols was reviewed to determine the current practices and where improvements may be needed. A survey of SHAs was also conducted to determine the types, characteristics, and ranges of fly ash content currently used in the United States and those likely to be used in the future. Characterization of coal fly ash. The sources were selected to broadly repre- sent the range of CFA currently used in highway construction.
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These tasks are briefly described in this section; details are provided in the following sections of this chapter. Review of existing specification and testing environment. The literature pertaining to CFA specifications and testing protocols was reviewed to determine the current practices and where improvements may be needed.
A survey of SHAs was also conducted to determine the types, characteristics, and ranges of fly ash content currently used in the United States and those likely to be used in the future.
Characterization of coal fly ash. The sources were selected to broadly repre- sent the range of CFA currently used in highway construction. A characterization protocol was then applied to establish baseline properties of each source. This protocol included all tests currently and commonly used to characterize CFA to provide a means for determining the strengths and weak- nesses of these test methods when applied to a wide range of CFA types.
It also helped identify other characteristics for use in developing new tests. Characterization of strength activity. Chemical charac- terization is based on the bulk chemical composition, which indirectly infers if a fly ash is pozzolanic or has potential for hydraulic reactions in a concrete mixture. The current pozzo- lanic and strength activity tests were reported as not adequately predicting field performance and in some cases incorrectly identifying inert materials as being reactive Schlorholtz, This research evaluated the existing test for pozzola- nic activity i.
Characterization of the effects of carbon on air entrain- ment. The residual carbon contained within fly ash can adversely affect air entrainment in concrete as carbon can adsorb the AEA, thereby reducing the effectiveness of the admixture for producing an adequate air-void system Mehta and Monteiro, The current LOI test estimates the total residual car- bon, but does not determine the adsorption properties of the carbon.
In this project, four different tests for measuring the effect of carbon on air entrainment were investigated for inclusion in a new specification. Assessing ASR mitigation. Also, there was a need to identify quicker, more effective tests for assess- ing ASR mitigation.
Therefore, existing test methods and a proposed rapid method for determining the effectiveness of a CFA for mitigating ASR in a concrete mixture were evalu- ated.
The proposed test method was the alkali leaching test Shehata and Thomas, Also, a number of standard tests were performed on different fly ash sources and the methods used are summarized in this C H A P T E R 3 Methodology 9 section.
Additionally, a number of new tests were developed or evaluated; the process used to refine these tests and their method of application is also summarized. Additional information on the results and procedures is provided in Attachment C. These sources were identified through a survey of SHAs and contacts within the industry. Material certifications were acquired for CFA sources from over coal combustors located in the United States and compared with a database of CFA properties assembled by the research team.
However, other factors were considered such as the geographic distribution, types of coal, combustor, and pollution control measures used at the power plant.
Based on the characterization study, suitable sources were identified and used where appropriate. The research team obtained additional CFA sources for use in developing the foam index, iodine number, and direct adsorption isotherm tests. Also, for developing these tests, it was necessary to blend ashes to achieve target values of LOI. The blending ratios used were , , and , respectively. A listing of all CFA sources used in the experiments conducted is presented in Table 3.
Portland Cement Sources Three different sources of portland cement designated PC-1, PC-2, and PC-3 were used in the research; the nomi- nal properties provided on mill certifications are summa- rized in Attachment C.
The chemical compositions of these cements were determined using x-ray fluorescence spectros- copy XRF and x-ray diffraction XRD , and other tests were conducted to determine relevant physical properties.
Also, for comparison, selected tests were performed using a fourth portland cement source PC-4 ; results of these tests are dis- cussed in Attachment C. The most commonly used, pre-approved AEA in each category was chosen as the pri- mary AEA in experiments dealing with new tests for evaluat- ing the effects of CFA on air entrainment. The primary AEAs are listed in Table 3. In later steps, two AEAs were added i. AEA-6 was included because of its observed low adsorption capacity, and AEA-9 was included in selected tests to verify the results obtained with AEA Other AEAs were included in limited tests for developing the direct adsorption isotherm test.
CFA and Cement Sample Processing The multiple buckets for each CFA source were combined and homogenized in a rotating drum mixer and a 7 to 9 lb 10 grab sample was obtained for the characterization study. The remainder was placed in a watertight plastic drum, labeled, and placed in storage. The grab sample was further homog- enized by quickly mixing it in a plastic bag and then a g sub-sample was extracted using a sampling tube.
The port- land cement used in the study was all obtained from the same production lot. The complete process used for obtaining sam- ples of ash for the various tests is discussed in Attachment C.
These materials were tested prior to use to deter- mine their basic chemical or physical properties and compli- ance with relevant specifications. All of these materials are covered by standards except the inert fillers.
The reported properties of these inert filler materials are summarized in Attachment C. However, some properties were measured using non-standard test methods e. The standard tests were generally conducted twice i. CFA sources and tests. Table 3. Cement PC-2 was used for the strength and pozzolanic activity indices, auto- clave expansion, and air content tests. The samples were fused using a lithium borate flux to produce a glass disk.
Specific samples were also pressed into pellets to better evaluate the sulfur content of the ashes. The mortars were mixed in nine cube batches; the index values were calculated after 7, 28, and 90 days of standard curing i.
Control mixtures containing only cement were also mixed on each day. The precision of the test method was evaluated by making seven replicate mixtures containing CFA.
The mortars were mixed in six cube batches; the index values were calculated after 7 and 28 days of accelerated curing i. A control mixture containing only cement was also mixed on each day. The results reflect the average of three tests at 7 and 28 days.
The precision of the test method was evaluated by making six replicate mixtures contain- ing CFA. Control mixtures containing only cement were also mixed on most days to accompany the mixtures containing CFA. At least three repetitions individual batches mixed on different days with each control cement i. In addition, a set of control specimens was made using a very-low-alkali cement that exhibited a nearly negligible expansion i.
Test results provided the average of tests on three specimens after 14, 28, and 56 days of accelerated curing i. Selected specimens were monitored until 90 days. INF-2 was also included in the study to evaluate the effect of cement replacement. The precision of the test method was evaluated by testing six replicate mixtures. Test specimens were backpacked into a sample holder and then scanned from about 5 to 70 degrees two-theta using a copper x-ray tube and diffracted beam monochromator.
Step-size and counting time were selected to produce reasonably smooth diffractograms. Glass con- tent was estimated using the diffuse scattering halo present in the diffractograms. Both the relative intensity ratio method RIR and the Rietveld method were used to obtain estimates of phase and glass concentrations. The quantitative measure- ments were repeated multiple times to produce an estimate of the precision of the determinations.
In addition, the residue from the thermal analysis test was analyzed using XRD to determine the mineralogy of the devitrified glass. The CFA sources listed in Table 3. Three 2 in. A compressive testing machine of , lb capacity specifically fitted for testing mortar cubes was used for all tests. Another approach was to modify the KHI previously used for evaluating the reactivity of blast furnace slags Keil, ; Lea, ; Hooton and Emery, ; Pal et al.
The KHI is expressed by Equation 3. The difference between this method and other strength activity tests is the KHI test allows for separation of the pozzolanic and hydraulic effects from the physical filler effects. Mortar cubes were tested at ages of 7, 28, and 56 days. The ground quartz specified in the original Keil method was replaced with inert fillers INF-1, INF-2, and INF-3 in an attempt to find an appropriate commercially available filler material for use in the test method.
Strength tests were con- ducted at 7, 28, and 56 days of age. These were the only tests conducted with PC-4 and were undertaken to verify results obtained with PC The results of these tests are provided in Attachment C.
Characterization of the Effects of Carbon on Air Entrainment Foam Drainage Test The objective of the foam drainage test is to assess inter- actions between cement, or combinations of cementitious materials, and AEA solutions.
The procedure was evaluated to determine if differences in the potential for a CFA to affect air entrainment could be detected. These different procedures are reported in the literature: Gutmann , Cross et al. The test methods by Cross et al. These test procedures were modified by using only CFA as the cementi- tious material and were evaluated to determine if CFA and AEA interactions could be detected further discussion of the methodology is provided in Attachment C.
The test results indicated that, in most cases, the test does not adequately dis- tinguish the effects of CFAs with significantly different levels of LOI on air entrainment. Because the other tests evaluated in this research showed more promise e. Another minor yet significant vari- able is the dimensions of the test container. Because of the extensive number of published tests and the multiple varia- tions of the test, it was decided to evaluate these tests for subjec- tivity, reproducibility, and ease of use additional discussion of the test evaluation is presented in Attachment C.
The evalua- tion found the test proposed by Harris et al. However, a num- ber of modifications were considered. Standardized Shaking The process of evaluating the various foam index tests also considered ways of modifying and improving each test with regards to accuracy, reproducibility, or ease of performance. One common concern with all tests was the reproducibil- ity of the agitation process.
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