The quality and performance of hotmix asphalt concrete will be different for each day. All these properties are related to the mineralogy, structure and chemistry of the coarse aggregate. The rock they are mining consists of the Jagger Bend Formation deposited in the Permian period.
Much of the material mined in the quarry is composed of lower quality shale and sandstone lenses as depicted in Figure 3. It is the middle 6 feet that contains all the rock that produces poor quality aggregate. Working face of the black pit showing four different units varying in quality as an assembly.
Researchers conducted a detailed investigation of the Clements Pit in the San Angelo District (Figure 8). Bioturbation (burrows) was abundant in good-quality aggregate (Figure 9), and there was very little poor-quality rock in this particular section of the quarry. Vesicular basalt from top of Smith Pit with red clay-filling vesicles (air bubbles).
The aggregates in the Smith Pit are very similar to the Behne Pit, but they appear to be more weathered near the top of the quarry (i.e., the ground surface).
Ray Diffraction of HMAC Samples
The fine clay (Figure 21) is dominated by smectite (S), with smaller amounts of kaolinite (K), mica (M) and goethite (G). XRD of the sludge fraction of limestone pit number 2 shows quartz as the dominant mineral. XRD patterns of the fine clay fraction from limestone pit #2 showing a predominance of smectite (S).
The mineralogy of the Limestone Cave #1 sample is similar to that of Limestone Cave #2. This XRD pattern is of the –200 fraction from Limestone Pit #1 before it was subjected to any chemical pretreatment (to remove calcite) or size fractionation. Many transportation departments commonly use the Al2O3 content or insoluble residue as an indicator of the clay content of the aggregate source based on observations in several research studies (Shakoor et al., 1982).
Based on the limited data, there is no clear correlation between the aggregate quality measured by these two tests and the alumina content. Based on observations from this research project and other work done by the researchers, the authors must agree with Mckirahan et al. 2004) on the importance of clay mineral type in influencing durability. Based on the data obtained in this study, the researchers speculate that clay mineralogy may be the most important factor controlling aggregate durability.
From the data on the two limestone aggregates used in the HMAC portion of this project, one would have to conclude that there is a certain threshold of clay that causes adverse effects on aggregate quality because both aggregates contained very similar clay rheologies, but the lower quality aggregate contained a higher percentage of smectite. Kandhal and Parker (1998) conducted a thorough investigation of hot mix asphalt concrete performance issues and current test methods used to identify poor quality coarse and fine aggregates. The question is not what a poor quality aggregate is, but how much of a poor quality aggregate can be added to hot mix asphalt concrete and maintain the quality of the pavement layer.
The Project Monitoring Committee informed the researchers that most of the coarse aggregate problems when using hot asphalt concrete in Texas are limestone. First, the researchers wanted to examine the effects of poor quality coarse limestone aggregate on HMAC performance. With the exception of the Micro-Deval and sulfate strength tests, a brief description of the above aggregate tests and their results is presented below.
Sample 2 Average
D and MSS Samples over Time
The number of quarry samples R2 Time (years) .. MSS) increases, there is a decrease in the correlation of the two test methods as observed in the lower values of R2. There is a one-to-one correlation between the M-D and MSS test results as illustrated in Figure 41, but there is a large difference in results. For example, if the MSS percent loss is 31, then one can be 95 percent confident that the M-D percent loss will be between 18 and 44.
Micro-Deval and magnesium sulfate resistance test results for the Clements pit are shown in Figure 41. The scatter in the data indicates difficulty in obtaining reproducible results due to the variability of the material from sample to sample. Micro-Deval and magnesium sulfate resistance test results for the other nine quarries are shown in Appendix C.
D and MSS Samples Lab Evaluation
- RAY FLUORESCENCE DATA
Over the course of this study, aggregate absorption continued to emerge as a contributing factor in all test results. This correlation should not be surprising, since the test for sulfate health relies on the formation of sodium or magnesium sulfate crystals in the pores of the rock, causing the aggregate to break down. 2000) statistically determined that at a 95 percent confidence interval, aggregates with an absorption of less than 2.1 percent exhibit less than 30 percent MSS loss if the M-D loss is less than 25 percent. It is well documented that soft, absorbent aggregates are less durable (Harvey et al., 1974; Hudec and Rogers, 1976) than a hard, nonporous aggregate of the same mineralogy.
Perhaps acceptance criteria could be developed based on mineralogy and could actually reflect how the aggregate performs in the field. The research carried out in this project was divided into two phases, with the first phase focusing on the detection of poor quality aggregates in the field and the second phase on how much poor coarse aggregate can be added to the HMAC pressure without causing premature failure. pressure failure. road construction. Most of the results of the first phase are presented in Report 0-4523-1, but some results are presented in the first two chapters of this report.
All research conducted in Phase II is presented in the remainder of this report. The introduction of marginal, coarse limestone aggregates into the mixture had only a small clear influence on the rutting potential of the mixture as measured by the Hamburg test or derived from the dynamic modulus test. The introduction of marginal coarse limestone aggregates on the fatigue life derived from the dynamic modulus was not clear.
Using the AIMS imaging device revealed that surface texture can be used to separate the coarse aggregate from the poor quality limestone used in this project. In order to place limits on what level of marginal materials has a serious impact on the performance of the mixture, it is important to include the repeatability of the overlap test. In repeatability studies conducted by Zhou (personal communication), it was concluded that using triplicate samples the average number of cycles to failure will be within 10 percent of the average for that mixture.
The quality of the basalt seems to be tied to the amount of decomposition or. Based on the Micro-Deval results for the three limestones evaluated in Chapter 3, a conservative estimate for obtaining less than 10 percent poor-quality coarse limestone aggregates would be a Micro-Deval percent loss in excess of 20. In Transportation Research Record # 1837, Washington D.C., p. 2000) Loaded Wheel Testers in the United States: State of the Practice.
In Geological Association of Canada Program with Abstracts, p. 1998) Laboratory repeatability of the Hamburg wheel tracking device and replicating wheel tracking devices among different laboratories. In Journal of the Association of Asphalt Paving Technologists, v. 1998) Aggregate Tests Related to Asphalt Concrete Performance in Pavements.
