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371.
Lin Li Craig H. Benson Tuncer B. Edil Bulent Hatipoglu 《Geotechnical and Geological Engineering》2008,26(2):177-187
A case history is described where Class C fly ash was used to stabilize recycled pavement material (RPM) during construction
of a flexible pavement in Waseca, MN, USA. The project consisted of pulverizing the existing hot-mix asphalt (HMA), base,
and subgrade to a depth of 300 mm to form RPM, blending the RPM with fly ash (10% by dry weight) and water, compacting the
RPM, and placement of a new HMA surface. California bearing ratio (CBR), resilient modulus (Mr), and unconfined compression (qu) tests were conducted on the RPM alone and the fly ash stabilized RPM (SRPM) prepared in the field and laboratory to evaluate
how addition of fly ash improved the strength and stiffness. After 7 days of curing, SRPM prepared in the laboratory had CBR
ranging between 70 and 94, Mr between 78 and 119 MPa, and qu between 284 and 454 kPa, whereas the RPM alone had CBR between 3 and 17 and Mr between 46 and 50 MPa. Lower CBR, Mr, and qu were obtained for SRPM mixed in the field relative to the SRPM mixed in the laboratory (64% lower for CBR, 25% lower for
Mr, and 50% lower for qu). In situ falling weight deflectometer testing conducted 1 year after construction showed no degradation in the modulus of
the SRPM, even though the SRPM underwent a freeze–thaw cycle. Analysis of leachate collected in the lysimeter showed that
concentrations of all trace elements were below USEPA maximum contaminant levels. 相似文献
372.
M. Rama Rao A. Sreerama Rao R. Dayakara Babu 《Geotechnical and Geological Engineering》2008,26(2):189-197
Expansive clays swell and shrink seasonally when subjected to changes in the moisture regime causing substantial distress
to the structures built in them. Techniques like sand cushion and cohesive non-swelling soil (CNS) layer have been tried to
arrest heave and consequent damages to structures. Sand cushion has been proved to be counter-productive. Studies have indicated
that even though CNS layer was effective initially, it became less effective after the first cycle of swelling and shrinkage.
Research carried out by the authors, using cement-stabilized fly ash as a cushioning material, has shown that it was quite
effective in arresting heave. Fly ash cushion, stabilized with 10% cement with thickness equal to that of the expansive soil
bed reduces heave by about 75% in the first instance. With subsequent swell-shrink cycles, the performance further improves,
unlike in the case of a black cotton soil provided with a CNS cushion. At the end of fourth cycle of swelling, the reduction
in the amount of heave is as high as 99.1%. 相似文献
373.
Rachna Raj 《Journal of Earth System Science》2008,117(1):41-48
This communication reports the occurrence of an ash layer intercalated within the late Quaternary alluvial succession of the
Madhumati River, a tributary of the lower Narmada River. Petrographic, morphological and chemical details of glass shards
and pumice fragments have formed the basis of this study. The ash has been correlated with the Youngest Toba Tuff. The finding
of ash layer interbedded in Quaternary alluvial sequences of western Indian continental margin is significant, as ash being
datable material, a near precise time-controlled stratigraphy can be interpreted for the Quaternary sediments of western India.
The distant volcanic source of this ash requires a fresh re-assessment of ash volume and palaeoclimatic interpretations. 相似文献
374.
A. Guedes B. Valentim A.C. Prieto A. Sanz D. Flores F. Noronha 《International Journal of Coal Geology》2008,73(3-4):359-370
Fly ash samples were collected from a Portuguese power plant that burns low-sulphur coals from South Africa, U.S.A., Colombia, and Australia. The fly ashes were collected from the hoppers of the economizers, air heaters, electrostatic precipitators, and from the stack. The power plant air monitoring system was also sampled. The fly ash characterization was conducted by micro-Raman spectroscopy (MRS). The micro-Raman spectroscopic analysis permitted an efficient identification and characterization of different inorganic and organic materials present in fly ash: quartz, hematite, magnetite, calcite, glass, aluminium and calcium oxides, and different types of organic constituents.The study of the structural evolution of the unburned carbon/char material during their path through the power plant, though the use of Raman spectra and Raman parameters reveal that despite the high temperatures they reached, these materials are still structurally disordered. However, a structural evolution occurs in the char from the economizer up to the electrostatic precipitators where the char is structurally more disordered.The different features of the Raman spectra observed for carbon particles collected from the stack, together with the high range of variation of the Raman parameters, confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot).The filters from the surroundings contain a variety of carbon particles with Raman parameters different from the ones obtained in the fly ash hoppers and stack. These are diesel particles as indicated by the values of WD1, FWHMD1, FWHMG, WG and ID1/IG obtained. 相似文献
375.
376.
Volcanism is a natural climate force that causes variations in temperatures. The Aptian Oceanic Anoxic Event 1a (OAE-1a) was preceded by a prominent negative C-isotope excursion attributed to major volcanism of the Ontong Java plateau (OJP), which presumably resulted in a pCO2 increase and a climatic change. However, the OJP alone may not adequately explain some important isotopic signatures such as the negative strontium-isotope excursion from 125 Ma to 113 Ma that is recorded in the corresponding marine deposits. We present an independent and hitherto undocumented case, the giant Aptian volcanism in the Songliao Basin and northeast Asia (SB-V) on the Cretaceous active continental margin between the Eurasian and the Pacific plates, which covered an area of ca. 2.3 × 106 km2, nearly matching the simultaneous case of the OJP. Intensive strong, explosive volcanic eruptions of the SB-V occurred at 121–109 Ma and introduced a large volume of fine-grained volcanic ash and degassing volatiles into the atmosphere. The Aptian isotopic ratios (87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb) of marine carbonates from the Mid-Pacific shift in values between their Barremian pre-excursion high values and the negative magmatic values of the SB-V. The transient global cooling at the onset of the OAE-1a coincided with the beginning of the violent acidic eruption of the SB-V (119.9–120.2 Ma). We therefore infer that the SB-V must have played a role in the Aptian global climatic changes and OAE-1a through the heavy fall of volcanic dust and the outgassing of aerosol and greenhouse gases. 相似文献
377.
378.
379.
青海丰台遗址是一处卡约文化遗址,约3200～2800aB.P.。通过对其灰坑中提取的淀粉粒分析了该区域当时先民们对植物利用情况。灰坑中包含了来自于小麦族（小麦属、大麦属）、粟、百合科及块根块茎类植物的淀粉粒,还包括可能来自于高粱（Sorghum bicolor(L.)Moench）、豆科豇豆属,或豌豆属及鹰嘴豆属的淀粉粒,但是高粱在该遗址中以前还未发现过,是否含有高粱淀粉粒需要其他证据验证。从发现的淀粉粒种类来看当时先民们利用植物的多样性。另外,结合浮选结果发现,该遗址中小麦族植物包括大麦（Hordeum vulgare L.）和小麦（Triticum aestivum L.）,但以大麦为主,可能是先民们对气候环境变化适应的结果。 相似文献
380.