Lupine Publishers Environmental and Soil Science

Friday, 11 December 2020

Lupine Publishers | Stiffening of Clay by the Use of Paper Fly Ashes

Lupine publishers | Open Access Journal of Environmental and Soil Sciences

Abstract

To improve the stiffness and bearing capacity of natural soils, traditionally lime or cement is used. This research focuses on the performance of an industrial residual product paper fly ash (generally treated as waste) as an alternative binder for soil stabilization. The present report summarizes the research carried out at the Ghent University. The research focused on the stabilization of kaolinite and bentonite clay. The experimental research consisted on monitoring the evolution of stiffening by time of a number of soil samples mixed with paper fly ashes. To this end, a non-destructive test was implemented to evaluate the small-strain stiffness of each specimen at different stages of curing. Kaolinite clay was chosen as reference clay material for stabilization. A commercial processed kaolin Rotoclay HB (Goonvean, St. Austell, UK) was used in this investigation. Kaolinite shows relatively low plasticity levels comparable to commonly found fine-grained soils. The non-destructive free resonant column test was used to evaluate the small-strain Young’s modulus (E0 ) of the soil specimens after stabilization with paper fly ash. The limited scatter of data suggests good repeatability and reliability. The first conclusions with regard to the application for soil stabilization are discussed.

Keywords: Soil Improvement; Paper Fly Ashes; Lime; Kaolinite; Bentonite; Free Resonant Column Test

Introduction

A limited bearing capacity of the subsurface may be the result of a bad quality and/or an insufficient compaction of the natural soil. For sandy soils the technique of improvement is in many cases compaction. For fine graded soils, and in case compaction doesn’t result in a higher bearing capacity, the soil can be mixed with stabilizing material. Traditionally lime or cement is used. Åhnberg [1] made an evaluation of the effect of different binders on the mechanical characteristics of clayey soils. In this research no direct relation could be made between the types of binders and the results of the modified soil characteristics. The authors confirmed that the change in strength of the soil depends on a number of factors. Previous research at the Ghent University proved that mixing paper fly ash improved the bearing capacity. Recently more research was carried out to confirm these results. Paper fly ash, with a significant lime content, results from the process of paper production. It is a residual product after incineration of paper and wood. The working effect of paper fly ashes as a binder are still insufficiently studied. The paper fly ashes discussed in this article have a large amount of free lime (9%). When paper fly ashes are mixed with clay two reactions occur [2]. In the first reaction there is an exchange of the cations in the soil and a flocculation immediately after mixing the binder with the clay. The second reaction is the pozzolanic reaction. This is a very slow reaction between CaO, H₂O, SiO₂ and Al₂O₃. In a previous study, made by Servaco [3] a lot of test results on the composition of paper fly ash were examined. In a later research Libbrecht [4] proposed 5% as an optimum percentage for mixing with silt. For this content the maximum CBR-value was reached. Out of a detailed research on the characteristics of paper fly ashes, made by the BAS Research and Technology Center [5], it could be concluded that paper fly ash contains a large percentage (13 %) of the mineral belite. Belite is also found in Portland cement and ensures the strength development over time. In 2018 [6] a first research on the influence of paper fly ashes on the stability of clay was made.

Materials and Methods

Kaolin clay was chosen as reference clay material for stabilization. A commercial processed kaolin Rotoclay HB (Goonvean, St. Austell, UK) was used in this investigation. Kaolinite shows relatively low plasticity levels, comparable to commonly found fine-grained soils. Table 1 summarizes some properties of this material. A freshly produced batch of paper fly ashes was provided by ATA International (commercial name Ecolime). The stiffening of Kaolin clay specimens stabilized with Ecolime at 6% dosage was monitored for a curing period of almost 200 days. The dosage of Ecolime was set based on the Eades & Grim test which determines the saturation dosage [7]. The test consists in measuring the pH of different soil-additive mixtures at different dosages and comparing them to the pH of the additive saturated solution (reference pH). The results of this test are illustrated in Figure 1. The upper boundary of Ecolime dosage for Kaolin clay treatment is about 6% in dry weight. Higher amounts of additive will produce no additional improvement. Therefore, it was decided to prepare samples at a dosage of 6%. Kaolin clay and Ecolime (at a dosage of 6%) were initially dry mixed in a dough mixer to ensure homogeneous distribution of the additive. Then, water was added to bring the mixture close to the optimum water content for standard Proctor compaction (w = 27%). Then, a number of specimens were compacted and cylindrical samples with a diameter of 50 mm and height of 100 mm were obtained through cutting and trimming. All specimens were allowed to cure in a humid environment at constant temperature of about 20^oC.

The non-destructive free-free resonant column test was implemented here to evaluate the small-strain Young’s modulus (E₀) of the soil specimens stabilized with Ecolime. The testing setup is illustrated in Figure 2. It consists of an accelerometer put in contact with the soil specimen at one end. At the other end, the soil specimen is impacted with a light hammer. The sample is laid horizontally on soft foam. The impact of the hammer generates waves of a broad range of frequencies. However, only the waves at a frequency similar to the fundamental frequency of the specimen will be amplified on its way to the accelerometer. Then, the signal captured with the accelerometer can be analyzed to evaluate the fundamental frequency of vibration of the specimen. Finally, this frequency can be correlated to the stiffness E₀ through elasticity theory based formulations. The stiffening of kaolinite and kaolinitebentonite clay specimens stabilized with Ecolime at 6% dosage was monitored for a curing period of almost 200 days. The samples KEx refer to samples of kaolinite clay stabilized with 6% of Ecolime. The Figure 4 shows the comparison between the increase of stiffness between samples of kaolinite clay (KEx) and samples of a mixture of kaolinite clay (70%) (KEx) and montmorillonite (bentonite) clay (30%) (KBEx).

Results and Discussion

The results are illustrated in Figures 3 & 4. Figure 3 shows E₀ -measurements on 12 specimens with the same dosage of 6% and natural kaolinite (K). The limited scatter of data suggests good repeatability and reliability. Moreover, the non-destructive technique produced a well-defined and continuous E₀ increasing pattern. E₀ was observed to increase almost linearly with time up to the 60th day of curing approximately. After that, the stiffness increasing rate significantly decreased. The evolution of E₀ reflects the evolution of interparticle cementation in the clay fabric due to the addition of paper fly ash. However, the beneficial impact of the additive may also be affected by the composition and properties of the natural soil and local groundwater. In Figure 4 a difference can be seen between the kaolinite and the kaolinite-bentonite samples. The kaolinite-bentonite samples have a bigger initial E₀ - modulus than the samples made from pure kaolinite. The different properties of the various families of clay minerals can be explained partly by the different levels of activity on the surface of the clay particle. Expansive clay minerals such as bentonite exhibit a high cation exchange capacity, whereas non-expansive clay minerals like kaolinite have a relative low cation exchange capacity.

Conclusion

The laboratory tests, in particular the free resonant column tests, indicate that a stabilization with paper fly ashes or with lime have similar properties. For soils with a high amount of kaolinite, paper fly ash has the same stabilization effect as lime. >For soils with a high amount of bentonite, lime is a better binder. After 28 days the effect of stabilization with paper fly ash is comparable with the stabilization with lime. Although the results are very promising, it remains important to study the chemical reactions in the sample with the X-ray diffraction method. The beneficial impact of the additive may also be affected by the composition and properties of the natural soil and local groundwater. More research is needed to confirm these results.

https://lupinepublishers.com/environmental-soil-science-journal/pdf/OAJESS.MS.ID.000150.pdf

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Friday, 4 December 2020

Lupine Publishers | We Can Cut Global Warming

Lupine Publishers | Open Access Journal of Environmental and Soil Sciences

Short Communication

It’s time to recognize that Global Warming is a FACT (visible in the NASA photo below), which means the U.S. needs to reduce our CO₂ emissions by a national energy transition from oil and carbon to hydrogen and solar fuels. Don’t believe it? Just look at the photos and ask every “Global Warming denier” (especially President Trump) to explain the 300,000 square miles of sea-ice between the ice cap over the North Pole and the red line that melted between 1979 and 2012. Melting polar ice along with melting glaciers (which have turned into flowing rivers in the last century) have produced water that had to go somewhere -- and that’s into the world’s oceans (whose warming melted the polar sea-ice from the bottom). Warm oceans breed hurricanes. After this year’s example of coastal flooding, any residual doubts should be gone just ask the population of Houston and other communities flooded from this year’s hurricanes. Comparable changes thousands of years ago took centuries -- not just the 33 years between 1979 and 2012. There’s scientific consensus that Global Warming is largely due to a greenhouse effect from emissions of carbon dioxide. The major sources of CO₂ are oil and coal, fossil fuels that have been the principal energy sources for industrial societies. America’s substantial contribution to Global Warming has received virtually no media coverage in the U.S.

The world’s leading sources of CO₂ emissions in 2007 were China (6.0 Billion tons) and the U.S. (5.768 Billion tons); no other country emitted over Russia’s 1.6 Billion tons (OECD in Figures 2009 [Paris: OECD, 2009], pp. 48-49). Global warming can be greatly reduced if not ended by substituting zero CO₂ emitting fuels (hydrogen and solar energy) for CO₂ polluting fossil fuels (oil and coal) -- and using solar panels with new battery technologies to capture this zero CO₂ energy source. Our country ought to take the lead, stimulating our market economy to complete current work on improvements like 3D sheets of solar collectors to cover the roof-tops of houses as well as hydrogen fuel-cells and larger capacity batteries for American autos and trucks. Apart from two articles in the “Science Times” section of New York Times (Jan. 3, 2016, pp. D1-3), most Americans haven’t been told that Europeans are developing the new technologies needed for Zero-CO₂ fuels. America will get nowhere by following Donald Trump (whose idea of economic development is the $8Billion dollar Dakota Access pipeline as a gift to America’s oil cartel and “saving” the coal industry) will get America nowhere. Since all major automakers have developed pollution free hydrogen cars and many are following Tesla toward electric autos, within a decade or two new oil pipelines will be obsolete. Solar panels are already covering rooftops.

Further innovations in the production and implementation of hydrogen and solar energy are needed to complete the transition away from fossil fuels by cutting costs and improving efficiency. To implement these goals, lithium ion batteries with greatly increased storage capacity (needed because sun shines in daytime, electricity is used at night) are being developed. Especially for suburban and rural housing, development of more efficient inexpensive solar collectors and batteries will give many households a self-sufficient energy supply. The investments needed to bring to market less expensive zero CO₂ fuels will not only generate economic activity in the U.S. (a boom that will create thousands of jobs); it will also multiply technologies patented in America that can find international markets (like GM’s hydrogen patents sold to Audi in Europe).

America’s mass media and educated public should demand government subsidies to speed the technological developments needed for a more rapid transition to the age of zero CO₂ fuels. How long will it take for American businessmen, politicians, and journalists (not to mention our silent scientists) to recognize the economic boom that will accompany the transition from fossil fuels to the age of solar and hydrogen energy .

This NASA satellite photograph of the area covered by Arctic sea-ice on Aug. 26, 2012 shows that the melting of the North Pole’s icecap in the 33 years since 1979 covered at least 300,000 square miles. In this photo, the Polar sea-ice had the smallest extent that had ever been recorded in more than three decades of satellite measurements, according to scientists from NASA and the National Snow and Ice Data Center. This melting is due to human activities because the area between the red line and the current sea ice is too large to have melted so rapidly from natural causes. (Source: http://www.nrdc.org/globalwarming/qthinice.asp). NOTE: This photograph of the sea-ice covering the North Pole and the complementary photo of the Northern Pacific Ocean (Figure 2) should suffice as evidence that Global Warming has had similar effects in the melting of sea-ice in both areas. This confirms the evidence that sea-ice melts on its lower surface in contact with the ocean (not from the upper surface in contact with the earth’s atmosphere).

Arctic sea ice extent for December 2017 averaged 11.75 million square kilometers (4.54 million square miles), the second lowest in the 1979 to 2017 satellite record. This was 1.09 million square kilometers (420,900 square miles) below the 1981 to 2010 average and 280,000 square kilometers (108,100 square miles) above the record low December extent recorded in 2016. Extent at the end of the month was below average in the far northern Atlantic Ocean and Barents Sea, slightly above average in western Hudson Bay, and continued to be below average in the Bering and Chukchi Seas. Near-average conditions prevailed along the eastern coast of Greenland and in the Sea of Okhotsk. Arctic sea ice extent for December 2017 averaged 11.75 million square kilometers (4.54 million square miles), the second lowest in the 1979 to 2017 satellite record. This was 1.09 million square kilometers (420,900 square miles) below the 1981 to 2010 average and 280,000 square kilometers (108,100 square miles) above the record low December extent recorded in 2016. Extent at the end of the month was below average in the far northern Atlantic Ocean and Barents Sea, slightly above average in western Hudson Bay, and continued to be below average in the Bering and Chukchi Seas. Near-average conditions prevailed along the eastern coast of Greenland and in the Sea of Okhotsk. Read scientific analysis on Arctic sea ice conditions. We provide an update during the first week of each month, or more frequently as conditions warrant.

E.O. Wheeler’s 1921 photo of West Rongbuck Glacier at the foot of Mount Everest (the tallest peak in the center of the photos, and David Breashears’ 2009 photo showing a flowing river and bare mountains at the same Himalaya scene (http://www.nrdc. org/globalwarming/qthinice.asp). Unlike the cycles of the earth’s warmer temperature thousands of years ago (studied in deep Antarctic ice), this current evidence of Global Warming took place in just 88 years. Combining Figures 1 & 2 provides images of changes at both sea level (both the North and South Poles) and in the high Himalayan mountains. Water from this melting of massive amounts of ice and snow is producing rising sea levels along our shores that have already flooded Miami and Houston when hurricane winds produce surging seas.

https://lupinepublishers.com/environmental-soil-science-journal/pdf/OAJESS.MS.ID.000149.pdf

https://lupinepublishers.com/environmental-soil-science-journal/fulltext/we-can-cut-global-warming.ID.000149.php