Showing papers on "Lime published in 1999"

Arsenic immobilization by calcium arsenate formation

Abstract: Lime additions to arsenic-containing wastes have been proven to be beneficial in reducing the mobility of dissolved arsenic, presumably through the formation of low-solubility calcium arsenates. Ho...

Effectiveness of Portland Cement and Lime in Stabilizing Clay Soils

Abstract: Pavement subgrades constructed with clay soils can cause significant pavement distress because of moisture-induced volume changes and low subgrade support values. Lime is well known for its ability to stabilize plastic clays; however, portland cement also provides highly effective clay stabilization, usually with the added benefit of higher strength gain. Stabilizing clays with cement or lime can improve subgrade properties at a lower cost than either removing and replacing material or increasing the base thickness to reduce subgrade stress. The clay soil stabilization mechanism for the calcium-based stabilizers portland cement and lime is reviewed. These materials modify soil properties through cation exchange, flocculation and agglomeration, and pozzolanic reaction. Additionally, cement provides hydration products, which increase the strength and support values of the subgrade materials as well as enhance the permanence of the treatment. Comparative laboratory and field performance studies by others, fo...

Lime-induced loss of soil organic carbon and effect on aggregate stability

Abstract: We investigated the decline in soil organic C on an Oxic Paleustalf (red earth) as a result of lime application (1.5 t CaCO(3) ha(-1)) in New South Wales, Australia and determined how loss of organic C was related to soil aggregate stability changes. Organic C lost as a result of liming was mainly (up to 84% of total loss) in the form of light fraction (specific gravity < 1.8) bound to macroaggregates. With liming, a given level of aggregate stability was achieved at a lower soil organic C level in limed soil (e.g., total C level for a 50% aggregate stability was 13.0 and 17.8 g kg(-1) for limed and unlimed soils, respectively). Increased aggregate stability in limed soils suggested formation of new bonding involved Ca bridges.

Early strength development and hydration of alkali-activated blast furnace slag/fly ash blends

Abstract: This study concerns the effect of two types of fly ash and the addition of lime on the strength development and hydration of sodium hydroxide- and sodium silicate-activated slag/fly ash blends which consisted of 50% fly ash and 50% slag by mass. Performance was compared to that of 100% slag cements. When NaOH was used as an activator, the slag replacement with ASTM Type F fly ash did not show a significant effect on either the strength development or hydration; Type C fly ash did not affect the strength development, but affected the hydration process due to the presence of C3A in the fly ash. Both fly ashes had a significant effect on the hydration and strength development when Na2SiO3 was used as an activator. The addition of a small amount of hydrated lime significantly increased the early-age strength but slightly decreased the later-age strength of the activated slag/fly ash blends. Measurement of the heat evolution during hydration indicated that the addition of the hydrated lime had a slight effect ...

Biological and chemical properties of arable soils affected by long-term organic and inorganic fertilizer applications

Abstract: Using soils from field plots in four different arable crop experiments that have received combinations of manure, lime and inorganic N, P and K for up to 20 years, the effects of these fertilizers on soil chemical properties and estimates of soil microbial community size and activity were studied. The soil pH was increased or unaffected by the addition of organic manure plus inorganic fertilizers applied in conjunction with lime, but decreased in the absence of liming. The soil C and N contents were greater for all fertilized treatments compared to the control, yet in all cases the soil samples from fertilized plots had smaller C:N ratios than soil from the unfertilized plots. The soil concentrations of all the other inorganic nutrients measured were greater following fertilizer applications compared with the unfertilized plots, and this effect was most marked for P and K in soils from plots that had received the largest amounts of these nutrients as fertilizers. Both biomass C determined by chloroform fumigation and glucose-induced respiration tended to increase as a result of manure and inorganic fertilizer applications, although soils which received the largest additions of inorganic fertilizers in the absence of lime contained less biomass C than those to which lime had been added. Dehydrogenase activity was lower in soils that had received the largest amounts of fertilizers, and was further decreased in the absence of lime. This suggests that dehydrogenase activity was highly sensitive to the inhibitory effects associated with large fertilizer additions. Potential denitrification and anaerobic respiration determined in one soil were increased by fertilizer application but, as with both the microbial biomass and dehydrogenase activity, there were significant reductions in both N2O and CO2 production in soils which received the largest additions of inorganic fertilizers in the absence of lime. In contrast, the size of the denitrifying component of the soil microbial community, as indicated by denitrifying enzyme activity, was unaffected by the absence of lime at the largest rate of inorganic fertilizer applications. The results indicated differences in the composition or function of microbial communities in the soils in response to long-term organic and inorganic fertilization, especially when the soils were not limited.

Long-term effects of fertilizer on soil nutrient concentration, yield, forage quality and floristic composition of a hay meadow in the Eifel mountains, Germany.

Abstract: A long-term fertilizer experiment, which was set up in 1941 on extensively grazed heathland, naturally dominated by Calluna vulgaris L. and Nardus stricta L., is presented. The turf layer was grubbed and reseeded with a grass/legume mixture, and plots were fertilized with (a) lime only as calcium (including magnesium), (2) lime and nitrogen (Ca/N), (3) lime, nitrogen and phosphorus (Ca/N/P2O5) and (4) lime, nitrogen, phosphorus and potassium (Ca/N/P2O5/KCl and Ca/N/P2O5/K2SO4). Since 1941 these experimental plots have been mown but not grazed. After 50 years of imposing the experimental treatments, dry-matter (DM) yield was found to be positively affected by N, P and K application. Soil N and P concentrations were significantly higher in fertilized than in unfertilized plots. No differences in soil K concentration were found between the two treatments with KCl and K2SO4. Net energy concentration in the plant DM was highest with the Ca/N treatment, but differences were slight. Crude protein concentrations varied from about 110 to 170 g kg–1 DM. In all plots and all years protein concentrations were lower in the first cuts than in the second cuts. Considerable differences in floristic composition were found between different fertilizer treatments. The treatments receiving only Ca contained more than sixty species, many of them representative of oligotrophic extensively managed grassland. In fully fertilized plots, herbs were suppressed by tall-growing grasses. In these plots the number of species was low.

Coal Ash Utilization in Asphalt Concrete Mixtures

Abstract: Dwindling supplies and rising costs of natural resources used in road construction as well as concerns over shrinking landfill spaces prompt researchers to investigate the use of waste products, such as coal ash, as substitute materials in highway construction. This research examines the effect of coal ash (i.e., fly and bottom ash) when used as partial replacement of fine aggregate in asphalt concrete mixtures. Specimens were made using three aggregate sources, two ash sources, three ash percentages (0%, 6%, and 8%), and hydrated lime. Selected physical properties (e.g., tensile strength) were measured and statistically analyzed. Results indicated that partial substitution of fine aggregates by coal ash had a moderate detrimental effect on short-term tensile strengths. However, a number of coal ash/lime mixtures met the minimum tensile strength requirements set by the South Carolina Department of Transportation. A limited field study was also conducted to study the environmental effects of coal ash mixtures as detected by heavy-metal concentrations in nearby soils. Results showed that 3 months after placement metal concentrations in soils were not substantially altered.

Elimination of Phosphorus from Waste Water by Crystallization

Abstract: Precipitation by Fe and Al salts or lime, which is the main process used in Germany for phosphorus removal, entails some problems, such as increasing the anion concentration of the water, and problems in recovering the phosphorus from the precipitation sludge. Therefore, a process for phosphorus removal from waste water was developed, which involves a direct precipitation of Calcium phosphate induced by Calcite as the seeding material. The pH was adjusted with lime, but some experiments were done with MgO as well. Basic investigations led to possible applications with both municipal waste waters with low phosphorus concentrations and industrial effluents with considerably higher phosphorus contents of up to 400 mg l−1 P. Continuous bench scale experiments with a stirred reactor to remove phosphorus from the waste water of a motorcar factory were completed. Based on the good results achieved, a full scale device for the treatment of 160 m3 per hour was commissioned in July 1996 and has been run successfull...

Gypsum-cement system for construction materials

Abstract: A composition for use in construction materials, which may be substituted for high performance concrete, patching materials, joint compounds, and the like, such as backer boards or panels, which includes a settable calcium sulfate, preferably a hemihydrate, Portland cement, a finely divided pozzolanic material, lime, and an aggregate, optionally including other additives. The volume ratio of the aggregate to the combined calcium sulfate, Portland cement, pozzolanic material, and lime (a cementitious binder) is equal to or greater than 2/1. Panels made from this composition are useful, particularly when exposed to water since they have good dimensional stability.

Regulation of potential denitrification by soil pH in long-term fertilized arable soils

Abstract: The denitrifying enzyme activity (DEA), denitrification potential (DP) and anaerobic respiration (RESP) together with chemical characteristics were measured in three contrasting soils collected from experimental arable plots that had been subjected to long-term (21–23 years) fertilizer treatments. The plots sampled were either unfertilized or had received either annual inorganic NPK, manure and lime, or inorganic NPK and manure treatments. Addition of inorganic NPK, manure and lime led to large increases in the DEA for two of the three soils, but in the absence of lime, inorganic NPK and manure caused only small increases in DEA compared to unfertilized soils. Both DP and RESP were increased by the addition of inorganic NPK, manure and lime, but were substantially decreased by fertilizer treatments without lime. In most cases there was a simple relationship between soil pH and either DEA and DP, with those treatments that reduced soil pH also leading to reduced denitrification and vice versa. The effects of artificially increasing the pH to a value close to the pH in unfertilized soils (6.3) by addition of NaOH to the soils that had received inorganic NPK, and which had the lowest soil pH values, were to increase substantially DEA, DP and RESP. In soil from one of the sites that had been stored for 5 weeks, the DP values responded differently between the fertilizer treatments. The DP value was lowest in the soil that had inorganic NPK and manure, higher in the soil that received inorganic NPK, manure and lime and it was the highest in unfertilized (control) soil. The soil pH values for these treatments were 4.47, 5.79 and 6.58, respectively. However, when the soil pHs were adjusted by addition of either H2SO4 or NaOH to give a range between pH 2 and 12, the DP values from all three fertilizer treatments showed almost identical responses. The optimum pH value for DP was between 7 and 8 for all three fertilizer treatments. Substrate-induced respiration values from all fertilizer treatments showed a similar trend to DP when the soil pHs were modified. The results show that soil pH was an important factor which in the studied soils controls the microbial community in general and the community of denitrifiers in particular. However, denitrifiers showed a high pH resilience leading to no marked change of the pH optimum for potential denitrification.

The Role of Gypsum in Production of Sulfate-Induced Deformation of Lime-Stabilized Soils

Abstract: Gypsum is a major source of sulfate that produces sulfate-induced heave in lime-treated soils beneath roads and other paved structures. This deformation of pavement subgrade is known to result from the growth of the basic hydrous calcium aluminum sulfate mineral, ettringite, or a silica-bearing analog, thaumasite. The problem occurs in soils that have been treated with lime (CaO) for subgrade stabilization. Gypsum is a common sulfate mineral in sedimentary rocks and soils, and in north Texas it is present in soils developed on the montmorillonitic Eagle Ford Group shales (Upper Cretaceous). Because these soils are highly unstable the conventional treatment for road subgrade includes the addition of lime (CaO) or some other cementitious material such as fly ash or Portland cement. The pyrite-bearing Eagle Ford shale contains gypsum (CaSO4 • 2H2O) produced by reaction of calcium carbonate in the shale with acid sulfate from oxidation weathering of pyrite (FeS2). Sulfate movement upward in the soils can occur by capillarity, and it can be carried downward by infiltration, an often incomplete or interrupted event that leaves gypsum stranded as a soil evaporite. Once formed, the moderately soluble gypsum is retained in the clay-rich soils because of their low hydraulic conductivities, which makes them, in essence, reservoirs of gypsum. Experiments performed for this study confirm that gypsum in a lime-treated subgrade soil can supply sulfate for the growth of the expansive mineral ettringite. No sulfate external to the subgrade of the road is necessary for the reaction to occur. Gypsum is widely distributed in soils and surface outcrops in the western U.S. and should be the first mineral suspected where sulfate-induced heave has been diagnosed. Although gypsum is a moderately soluble mineral, it may be abundant in soils in regions with humid climates if its sulfate is derived from pyritic black shales by oxidation during soil formation. Eagle Ford soils do not produce sulfate-induced heave everywhere that road base has been lime-treated, but the problem is observed most frequently where roads follow streams, or run across low-lying areas or hillside slopes. Other studies have documented a correlation between deformation and major precipitation events. Ground water, soil water, and surface drainage regimes appear to control the specific sites at which severe deformation may take place within the stratigraphically-controlled belts of gypsum-bearing soils. Soluble sulfate tests currently in use to identify soils with the potential for sulfate-induced heave are known for inconsistent results. Total sulfate in a soil is a better predictor of the problem, and when gypsum is the sulfate mineral it can be determined quantitatively by existing laboratory methods. Stratigraphy is a first-order guide to where sulfate-induced heave may occur in the north Texas region, thus geologic maps of the Eagle Ford shale outcrop belt are also indicators of areas of possible sulfate-induced deformation.

An Investigation Into the Mechanism by Which Synthetic Zeolites Reduce Labile Metal Concentrations in Soils

Abstract: The addition of synthetic zeolites and similar materials to metal contaminated soils has been shown to reduce soil phytotoxicity and to improve the quality of plant growth on such amended soils. To gain an understanding of the mechanism by which the phytotoxicity of contaminated soils is reduced when treated with synthetic zeolites, sequential extraction procedures and soil solution techniques have been used to identify changes associated with metal speciation in amended soils. Sequential extraction data and changes in soil solution composition are presented for three different contaminated soils, amended with three synthetic zeolites (P, 4A and Y) at concentrations of 0.5%, 1% and 5% w/w, or lime at 1%. The soils were collected from the site of a metal refinery, an old lead zinc mine spoil tip and from a field which had been treated with sewage sludge. After incubation of the zeolite treated soils for between one and three months, results showed a reduction in the metal content of the ammonium acetate fraction between 42% and 70%, depending on soil, zeolite and rate of addition, compared with the unamended soils. In addition, soil solution experiments indicated that synthetic zeolite amendments were more efficient at reducing metal content than comparable lime treatment. The mechanism by which synthetic zeolites reduce metal bioavailability in contaminated soils is discussed and compared to other amendments.

Response of field-grown maize to applied magnesium in acidic soils in north-eastern Australia

Abstract: Split-plot field experiments, with main plots consisting of various rates of calcitic lime and single rates of dolomite, gypsum, and calcium silicate, were conducted at each of 4 sites to determine the effect of band-applied magnesium (Mg) on maize yield. The sites were acidic with pH values of 4.5, 4.9, 5.0, and 6.1 and exchangeable Mg levels of 0.16, 0.10, 6.0, and 2.0 cmol(+)/kg, respectively. Magnesium significantly (P < 0.05) increased grain yield at the 2 low-Mg sites, both of which were strongly acidic and responsive to lime application, but the nature of the Mg × lime interaction was different at each of the 2 responsive sites. The absence of a response to Mg at lime rates ≥1 t/ha at one responsive site was attributed to the presence of small amounts of Mg in the calcitic lime and/or an improved root environment enabling better exploitation of the soil Mg. Supplying a readily soluble source of Mg in the fertiliser band also resulted in increased grain yield in the gypsum, dolomite, and calcium silicate treatments at the 2 Mg-responsive sites. When the initial soil pH was strongly acidic, exchangeable Mg levels increased with increasing lime rate, suggesting that the small quantities of Mg that occur in the majority of liming materials may be of importance with respect to Mg nutrition. In contrast, gypsum application exacerbated the Mg deficiency at one site. The relationship between grain yield response and soil Mg level across all sites indicated that above an exchangeable Mg level of 0.27 cmol(+)/kg there would be little likelihood of a response to applied Mg.

Hydromagnesite development in magnesian lime mortars

Abstract: The bond which develops during curing in lime paste mortars in the presence of Mg(OH)2 or MgO and moisture in lime paste is a result of the growth of a new phase. Scanning electron microscopy studies along with X-ray analyses show this new phase to consist of common hydromagnesite (Mg5(CO3)4(OH)2,4H2O). This development is accompanied by an increase in the mechanical strengths of lime mortars.