Showing papers on "Lime published in 1983"

Changes in soil properties after 10 years continuous non-tilled and conventionally tilled corn

Abstract: Soil properties were evaluated after 10 years of continuous non-tilled and conventionally tilled corn (Zea mays L.) production on a Maury silt loam (Typic Paleudalfs) soil, which had been in bluegrass (Poa pratensis L.) for 50 years. On limed and nonlimed plots soil samples from 0, 84, 168 and 336 kg/ha N treatments were taken in the 0–5, 5–15 and 15–30 cm layers for determination of organic C and N, soil pH, and exchangeable Al, Mn, Ca, Mg, K. Tillage treatments had no effect on soil bulk density in the 0–15 cm layer. In the 0–5 cm surface layer, organic C and N were approximately twice as high with no-tillage as with conventional tillage; N fertilizer induced a high level of both organic C and organic N. No-tillage decreased soil pH for unlimed plots as compared to conventional tillage, especially at high N-rates, which produced an increase in exchangeable Al and Mn and a decrease in exchangeable Ca down to the 30 cm depth. When lime was applied, the pH of the surface soil was slightly higher under no-tillage. On treatments receiving lime, exchangeable Al and Mn levels were very low with no significant difference in tillage systems. At low rates of N fertilization the 10-year average corn yield was higher for conventional tillage than for no-tillage, but at high rates of N fertilization it was equal or higher for no-tillage treatments receiving lime. Unlimed no-tillage treatments produced lower yields at all N levels during 1975–1979. Deterioration of soil physical properties was not observed.

Egyptian blue — Cuprorivaite a window to ancient Egyptian technology

Abstract: Egyptian Blue, a multicomponent synthetic blue pigment has been recorded in ancient Egypt since the Fourth Dynasty of the Old Kingdom (2600–2480 B.C.). The pigment consisting of cuprorivaite (CaCuSi4O10) with variable amounts of wollastonite (CaSiO3), Cu-rich glass and cuprite (Cu3O) or tenorite (CuO) was prepared by melting the copper-rich ingredient with lime and desert sand. Low melting temperatures (below 742 °C) were achieved by addition of flux-like plant ashes. The high quality of the pigments collected from monuments of the Fifth Dynasty (2480–2320 B.C.) may indicate that the first manufacture was in early dynastic or perhaps predynastic eras. During the reign of Thutmosis III (18th Dynasty, 1490–1436 B.C.) probably bronze filings were first applied as starting material, thus indicating a technological innovation. This new method was employed till the Roman times.

The effects of liming and soil pH on carbon and nitrog contained in the soil biomass

Abstract: The C and N in the biomass of soils from eight grassland field experiments where lime had been applied was determined by the chloroform fumigation method. Lime application increased C and N in the biomass by approximately 30% overall, although there was no effect at two sites. In the unlimed plots basal CO2 production, biomass C, and flush of mineral N production (FN) increased with soil pH. Biomass C and FN were correlated with total N content but not with organic C.Differences in the apparent C/N ratio of the biomass were found in unlimed soils of pH ≤ 4·5 and in those of pH > 4·5, the ratios being 4·2 and 5·8 respectively. For limed soils the ratio was 5·2. It is probable that the chloroform fumigation method is not suited to soils of very low pH, and that the C/N ratio obtained in soils of pH < 4·5 is artificially low.

Modification of soil physical properties by addition of calcium compounds

Abstract: In a soil to which gypsum, calcium carbonate or cement was added, the content of dispersible clay was related to both exchangeable sodium percentage (ESP) and electrical conductivity (EC). The electrolyte concentration in the soil which could be maintained by addition of calcium carbonate was such that an ESP of >3 was required to maintain clay coagulation. Small amounts of gypsum (0.2% w/w) coagulated most of the clay by lowering the ESP and raising the electrolyte concentration. However, the clay gradually dispersed as the soil was subjected to wetting and drying cycles and the electrolyte concentration was decreased. The most efficient use of gypsum would appear to be as small annual additions. The addition of cement resulted in the stabilization of particles 250-2000 µm diameter, i.e. cementation as opposed to coagulation. Both processes resulted in changes to various physical properties and mechanical properties of the soil. It is suggested that both coagulation and cementation in a soil may be achieved by the addition of gypsum and cement or lime, with significant improvements of soil structure. In soils with gypsum added the germination and total yield of dry matter of wheat were improved significantly, but the opposite trend was recorded for soils treated with cement.

Studies of Polymer-Filler Interaction, Network Structure, Physical Properties, and Fracture of Silica-and Clay-Filled EPDM Rubber in the Presence of a Silane Coupling Agent

Abstract: 1. A silane coupling agent (Si-69) reduces the viscosity and increases the scorch lime in silica- and clay-filled EPDM. The cure lime of silica-filled mixes remained unchanged and that of ...

Kiln dust-fly ash systems for highway bases and subbases

Abstract: Production of lime and portland cement results in the annual generation of more than 20 million tons of kiln dust, mostly cement kiln dust. The purpose of this investigation was to determine the effectiveness of substituting kiln dusts for hydrated lime in lime-fly ash-aggregate road base systems. A total of 45 kilm dust samples, including 33 cement dusts and 12 lime dusts, were obtained in accordance with a standard sampling procedure. In addition, 18 fly ashes (including 5 Class C ash samples) and 6 aggregates were included in the sampling program. Kiln dust and fly ash samples were characterized by Trow, Ltd. to determine physical properties and chemical, as well as mineralogical, composition. Optimum kiln dust-fly ash ratios were developed for 66 mix combinations. Kiln dust-fly ash-aggregate compressive strength tests were performed. Engineering properties (durability, volume stability, etc.) of optimum mix combinations were tested and compared with conventional lime-fly ash-aggregate mixtures. Most kiln dust-fly ash-aggregate mixes were comparable to, and in many cases demonstrated higher early strength development than, lime-fly ash-aggregate mixes. Optimum mix strengths for kiln dust-fly ash-aggregate compositions were generally attained at kiln dust-fly ash ratios of 2:1 using cement liln dust and 1:1 using lime liln dust. By contrast, most lime-fly ash-aggregate mixes have lime-fly ash ratios of 1:3 or 1:4. Therefore, higher concentrations of kiln dust are required compared to commercial lime. Mixes containing Class C fly ash developed higher strengths than comparable mixes with Class F fly ash. (FHWA)

Removing uranium from drinking water by metal hydroxides and anion-exchange resin

Abstract: Results of bench-scale testing on uranium removal from a natural water that was chosen as a good representative of uranium-bearing waters indicated that conventional coagulant and lime softening treatment removes more than 85 percent of dissolved uranium (83 ..mu..g U/L) when an optimum pH and dosage were provided. A strong base anion-exchange column is a recommended option for the treatment of private well waters containing uranium at higher than desirable levels.

Chemical changes in concentrated, acidic, metal-bearing wastewaters when treated with lime.

Abstract: Lime neutralization of acidic wastewaters can prove to be an effective treatment process provided sufficient lime is added. The chemical changes that occur in the system are extensive and varied. Precipitation is predominant with complexation, oxidation and adsorption playing major roles. Total chemical analyses have identified the chemical changes, and controlled laboratory simulations have identified the relative importance of the physical-chemical processes. Exchange of oxygen and carbon dioxide are discussed, and optimum lime addition rates are predicted by thermodynamic computer simulation.

Soil Acidity and Liming: II. Evaluation of Using Aluminum Extracted by Various Chloride Salts for Determining Lime Requirements

Abstract: Neutralization of soil Al to a minimum value is one approach to liming acid soils. The objective of this study was to determine which chloride extracting solution removed the quantity of soil Al that readily reacts with limestone and reduces the Al saturation to < 15%. Soils were incubated for 8 weeks after being limed at rates needed to neutralize the Al removed by KCl, LaCl/sub 3/, and CuCl/sub 2/. Six soils with a range in organic matter contents were used. When the Al extracted by KCl was used to predict the lime rate, soils containing organic matter had a large amount of residual KCl-extractable Al and a soil pH below 5.0. The lime rate predicted by the Al removed with LaCl/sub 3/ reduced the residual Al to < 15% Al saturation for all soils. If residual Al is the criterion for evaluating limed soiled, then LaCl/sub 3/ is the best extracting solution. The LaCl/sub 3/ not only removes the same amount of Al as KCl from the clay fraction of the soil, but also removes organically bound Al that influences the soil solution Al.

Effects of lime and artificial acid rain on the enchytraeid (Oligochaeta) fauna in coniferous forest

Abstract: Effects of lime and artificial rain of varying acidity on the enchytraeid fauna were studied in 4 field experiments in coniferous forest. Artificial rain was applied 5 months per year in quantities of 25 or 50 mm per month and with pH values from about 6 to 2. The “rain” was produced by mixing groundwater and sulphuric acid. The greatest total abundance of enchytraeids and the greatest population densities of Cognettia sphagnetorum and Mesenchytraeus pelicensis were found in plots supplied “rain” of pH 6, pH 4 and pH 3. Their abundances were lowered by additional acidification (pH 2.5 and 2) and also by liming. Species like Enchytronia parva and especially Enchytraeus buchholzi and Fredericia parnoniana were mostly stimulated by liming.

Effects of lime on the chemical composition of ryegrass and white clover grown on a yellow-brown loam

Abstract: The effects of lime (7.25 tlha) both on the chemical composition of ryegrass (Lolium perenne) and white clover (Trifolium repens), and on changes in soil chemistry, were measured in a 2-year field study on a Stratford coarse sandy loam. The major effects of liming were increases in plant Ca and Mo, and decreases in plant Mg and Mn concentrations. Liming increased soil exchangeable Mg, Na, and (to a lesser extent) K, because of an increase in effective cation exchange capacity. The decrease in plant Mg despite increases in soil Mg was attributed to the antagonistic effect of Ca on plant Mg uptake. This was believed to be a factor in the increased incidence of hypomagnesaemia caused by liming on this soil. It was estimated that 0.65 t Calha were lost through leaching, removal of animal products, and transfer to unproductive areas every year.

Process for recovering terephthalic acid from waste polyethylene terephthalate

Abstract: Terephthalic acid (TPA) is recovered from used polyethylene terephthalate beverage containers by reacting comminuted containers in a reaction zone with an aqueous medium containing ammonium hydroxide at elevated temperatures and pressures to form a water soluble diammonium salt of TPA, separating any undissolved solids from the reaction product, acidifying the remaining reaction product to liberate TPA, and separating the precipitated TPA. A portion of the liquid remaining after separation of TPA can be mixed with lime or slaked lime, the resulting mixture treated in an ammonia stripper to remove ammonia therefrom and the ammonia overheads from the stripper blended with another portion of the liquid remaining after separation of TPA to form a stream containing ammonium hydroxide which is recycled to the reaction zone. Ethylene glycol can be recovered from the bottoms from the ammonia stripper by distillation.

Effect of Lime and Phosphate Applications on the Adsorption of Phosphate, Sulfate, and Molybdate by a Spodosol

Abstract: We examined interactions of lime and phosphate and subsequent adsorption of phosphate, sulfate, and molybdate by a Spodosol, using incubation and isotherm studies. Incubation of the soil with lime decreased the quantity of added phosphate that could be extracted with sodium bicarbonate or anion exchange resin. When lime and phosphate were added simultaneously, liming increased phosphate adsorption. When the soil was incubated with lime and the moist soil then equilibrated (1:10 soil-solution ratio) with 5-üg/ml solutions of Mo, P, or S, liming increased subsequent adsorption of phosphate, had no effect on that of sulfate, but decreased that of molybdate. It is suggested that liming resulted in the formation of new, highly active, adsorbing surfaces in the soil through the precipitation of exchangeable aluminum as amorphous polymeric hydroxy-Al cations. The formation of these new surfaces had the greatest effect on phosphate adsorption and the least on that of molybdate, because in general, the magnitude of the decrease in specific adsorption of anions by soil surfaces as pH increases follows the order phosphate > sulfate > molybdate. Incubation of the soil with lime, phosphate, or both followed by air-drying, increased the net negative soil charge and clearly decreased subsequent adsorption of phosphate, sulfate, and molybdate by the soil. Evidently, air-drying significantly altered the surface charge characteristics of the limed soil, for liming increased phosphate adsorption by moist soils, but decreased that by air-dried soil. Crystallization of the amorphous hydroxy-Al surfaces, during air-drying, may explain the different adsorption characteristics of moist and air-dried limed soil with respect to phosphate and to a lesser extent sulfate.

Quicklime slaking process

Abstract: A method for forming a lime slurry in which a sulfate compound is mixed with an aqueous slaking medium and in which the resulting sulfate/water mixture is admixed with calcium oxide.

Process for producing agglomerates, such as pellets or briquettes, and for metal production from these

Abstract: A process for producing agglomerates, such as pellets or briquettes, of high strength from a mixture of fine metal oxide material and reduction carbon is to be provided which can be carried out at low engineering cost even where no or insufficient waste heat energy is available. Using a mixture which, in addition to fine metal oxide material such as iron oxide (Fe2O3) or roasted pyrite and coal dust, in particular reduction carbon, such as lignite coke dust, also contains cement and/or lime as binders and in which the mixing partners are brought before the homogeneous mixing to a grain fineness of < 100 mu m, preferably < 65 mu m, pelleted or briquetted after the mixing and then stored under normal pressure (760 mm Hg) and normal temperature (10 to 25 DEG C), this is achieved by adjusting the mixing proportion of cement and/or lime to at most 10 % and using the carbon mixing partner with a water content of up to 15 %, pelleting or briquetting the mixture within a time of less than 30 minutes after the binder addition and at the same time bringing it to an increased water content of between 18 and 26 %, and finally stacking the pellets or briquettes in layers under weather protection and thus hardening them in the open air for 3 to 14 days, preferably 8 to 9 days.

The Response of Eucalyptus grandis to Fertilising with Nitrogen, Phosphorus, Potassium and Dolomitic Lime on a Mispah Soil Series

Abstract: SYNOPSIS The final results are presented of a comprehensive N, P,K and dolomitic lime factorial experiment with Eucalyptus grandis planted on a fully cultivated Mispah soil series. On this marginal site, fertilising had a marked effect on the growth of E. grandis as measured at clearfelling at eight years and three months. The response to single fertiliser elements was greatest for potassium, followed by phosphorus and nitrogen, dolomitic lime having a depressive effect. The best N:P elemental fertiliser ratio was 3:1, while that for P:K was 1:3. Overall, an elemental N:P:K mixture of 3:1:3 was superior, increasing growth with rate of application. Fertilising with 100 g LAN (26% N), 100 g single superphosphate (8,3% P) and 50 g potassium chloride (50% K) increased yields at clearfelling from 56,7 t/ha for no fertiliser to 85.0 t/ha, an improvement of 49,8%. This fertiliser application is recommended for planting E. grandis on shallow soils derived from Ecca shale. Fertiliser treatments also affected form ...

LIME REQUIREMENT DETERMINATION OF ACID ORGANIC SOILS USING BUFFER-pH METHODS

Abstract: The aims of this study were to calibrate and assess the accuracy of seven buffer solutions for determining the lime requirement (LR) of organic soils using buffer-pH methodology. The various buffers were evaluated by comparing the precision of regression equations adjusted to the relationships between the LR rates required to achieve pH 5.0 (0.01 M CaCl2; ≈ 5.4 (H2O)), as determined by incubation, and soil-buffer pH values. The buffers tested and their initial pH values were as follows: Shoemaker, McLean and Pratt (SMP), pH 7.5; Woodruff, pH 7.0; Yuan, pH 7.0 and 6.0; Mehlich, pH 6.6; 0.1 N Ca(OAc)2, pH 5.5; 0.1 N Ba(OAc)2, pH 5.5; and 0.1 N NH4OAc, pH 5.5.Results indicate that the liming material had reacted with the CaCO3 neutralizable acidity of these soils within 2 mo as the pH values of the incubated samples did not change materially from the 2nd to the 8th month of incubation. Furthermore, the pH values of the soils utilized in this study increased linearly with increasing rates of applied CaCO3. In...

Process for the reduction of the sodium hydroxide losses of the Bayer-type alumina production

Abstract: The invention relates to a process for the reduction of sodium hydroxide losses of the Bayer-cycle by modified causticization of red mud which comprises subjecting an optionally previously concentrated red mud slurry led off from the red mud washing line by ramification and containing a liquid phase which has a concentration of 5-40 g. caustic Na 2 0/1. caustification by adjusting the lime content expressed as CaO through addition of lime or lime milk to 1-3.2 moles per mole Al 2 O 3 , preferably to 2-2.5 moles per mole Al 2 O 3 , related to the total Al 2 O 3 content of the slurry; stirring the slurry for 0.3-5 hours at a temperature of 70°-110° C., preferably at 80°-100° C.; adding to the slurry 3-4 moles, preferably 3.2-3.4 moles, of soda related to 1 mole of the originally dissolved Al 2 O 3 , and continuing the stirring for 1-4 hours at 80°-100° C., preferably at a temperature of 90°-95° C.; if necessary causticizing the excess of soda by adding lime or lime milk by methods known per se; if desired concentrating the slurry thus obtained and re-introducing the liquid phase thereof to the red mud washing unit which corresponds to the sodium hydroxide content thereof; and re-entering the slurry to the red mud washing line. The advantages of the process of the present invention are as follows: the sodium hydroxide losses of different origin of Bayer-type alumina production are recovered by a single operation step, the process is simple, requires no expensive equipment and is economical.

Manufacture of air purifying agent

Abstract: PURPOSE: To manufacture an air purifying agent having excellent water resistance, strength, and air pollutant removing efficiency by adding water to potassium permanganate, zeolite, slaked lime, and colloidal silica, kneading, molding, and drying. CONSTITUTION: 3W30pts.wt. potassium permanganate, 10W70pts.wt. zeolite, and 6W70pts.wt. slaked lime and colloidal silica are blended to obtain 100pts.wt. total solids. Then 10W100pts.wt. water is added to the 100pts.wt. total solids, and the mixture is kneaded, molded, and then dried at 50W150°C. In that case, slaked lime and colloidal silica are blended in 0.5W10mol ratio of CaO/SiO 2 . The air purifying agent thus obtained exhibits a high absorbing and adsorbing performance of harmful gases such as NO x , SO x , and gaseous NH 3 , and does not disintegrate even in water. The agent, having water resistance and high particle strength, without generating dust, and easy to handle, can be utilized industrially. COPYRIGHT: (C)1985,JPO&Japio

Response of rapeseed (Brassica napus) to phosphorus, boron and lime on an acid soil near Canberra

Abstract: The failure of a rape crop on a light-textured acid soil was investigated by a factorial field experiment with four rates of lime (0, 500, 1000 and 2000 kg/ha), four rates of phosphorus (0, 13, 28, 42 kg/ha) and, at stem extension, two levels of a boron spray (0, 0.6 kg/ha). The second crop failed in the same way as the first unless phosphorus was applied at sowing; the lowest rate was adequate, and higher rates did not increase the response. On the phosphate-treated plots the boron spray increased seed yield (measured on hand-harvested quadrats) substantially (75%) as the result of a small increase in flower number (32%) and a large increase in pod number (1 16%). Machine-harvested yields on the 'plus boron' plots were reduced by shattering and were 40% higher than controls (P<0.01). There was no response to lime applied one month before sowing and no interaction of lime with boron or phosphorus. The boron response was not lime-induced. The mechanism of the response to phosphorus and the questions raised by the lack of response in yield to lime in relation to aluminium and manganese toxicity were not resolved. The results indicate that phosphorus should receive at least as much attention as lime in the investigation of rape-growing on acid soils. Boron should also be investigated because of its important role in seed set of rape.

The effect of soil pH and chemical form of nitrogen fertilizer on heavy-metal contents in ryegrass

Abstract: Ryegrass was grown in pots containing metal-enriched soil which was adjusted to different pH levels with acid or lime, and supplied with either ammonium sulphate or calcium nitrate as the N fertilizer.

Soil and lime requirement tests for the 50 states and Puerto Rico

Abstract: The purpose for liming acid soils is to adjust their pH to a level where most plant toxic elements are rendered nontoxic and the availability of most essential elements for plants are near maximum. The sources of soil acidity and its development, the predominant cations, and the measurement of soil acidity, as well as soil test procedures used for determining lime requirement, are discussed. The purpose of this paper is to discuss the strengths and weaknesses of soil testing methods for determining lime requirements, their interpretation, and their application, as related to soil properties, tillage systems, and cropping patterns. The soil tests discussed will not include all procedures that have been developed but will include those tests currently being used by 50 states and Puerto Rico. Additional index words: Lime requirement, Soil pH, Soil testing, and Soil acidity. THwE purpose of liming is to adjust soil pH to a level here most plant toxic elements are rendered nontoxic, and the availability of most essential elements for plants is near maximum. Therefore, it is very important to have a test that indicates the amount of lime required to raise the pH of a given acid soil to a selected level. The term pH is used to express the degree of acidity or alkalinity. The numbers used to express pH are negative logarithmic numbers (to the base 10). Therefore, pH --log10 [H÷]. The entire pH scale ranges from 0 to 14 with pH 7 being neutral. Most agricultural soils range from 4 to 8. The pH of a soil actually expresses that part of acidity that is present in an equilibrated system in the form of hydrogen (H) ions, regardless of their source. Since the reserve acidity of acid-producing ions is not included in pH measurements, as long as the ions stay undissociated, soil pH alone does not reflect the soil’s acid-producing potential nor the amount of lime needed for crop production on it (14). Controlling soil acidity in certain soils may be as important for maximum crop yields as fertilizing, irrigating, and pest control. Soil acidity can be corrected when acidic ions, such as H or AI ions, are replaced with Ca or Mg ions. Of several liming materials (4, 33), finely ’ Contribution from the Dep. of Agronomy and from Soil, Water, and Air Sciences, USDA-ARS, published with the approval of the director of the Colorado State Univ. Exp. Stn. as Scientific Series Paper no. 2745. This paper is based on an invitational paper presented at the National Conference onAgricultural Limestone, Nashville, Tenn., 16-18 Oct. 1980. ’Professor of agronomy, Colorado State Univ. and national research program leader, Soil Productivity and Environmental Qualiiy, USDA-ARS, Fort Collins, Colo. ground limestone is one of the most commonly used materials for correcting soil acidity. The lime requirement (LR) is the quantity of agricultural grade lime required to neutralize soil acidity and to increase soil pH from an initial to a final desired value. SOURCES OF SOIL ACIDITY Soil acidity develops over thousands of years in humid regions as precipitation in excess of plant use percolates through the soil and leaches Ca, Mg, and other basic cations from the surface soil. Growing plants also remove Ca and Mg from the soil. The lost Ca and Mg are replaced by H and A1, resulting in increased soil acidity. The use of acid-forming fertilizers also contributes to soil acidity. Soil leaching and the subsequent removal of the basic cations Ca, Mg, and K from the surface of the colloidal particles (clay and organic matter) is enhanced by root activity that generates CO2. Eventually, CO, reacts with water to produce carbonic acid (24), HxO + CO2"-"H2CO~ [1] H2CO~ ~" H÷ + HCO~[21 which then breaks down to release protons or H ions (H+), thus lowering the soil pH [1 and 2]. The decomposition of organic matter and the release of organic acids in the soil also generates H ions that replace basic cations on the surface of the soil colloids. For many years, it was assumed that soils with a low pH were primarily H-saturated. However, research has shown that A1 was the predominant cation in acid mineral soils with a pH of 5 or lower (6). Aluminum considered an acidic cation since H ions are released during hydrolysis of the water associated with the AI ions [3]. AP÷ + 3H=O -" AI(OH)~ + ÷ [3] Although H and AI ions are the two main components of soil acidity in most acid soils, their relationships in soils are certainly more complicated than they are in pure solution, since AI ions may also exist in soil in hydroxy AI forms (42). Exchangeable AI is generally the predominant cation in the leached soil from the Southeastern USA and from tropical regions when the soil pH is 5 or less (13). addition to contributing to soil acidity, A1 and Mn are toxic to plants and are, thus, important growth-limiting factors in many acid soils of the world. Foy and Fleming (10) indicated that AI toxicity is particularly severe at 10 JOURNAL OF AGRONOMIC EDUCATION, VOL. 12, 1983 soil pH of 5.0 or below, but may occur at pH levels as high as 5.5. Manganese toxicity generally occurs at soil pH levels of 5.5 or below in well-drained soils, although it can occur at pH 6.0 or above in flooded or compacted soils, if the soil-parent materials contain sufficient total Mn (35). The chemical activity of soil-solution Al likely includes factors not adequately represented in a simple soil pH measurement. Pearson et al. (27) showed a close relationship between soil-solution A1 content, expressed in terms of chemical activity and soil-solution pH for three Southeastern USA soils, and three Puerto Rican soils. Kamprath (13), who made both field and greenhouse studies, concluded for maximum yields that the A1 saturation of a field soil should be less than 45o70 for corn, 20°70 for soybeans, and 10°7o for cotton.

Properties and behaviour of lime- rice husk ash cements

Abstract: The utilization of agricultural residues for building is particularly attractive in developing countries where indigenous resources for building are hard pressed to cope with the demand. The use of rice husks, essentially a waste material in most countries, as a source for a pozzolanic material, is described. The behaviour of lime- rice husk ash mixes, in terms of strength, shrinkage, durability and microstructure, are examined. It is shown that although maximum strengths are achieved with low lime mixes, the effects of lime leaching could seriously impair the durability and indeed the long term strength of these mixes. Accordingly, it is proposed that the optimum ratio of lime: rice husk ash should be about 1:1. Further, it is shown that within the limits of carbon contents likely to be encountered in the field, strength development is unaffected, though some retardation in initial and final set may occur. Finally, as would be expected, examination of the microstructure indicates an incoherent matrix of poorly crystallized calcium hydroxide, ash fragments and an ill defined calcium silicate hydrate structure. X- ray diffraction analysis indicates that the latter is of the csh(i) type. (Author/TRRL)