Lime Treatment of Soils

However, in the following areas, lime still plays an important role  

The ability of lime to dry, modify and stabilise clay soils has been known for many years. However, its systematic use only started in the late 1940s in the USA, when the techniques of soil mechanics testing were applied to lime-soil mixtures. They demonstrated in quantitative terms that lime treated layers could, with confidence, be designed into the construction of roads, runways, car parks etc. 

The benefits of lime treatment of soils, in terms of cost, performance, durability and environmental impact, have been widely promoted in the USA [26.1], where it has been used in the construction of thousands of miles of roads and in major projects such as the Dallas Fort Worth airport [26.2]. A few other countries (notably France, Germany, Sweden, South Africa, Austraha and New Zealand) have recognised the benefits of lime treatment and are using it extensively as an alternative to traditional methods of construction. Typical projects which have benefited from the technique are listed in Table 26.1. 

In most countries, however, progress to adopt lime treatment as a standard construction technique has been slow [26.8]. The reasons for this undoubtedly include  

Reclamation of redundant docklands Reclamation of contaminated land Structural fill 

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Table 26.1. Typical projects using lime treatment of soils...

Calcium oxide or quick lime is used in the treatment of soil. 

D. Sampling directly after agrochemical treatment of soils (herbicides, pesticides, fertilizers, lime etc.) should not be performed. 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

The extent of the vineyards that produce the finer wines is well known to be very limited. The differences of soil and treatment do not appear sufficient to account for this fact,- Although the best vines are grown on a calcareous soil, as on the chalk hills of Champagne and the albarizas of Xeres, of which carbonate of lime forms two-thirds, and in three-fourths of the more celebrated vineyards this is the ease, though the necessity of such a description of soil has been denied. 

Mn nutrition of wheat was found to be dependent on the P status of soil as well as on its pH and Mn status (Neilson et ah, 1992). Concentrations of Mn were depressed in leaf tissue of plants from lime soils and also in high P soils. The depressed values for lime treatments were explained in terms of depressed soils solution Mn concentrations resulting from elevated pH. It was suggested that high soil P resulted in elevated plant P which interfered in the uptake and/or translocation of Mn. 

Calcium carbonate as limestone was used to build the Roman aqueduct in Figure 7-6. When calcium carbonate decomposes, it forms an oxide of calcium called lime. Lime is one of the most important industrial compounds. For example, lime plays a role in the manufacture of steel, paper, and glass. Gardeners use lime to make soil less acidic. Wastewater treatment plants use lime, as do devices that remove pollutants from smokestacks. Lime is mixed with sand and water to form a paste called mortar. 

Lime treatment involves the use of quicklime, or slaked lime, either as powdered hydrated lime, or as a milk of lime (N.B., it does not use the product marketed as agricultural lime , which is generally calcium carbonate and which does not have the same effect on soils). The effect of lime on soils can be divided into three stages drying, modification, and stabilisation. 

Lime treatment can be effective on a wide range of soils, ranging from clayey gravels to clays. The effectiveness of lime depends both on the level of clay and on its ability to react. In all cases where lime treatment is proposed, adequate testing should be done to enable the most appropriate treatment to be determined. 

The presence of sulfates in the soil and/or ground water, or of sulfides, which can be oxidised to sulfates, has been one of the main causes of problems with lime treatment. This is because sulfates react with the cementitious products of stabilisation to produce ettringite (3Ca0.Al203.3CaS04.32H20), which can cause swelling and disruption of the stabilised layer. 

Because of localised variations in the composition and properties of soil, a detailed survey of the soil and quality of the ground water over the proposed area for lime treatment should always be done. Both the soil and the ground water should be sampled and tested thoroughly and systematically. 

Quicklimes used for lime treatment should (provisionally) meet the requirements of Types CL 70, CL 80, or CL 90 as specified in ENV 459-1 [26.18] and summarised in Table 26.2. It requires that the MgO content in building limes used for soil stabilisation should not exceed 5 % in CL 70, and 10 % in CL 80 and CL 90. In the long-term, however, [26.17] will specify the characteristics for limes used in road construction. A high reactivity, as defined in section 13.2, is an advantage when quicklime is used for drying a site. 

A variety of binders are used for road bases and sub-bases, capping layers, soil stabilisation and soil improvement, depending on the availability of materials and local traditions. This section refers to factory blended mixtures of binders. In-situ treatment of materials, using lime and other binders is described in section 26.3. 

Lime products have been used to raise the pH of soils contaminated with cadmium and other heavy metals. This treatment immobilises the metals and enables the land to be used for growing forage crops and grasses [32.33]. 

KUn dusts (KD) - CKD and lime kUn dusts (LKD) have been used as stabilizing and sobdifying agents in the treatment of soft or wet soils for engineering purposes and for environmental remediation... 

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