This study presents the improvements achieved as a result of the lime stabilization application conducted by the joint effort of the Turkish Association of Lime Industrialists and the General Directorate of Rural Services on the 200 m long section of the Ankara Province Yukari Yurtcu Village road where green and brown clays are dominant. The study also numerically demonstrates the impacts of these improvements on the road section based on the results of various laboratory and field tests. The lime stabilization in field conditions was performed with 5% lime for both clays and was applied as a 30 cm thick single layer. In the soaked California bearing-ratio (CBR) tests conducted in the laboratory, increases that reach up from 16 and 21 times compared to initial soaked CBR values were observed in green and brown clays, respectively, at the end of 28 days. The high increases observed in soaked CBR values would reduce the upper layer thickness of the roads. The similar improvements are also achieved in unconfined compression and plate loading tests. The comparisons performed with the plate loading tests clearly demonstrated the behavior of the surface to lime and its cure impact.

A field application for lime stabilization

Clay soils create many problems for highway construction and they have to be replaced or improved by stabilization for satisfactory performance. Lime stabilization is a well-established technique to improve the performance of clays. Cementitious minerals form upon mixing of clay with lime causing an improvement in strength and durability. In the study, the changes in the microfabric of long-term cured lime-stabilized kaolinite clay using X-ray diffraction pattern, scanning electron microscope and unconfined compressive strength (UCS) is presented. Unconfined compression test samples at two different lime contents (4 and 12% by weight) were prepared and cured in a humidity room for long time curing. The UCS of pure kaolinite was originally 125 kPa, which increased to 1,015 kPa after 1 month and to 2,640 kPa (21 times the initial value) after 10 years for cured lime-stabilized kaolinite samples. Similar long-term strength increases were also observed for stabilized kaolinite with 12% lime. Calcium aluminate silicate hydrate minerals were detected in the structure of the kaolinite. This suggests pozzolanic reactions with lime stabilization may continue in the long-term for up to 10 years.

Long-term behavior of lime-stabilized kaolinite clay

The pozzolanic properties of fly ash, which enable it to react with lime to form cementitious products, have made fly ash a good quality base or subbase course material when used with lime or cement to stabilize aggregates and soils, or when used alone with lime or cement. Strength and durability criteria have been established for this application, and appropriate testing procedures have been developed. Construction procedures utilize standard equipment and techniques for central mixing or mix in-place operations. Fly ash is used as embankment or structural backfill material over weak or compressible soils because of the reduced surcharge that results from its light unit weight. In addition, its good shear strength properties result in low compressibility and good stability characteristics. Economies can be realized in the design of retaining structures backfilled with lightweight fly ash. Fly ash improves the flow properties and strength characteristics of grouts. It can be used alone for void-filling, or used in conjunction with Portland cement, lime, clay, sand, and gravel to develop grouts for applications related to highway structures.

Fly ash as a construction material for highways. A manual. Final report

Mineralogical and engineering properties of compacted soil-lime mixes

Experimental data indicate the possible stabilization of unpulverized soil lumps to some depth by lime diffusion. Lime soil and lime flyash interaction may both contribute to strength. A mix design procedure is suggested for the derivation of the highest strength to lime content ratio in soil lime flyash mixtures (A).

Some factors influencing the strength of soil lime flyash mixtures

The mineralogical and micromorphological changes occuring in fly ash-lime stabilized bentonite were observed and related to changes in elastic moduli of the stabilized mixture. Compacted fly ash, fly ash-lime, bentonite-1ime, bentonite-fly ash, and bentonite-fly ash-lime mixtures were prepared and cured at 23°C and 50°C, for 1, 28, 90 and 180 days. The development of microstructure and cementitous crystals were observed by a scanning electron microscoi in energy dispersive spectrum analyzer and a X-Ray diffractometer. The elastic moduli and strengths were obtained from unconsolidated undrained triaxial and unconfined compressive strength tests. The physical test results were compared with changes observed by scanning electron microscopy and X-Ray diffraction. CSH gel Type I, II and III, ettringite, afwillite and tetracalcium aluminate thirteen hydrate crystals were identified in the cured specimens. The elastic modulus of the fly ash-lime stabilized bentonite was higher than the untreated bentonite and the increase in elastic modulus corresponded to the curing times when new cementitious crystals were observed. Acicular crystals (CSH Type I and II) and ettringite crystals spanned the pores and increased the contact points where blocky aggregates of equant crystals (CSH III) engulfed the fly ash grains providing support. The compressive strength increased, and the strain at failure decreased resulting in an increase in the elastic modulus. Some fly ash grains providing support for montmorillonite aggregates dissolved and created weak spots in the matrix, causing a decrease in elastic modulus at longer curing periods. At 50°C curing temperature the same cementitious crystals were observed as at 23°C. However, the rate of the reactions increased considerably.

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Gokhan I Baykal

Papers

The Effect of Micromorphological Development on the Elastic Moduli of Fly Ash-Lime Stabilized Bentonite.