Mirjana Vukićević

Stabilization of fine-grained soils with fly ash

Results of laboratory research focusing on soil stabilization, using fly ash without activators, are presented in the paper. Two types of fine-grained soils were tested: low to medium plasticity clay and very expansive, medium to high plasticity clay. Soil-fly ash mixtures were prepared at optimum fly ash contents (15 and 20 %). The effects of fly ash on the soil plasticity, moisture-density relationship, unconfined compressive strength, shear strength parameters, CBR (California Bearing Ratio) values, deformation parameters, and swell potential, were evaluated. Results obtained show that the use uf fly ash can significantly contribute to the improvement of soil properties.

Validation and implementation of HASP constitutive model for overconsolidated clays

Značajan deo u oblasti konstitutivnog modeliranja tla predstavlja opisivanje naponsko-deformacijskih relacija prekonsolidovanih glina. Prekonsolidovane gline su u prošlosti bile opterećene vertikalnim efektivnim naponom koji je veći od tekuće veličine vertikalnog efektivnog napona. Prekonsolidacija može biti i posledica izvođenja različitih građevinskih radova na tlu i u tlu. U poređenju s normalno konsolidovanim glinama, imaju manji koeficijent poroznosti i veću smičuću čvrstoću. U prirodi su najčešće ispucale, što dovodi do nehomogenog polja deformacija. Iz tog razloga, ispoljavaju složen oblik ponašanja pri lomu. Veliki broj konstitutivnih modela za prekonsolidovane gline razvijen je koristeći koncept kritičnog stanja [35, 38] i Modifikovani Cam Clay (MCC) model [36]. MCC model se može, pri monotonom opterećenju, koristiti s velikom pouzdanošću za normalno konsolidovane i lako prekonsolidovane gline. Za jako prekonsolidovane gline, MCC model precenjuje smičući napon pri lomu i predviđa nagli prelaz iz elastične oblasti u elastoplastičnu oblast, što nije u skladu sa eksperimentalnim podacima koji pokazuju postepeno smanjenje krutosti prilikom opterećivanja. Za prevazilaženje nedostataka MCC modela, korišćeni su različiti koncepti. Zienkiewicz i Naylor [52] u relacije konstitutivnog modela uveli su matematički opis površi Hvorsleva, što su u svojim modifikacijama sledili i

Stabilization of Low Bearing Soil Using Fly Ash and Chemical Additive Polybond

The results of laboratory research of high plasticity clay stabilization using liquid chemical additive Polybond and the fly ash from Serbian thermal electric power plant Kostolac are presented in this paper. In order to determine the effects of stabilization, extensive laboratory study of physical and mechanical properties of the stabilized soil (unconfined compression strength, shear strength parameters, CBR, deformation parameters, swelling, coefficient of permeability, resistance to freezing) were performed. The results of the research clearly indicate the positive effects of the clay stabilization using Polybond, as well as fly ash, and confirm that these additives can be successfully applied as a clayey soil stabilizers in various practical applications such as: stabilization of low bearing subgrade, construction of embankments and geotechnical structures of low permeability, improvement of mechanical properties of top subgrade layers etc. The use of stabilizers reduces energy consumption, as well as the usage of natural materials such as stone aggregates.

Fly ash and slag utilization for the Serbian railway substructure

Approximately 7 million tons of fly ash and slag are produced in thermal power plants in Serbia every year, only 3% of which is used in the cement industry. About 300 million tons of the ash-slag mixture are disposed in landfills, occupying an area of approximately 1600 hectares and generating environmental issues. Fly ash from Serbian power plants has pozzolanic properties and due to low concentration of calcium compounds (less than 10% CaO), they do not have self-cementing properties. According to the ASTM C618-15, this ash is from class F. According to the European Standard EN 197-1:2011, this ash is siliceous (type V) ash. From April 2014 to May 2015, an investigation of engineering properties of fly ash and mixtures of fly ash and slag from landfill (without or with binders of cement/lime) was conducted at the Laboratory of Soil Mechanics at the Faculty of Civil Engineering of the University of Belgrade (Serbia) and at the Institute for Testing of Materials – IMS Institute in Belgrade. The laboratory test results were showed in the study ‘Utilization of fly ash and slag produced in the TPP JP EPS thermal power plants for construction of railways’. Four kinds of waste materials from Serbian power plants were laboratory tested: (a) an ash-slag mixture from landfills at the ‘Nikola Tesla A’ thermal power plant; (b) fly ash from silos in the ‘Nikola Tesla B’ thermal power plant; (c) an ash-slag mixture from landfills at the ‘Kostolac A’ and ‘Kostolac B’ thermal power plants and ‘Srednje kostolacko ostrvo’ landfill; (d) fly ash from the ‘Kostolac’ thermal power plant. The following physical and mechanical properties of ash and mixtures were investigated: grain size distribution, Atterberg limits, specific gravity, moisture-density relationship, shear strength parameters in terms of effective stresses, California Bearing Ratio (CBR), and deformation parameters. The paper presents the results of laboratory tests of the materials with and without binders, and based on the laboratory results and previous research, the paper presents possibilities of using fly ash and slag for the construction of railway substructure in the planned construction and reconstruction of railway network in Serbia. The obtained results indicate that tested fly ash and ash-slag mixture have met the technical requirements and that they have the potential to be used in railway substructure. First published online 12 December 2016

Stabilizacija sitnozrnatog tla letećim pepelom

Results of laboratory research focusing on soil stabilization, using fly ash without activators, are presented in the paper. Two types of fine-grained soils were tested: low to medium plasticity clay and very expansive, medium to high plasticity clay. Soil-fly ash mixtures were prepared at optimum fly ash contents (15 and 20 %). The effects of fly ash on the soil plasticity, moisture-density relationship, unconfined compressive strength, shear strength parameters, CBR (California Bearing Ratio) values, deformation parameters, and swell potential, were evaluated. Results obtained show that the use uf fly ash can significantly contribute to the improvement of soil properties.