Compaction and shear strength characteristics of colemanite ore waste modified active belite cement stabilized high plasticity soils
Highlights
► Reducing energy consumption in cement production is of global concern. ► Active belite cement production seems to be more environmental friendly that of OPC. ► BC inclusion results in a more brittle failure compared to OPC inclusion. ► BC can effectively improve the engineering properties of clay soils. ► The variation of friction angle with cement dosage and curing periods scatters.
Introduction
It was reported in the Intergovernmental Panel on Climate Change (IPCC) that most of the increases in temperature (or global warming) observed since the middle of the 20th century was caused by gradually increasing concentrations of greenhouse gases (IPCC, 2007). According to the Kyoto Protocol, which is an international agreement linked to the United Nations Framework Convention on Climate Change (UNFCCC), CO2 is the most important anthropogenic greenhouse gas and cement production generates more CO2 emission than any other industrial process. Due to large quantities of fuel used during manufacture and the release of carbon dioxide from raw materials, the cement industry contributes to about 5% of global anthropogenic CO2 emissions (Worrell et al., 2001). In the near future, the field of cement application will expand in parallel with new developments. Therefore, conducting researches to find alternative raw materials and to reduce energy consumption in cement production is of global concern. In this context, colemanite ore waste (CW), the by-product of the reaction of colemanite ore and sulfuric acid generated during the production of boric acid, modified active belite cement (BC) is produced in Turkey. This study aims to investigate the usability of this innovative CW modified active belite cement (BC) in soil treatment applications.
Before introducing a detailed discussion of the current literature on the mechanical stabilization of fine grained soils with cement, the reader will be informed briefly about colemanite mineral, colemanite ore waste (CW), CW modified active belite cement (BC), and superiority of BC over ordinary portland cement (OPC) with regard to environmental impacts elaborated in succeeding paragraphs.
Section snippets
Colemanite ore waste (CW)
Colemanite, which is an important borate ore, is mainly used in the production of various boron compounds such as boric acid, borax and boron oxide (Garrett, 1998, Helvaci and Alonso, 2000). During the production of boric acid, a large quantity of about 120,000 tonnes of colemanite ore waste (CW) is generated per year (Yakar et al., 1999). This CW causes various environmental problems when discharged directly to the environment. Moreover, the disposal of this huge quantity of CW is becoming more
Colemanite ore waste (CW) modified active belite cement (BC)
Being the most important raw material of cement production, limestone (CaCO3) is primarily used for CaO requirement. During the calcination process (CaCO3 + energy → CaO + CO2), limestone (CaCO3) is calcined at a temperature above 900 °C and as a result of this process a high amount of CO2 gas is emitted to the atmosphere. On the other hand, colemonite contains CaO component in its constitution, thus it can be directly used in cement production without any pre-calcination operation. Using
Review of literature on modification of clay soils with cement
The modification of clay soils with cement to improve their engineering properties is well recognized and widely practiced. Through stabilization, the plasticity of soil is reduced, it becomes more workable, and its compressive strength and load bearing properties are improved. Such improvements are the result of a number of chemical processes that take place in the presence of cement (Bhattacharja and Bhatty, 2003). Several factors such as plasticity of soil, types and amounts of cement,
Clay
The soil used in this study was obtained from a test pit inside the Technical Research and Quality Control Laboratory campus of State Hydraulic Works in Ankara, the capital of Turkey. The test pit was excavated at a depth of about 1.5 m by backhoe power equipment to obtain disturbed samples. A nearly 0.5 m thick layer of agricultural loam comprising the top soil was clearly removed from the area and block samples were taken at depths from 1.0 m to 1.5 m. No ground water table level was observed.
Composing BC–Clay and OPC–Clay samples
The mixture design of either BC or OPC amended clay samples was based on dry weight percentages of BC or OPC in the clay matrix, respectively. BC and OPC dosages were selected as 1.0%, 2.5%, 5.0%, 7.5% and 10.0% (e.g., dry mass of BC or OPC/dry mass of clay), individually. Specimens stabilized with either BC or OPC were prepared from soils sifted through a No.4 (4.75 mm) USA standard sieve and tested in exactly the same manner.
Determination of laboratory compaction characteristics
Maximum dry unit weights of BC–Clay and OPC–Clay mixtures were achieved by applying an energy level of 600 kN-m/m3, which is equivalent to the (ASTM D 698-00a, 2002), the recommended standard compactive effort. During these tests, dry cement was mechanically mixed with dry clay prior to compaction until homogenous BC–Clay and OPC–Clay mixtures were obtained. All mixtures were then initially mixed with a certain amount of water, i.e. 12%–16% for the first compaction tests. Henceforward, samples
Preparation of BC–Clay and OPC–Clay samples for strength tests
A compaction mold was used to prepare cylindrical compacted samples at optimum water content and maximum dry unit weight during sample preparation. The compaction mold was designed for unconfined compression and triaxial testing specimens with a height-to-diameter ratio of 2.01. The compaction mold apparatus was made of stainless steel, and split into two parts longitudinally.
Before compaction, the inner surface of the split mold was lightly lubricated to prevent the sample from being damaged
Unconfined compression and undrained triaxial compression shear tests
Unconfined compression tests and undrained triaxial compression shear tests were performed on the specimens using strain-controlled application of the axial load in accordance with ASTM D, 2166-00 (2002) and ASTM D 2850 standards, respectively (ASTM D 2166-00, 2002, ASTM D 2850-03a, 2002). ASTM D 2850 recommends applying the axial load to produce axial strain at a rate of approximately 1.0 mm/min for plastic materials and 0.3 mm/min for brittle materials that achieve maximum deviator stress at
Compaction characteristics
The compaction curves of untreated soil, BC–Clay and OPC–Clay samples shown in Fig. 2, were developed by plotting the dry unit weight of the compacted samples with reference to their corresponding water content.
From Fig. 2 it is seen that as the cement content increases for both BC–Clay mixtures and OPC–Clay mixtures flatness of the bell-shaped compaction curve increases. Thus optimum moisture content values of the mixtures are no longer singular peaks but points on the plateau of the
Conclusions
Several series of laboratory tests were performed to evaluate compaction characteristics, uniaxial deviator stress-axial strain behavior, unconfined compressive strength (UCS), secant modulus (E50), undrained shear strength of the untreated soil, and BC–Clay and OPC–Clay mixtures. In order to make this an unbiased comparative study, both BC–Clay and OPC–Clay mixtures were prepared and tested under similar conditions. The following conclusions were drawn from this experimental study,
- 1.
While both
Acknowledgments
This study is partially sponsored by the State Hydraulic Works of Turkey, whose support is gratefully acknowledged. The authors are also indebted to Mr. Burhanettin Unal, Mr. Ismail Gurler, Mr. Nutku Koc and Mr. Mustafa Keser for their technical assistance.
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