Compaction and shear strength characteristics of colemanite ore waste modified active belite cement stabilized high plasticity soils

doi:10.1016/j.enggeo.2013.01.003

Engineering Geology

Volume 155, 14 March 2013, Pages 45-53

https://doi.org/10.1016/j.enggeo.2013.01.003 Get rights and content

Abstract

An experimental investigation was undertaken to evaluate the mechanical behavior of soil–cement mixtures. The primary motivation for the study was to investigate the innovative use of colemanite ore waste (CW) modified active belite cement (BC) in soil stabilization engineering (applications). The specific objectives of the research were to evaluate and compare: (1) compaction characteristics, (2) unconfined compressive stress-axial strain behavior, (3) unconfined compressive strength, (4) Young's secant modulus of elasticity, and (5) undrained shear strength characteristics of belite cement (BC)–clay and ordinary portland cement (OPC)–clay mixtures. BC and OPC were mechanically mixed with clay in five different dosages, i.e. 1.0%, 2.5%, 5.0%, 7.5% and 10.0% by using dry weight of clay, separately. Compaction characteristics of untreated soil, BC–clay and OPC–clay mixtures were evaluated at standard Proctor compaction energy. For a meaningful comparison of unconfined compression and triaxial test results, all specimens (untreated soil, BC–clay and OPC–clay mixtures) were prepared at maximum dry unit weight and optimum water content. Cylindrical samples of 50.0 mm in diameter and 100.5 mm in length were compacted in three layers and their strength characteristics were investigated at 1-, 7-, 14-, and 28-days curing times. Results of unconfined compression tests showed that cement dosage less than 5% has little effect on unconfined compressive strength (UCS) and exhibits ductile type of failure for both OPC–Clay and BC–Clay mixtures. In contrast, for cement content equal or greater than 5%, cement treatment significantly improved UCS and displayed brittle stress–strain behavior especially for BC–Clay mixtures. Similar behavior is obtained from undrained triaxial tests. The variation of undrained cohesion intercepts with respect to cement type, cement content and curing time is more sensitive than that of undrained internal friction angle.

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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Compaction and shear strength characteristics of colemanite ore waste modified active belite cement stabilized high plasticity soils

Abstract

Highlights

Introduction

Section snippets

Colemanite ore waste (CW)

Colemanite ore waste (CW) modified active belite cement (BC)

Review of literature on modification of clay soils with cement

Clay

Composing BC–Clay and OPC–Clay samples

Determination of laboratory compaction characteristics

Preparation of BC–Clay and OPC–Clay samples for strength tests

Unconfined compression and undrained triaxial compression shear tests

Compaction characteristics

Conclusions

Acknowledgments

Construction and Building Materials

Cement and Concrete Research

Engineering Geology

Cement and Concrete Research

Construction and Building Materials

Building and Environment

Building and Environment

Engineering Geology

Cement and Concrete Research

Cement and Concrete Research

Applied Clay Science

Compressive strength of cement stabilized soils. A new statistical model

Electronic Journal of Geotechnical Engineering

Behavior of expansive soils treated with eco-cement

Bulletin of the Polytechnic Institute of Iasi — Construction & A

Standard test method for unconfined compressive strength of cohesive soil

Standard practice for classification of soils for engineering purposes (unified soil classification system)

Standard test method for unconsolidated-undrained triaxial compression test on cohesive soils

Standard test method for particle-size analysis of soils

Standard test methods for liquid limit, plastic limit, and plasticity index of soils

Standard test methods for laboratory compaction characteristics of soil using standard effort (12,400 ft-lbf/ft3(600 kN-m/m3))

Standard test method for specific gravity of soil solids by water pycnometer