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Geo-environmental application of municipal solid waste incinerator ash stabilized with cement
Accepted Manuscript Geo-environmental application of municipal solid waste incineration ash stabilized with Cement Davinder Singh, Assistant Professor, Arvind Kumar, Professor PII:
S1674-7755(16)30071-3
DOI:
10.1016/j.jrmge.2016.11.008
Reference:
JRMGE 314
To appear in:
Journal of Rock Mechanics and Geotechnical Engineering
Received Date: 27 July 2016 Revised Date:
26 October 2016
Accepted Date: 7 November 2016
Please cite this article as: Singh D, Kumar A, Geo-environmental application of municipal solid waste incineration ash stabilized with Cement, Journal of Rock Mechanics and Geotechnical Engineering (2017), doi: 10.1016/j.jrmge.2016.11.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Geo-environmental application of municipal solid waste incineration ash stabilized with
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Cement
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Davinder Singh* and Arvind Kumar**
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Assistant Professor, Department of Civil Engineering, Dr. B.R. Ambedkar NIT Jalandhar,
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Punjab India *
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Professor, Department of Civil Engineering, Dr. B.R. Ambedkar NIT Jalandhar, Punjab,
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India**
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Abstract
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The behavior of soluble salts contained in the municipal solid waste incinerator ash
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significantly affects the strength development and hardening reaction when it is introduced
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with cement. The present study emphasizes on the compaction and strength behavior of mix
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specimen of cement and MSWI ash. Series of tests such as unconfined compressive strength,
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split tensile strength and California bearing ratio and pH tests were carried out. Prior to this,
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the specimens were cured for 7, 14, and 28 days. The test results depicted that the maximum
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dry density decreases and optimum moisture content increases with the addition of cement.
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The test results also revealed that the cement inclusion increased the strength of the mix
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specimens. Thus, the combination of MSWI ash and cement can be used as light weight
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filling material in different structures like embankment and road construction.
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Keywords: Municipal solid waste incinerator ash; Cement; Compaction; Stabilization; CBR
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Test; Geotechnical properties
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1. Introduction
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The safe disposal of waste materials such as municipal, industrial and hazardous waste has
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been one of the big challenges in urban cities as well as in rural environment in recent days.
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Such wastes pose environmental pollution problems for the surrounding disposal area because
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some of the part of it not being biodegradable (Muntohar et al., 2012). The incineration of
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municipal solid waste is a common practice to reduce its volume to be disposed in a landfill
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(Show et al., 2003). Some of the research has shown that the MSWI ash can be utilized for
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geotechnical applications such as aggregate in road construction, embankment and landfills
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(Sherwood et al., 1986; Poran and Ahtchi Ali, 1989; Forteza et al., 2004; Mohamedzein et al.,
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2006). The other application of municipal solid waste incineration (MSWI) ash is mixed with
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soils, lime, cement or concrete, which improves the physical properties of finished product
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(Balasubranium et al., 1999; Kaniraj and Gayathri, 2003). The use of MSWI ash in
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geotechnical application can solve many geo-environmental problems and the related issues
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(Kamon et al., 2000; Gao et al., 2011). The addition of cement only contributes to the
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containment of heavy metals due to the high level of alkalinity (Show et al., 2003; Shah and
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Ahmad, 2008). Rahman, (1986) studied the potential use of rice husk ash incorporated with
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lime and cement in lateritic soil stabilization and recommended the use of 7 % cement for base
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materials, 5 % lime for sub-base materials and 18 % rice husk ash as a sub-base material. In
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another study conducted by Prabakar et al., (2004) suggested that the addition of fly ash
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improves the engineering properties of soil and it is cost-effective material for stabilization of
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clay soil. Some of the researchers have worked on physico-chemical parameter as a governing
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agent to change the properties of final product. On the same dais, a few of the studies confined
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on pH parameter as a governing agent which significantly affects the chemical properties of
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both soil and fly ash (Sharma and Kalra, 2006; Cetin and Pehlivan, 2007). Davidson et al.,
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(1965) proposed a minimum pH of 12.4 favoured the pozzolanic reactions between soil and
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lime, and recommended the minimum lime requirement, regarded as a lime fixation point. The
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addition of lime affects the plasticity as well as increased optimum moisture content (OMC) of
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mix specimen (Bell, 1996). Simultaneously, it decreases the maximum dry density (MDD) and
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increases the California bearing ratio (CBR). The study conducted by Chauhan et al., (2008)
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concluded that the OMC increases and MDD decreases with increased percentage of fly ash
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mixed with locally available soil. Muhunthan et al., (2004) studied the properties of
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incineration fly ash, bottom ash and their blends. In their study, they recommended the use of
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these materials in embankment construction view point. Sharma et al., (2012) concluded that
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unconfined compressive strength (UCS) and CBR of soil increases substantially when 20 % fly
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ash and 8.5 % lime mixed with each other. On the same dais, Ramlakhan et al., (2013)
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concluded that the OMC and CBR value increases and MDD decreases with increased
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percentage of lime and fly ash. Simultaneously, the value of MDD decreases, and OMC
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increases. The study conducted by Gay and Schad, (2000) revealed that the combination of
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lime and cement amplify the strength and stiffness. Besides, the addition of cement is helpful
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in improvement of cohesion soil also. Some of the study recommended the use of rubber tires
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in highway and other construction purposes (Ahmed and Lovell, 1993; Upton and Machan,
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1993). The construction of buildings, roads and other civil engineering structures on weak
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or soft soil are generally associated with certain threats because such soil is susceptible to
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differential settlements due to its poor shear strength and high compressibility. Hence, there
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is a need to improve certain desired properties i.e. bearing capacity, shear strength and CBR
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of subgrade soil.
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In this context, various cement stabilization techniques including jet grouting and deep
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cement mixing have been used worldwide for stability, deformation control of land reclamation
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and road construction (Fatahi et al., 2012). These techniques are based on mixing cement with
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soil due to which the soil becomes more resistant. The indeed soil can be stabilized using
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different sort of binders i.e. lime or cement, as the strength characteristics are reached faster
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with their addition. However, the cement treated with soil or ash is more prone to shrinkage
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and may be associated with certain ruptures when used as a base material (Gray et al., 1994).
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On the basis of outcomes suggested by various researchers, the geotechnical properties of mix
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specimens of MSWI ash and cement were supposed to be a hidden application and it may
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change the characteristics of finished product. Thus, the study was aimed to evaluate the
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effects of cement stabilization on the geotechnical properties of MSWI ash mixtures such as
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compaction, unconfined compressive strength, split tensile strength, California bearing ratio
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and pH value etc.
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2. Materials and Methods
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2.1 Cement stabilization
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The soil polished with cement stabilization has become the potential alternative in all aspects
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for many geotechnical engineering problems, such as different structures like embankment,
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road and railways construction. During experimentation, the added value of cement in MSWI
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ash was varied from 0 to 8%. After this, the test specimens were subjected to compaction,
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unconfined compression strength, split tensile strength (STS), CBR tests and pH value to
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evaluate the various physical and mechanical properties. The mix specimens were cured for 7,
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14 and 28 days.
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2.2 Experimental design
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2.2.1 Municipal solid waste incineration (MSWI) ash
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The MSWI ash used in present study was procured from the Municipal Solid Waste
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Incineration Plant, Chandigarh. The various physical and chemical compositions of the MSWI
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ash are summarized in Table 1 and 2. The particle size distribution (ASTM D 6913-04 2000)
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curve for MSWI ash was obtained by wet sieve analysis. The sieve analysis results revealed
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that 84.6 % of the particles exist in the range of 1.18 mm to 75 µm and implying that the
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MSWI ash consists of coarse sand particles. The grain size for the ash falls within the typical
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range for poorly graded sand with silt (SP-SM). Table 2 shows that the MSWI ash used in the
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present study consists largely of calcium and silicon with considerable amounts of potassium,
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iron, aluminum, magnesium and sodium. The high level of Ca and Si contents are the main
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strength contributing agents in portland cement. It is likely that the MSWI ash can also be used
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as a cement admixture or pozzolanic material.
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2.2.2 Physical properties of cement
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An Ordinary Portland Cement (OPC) of 43 Grades was used for the study. It was procured from
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the local market of institutional area. The physical properties of cement are illustrated in the Table
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3.
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2.2.3 Compaction tests
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The tests were performed as per Indian Standard specification for Modified Proctor
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compaction tests as ASTM D (1557-78) to determine the MDD and the OMC of the MSWI
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ash. The heavy compaction tests were carried out on the MSWI ash and mix specimens at
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various moisture contents and allowed to equilibrate for 24 h prior to compaction. A sample
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weighing 3.0 kg passing through 4.75 mm sieve was taken for conducting the compaction test
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in a standard proctor mould of capacity 1000 cc. The water was added to MSWI ash and mixed
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thoroughly without formation of any lumps. Thereafter, the samples was poured in standard
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mould in five layers and compacted by applying 25 blows per layer using a standard rammer
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weighing 4.89 kg and falling through a height of 300 mm.
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2.2.4 Unconfined compressive strength (UCS) test
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The UCS tests were carried out on cylindrical specimens of 38 mm diameter and 76 mm long
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according to ASTM D 2166-98. The MSWI ash-cement mixtures were compacted at OMC and
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MDD in standard moulds. The mixture was compacted in five layers and each layer was
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compacted using rammer under a free fall of 450 mm. From moulds, the specimen of 38 mm
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diameter and 76 mm long were extracted and stored in desiccators partially filled with water at
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room temperature for curing. After this, the samples were tested after 7, 14 and 28 days of
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curing period. The UCS was determined at a loading rate of 1.14 mm/min. The average of
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three specimens of result was reported as the UCS value.
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2.2.5 Split tensile strength (STS) tests
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For conducting the STS test, cylindrical specimens of size 38 mm diameter and 76 mm length
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were prepared at OMC and MDD in the same manner as in case of UCS tests. The STS was
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calculated according to ASTM C 496-96, and it is as follows:
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Split tensile strength, T = గௗ
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Where, P = failure load, L = length of the specimen, d = diameter of the specimen
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2.2.6 California bearing ratio (CBR) tests
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The CBR tests were carried out according to ASTM D1883-05 on specimens of 152 mm
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diameter and 170 mm height compacted in five layer (56 blows under rammer weighing 4.89
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kg) falling through a height of 300 mm to maximum dry density at optimum moisture content.
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The soaked CBR tests were conducted after soaking the specimens for 96 h in water. A 50 mm
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diameter and 100 mm long metal plunger was allowed to penetrate the specimens at strain rate
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of 1.25 mm/min using CBR testing machine. The CBR value was determined corresponding to
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2.5 and 5 mm settlements.
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2.2.7 pH test
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The pH test was performed according to ASTM D 4972-13 to determine the optimum
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combinations of mix specimens. For this, a 30 gm of MSWI ash with different percentage of
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cement, passing through 425 IS sieve was mixed in 75 ml of distilled water. The MSWI ash
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mixed with distilled water was allowed to stand for a period of 1 h and stirred once in every 15
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min. After 1 h, the MSWI ash was stirred, and electrode rod inserted in the beaker and pH
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value was noted on the digital pH meter when it started showing a constant reading.
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3. Result and discussion
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3.1 Compaction test
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The geotechnical properties of MSWI ash depends on the OMC and MDD at which the MSWI
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ash was compacted. The results of OMC and MDD for MSWI ash stabilized with different
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content of cement are presented in fig. 1. It was observed that with the increase in cement
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content, MDD of MSWI ash-cement mixture decreased and OMC increased. The OMC varied
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from 11 to 13.4% while MDD from 16.8 to 16.5 kN/m3. It is due to the reasons that cement
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reacts quickly with the MSWI ash and fine fraction of the soil as pozzolanic material in which
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they form clusters like coarse aggregate. These cluster occupied large space thus increasing
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their volume and consequently decreasing the MDD. The presence of MSWI ash having a low
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specific gravity than soil may be the cause for the reduced dry density (Ferreira et al., 2003;
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Kumar et al., 2007; Okonkwo et al., 2012). Since, the bottom MSWI ash have the capacity of
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absorbing large amount of water, thus the OMC are markedly high in such cases (Izquierdo et
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al., 2011). Furthermore, when the cement content increased from 6 to 8%, the change in OMC
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and MDD found to be negligible. It shows that the addition of cement content by more than 6%
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is not advantageous, and also becomes uneconomical. In literature, the various researchers
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have reported an additional reason behind increased OMC. They have found that such
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condition may arise due to the heat of hydration, when the system is interacted with cement
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(Forteza et al., 2004; Kumar and Gupta, 2016).
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3.2 Unconfined compressive strength (UCS) test results
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The UCS tests were conducted on mix specimens, in which the percentage of cement in MSWI
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ash was varied from 0 to 8 %. The effect of addition of MSWI ash and cement on UCS is
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shown in fig. 2. After the curing period of 7, 14 and 28 days, it was observed that the UCS
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value of stabilized mix specimens was found to be increased with the addition of cement
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content. On the 7th day, it was exhibited as 343, 386, 441 and 515 kN/m2 for 2, 4, 6 and 8 %
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cement, respectively. Similarly, after 28 days, the UCS value of mix specimens was
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experienced as 555, 630, 675 and 745 kN/m2 at respective cement content. This augmentation
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may be due to the increase in availability of alkali (byproduct of hydration of cement) and
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responsible for pozzolanic reaction (Chore and Vaidya, 2015). Furthermore, the rate of gain in
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strength was also found to be increase. The maximum strength was observed for the stabilized
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mix having 6 to 8% cement content. The UCS value of mix specimens showing that the
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strength increased as the curing period increased. This may be attributed to the time
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dependency of pozzolanic reactions and stabilization of lime. The both are long term processes,
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as evidenced by some of the researchers (Rao and Rajaskaran, 1996). It was experienced that
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the UCS of mix specimens after 7, 14, and 28 days of curing period found to be higher
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throughout the study period than those of respective MSWI ash specimen having 0 % cement.
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In literature also, the various researchers have reported the similar kind of pattern (Ola, 1977;
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Rahman, 1987; Bell, 1996).
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3.3 Split tensile strength (STS) test results
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The fig. 3 represents the effect of curing period on STS of all mix specimens. The addition of
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different percentage of cement affects the STS value of mix specimens very significantly. It
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was observed that the STS value augmented with curing period and possessed the highest value
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when it is introduced with cement, varied from 6 to 8%. The reason behind is the time
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dependency of pozzolanic reactions and stabilization of lime. The both are long term processes,
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as evidenced by some of the researchers (Rao and Rajasekaran 1996). Beside this, the STS of
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MSWI ash-cement mixtures after 7, 14 and 28 days of curing period were found to be higher
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than that of MSWI ash specimens. The higher strength of cement stabilized of MSWI ash as
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compared to MSWI ash alone are also the evidence of cementing and pozzolanic properties
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(Rahman, 1987).
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3.4 Stress-strain behavior of the MSWI ash-Cement mixtures
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The effect of cement content on the stress-strain behavior of the various mixtures is shown in
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fig. 4. The plot shows an increasing pattern in axial strain and axial stress. It can be clearly
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seen that with the increase in cement content, varied from 2 to 8% in the mixtures, the peak
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stress increases. This dramatically augmentation in peak stresses with increase in cement
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content and cemented ash mixtures exhibited a marked stiffness and brittleness. For this, the
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failure strain was observed as 2.5%. This may be attributed to the increase in cement content,
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the cementations bond between the particles increases that leads to a higher value of stress,
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cohesion and internal friction (Mishra and Ravindra, 2015). Same kind of pattern has been
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evidenced by some of the researcher in their study (Liu et al., 2006).
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3.5 pH tests
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The pH test conducted on mix specimens were resulted as a cumulative effect during the entire
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study. At 0 % cement the pH of specimen was found as 8.11. This seems to be slightly alkaline
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in nature, while at 8 % cement it showed as 11.36. The increase in pH value may be due to
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alkaline nature of cement and the availability of various metallic compounds as evidenced in
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this study. Besides, it goes on increasing with further increase in cement content, as shown in
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the fig. 5. It, therefore, follows on aforementioned that the higher the cement content, the
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higher the resulting pH of the mix specimen.
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3.6 California bearing ratio (CBR) test results
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The trend of change in CBR values with addition of MSWI ash and cement is shown in the
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fig.6. The addition of cement in MSWI ash increases the CBR value that may be due to the
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interlocking of ash particles and variation in the cohesive nature of the cement (Sharma
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and Hymavathi, 2016). The Table 4 shows the unsoaked and soaked CBR values of MSWI
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ash with addition of different percentage of cement. It was found to be increased due to
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cation exchange reaction between MSWI ashes and cement that resulting it in bonding
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phenomenon. In literature also, the various author have reported the similar kind of pattern
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(Ogundipe Moses 2013; Khalid et al., 2014).
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4. Conclusions
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On the basis of the present study, the following conclusions were made;
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The combination of MSWI ash and cement increased the strength of finished product. This is largely due to the physical and chemical characteristics of the MSWI ash which
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favors the pozzolanic reactions. The pozzolanic reactions play a major role during
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stabilization.
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The MDD of cement stabilized MSWI ash slightly decreases with the increase in
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cement content and OMC increases with increase in the cement content.
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With the increase in cement content, the value of MDD is decreases and OMC
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increases. This decreasing pattern of MDD is because of the MSWI ash, having a low
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specific gravity than that of sand. The OMC value is increased because of the higher
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water absorption of MSWI ash.
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the MSWI ash property.
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It was also concluded that the higher the cement content, greater the improvement in
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The unconfined compressive strength and split tensile strength increases with increase in curing period. The rate of gaining the strength in most of the cases are rapid during
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initial phase of curing, i.e. upto 7 days of curing.
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The soaked CBR value of MSWI ash is increased with the addition of cement. It is proposed that mix specimens of MSWI ash and cement can also be effectively used as a
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base material for the roads, back filling, and improvement of soil bearing capacity
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of the structure.
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Ahmed I, Lovell CW. Use of rubber tires in highway construction. Utilization of waste materials in civil engineering construction. 1992; 166-81.
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properties of cement-stabilized lateritic. International Journal of Sustainable
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Construction Engineering Technology. 2012; 3(1): 18-25.
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1977; 11(4): 305-17.
335
•
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lateritic soils. Soil Found. 1987; 27 (2), 61-65.
construction. Building and Environment. 1986; 21(1):57-61. •
•
•
352 353
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Sharma NK, Swain SK, Sahoo UC. Stabilization of a clayey soil with fly ash and lime:
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Shah SS, Ahmad MS. Stabilization of heavy metal containing waste using fly ash and cement. Indian Geotechnical Journal. 2008; 38(1):89-100.
349 350
Rao SN, Rajasekaran G. Reaction products formed in lime-stabilized marine clays. Journal of geotechnical engineering. 1996; 122(5):329-36.
347 348
Ramlakhan B, Kumar SA, Arora TR. Effect of lime and fly ash on engineering properties of black cotton soil. IJETAE. 2013; 3(11):535-41.
345 346
Rahman MA. The potentials of some stabilizers for the use of lateritic soil in
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343 344
Rahman MA. Effects of cement-rice husk ash mixtures on geotechnical properties of
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341 342
Prabakar J, Dendorkar N, Morchhale RK. Influence of fly ash on strength behavior of typical soils. Construction and Building Materials. 2004; 18(4): 263-7.
339 340
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geotechnical engineering. 1989; 115(8): 1118-33.
337 338
Poran CJ, Ahtchi-Ali F. Properties of solid waste incinerator fly ash. Journal of
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Ola SA. The potentials of lime stabilization of lateritic soils. Engineering Geology.
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a micro level investigation. Geotechnical and geological engineering. 2012; 30(5):1197-205.
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Sharma RK, Hymavathi J. Effect of fly ash, construction demolition waste and lime on
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geotechnical characteristics of a clayey soil: a comparative study. Environmental Earth
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Sciences. 2016; 75(5):1-1.
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of crops'. Journal of scientific and industrial research. 2006; 65:383-90.
357
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Rep., London, 1986; 49.
359 360
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Upton RJ, Machan G. Use of shredded tires for lightweight fill. Transportation Research Record. 1993; (1422).
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Show KY, Tay JH, Goh AT. Reuse of incinerator fly ash in soft soil stabilization. Journal of materials in civil engineering. 2003; 15(4):335-43.
361 362
Sherwood PT, Ryley MD. The use of pulverised fuel ash in road construction. RRL
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Sharma SK, Kalra N. Effect of flyash incorporation on soil properties and productivity
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Table 1 Physical and engineering properties of MSWI ash.
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Table 2 Chemical composition of MSW incinerator ash.
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Table 3 Physical properties of OPC cement.
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Table 4 CBR value of mix specimens at varying degree of cement content.
Table 1 Physical and engineering properties of MSWI ash.
Values
Specific gravity
2.05
Loss on ignition (%)
8.67
3
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Maximum dry density, MDD (kN/m )
Optimum Moisture content, OMC (%) Angle of internal friction ф
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Cohesion
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Properties
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16.8 11
36.5° 0.0
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Table 2 Chemical composition of MSW incinerator ash. Values (%)
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Compounds Silicon dioxide (SiO2 )
55.37
Aluminum oxide (Al2O3)
9.20
Calcium oxide (CaO)
19.39 4.93
SC
Ferric oxide (Fe2O3) Magnesium oxide (MgO)
0.41
Sodium oxide (Na2O)
0.24
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Potassium oxide (K2O) Sulphur dioxide (SO2) Phosphate as (P2O5 ) Chloride as Cl Nitrogen as N
Chromium as Cr Lead as Pb Zinc as Zn Cadmium as Cd
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Copper as Cu
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Barium as Ba
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Organic Carbon
0.43
1.53 0.07 0.44 0.12 0.96 0.11 0.051 0.07 0.02
7.45 mg/kg 94.4 mg/kg
Table 3 Physical properties of OPC cement. Properties
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Value
Fineness (%)
3
3.14
Standard Consistency %
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Specific gravity G
Final setting time, minute
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Soundness (Cement Expansion, mm)
33 30
600 3
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Table 4 CBR value of mix specimens at varying degree of cement content.
MSWI ash (%)
Cement (%)
California Bearing Ratio (% ) Unsoaked
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S. No.
Soaked
100
0
15
2
98
2
17
3
96
4
22
32
4
94
6
30
40
5
92
8
34
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Fig. 1. Maximum dry density (MDD) and optimum moisture content (OMC) variation in mix specimens of varying degree of cement content
cement, and MSWI ash after curing periods
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Fig. 2. Variation of unconfined compressive strength (UCS) with different combinations of
Fig. 3. Variation of split tensile strength (STS) with different combinations of cement and MSWI
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ash after curing periods
Fig. 4. Stress-strain curve varying cement content after 28 days curing periods Fig. 5. pH of –mix specimen at varying content of cement
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Fig. 6. Laboratory result for CBR value under soaked condition
OMC
16.8
16 14 12
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16.75 16.7 16.65 16.6 16.55 16.5 16.45 0%
2%
4%
6%
8%
10 8 6 4 2
Optimum Moisture Content (%)
MDD
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Maximum Dry Density (kN/m3)
16.85
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0 10%
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Cement (%)
Fig. 1. Maximum dry density (MDD) and optimum moisture content (OMC) variation in mix
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specimens of varying degree of cement content
800
2 % cement
4 % cement
6 % Cement
700
8 % Cement
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500 400 300 200 100 0 0
7
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UCS kN/m2
600
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14
28
Curing period (days )
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Fig. 2. Variation of unconfined compressive strength (UCS) with different combinations of cement, and MSWI ash after curing periods
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120
14 days
100 80 60
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STS (kN/m2)
28 days
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7 days
40
0 0%
2%
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4%
6%
8%
10%
Cement (%)
Fig. 3. Variation of split tensile strength (STS) with different combinations of cement and MSWI
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ash after curing periods
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2% Cement
4% Cement
6% Cement
8% Cement
600
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400
300
6.0
5.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
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100
5.5
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200
4.5
Axial Stress (kN/m2)
500
Axial Strain (%)
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Fig. 4. Stress-strain curve varying cement content after 28 days curing periods
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pH Value
12
10
6 0
2
4
6
8
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Cement (%)
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Fig. 5. pH of –mix specimen at varying content of cement
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35 30
0 % Cement
2 % Cement
6 % Cement
8 % Cement
4 % Cement
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15 10 5 0 2.5
5
7.5
10
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0
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20
12.5
Penetration (mm)
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Fig. 6. Laboratory result for CBR value under soaked condition
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Load (kN)
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Research Highlights
The soaked CBR value of MSWI ash increases with the addition of cement
MSWI ash which favored the pozzolanic reactions
Unconfined compressive strength and split tensile strength of mix specimen increases with increase in curing period
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The specimen seems to be slightly alkaline in nature
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S1674-7755(16)30071-3
DOI:
10.1016/j.jrmge.2016.11.008
Reference:
JRMGE 314
To appear in:
Journal of Rock Mechanics and Geotechnical Engineering
Received Date: 27 July 2016 Revised Date:
26 October 2016
Accepted Date: 7 November 2016
Please cite this article as: Singh D, Kumar A, Geo-environmental application of municipal solid waste incineration ash stabilized with Cement, Journal of Rock Mechanics and Geotechnical Engineering (2017), doi: 10.1016/j.jrmge.2016.11.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Geo-environmental application of municipal solid waste incineration ash stabilized with
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Cement
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Davinder Singh* and Arvind Kumar**
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Assistant Professor, Department of Civil Engineering, Dr. B.R. Ambedkar NIT Jalandhar,
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Punjab India *
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Professor, Department of Civil Engineering, Dr. B.R. Ambedkar NIT Jalandhar, Punjab,
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India**
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Abstract
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The behavior of soluble salts contained in the municipal solid waste incinerator ash
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significantly affects the strength development and hardening reaction when it is introduced
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with cement. The present study emphasizes on the compaction and strength behavior of mix
23
specimen of cement and MSWI ash. Series of tests such as unconfined compressive strength,
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split tensile strength and California bearing ratio and pH tests were carried out. Prior to this,
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the specimens were cured for 7, 14, and 28 days. The test results depicted that the maximum
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dry density decreases and optimum moisture content increases with the addition of cement.
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The test results also revealed that the cement inclusion increased the strength of the mix
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specimens. Thus, the combination of MSWI ash and cement can be used as light weight
29
filling material in different structures like embankment and road construction.
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Keywords: Municipal solid waste incinerator ash; Cement; Compaction; Stabilization; CBR
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Test; Geotechnical properties
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1. Introduction
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The safe disposal of waste materials such as municipal, industrial and hazardous waste has
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been one of the big challenges in urban cities as well as in rural environment in recent days.
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Such wastes pose environmental pollution problems for the surrounding disposal area because
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some of the part of it not being biodegradable (Muntohar et al., 2012). The incineration of
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municipal solid waste is a common practice to reduce its volume to be disposed in a landfill
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(Show et al., 2003). Some of the research has shown that the MSWI ash can be utilized for
39
geotechnical applications such as aggregate in road construction, embankment and landfills
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(Sherwood et al., 1986; Poran and Ahtchi Ali, 1989; Forteza et al., 2004; Mohamedzein et al.,
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2006). The other application of municipal solid waste incineration (MSWI) ash is mixed with
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soils, lime, cement or concrete, which improves the physical properties of finished product
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(Balasubranium et al., 1999; Kaniraj and Gayathri, 2003). The use of MSWI ash in
44
geotechnical application can solve many geo-environmental problems and the related issues
45
(Kamon et al., 2000; Gao et al., 2011). The addition of cement only contributes to the
46
containment of heavy metals due to the high level of alkalinity (Show et al., 2003; Shah and
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Ahmad, 2008). Rahman, (1986) studied the potential use of rice husk ash incorporated with
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lime and cement in lateritic soil stabilization and recommended the use of 7 % cement for base
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materials, 5 % lime for sub-base materials and 18 % rice husk ash as a sub-base material. In
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another study conducted by Prabakar et al., (2004) suggested that the addition of fly ash
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improves the engineering properties of soil and it is cost-effective material for stabilization of
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clay soil. Some of the researchers have worked on physico-chemical parameter as a governing
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agent to change the properties of final product. On the same dais, a few of the studies confined
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on pH parameter as a governing agent which significantly affects the chemical properties of
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both soil and fly ash (Sharma and Kalra, 2006; Cetin and Pehlivan, 2007). Davidson et al.,
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(1965) proposed a minimum pH of 12.4 favoured the pozzolanic reactions between soil and
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lime, and recommended the minimum lime requirement, regarded as a lime fixation point. The
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addition of lime affects the plasticity as well as increased optimum moisture content (OMC) of
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mix specimen (Bell, 1996). Simultaneously, it decreases the maximum dry density (MDD) and
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increases the California bearing ratio (CBR). The study conducted by Chauhan et al., (2008)
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concluded that the OMC increases and MDD decreases with increased percentage of fly ash
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mixed with locally available soil. Muhunthan et al., (2004) studied the properties of
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incineration fly ash, bottom ash and their blends. In their study, they recommended the use of
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these materials in embankment construction view point. Sharma et al., (2012) concluded that
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unconfined compressive strength (UCS) and CBR of soil increases substantially when 20 % fly
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ash and 8.5 % lime mixed with each other. On the same dais, Ramlakhan et al., (2013)
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concluded that the OMC and CBR value increases and MDD decreases with increased
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percentage of lime and fly ash. Simultaneously, the value of MDD decreases, and OMC
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increases. The study conducted by Gay and Schad, (2000) revealed that the combination of
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lime and cement amplify the strength and stiffness. Besides, the addition of cement is helpful
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in improvement of cohesion soil also. Some of the study recommended the use of rubber tires
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in highway and other construction purposes (Ahmed and Lovell, 1993; Upton and Machan,
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1993). The construction of buildings, roads and other civil engineering structures on weak
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or soft soil are generally associated with certain threats because such soil is susceptible to
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differential settlements due to its poor shear strength and high compressibility. Hence, there
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is a need to improve certain desired properties i.e. bearing capacity, shear strength and CBR
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of subgrade soil.
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In this context, various cement stabilization techniques including jet grouting and deep
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cement mixing have been used worldwide for stability, deformation control of land reclamation
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and road construction (Fatahi et al., 2012). These techniques are based on mixing cement with
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soil due to which the soil becomes more resistant. The indeed soil can be stabilized using
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different sort of binders i.e. lime or cement, as the strength characteristics are reached faster
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with their addition. However, the cement treated with soil or ash is more prone to shrinkage
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and may be associated with certain ruptures when used as a base material (Gray et al., 1994).
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On the basis of outcomes suggested by various researchers, the geotechnical properties of mix
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specimens of MSWI ash and cement were supposed to be a hidden application and it may
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change the characteristics of finished product. Thus, the study was aimed to evaluate the
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effects of cement stabilization on the geotechnical properties of MSWI ash mixtures such as
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compaction, unconfined compressive strength, split tensile strength, California bearing ratio
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and pH value etc.
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2. Materials and Methods
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2.1 Cement stabilization
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The soil polished with cement stabilization has become the potential alternative in all aspects
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for many geotechnical engineering problems, such as different structures like embankment,
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road and railways construction. During experimentation, the added value of cement in MSWI
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ash was varied from 0 to 8%. After this, the test specimens were subjected to compaction,
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unconfined compression strength, split tensile strength (STS), CBR tests and pH value to
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evaluate the various physical and mechanical properties. The mix specimens were cured for 7,
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14 and 28 days.
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2.2 Experimental design
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2.2.1 Municipal solid waste incineration (MSWI) ash
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The MSWI ash used in present study was procured from the Municipal Solid Waste
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Incineration Plant, Chandigarh. The various physical and chemical compositions of the MSWI
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ash are summarized in Table 1 and 2. The particle size distribution (ASTM D 6913-04 2000)
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curve for MSWI ash was obtained by wet sieve analysis. The sieve analysis results revealed
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that 84.6 % of the particles exist in the range of 1.18 mm to 75 µm and implying that the
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MSWI ash consists of coarse sand particles. The grain size for the ash falls within the typical
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range for poorly graded sand with silt (SP-SM). Table 2 shows that the MSWI ash used in the
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present study consists largely of calcium and silicon with considerable amounts of potassium,
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iron, aluminum, magnesium and sodium. The high level of Ca and Si contents are the main
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strength contributing agents in portland cement. It is likely that the MSWI ash can also be used
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as a cement admixture or pozzolanic material.
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2.2.2 Physical properties of cement
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An Ordinary Portland Cement (OPC) of 43 Grades was used for the study. It was procured from
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the local market of institutional area. The physical properties of cement are illustrated in the Table
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3.
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2.2.3 Compaction tests
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The tests were performed as per Indian Standard specification for Modified Proctor
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compaction tests as ASTM D (1557-78) to determine the MDD and the OMC of the MSWI
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ash. The heavy compaction tests were carried out on the MSWI ash and mix specimens at
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various moisture contents and allowed to equilibrate for 24 h prior to compaction. A sample
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weighing 3.0 kg passing through 4.75 mm sieve was taken for conducting the compaction test
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in a standard proctor mould of capacity 1000 cc. The water was added to MSWI ash and mixed
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thoroughly without formation of any lumps. Thereafter, the samples was poured in standard
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mould in five layers and compacted by applying 25 blows per layer using a standard rammer
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weighing 4.89 kg and falling through a height of 300 mm.
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2.2.4 Unconfined compressive strength (UCS) test
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The UCS tests were carried out on cylindrical specimens of 38 mm diameter and 76 mm long
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according to ASTM D 2166-98. The MSWI ash-cement mixtures were compacted at OMC and
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MDD in standard moulds. The mixture was compacted in five layers and each layer was
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compacted using rammer under a free fall of 450 mm. From moulds, the specimen of 38 mm
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diameter and 76 mm long were extracted and stored in desiccators partially filled with water at
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room temperature for curing. After this, the samples were tested after 7, 14 and 28 days of
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curing period. The UCS was determined at a loading rate of 1.14 mm/min. The average of
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three specimens of result was reported as the UCS value.
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2.2.5 Split tensile strength (STS) tests
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For conducting the STS test, cylindrical specimens of size 38 mm diameter and 76 mm length
138
were prepared at OMC and MDD in the same manner as in case of UCS tests. The STS was
139
calculated according to ASTM C 496-96, and it is as follows:
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Split tensile strength, T = గௗ
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Where, P = failure load, L = length of the specimen, d = diameter of the specimen
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2.2.6 California bearing ratio (CBR) tests
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The CBR tests were carried out according to ASTM D1883-05 on specimens of 152 mm
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diameter and 170 mm height compacted in five layer (56 blows under rammer weighing 4.89
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kg) falling through a height of 300 mm to maximum dry density at optimum moisture content.
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The soaked CBR tests were conducted after soaking the specimens for 96 h in water. A 50 mm
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diameter and 100 mm long metal plunger was allowed to penetrate the specimens at strain rate
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of 1.25 mm/min using CBR testing machine. The CBR value was determined corresponding to
149
2.5 and 5 mm settlements.
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2.2.7 pH test
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The pH test was performed according to ASTM D 4972-13 to determine the optimum
152
combinations of mix specimens. For this, a 30 gm of MSWI ash with different percentage of
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cement, passing through 425 IS sieve was mixed in 75 ml of distilled water. The MSWI ash
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mixed with distilled water was allowed to stand for a period of 1 h and stirred once in every 15
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min. After 1 h, the MSWI ash was stirred, and electrode rod inserted in the beaker and pH
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value was noted on the digital pH meter when it started showing a constant reading.
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3. Result and discussion
158
3.1 Compaction test
159
The geotechnical properties of MSWI ash depends on the OMC and MDD at which the MSWI
160
ash was compacted. The results of OMC and MDD for MSWI ash stabilized with different
161
content of cement are presented in fig. 1. It was observed that with the increase in cement
162
content, MDD of MSWI ash-cement mixture decreased and OMC increased. The OMC varied
163
from 11 to 13.4% while MDD from 16.8 to 16.5 kN/m3. It is due to the reasons that cement
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reacts quickly with the MSWI ash and fine fraction of the soil as pozzolanic material in which
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they form clusters like coarse aggregate. These cluster occupied large space thus increasing
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their volume and consequently decreasing the MDD. The presence of MSWI ash having a low
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specific gravity than soil may be the cause for the reduced dry density (Ferreira et al., 2003;
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Kumar et al., 2007; Okonkwo et al., 2012). Since, the bottom MSWI ash have the capacity of
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absorbing large amount of water, thus the OMC are markedly high in such cases (Izquierdo et
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al., 2011). Furthermore, when the cement content increased from 6 to 8%, the change in OMC
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and MDD found to be negligible. It shows that the addition of cement content by more than 6%
172
is not advantageous, and also becomes uneconomical. In literature, the various researchers
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have reported an additional reason behind increased OMC. They have found that such
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condition may arise due to the heat of hydration, when the system is interacted with cement
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(Forteza et al., 2004; Kumar and Gupta, 2016).
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3.2 Unconfined compressive strength (UCS) test results
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The UCS tests were conducted on mix specimens, in which the percentage of cement in MSWI
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ash was varied from 0 to 8 %. The effect of addition of MSWI ash and cement on UCS is
179
shown in fig. 2. After the curing period of 7, 14 and 28 days, it was observed that the UCS
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value of stabilized mix specimens was found to be increased with the addition of cement
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content. On the 7th day, it was exhibited as 343, 386, 441 and 515 kN/m2 for 2, 4, 6 and 8 %
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cement, respectively. Similarly, after 28 days, the UCS value of mix specimens was
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experienced as 555, 630, 675 and 745 kN/m2 at respective cement content. This augmentation
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may be due to the increase in availability of alkali (byproduct of hydration of cement) and
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responsible for pozzolanic reaction (Chore and Vaidya, 2015). Furthermore, the rate of gain in
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strength was also found to be increase. The maximum strength was observed for the stabilized
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mix having 6 to 8% cement content. The UCS value of mix specimens showing that the
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strength increased as the curing period increased. This may be attributed to the time
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dependency of pozzolanic reactions and stabilization of lime. The both are long term processes,
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as evidenced by some of the researchers (Rao and Rajaskaran, 1996). It was experienced that
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the UCS of mix specimens after 7, 14, and 28 days of curing period found to be higher
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throughout the study period than those of respective MSWI ash specimen having 0 % cement.
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In literature also, the various researchers have reported the similar kind of pattern (Ola, 1977;
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Rahman, 1987; Bell, 1996).
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3.3 Split tensile strength (STS) test results
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The fig. 3 represents the effect of curing period on STS of all mix specimens. The addition of
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different percentage of cement affects the STS value of mix specimens very significantly. It
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was observed that the STS value augmented with curing period and possessed the highest value
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when it is introduced with cement, varied from 6 to 8%. The reason behind is the time
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dependency of pozzolanic reactions and stabilization of lime. The both are long term processes,
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as evidenced by some of the researchers (Rao and Rajasekaran 1996). Beside this, the STS of
202
MSWI ash-cement mixtures after 7, 14 and 28 days of curing period were found to be higher
203
than that of MSWI ash specimens. The higher strength of cement stabilized of MSWI ash as
204
compared to MSWI ash alone are also the evidence of cementing and pozzolanic properties
205
(Rahman, 1987).
206
3.4 Stress-strain behavior of the MSWI ash-Cement mixtures
207
The effect of cement content on the stress-strain behavior of the various mixtures is shown in
208
fig. 4. The plot shows an increasing pattern in axial strain and axial stress. It can be clearly
209
seen that with the increase in cement content, varied from 2 to 8% in the mixtures, the peak
210
stress increases. This dramatically augmentation in peak stresses with increase in cement
211
content and cemented ash mixtures exhibited a marked stiffness and brittleness. For this, the
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failure strain was observed as 2.5%. This may be attributed to the increase in cement content,
213
the cementations bond between the particles increases that leads to a higher value of stress,
214
cohesion and internal friction (Mishra and Ravindra, 2015). Same kind of pattern has been
215
evidenced by some of the researcher in their study (Liu et al., 2006).
216
3.5 pH tests
217
The pH test conducted on mix specimens were resulted as a cumulative effect during the entire
218
study. At 0 % cement the pH of specimen was found as 8.11. This seems to be slightly alkaline
219
in nature, while at 8 % cement it showed as 11.36. The increase in pH value may be due to
220
alkaline nature of cement and the availability of various metallic compounds as evidenced in
221
this study. Besides, it goes on increasing with further increase in cement content, as shown in
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the fig. 5. It, therefore, follows on aforementioned that the higher the cement content, the
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higher the resulting pH of the mix specimen.
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3.6 California bearing ratio (CBR) test results
225
The trend of change in CBR values with addition of MSWI ash and cement is shown in the
226
fig.6. The addition of cement in MSWI ash increases the CBR value that may be due to the
227
interlocking of ash particles and variation in the cohesive nature of the cement (Sharma
228
and Hymavathi, 2016). The Table 4 shows the unsoaked and soaked CBR values of MSWI
229
ash with addition of different percentage of cement. It was found to be increased due to
230
cation exchange reaction between MSWI ashes and cement that resulting it in bonding
231
phenomenon. In literature also, the various author have reported the similar kind of pattern
232
(Ogundipe Moses 2013; Khalid et al., 2014).
233
4. Conclusions
234
On the basis of the present study, the following conclusions were made;
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The combination of MSWI ash and cement increased the strength of finished product. This is largely due to the physical and chemical characteristics of the MSWI ash which
237
favors the pozzolanic reactions. The pozzolanic reactions play a major role during
238
stabilization.
240 241
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The MDD of cement stabilized MSWI ash slightly decreases with the increase in
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cement content and OMC increases with increase in the cement content.
•
With the increase in cement content, the value of MDD is decreases and OMC
242
increases. This decreasing pattern of MDD is because of the MSWI ash, having a low
243
specific gravity than that of sand. The OMC value is increased because of the higher
244
water absorption of MSWI ash.
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the MSWI ash property.
246 247
It was also concluded that the higher the cement content, greater the improvement in
•
The unconfined compressive strength and split tensile strength increases with increase in curing period. The rate of gaining the strength in most of the cases are rapid during
249
initial phase of curing, i.e. upto 7 days of curing.
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The soaked CBR value of MSWI ash is increased with the addition of cement. It is proposed that mix specimens of MSWI ash and cement can also be effectively used as a
252
base material for the roads, back filling, and improvement of soil bearing capacity
253
of the structure.
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Ahmed I, Lovell CW. Use of rubber tires in highway construction. Utilization of waste materials in civil engineering construction. 1992; 166-81.
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Table 1 Physical and engineering properties of MSWI ash.
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Table 2 Chemical composition of MSW incinerator ash.
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Table 3 Physical properties of OPC cement.
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Table 4 CBR value of mix specimens at varying degree of cement content.
Table 1 Physical and engineering properties of MSWI ash.
Values
Specific gravity
2.05
Loss on ignition (%)
8.67
3
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Maximum dry density, MDD (kN/m )
Optimum Moisture content, OMC (%) Angle of internal friction ф
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Cohesion
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Properties
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16.8 11
36.5° 0.0
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Table 2 Chemical composition of MSW incinerator ash. Values (%)
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Compounds Silicon dioxide (SiO2 )
55.37
Aluminum oxide (Al2O3)
9.20
Calcium oxide (CaO)
19.39 4.93
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Ferric oxide (Fe2O3) Magnesium oxide (MgO)
0.41
Sodium oxide (Na2O)
0.24
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Potassium oxide (K2O) Sulphur dioxide (SO2) Phosphate as (P2O5 ) Chloride as Cl Nitrogen as N
Chromium as Cr Lead as Pb Zinc as Zn Cadmium as Cd
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Copper as Cu
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Barium as Ba
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Organic Carbon
0.43
1.53 0.07 0.44 0.12 0.96 0.11 0.051 0.07 0.02
7.45 mg/kg 94.4 mg/kg
Table 3 Physical properties of OPC cement. Properties
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Value
Fineness (%)
3
3.14
Standard Consistency %
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Initial setting time, minute
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Specific gravity G
Final setting time, minute
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Soundness (Cement Expansion, mm)
33 30
600 3
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Table 4 CBR value of mix specimens at varying degree of cement content.
MSWI ash (%)
Cement (%)
California Bearing Ratio (% ) Unsoaked
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S. No.
Soaked
100
0
15
2
98
2
17
3
96
4
22
32
4
94
6
30
40
5
92
8
34
50
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1
19 23
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Fig. 1. Maximum dry density (MDD) and optimum moisture content (OMC) variation in mix specimens of varying degree of cement content
cement, and MSWI ash after curing periods
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Fig. 2. Variation of unconfined compressive strength (UCS) with different combinations of
Fig. 3. Variation of split tensile strength (STS) with different combinations of cement and MSWI
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ash after curing periods
Fig. 4. Stress-strain curve varying cement content after 28 days curing periods Fig. 5. pH of –mix specimen at varying content of cement
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Fig. 6. Laboratory result for CBR value under soaked condition
OMC
16.8
16 14 12
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16.75 16.7 16.65 16.6 16.55 16.5 16.45 0%
2%
4%
6%
8%
10 8 6 4 2
Optimum Moisture Content (%)
MDD
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Maximum Dry Density (kN/m3)
16.85
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0 10%
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Cement (%)
Fig. 1. Maximum dry density (MDD) and optimum moisture content (OMC) variation in mix
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specimens of varying degree of cement content
800
2 % cement
4 % cement
6 % Cement
700
8 % Cement
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500 400 300 200 100 0 0
7
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UCS kN/m2
600
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28
Curing period (days )
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Fig. 2. Variation of unconfined compressive strength (UCS) with different combinations of cement, and MSWI ash after curing periods
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120
14 days
100 80 60
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STS (kN/m2)
28 days
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7 days
40
0 0%
2%
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4%
6%
8%
10%
Cement (%)
Fig. 3. Variation of split tensile strength (STS) with different combinations of cement and MSWI
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ash after curing periods
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2% Cement
4% Cement
6% Cement
8% Cement
600
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400
300
6.0
5.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
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5.5
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200
4.5
Axial Stress (kN/m2)
500
Axial Strain (%)
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Fig. 4. Stress-strain curve varying cement content after 28 days curing periods
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pH Value
12
10
6 0
2
4
6
8
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Cement (%)
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8
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Fig. 5. pH of –mix specimen at varying content of cement
10
12
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35 30
0 % Cement
2 % Cement
6 % Cement
8 % Cement
4 % Cement
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15 10 5 0 2.5
5
7.5
10
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20
12.5
Penetration (mm)
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Fig. 6. Laboratory result for CBR value under soaked condition
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Load (kN)
25
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Research Highlights
The soaked CBR value of MSWI ash increases with the addition of cement
MSWI ash which favored the pozzolanic reactions
Unconfined compressive strength and split tensile strength of mix specimen increases with increase in curing period
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The specimen seems to be slightly alkaline in nature
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