Verification of the Effect of Raw Materials Mill Dust on Soil Stabilization: An Experimental Study

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 172-177

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

https://doi.org/10.47277/JETT/9(1)183

Verification of the Effect of Raw Materials Mill Dust

on Soil Stabilization: An Experimental Study

Fatima Alsaleh , Feras Al Adday , Ahmed Al-Abu Hussein

Department of Transportation Engineering, Faculty of Civil Engineering, University of Aleppo,

Middle East University, Amman, Jordan

Received: 26/07/2020

Accepted: 21/10/2020

Published: 20/03/2021

Abstract

Cement plants produce large quantities of dust, which is an important source of pollution. Among these pollutants is raw materials mill

dust (RMMD), it is a dust produced during the grinding of raw materials. RMMD differs in chemical composition from cement kiln dust

(

CKD), where CKD is a by-product that collects in the electrostatic filters of a cement kiln. A lot of studies have been done around the world

to find effective ways to recycle CKD and use it again in soil stabilization to avoid the failure of the entire pavement in the future as well as

an economical and environmental solution, while there is a dearth of research done on RMMD. In this study, the performance of a weak

subgrade for one of the sites in Aleppo city was examined, where its physical and mechanical properties (plasticity index, maximum dry

density, optimum water content, and California bearing ratio (CBR)), were determined. Then RMMD was added to the subgrade samples

according to five ratios 0, 5, 10, 15, and 20% of the dry weight of the soil. The research concluded that adding the RMMD to the weak

subgrade by 20% of its dry weight is the optimal ratio, improved its performance, as the plasticity index decreased by 13%, and the CBR

increased up to 63 %. Thus, the bearing capacity increases, it saves costs and reduces future pavement maintenance.

Keywords: Soil Stabilization, Weak Soil, Mill Dust, Chemical additive

which the bearing capacity is enhanced by compaction of the soil

Introduction

to a sufficient degree, or by means of piles or application of an

external load on the soil or the use of good drainage of water, or

stone columns [15, 16]. The second technique is chemical

stabilization of soil by a chemical reaction between weak soils

and the added active substance [17, 18]. Among these materials

are lime, gypsum, cement, asphalt, resin, fly ash, and other

materials such as industrial or natural wastes such as the CKD and

rice husk ash [15, 19, 20, 21, 22, and 23]. The common soil

additives are lime and cement (traditional stabilizers) [24].

RMMD is of great importance in the field of civil engineering and

its projects, and one of these uses is to improve weak soils. The

flying dust is captured and collected from the raw material mill of

the cement factory in Hama, Syria through two types of filters,

Electrostatic and Baghouse Filters as well as for the dust flying

throughout the entire manufacturing process of cement.

RMMD has been chosen as a weak soil stabilizer for several

reasons, the most important of which is its large quantities and it

is being a completely new material in this topic of soil

stabilization in road pavement. The fact that the total quantity of

the electric filter of the raw material mill is large when compared

to the Baghouse filter, the research has focused on studying its

effect on soil performance.

The great growth in modern buildings imposed the need for

lands with good bearing capacity to safely withstand high

pressures [1]. One of the important issues facing the pavement

engineer is to provide economically viable layer thicknesses that

are compatible with the site's soil characteristics [2, 3]. The

general case is the lack of alternative design solutions to avoid

weak soils, hence it is necessary to search for low-cost

experimental alternatives [4, 5]. The weak soil has the high

compressibility, poor shear strength, high ratio of moisture, low

workability, which produces extra settlements of soil, and this

makes the construction process on such soils a high probability

issue [6]. For road pavements, soil properties have a major

influence in determining the thickness of the layers above [7].

Thus, road performance and service are greatly influenced by the

stability and stiffness of the subgrade [8, 9]. Consequently, these

soil must be stabilized or treated to increase in its geotechnical

characteristics. the term soil stabilization is a technique in which

weak soil properties are improved to fulfil its functions

(

operational conditions of the road and the subsequent volumetric

changes of soil) as the foundation for the structures based on it

10, 11, 12, 13]. There are two techniques that are widely used for

soil stabilization [14]. The first method is a mechanical method in

[

Corresponding author: Fatima Alsaleh, Department of Transportation Engineering, Faculty of Civil Engineering, University of Aleppo. E-

mail: falkhalil@meu.edu.jo

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Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 172-177

Figure 1: shows the parts of the cement factory, with electrical and Baghouse filters [27]

- Quarries, 2- Crushers, 3- The homogenizing process, 4- The assembly process, 5- Feed silos of the raw material mill, 6- The main

chimney, 7- Electric and Baghouse filters, 8- The raw material mill, 9- Raw material feeding silos, 10- gas temperature adjustment tower,

1- filters, 12- mixing chambers, 13- preheating tower (spiral), 14- raw coal, 15- coal mill, 16- filters, 17- tube cooler, 18- Electrical and

Baghouse filters, 19- clinker cooler, 20- rotary kiln, 21- clinker silos, 22- gypsum / plaster, 23- assorted metals, 24- sorters, 25- cement

mill (finishing), 26- filters, 27- packaging 28- Loading and transport platform.

It should be noted that their physical and chemical properties

between them are similar. Engineers strive for low-cost

alternatives while maintaining appropriate performance, as

materials with good specifications require high cost [25, 26].

Figure 1 shows the parts of the Hama Cement Factory and the

location of the electrical filter for the raw materials mill [27].

its physical properties. There is a difference in the chemical

composition of RMMD and CKD, and this has been proven by

laboratory experiments, but there is a percentage of up to 48.3%

of Cao that is somewhat close to the composition of CKD.

Methodology

Improving the performance of the subgrade by using RMMD

as an additive to their structure was investigated, by studying the

effect of adding RMMD on its physical and mechanical

properties.

.1 Materials used

Subgrade materials: Soil samples from one of the sites near

the city of Aleppo were brought to the laboratory, where the

required quantity was taken at a depth exceeding 50 cm. A grain

size analysis, soil classification, the optimum moisture content

(

OMC), shear resistance, and CBR were carried out. Table 1

shows the characteristics of the subgrade soil. Figure 2 shows a

grain size analysis.

0.01

0.1

100

RMMD: It is a by-product material that is generally produced

when grinding raw materials in the cement factory, the city of

Hama, Syria. It has been added to soil samples according to 0, 5,

Siev openning(mm)

Figure 2: The soil gradation

0, 15, and 20% of the dry weight of the soil. Regarding the

chemical composition of RMMD, which was adopted as an

additive to soil samples, it is shown in table 2, and table 3 shows

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Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 172-177

Table 1: Subgrade properties

Oven and coolant: The homogeneous raw materials are

pulled from the bottom of the storage silo into the feed slot of a

multi-stage primary heating tower, and the tower may reach a

height of 280 m. Natural gas or diesel oil is used as a source of

heat energy, and hot air from clinker cooling is used as an

additional source of heat. The kiln is tilted slightly on the

horizontal plane to allow a slow movement of solids down, so the

distance is cut to the feed hole at the top of the oven to the lower

end (combustion) where high-temperature combustion gases are

generated in a period of 1 to 3 hours, while Combustion gases

move upward in the current opposite to the movement of solids.

The hot combustion gases heat the raw materials at the oven feed

slot and provide calcium carbonate [28][29].

Properties

Value

Clay and silt%

Sand%

28.6%

Grain Size

Analysis

57.88%

13.52%

Gravel%

LL%, liquid limit,

ASTM D 4318

PL% ,plasticity limit,

ASTM D 4318

Atterberg

Limits

PI% (plasticity index)

MDD (gr/cm ) ASTM D 698

1.72

Modified

Proctor

Final milling and packing: The clinker is transported to

special mills, where the gypsum is added to it and the product is

packed in bags to be exported and marketed [28].

OMC %, ASTM D 698

17.8

USCS, ASTM D 2487

AASHTO

Soil

Classification

A-2-7

10.5 %

3 Results and discussion

.1 Plasticity characteristics (LL, PL, PI)

The effects of adding RMMD on LL, PL, and PI of soil are

CBR, ASTM D1883-05

shown in Figure 3. The LL and PL decline with the addition of

RMMD. This may be attributed to Cationic interchange of soil

units with calcium ions which leads to drop LL because of

suppression of flocculated clay clusters (this decreases the soil's

attraction to water) [30, 31], which, in turn, decreases in the PI of

subgrade soil. A decrease in PI is a clear indication of

improvement of soil physical properties as it increases

workability [21]. The best PI decrease was reached at 20%

RMMD, the largest decrease in PI was at 20% RMMD, dropping

from 19 for subgrade soils to 15 for stabilized soil. In this regard,

a relationship between the PI and the percentages of RMMD for

the subgrade soil can be presented, as shown in Figure 4.

Table 2: Chemical composition of RMMD

Composition

percent

38.47

7.47

SiO

2.65

1.42

MgO

CaO

Total

L.S.F

S.M

1.48

48.30

99.78

193.51

1.84

5.0

0.0

5.0

0.0

5.0

0.0

PI LL PL

A.M

1.86

Table3: Physical properties of RMMD

Properties

Value

2.69

15.0

0.0

Specific gravity, ASTM D 854

Specific surface (cm /gr)

Moisture %, ASTM D 698

7812

0.7

RMMD %

.2 Main processes in the operating line of the cement industry

Figure 3: LL, PL, and PI changes versus RMMD %

Crushing and mixing of raw materials:

Raw materials of limestone, silicates, clays and surface dust

are crushed by milling mechanisms, then sifted and transported,

to be stored as piles in open or covered areas [28].

3.2 Compaction characteristics (MDD, OMC)

Figure 5 shows the general behavior of the subgrade soil, a

gradual increase in the moisture content leads to increase the dry

density up to maximum value, and then begins to decrease, and

this is true for all RMMD ratios. OMC and MDD can be inferred

for each addition of RMMD, Figure 6, 7 illustrate the relationship

between the RMMD% and OMC and MDD. An increase in MDD

value was observed, and this is an indication of improved

subgrade characteristics. The mechanism of the increase can be

explained by the effect of both the fineness of the RMMD and

specific surface of the RMMD and flocculation. The more fine-

grained of RMMD was able to fill larger spaces of soil whereas

Milling: Raw materials are introduced into a rotary dryer (in

case the moisture is more than a certain percentage), where they

are dried by hot air, then the raw materials are crushed in raw

materials mills and transferred to pre-mixing storage silos, where

they become homogeneous through compacting and drawing

process, then the homogeneous raw materials are transferred from

storage silos or other types from pre-mixing storage places to

mixing places. The process of blending is 30% of clay, and 70%

of limestone [28]

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Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 172-177

the higher specific surface of the RMMD to the soil encouraged

MDD increase.

to an increase in the bearing capacity of the soil, as different

studies have shown that the creation of calcium hydroxide

(

Ca(OH)2) produced during the process of hydration of RMMD

with water, this hydrate compound absorbed by the clay unites

help to stabilize flocculated fine clay, as a result the adjustment

of the clay microstructure has been occurred [21].

PI= -0.0013(RMMD)2 - 0.0749(RMMD) + 17.85

8.0

7.5

7.0

6.5

6.0

5.5

5.0

R² = 0.9769

MDD = 0.000003(RMMD)2 + 0.0022(RMMD) + 1.7229

.79

.78

.77

.76

.75

R² = 0.9526

1.74

RMMD %

Figure 4: The relationship between the PI and RMMD %

.73

.72

.71

RMMD %

REMF0

REMF5

REMF10

REMF15

REMF20

Figure 7: MDD according to the RMMD%

.84

.82

.80

.78

.76

.74

.72

.70

.68

.66

.64

.62

.60

CBR = 0.0186RMMD2 - 0.0094RMMD+

10.369

R² = 0.9

Moisture content %

Figure 5: variations of dry density of subgrade soil according to

the moisture content and RMMD%

RMMD %

OMC = -0.0014(RMMD)2 - 0.0734(RMMD) + 17.849

8.0

7.5

7.0

6.5

6.0

5.5

R² = 0.9772

Figure 8: CBR according to the RMMD%

Increase in the CBR of modified samples by the RMD

considered a sustainable solution to the problem of solid waste

harmful to the environment [34, 35].

Conclusion

Based on the investigations carried out in this research,

RMMD can be considered a soil stabilizer, as its use improves the

mechanical and physical properties of subgrade soil. The CBR

value increased up to 63% when adding 20% of the RMMD

compared to the reference samples (0% of the RMMD). The

plasticity index of the soil decreased by 13% when adding 20%

of RMMD. Furthermore, MDD increases with an increase

RMMD ratio, and the OMC value decreases as the RMMD ratio

increases. In addition to the above, the use of RMMD in soil

stabilization constitutes a new scientific start for researchers to

explore other soil properties. It is also considered sustainable

sources of low-cost additives (reducing the thickness of road

layers) and using these materials in soil stabilization will preserve

the environment from harmful effects.

RMMD %

Figure 6: OMC % according to the RMMD%

.3 Mechanical properties (CBR)

The CBR test is performed to calculate the bearing capacity

of the subgrade or base course of highway pavement [32, 33].The

CBR experiment was conducted with consideration of the OMC

corresponding to the MDD for each of the samples (0, 5, 10, 15,

and 20 % of RMMD). The samples were submerged in water for

days to suit the most dangerous situation. The CBR value have

been increased 64 % at adding 20% of RDDM as shown in Figure

. This indicates that increasing the percentage of RMMD leads

175

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 172-177

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Aknowledgment

The researchers thank very much to the Faculty of Civil

Engineering at the University of Aleppo and Hama Cement

Factory for their support in carrying out the laboratory

experiments for this work. The authors are grateful to the Middle

East University, Amman, Jordan for the financial support granted

to cover the publication fee of this research article.

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