Stabilization Of Pavement Material Using Waste Brick Kiln Dust

Stabilization Of Pavement Material Using Waste Brick Kiln Dust

Depaa. Ra. B, Assistant Professor, Dept Of Civil Engineering

R.M.K Engg College, Chennai

This paper throws light on the suitability of waste Brick Kiln Dust (BKD) as soil stabilizer for use in pavement. The role of brick kiln dust in improving the characteristics of expansive subgrade material and other sub base material is analyzed. The amount of cost savings for a pavement when it is stabilized with brick kiln dust is also studied.

Initially, the physical properties of clay, brick kiln dust and red soil have been studied by conducting wet sieve analysis, Liquid Limit (LL) and Plastic Limit (PL) tests. Then, for the purpose of determining the strength of virgin and stabilized materials, California Bearing Ratio (CBR) test have been conducted.

The results of the experimental research show that brick kiln dust can effectively be used as a soil stabilizer for both subgrade and sub base layers as the CBR value of both is increased. A considerable amount of cost savings is also possible when the expansive clay soil is stabilized with BKD.

1. Infrastructure projects such as highways, railways, water reservoirs, reclamation etc. require earth material in very large quantity [1]. Quite often, large areas are covered with highly plastic and expansive soil, which is not suitable for such purpose.

   The problem of expansive soils is a worldwide one that poses several challenges for Civil Engineers. They can cause extensive damage to structures if not adequately treated [2]. Extensive laboratory / field trials carried out by various researchers have shown promising results for application of such expansive soil after stabilization with additives / stabilizers [3]. Ultimately, the main reason for using stabilization will usually be cost savings [4]. The Engineer is trying to build a problem-free pavement that will last for its intended design life for the most economic price [5]. The cost savings associated with stabilization can take many forms including reduced construction costs, reduced maintenance costs throughout the life of the

   pavement or an extension of the normal pavement life [6].

   With growing environmental consciousness at all levels of society, the pollution caused by the brick industry is coming under close scrutiny from environmentalists and the government [7]. In order to minimize the rate of air pollution caused due to the emission of brick kiln dust [8], it can be effectively used as a stabilizing agent for expansive soils like clay. On the whole, the CBR value of subgrade and sub base layers will be increased when brick kiln dust is used as a stabilizing agent for pavement materials.

2. Highly expansive clay has been collected from Ganapathy area in Coimbatore city. Brick kiln dust has been collected from brick kiln units in Kalapanaickanpalayam in Coimbatore city. The physical properties of clay, red soil and brick kiln dust have been studied by conducting wet sieve analysis, liquid limit and plastic limit tests.

   Optimum proportion of brick kiln dust to be mixed with clay (subgrade) and red soil (sub base) has been arrived at so as to have a mix with a Plasticity Index (PI) of 6% or less. Optimum moisture content has been found out by carrying out Standard Proctor Compaction Test (SPCT). The change in strength of clay and red soil after being mixed with brick kiln dust has been determined by conducting CBR test. Based on the test results, flexible pavement has been designed with and without buffer layer and the percentage of cost savings of stabilized pavement with respect to unstabilized pavement is arrived.

3. The results of classification tests conducted on the various materials used in the present study are given in table 1:

   Material	Grain size distribution			Liquid limit (%)	Plastic limit (%)	Plasticity index (%)	IS classification
   	Gravel (%)	Sand (%)	Fines (%)
   Clay	0	16	84	51	42	9	CH
   Red soil	18	56	26	45	30	15	SM
   BKD	0	82	18	Non – plastic		0	SM

   Table 1. Classification test results

   1. Liquid limit tests have been conducted for various trial proportions of clay and BKD and optimum quantity of BKD to be mixed with clay is found out such that liquid limit of the mix is not more than 30%. The results of liquid limit tests performed on various mixes are given in table 2:

      Proportion of clay with BKD	Liquid limit (%)
      80:20	48
      50:50	40
      40:60	30

      Table 2. Liquid limit tests on mixes

      The table 2 shows that a mix of clay and BKD in the proportion of 40:60 yields a liquid limit of 30%.

      Liquid limit and plastic limit tests have been conducted for various trial proportions of red soil and BKD and optimum quantity of BKD to be mixed with red soil is found out such that plasticity index of the mix is not more than 6%. The results of plasticity index tests performed on various mixes are given in table 3:

      Proportion of red soil : BKD	Liquid limit (%)	Plastic limit (%)	Plasticity index (%)
      100:0	45	35	10
      60:40	26	18	8
      50:50	16	11	5

      Table 3. Plasticity index tests

      From the above results, the optimum proportion of Red soil:BKD is found to be 50:50

   2. The objective of Standard Proctor Compaction Test is to determine the optimum moisture content so that it could be used for compacting the pavement material in the CBR mould. The results of the tests are given in Fig. 1 to 4.

      1.545

      Dry density (gm/ml)

      Dry density (gm/ml)

      1.54

      1.535

      1.53

      1.525

      1.52

      1.515

      1.51

      1.505

      OMC = 15%

      12 13 14 15 16 17 18 19 20

      Moisture content (%)

      1.64

      Dry density (gm/ml)

      Dry density (gm/ml)

      1.62

      1.6

      1.58

      1.56

      1.54

      1.52

      1.5

      OMC = 18%

      10 12 14 16 18 20 22 24 26

      Moisture content (%)

      Fig.1. SPCT on clay Fig.2. SPCT on clay + BKD

      1.94

      Dry density (gm/ml)

      Dry density (gm/ml)

      1.92

      1.9

      1.88

      1.86

      1.84

      1.82

      1.8

      OMC =12%

      6 8 10 12 14 16

      Moisture content (%)

      1.9

      Dry density (gm/ml)

      Dry density (gm/ml)

      1.85

      1.8

      1.75

      1.7

      1.65

      OMC = 12%

      4 9 14 19

      Moisture content (%)

      Fig.3. SPCT on red soil Fig.4. SPCT on red soil + BKD

   3. The California Bearing Ratio (CBR) test is a penetration test meant for the evaluation of strength of pavement material. For the design of flexible pavement as per IRC:37-2001 [10], the CBR values of various components of the pavement are used. The results of the CBR tests are presented from fig. 5 to 8

      20

      18

      16

      14

      12

      10

      8

      6

      4

      2

      0

      2.5

      CBR = 0.6%

      350

      300

      250

      200

      150

      100

      50

      0

      CBR 2.5 = 4.5%

      CBR 5.0 = 6.3%

      CBR = 7%

      20

      18

      16

      14

      12

      10

      8

      6

      4

      2

      0

      2.5

      CBR = 0.6%

      350

      300

      250

      200

      150

      100

      50

      0

      CBR 2.5 = 4.5%

      CBR 5.0 = 6.3%

      CBR = 7%

      0 1 2 3 4 5 6 7 8 9 1011121314

      Penetration (mm)

      0 1 2 3 4 5 6 7 8 9 1011121314

      Penetration (mm)

      0 1 2 3 4 5 6 7 8 9 1011121314

      Penetration (mm)

      0 1 2 3 4 5 6 7 8 9 1011121314

      Penetration (mm)

      CBR = 0.5%

      CBR = 0.5%

      5.0

      CBR = 0.6%

      5.0

      CBR = 0.6%

      Load (kg)

      Load (kg)

      Load (kg)

      Load (kg)

      Fig.5. CBR test on clay Fig.6. CBR test on clay + BKD

      80

      70

      60

      50

      40

      30

      20

      10

      0

      80

      70

      60

      50

      40

      30

      20

      10

      0

      700

      600

      Load (kg)

      Load (kg)

      Load (kg)

      Load (kg)

      500

      400

      CBR 2.5 = 1.9%

      CBR 5.0 = 2.0%

      CBR = 2.0%

      CBR 2.5 = 1.9%

      CBR 5.0 = 2.0%

      CBR = 2.0%

      300

      200

      100

      0

      0 1 2 3 4 5 6 7 8 9 10 11 12 13

      Penetration (mm)

      0 1 2 3 4 5 6 7 8 9 10 11 12 13

      Penetration (mm)

      CBR 2.5 = 21%

      CBR 5.0 = 20%

      CBR = 21%

      0 1 2 3 4 5 6 7 8 9 10 11 12 13

      Penetration (mm)

      Fig.7. CBR test on red soil Fig.8. CBR test on red soil + BKD

4. 1. As per clause 4.2.1.5 of IRC: 37-2001, the subgrade must have a minimum CBR value of 2%. When highly expansive soil is present as a subgrade material, buffer layer having thickness ranging from 0.6m to 1.0m needs to be provided. The first step in pavement design is to estimate the cumulative number of standard axles to be catered for the design, which is calculated as follows:

      N = {365 [(1+r)n 1] * A * D * F} / r

      Where,

      N = Cumulative number of standard axles to be catered for the design in terms of msa

      A = Initial traffic in the year of completion of construction in terms of number of commercial vehicles per day (cv/day)

      D = Lane distribution factor (As per clause 3.3.5.1 of IRC37:2001, assumed as 1) F = Vehicle damage factor (As per clause 3.3.4.4 of IRC37:2001, assumed as 1.5)

      n = Design life in years (As per clause 3.3.3.2 of IRC37:2001, assumed as 15 years)

      r = Annual growth rate of commercial vehicles (As per clause 3.3.2.2 of IRC37:2001, assumed as 7.5%)

      The initial traffic in the year of completion of construction can be calculated as, A = P (1+r)x

      Where,

      P = number of commercial vehicles as per last count (assumed as 120)

      x = number of years between last count and year of completion of construction (assumed as 2 years). Substituting the respective values, A = 139 and N = 2 msa

      From plate 1 of IRC37:2001, for the minimum CBR value of 2%, the total pavement thickness is 715mm. The recommended pavement structure is given in fig. 9:

      Premix carpet

      Bituminous Macadam

      Base

      Sub base

      Buffer layer

      20 mm

      50 mm

      225 mm

      440 mm

      600 mm

      Expansive sub grade

      Fig.9. Pavement structure with buffer layer

   Since the treated subgrade is not only less expansive (LL < 35%) but also has an enhanced CBR of 6%. From plate 1 of IRC37:2001, for the CBR value of 6%, total thickness of the pavement is 450mm. The recommended structure of the pavement is given in Fig. 10

   Premix carpet Bituminous Macadam

   Base

   Sub base

   20 mm

   50 mm

   225 mm

   175 mm

   Treated sub grade

   Fig.10. Pavement structure without buffer layer

5. The quantity of various materials and cost of pavement per unit area for pavement structure with buffer layer are given in tables 5.1 and 5.2 respectively.

   Table 5.1. With buffer layer calculation of quantities

   S.No	Particulars of items of works	No	Length (m)	Width (m)	Depth (m)	quantity
   1	Compaction of subgrade	1	1	1	0.5	0.5m3
   2	Buffer layer	1	1	1	0.6	0.6m3
   3	Sub base layer	1	1	1	0.440	0.440m3
   4	Base	1	1	1	0.225	0.225m3
   5	BM	1	1	1	0.050	0.050m3
   6	Premix carpet	1	1	1	–	1m2

   Table 5.2. With buffer layer abstract of cost

   S.No	Particulars of items of works	Qty	Unit	Rate Rs Ps		Per	Amount Rs Ps
   1	Compaction of subgrade	0.5	m3	120	00	m3	60	00
   2	Buffer layer	0.6	m3	300	00	m3	180	00
   3	Sub base layer	0.440	m3	600	00	m3	264	00
   4	Base	0.225	m3	1100	00	m3	247	50
   5	BM	0.050	m3	6000	00	m3	300	00
   6	Premix carpet	1	m2	30	00	m2	30	00
   Total cost = Rs.1081.50

   Similarly, the quantity of various materials and cost of pavement per unit area for pavement structure without buffer layer are given i tables 5.3 and 5.4 respectively.

   1. Without buffer layer calculation of quantities

      S.No	Particulars of items of works	No	Length (m)	Width (m)	Depth (m)	quantity
      1	Compaction of subgrade	1	1	1	0.5	0.5m3
      2	Sub base layer	1	1	1	0.175	0.175m3
      3	Base	1	1	1	0.225	0.225m3
      4	BM	1	1	1	0.050	0.050m3
      5	Premix carpet	1	1	1	–	1m2

   2. Without buffer layer abstract of cost

   S.No	Particulars of items of works	Qty	Unit	Rate Rs Ps		Per	Amount Rs Ps
   1	Compaction of subgrade	0.5	m3	150	00	m3	75	00
   2	Sub base layer	0.175	m3	600	00	m3	105	00
   3	Base	0.225	m3	1100	00	m3	247	50
   4	BM	0.050	m3	6000	00	m3	300	00
   5	Premix carpet	1	m2	30	00	m2	30	00
   Total cost = Rs.757.50

   Comparison of table 5.2 and 5.4 shows a cost reduction of 30% when the expansive subgrade is treated with BKD.

From the test results and cost estimation, the following conclusions have been made:

1. The stabilization process of clay and red soil with Brick Kiln Dust is very effective.

2. The CBR value of clay is increased from 0.6% to 6% and that of red soil is increased from 2% to 21%.

3. Addition of BKD to expansive subgrade not only reduces expansive nature of subgrade but also increases its CBR value.

4. Reduction of expansive nature of subgrade eliminates buffer layer and increase of CBR value reduces the overall thickness of pavement.

5. Elimination of buffer layer and reduction of overall thickness of pavement offsets the cost and mixing cost of Brick Kiln Dust with clay so much that a reduction in overall cost of 30% is effected.

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