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Use of copper blasting grit waste in asphalt mixes in Bahrain
Use of copper blasting grit waste in asphalt mixes in Bahrain M H Al-Sayed* and I M Madany** Abstract - The Arab Ship Building and Repair Yard Company (ASRY) in Bahrain generates approximately 6000 tons per year of solid waste. The waste is a spent copper grit used for sand blasting in the cleaning operations of tankers in the dock yard. This study investigates the possibility of recycling the waste as a fine aggregate in the road construction industry. Asphalt mixes were prepared with five different grit:sand ratios. The Marshall test method was used to evaluate the mix-design. Parameters studied included Marshall stability (kN), Marshall flow (mm), Marshall quotient (kN/mm), voids in the mix (%), voids in the mineral aggregate (%) and the voids filled with bitumen (%). The results confirmed that copper grit waste can be utilized as a substitute for normal sand in asphalt mixes used in Bahrain. In a previous study on the utilization of copper blasting grit waste [1], it was reported that the grit waste could substitute for madne sand used in mortars for concrete blockworks, and in non-reinforced concrete blocks. Previous results showed also that the utilization of the waste in prsoast concrete blocks might be advantageous. This paper presents the results of an investigation into the use of copper blasting grit waste as a substitute for fine aggregate in asphalt mixes. Copper grit waste is found in ship building and repair yards throughout the world and it is hoped that this paper may be of widespread industrial interest. Materials and method
Asphalt mixes Nearly all main highways and roads in Bahrain are constructed using asphalt pavements which consist of coarse and fine aggregate, mineral filler, and a bituminous binder. The coarse aggregate is crushed limestone with particle size ranging from 2.36 mm to 28 mm. The fine aggregate is a mixture of marine sand, which is dredged from the sea, and crushed limestone. The sand size ranges between 0.15 mm and 2.36 mm. The mineral filler normally used is a limestone powder, 85 percent of which passes the 0.075 mm sieve. The aggregate mix is bound together with a 60/70 penetration grade bitumen. A typical wearing course of compacted layers consists of about 55% of coarse aggregate, 38% of fine aggregate and 7% of a limestone filler. The optimum binder content is between 4 and 8% by weight of the mix, depending on the mix-design. Material properties The gradation of aggregate used was on the requirements of the Bahrain Ministry of Works, Power and Water (PWD) for wearing courses [2]. The properties of the aggregates and the binder are shown in Tables 1 and 2. A description of the properties of the copper grit slag was published in a previous study [1]. The selected fraction of fine aggregate was blended with copper grit in different proportions. The coarse aggregate and mineral filler fractions were kept constant throughout the study. The ratios of grit/sand were: 0/100 as the control mix, 25/75, 50•50, 80120 and 100/0. The binder content of each aggregate mix was optimized using the Marshall mix-design [3]. Standard Marshall test samples (63.5 mm in height, 101.6 mm in diameter) were compacted, using five different bitumen contents of 3, 4, 5, 6 and 7% by weight. Triplicate samples *Department of Civil Engineering, University of Bahrain, P.O. Box 32038, Bahrain **Arabian Gulf University, P.O. Box 26671, Bahrain. CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1 9 9 2
Table 1 Sieve analysis of grit, sand and course aggregate used in the study % Passing Sieve size (mm) 20 14 10 5 2.36 1.18 0.600 0.425 0.300 0.150 0.075
Grit
100.0 99.2 97.6 90.3 68.8 40.5 27.0 8.9 2,4
Sand
Coarse aggregate 100 89 80 68
100.0 98.7 96.7 85.3 51.1 23.8 0.8
Table 2 Physical properties of grit, sand and coarse aggregate used in the study Property
Grit
Sand
Coarse Aggregate
Water absorption (%) Apparent specific gravity
0.27 3.39
0.82 2.69
1.88 2.66
were produced for each binder content. The stability and flow values of each sample after compaction were tested by the Marshall method. The Marshall method is considered by the authors to be more accepted world wide than any other. It is simple to use and relatively inexpensive. It was considered therefore, that to use any other test method would limit the usefulness of the results to a narrow area.
Preparation of specimens and test methods The same amount of material was used for each sample in an effort to obtain approximately the same height of the specimens. The mix was first partially compacted using a heated standard rod, fifteen times around the edge and five times in the centre. The whole mould was then fixed in the Marshall compaction machine which consists of a 4.5 kg hammer falling from a distance of 457mm. Both sides of the samples were compacted 75 times. The compacted samples were allowed to cool at room temperature. The density of the samples was then determined by weighing in air and in water. Samples were then tested at 60°C in the Marshall machine [2,3,4] and the deformation stability (in kN) and the flow of the samples (in mm) were recorded. The same procedure was repeated for all five mix-designs and for all samples.
0950.0618/92/020113-04 © 1992Buttetworth-HeinemennLtd
113
Use of copper blasting grit waste in asphalt mixes in Bahrain Grit:Sand A
A
I00:0
X [] O (3
X [] O E]
80:20 50:50 25:75 0:I00
2.600
(J
~E U
2.550
2. 500
2.450 m
-~
2.400
×
2.350 Q.
CJ
2.300
v
2.250 I
I
I
I
I
3
4
5
6
7
Bitumen c o n t e n t ( ~ w / w )
Effect of varying grit to sand ratios on the mix density versus
Figl
bitumen content of asphaltic concrete mixes G r i t : Sand
20
18
A.
~
100:0
X [] © 0
X [3 O 0
80:20
50:50 25:75 0:I00
x
Table 3
16
u
Bahrain Specification for wearing course asphaltic concrete mixes
Marshall moulds - number of blows Index of retained strength, % (kN/kN) Optimum bitumen content, % (wt) Marshall stability, kN Marshall flow, mm Voids in mix, % (vol) Voids filled with bitumen, % vol) Voids in mineral aggregates, % (vol)
14
O
=o
z
Results and discuuion Figure 1 represents the mix density plotted against bitumen content for the various grit/sand ratios. It is evident that the density increases as the grit/sand ratio increases. The highest density value of 2.579 g cm -3 was obtained at a grit/sand ratio of 100/0, with 5 % bitumen content. The lowest mix density was found to be 2.363 g cm -3 at the grit/sand ratio of 0/100 with 6.66o/0 bitumen. This behaviour can be explained by the fact that the specific gravity of the copper slag grit is 3.39, as shown in Table 2, while the specific gravity of the mineral filler, sand and coarse aggregate range between 2.5 and 2.7. The grit is also more uniformly graded than the sand. This allows better compaction with fewer voids in the aggregate skeleton, and hence the mix has a higher density. All the curves in Fig 1 show clear optimum density values. Excessive bitumen content (beyond the optimum) can lead to problems in the field with regard to bleeding and deformation, especially in the long hot summer prevailing in Bahrain. Figure 1 also demonstrates that the optimum bitumen content decreases as the grit/sand ratio increases. This translates into a saving on the quantity of bituminous binder needed for the mix. The reason for such behaviour may be attributed to the low absorptivity of grit compared to sand. This is duB tO the presence of high percentages of heavy metals in the grit[l]. Figure 2 shows the variation of Marshall stability, expressed in kN, with percentage bitumen content for the five systems investigated. All mixes showed clear optimum stability values, with the exception of the 10010 ratio. The stability at 5 % bitumen content ranged from 16.5 kN for the 0/100 system to 10.7 kN for the 100/0 ratio. It can be seen that the minimum stability criterion of 8 kN required by Bahrain specification [2], is satisfied by all the mixes. The highest stability value obtained with a grit/sand ratio of 100/0 (15.5 kN) was with a bitumen content of 3 0 . Howeover, this low bitumen content may cause serious problems in the field with regard to cracking and disintegration, due to the lack of proper mixing and inadequate compaction. This is why Bahrain specification requires an optimum range of bitumen content of 4 - 8 % , as presented in Table 3. When the optimum bitumen content for the 100/0 ratio was determined, therefore, it was found to be 4.4% - which is within the Bahrain Standard Limits as shown in Table 4.
12
V
1o
75 75, minimum 4-8 8, minimum 2-4 3-6 70-80 14, minimum
in
8
Table 4 Values of engineering properties of various grit/sand asphaltic concrete mixes, at optimum bitumen content* (OBC)
6 Grit I sand ratio by weight 100/0 80/20
I
I
I
I
I
3
q
5
6
7
Bitumen c o n t e n t [ ~ w / w )
~2
Effect of varying grit to sand ratios on the Marshall stability versus bitumen content of asphaltic concrete mixes
114
Marshall stability, kN 12.5 Marshall flow, mm 2.3 Marshall quotient, kN/mm 5.8 Mix voids, % Vol 3.8 Filled voids, % Vol 75 Aggregate voids, %Vol. 14.7 OBC, Bahrain* 4.35 * OBC
13.4 2.1 7.7 2.7 82 15.2 5.05
50/50 14.7 2.9 4.9 3.5 78 15.8 5.20
2,5/75 0/100 16.0 3.3 4.8 2.7 81 16.4 5.57
16.5 2.6 5.8 3.0 80 15.1 5.71
Bahrain Specification [2] minimum, 8 2-4 minimum, 2.5 3-6 7 0 - 80 minimum, 14 4-8
at maximum stability + BC at maximum density + BC at median of voids + BC at median filled with bitumen) divided by 4.
= (BC
CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1992
M H Al-Sayed and I M Madsny
Grit:Sand 11
11 100:0
X
X
80:20
[]
[]
50:50
E)
O
25:75
(3
[3
0:100
Grit:Sand 10
x
s
II
100:0
,~. []
X []
80:20 50:50
C
C
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13
{3 0:100
( B a h r a i n s p e c i f i c a t i o n limit}
o o=
,~.
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<
3
(B.S.L.)
2
_ .._,____
_._ _ _,__ _ _ _ __ __ _ _ . s ._,-- L _
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I
I
I
I
3
4
5
6
7
~"E}-
Bitumen c o n t e n t ( % w / w )
3
Effect of varying grit to sand ratios on the Marshall flow
Fig3
4
5
6
7
Bitumen c o n t e n t ( ~ w / w )
versus bitumen content of asphaltic concrete mixes
Fig5
Effect of varying grit to sand ratios on the percent air voids versus bitumen content of asphaltic concrete mixes
Grit:Sand 10
.A.
~
I00:0
Figures 3 and 4 present the effect of varying the grit/sand ratio on the Marshall flow (MF) expressed in mm, and on the Marshall quotient (MQ) expressed as kN/mm, (stability, kN, divided by flow, mm), at different bitumen content levels. The 13 ~] 0:100 flow values obtained for all mixes for the range of bitumen contents between 3% and 6% satisfy the Bahrain specification [2] criteria for Marshall flow of 2 - 4 mm, as shown on Fig 3. ~" 7 The MQ criteria (see Fig 4) are not specified in Bahrain E standards. Good correlation between MQ and pavement z deformation was found by other researchers [5], Le. the higher 6 the MQ value of the mix the less the deformation of the 0J pavement in the field under traffic. Figure 4 illustrates that o \ the satisfactory grit/sand ratios are above the minimum MQ 5 O" value of 2.5 kN/mm. Some agencies [5] specify MQ minimum to values ranging from 1.5 to 3.0 depending on the type of mix .C required. 4 to The percent voids in the mix, the percent voids filled with \ binder and the percent voids in the mineral aggregate are illustrated in Figs 5, 6 and 7. It can be seen that as the bitumen content increases, the percentage of voids in the mix ...... -Minim~r~impli~d ~I.Q ~-. . . . . . . . . . . \ decreases. This is typical in asphalt mixes, since the binder ( Bahrain specification) will fill the voids between the aggregate particles. Figure 5 shows that all five systems satisfy the 3 - 6 % limit of air voids in the mix required by Bahrain specification [2]. The optimum bitumen content (OBC) according to Bahrain specification is based on the bitmmen content which gives I I I I I maximum stability and density, traded against the bitumen 7 3 4 5 6 contents for median voids in the mix and voids filled with bitumen. The average bitumen content from all these criteria Bitumen c o n t e n t ( ~ w / w ) is considered to be the design optimum bitumen content. Table 4 shows the engineering properties of the five Effect of varying grit to sand ratios on the Marshall quotient F/g4 systems studied, determined at OBC. It is clear that grit/sand versus bitumen content of asphaltic concrete mixes X
)~
80:20
[]
[]
50:50 25:75
\
CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1992
115
Use of copper blasting grit waste in asphalt mixes in Bahrain
,~, ;~, [] O (3
I00
90
Grit:Sand I00:0 80:20 50:50 25:75 0:I00
Z~ X [] O [3
Grit:Sand 20
19
A
~
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×
×
80:20
[] (3
[] 50:50 E) 25:75
13
[3 0:I00
( Bahrain specification/ 18
=o
70
"~
60
~
50
(B.S.L.)
17
o
16
15 c
E
4o
c
30
>
14
12
10
11 I
I
I
i
I
3
4
5
6
7
Minimum V.M.A. (Bahrain specification)
13
20
0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
I
I
I
I
I
3
4
5
6
7
Bitumen content (%w/w)
Fig6
Effect of varying grit to sand ratios on the filled voids versus bitumen content of asphaltic concrete mixes
ratios of 10010, 50•50 and 01100 satisfy all the requirements. The other two systems - 80/20 and 25/75 - satisfied the Marshall stability, Marshall flow, aggregate voids and the OBC requirements. However these two systems were slightly outside the specification limits for voids in the mix and voids filled with bitumen. Conclusions From the results and preceding discussion, the following can be concluded: • Copper slag grit can be utilized as fine aggregate in asphaltic concrete wearing courses used in Bahrain. • The best results were obtained with grit/sand ratios of 100/0 and 50/50. • The stabilitiec of all the grit/sand asphalt mixes were well above the minimum (8 kN) criteria of the Bahrain specification. • The optimum bitumen content by weight for the various grit/sand ratios ranged from 4.4% and 5.7%, which satisfied Bahrein specification.
116
Bitumen content (%w/w)
Fig7
Effect of varying grit to sand ratios on the aggregate voids versus bitumen content of asphaltic concrete mixes
• The optimum bitumen content decreases as the grit/sand ratio increases.
References 1 Madany, I M, Al..~e~fed, M H and Rsveendnm, E. Utilization of copper blasting grit waste as a construction matedal, Waste Management, 3, 1991, 35-40 2 General specification for road works, September, 1987, Ministry of Works, Power and Water, Manama, State of Bahrain. 3 Mix design methods for asphalt concrete and other hot-mix types. Manual series No. 2 (MS-2), The Asphalt Institute, College Park, Maryland, USA, 1984 4 BS 598, Part 3: 1985. Sampling end examination of bituminous mixtures for roads and other paved areas. British Standards Institution, London, 1985 5 Knlght, Dowdeetvell, D A and Brlen, D. Designing rolled asphalt wearing courses to resist deformation. Proc Conf. The Performance of Rolled Asphalt Road Surfacings. Institute of Civil Engineers, 1980, pp 123-134
CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1992
Asphalt mixes Nearly all main highways and roads in Bahrain are constructed using asphalt pavements which consist of coarse and fine aggregate, mineral filler, and a bituminous binder. The coarse aggregate is crushed limestone with particle size ranging from 2.36 mm to 28 mm. The fine aggregate is a mixture of marine sand, which is dredged from the sea, and crushed limestone. The sand size ranges between 0.15 mm and 2.36 mm. The mineral filler normally used is a limestone powder, 85 percent of which passes the 0.075 mm sieve. The aggregate mix is bound together with a 60/70 penetration grade bitumen. A typical wearing course of compacted layers consists of about 55% of coarse aggregate, 38% of fine aggregate and 7% of a limestone filler. The optimum binder content is between 4 and 8% by weight of the mix, depending on the mix-design. Material properties The gradation of aggregate used was on the requirements of the Bahrain Ministry of Works, Power and Water (PWD) for wearing courses [2]. The properties of the aggregates and the binder are shown in Tables 1 and 2. A description of the properties of the copper grit slag was published in a previous study [1]. The selected fraction of fine aggregate was blended with copper grit in different proportions. The coarse aggregate and mineral filler fractions were kept constant throughout the study. The ratios of grit/sand were: 0/100 as the control mix, 25/75, 50•50, 80120 and 100/0. The binder content of each aggregate mix was optimized using the Marshall mix-design [3]. Standard Marshall test samples (63.5 mm in height, 101.6 mm in diameter) were compacted, using five different bitumen contents of 3, 4, 5, 6 and 7% by weight. Triplicate samples *Department of Civil Engineering, University of Bahrain, P.O. Box 32038, Bahrain **Arabian Gulf University, P.O. Box 26671, Bahrain. CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1 9 9 2
Table 1 Sieve analysis of grit, sand and course aggregate used in the study % Passing Sieve size (mm) 20 14 10 5 2.36 1.18 0.600 0.425 0.300 0.150 0.075
Grit
100.0 99.2 97.6 90.3 68.8 40.5 27.0 8.9 2,4
Sand
Coarse aggregate 100 89 80 68
100.0 98.7 96.7 85.3 51.1 23.8 0.8
Table 2 Physical properties of grit, sand and coarse aggregate used in the study Property
Grit
Sand
Coarse Aggregate
Water absorption (%) Apparent specific gravity
0.27 3.39
0.82 2.69
1.88 2.66
were produced for each binder content. The stability and flow values of each sample after compaction were tested by the Marshall method. The Marshall method is considered by the authors to be more accepted world wide than any other. It is simple to use and relatively inexpensive. It was considered therefore, that to use any other test method would limit the usefulness of the results to a narrow area.
Preparation of specimens and test methods The same amount of material was used for each sample in an effort to obtain approximately the same height of the specimens. The mix was first partially compacted using a heated standard rod, fifteen times around the edge and five times in the centre. The whole mould was then fixed in the Marshall compaction machine which consists of a 4.5 kg hammer falling from a distance of 457mm. Both sides of the samples were compacted 75 times. The compacted samples were allowed to cool at room temperature. The density of the samples was then determined by weighing in air and in water. Samples were then tested at 60°C in the Marshall machine [2,3,4] and the deformation stability (in kN) and the flow of the samples (in mm) were recorded. The same procedure was repeated for all five mix-designs and for all samples.
0950.0618/92/020113-04 © 1992Buttetworth-HeinemennLtd
113
Use of copper blasting grit waste in asphalt mixes in Bahrain Grit:Sand A
A
I00:0
X [] O (3
X [] O E]
80:20 50:50 25:75 0:I00
2.600
(J
~E U
2.550
2. 500
2.450 m
-~
2.400
×
2.350 Q.
CJ
2.300
v
2.250 I
I
I
I
I
3
4
5
6
7
Bitumen c o n t e n t ( ~ w / w )
Effect of varying grit to sand ratios on the mix density versus
Figl
bitumen content of asphaltic concrete mixes G r i t : Sand
20
18
A.
~
100:0
X [] © 0
X [3 O 0
80:20
50:50 25:75 0:I00
x
Table 3
16
u
Bahrain Specification for wearing course asphaltic concrete mixes
Marshall moulds - number of blows Index of retained strength, % (kN/kN) Optimum bitumen content, % (wt) Marshall stability, kN Marshall flow, mm Voids in mix, % (vol) Voids filled with bitumen, % vol) Voids in mineral aggregates, % (vol)
14
O
=o
z
Results and discuuion Figure 1 represents the mix density plotted against bitumen content for the various grit/sand ratios. It is evident that the density increases as the grit/sand ratio increases. The highest density value of 2.579 g cm -3 was obtained at a grit/sand ratio of 100/0, with 5 % bitumen content. The lowest mix density was found to be 2.363 g cm -3 at the grit/sand ratio of 0/100 with 6.66o/0 bitumen. This behaviour can be explained by the fact that the specific gravity of the copper slag grit is 3.39, as shown in Table 2, while the specific gravity of the mineral filler, sand and coarse aggregate range between 2.5 and 2.7. The grit is also more uniformly graded than the sand. This allows better compaction with fewer voids in the aggregate skeleton, and hence the mix has a higher density. All the curves in Fig 1 show clear optimum density values. Excessive bitumen content (beyond the optimum) can lead to problems in the field with regard to bleeding and deformation, especially in the long hot summer prevailing in Bahrain. Figure 1 also demonstrates that the optimum bitumen content decreases as the grit/sand ratio increases. This translates into a saving on the quantity of bituminous binder needed for the mix. The reason for such behaviour may be attributed to the low absorptivity of grit compared to sand. This is duB tO the presence of high percentages of heavy metals in the grit[l]. Figure 2 shows the variation of Marshall stability, expressed in kN, with percentage bitumen content for the five systems investigated. All mixes showed clear optimum stability values, with the exception of the 10010 ratio. The stability at 5 % bitumen content ranged from 16.5 kN for the 0/100 system to 10.7 kN for the 100/0 ratio. It can be seen that the minimum stability criterion of 8 kN required by Bahrain specification [2], is satisfied by all the mixes. The highest stability value obtained with a grit/sand ratio of 100/0 (15.5 kN) was with a bitumen content of 3 0 . Howeover, this low bitumen content may cause serious problems in the field with regard to cracking and disintegration, due to the lack of proper mixing and inadequate compaction. This is why Bahrain specification requires an optimum range of bitumen content of 4 - 8 % , as presented in Table 3. When the optimum bitumen content for the 100/0 ratio was determined, therefore, it was found to be 4.4% - which is within the Bahrain Standard Limits as shown in Table 4.
12
V
1o
75 75, minimum 4-8 8, minimum 2-4 3-6 70-80 14, minimum
in
8
Table 4 Values of engineering properties of various grit/sand asphaltic concrete mixes, at optimum bitumen content* (OBC)
6 Grit I sand ratio by weight 100/0 80/20
I
I
I
I
I
3
q
5
6
7
Bitumen c o n t e n t [ ~ w / w )
~2
Effect of varying grit to sand ratios on the Marshall stability versus bitumen content of asphaltic concrete mixes
114
Marshall stability, kN 12.5 Marshall flow, mm 2.3 Marshall quotient, kN/mm 5.8 Mix voids, % Vol 3.8 Filled voids, % Vol 75 Aggregate voids, %Vol. 14.7 OBC, Bahrain* 4.35 * OBC
13.4 2.1 7.7 2.7 82 15.2 5.05
50/50 14.7 2.9 4.9 3.5 78 15.8 5.20
2,5/75 0/100 16.0 3.3 4.8 2.7 81 16.4 5.57
16.5 2.6 5.8 3.0 80 15.1 5.71
Bahrain Specification [2] minimum, 8 2-4 minimum, 2.5 3-6 7 0 - 80 minimum, 14 4-8
at maximum stability + BC at maximum density + BC at median of voids + BC at median filled with bitumen) divided by 4.
= (BC
CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1992
M H Al-Sayed and I M Madsny
Grit:Sand 11
11 100:0
X
X
80:20
[]
[]
50:50
E)
O
25:75
(3
[3
0:100
Grit:Sand 10
x
s
II
100:0
,~. []
X []
80:20 50:50
C
C
25:75
13
{3 0:100
( B a h r a i n s p e c i f i c a t i o n limit}
o o=
,~.
0J
o > l_
<
3
(B.S.L.)
2
_ .._,____
_._ _ _,__ _ _ _ __ __ _ _ . s ._,-- L _
I
I
I
I
I
3
4
5
6
7
~"E}-
Bitumen c o n t e n t ( % w / w )
3
Effect of varying grit to sand ratios on the Marshall flow
Fig3
4
5
6
7
Bitumen c o n t e n t ( ~ w / w )
versus bitumen content of asphaltic concrete mixes
Fig5
Effect of varying grit to sand ratios on the percent air voids versus bitumen content of asphaltic concrete mixes
Grit:Sand 10
.A.
~
I00:0
Figures 3 and 4 present the effect of varying the grit/sand ratio on the Marshall flow (MF) expressed in mm, and on the Marshall quotient (MQ) expressed as kN/mm, (stability, kN, divided by flow, mm), at different bitumen content levels. The 13 ~] 0:100 flow values obtained for all mixes for the range of bitumen contents between 3% and 6% satisfy the Bahrain specification [2] criteria for Marshall flow of 2 - 4 mm, as shown on Fig 3. ~" 7 The MQ criteria (see Fig 4) are not specified in Bahrain E standards. Good correlation between MQ and pavement z deformation was found by other researchers [5], Le. the higher 6 the MQ value of the mix the less the deformation of the 0J pavement in the field under traffic. Figure 4 illustrates that o \ the satisfactory grit/sand ratios are above the minimum MQ 5 O" value of 2.5 kN/mm. Some agencies [5] specify MQ minimum to values ranging from 1.5 to 3.0 depending on the type of mix .C required. 4 to The percent voids in the mix, the percent voids filled with \ binder and the percent voids in the mineral aggregate are illustrated in Figs 5, 6 and 7. It can be seen that as the bitumen content increases, the percentage of voids in the mix ...... -Minim~r~impli~d ~I.Q ~-. . . . . . . . . . . \ decreases. This is typical in asphalt mixes, since the binder ( Bahrain specification) will fill the voids between the aggregate particles. Figure 5 shows that all five systems satisfy the 3 - 6 % limit of air voids in the mix required by Bahrain specification [2]. The optimum bitumen content (OBC) according to Bahrain specification is based on the bitmmen content which gives I I I I I maximum stability and density, traded against the bitumen 7 3 4 5 6 contents for median voids in the mix and voids filled with bitumen. The average bitumen content from all these criteria Bitumen c o n t e n t ( ~ w / w ) is considered to be the design optimum bitumen content. Table 4 shows the engineering properties of the five Effect of varying grit to sand ratios on the Marshall quotient F/g4 systems studied, determined at OBC. It is clear that grit/sand versus bitumen content of asphaltic concrete mixes X
)~
80:20
[]
[]
50:50 25:75
\
CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1992
115
Use of copper blasting grit waste in asphalt mixes in Bahrain
,~, ;~, [] O (3
I00
90
Grit:Sand I00:0 80:20 50:50 25:75 0:I00
Z~ X [] O [3
Grit:Sand 20
19
A
~
100:0
×
×
80:20
[] (3
[] 50:50 E) 25:75
13
[3 0:I00
( Bahrain specification/ 18
=o
70
"~
60
~
50
(B.S.L.)
17
o
16
15 c
E
4o
c
30
>
14
12
10
11 I
I
I
i
I
3
4
5
6
7
Minimum V.M.A. (Bahrain specification)
13
20
0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
I
I
I
I
I
3
4
5
6
7
Bitumen content (%w/w)
Fig6
Effect of varying grit to sand ratios on the filled voids versus bitumen content of asphaltic concrete mixes
ratios of 10010, 50•50 and 01100 satisfy all the requirements. The other two systems - 80/20 and 25/75 - satisfied the Marshall stability, Marshall flow, aggregate voids and the OBC requirements. However these two systems were slightly outside the specification limits for voids in the mix and voids filled with bitumen. Conclusions From the results and preceding discussion, the following can be concluded: • Copper slag grit can be utilized as fine aggregate in asphaltic concrete wearing courses used in Bahrain. • The best results were obtained with grit/sand ratios of 100/0 and 50/50. • The stabilitiec of all the grit/sand asphalt mixes were well above the minimum (8 kN) criteria of the Bahrain specification. • The optimum bitumen content by weight for the various grit/sand ratios ranged from 4.4% and 5.7%, which satisfied Bahrein specification.
116
Bitumen content (%w/w)
Fig7
Effect of varying grit to sand ratios on the aggregate voids versus bitumen content of asphaltic concrete mixes
• The optimum bitumen content decreases as the grit/sand ratio increases.
References 1 Madany, I M, Al..~e~fed, M H and Rsveendnm, E. Utilization of copper blasting grit waste as a construction matedal, Waste Management, 3, 1991, 35-40 2 General specification for road works, September, 1987, Ministry of Works, Power and Water, Manama, State of Bahrain. 3 Mix design methods for asphalt concrete and other hot-mix types. Manual series No. 2 (MS-2), The Asphalt Institute, College Park, Maryland, USA, 1984 4 BS 598, Part 3: 1985. Sampling end examination of bituminous mixtures for roads and other paved areas. British Standards Institution, London, 1985 5 Knlght, Dowdeetvell, D A and Brlen, D. Designing rolled asphalt wearing courses to resist deformation. Proc Conf. The Performance of Rolled Asphalt Road Surfacings. Institute of Civil Engineers, 1980, pp 123-134
CONSTRUCTION & BUILDING MATERIALS Vol. 6 No. 2 1992