QUANTIFYING THE AMOUNT OF METALS IN ASPHALT BINDERS TO COMPLY WITH ENVIRONMENTAL REGULATIONS
The threat to safe drinking water is one of the greatest pollution problems in the world today. Less than 1% of the water on earth is clean and available for potable drinking water. Sources of human drinking water are a mixture of groundwater aquifers and surface water reservoirs. It is vitally important for the safety of these water that the sources be protected from pollutants. A signifi cant source of pollution to drinking water supplies comes from the discharge of untreated or under treated storm water runoff. (1) More importantly runoff from Asphalt roadways. In addition to leachable material in the Asphalt there are also surface deposits of toxic elements from road traffi c. This article reviews these sources and proposes a scheme for measuring and quantifying the amounts of metals in their source materials used to bind asphalt used in making roads
Background
Heavy metals can directly harm public health by entering the body via soil and dust, dermal contact or breathing The typical elements Cd, Pb, Zn, and Cu in the roadside soils coming from traffi c activity can be transported through the food chain into the human body and thus be very toxic to people. In agricultural areas, intake of heavy metals through the soil-crop system could play a predominant role in human exposure to heavy metals]. In general, heavy metals with high concentrations in the environment result in health problems adversely affecting the nervous, blood forming, cardiovascular, renal and reproductive systems. The consequences of heavy metal pollution include reduced intelligence, attention defi cit and behavioral abnormality, as well as contribution to cardiovascular disease in adults . Some trace metals (such as Cu and Zn) are harmless in small amounts, but the others (mainly Pb, As, Hg and Cd), even at extremely low concentrations, are toxic and are potential cofactors, initiators or promoters in many diseases, including increased risk of cancer. However, it is not easy to remove heavy metals from the soils because of their irreversible immobilization within different soil components .
. Bitumen and mineral fi ller materials in asphalt road surfaces contain different heavy metal species, including Cu, Zn, Cd, and Pb . Heavy metals can be transported into the roadside soils by atmospheric precipitation or road runoff . Public health concerns of contamination of aquifers is assessed as being a severe threat. (2) Roadway runoff can include breakdown products from Asphalt emulsifi ers since a signifi cant metal concentration is found in the polar fraction of Asphalt Binders as measured on the Schieff scale. (3). This is of concern to environmental protection agencies like the Federal Highway Administration and the state DOTs, trying to balance longevity with safety concerns for road construction materials.
Table 1: Elemental analysis of asphalts from different crude sources.
Crude sources C (wt%) Mexican blend 83.77 85.78
Arkansas- Louisiana
Boscan California
82.90 86.77
H (wt%) 9.91
10.19
10.45 10.94
N (wt%) 0.28 0.26
0.78 1.10
Economic factors lead Asphalt makers to look for alternative material sources and to use recycled materials to deal with the waste produced by aging road surfaces and used motor and vegetable oils are natural emulsifi ers for recycled asphalt paving and are readily available at low cost. The concern is the deleterious elements that are found in these materials and the need is to blend the oils correctly to minimize the concentration of metals and other organic components deemed to be public health concerns.
Typical Asphalt Compositions `Vanadium and Nickel are naturally occurring in Crude Oil sources And are inherently found in Asphalt as obtained from refi neries
Table 2 - Naturally occurring metal levels in Nigerian Bitumen Outcrops.
Sample VAB OI IL
LD Fe 38.00 283.00
1537.00 553.00
Pb
12.00 11.00 27.00 11.00
Cu
3.00 4.00
10.00 5.00
Cd
4.00 8.00 7.00
15.00 Ni
42.00 20.00 62.00 9.00
Mn 6.00
4.001 3.00 5.00
V
10.00 50.00
100.001 150.00
S (wt%) 5.25 3.41
5.43 0.99
O (wt%) 0.77 0.36
0.29 0.20
V (mg/kg) 180
7 1380 4 Liquid Asphalt Components
With the increasing price of petroleum-based asphalt in recent years, people have started to seek alternative binders to petroleum asphalt that can be used in pavement construction (Aziz et al. 2015; Huang et al. 2012). Some examples of asphalt alternatives include bio asphalt derived from waste cooking oil (Wen et al. 2013), waste engine oil (Jia et al. 2014Jia et al. , 2015), and biochar derived from bio-oil used as a bio modifi er for asphalt cement (Zhao et al. 2014a, b
Elemental Composition Ranges Determined by Research
It stands to reason that engine oil additives would also be present in the Asphalt from waste engine oil and one would expect to see
Ni (mg/kg) 22
4 109 6
OCTOBER / NOVEMBER •
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