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Concrete In Australia : March 2013
Concrete in Australia Vol 39 No 1 53 concrete prisms containing particular hazardous waste were placed in a Soxhlet Extractor, as shown in Figure 1. e flask at the bottom of the extractor was heated; the water vapour condensed in the cooling section at the top and distilled water then gradually filled the middle section. As the water level reached the siphon, it drained into the bottom flask. Any potentially soluble material was deposited in the flask, thus representing the extent of chemical weathering of concrete, subjected to the cycles of wetting and drying (Samarin, 1979). After many hundreds of cycles, representing exposure of concrete to tropical rain with the subsequent drying, the water in the flask was chemically analysed in order to detect traces of hazardous material, which had the potential of being leached from the concrete. When concrete was produced in accordance with the theoretical and practical methodology, as described above, even after many hundreds of cycles, only negligible amounts, in effect only traces of hazardous material were detected. Even so, for the additional safety of disposal, it was proposed to incorporate this concrete into a base of special highway pavements (Samarin, 1997). 3.0 NEW CONCEPT OF PAVEMENT CONSTRUCTION INCORPORATING WASTE DISPOSAL An interesting historical heritage that provides us with the evidence of extreme endurance, of practically maintenance- free performance of pavements, is the method used RAINFALL ELUVIATE DRAINAGE LESSIVATE ZONE OF WATER -- TABLE FLUCTUATION ATMOSPHERIC ZONE CONCRETE OR MORTAR SPECIMEN IN A PAPER THIMBLE Figure 1. Soxhlet Extractor adopted for weathering test. in construction of the ancient Roman roads. Romans implemented three basic methods of road construction. In the countryside, where only minor movements of military and civilians were expected via terrena -- a plain road was formed simply by levelling the earth surface. In the areas of more intense and important traffic, via glareata -- a roadway surfaced with gravel provided a more reliable thoroughfare. But the pinnacle of Roman ingenuity was via munita -- a complex and enduring construction (Vitruvius, 1960). Of these, the Appian Way -- Via Appia, completed in 312 BC, was considered "the queen of the long roads". Its total length was some 560 km, connecting Italy s southeast coast with Rome. During the Second World War, the Appian Way served as a reliable thoroughfare for the advancement of the allied troops towards Rome. e riding surface of this pavement was formed in stones, which were cut in such a way that they fitted tightly. e sub- base contained broken stones or pebbles, which were cemented together with mortar, consisting of sand and yet another ingenious Roman invention -- hydraulic cement. is cement, as described by Vitruvius, was composed of lime and volcanic ash, an invention, the knowledge of which was lost in Europe in the Middle Ages, and rediscovered only as a Portland cement, which was patented by John Aspdin in 1824. But the concept taken from via munita, which I am proposing to incorporate into the modern pavement, is its base, which in via munita consisted of broken stones placed on the bottom of the trench, and upon which the entire roadway was then erected. If, when constructing major interstate highways, a "raft foundation" containing special concrete in which hazardous wastes are encapsulated is formed, then the two major problems facing safe vehicular travel and safe waste disposal can be effectively and efficiently solved. As most of the road surface pavement failures (cracking, subsidence and pot-holes) are the result of increased plasticity or even liquefaction of the base, which is then unable to support the top layers, a "raft foundation should successfully prevent this from happening. Incorporation of hazardous wastes into the "raft foundation" made with special concrete, as described above, should provide additional safety from their potential environmental impact. Obviously, the price of this construction is expected to be somewhat higher than the existing methods of highway design, but if the cost of the current methods of hazardous wastes disposal becomes an integral part of a road construction, I believe that not only the total expenditure will be less or comparable, but the enormous savings in the long term maintenance, in the avoidance of accidents, which often lead to the injuries and even death of road users, can more than justify this method of "construction-disposal" of our highways. I would also like to mention that the cost of ingredients of the proposed highly durable concrete should be comparable or even less, than the cost of constituents in most of the conventional high strength concretes. 4.0 CONCLUSION e combined method of highway construction and