Erratic results in the determination of tungsten led to a study of the variables influencing the stannous chloride thiocyanate method. Free acid and chloride concentrations determine the degree of reduction of the tungsten. With 7.00, 5.95, and 3.63 moles of chloride per liter, the lower limits of free acid to achieve complete reduction are 9.5,11.2, and 13.9 moles per liter, respectively. The thio-

The formation of ice and snow on road pavement surfaces is a recurring problem, creating hazardous driving conditions, restricting public mobility as well as having adverse economic effects. It would be desirable to develop new and improved ways of modifying the pavement surface, to prevent or at least delay the build-up of ice and to weaken the pavement-ice bond, and making the ice which forms easier to remove. This development could lead to economic, environmental and safety benefits for winter service providers and road users. This paper describes how environmental scanning electron microscopy was used to examine the mechanism by which de-icing chemicals, added as a filler replacement to bituminous materials, can be transferred to the pavement surface. The paper assesses the potential for chemical modifications to reduce the adhesion between ice and the pavement surface by means of work of adhesion calculations, based on surface energy parameters and a new physical ice bond test. The paper also examines the influence that the chemical modifications have on the durability of the pavement surface course.

No abstract

In the UK, current specifications permit up to 10% of reclaimed asphalt (RA) to be routinely incorporated into the surface courses. The incorporation of RA provides significant economic and environmental benefits by effectively using recycled materials. Trials of thin surface course systems incorporating RA contents of more than 10% have been installed on the Strategic Road Network (SRN) since 2004. These trials demonstrated the feasibility of incorporating higher RA contents and the necessary quality controls. The sites have now been in service for a significant period of time and provide an opportunity to understand their performance. This paper summarises current practice and trials undertaken incorporating RA content >10% in the UK. The paper presents detailed analysis of the performance of the M25 J6-7 & 7-8 Clockwise (installed in 2007 incorporating 23% RA) and M25 J6-7 Anti-clockwise (installed in 2009 incorporating 40% RA). The paper provides quantifiable evidence regarding the performance of surface course materials containing RA >10%. The analysis demonstrates that surface courses containing RA have performed equivalently to control sections containing no RA over a significant period of time. The trials indicate that the inclusion of RA, when subject to the appropriate quality control processes, has had no detrimental impact upon on the skid resistance. The conclusions support the incremental increase of the maximum permitted RA content from 10% to 20% with appropriate quality controls in the future revision of PD6691.

No abstract