Field Of Road Construction Research Articles

Step-frequency radar applied on thin road layers

In the field of road construction and maintenance, the need for information on the thickness of very thin road layers is not satisfied by means of commercial pulse GPR, due to the inability of such devices to operate over ranges of several gigahertz. As a result, research has focused on the design of a step-frequency radar technique, able to work with very high-frequency synthetic pulses. An ultrawide band antenna, belonging to the family of Vivaldi antennas, has been developed for road applications. It has been created using stripline technology and yields a band width greater than one decade. During an initial step, this antenna was tested on various bituminous concrete samples with a network analyzer. Different parameters were studied, including band width, offset between antennas, and height and shape of the frequency-dependent pulse. A second step involved GPR dynamic measurements. A customized software program enabled recording data from the network analyzer. Several radar profiles were developed from selected road construction and maintenance test sites (e.g. the Circular Pavement Fatigue Test Track, composed of a number of known structures). Results show improved resolution when compared to a commercial impulse GPR system.

Experience in judging controversial road projects

Abstract Road construction of all kinds, especially of urban motorways, has in recent years acquired a very bad reputation in industrialized countries. Traffic engineers are, because of their attitude, not entirely without blame for this development. With their attention glued nearly hypnotically to dimensions and technical design, considerations about the meaning and function of the construction are very often neglected, all the more since the engineers might otherwise risk their own jobs. It is, however, becoming increasingly clear that the cause of the scepticism and uneasiness prevailing in the public is the lack of a comprehensive judgement. Using a concrete example, this paper describes how decision‐making can degenerate when such judgement is omitted. Using a second example, it is then demonstrated how such a comprehensive judgement can be integrated in decision‐making from the very beginning. Such an integration sets very high methodological and procedural standards and constructive aids are offered for this purpose. It is shown that, while the substantial findings of a comprehensive judgement should be logically consistent, plausible and up to the latest standard of knowledge, the nature and intelligibility of the presentation and the preparedness for a publicly presented explanation in the form of ‘after‐care’ are of much greater importance for decision‐making in the political sphere. This ‘after‐care’ should accordingly become an indispensable component of the decision‐making process. All those involved should become aware of the fact that a ‘positive’ result of decision‐making in the field of road construction is not a priori defined as the construction of road and a ‘negative’ one as its prevention. The actual positive result is rather the creation of a consciousness of the problem on hand, which can serve as a basis on which a decision is taken in full realization of all its consequences.

The waterproofing of soil by resinous materials

AbstractThe stability of cohesive soils is determined largely by their moisture content, and methods of waterproofing or “stabilizing” soils have an important application in the field of road construction. This paper describes study made at the Road Research Laboratory of a method of waterproofing such soils by the addition of small quantities of two natural resinous match, “Vinsol” resin and rosin. The study consisted of an investigation of the properties of soil containing resin, and of the mechanism whereby the waterproofing action is obtained. It was found that a maximum waterproofing effect is obtained with concentrations of resin of the order of I% by weight of the soil, that the effect may take some time to develop, and that the presence of resin affects the compaction properties of the soil. The waterproofing obtained is only operative when the soil has an acidic reaction, but it is shown that a resinous emulsion can be used to waterproof chalky soil. The Kozeny equation for the rate of capillary absorption of water by soil has been used in assessing the reduction in the rate of absorption caused by the addition of “Vinsol” resin to soil. It is considered improbable that the addition of resin reduces the rate of absorption, either by blocking the major soil pores, or by adsorption on the surfaces of the soil particles. It is shown that a reduction in surface tension, as measured by the force exerted on a stirrup dipping into water, is also not a determining factor. It is considered that the most probable mechanism is one in which molecular films of resin spread out at the air water interfaces in the moist soil. These films resist the entrance of further water owing to the tendency to reduce the total area of the interface, and the compressive strength of the film becomes the determining factor once the film is spread, by reducing the effective surface tension of the soil water. Pressure/ area relationships for films of the resinous materials investigated are presented, showing that the reduction in surface tension obtained due to the compressive strength of the films is of the required order.