The features of the different types of surfaced and unsurfaced road used in tropical countries are described, and an indication is given of some of the typical engineering features of tropical soils, using the ‘red coffee’ soil of Kenya as an example.Natural gravels are used extensivly in road building in tropical countries and the different types of gravel are describedSoil stabilisation is increasingly used to make road bases, and notes are given on the different processes employed. The paper concludes with information on some soft aggregates used in roadmaking, on bituminous surfacings, on the derivation of thermoplastic white‐line material suitable for use in the tropics, and on the control of roadside vegetation.

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AUTHORS' PRESENTATIONIn introducing a major new item of equipment such as a slip-form paver it was vitally important that its performance and operational characteristics should be evaluated and understood from the outset.139. The design of a satisfactory dowel bar support system had proved elusive for a number of years, although many arrangements had been tried. The Cromwell trials faced up to the problem, which was more acute with slip-form pavers, and the welded assembly with bent stalk feet in its final form had a substantial claim to general adoption as the standard British joint for use with conventional as well as slip-form construction. This would take much of the uncertainty out of present-day construction. 140.There had been a tendency to identify slip-form pavers with large-scale construction and very high outputs, but this overlooked their singular capacity to perform satisfactorily at lower output levels. The Authors believed that there was a much wider field of operation open to these pavers than had hitherto been contemplated, housing estate roads being one example.141. The pooling of resources of design; research and contracting interests at Cromwell in mutual consultation and co-operation throughout the planning and execution of the trials resulted in the development of designs and viable techniques in a remarkably short time, and this form of joint effort led to development in pavement construction which could not occur under normal construction processes.Sir William Glanville (Past-President) said the Authors had been responsible for one of the biggest and most important experiments in mechanized concrete construction which had ever been made in Britain. He had found the Paper particularly valuable because the Authors had described fully the difficulties they had encountered and how they had overcome them, and had pointed out quite frankly that some difficulties still remained.143. The Authors had shown very considerable ingenuity in overcoming difficulties and had demonstrated that with ski11 and intelligent supervision the dip-form paver could be made to work, and work well, both for plain concrete and for reinforced concrete. Sir William had no doubt at all that, given further opportunities for experiment, which he hoped that they would have, the Authors would overcome the remaining difficulties which they mentioned and develop still further the potentialities of the machine. The machine had, of course, a voracious appetite for concrete, and the team operating the machine needed to know not only how to operate it in a general sense but how to deal quickly with the ordinary run of problems, such as changing weather conditions and unexpected variations in aggregates. It seemed to him that it was one thing to operate the machine in the predictable weather of California and quite another to operate it in Britain. What was perhaps even more