The paper presents a review on the role of silica fume in concrete, based mainly on the experience of the author and that of his colleagues. Statistics on the amount of silica fume pro-duction, its composition , quality and the way it is handled and proportioned for making concrete are described briefly. Various factors such as water/cement ratio, temperature of curing, super-plasticizer, etc., that influence the physical and mechanical properties of freshandhardened concrete are also discussed. Factors that determine the economy in the use of silica fume is emphasized. A brief survey of the literature pertaining to silica fume concrete is also included.

The paper describes a model for the calculation of the strength of concrete with secondary materials. The model is based upon the type of correlation between strength and water-cement ratio (or water + air to cement ratio) originally suggested by Feret and later modified by Bolomey. An important additional parameter is introduced, viz: Er = efficiency function, describing the influence of the secondary material on the concrete strength The variation of E has been studied by means of experiments dea-ling with the binding of CaO or with the strength of concrete containing fly ash or silica fume. The study leads to a formula for strength: f c = KB(l + ${p,)) (A - kB) where HP,) = k,P, for fly ash $Cp,) = 1 - (1 - P,)~ for silica fume P is the relative quantity of secondary material, kn and n characteristics of its binding capacity. The formulae have been verified by means of a great number of test results, mainly from France and Scandinavia. The paper contributes to a balanced technical evaluation of secondary materials and to rational mix design.

The energy crisis calls for economy in all fields. Roadmaking, which consumes a great amount of materials of all kinds, is of all civil engineering sectors one in which the constructor can - all other things being equal - take the greatest technical risks. In this field, innovation is permanent, and the For more than 20 years past, French roadmaking techniques have made use of industrial wastes, those whose properties make them veritable hydraulic or pozzolanic binders : blast furnace lag and fly-ash. Some years ago, under the pressure of the need to economize materials and energy, there was a rediscovery of the value of rigid structures consuming a lesser quantity ofmaterials, using binders involving a lesser consumption of energy, and above all not requiring a bituminous wearing course. By extrapolating operational techniques, internally vibrated pavement concrete and compacted treated gravels, an attempt was made to establish a better recognition of the binding properties of slag and fly-ash in order to achieve highly economical techniques of rigid pavement construction. Some motorways were recently built in which cement was re-placed by around 30 % by fly-ash or pulverized slag. This communication describes how the characteristics of these concretes were worked out, how they were obtained and applied throughout the im-technique. plementation of the project, how systems of control were adapted, and what difficulties were encountered. Simultaneously, a promising evolution of the technique of rigid pavements having recourse to the pozzolanic properties of fly-ash is emerging : compacted concrete. This communication indicates the principal properties of the material as revealed in the laboratory and on experimental sites, together with the difficulties encountered and the possibilities of development of this Taking advantage of the binding properties of industrial by-products does not present major technical difficulties provided that in each case allowance is made for contractual demands, means of control, and in certain cases methods of production and laying. The risks assumed by the contractor are higher than if he uses a standardized industrial product, guaranteed by the producer ; but in many cases, the economy achieved amply offsets the additional control required to cover those risks, passage from the laboratory to the working site is a very rapid one.

This paper discusses the air permeability and cabonation of mortars made with different cements. Two types of testing apparatus for the permeability of air were fabricated. One apparatus was designed for use with a disk specimen and the other was utilized to estimate the permeability of mortar and concrete in situ. The effects of the variables such as type of cement, mix-proportion, curing condition and age of mortar on air permeability were studied. A relationship between the permeability of air and the depth of carbonation for cement mortars was found.

Blends of separately ground (fine) granulated blast furnace slag with portland cement generally possess properties equivalent to or in ways superior to typical portland cements. Heats of hydration, apparent activation energies for reaction, and structure development are modified in high slag content mixtures. By three days the strength development of blends is equivalent to that of pure portland cement at normal temperatures but this stage is achieved more rapidly at elevated temperatures, while a very fine pore structure is developed with longer time. Phase changes, microstructural and property development including permeability development as a function of time are discussed.