The diffusion mechanisms of chloride ions into ordinary and high performance mortars were studied. Four different mortar mixtures were tested. Test parameters included the water/binder ratio (0.25 and 0.45) and the use of silica fume. An ASTM type III cement was used in the preparation of the 0.25 water/binder ratio mortars while the 0.45 water/binder ratio mixtures were prepared with an ASTM type I. For all mixtures, the sand volume fraction was maintained constant at 50%. The diffusion properties of the mortars were studied according to two different experimental procedures. In a first series of tests, apparent diffusion coefficients were calculated from chloride ion profiles measured after a 12-month immersion period. In a second series, a migration test (where the chloride ion penetration is accelerated by the application of an electrical potential of 10 volts) was used to investigate the transport properties of the four mortars. All test results clearly show that the reduction of the water/binder ratio and the use of silica fume contribute significantly to the reduction of the chloride ion penetration. The consequences of these results on the long-term durability of high-performance concrete structures and, more specifically, on their ability to resist to reinforcing steel corrosion are discussed. The ability of the accelerated migration test to reliably predict the penetration of chlorides in cement-based materials after only a 14-day test period is also discussed.

High strength concrete (HSC) is defined by FIP/CEB as “concrete with a cylinder strength above 60 MPa (-87OOpsi) and up to 130 MPa (-18900 psi), the practical upper limit for concretes with ordinary aggregates. It also includes lightweight aggregate concrete with a cement paste of similar properties “. FIP/CEB similarly regards high performance concrete as material with water-binder ratio (w/b) less than 0.40 According to these definitions all concrete installations built in Norway in the 1990s for the oil and gas-fields in the North Sea and most highway structures are built with HSC/HPC. This amounts to about 20 - 25 % of our total domestic concrete production. Norway was the first nation in the world to have HSC with characteristic cube strengths up to 105 MPa (~ 15300 psi) incorporated in its code of design, NS 3473, in 1989. This paper describes the main Norwegian experience by using these qualities in full scale. The presentation is supplemented by some case studies illustrating some typical applications. The main lesson from some 15 years experience is that the introduction of these “hi-tech” concrete grades should be accompanied by a proper upgrading of the workforce’s competence on all levels to ensure the intended quality.

A public-private partnership has been chosen to ignite the introduction of RPC into the United States construction market. This research and development project is being conducted under the Construction Productivity Advancement Research (CPAR) program of the US Army Corps of Engineers. The project was initiated in the fall of 1994 and it will run for three years. The program goal is to verify product integrity and gain industry acceptance and commercialization by developing and demonstrating the technical and economic viability of RPC for producing culvert/sewer pipes, pressure pipes and piles. T h e primary technology transfer has been completed, US component material source identification has been brought into action and material property verification has been initiated. Other US products development efforts have been initiated. These applications include : 0 0 spun cast concrete poles, impact resistant railroad ties and grade crossing planks.

The ratio between the in-place compressive strength of high performance concretes and the strength of standard 28-day cylinders is investigated. Strength data for 771 cores from 3 1 large elements cast using 22 concrete mixes reported in five investigations by others are analysed. It is observed that the ratio of in-place strength to standard cylinder strength decreases as the maximum temperature sustained during hydration increases. If the concrete mix contains silica fume, Class C fly ash, or slag, the ratio of the in-place strength at 28 days to the standard 28-day cylinder strength of the same concrete is markedly less than that observed for concretes which do not contain supplementary cementitious materials. In all elements investigated, the average in-place strength continued to increase after 28 days. The relative strength gain of silica fume concretes after 28 days was significantly less than that of conventional concretes.

This paper reviews the ACI-318 Building Code requirements concerning the design of slabs post-tensioned with unbonded tendons. The design of a simply supported one-way slab is considered in detail. By taking into account all requirements (in service and at ultimate), it is shown that use of high strength concrete results in savings in the number of tendons or in slab depth when compared to a design in normal strength concrete. Tests up to failure of two similar two-span slabs, one in normal strength concrete (f'c = 40 MPa), the other in high strength concrete (f'c = 75 MPa I reveal a better ultimate load behavior for the high strength slab which exhibited more ductility than the normal strength slab. ACI requirements proved to be adequate for estimating the service load and conservative for predicting the actual carrying capacity.