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SP-167 This ACI special publication is a collection of 15 symposium papers that were presented in three sessions at the ACI Fall Convention in Montreal in November of 1995. The authors were asked to present a view of activities on high-strength concrete from work done in their respective countries: Japan, France, Norway, Holland, Germany, Canada and the United States. The following titles are contained within this informative document.

This investigation was performed to access the applicability of conventional maturity functions to high strength concretes incorporating silica fume and superplasticizer. Concrete specimens were allowed to cure under three temperatures simulating hot weather, laboratory, and cold weather conditions. Both linear and exponential strength-maturity functions predicted different values of strength for different concrete curing temperatures for the same value of maturity, as has been observed by other researchers. Of these two unctions, the exponential performed somewhat better in this regard for elatively low values of maturity. Concrete strength-gain behavior was influenced by the presence of silica ume and the high amount of super-plasticizer in the mixture. Strength-maturity equations already developed for normal strength concrete underestimated strength at low maturity ages and overestimated strength at high maturity. It is suggested that further studies should be done to evaluate such effects in those relationships.

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.

Moisture migration in non-uniformly heated concrete is a complex phenomenon. It depends upon many factors, both intrinsic to the concrete mix and its local environment. At temperatures above 100°C pore vapour pressures dominate the mass transfer behaviour and lead to creation of dry zones containing superheated steam and zones of excessive wetness and physical saturation where condensation has occurred. Spalling of concrete, in fire, is strongly related to the water content of concrete at the time of heating and its moisture flow properties. During heating, as the temperature rises, the free water, contained in the porous structure of concrete, will expand whilst sustaining an increasing saturated vapour pressure. The continuous expansion of water together with the moisture flow frequently leads to physical saturation of the pores. Further heating will then generate additional strains in the solid envelope surrounding the pores and can lead to cracking and hydraulic fracture of the solid skeleton. High strength concrete is particularly vulnerable to this behaviour because of its inherent, low porosity, low permeability to water flow and high percentage of initial pore saturation. This paper describes numerical/theoretical modelling procedures, for the prediction of temperature-dependent moisture flow in non-uniformly heated concrete. The flow is considered to be governed dominantly by the pore pressures. A mathematical description is also provided to help understand the spalling process caused by the hydraulic fracture of the solid skeleton during heating of the water in saturated pores.

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.