Bétons autoplaçants à haute résistance, mûris à la vapeur, utilisés pour les éléments préfabriqués et précontraints

Abstract

Self-consolidating concrete (SCC) is widely used for several types of structural applications. The high workability of such concrete has been turned into tangible benefits in precast, prestress manufactories in terms of enhancement of the overall quality of the final product and high productivity. The range of benefits offered by SCC goes beyond fundamental aspects of concrete quality and productivity; it includes a major improvement in the health and safety of workers and the reduction of noise level on construction sites. Furthermore, to improve the productivity in the precast manufacturing plants, steam-curing is often used to expedite strength gain and shorten the construction cycle. It is well established that mechanical properties of steam-cured SCC are affected by mixture composition and can vary widely with the steam-curing parameters. The research project presented here aims to address the significance of mixture parameters governing the performance of SCC for precast applications. Two classes of SCC with design compressive strengths of 60 and 80 MPa at 56 days were investigated. The examined mixture parameters include the w/cm, binder content and type, and the type of superplasticizer. In addition, this research seeks to assess the effect of steam-curing parameters on early-mechanical properties of SCC and to optimize a steam-curing regime to meet fabrication requirements with efficiency and economy. The studied steam-curing parameters include the maximum curing temperature, the preset period prior to heat treatment, and the rate of heating. The employed mixtures proportioning and steam-curing regimes to achieve the anticipated early-strength were proposed by an experimental factorial design to cover a wide scope of SCC mix designs and steam-curing regimes. Among the modeled mixture parameters, the w/cm and binder content were shown to play key roles on the majority of steam-cured mechanical properties and workability criteria. Among the steam-curing parameters, the maximum steam-curing temperature was shown to have a dominant effect on early-age strength. The preset period exhibited a major influence on mechanical properties as well. SCC cured under a maximum chamber temperature of 65ÀC and a longer preset period of 5 hours was found to develop higher early-compressive strength. Beyond limits, increasing maximum curing temperature can adversely affect the strength development leading to a lower early-compressive strength. The early heat treatment was found to decrease early-age strength. Longer preset period of 5 hours is then recommended in terms of fuel and time saving in manufacturing plants.