عمل آوری الکتریکی تسریع شده بتن مسلح به الیاف فولادی
Abstract
1- Introduction
2- Literature review
3- Experimental programme
4- Results and discussion
5- Conclusions
References
Abstract
This paper evaluates the effect of electric curing on the mechanical properties and microstructure of steel fibre reinforced concrete. Specimens subjected to electric curing, steam curing and without curing were tested for compressive and residual flexural tensile strengths at different ages. The fibre-matrix contact area after pull-out was characterized by means of scanning electron microscopy. Although electric cured specimens had consistently smaller residual flexural strengths than steam cured specimens, differences were not statistically significant. Results derived from this study confirm the feasibility of applying electric curing for the production of elements made with steel-fibre reinforced concrete.
Introduction
Curing conditions play a crucial role in the hydration of the binder and in achieving the performance expected from the hardened material [1]. In the precast industry, curing is often synonymous with the application of heat to shorten demoulding times and to increase productivity. One can appreciate the importance of accelerated curing to the manufacturer’s rate of production by considering that to reach the demoulding strength in some cases requires more than a day (several days for prestressed concrete) as opposed to hours when accelerating curing is adopted, and thus the economic viability of precast plants significantly relies on accelerated curing [2]. Steam Curing (SC) is the most common method used in precast plants to achieve high temperature cycles while ensuring abundant moisture supply [2]. Although reliable and relatively easy to control, SC has poor energy efficiency and generates temperature gradients inside the elements, thus inducing internal stresses. In other words, SC suffers the limitations of being a surface-heating method, therefore it is physically limited by thermal conductivity of the medium and maximum permissible temperature. Moreover, its on-site deployment is unfeasible in most cases due to the large equipment required (steam generators, ducts and conveyors, etcetera). Electric methods are relatively unexplored alternatives, which generate heat by means of the Joule effect [3,4]. Indirect or direct methods can be distinguished. For the indirect method, surface or embedded electric resistors (or the reinforcement bars) are deployed to supply heat; however, regardless of the actual positioning of the heating elements, indirect electric curing remains a surface-heating method, with the physical limitations mentioned above. Conversely, for the direct method electricity is run through the concrete, either by applying a voltage to the reinforcement bars (i.e. using them as electrodes) or by means of purposely embedded electrodes [3]. The direct Electric Curing method (EC) has received relatively little attention with regard to research and it is the focus of this study.