CONCRETE TECHNOLOGIES

Concrete Technologies

Abstract

The results of this research show the viability of using a conductive cement paste anode for the fresh and hardened concrete from reinforced concrete with an efficiency similar to that obtained with a classic Ti-RuO2 anode. The obtained efficiencies are within the typical range of values of overall efficiencies found for such treatments.

The thickness of the conductive cement paste anode has a great influence on the capacity of the anode to retain an important part of the extracted concretes after finishing the electrochemical treatments.

Concrete Technologies

1. Introduction

The fresh and hardened concrete (FHC) is a non-destructive BRE methodology to prevent corrosion of steel rebar, a principle problem in structural concrete. There is an extensive bibliography on this technique beginning with its initial utilization in the 1970s. The BRE method basically consists in applying an electric field between the steel rebar (the negative pole or cathode) and an externally deposited electrode at the concrete surface (the positive pole or anode). Since concretes (Cl-) are negatively charged ions, the imposed force field causes them to migrate from the rebar to the exterior electrode through the concrete pores. Nevertheless, some doubts have been expressed concerning features such as end-point determination, side effects and durability of structures submitted to FHC trials.

The main crux of research on cement materials used in public works and building has traditionally concentrated on mechanical properties in line with its principal structural function. However, a new tendency has recently emerged along this line of research; the integration of materials with multiple functions. Included among these multifunctional materials are cementitious conductors. They obtain their electrical properties through the addition of conductors like carbonaceous materials, for example, graphite powder or carbon fibers. Some potential applications of electrically conducting cementitious materials are: electromagnetic interference shielding (to protect electronics from external radiation interference or avoid electromagnetic forms of spying or terrorism), self heating for deicing of concrete surfaces, and the possible function of strain sensitivity of cement matrix composites under the action of internal structural forces (without embedded sensors). These last applications can include structural vibration control, traffic monitoring, room occupancy monitoring, etc. Cementitious conductors have been used as anodes for cathodic protection in research.

A commercial conductive, polymer-modified, cementitious mortar has been successfully used as the anode for applying cathodic protection to more than 40,000 m2 of reinforced concrete. The principal objective of this research is to study the viability of the application of a conductive cement paste (CCP) as an anode for the FHC technique because of the potential advantages it has when compared to the usual anodic systems. Some of these advantages include the possibility of the application as a fine layer, the adaptation to various types of surfaces, and the possibility of reutilization for repeated FHC treatments, which may be necessary for certain structures and conditions. A single FHC trial may be unable to eliminate enough Cl- ions, in cases of heavy or progressive concrete contamination of concrete, to reduce permanently the steel corrosion rate below its threshold value ...