Influence of the Air-Entraining Agent in the Concrete Coating on the Reinforcement Corrosion Process in Case of Simultaneous Action of Chlorides and Frost

Abstract

The paper presents the test results to evaluate the effect of air-entraining agent addition on the intensity of reinforcement corrosion in concrete with blast-furnace slag cement in the case of simultaneous action of chloride corrosion and frost. Two groups of reinforced concrete specimens were prepared for the study. The first group of specimens included air-entraining agent addition and the other group was prepared without air-entraining agent. The blast-furnace slag cement (CEM III/A) was used for the specimens. Two parallel reinforcing rods were placed in each specimen. The specimens were subjected to 120 cycles of freezing and thawing in 3% NaCl solution to induce corrosion on the reinforcement. To determine the occurrence of the reinforcement corrosion and estimate the corrosion activity the non-destructive electrochemical galvanostatic pulse method was used. On each specimen the corrosion current density of the reinforcement was measured as well as the reinforcement stationary potential and the concrete coating resistivity, i.e. values indicating the ongoing reinforcement corrosion. Measurements were made on all specimens in two steps: before freezing and thawing cycles in 3% NaCl solution and after the cycles. The analysis of the obtained results allowed to determine differences in corrosion processes intensity on the reinforced bars in the concrete specimens depending on whether or not the air-entraining agent was added. Based on the analysis it was found that in the case of simultaneous action of chloride corrosion and frost it is advisable to use both blast-furnace slag cement and air-entraining agent. The use of only blast-furnace slag cement (although it is a chloride resistant cement), without the addition of airentraining agent is insufficient.Keywords: reinforcement corrosion in concrete, influence of chlorides and frost, galvanostatic pulse method, blast-furnace slag cement, air-entraining agent

Electrochemical Diagnostics of Sprayed Fiber-Reinforced Concrete Corrosion

“…The values obtained from the measurements of the concrete cover resistivity on all measurement points of all analyzed specimens, on both stage I and stage II of the tests, were Θ < 10 kΩ•cm ( Figure 10), which would indicate "high probability of corrosion." However, in this particular case, the measured values were unreliable due to the fact that the specimens were still fresh, and the hardening process had most likely not ended by the time of the test [19,25,29]. The mean values of shrinkage strain determined from surface measurements of all B1 and B2 specimens are provided in Figure 11.…”

“…Chloride corrosion is a pitting spot corrosion which can burst the concrete cover from the inside without any visible changes on the surface of the concrete element ( Figure 4). This type of corrosion affects structures located at seasides which either have direct contact with seawater, or are exposed to the so-called sea fog, and also all types of civil engineering structures (mostly roads) that in winter are de-iced with agents containing sodium chloride (NaCl) [24,29]. The spread of chloride corrosion is often mediated by frost, as the water freezing in the concrete pores generates stress, which leads to cracking of the concrete, thus opening the way for chloride ions which diffuse into the concrete cover and damage the passive film which protects the reinforcement.…”

Manufacturing Errors of Concrete Cover as a Reason of Reinforcement Corrosion in a Precast Element—Case Study

“…One of the few devices available on the market for the simultaneous measurement of three electrical quantities stationary potential of reinforcement (E st ), concrete cover resistivity (Θ), and the corrosion current density (i cor ) is the GP-5000 GalvaPulse TM set (Figure 2a) [30][31][32][33]. The advantage of using the GalvaPulse TM device (compared to devices used in half-cell potential measurements) is the relatively short measurement time, which is usually no more than a few seconds at one point.…”

Influence of the Type of Cement and the Addition of an Air-Entraining Agent on the Effectiveness of Concrete Cover in the Protection of Reinforcement against Corrosion

“…The internal stresses that arises can lead to numerous microcracks in the lagging, which reduces its tightness [ 1 , 2 , 16 , 32 , 33 , 34 ]. In order to protect the structural elements in such cases, it is recommended to add air-entraining agents to the concrete mix [ 33 , 34 , 35 ]. By adding an air-entraining agent, the concrete forms air bubbles or closed pores that are not completely filled with water, which take excess water from the capillary pores during ice crystallization.…”