Eric I. Moreno

PRACTICAL EVALUATION OF RESISTIVITY OF CONCRETE IN TEST CYLINDERS USING A WENNER ARRAY PROBE

Cell constant correction values (K) for concrete resistivity measurements on cylindrical test samples performed with the four-point Wenner array probe technique are presented. Specimens dimensions correspond to standard cylinder sizes used for compressive strength or rapid chloride permeability tests, as well as typical concrete core sizes. The values of K were determined experimentally and numerically, by means of Finite Element (FE) simulation. The effect of different maximum aggregate sizes and aggregate types on the variability of the resistivity readings was evaluated. Cell constant correction values are given to allow quick determination of concrete resistivity.

THE TIME-DOMAIN RESPONSE OF A CORRODING SYSTEM WITH CONSTANT PHASE ANGLE INTERFACIAL COMPONENT: APPLICATION TO STEEL IN CONCRETE

Abstract The time-domain response of reinforcing steel in concrete during a polarization resistance test was examined based on the electrochemical impedance spectroscopy behavior of the system. The analysis considered the effect of apparent interfacial capacitances that approached the behavior of a constant phase angle element (CPE). The response of an interface behaving as the parallel combination of a polarization resistance and a CPE was examined analytically. The calculations showed that significant error could develop in the estimation of corrosion rates from the apparent polarization resistance obtained during a potential scan experiment. The predicted error was largest when corrosion rates were small. The error could be significant at commonly used potential scan rates (0.1 mV s−1) and constant phase element exponents (0.7

Characterization of Activated Titanium Solid Reference Electrodes for Corrosion Testing of Steel in Concrete

Abstract Small bars of Ti activated with mixed-metal oxide (commercially produced for permanent impressed-current anodes in cathodic protection) were used as embedded reference electrodes (RE) in c...

Evolution of pH during in-situ leaching in small concrete cavities

Small amounts (0.4 cc) of neutral water placed in small cylindrical cavities (5 mm diameter) in concrete exposed to 100% relative humidity first developed a pH comparable to that of a saturated Ca(OH)2 solution. The pH then increased over a period of days-weeks toward a higher terminal value. A micro pH electrode arrangement was used. This behavior was observed in samples of 12 different concrete mix designs, including some with pozzolanic additions. The average terminal cavity pH closely approached that of expressed pore water from the same concretes. A simplified mathematical model reproduced the experimentally observed behavior. The model assumed inward diffusional transport of the pH-determining species in the surrounding concrete pore solution. The experimental results were consistent with the model predictions when using diffusion parameters on the order of those previously reported for alkali cations in concrete. The cavity size, cavity water content, and exposure to atmospheric CO2 should be minimized when attempting to obtain cavity pH values approaching those of the surrounding pore water.

Influence of marine micro-climates on carbonation of reinforced concrete buildings

Although chloride is the main source for corrosion of reinforcing steel in coastal buildings, concrete carbonation leads to a uniform corrosion of the steel that would accelerate the crack formation and decrease the structures service life. The objective of this investigation was to study the effect of carbonation on public buildings located up to 800 m from the seashore. The results, based on the analysis of carbonation depth, resistivity, compressive strength and porosity data suggested that risk of concrete deterioration due to carbonation increases with the distance from the seashore as well as with the elevation. Generally, higher carbonation coefficients corresponded to the top sections of the evaluated buildings where the measured relative humidity was lower. However, concrete cracks due to corrosion were found in the lower sections where humidity was higher. Data from laboratory specimens exposed to the same tropical marine environment for 5 years were used to correlate the findings from the public buildings.

EVALUATION OF ELECTROCHEMICAL IMPEDANCE WITH CONSTANT PHASE ANGLE COMPONENT FROM THE GALVANOSTATIC STEP RESPONSE OF STEEL IN CONCRETE

A current step excitation method for obtaining the parameters of a system characterized by a solution resistance R s in series with the parallel combination of a polarization resistance Rp with a constant phase angle element (cpe) is described. The cpe has a base admittance Y 0 and a frequency exponent n. A numerical procedure is developed to obtain the value of the system parameters (Rp, Y 0 , n and R s ) by analysis of the potential response of the system to the current excitation step. Experiments with specimens of galvanized steel in concrete are reported in which the galvanostatic step technique is applied and the analysis procedure is performed. Good agreement with the results of independent electrochemical impedance spectroscopy (EIS) of the same specimens is demonstrated.

An Improved Method for Estimating Polarization Resistance from Small-Amplitude Potentiodynamic Scans in Concrete

Abstract Many corroding interfaces exhibit electrochemical impedance response similar to that of a polarization resistance (Rp) associated with the corrosion process, in parallel with a constant phase angle element (CPE) having relatively large admittance. Such conditions are encountered often in the case of steel in concrete. While polarization measurements using a forward and reverse potential scan rate (dV/dt) can be helpful to subtract the contribution of an ideal interfacial capacitance (C) by using a C dV/dt correction, in concrete the pronounced frequency dispersion of the CPE complicates the time-domain response, and correction is not straightforward. A solution to this problem was presented and applied to evaluate the CPE parameters and estimate Rp of steel in concrete from cyclic-scan polarization measurements. The technique was demonstrated for experiments with plain steel and galvanized rebar in concrete.

Durability Indicators in High Absorption Recycled Aggregate Concrete

The use of recycled aggregates in structural concrete production has the inconvenience of increasing the fluid transport properties, such as porosity, sorptivity, and permeability, which reduces the resistance against penetration of environmental loads such as carbon dioxide and chloride ion. In this paper, behavior of ten concrete mixtures with different percentages of coarse aggregate replacement was studied. The recycled material was recovered by crushing of concrete rubble and had high absorption values. The results showed that it is possible to achieve good resistance to carbonation and chloride penetration with up to 50% replacement of recycled coarse aggregate for 0.5 water/cement ratio. Finally, new indexes for porosity and sorptivity were proposed to assess the quality of concrete.

Concrete Carbonation in Ibero-American Countries DURACON Project: Six-Year Evaluation

Concrete carbonation data from 16 test sites in 9 countries (Bolivia, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal, and Venezuela) were compared to identify concrete performance du...

Carbonation Coefficients from Concrete Made with High-Absorption Limestone Aggregate

Normal aggregates employed in concrete have absorption levels in the range of 0.2% to 4% for coarse aggregate and 0.2 to 2% for fine aggregate. However, some aggregates have absorption levels above these values. As the porosity of concrete is related to the porosity of both the cement paste and the aggregate and the carbonation rate is a function, among other things, of the porosity of the material, there is concern about the effect of this high porosity material in achieving good quality concrete from the durability point of view. Thus, the objective of this investigation was to study the carbonation rates of concrete specimens made with high-absorption limestone aggregate. Four different water/cement ratios were used, and cylindrical concrete specimens were exposed to accelerated carbonation. High porosity values were obtained for concrete specimens beyond the expected limits for durable concrete. However, carbonation coefficients related to normal quality concrete were obtained for the lowest water/cement ratio employed suggesting that durable concrete may be obtained with this material despite the high porosity.