R.E. Beddoe

Bio: R.E. Beddoe is an academic researcher. The author has contributed to research in topics: Supercooling & Aqueous solution. The author has an hindex of 1, co-authored 1 publications receiving 27 citations.

A low-temperature DSC investigation of hardened cement paste subjected to chloride action

Abstract: Differential scanning calorimetry (dsc) was used to investigate the freezing behaviour (-175 deg c to 20 deg C) of hardened cement paste (hcp) subjected to nacl and cacl2 solutions containing up to 5.4 mol cl/l. Thermograms were also recorded for samples dried to relative humidities (rh) between 61% and 96%. The low-temperature phase transition at -38 deg c exhibited the freezing behaviour of an aqueous solution in gel pores of approximately equal to 4 nm radius. Chloride ions strongly reduce the coupling forces between gel particles and structure the gel pore water. On desorption critical behaviour of the low-temperature transition energy was observed at 0.52 mol cl/l which is the concentration most damaging to hcp. Above 1.3 mol cl/l freezing of supercooled bulk water in macropores was observed at more than one temperature. (Author/TRRL)

A review of salt scaling: II. Mechanisms

Abstract: Salt scaling is a major durability issue for concrete. Despite this, and an extensive research effort, the cause of this damage is unknown. Therefore, no means for preventing salt scaling can be identified. One of the primary reasons for this shortcoming is the lack of a critical review on the state of the research in this field. Such a compilation is presented in this series of articles. In Part I, the characteristics of salt scaling were outlined. In this article, proposed mechanisms are discussed, and their adequacy is judged based on their ability to account for the phenomenology.

A review of salt scaling: I. Phenomenology

Abstract: Salt scaling is a major durability issue for concrete, so the phenomenon has been the subject of an extensive research effort. Nevertheless, there is no agreement regarding the cause of this damage, so no means for preventing salt scaling can be identified. One of the primary reasons for this shortcoming is the lack of a critical review of the research in this field. Such a compilation is presented in the present series of articles. In Part I, we review the experimental studies that have revealed the phenomenology of salt scaling. In Part II, proposed mechanisms for scaling are discussed, and the adequacy of these mechanisms is judged based on their ability to account for the characteristics outlined here.

Mechanism for Salt Scaling

Abstract: Over the past 60 years, concrete infrastructure in cold climates has deteriorated by “salt scaling,” which is superficial damage that occurs during freezing in the presence of saline water. It reduces mechanical integrity and necessitates expensive repair or replacement. The phenomenon can be demonstrated by pooling a solution on a block of concrete and subjecting it to freeze/thaw cycles. The most remarkable feature of salt scaling is that the damage is absent if the pool contains pure water, it becomes serious at concentrations of a few weight percent, and then stops at concentrations above about 6 wt%. In spite of a wealth of research, the mechanism responsible for this damage has only recently been identified. In this article, we show that salt scaling is a consequence of the fracture behavior of ice. The stress arises from thermal expansion mismatch between ice and concrete, which puts the ice in tension as the temperature drops. Considering the mechanical and viscoelastic properties of ice, it is shown that this mismatch will not cause pure ice to crack, but moderately concentrated solutions are expected to crack. Cracks in the brine ice penetrate into the substrate, resulting in superficial damage. At high concentrations, the ice does not form a rigid enough structure to result in significant stress, so no damage occurs. The morphology of cracking is predicted by fracture mechanics.

Corrosion behavior of steel submitted to chloride and sulphate ions in simulated concrete pore solution

Abstract: Electrochemical measurements of open circuit potential, linear polarization and electrochemical impedance spectroscopy (EIS) were utilized to investigate the corrosion behavior and chloride threshold value (CTV) of reinforcing steels submitted to chloride and sulphate attack in simulated concrete pore solution in this study. Determination of corrosion initiation was made by combining half-cell potential (Ecorr) with corrosion current density (Icorr) as well as EIS curves. Results showed that electrochemical measurements were effective in detecting corrosion behavior of steels. CTV of steels was 0.5–0.6 mol/L in simulated concrete pore solution contaminated by chloride ions while threshold value of steels submitted to sulphate ions was 0.2–0.3 mol/L. The concomitant presence of chloride and sulphate ions led to higher corrosion current density which indicated sulphate ions accelerated the corrosion of reinforcing steels in simulated concrete pore solution.

Measuring Freeze and Thaw Damage in Mortars Containing Deicing Salt Using a Low-Temperature Longitudinal Guarded Comparative Calorimeter and Acoustic Emission

Abstract: Deicing salts are often applied to the surface of pavements and bridge decks in the winter to melt ice, thereby improving safety for the traveling public. In this paper, the influence of NaCl deicing salt on freezing and thawing temperatures of pore solution and corresponding damage of mortar specimens were investigated. A low-temperature longitudinal guarded comparative calorimeter (LGCC) was developed to cool down a mortar sample at a rate of 2°C/h and to re-heat the mortar at a rate of 4°C/h. Heat flux during freezing and thawing cycles was monitored, and the temperatures at which freezing and thawing events occurred were detected. During cooling and heating, acoustic emission (AE) activity was measured to quantify the damage (cracking) caused by aggregate/paste thermal mismatch and/or phase changes. The results show that NaCl solution in a mortar sample freezes at a lower temperature than the value expected from its bulk phase diagram because of under-cooling. Conversely, the frozen solution in mortar melts at the same melting temperature as the bulk frozen NaCl solution. As the salt concentration increases, the freezing temperature is lowered. For samples containing more highly concentrated solutions, an additional exothermic event is observed whose corresponding temperature is greater than the aqueous NaCl liquidus line in the phase diagram. Damage also begins to occur at this temperature. For mortar samples saturated by solutions with 5 % and 15 % NaCl by mass, greater freeze/thaw damage is observed. The AE calorimeter developed herein is applicable for investigating damage behavior during freezing and thawing of different phases in pore solution (in mortars).