Assessment of Non-destructive Methods for Evaluating the Performance of Surface Treatments on Concrete

Hydrophobic films are frequently applied to concrete structures to reduce water ingress and provide protection against weathering and chemical attacks. However, these waterproof coatings tend to deteriorate with time and require reapplication to maintain their effectiveness. Deciding when the retreatment should be applied and how to assess existing treated surfaces can sometimes be a challenging task for owners of concrete structures. Consequently, this paper presents findings on the assessment of absorption characteristics of surface-treated concrete using several techniques. Three non-destructive test methods were used to evaluate the efficacy of surface treatment under different curing conditions and with varying numbers of treatments. The methods employed were the initial surface absorption test, Karsten tube test and electrical conductivity test (wet method). The results show that the employed methods were all able to distinguish between treated and untreated surfaces. Treated samples exhibited better resistance to water absorption and electrical conductivity than untreated ones, and the absorption characteristics were found to be influenced by the number of treatments and curing regimes. All three test methods were effective in assessing surface treatment quality, with the Karsten tube test being the most practical for in-situ evaluation due to the simplicity of its setup

Evaluation of corrosion damage in reinforced concrete structures in terms of the rebar’s residual cross-section

Corroding reinforced concrete structures are frequently assessed to determine the rate of corrosion propagation and the level of deterioration, which might compromise the structure’s reliability. Appropriate measures should be considered in deciding when and how to implement maintenance if safety must be ensured. However, the influential factor that governs or informs such decisions is corrosion damage quantification. Nonetheless, the current non-destructive methods of corrosion damage quantification often lead to ambiguity, and most do not evaluate corrosion damage in terms of the rebar’s cross-section loss, which is the primary effect of corrosion. To address these shortcomings, this paper proposes an effective, reliable, and less-complicated model for quantifying corrosion damage in reinforced concrete structures based on the cross-sectional area of the corroding bar. The study was conducted through experimental (laboratory-based) and numerical investigations of the relationship between the level of corrosion and the corrosion-induced crack width. Based on the investigations’ findings, appropriate relationships and essential parameters were identified, and the model was derived analytically. The derived model assesses corrosion damage in terms of the corroding bar’s residual cross-section and requires only a few input parameters, which can be obtained by non-destructive testing if not known. The model was tested against data obtained from the laboratory experiment and against other experimental and analytical data from the literature, and the results showed a good correlation

Effects of sodium oxide content on the durability of alkali-activated mortar utilizing botswana copper mine tailings and fly ash

This investigation aims to provide experimental data on the performance of alkali-activated mortar made of copper mine tailings (CMT) and fly ash (FA) exposed to acid-sulphate attacks and elevated temperature environments as a measure of durability. FA was used as a replacement material, substituting 20 to 40% of the CMT by mass, and sodium hydroxide was the alkaline activator, which was added in terms of Na2O content by mass of the total binder at 5%, 10%, and 15%. The durability performance of alkali-activated mortar was evaluated against 5 % and 10% concentrations of sulphuric and hydrochloric acids, and magnesium and sodium sulphates up to 180 days of exposure, as well as elevated temperature environment. The specimens were first visually examined, and weight change was measured before being exposed to an elevated temperature environment and the residual compressive strength was measured. It was observed that Na2O content and elevated temperature environment influence the residual compressive strength of alkali-activated mortar. Increasing the Na2O content for all CMT-FA-based mortar samples performed well in sulphates and acids mediums in terms of durability, but with a slight reduction in its durability performance in terms of residual compressive strength. However, these effects were more profound in samples exposed to acids, particularly those with lower FA replacement levels and sodium oxide content. For the high-temperature exposure, the residual compressive strength of all CMT-FA samples was much higher than the initial values. The findings also revealed that the partial replacement of CMT by FA significantly improved the residual compressive strength in terms of the durability performance of the alkali-activated morta