Long-term Durability Of Concrete Research Articles

Cost effectiveness of reinforcement alternatives for a concrete water chlorination tank

Reinforced concrete tanks in water/wastewater treatment plants are susceptible to severe corrosion due to aggressive exposure conditions resulting from the application of certain treatment chemicals and methods. Non-corrosive materials, such as stainless steel or fiber reinforced polymer (FRP), may be attractive alternative reinforcement options for such concrete structures. However, the high initial cost of such materials imposes constraints on their use, although such thinking ignores improvements in long-term concrete durability. The current paper addresses the use of non-corrosive reinforcement in a concrete water chlorination tank using life-cycle cost analysis (LCCA) that aims to evaluate the cost effectiveness of different reinforcement alternatives. A comparison was established between four concrete reinforcing materials, namely, black steel, epoxy coated steel, stainless steel, and glass-FRP (GFRP) through a 100-year analysis period.The results of this study suggest that the use of non-corrosive reinforcement helps achieve a considerable long-term cost saving. LCCA showed that GFRP becomes more economical than black steel in 35 years following construction. The net present cost (NPC) obtained for the GFRP-reinforced concrete was approximately 43% lower than that of the black steel reinforced concrete. The use of stainless steel also had a potential advantage but was less cost-effective than GFRP, with a 50-year payback period and an NPC 25% lower than that of the conventional design. Epoxy coated steel also showed a long-term cost benefit when compared to black steel, with approximately 11% reduction in NPC and 15-year extension in the service life. Sensitivity analyses were performed to assess the effects of the analysis period, discount rate, construction costs, concrete strength, and the use of supplementary cementitious materials on the LCCA outcomes.

Quantitative measurements of curing methods for concrete bridge decks

This paper gives a quantitative comparison of how different curing methods impact the rate of drying and subsequent penetration of lime water and chloride penetration of concrete. Laboratory work is used to investigate a bridge deck concrete mixture cured by two different curing compounds, wet curing of different lengths, and then no curing. The results confirm that wet curing methods reduce the ingress of external chemicals more effectively. The wet curing for even one day provided significant improvement over both curing compounds and no curing. To confirm the findings in the field eight bridge decks were investigated that were cured with a curing compound and wet curing. The field investigation confirms the findings of the laboratory testing and emphasizes the importance of wet curing for long term durability of concrete. This paper provides important quantitative data that can be used to compare these methods and help with making decisions about different curing practices and the impact on the service life of concrete.

Effect of barium-based phase change material (PCM) to control the heat of hydration on the mechanical properties of mass concrete

Thermal stress in mass concrete is a critical factor that is used in determining serviceability, and long-term durability of concrete. Phase change material (PCM) can be considered to mitigate such thermal stress in massive concrete structures. Based on related research results, barium-based PCM was selected as the latent heat binder. This study focuses on the appropriate mix design of selected PCMs. The test results indicate that the application of barium-based PCM in mass concrete mixtures is effective in controlling the hydration heat with manageable negative effects on the mechanical properties and durability of the concrete. Based on the experimental results, the proposed mixing methods were implemented at a construction site. The maximum temperature at the core of the structure was maintained at around 58°C, which indicates that the hydration temperature could be controlled effectively.

Review of Properties of Concrete , 5th Ed., by A. M. NevillePrentice Hall, Pearson, San Francisco, CA; 2012; ISBN 0273755803 and 978-0273755807; 846 pp.; $160 (paperback).

Review of <i>Properties of Concrete</i> , 5th Ed., by A. M. NevillePrentice Hall, Pearson, San Francisco, CA; 2012; ISBN 0273755803 and 978-0273755807; 846 pp.; $160 (paperback).

Permeation Properties of Bacterial Concrete

An experimental study on effect of calcifying bacteria on permeation properties (such as absorptivity and sorptivity) of bacterial concrete is outlined in this paper. The rate of water absorption, water absorption capacity, sorptivity and porosity tests were then performed on the samples of concrete treated with bacteria of ordinary (M20), standard (M40) and high strength (M60 and M80) grades, to assess the enhancement of permeation properties due to biomineralization in bacterial concrete. The results show that, absorptivity, sorptivity and porosity of bacterial concrete are much lower than the corresponding characteristics of controlled concrete. These characteristics are noticeably enhanced by the addition of bacillus subtilis JC3 to the concrete. It also indicated from the chemical analysis that the cement-phase composition of bacterial concrete has significant amount of calcium precipitate compound. The study of porosity is fundamental for understanding phenomena of water transport within pore structure and interactions between concrete and water. Water can penetrate a solid because there are interconnected channels (pores) inside the solid that facilitate its transportation.The long-term durability of concrete is affected to a large extent by its permeability. Therefore, the permeation properties, rather than mechanical properties, are the important factors to study in relation to concrete durability. As a consequence, a considerable effort has to be directed toward investigation of such properties in the present study. Keywords - bacterial concrete, bacillus subtilis JC3, Permeation, Porosity, Sorptivity, Water Absorption Capacity.

The Durability Failure of Pre-Damaged Concrete Induced by Mechanical Load

Chloride ion penetration and freezing and thawing damage are the two main factors that affect the durability of concrete structures. Through the chloride ion penetration test and freezing and thawing test of concrete specimens after tensile and compressive loading, the influence of load-induced damage on the long-term durability of concrete was studied. The results showed that the apparent chloride diffusion coefficient of concrete increased by 6.4% and 34%, and the surface chloride concentration increased 10% and 40%, respectively, both of which showed the "negative effect" when the uniaxial tensile load level reached the 65% and 75% of the ultimate capacity. However, with the increasing uniaxial compressive load level, the impact on the frost resistance of concrete experienced a transformation from the "positive effect" to the "negative effect".

Characterization for Long-Aged Hardened Cement Collected from Old Structures by Modern Technique for Chemical Analysis

Chemical analysis of cementitious material used in old structures yields empirical information concerning the long term-durability of concrete. Chemical analysis is also useful for scientific research on historical structures as a cultural heritage. Since the materials used in old structures have peculiarities deriving from the long time elapsed since the construction of the structures, it is necessary to take them into consideration for analysis. In this paper, guidelines for carrying out a systematic and effective analysis of old hardened cement even for small samples are proposed. Based on these guidelines, evaluation of a material such as hardened cement collected from actual old structures by X-ray fluorescent analysis, analysis of the acid-soluble part, powder X-ray diffraction and electron probe microanalysis were carried out, and the usefulness of the information obtained by these analyses is discussed.

Prediction of the long-term durability of lightweight aggregate concrete mixtures under severe marine environment

As part of the U.S. Navy program for the Modular Hybrid Pier development, a predictive durability analysis has been carried out to establish the feasibility of using lightweight aggregate concrete mixtures to achieve the 100-year design life under severe marine conditions. The long-term durability of concrete was predicted using both laboratory testing and numerical modeling.

Accelerated Test for Measuring Sulfate Resistance of Calcium Sulfoaluminate, Calcium Aluminate, and Portland Cements

Sulfate ions present in soil, ground water, seawater, decaying organic matter, and industrial effluents are known to have an adverse effect on long-term durability of concrete. However, American Society for Testing and Materials (ASTM) test methods for predicting sulfate resistance have been criticized for failing to adequately predict field performance. In this investigation, cement pastes were tested by an accelerated test method where pH and sulfate concentration remained constant, conditions that are more representative of field conditions. A total of eight cements were tested: three portland cements (Type I/II, Type III, and Type V); one calcium aluminate cement (CA1); two calcium sulfoaluminate cements (CSA1 and CSA2); and two blends containing calcium aluminate, anhydrite, and portland cement (CAPC1 and CAPC2). After 63 days of exposure to a 4% Na₂SO₄ solution where the pH was maintained at 7.2, sulfate resistance of the cements can be described by: CA1 = CSA2 = Type I/II > Type V > Type III > CAPC2 > CAPC1 > CSA1.

The microstructure of concrete cured at elevated temperatures

The temperature and relative humidity pertaining during curing influence the strength development, microstructure, and long term durability of concrete. Optical and electron microscopy techniques have been used to assess the microstructural characteristics of laboratory prepared concrete and case study material cured under a range of temperature and humidity regimes. Microstructural examination of two month old concrete cured at 16 °C, 42 °C and 46 °C has revealed no marked differences in the spatial distribution, morphology, and volume of hydrates and other microstructural features present. A network of microcracks was evident within the matrix of all the concretes, with that cured at 85 °C, and the sample with eighteen years in-service use, showing a higher degree of microcracking. The concretes prepared at temperatures above 46 °C were also found to have significant development of hydrates, particularly ettringite, within pores and microcracks, together with a generally coarser microstructure.