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Chloride ingress in reinforced concrete induces corrosion and consequent spilling and structural weakness, and it occurs world-wide and imposes an enormous cost. Yet it can be resisted by using test methods and relevant models for service life prediction.Resistance of Concrete to Chloride Ingress sets out current understanding of chloride transport
Permeability is an important property to consider when designing concrete for long service lives but unfortunately requires long-term testing to be accurately measured. Short-term test methods to estimate permeability such as rapid chloride permeability (RCP), bulk resistivity (BR), and surface resistivity (SR) have therefore been developed. In this study, three short-term test methods are performed, and the results compared, RCP testing is performed using accelerated curing to determine whether testing can be shortened, and the effects of SCMs on results are examined. It was observed that all three test methods had strong positive correlations with one another. RCP testing performed on specimens subjected to an accelerated-curing regime for 28 days had a strong positive correlation with specimens that were cured in standard conditions for 91 days. The addition of SCMs improves concrete permeability; the beneficial effect of SCMs increases with the maturity of the concrete.
Disposal of aged concrete pavements involves great cost and (due to volumes involved) can be detrimental to environment when all of this material is deposited in landfills. It is therefore cost-effective to recycle crushed concrete as coarse aggregates (referred hereafter as RCA) to replace natural aggregates (NA) during construction of new concrete pavements. This approach reduces the need for quarrying of natural aggregates and saves space in the landfills. The main focus of this study was on determining the chloride penetration resistance of pavement concretes containing various levels (0, 30 and 100%) of RCA as a replacement for NA. All concrete mixtures used in this study were designed to meet the fresh properties and flexural strength requirements specified for pavements by the Indiana Department of Transportation (INDOT). The resistance to chloride ion penetration was determined using two electrical migration tests: rapid chloride permeability (RCP) test (as per ASTM C1202) and non-steady state migration test (as per NT BUILD 492). Before the initiation of the RCP test, all specimens were first subjected to 250mVAC potential scan using SolartronTM 1260 gain-phase impedance analyzer. The impedance spectra (collected over a frequency range of 0.1Hz to 10MHz) were used to obtain bulk resistance (Rb) of the concrete. The steady state diffusion coefficients were calculated using RCP test data in Nernst-Plank and empirical equations. The general trends obtained from the chloride penetration resistance results indicate that initial current values from RCP test can be used to predict the performance of concretes containing RCA. Mixtures with 30% RCA performed similar to 0% RCA mixture while the resistance to chloride penetration of concrete with 100% RCA was somewhat reduced.
External sulphate attack on concrete can lead to cracking, expansion and sometimes loss of cohesiveness of hardened cement paste. Therefore, aside from using sulphate resistant cementitious binders, it is important to design concrete which can resist sulphate penetration. In this research, both ASTM C1202 and NT Build 492 electrical migration tests were modified such that sulphate rather than chloride penetration resistances were measured. Modifications included exposing concrete specimens to Na2SO 4 rather than NaCl solutions and measuring the depth of sulphate penetration visually using BaCl2+KMnO4 rather than AgNO3 solution. Nine concrete mixtures of varying w/cm, slag replacement and cement types were tested in both original standard tests and modified tests to evaluate the influence of these material variables on test results and compare chloride to sulphate results. It was found that while migration coefficients and total charge passing were lower for sulphate, the influence of material variables were relatively similar.
"This procedure is for the rapid evaluation of chloride penetration resistance of concrete, from non-steady-state migration experiments." -- Page 1.
Science and Technology of Concrete Admixtures presents admixtures from both a theoretical and practical point-of-view. The authors emphasize key concepts that can be used to better understand the working mechanisms of these products by presenting a concise overview on the fundamental behavior of Portland cement and hydraulic binders as well as their chemical admixtures, also discussing recent effects in concrete in terms of rheology, mechanics, durability, and sustainability, but never forgetting the fundamental role played by the water/binder ratio and proper curing in concrete technology. Part One presents basic knowledge on Portland cement and concrete, while Part Two deals with the chemical and physical background needed to better understand what admixtures are chemically, and through which mechanism they modify the properties of the fresh and hardened concrete. Subsequent sections present discussions on admixtures technology and two particular types of concrete, self-consolidating and ultra-high strength concretes, with final remarks on their future. Combines the knowledge of two leading authors to present both the scientific and technology of admixtures Explains what admixtures are from a chemical point-of-view and illustrates by which mechanisms they modify the properties of fresh and hardened concrete Presents a fundamental, practical, and innovative reference book on the topic Contains three detailed appendices that can be used to learn how to use admixtures more efficiently