To address sustainability issues, concrete design and specification must consider a variety of evaluation criteria, necessitating analytical methods that can optimize mixes to meet performance requirements while maximizing sustainability. This paper proposes the desirability approach, a multi-response optimization technique, as a new method for the sustainability evaluation of concrete materials. A demonstration study, using four sustainability indicators and six concrete mixes with varying binder compositions and aggregate types, is presented that explores how changing the shape of the desirability function, which translates indicator values to desirability, affects the sustainability evaluation output. Treating the function shapes as a source of uncertainty, sustainability evaluation is conducted with uncertainty analysis to produce a sustainability score distribution for each mix, which is described by statistical measures. Mixes with the highest and lowest indicator values exhibited the least variance in their scores, as these values were unaffected by the function shape. Sensitivity analysis, which measures the contribution of the sources of uncertainty to the total output uncertainty, found that the interactions when varying multiple function shapes simultaneously were the most influential source of uncertainty, which may be caused by multi-collinearity among the indicators. It was also found that sustainability scores calculated by geometric aggregation were lower than those calculated by linear aggregation.
Much is left unknown about applicable conditions of the method or quantification of the cathodic protection range. In particular, little has been studied about how the range or effect of cathodic protection is influenced by such factors as the thickness of reinforcing bars (rebars) to be protected, combined deterioration by carbonation and mixed chloride, amount of chloride ions and carbonation depth. This study experimentally evaluated the effect of differences in the chloride ion content in concrete, the carbonation depth or the rebar thickness on the cathodic protection range of the embedded sacrificial anode method. The results of the experiment were that the smaller the carbonation depth, the amount of chloride ions or the rebar thickness, the larger the amount of depolarization of the rebars in the concrete to be protected was. That is, for corrosion protection of rebars near patch repair areas embedded with sacrificial anodes, it would be appropriate to make the steel surface area of components smaller and the salt damage environment less corrosive.
The long-term performance of a cement-based barrier system, envisaged worldwide in many concepts for deep geological storage of radioactive waste, depends on its material properties and how they evolve with time. Chemical interactions with the service environment may lead to mineralogical alterations and related physico-chemical changes at material interfaces, influencing radionuclide migration. Predictive (reactive) transport modelling therefore requires information on transport properties (e.g. sorption properties, porosity) of aged cement matrices.
Radionuclide binding by fresh and aged cement matrices (> 10 years) has been investigated using two different aged cementitious materials retrieved from long-term in-situ rock laboratory (at the Mont Terri and Grimsel test sites, Switzerland) experiments to provide sorption data for use in predictive modelling and interpretation of the field diffusion experiments. For this purpose, the uptake of 36Cl, 125I, 3H (HTO) and 14C has been investigated in a series of batch sorption experiments. Fresh cement paste shows the strongest sorption for 36Cl and 125I due to the largest proportion of radionuclide sorbing cement phases (ettringite, C-S-H, AFm). Measured sorption values for 36Cl and 125I on the aged cement matrices are about an order of magnitude lower. Sorption values for HTO and 14C-formate on cementitious materials are generally very low, suggesting only weak interaction with the surfaces of the cement minerals.
In order to develop a safe technology for recycling municipal solid waste incineration fly ash (MSWI-FA), the authors have attempted to produce foamed geopolymers with addition of MSWI-FA, and have investigated their various properties, including bulk density, strength, thermal conductivity, and leaching concentration of heavy metals and chlorine, etc. The polymerization reaction products, crystalline compounds and microstructure were also examined through X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analyses. It was found that it is possible to produce foamed geopolymer with a bulk density of less than 0.5 and a uniform distribution of air voids, by adding metallic aluminum powder as foaming agent and using less than 20% MSWI-FA and suitable alkali activator having low NaOH mole concentration. CaCl(OH)2 Ca(OH)2, CaO and KCl, initially included in the MSWI-FA, were not found in the foamed geopolymers. The geopolymers, which used ground granulated blast furnace slag (BFS), coal fly ah and MSWI-FA as precursors, were mainly composed of C-A-S-H gels, incompletely reacted precursors and a small amount of N-A-S-H gels. The foamed geopolymer had very high immobilization capacity of heavy metals (Cd, Cr, Cu, Mn, Pb, Zn), not varying with the pH of leachate. The immobilization efficiency of As changed with the pH of leachate and BFS content. When the BFS content was not less than 60%, the leaching concentrations of all the traced heavy metals including As were low, satisfying the environmental criteria of Japan for recycled construction materials without direct contact with water. The chlorine immobilization capacity of the foamed geopolymers is expected to exceed 70% in long-term age.
This study aimed to develop a method for the reasonable prediction of chloride ingress into concrete under unsaturated conditions. To achieve this, the connectivity of both the pore networks and the water paths in hardened cement paste were investigated and modeled in the existing numerical analytical system. Previous measurement results for the continuous porosity in hardened cement paste were reorganized, and the relationship between the total porosity and continuous porosity was clarified and formulated as the pore connectivity. In addition, the connectivity of the liquid water in unsaturated pore structures was formulated referring to previous numerical studies, suggesting that the connectivity of the liquid water decreases at a lower degree of saturation. Furthermore, by calculating the chloride transport considering the pore connectivity and the liquid water connectivity under unsaturated conditions, the chloride penetration into unsaturated concrete, including an airborne chloride environment, could be reproduced more realistically than was previously possible.
In concrete structures, opened cracks contribute significantly to the transfer of shear and normal stresses through the contact forces occurring between fractured surfaces. Such contact forces are due to protruding asperities, engaged by interlocking and friction. In this paper, the role played by roughness on shear resistance is investigated numerically. First, micro computed tomography and digital microscope measures of concrete surfaces are used to validate a novel numerical generator of realistic cracked concrete surfaces. Secondly, a contact solver based on the boundary integral approach allows an extremely fine description of typical cracked surface topologies. Roughness changes drastically the predictions, so that the shear resistance computed numerically matches the prior experimental results reported in the literature. The proposed model does not need any fitting procedure, making it a reliable and physically based method for predicting shear transfer phenomena in concrete. An empirical power-law predicting the shear resistance in concrete is a direct outcome, which accounts for micro-scale roughness and aggregate distribution.
This study aims to assess the degradation of below-grade concrete of nuclear power plants (NPP) in Japan, considering possible acid and sulfate attacks. A survey on the underground environments of several NPPs and residential buildings across the country was conducted, and their associated concrete performance was evaluated where concrete samples from core drillings were available. Moreover, acid and sulfate exposure tests on mortar specimens lasting for up to four years were carried out in the laboratory to simulate actual field situations. The effects of exposure conditions, such as solution concentrations, temperature, and immersion conditions, were examined. The surveyed environments were classified into non-aggressive or slightly aggressive environments. The concrete core samples investigated showed insignificant degradation and satisfactory strength after 40 years of exposure. The laboratory test results showed that the accelerated tests using highly concentrated solutions could exacerbate the extent of decalcification and even alter the degradation mechanism for magnesium sulfates. Therefore, a close-to-reality concentration is preferred for reproducing field situations. The carbonation/neutralization depth was used as an indicator to estimate the degradation extent. The measured values in the laboratory using low-concentration solutions correlated well with the field results, suggesting that the below-grade concrete’s degradation in the NPPs investigated may be less than 10 mm after 60 years of exposure.