RESUMEN
In this review by TC- 282 CCL, a comprehensive examination of various facets of chloride ingress in calcined clay-based concrete in aggressive chloride-rich environments is presented due to its significance in making reinforced concrete structures susceptible to chloride-induced corrosion damages. The review presents a summary of available literature focusing on materials characteristics influencing the chloride resistance of calcined clay-based concrete, such as different clay purity, kaolinite content and other clay minerals, underscoring the significance of pore refinement, pore solution composition, and chloride binding mechanisms. Further, the studies dealing with the performance at the concrete scale, with a particular emphasis on transport properties, curing methods, and mix design, are highlighted. Benchmarking calcined clay mixes with fly ash or slag-based concrete mixes that are widely used in aggressive chloride conditions instead of OPC is recommended. Such comparison could extend the usage of calcined clay as a performance-enhancing mineral admixture in the form of calcined clay or LC2 (limestone-calcined clay). The chloride diffusion coefficient in calcined clay concrete is reported to be significantly lower (about 5-10 times in most literature available so far) compared to OPC, and even lower compared to fly ash and slag-based concrete at early curing ages reported across recent literature made with different types of cements and concrete mixes. Limited studies dealing with reinforcement corrosion point out that calcined clay delays corrosion initiation and reduces corrosion rates despite the reduction in critical chloride threshold. Most of these results on corrosion performance are mainly from laboratory studies and warrant field evaluation in future. Finally, two case studies demonstrating the application of calcined clay-based concrete in real-world marine exposure conditions are discussed to showcase the promising potential of employing low-purity calcined clay-based concrete for reducing carbon footprint and improving durability performance in chloride exposure.
RESUMEN
Present study characterizes municipal solid waste incineration bottom ash (MIBA) from three incineration plants in Delhi with an intent to serve the dual objectives: a) assessing the disposal/reuse options for Delhi MIBA, b) evaluating variability in results across the countries (including India) and assessing if is significant enough to influence the fate of MIBA of varied origin. A review on leaching studies of MIBA (50 research papers) was conducted which aided in achieving both the objectives. Delhi MIBA samples were analysed for chemical composition. The two commonly adopted leaching tests i.e., TCLP and EN 12457-2, were conducted and the results were checked against regulatory threshold levels (RTLs) to achieve the first objective. Leaching concentration of the contaminants was compared with the compiled literature and RTLs to accomplish the second objective. The compendium of literature most importantly revealed the physicochemical parameters which are pivotal in determining the fate of MIBA but have been missing from many studies. Ten such parameters were identified: Cr, Cu, Mo, Sb, Cl-,SO42-, Cd, Pb, Ni and Zn and are referred as contaminants of concern (CoCs). Delhi MIBA was found suitable for disposal to non-hazardous waste landfills and unsuitable for unrestricted reuse. CoCs identified in Delhi MIBA were identical to those observed in literature (except Cd, Pb and Zn). The variability in leaching concentration of CoCs, observed from comparative assessment of results, spanned nearly 2 to 3 log10 magnitudes for Cu, Cr, Pb, Sb and Zn while 1 to 2 log10 magnitudes for Mo, Cl-andSO42-.