Abstract
In this work, three different samples of solid industrial wastes cement kiln dust (CKD), granulated blast furnace slag and marble sludge were employed in a cold bonding pelletization process for the sustainable production of artificial aggregates. The activating action of CKD components on the hydraulic behavior of the slag was explored by evaluating the neo-formed phases present in several hydrated pastes. Particularly, the influence of free CaO and sulfates amount in the two CKD samples on slag reactivity was evaluated. Cold bonded artificial aggregates were characterized by determining physical and mechanical properties of two selected size fractions of the granules for each studied mixture. Eighteen types of granules were employed in C28/35 concrete manufacture where coarser natural aggregate were substituted with the artificial ones. Finally, lightweight concretes were obtained, proving the suitability of the cold bonding pelletization process in artificial aggregate sustainable production.
Highlights
In 2010, the total amount of concrete used in Italy was 98.2 million cubic meters
CKD1 contains smaller amounts of calcite and high amounts of free lime indicating that more Ca2+ will be available for a pozzolanic reaction
The X-ray diffraction (XRD) spectra related to the system S1 (Figure 3), containing CKD1 and granulated blast furnace slag (GBFS), hydrated up to days show the presence of the main peak for calcite at 29.4° 2θ that overlaps the well known broad diffusion peaks, at approximately 29.0° 2θ, assigned to calcium-silicate-hydrate (C–S–H) phases
Summary
In 2010, the total amount of concrete used in Italy was 98.2 million cubic meters. The manufacture of these building materials required 186.6 million tons of aggregates, 222,000 tons of additives and Materials 2013, 6 about 40 million tons of cement. The production of artificial aggregates may be accomplished by two different types of processes: cold-bonding cementitious pelletization and high temperature sintering The latter technology has been extensively studied and the relevant literature is rich in applications for recycling waste materials such as fly ash and slag from coal combustion and from the incineration of solid wastes, metallurgical slags, cement kiln dust, tailings from mining and quarrying, sediments, etc. Two industrial processes based on cold bonded cementitious mixtures are already applied to obtain commercial artificial aggregates: the Aardelite process, based on coal, fly ash and lime mixtures [55] and the Mapintec process, in which aggregate producing plants employ contaminated soils and cement-based mixtures [56] These plants yield artificial aggregates whose technological properties have been widely tested in a number of civil engineering applications. After 28-day curing, cubic specimens, were tested from the technological point of view and compared with conventional concrete
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