Properties of interfacial transition zones in recycled aggregate concrete tested by nanoindentation
TL;DR: In this paper, the properties of new Interfacial Transition Zone (ITZ) and old ITZ in Recycled Aggregate Concrete (RAC) were investigated by atomic force microscopy (AFM), Scanning Electron Microscopy (SEM) and nanoindentation.
Abstract: The properties of new Interfacial Transition Zone (ITZ) and old ITZ in Recycled Aggregate Concrete (RAC) were investigated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and nanoindentation. From the SEM images, obvious voids and high concentration of calcium hydroxide can be found in both old ITZ and new ITZ in RAC. Based on the nanoindentation study, it is indicated that the thicknesses of old and new ITZs are in the range 40–50 μm and in the range 55–65 μm, respectively. It is also found that the average indentation modulus of old ITZ is 70–80% of that of old paste matrix, while the average indentation modulus of new ITZ is 80–90% of that of new paste matrix. Additionally, the influences of mix proportion, aggregate types and hydration age on the properties of ITZs in RAC are discussed in this study.
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TL;DR: A brief status of recycled aggregate concrete made from recycled aggregate, summarizes and critically analyses some of the most important research findings over the past few years regarding the material aspects is given in this article.
763 citations
TL;DR: In this paper, the authors present the status of construction and demolition waste generation around the world and subsequently provide a critical review of the recent studies conducted to improve the properties of recycled aggregate concrete through different supplementary materials.
544 citations
TL;DR: In this paper, the authors provide an account of properties of concrete prepared with recycled aggregate, analyses the important findings on Recycled Aggregate Concrete (RAC) in the recent time and discusses the suitability of its usage in construction.
377 citations
TL;DR: In this paper, the authors analyzed the mechanical performance of concrete with recycled aggregates from construction and demolition waste (CDW) from various locations in Portugal and concluded that the use of RA worsens most of the properties tested, especially when fine RA are used.
318 citations
TL;DR: In this paper, the combined effects of ground granulated blast furnace slag (GGBS) and fly ash considering water-binder (W/B) ratio on the fresh and hardened properties of alkali activated GRAC were investigated.
Abstract: Geopolymer binder and recycled aggregates are considered as the two important sustainable ingredients in concrete production. Ground granulated blast furnace slag (GGBS) and fly ash combination based geopolymeric recycled aggregates concretes (GRAC) were prepared as a substitution of normal concrete in order to reduce the consumption of ordinary Portland cement and natural aggregates as well as to make use of demolished waste concrete. The aim of this study is to investigate the combined effects of GGBS and fly ash considering water-binder (W/B) ratio on the fresh and hardened properties of alkali activated GRAC. The slump, setting time, compressive strength, stress-strain relation, elastic modulus, Poisson's ratio, toughness and failure mode of alkali activated GGBS and fly ash based GRAC containing 100% recycled coarse aggregates were experimentally examined. In addition, the hydration mechanisms were studied by XRD and SEM. Finally, the failure mechanism of this kind of novel green concrete subjected to compression was revealed. The results show that GGBS and fly ash exhibits a superior synergetic effect on the performance of GRAC, i.e. fly ash and GGBS are mainly responsible for the workability and mechanical properties, respectively. GGBS/fly ash ratio has a significant influence on the fresh and hardened properties of GRAC. Moreover, the effect of W/B ratio on GRAC strongly depends on the GGBS/fly ash ratio. GGBS content at less than 25% was found to slightly influence the consistency and compressive strength of GRAC. The combination of 50% GGBS and 50% fly ash with a 0.5 W/B ratio could provide excellent mechanical performance and workability for GRAC.
287 citations
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TL;DR: In this paper, the authors used a Berkovich indenter to determine hardness and elastic modulus from indentation load-displacement data, and showed that the curve of the curve is not linear, even in the initial stages of the unloading process.
Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
22,557 citations
TL;DR: In this paper, a two types of calcium-silicate-hydrate (C-S-H) exist in cement-based materials, but less is known about how the two types affect the mechanical properties.
960 citations
TL;DR: In this article, the authors describe the so called interfacial transition zone (ITZ) in concrete as the region of the cement paste around the aggregate particles, which is perturbed by the presence of the aggregate, and show that the higher porosity present initially is significantly diminished by the migration of ions during hydration.
Abstract: This paper describes the so called interfacial transition zone—ITZ—in concrete. This is the region of the cement paste around the aggregate particles, which is perturbed by the presence of the aggregate. Its origin lies in the packing of the cement grains against the much larger aggregate, which leads to a local increase in porosity and predominance of smaller cement particles in this region. The ITZ is region of gradual transition and is highly heterogeneous, nevertheless the average microstructural features may be measured by analysis of a large numbers of backscattered electron images of polished concrete samples. Such measurements show that the higher porosity present initially is significantly diminished by the migration of ions during hydration.
945 citations
TL;DR: In this article, the influence of these aggregates (recycled and natural) on the microstructure and compressive strength of the new concrete were studied, and the results are explained by the differences in porosity and pore structure of the two types of aggregates, and possible interactions between the aggregates and the cement paste.
746 citations
TL;DR: A series of investigations on the mechanical property, durability, and structural performance of recycled aggregate concrete (RAC) have been carried out in the past 15 years (1996-2011) in China.
739 citations