Reutilización de árido mixto reciclado procedente de los residuos de la construcción y demolición en la fabricación de hormigones

Este artículo recoge el estudio de la viabilidad de la utilización de árido grueso mixto reciclado procedente de los residuos de la construcción y demolición como sustituto parcial del árido grueso natural, en la fabricación de hormigones con una resistencia característica de 30 MPa. El árido mixto reciclado utilizado tiene una calidad media – baja, debido a que el contenido de asfalto y partículas flotantes es elevado. La propiedades físicas (densidad y trabajabilidad) y mecánicas (resistencia a compresión y tracción) fueron estudiadas en los hormigones reciclados con un porcentaje de sustitución del 50% en peso de árido natural, con y sin partículas flotantes. Los resultados obtenidos, muestran que la incorporación de este árido reciclado no tiene un efecto negativo en la trabajabilidad de los hormigones en estado fresco. Respecto a la densidad y las propiedades mecánicas, se observa como disminuyen estas propiedades a medida que aumenta el contenido de árido mixto reciclado y de partículas flotantes. Finalmente, a la luz de estos resultados se puede señalar que estos áridos mixtos reciclados pueden emplearse en la fabricación de hormigones destinados a la edificación u otras aplicaciones

Hydration of C3S, C2S and their Blends. Micro- and Nanoscale Characterization

This study forms part of wider research conducted under a EU 7 th Framework Programme (COmputationally Driven design of Innovative CEment-based materials or CODICE). The ultimate aim is the multi-scale modelling of the variations in mechanical performance in degraded and non-degraded cementitious matrices. The model is being experimentally validated by hydrating the main tri-calcium silicate (T1-C3S) and bi-calcium silicate (β-C2S), phases present in Portland cement and their blends. The present paper discusses micro- and nanoscale studies of the cementitious skeletons forming during the hydration of C3S, C2S and 70 % / 30 % blends of both C3S/C2S and C2S/C3S with a water/cement ratio of 0.4. The hydrated pastes were characterized at different curing ages with 29 Si NMR, SEM/TEM/EDS, BET, and nanoindentation. The findings served as a basis for the micro- and nanoscale characterization of the hydration products formed, especially C-S-H gels. Differences were identified in composition, structure and mechanical behaviour (nanoindentation), depending on whether the gels formed in C3S or C2S pastes. The C3S gels had more compact morphologies, smaller BET-N2 specific surface area and lesser porosity than the gels from C2S-rich pastes. The results of nanoindentation tests appear to indicate that the various C-S-H phases formed in hydrated C3S and C2S have the same mechanical properties as those formed in Portland cement paste. Compared to the C3S sample, the hydrated C2S specimen was dominated by the loose-packed (LP) and the low-density (LD) C-S-H phases, and had a much lower content of the high density (HD) C-S-H phas

Mapping of mechanical properties of cement paste microstructures

The presented study is related to the EU 7 th Framework Programme CODICE (COmputationally Driven design of Innovative CEment-based materials). The main aim of the project is the development of a multi-scale model for the computer based simulation of mechanical and durability performance of cementitious materials. This paper reports results of micro/nano scale characterisation and mechanical property mapping of cementitious skeletons formed by the cement hydration at different ages. Using the statistical nanoindentation and micro-mechanical property mapping technique, intrinsic properties of different hydrate phases, and also the possible interaction (or overlapping) of different phases (e.g. calcium-silcate-hydrates) has been studied. Results of the mapping and statistical indentation testing appear to suggest the possible existence of more hydrate phases than the commonly reported LD and HD C-S-H and CH phase

Nanomechanical Study of Cement Pastes by Statistical Nanoindentation and Peakforce QNM

The study is related to the EU 7th Framework Programme CODICE (COmputationally Driven design of Innovative CEment-based materials) project. The main aim of the project is the development of a multi-scale model for the computer based simulation of mechanical and durability performance of cementitious materials. As part of the task to study the micromechanical properties of computationally driven designs and validate the model predictions, extensive work on micro/nano-mechanical characterisation of cement-based materials has been conducted, which cover synthetic C3S, C2S pastes, cement pastes hydrated at different ages and pastes subjected to accelerated calcium leaching, etc. Statistical nanoindentation and micro-mechanical property mapping technique was used to study intrinsic properties of different hydrate phases and microstructures down to approximately 1 µm. A new experimental technique – Peakforce QNM was also used to examine mechanical properties of cement paste micro/nano-structures down to approximately 10 nm. The importance of proper specimen preparation is highlighted, particularly for the early-aged and leached samples due to their weak and fragile microstructure. The results obtained from the two experimental techniques are presented and advantages/limitations for each technique discussed

Effect of the constituents (asphalt, clay materials, floating particles and fines) of construction and demolition waste on the properties of recycled concretes

The present study explores the viability of reusing mixed recycled aggregate from construction and demolition waste as a partial (25 and 50 wt%) replacement for natural coarse aggregate in the manufacture of concretes with a compressive strength of 30 MPa. It further analyses the effect of some of the constituents (asphalt, clay-based materials, floating particles and fines) of these recycled aggregates on the properties of recycled concretes. Despite the high asphalt and floating particle content of the recycled aggregate used, came from waste management plant at Glasgow, it was found to have no adverse effect on the workability of the new concretes. Hardened concrete density and compressive strength were observed to decline with increasing replacement ratios, at a variable rate depending on the components of the recycled aggregate mix and the thickness of their ITZs (the thicker the weaker). While concrete with 25% recycled aggregate exhibited lower sorptivity than the reference concrete, absorption was higher when the replacement ratio was 50%. The findings showed that this type of recycled aggregate can be used in concrete manufactured for housing applications and confirmed the importance of good construction and demolition waste management to deliver high quality recycled aggregate.Peer reviewe