Steam curing effect on the properties of fly ash high performance recycled aggregates concrete

The aim of this study is to encourage the use of Recycled Concrete Aggregate (RCA) in High Performance Concrete (HPC) with fly ash. Three types of coarse RCA sourced from medium to high strength concretes were employed in 100% replacement. In order to boost their mechanical performance at early age, steam curing was assessed. The physical, mechanical and durability properties of Recycled Aggregate Concretes (RAC) were compared to those from Natural Aggregate Concrete (NAC). According to the results, natural aggregates could be completely replaced by RCA if they are sourced from similar parent HPC. Lower quality RCAs decreased the mechanical and durability behavior of HPC. However, the properties of RAC had higher long-term improvements than those from NAC due to the influence of fly ash. Despite steam curing produced higher early-age compressive strength, it had longterm negative effects. Nevertheless, RACs were less affected by long term effects of steam curing.Postprint (published version

Properties of plain concrete produced employing recycled aggregates and sea water

The final publication is available at Springer via http://dx.doi.org/10.1007/s40999-017-0229-0The generation of construction and demolition waste (C&DW) is a noteworthy environmental and economic concern. The development of new applications in which Recycled Mixed Aggregates (RMA) can be used will lead to a reduction of landfills growth. Moreover, the use of seawater shall represent another advance in sustainability due to the consequent reduction of fresh water consumption, which can be a limited resource in certain areas. Although seawater is not generally recommended for concrete production, especially in reinforced concretes, seawater could be a viable replacement for fresh water in the production of plain concretes. This study intends to analyse the possibility of using RMA and seawater in the production of concrete to be used in port sites. This study is based on three different parameters: cement class, water source and RMA content. The results highlighted the beneficial effects of using type III cement, especially with regard to durability properties. The concretes produced employing RMA and type III cement achieved lower value of sorptivity coefficient and higher values of ultrasonic pulse velocity (UPV), chloride ion penetration resistance and electrical resistivity than those produced with natural aggregates and type I cement. Moreover, the use of seawater in concretes with type III cement not only produced higher density and lower absorption capacity but also higher mechanical properties by creating a denser cement matrix, which proved to suffer low decrease by RMA addition.Peer ReviewedPostprint (author's final draft

Utilización del hormigón con árido reciclado en la ciudad de Barcelona

Debido a la necesidad de introducir áridos reciclados en el mercado y concretamente en Barcelona, se realizó un exhaustivo trabajo experimental en el laboratorio de Materiales de Construcción donde se determinaron las propiedades físico- químico mecánico de los áridos reciclados producidos de las dos plantas más importantes pertenecientes a Gestora de Runes de Catalunya s.a. (GRC) y se analizó el comportamiento de hormigones fabricados con áridos gruesos reciclados. A partir de los resultados experimentales, Vías y Construcciones S.A. y Lafarge ejecutaron como pruebas piloto la construcción de dos aceras de hormigón reciclado (HR) de adecuadas propiedades en MercaBarn

Evaluation of eco-efficient concretes produced with fly ash and uncarbonated recycled aggregates

The fabrication of conventional concrete, as well as remains from demolition, has a high environmental impact. This paper assessed the eco-efficiency of concrete made with uncarbonated recycled concrete aggregates (RCA) and fly ash (FA). Two concrete series were produced with an effective water/cement ratio of 0.50 (Series 1) and 0.40 (Series 2). In both series, concretes were produced using 0% and 50% of RCA with 0%, 25% and 50% FA. After analysing the compressive strength, and carbonation and chloride resistance of those concretes, their eco-efficiency based on the binder intensity and CO2-eq intensity was assessed. We found that the use of 50% uncarbonated RCA improved the properties of concretes produced with FA with respect to using natural aggregates. The concrete made of 25% FA plus RCA was considered the most eco-efficient based on the tests of compressive, carbonation and chloride properties with the values of 4.1 kg CO2 m-3 MPa-1, 76.3 kg CO2 m-3 mm-1 year0.5 and 0.079 kg CO2 m-3 C-1, respectively. The uncarbonated RCA improved carbonation resistance, and FA improved chloride resistance. It can be concluded that the use of 50% un-carbonated RCA combined with FA considerably enhanced the properties of hardened concrete and their eco-efficiency with respect to concretes produced with natural aggregates.The author thanks Fernando Álvarez and Carles Arraz for their collaboration in the experimental work and the staff of the Laboratory of Technology of Structures and Materials “Lluis Agulló” of the UPC for their support.Peer ReviewedObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats SosteniblesObjectius de Desenvolupament Sostenible::12 - Producció i Consum ResponsablesObjectius de Desenvolupament Sostenible::13 - Acció per al ClimaPostprint (published version

Structural behaviour of prestressed concrete sleepers produced with high performance recycled aggregate concrete

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0966-6A comparative analysis of the structural behaviour of prestressed concrete sleepers made with high performance concrete (HPC) and high performance recycled aggregate concrete (HPRAC) is presented in this study. Two types of HPRAC sleepers were tested, using 50 and 100% of recycled concrete aggregate (RCA) in replacement of coarse natural aggregates. The RCA employed in this research was sourced from crushing rejected HPC sleepers. The aim of this study was to determine through analysis if the HPRAC sleepers’ behaviour fulfilled the European minimum requirements standards for prestressed concrete sleepers and compare their experimental behaviour with that of the HPC sleepers. The three types of prestressed concrete sleepers were subjected to static load tests at rail-seat and centre section (positive and negative load). In the centre section tests a comparative study between the experimental results and the proposed values of four assessment methods of ultimate capacity was carried out. Dynamic load and fatigue tests were also performed at the rail-seat section. The HPRACs and HPC sleepers met all the structural requirements for prestressed concrete sleepers. The experimental results determined the satisfactory performance of the HPRAC-50 and the HPRAC-100, which was very similar to that of the HPC sleepers. The load–strain behaviour recorded via the use of strain gauges on the prestressing bars revealed slightly higher stiffness of the HPC sleepers. The values obtained from the four assessment methods of ultimate capacity were also accurate when applied to HPRAC.Peer ReviewedPostprint (author's final draft

Influence of the quality of recycled aggregates on the mechanical and durability properties of high performance concrete

The final publication is available at Springer via http://dx.doi.org/10.1007/s12649-016-9637-7The main objective of this experimental work is to analyse the effect of recycled aggregates (RA), on the basis of the study of the various qualities, of the physical, mechanical and durability properties of high performance concrete (HPC). Five types of recycled aggregates: three coarse RA sourced from parent concretes of 100, 60 and 40 MPa, as well as one coarse mixed recycled aggregate and one fine ceramic waste aggregate were used as replacement for natural aggregates (NA). Two types of coarse NA and two types of river sands were employed for concrete production. On the basis of the findings of our research it was determined that the reduction in quality and the increase in the amount of RA substitution produced a decline in the properties of HPC. According to our analysis of the mechanical properties, a 100 % replacement of coarse NA for recycled concrete aggregates can be employed, providing the RA has been sourced from a 60 MPa minimum-strength concrete. Nevertheless, durability behaviour was greatly influenced by the use of RA, and consequently replacement ratios of high quality RA should be reduced to 50 % to achieve similar behaviour patterns to those of NA concrete. Moreover, severe reductions of RA qualities (sourced from 40 MPa strength concretes or mixed waste) only permitted 20 % replacement ratios on HPC production. However, those concretes containing fine ceramic RA (up to 30 %) reached higher compressive strength, higher chloride-ion penetration resistance and higher improvements of durability properties at longer ages than those concretes produced using NA concrete.Peer ReviewedPostprint (author's final draft

Influence of high volume fly ash and recycled aggregates in chloride and carbonation resistance of concrete

This paper deals with the evaluation of the influence of recycled concrete aggregate (RCA) and the employment of high volume of fly ash (FA) on the physical, mechanical and durability (chloride ion penetration and carbonation) properties of concretes. The obtained values of which, being compared to those of conventional concretes. Concrete was produced using 0%, 25% and 50% FA in replacement of Portland cement, and 0% and 50% of RCA in substitution of natural aggregates. All the concretes were produced employing an effective water-cement ratio of 0.50. The physical properties at 28 days and the compressive strength at 7, 28 and 90 days were determined in all the concretes produced as well as the assessment of durability (penetration of chlorides and depth of carbonation) on all concrete mixtures. The depth of the carbonation was determined after submitting every concrete sample to a series of accelerated tests at 20% of CO2 concentration during 7, 14 and 28 days after the curing period in the humidity room and pre-condition in the laboratory. The chloride penetration was determined at 28 and 90 days of curing. It was concluded that the employment of 50% of un-carbonated RCA increased the early strength of concrete produced using FA, and at late ages, RCA concretes achieved similar strength when 25% of FA was employed. The concrete produced with 50% of FA achieved the highest resistance to chloride ion penetration also when RCA was employed. Although the use of FA increased the carbonation depth of the concrete samples, the employment of the un-carbonated RCA reduced that effect. The employment of RCA with CEM II or binder with 25% of FA caused the lowest carbonation depth.Postprint (published version

Influence of plastic recycled aggregates in the hardened properties of concretes

The use of the new resource of man-made plastic aggregates as an alternative to natural aggregate could be a viable answer for developing new construction material. Not only would we eliminate a harmful waste but also preserve natural resources from overexploitation. This paper deals with the production and analysis of the properties of concretes employing recycled plastic (being high-density polyethene) aggregates in replacement of up to 75% of natural aggregates. The analysis of the concrete properties was undertaken in the fresh state and hardened state after 28 days of curing. The results revealed that the employment of a higher percentage of plastic particles in substitution for natural aggregates resulted in a decrease in the density of concrete as well as its thermal conductivity. The compressive strength of concretes also decreased; however, the toughness of the recycled plastic aggregates concretes increased with respet to that of conventional concrete.Postprint (published version

The assessment of ceramic and mixed recycled aggregates for high strength and low shrinkage concretes

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-018-1244-6Very few studies on recycled aggregate concretes (RC) have been extended to the use of recycled ceramic and mixed aggregates in relation with high strength concretes. In the main they concentrate only on the analysis of the physical and mechanical properties. This study deals with the investigation of the influence that different percentages (up to 30% substitution for natural aggregates) of high porous ceramic and mixed recycled aggregates have over the plastic, autogenous and drying shrinkage of the concretes. The physical and mechanical properties as well as the chloride resistance were also determine in order to assess the viability of the use of ceramic and mixed recycled aggregates in high strength concretes. The results revealed that the employment of highly porous recycled aggregates reduced the plastic and autogenous shrinkage values of the concrete with respect to those obtained by conventional concrete (CC). Although the total drying shrinkage of the recycled concrete proved to be 25% higher than that of the CC concrete, the CC concrete had in fact a higher shrinkage value than that of the RCfrom7 to 150 days of drying. It can be concluded that the RC concrete produced employing up to 30% of fine ceramic aggregates (FCA, with 12% of absorption capacity) achieved the lowest shrinkage values and higher mechanical and chloride ion resistance. In addition, the concrete produced with low percentage (10–15%) of recycledmixed aggregates also had similar properties to conventional concrete.Peer ReviewedPostprint (author's final draft