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

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

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

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

Estudio de la aplicación del árido reciclado mixto en hormigón poroso y como relleno de zanjas en la ciudad de Barcelona

En este artículo se presentan dos pruebas piloto llevadas a cabo como iniciativas innovadoras en la reutilización de RCD en la ciudad de Barcelona. Por un lado se estudió el uso de árido reciclado mixto (ARM) en la fabricación de hormigón poroso como base de una pavimentación drenante. Una vez caracterizado el hormigón a nivel de laboratorio, se llevó a cabo la prueba piloto. A nivel probeta se determinó la densidad, resistencia a compresión y la permeabilidad asi como los componentes lixiviados. La permeabilidad también se determinó in situ. Por otro lado, el material de escombro de zanjas se analizó para utilizarlo como material reciclado de relleno de zanjas. El material fue validado de acuerdo a los ensayos del PG3 de Proctor Modificado, CBR, Límite líquido, límite plástico e índice de plasticidad. De acuerdo a los resultados obtenidos, los ARM fueron validados para los casos de estudio llevados a cabo. This study details two pilot tests carried out within the city of Barcelona, concerning the reuse of CDW in innovative initiatives. The first case study deals with the use of mixed recycled aggregate (MRA) in the production of a pervious concrete to be employed as a draining base for paving. Once the pervious concrete had been characterized within the laboratory, a pilot test was carried out and the concrete’s properties of density, compressive strength, permeability and leached components were determined by test specimens. Permeability was also tested on-site. The second case study deals with an analysis of the debris material obtained from trenches in order to determine its suitability as recycled material for trenches backfilling. The material was validated in accordance to PG3 requirements of modified proctor, CBR, liquid limit, plastic limit and plasticity index. In accordance with the obtained results, the MRA were validated for defined case studies.Peer ReviewedPostprint (published version

Application of low grade recycled aggregates for non-structural concrete production in the city of Barcelona

In this research work the applicability of low grade recycled coarse aggregates (RA) on nonstructural concrete production was evaluated. Two types of RA were used, produced by recycling plants located in Barcelona. The properties of RA and limestone aggregates were determined. Conventional concrete as well as concretes made with 50% and 100% of RA were produced. Three types of cements, CEM II/A-L 42,5 N, CEM I 52,5 R and CEM I 42,5 N-SR were used in each type of concrete production. The physical, mechanical and durability (sorptivity and resistance to sulfate attack) properties of all the concretes were determined. According to the results, the concretes produced with 100% of RA obtained the lowest quality properties when cement with limestone additions was used. CEM I cement would be adequate using as maximum 50% of RA for concrete production. Finally, a pilot test was conducted to verify the large scale behavior.Postprint (published version

Influence of seawater and blast furnace cement employment on recycled aggregate concretes’ properties

Recycled aggregates of mixed composition (MRA) may exhibit great variability in their properties, which in turn reduces their applicability. This study intends to extend the use of MRA in a broadened scope of applications by producing recycled aggregate concretes (RAC), which were mixed using two different types of cement, ordinary Portland cement and cement incorporating blast-furnace slag, and two types of water, fresh and seawater. The testing programme included analyses of the properties of concrete in its fresh (setting time and plastic shrinkage) and hardened state (physical, mechanical and drying shrinkage). The results showed that all of the physical and several of the mechanical properties as well as drying shrinkage were negatively influenced by the use of MRA. In contrast, however, the plastic shrinkage and flexural strength were improved. The use of seawater improved the mechanical properties, reduced setting time and increased drying shrinkage, however, it was found that the cement type was more influential on most of the properties. The use of seawater and cement with blast-furnace slag improved the performances of the RAC.Peer ReviewedPostprint (author's final draft

Effects of using recycled concrete aggregates on the shrinkage of high performance concrete

Over the past twenty years the use of Recycled Concrete Aggregate (RCA) has been mostly limited to normal-strength concretes. However, satisfactory properties have been found in previous studies dealing with the use of RCA sourced from medium to high strength concrete in the production of High Performance Concrete (HPC). In this study the effects of RCA were investigated in the plastic, autogenous and drying shrinkage of HPC. The quality of the RCA (sourced from concretes of 100, 60 and 40 MPa) and the replacement ratio (20, 50 and 100%) were assessed. The results revealed that the plastic and drying shrinkage became higher as the quality of the RCA decreased and the replacement ratio increased. However, a reduction in the autogenous shrinkage was proved to be possible by the employment of a higher content of lower quality RCA, as this, in fact, acted as internal curing agent. The effects of the internal curing explained the similar or higher compressive strength results of concretes containing RCA when compared to those obtained from the reference concrete.Peer ReviewedPostprint (author's final draft

Influence of steam curing on the pore structures and mechanical properties of fly-ash high performance concrete prepared with recycled aggregates

In this research work, High Performance Concrete (HPC) was produced employing 30% of fly ash and 70% of Portland cement as binder materials. Three types of coarse recycled concrete aggregates (RCA) sourced from medium to high strength concretes were employed as 100% replacement of natural aggregates for recycled aggregate concrete (RAC) production. The specimens of four types of concretes (natural aggregate concrete (NAC) and three RACs) were subjected to initial steam curing besides the conventional curing process. The use of high quality RCA (>100 MPa) in HPC produced RAC with similar or improved pore structures, compressive and splitting tensile strengths, and modulus of elasticity to those of NAC. It was determined that the mechanical and physical behaviour of HPC decreased with the reduction of RCA quality. Nonetheless steam-cured RACs had greater reductions of porosity up to 90 days than NAC, which led to lower capillary pore volume.Peer ReviewedPostprint (published version