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Scarcity of fine natural aggregates suitable for concrete, the pollution caused by their mining and the great environmental impact produced by the final disposal of waste concrete, have all motivat...

The valorization of waste material for building applications has a long and successful history. Nowadays, byproducts such as fly ash, ground-granulated blast furnace slag (GGBFS), and silica fume are usual constituents of cement and concrete. These supplementary cementitious materials (SCMs) are recognized for enhancing certain properties of concrete, while also reducing its environmental impact. The huge amount of cement consumed globally demands additional sources of SCMs. A number of waste materials are prospective candidates, and reports on almost any type of waste being used in cementitious materials can be found in the present literature. The comprehensive study of their capabilities should comprise their ecological, economic, and engineering benefits. This chapter focuses on the effect of alternative SCMs from wastes on the transport properties of concrete. Transport properties are important for durability and performance in the service life of concrete structures. The most usually assessed transport properties are water transport (permeability, sorptivity, and absorption), gas permeability (oxygen and air), carbonation, ion transport (chloride penetration and lixiviation), and electrical resistivity. Although they are connected, there are specific features to observe for each case. The effect of SCMs on transport properties mainly depends on the chemical and physical modifications that they cause in the microstructure. Some properties are more affected by chemical changes, whereas others are more affected by physical changes. The analysis of transport properties in cementitious materials with waste used as SCMs allows developing the most convenient cementitious systems containing them. Alternative sources of SCMs are numerous; therefore a comprehensive analysis of all of them is rather difficult. This chapter offers a review of a limited number of types of waste that have been tested as SCMs in cement, mortar, and concrete. Byproducts that are already extensively used in the market (e.g., fly ash,GGBFS, limestone powder, and silica fume) are not included in this review. The selected materials are not necessarily the ones that demonstrate the most convenient technical or commercial features but the ones with which the authors have more experience. Some of the comments in this chapter are certainly applicable to other types of SCMs, so the content may still be valuable for readers interested in other types of SCMs not included in this section.

Recycled aggregate concrete is an eco-friendly material that is increasingly being used in new constructions. Nowadays, this application is mainly limited by user’s lack of confidence, as c...

The effect of recycled concrete aggregate (RCA) on concrete performance against external sulfate attack (ESA) is not yet fully known. In this paper, recycled aggregate concretes (RAC) with 0, 50, 75 and 100% of RCA contents were evaluated after 10 years of exposure immersed in 50g/l sodium sulfate solution. Sulfate ingress profiles were obtained by wet chemical analyses and FRX. Also, the mineralogy of the ingress profile was evaluated by thermogravimetric analyses. Finally, microcracking development in samples was evaluated by optical fluorescent microscopy image analysis. Although RAC showed a slight increase in sulfate ingress, due to its higher porosity (about 30% higher SO3 content near the surface for 50% or higher replacement ratio than control concrete), a dense new matrix still allows a good performance of RAC to external sulfate attack with even 100% RCA content. El efecto del árido reciclado de hormigón (AR) en el desempeño del hormigón frente al ataque externo por sulfatos (AES) no es aún del todo conocido. En este trabajo, se evaluaron hormigones con áridos reciclados (HAR) con 0, 50, 75 y 100% de AR, tras 10 años sumergidos en solución de sulfato de sodio 50g/l. Se obtuvieron perfiles de ingreso de sulfato mediante análisis químico vía húmeda y FRX. También se evaluó la mineralogía de los perfiles por termogravimetría y la microfisuración mediante microscopia óptica con fluorescencia. Aunque los HAR mostraron un leve incremento en el ingreso de sulfatos debido a su mayor porosidad (aproximadamente 30% más de SO3 en la superficie para reemplazos de 50% o mayores), una nueva matriz densa permite un aceptable desempeño del HAR frente al AES, aún con un 100% de AR. Fil: Santillan, Lautaro Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina Fil: Locati, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Villagrán Zaccardi, Yury Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina Fil: Zega, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina

The initial moisture condition of recycled concrete aggregates has a great influence on the fresh and hardened state of concrete. Water compensation is generally proposed with the aim of avoiding changes in the effective water-to-cement ratio and preventing water transfer from the mix to the porous aggregates. However, full compensation of water absorption of aggregates is not recommended. The issue remains unclear for recycled aggregates in general, and for fine recycled concrete aggregates (FRCA) in particular. Moreover, the water absorption of FRCA shows large variations depending on the determination method, making the value for the effective water-to-cement ratio even more uncertain. This paper entails a revision on the knowledge of the FRCA absorption kinetics and its consideration in mix proportioning. Own experimental results and data from the literature are analysed to show the relationship between the compressive strength of concrete and both the effective and total water-to-cement ratios. Compressive strength seems to be notably affected by how FRCA water absorption is taken into account in mix proportioning.

The performance of recycled aggregate concrete (RAC) under external sulphate attack (ESA) has not been fully clarified yet. The attached mortar on recycled aggregate particles increases the content of hydration products from Portland cement that are able to react with external sulphates. In addition, it increases the porosity of the resulting material, facilitating the penetration of ions. In this paper, we present experimental results focusing on the evaluation of the potential reactivity of recycled aggregates themselves. Weight and length variations of mortar bars made with fine recycled aggregates obtained from crushing concretes containing high and low C3A Portland cements were determined after exposure to sulphate solution at 38 °C. In addition, concrete cores with 25 and 75 mm in diameter exposed to sulphate solution at 20 °C were also evaluated. The results show no indication of significant reactivity of recycled aggregates with external sulphate.

The main feature of Self-Compacting Concrete (SCC) is its compactability under the action of its own weight, filling formworks and covering reinforcement without the need of applying external energy. Limestone filler is the most used supplementary cementitious materials for the production of SCC in the Buenos Aires Metropolitan Area, Argentina. Alternative sources for fillers can be found in residues from the exploitation of rocks. A good example is the quartzite mud resulting as a residue from the washing of manufactured sand in the Buenos Aires Province. The use of this waste would benefit the environment in reducing the demand for non-renewable natural resources and in adding value to the residue. In this paper, the performance in the fresh and hardened states of SCC made with 25, 50, 75, and 100% of the quartzite residue as a partial substitute of limestone filler is evaluated. Tests include spread, passing time, compressive strength, and capillary water absorption. Results show that the superplasticizer demand increases considerably with the content of the residue. Nevertheless, the properties of concrete in the fresh and hardened states show the feasibility of using the material to produce SCC.

Recycled concrete is still a material with some questionings about its true durable performance. Studies about recycled concretes exposed to external sulfate attack are very scarce. Generally, accelerated tests focused on the chemical attack are performed. However, studies on conventional concretes point out that structures deterioration by external sulfate attack is mainly due to the physical attack, and not merely by the chemical attack. Then, it is necessary to have results based on real exposure conditions, where transport mechanism and kinetics attack may be very different to that in accelerated test. In this paper, the performance of recycled concretes subjected to four recycling cycles and exposed to sulfate soil during eleven years is evaluated. Concretes were periodically assessed by visual inspection, weight variation and determination of dynamic modulus of elasticity. The results show that recycled concretes presented a satisfactory performance after eleven years of exposure, even better than pattern conventional concrete.

A petrographic method is proposed to semi-quantify the content of particles with reactive phases in fine recycled concrete aggregates (FRCA) affected by the alkali-silica reaction and the residual mortar (RM) adhered to them. This method is compared to the image analysis method. Quartered FRCA samples are studied by three petrographers, and the results are compared. Finally, the potential reactivity of the samples is evaluated by the accelerated mortar bar test (AMBT). According to the AMBT and petrographic method, the samples are qualified as potentially reactive, with a low degree of reactivity. The method is easy to perform and fast (compared to image analysis), but the results obtained by three petrographers show some differences that can mainly be attributed to the visual estimation of RM. Although more studies are needed to verify the effectiveness of the proposed method, the implemented technique shows great potential to semi-quantify reactive components in FRCA particles.

The high absorption of fine recycled aggregates is indicated as the main difference with respect to fine natural aggregates. This property determines the extra amount of water to be added during mixing to avoid a loss in workability when these aggregates are used for making concrete. Although several methods have been proposed for its determination, none of them has been standardized or has achieved full consensus. In this paper, a method for the determination of absorption based on electrical conductivity is applied. The results from this method and other particular methods proposed in the literature for this type of aggregate are analyzed and compared regarding their representativeness. The outcomes of this study show the suitability of the conductivity method for the effective determination of water absorption of fine recycled concrete aggregate, with relatively low variation and incidence of the operator. Fil: Sosa, M. E.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina Fil: Carrizo, Leandro Ezequiel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina Fil: Zega, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina Fil: Villagrán Zaccardi, Yury Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina

For the development of an intermediate radioactive waste repository, two different types of reinforced concrete were analyzed in terms of durability: one made with ordinary portland cement and the other one made with pozzolanic cement. The values for compressive strength, sorptivity and air permeability demonstrate that the formulations are compatible with the required application. The corrosion rate of rebar up to about 300 days of monitoring and obtained with sensors is below the threshold value required for this type of facilities, except when temperatures are high. The value for the same parameter monitored by the galvanostatic pulse technique using superficial counter electrode and guard electrode is always lower than the threshold value. Additionally, when applying the galvanostatic pulse technique using embedded electrodes, this parameter is comparable to the guard electrode method only when the polarization resistance is calculated through non-linear fitting.

Using waste materials for new products is a global trend undergoing rapid development. Recycling materials allows for a more efficient life cycle and contributes to environmental protection. In the construction field, this trend has gained importance because of the shortage of natural resources and because of environmental problems caused by storing building-demolition wastes. This situation has led to the search for new applications for these wastes, and their use as aggregates in concrete is an interesting alternative. In this paper, some characteristics of recycled coarse aggregates obtained by crushing waste ready-mix concrete, as well as the mechanical and durability properties of recycled concretes made by using 25, 50, and 75% of these aggregates, are presented. Recycled concretes show lower compressive strength than conventional concrete for the higher strength level, whereas the durability properties of the two are similar. Fil: Zega, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata; Argentina Fil: Di Maio, Angel Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata; Argentina

The recycled aggregates obtained from crushed waste concretes have different characteristics from those of natural aggregates. For that reason, the mixture proportions and the fresh and hardened properties of recycled concretes are different. The performance of recycled concrete exposed to high temperatures is not a very well-known subject since most studies have been conducted on conventional concretes. Recycled concretes with water/cement (w/c) ratios of 0.40 and 0.70, and made with three different types of natural coarse aggregate were exposed to 500 °C for 1 h. These concretes were evaluated by the ultrasonic method, resonance frequency, static modulus of elasticity and compressive strength, before and after heating, and compared with those obtained on similar conventional concretes containing the same type of natural coarse aggregate. The conventional and recycled concretes made with quartzitic coarse aggregate performed better after the heat treatment.

Many environmental problems caused by the large volumes of construction and demolition waste (C&DW), the lack of adequate deposition sites and the shortage of natural resources have led to the use of C&DW as replacement of natural aggregates in the production of new concrete. As in the case of natural aggregates, when recycled aggregates are used to manufacture structural concrete, the assessment of their physical, mechanical and durable characteristics is a key issue. The different physical and mechanical properties of the recycled coarse aggregate (RCA) are evaluated. RCA was obtained by crushing conventional concretes with different strength levels (different w/c ratios) containing four different types of natural coarse aggregates (three crushed stones and a siliceous gravel), which differ in shape, composition and surface texture. There is a significant influence of the natural coarse aggregate (NCA) on the properties of RCA, which in many cases is greater than that of the w/c ratio of the source concrete.

Recycled concrete use is necessary in order to decrease the environmental impact of the construction industry. Coarse aggregates from crushed concrete may lead to relatively high porosity in the resultant concrete. For this reason, recycled concrete may seem detrimental to the durability of reinforced concrete structures, particularly when they are exposed to marine environments. The objective of this paper is to analyze the influence of coarse aggregates from concrete on the chloride penetration rate and binding capacity of concrete under marine exposure. Concrete specimens were molded and exposed to a natural marine atmosphere. After exposure periods of 6, 12, and 18 months, ingress profiles of total and water soluble chlorides were measured. Results indicate that recycled aggregate incorporation causes two opposed effects on concrete: It increases its chloride penetration rate and chloride binding capacity. Therefore, water soluble chloride contents in conventional and recycled concrete series have similar values.

Recycled aggregate concretes, particularly those made with crushed concrete in replacement of the natural coarse aggregate, have been increasingly used in the last decades. Although compressive strength is not affected by the replacement of conventional coarse aggregates by recycled coarse aggregates (RCA), there is still some disagreement regarding their durable performance, particularly when they are exposed to severe conditions. This study evaluates the performance of recycled concretes made with different RCA contents (25%, 50%, 75% and 100%) exposed to sulphate soil for more than 10 years. Concretes designed with and without provisions for durability to sulphate attack were exposed. The specimens were half buried in sulphate soil and their condition was periodically assessed by visual inspection, weight loss and dynamic modulus of elasticity. Additionally, the extent of the attack on mortar-coarse aggregates interfaces was studied by stereomicroscopy and optical microscopy. Results to date indicate similar performances for recycled aggregate concretes and natural aggregate concretes with the same compressive strength level, even for a 100% RCA content. Fil: Zega, Claudio Javier. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Coelho Dos Santos, Gabriela Soledad. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Villagrán Zaccardi, Yury Andrés. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Di Maio, Angel Antonio. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Concrete exposure to high temperatures produces changes in its internal structure, for instance loss of its strength and deformation capacity, in extreme cases risking the service life of the structure. The damage level will depend on the temperature reached, exposure time, cooling velocity and type, size of the structural element and the material's own characteristics. In this paper results of conventional concretes (CC) made with a natural coarse aggregate and different water/cement (w/c) ratios exposed to high temperature are compared with those obtained with recycled concretes (RCs) of similar characteristics produced by employing 75% by volume of recycled coarse aggregate (crushed waste concretes). The concretes were evaluated by ultrasound and resonance frequency, and further determination of the static modulus of elasticity and compressive strength was possible. In all cases the parameters evaluated in concretes exposed to high temperatures are lower than in others with the same characteristics and without any type of processing. For exposure to 500°C for 1 h, the RC with a low w/c ratio performs better than the CC.

The use of recycled concrete represents a friendly environmental solution for minimizing the impact of construction and demolition wastes. In many countries, the incorporation of recycled coarse aggregates (RCA) is a common practice, the maximum contents of RCA being usually limited to around 25% of the total coarse aggregate content. The incorporation of higher volumes of RCA is a field of discussion mainly regarding the durable behaviour of concrete. This paper analyses different transport properties of 20 to 50 MPa compressive strength concretes prepared with variable contents of RCA (0%, 25%, and 75%). Eight types of RCA were obtained from concretes incorporating four different natural coarse aggregates: granitic, basaltic, and quartzitic crushed stones and siliceous river gravel. Capillary absorption, water penetration and chloride diffusion tests were done. The variation of transport properties with concrete compressive strength and the effect of RCA content on the variability of transport properties were analysed. According to the results obtained, the durable behaviour of recycled concretes will be different according to the transport mechanisms to which they are exposed and it can be as good as that of concretes made with natural coarse aggregates. Fil: Zega, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Área Tecnología del Hormigón; Argentina Fil: Di Maio, Angel Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Área Tecnología del Hormigón; Argentina Fil: Zerbino, Raul Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería. Departamento de Construcciones; Argentina

Using waste materials as aggregate for new concrete production is a growing tendency, because of several environmental problems. Recycled coarse aggregate (RCA) obtained from crushing waste concrete has lower density and greater absorption than natural aggregate, because of the higher porosity of the mortar attached to the RCA particles. Compressive strength level achieved in recycled concrete may be similar to that of conventional concrete. On the other hand, durable performance of recycled concrete is variable, and diverse evidence can be found in literature for different durability issues. In this paper, chloride ingress in conventional and recycled concrete, made with quartzite aggregate and blended Portland cement is evaluated when immersed in NaCl solution. Two strength levels (21 and 35 MPa) and two contents of RCA (25 and 75%), as substitute of natural quartzite aggregate, were considered. The chloride diffusion coefficient and the relationship between water-soluble chloride and bound chloride are analyzed.

Natural pozzolans are supplementary cementitious materials (SCMs) that may be used to improve the properties of mortar and concrete, through the formation of additional hydration products by pozzolanic action. Water reducers (WR) play a main role in high performance concrete in terms of durability, strength and surface finishing. A first optimization of constituent proportions in paste and/or mortar is convenient to assess the compatibility between the WR and the cementitious materials. The compatibility between cement and WR may be affected by SCMs, as they can also interact with the molecules of the admixture. However, the practical implication may be variable. This paper deals with the influence of different types and dosages of WRs in mortars made with pozzolanic Portland cement. Both medium and high ranges WRs have been used. Mortar fluidity has been tested by the spread and the slump tests. Results show different fluidizing capacities of WRs, among which polycarboxylate-based WR was the most compatible with the pozzolanic cement.

The use of construction waste materials as aggregates for concrete production is highly attractive compared to the use of non-renewable natural resources, promoting environmental protection and allowing the development of a new raw material. Several countries have recommendations for the use of recycled coarse aggregate in structural concrete, whereas the use of the fine fraction is limited because it may produce significant changes in some properties of concrete. However, during the last decade the use of recycled fine aggregates (RFA) has achieved a great international interest, mainly because of economic implications related to the shortage of natural sands suitable for the production of concrete, besides to allow an integral use of this type of waste. In this study, the durable behaviour of structural concretes made with different percentage of RFA (0%, 20%, and 30%) is evaluated. Different properties related to the durability of concretes such as absorption, sorptivity, water penetration under pressure, and carbonation are determined. In addition, the results of compressive strength, static modulus of elasticity and drying shrinkage are presented. The obtained results indicate that the recycled concretes have a suitable resistant and durable behaviour, according to the limits indicated by different international codes for structural concrete. Fil: Zega, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Di Maio, Angel Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

El reciclado de los residuos de construcción y demolición para ser empleados en la producción de hormigones, principalmente aquellos que provienen de la trituración de hormigones de desecho, se ha convertido en una alternativa de gran importancia respecto a la disminución de la contaminación ambiental, permitiendo además una reducción en la explotación de recursos naturales no renovales. Las propiedades que presentan los agregados reciclados se ven modificadas con relación a las que poseen los agregados naturales de densidad normal, principalmente su porosidad, densidad y resistencia. Estas diferencias son atribuidas al mortero de cemento que se encuentra adherido a las partículas de agregado natural, o bien constituyendo una partícula por sí mismo. Respecto al comportamiento resistente, los hormigones reciclados pueden presentar resistencias similares a las del hormigón de origen, dependiendo de la calidad y porcentaje de agregado reciclado utilizado. Sin embargo, el desempeño durable que presentan los hormigones reciclados podrá variar en función de las características de los hormigones, del porcentaje de agregado reciclado utilizado y de las condiciones a las cuales son expuestos. El objetivo principal del presente trabajo de Tesis consiste en determinar la influencia que tiene el nivel de resistencia y el tipo de agregado grueso natural (AGN) del hormigón de origen sobre las propiedades de los agregados gruesos reciclados (AGR). A tal fin, se elaboraron hormigones de razones a/c 0,45 y 0,65 empleando AGN de uso habitual en diferentes regiones del país, tales como piedra partida granítica, cuarcítica y basáltica, y canto rodado silíceo. Los AGR se obtuvieron de la trituración de dichos hormigones, analizándose diferentes propiedades físico‐mecánicas de los mismos, como granulometría, densidad, absorción, desgaste ʺLos Ángelesʺ, pasa tamiz de 75 μm, peso por unidad de volumen, porcentaje de vacíos, índices de lajosidad y elongación, y contenido de mortero, comparativamente con las correspondientes a los AGN. El comportamiento mecánico de los hormigones elaborados con 25 y 75 % de AGR se compara con el de los hormigones con 100 % de AGN. Para ello se realizaron evaluaciones de las resistencias a compresión, tracción por compresión diametral y módulo de rotura en flexión, determinándose también el módulo de elasticidad estático. Además, se realizaron valoraciones con ensayos semi‐destructivos (Break‐Off) y no destructivos (ultrasonido y frecuencia de resonancia) a fin de determinar las posibles modificaciones que pueden producirse debido a las características que poseen los AGR. Con el fin de adquirir un mayor conocimiento sobre la durabilidad de los hormigones reciclados, se analizan distintas propiedades de transporte comparándolas con las de hormigones de igual nivel resistente elaborados con agregados naturales. Se realizaron determinaciones de absorción de agua por inmersión, succión capilar, penetración de agua a presión y difusión de cloruro en inmersión. Además, se presentan los resultados obtenidos en experiencias de campo sobre hormigones expuestos en suelo con sulfato. De los resultados obtenidos surge que el tipo de AGN del hormigón de origen puede tener mayor influencia que la razón a/c sobre algunas propiedades de los AGR, como la densidad, la absorción de agua, la resistencia a la abrasión y el contenido de mortero. En cuanto a la resistencia a compresión, en los hormigones con 75 % de AGR se alcanzaron los mismos niveles resistentes que en los hormigones originales, mientras que en los elaborados con 25 % de AGR la resistencia se incrementó en aproximadamente 15 %. Con relación al comportamiento durable, en los hormigones con 75 % de AGR de granito y basalto los parámetros de transporte por capilaridad y permeabilidad duplican a los determinados en los hormigones originales, mientras que en los elaborados con 25 % de AGR de canto rodado se produce una disminución del orden del 25 %. Respecto a la difusión de cloruro, los hormigones con AGR de cuarcita y canto rodado muestran una mayor capacidad de retención de cloruro con relación a los hormigones originales, la cual se incrementa con el contenido de AGR. En base a los resultados obtenidos surge que, al igual que lo que sucede en los hormigones convencionales, la razón a/c es el principal factor que condiciona el desempeño durable de los hormigones reciclados, debiéndose considerar en segundo término el tipo de AGN empleado. Al incrementarse la razón a/c, el tipo y porcentaje de AGR utilizado se constituye en un factor de mayor importancia., Facultad de Ingeniería

Air entrainment is a good practice to improve the durability of concrete exposed to cycles of freezing and thawing. For a given admixture dosage, the air content will depend on mix proportions and the characteristics of the materials employed. The use of crushed waste concretes (recycled coarse aggregates), which have different characteristics and properties compared to natural coarse aggregates, could modify the air content and behavior of recycled concretes. In this paper, some fresh and hardened state properties of entrained air recycled concretes were evaluated and compared with those of entrained air conventional concrete. Recycled concretes were elaborated with 50, 75, and 100% replacement by volume of natural coarse aggregates by crushed waste concretes. The results indicate that the recycled concretes show a satisfactory mechanical and durable behavior, similar to or better than that of conventional one.