Microstructural analysis of siderurgical aggregate concrete reinforced with fibers

The development of cracks in concrete structures is one of the significant issues with maintaining high strength after hardening. One way to prevent and control this problem is to use fibers. This paper investigates concrete containing electric arc furnace slag aggregates reinforced with fibers. The fibers used in this study are steel fibers and three kinds of polypropylene fibers; polyolefin fibers (modified polypropylene), polypropylene homopolymer, and high-toughness polypropylene. By checking the compressive and flexural strength of concretes made with fibers, it can be seen that the best results at 28 days are found for concrete with steel fibers, namely 62 MPa with 0.9% of fibers. On the contrary, the lowest values are for concrete containing polyolefin fibers, 51 MPa, and the same percentage of fibers. Additionally, under flexural strength testing, at the age of 28 days, the strength of these samples with 0.9% of fibers was 9.54 MPa, a value that is comparable to test concrete with the same percentage of steel fibers, 10.67 MPa, despite the low workability of concrete containing polyolefin fibers with a slump of 25 mm. Moreover, the boundary transition area analysis shows that the excellent connection between the fibers and cement paste near the siderurgical aggregate has caused no cracks in this area. In contrast, cracks can be observed in critical areas near the natural aggregates

ITZ microanalysis of cement-based building materials with incorporation of siderurgical aggregates

With the depletion of natural resources, it is essential to use recycled materials and industrial wastes to adapt the expanding building sector to the environment. Slag from electric arc furnaces is one example that can be used as a siderurgical aggregate in concrete production. Studying the interfacial transition zone between the aggregate and the binder is necessary because the reaction between the aggregate and the binder can significantly impact the concrete's microstructure and mechanical properties. In order to examine any concrete sample with any physical or chemical structure, this study introduces the instruments used to conduct these studies and the methods for preparing concrete samples for the desired area. The results show that solvent exchange with Ethanol is the best method for draining water from the inner surface of the sample in the interfacial transition zone (ITZ) with minimal destruction. Also, the kind of sample and its information determine the type of coating that should be applied. Gold is the best choice to examine the topography of the sample surface because it has a higher electron return coefficient than other elements and produces images of higher quality. The epoxy with a viscosity of 550 cP (20 °C) or 150 cP (50 °C), a maximum curing temperature of 50 °C, a curing time of 8 h, and an epoxy-to-hardener ratio of 25 to 3 g is the best configuration for having the best sample for microanalysis

Macro- and micro- properties of multi-recycled aggregate concrete

ABSTRACT: In a future scenario in which all the concrete is recycled concrete, it will be necessary to recycle the recycled concrete. However, it is known that the recycling of concrete implies a loss of properties. This paper shows an innovative technique, the computerized microtomograph, used to evaluate closed porosity, volume of limestone aggregate fraction and volume of mortar of the multi-recycled aggregate concrete, in order to answer the question: how many times it is possible to recycle concrete? First, the source concrete mix using limestone coarse and fine aggregates was characterized. This mix was crushed to obtain a recycled aggregate that was used to manufacture the 1st generation or current recycled aggregate concrete. After the characterization of this 1st generation concrete, and in the same way, a 2nd and a 3rd generation concrete were obtained and characterized, using recycled aggregates from the 1st and 2nd concrete generations respectively. The evaluation by computerized axial tomography allows to know how the successive recycled affect the properties of the concrete. The results show that it is possible to observe the distribution and quantify the aggregate, cement paste and closed porosity contents of the recycled aggregate concrete showing that 3rd generation recycled concrete shows almost twice as much mortar as 1st generation one and demonstrates that it is only possible to recycle the concrete a finite number of times

Influence of curing conditions on recycled aggregate concrete

This paper presents the results of a study of permeability and its influence on the durability of recycled concrete exposed to an aggressive environment. Recycled concretes with 20%, 50% and 100% in weight ofrecycled aggregate and 24 effective w/c ratios have been exposed directly to a marine environment. Control specimens cured in a humidity chamber have been also tested in order to compare the influence of the curing environment. The durability of recycled aggregate concretes exposed to aggressive conditions decreases in terms of permeability, as the results show. However, the influence of the environment on the recycled concrete also depends on the quality of the cement paste. The differences between the control and the exposed concrete are lower for low water/cement (w/c) ratios. The lower capillarity obtained in the new cement paste of the recycled concretes with low w/c ratios isolates the porosity of the recycled aggregate, increasing the durability but with a rise in the cement content.The authors wish to thank the Spanish Ministry of the Environment for the funding of this research. The results contained herein have been achieved under the RECNHOR Project (funded by the Spanish Ministry of Environment) and under the CLEAM Project (funded by the Spanish Centre for Industrial Technology Development, CDTI), Code 3.2-358/200 5/3-B, led by the Economic InterestGrouping CLEAM-CENIT, AIE (Acciona, Dragados, Ferrovial, FCC,Sioux, OHL and Sacyr) and SMEs Informatica 68, Quilosa and Martinez Segovia and associates

Industrial Low-Clinker Precast Elements Using Recycled Aggregates

ABSTRACT: ncreasing amounts of sustainable concretes are being used as society becomes more aware of the environment. This paper attempts to evaluate the properties of precast concrete elements formed with recycled coarse aggregate and low clinker content cement using recycled additions. To this end, six different mix proportions were characterized: a reference concrete; 2 concretes with 25%wt. and 50%wt. substitution of coarse aggregate made using mixed construction and demolition wastes; and others with recycled cement with low clinker content. The compressive strength, the elastic modulus, and the durability indicator decrease with the proportions of recycled aggregate replacing aggregate, and it is accentuated with the incorporation of recycled cement. However, all the precast elements tested show good performance with slight reduction in the mechanical properties. To confirm the appropriate behaviour of New Jersey precast barriers, a test that simulated the impact of a vehicle was carried out.This research was funded by SODERCAN, S.A. (SODERCAN/FEDER) and BIA2013-48876-C3-2-R awarded by the Ministry of Science and Innovation

Multiple recycled aggregate properties analysed by X-ray microtomography

This paper presents a novel technique used to analyse the volume of adhered mortar to the recycled aggregate. A computerized microtomograph (?CT) device was used to evaluate the volume of the aggregate, the volume of natural aggregate and the volume of adhered mortar. To this end, a natural aggregate has been characterized, using the ?CT, with which a source concrete has been produced. Subsequently, the source concrete has been crushed to obtain a first cycle recycled aggregate. After the characterization of the first-generation of recycled aggregate, a new source concrete has been made with it to be subsequently crushed again obtaining a second-generation recycled aggregates. In the same way a third-generation recycled aggregate has been obtained and has been equally characterized. The results show that the compaction capacity of the aggregate is reduced after successive recycling. It has been possible to quantify how much the closed porosity of the recycled aggregate decreases with the number of times it is recycled. The loss of natural aggregate and increase of the volume of adhered mortar have also been evaluated using this technique.The Erasmus+Program, founded by the Staff Mobility for Teaching Program of the European Council 2016/217, between Instituto Superior Técnico - University of Lisbon and the LADICIM - University of Cantabria. CERIS and the Foundation for Science and Technology (FCT) for funding this research

Permeabilidad de hormigón reciclado estructural

En este trabajo se presentan los principales resultados obtenidos de una serie de investigaciones encaminadas a analizar las propiedades de durabilidad del hormigón estructural incorporando áridos reciclados de hormigón. Uno de los aspectos más desconocidos de los hormigones reciclados está relacionado con su durabilidad. La mayoría de los resultados encontrados en la literatura no son comparables entre sí debido a la heterogeneidad de los áridos reciclados, distintas relaciones agua/cemento, los tipos de cemento utilizados, etc. En esta investigación, se han comparado las características de 24 distintas dosificaciones de hormigón con sustitución parcial y total de árido reciclado. Se han analizado las propiedades físicas y mecánicas y la permeabilidad al agua y al oxígeno como indicadores de la durabilidad. La durabilidad de los hormigones fabricados con árido reciclado es menor a la de los hormigones de control debido a la alta porosidad que el árido reciclado introduce en el hormigón y que puede ser el origen de ciertos daños en la estructura. Estas pérdidas de durabilidad disminuyen para bajas relaciones agua/cemento. Sin embargo, tras el análisis mecánico se observa que la influencia del árido reciclado es menor para las altas relaciones agua/cemento

Study of Hillock and Zinc Whisker Evolution in Five Different Cable Tray Coatings

ABSTRACT: The main objective of this work is the study of the hillock and zinc whisker evolution of five different commercial zinc coatings applied on the same base steel wires of the patented EASYCONNECT system cable trays manufactured by VALDINOX Ltd.: white zinc alkaline electrolyte, yellow zinc trivalent electrolyte, acid zinc electrolyte, hot dip galvanized, and zinc nickel coating. The limited literature on the subject is summarized, and then the coating thickness, chemical composition, hardness and surface rugosity are characterized. The hillock and whisker density evolution are evaluated over a period of 12 months, considering the presence of compression bending stresses. It is concluded that the white alkaline and yellow trivalent coatings are the most affected, while the zinc-nickel shows the best behavior with no presence of whiskers; the acid zinc electrolyte also shows good results despite the delayed appearance of whiskers from the ninth month; the hot-dip galvanized coating does not show any presence of zinc whiskers or hillocks

Physical-Mechanical Properties of Cupola Slag Cement Paste

ABSTRACT: The high consumption of natural resources in the industrial sector makes it necessary to implement measures that enable the reuse of the waste generated, seeking to achieve circular economy. This work assesses the viability of an alternative to the use of CEM III B 32.5 R cement in mortars for the internal coating of centrifugally spun cast iron pipes for water piping. The proposal is to reuse the slag generated in the casting process after being finely ground, as an addition mixed with CEM I 52.5 R cement, which is basically Portland clinker. In order to analyse this possibility, an extensive experimental campaign was carried out, including the analysis of the cupola slag (micro-structural and chemical composition, leachates, setting time, vitrification, puzzolanicity and resistance to sulphate) and regarding the mortars (workability and mechanical properties). The experimental programme has shown that the optimum substitution is achieved with a replacement percentage of 20% of the cement, with which similar workability, superior mechanical properties and guaranteed resistance to sulphate attack are obtained. In addition, both economic and environmental savings are achieved by not having to transport or landfill the waste. In addition, the new cement is cheaper than the cement currently used

Viability of Cupola Slag as an Alternative Eco-Binder and Filler in Concrete and Mortars

ABSTRACT: Obtaining new materials capable of meeting society?s demands motivates the search for new solutions that are capable of satisfying twofold requirements: respect for the environment and obtaining more durable and resistant materials. Cupola slag is a by-product generated in the process of obtaining ductile iron. When the slag undergoes rapid cooling, its vitrification is favored, leaving the silica in an amorphous structure and, thus, susceptible to reacting. Through reaction, the slag can develop cementing properties and cement can consequently be partially replaced with residue, providing savings in economic and environmental costs compared to traditional hydraulic binders. In this study, the physical and chemical properties of cupola slag and its recovery process are analyzed. Mortars that incorporate traditional admixtures (fly ash and limestone filler) have been manufactured and consistency and mechanical properties have been compared with mortars that incorporate cupola slag admixture. Mortars have also been manufactured with normalized sand and with Portland cement replacements (0, 10, 20, and 30% by weight) with cupola slag, and both the consistency and the mechanical properties have been compared at 7, 28, 60, and 90 days. The results obtained show the suitability of cupola slag as a binder and as an admixture, with respect to the traditional ones, and how the mechanical properties tend to converge for all of the replacement levels characterized, for ages close to 90 days of age