Effect of Micro-Silica Addition into Electric Arc Furnace Steel Slag Eco-Efficient Concrete

ABSTRACT: Concrete produced from electric arc furnace steel slag aggregates is one of the items that is highly regarded due to its strength, environmental friendliness and cost-effectiveness. Despite the growing interest in using this type of concrete, there are still doubts about the mix proportions and addition effects of electric arc furnace steel slags. In this paper, the performance of replacing natural aggregates by electric arc furnace steel slags aggregate is comprehensively investigated and its effect on mechanical properties is analysed. The relationship between the percentage of replacement of natural aggregate using electric arc furnace steel slags aggregate in two parts of coarse aggregate and fine-grained aggregate and the effect of each of these parts on mechanical properties in concrete is investigated, which may identify the optimal mix proportions of each aggregate that help to improve the strength of the eco efficient concrete using electric arc furnace steel slags

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

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

Siderurgical aggregate cement-treated bases and concrete using foundry sand

ABSTRACT: Cement-treated bases are soils, gravels or manufactured aggregates mixed with certain quantities of cement and water in order to improve the characteristics of a base or sub-base layer. Due to the exploitation of natural aggregates, it is a matter of importance to avoid shortage of natural resources, which is why the use of recycled aggregates is a practical solution. In this paper we studied the feasibility of the use of untreated electric arc furnace slags and foundry sand in the development of cement-treated bases and slag aggregate concrete with a lower quantity of cement. We analyzed the physical, mechanical and durability characteristics of the aggregates, followed by the design of mixes to fabricate test specimens. With cement-treated bases, results showed an optimal moisture content of 5% and a dry density of 2.47 g/cm3. Cement-treated bases made with untreated slag aggregate, foundry sand and 4% of cement content showed an unconfined compression strength at seven days of 3.73 MPa. For siderurgical aggregate concrete mixes, compressive strength, modulus of elasticity and flexural strength tests were made. The results showed that the mixes had good mechanical properties but durability properties could be an issue

Influence of Partial and Total Replacement of Used Foundry Sand in Self-Compacting Concrete

ABSTRACT: In this work, the feasibility of partially and totally replacing natural sand with used foundry sand in self-compacting concrete was studied. Natural sand was replaced in 50% and 100% vol. by used foundry sand. The fresh state properties parameters analyzed in this study were slump flow, t500, V-funnel, Japanese ring and L-box following EFNARC guidelines. Results indicated an improvement in the fresh state properties when used foundry sand was utilized for partial and total replacement. The mechanical properties compressive strength and splitting tensile strength were obtained and analyzed at 7 and 28 days. Regarding the compressive strength, used foundry sand enhanced compressive strength by up to 67% compared to control concrete. For splitting tensile strength, the self-compacting concrete with 50% vol. of used foundry sand displayed a slight decrease (2.8%) compared with the control concrete. SEM images showed that the concretes with used foundry sand had a less porous and more compacted matrix than the control concrete. It was concluded that the incorporation of used foundry sand in large volumes can be utilized as a sustainable alternative natural fine aggregate

Recycled polyethylene fibres for structural concrete

Modern society demands more sustainable and economical construction elements. One of the available options for manufacturing this type of element is the valorisation of end-of-life waste, such as, for example, the recycling of polymers used in industry. The valorisation of these wastes reduces costs and avoids the pollution generated by their landfill disposal. With the aim of helping to obtain this type of material, this work describes a methodology for recycling polyethylene for the manufacture of fibres that will later be used as reinforcement for structural concrete. These fibres are manufactured using an injection moulding machine. Subsequently, their physical and mechanical properties are measured and compared with those of the material before it is crushed and injected. The aim of this comparison is to evaluate the recycling process and analyse the reduction of the physical-mechanical properties of the recycled polyethylene in the process. Finally, to determine the properties of the fibre concrete, three types of concrete were produced: a control concrete, a reinforced concrete with 2 kg/m³ of fibres, and a reinforced concrete with 4 kg/m³ of fibres. The results show an enhancement of mechanical properties when the fibres are incorporated, particularly the tensile strength; and they also show excellent performance controlling cracking in concrete.This research was funded by the LADICIM (Laboratory of Materials Science and Engineering), Universidad de Cantabria. E.T.S. de Ingenieros de Caminos, Canales y Puertos, Av./Los Castros 44, 39005 Santander, Spain

Micro- and macro -effects of additions and reinforcements on siderurgical aggregate concrete

Este estudio investiga el comportamiento del árido siderúrgico en el hormigón y su interacción con otros componentes. Explora la posibilidad de reemplazar el árido siderúrgico con árido natural, los efectos de los aditivos, las fibras y el efecto de las fibras cerca del árido siderúrgico. Se realizó un completo análisis con microscopio electrónico de barrido para estudiar la interacción entre la pasta de cemento y el árido siderúrgico. Los resultados muestran que las fibras en el hormigón siderúrgico restringen el agua y la permeabilidad, minimizan la formación de fracturas y mejoran la resistencia a la formación de grietas. Un mayor conteo de fibras reduce las fracturas y aumenta las resistencias a la compresión y flexión, complementando y contribuyendo a la resistencia del hormigón siderúrgico.This study investigates the behavior of siderurgical aggregate in concrete and its interaction with other components. It explores the possibility of replacing siderurgical aggregate with natural aggregate, the effects of additives, standard fibers, and fiber function near siderurgical aggregate. A scanning electron microscope test was conducted to analyze the interaction between cement paste and siderurgical aggregate. The results show that fibers in siderurgical concrete minimize fracture formation and improve resistance to cracking. Increased fiber count reduces fractures and increases compressive and flexural strengths, complementing and contributing to the strength of siderurgical concrete

Characterization of the Adherence Strength and the Aggregate-Paste Bond of Prestressed Concrete with Siderurgical Aggregates

ABSTRACT: Concrete with siderurgical aggregates (SA) is a sustainable construction material with great potential as structural concrete. For this reason, studies must be carried out on the behavior of concrete against prestressed elements, studies that open the door to new applications such as buildings, bridges or foundations. In this study, the feasibility of prestressed concrete is established with standardized adherence tests on beams reinforced with steel wires. The comparison between the concrete-reinforcement union of limestone concrete and concrete with siderurgical aggregates, has shown to be 23% higher in the case of the latter. This study is completed with the analysis of the paste-aggregate interface (ITZ) of both types of aggregate to support the results obtained in the adherence test. In addition, in order to know the bond strength of the pastes that incorporate SA, the micro-Vickers hardness of the pastes of the concrete mixes are determined, a hardness that has turned out to be proportional to the replacement of fine aggregates with SA.This research was co-financed by the European Regional Development Fund (ERDF) and the Ministry of Economy, Industry and Competitiveness (MINECO) within the framework of the project RTC-2016-5637-3. The research was possible thanks to the collaboration of the company INGECID, the department LADICIM (University of Cantabria) and the companies ROCACERO and SIDENOR, as well as the Department of Universities and Research, Environment and Social Policy of the Government of Cantabria (Spain)