Flora Faleschini

Recycled concrete containing EAF slag: environmental assessment through LCA

A significant number of “green concrete” are being developed to meet the growing request of reducing construction industry impacts, saving raw materials and preventing industrial by-products’ discard. Between these, black/oxidising electric arc furnace (EAF) slag has been found to be suitable for structural concrete applications when used as replacement of traditional coarse aggregate. This work presents an environmental impacts assessment related to the production of concrete containing EAF slag compared to a traditional one, through Life Cycle Analysis framework using a cradle-to-gate approach. Inventory data are mainly collected from experiments and refer to the considered materials, and the functional unit used to compare both concretes is representative of the same strength and durability/service life characteristics of the material. Results of this specific study show that concrete containing EAF slag as recycled aggregate is responsible of lower emissions production when compared with those related to concrete made with traditional aggregates.

Electric Arc Furnace Slag as Coarse Recycled Aggregate for Concrete Production

Electric arc furnace (EAF) slag is a by-product of steel production in electric arc furnaces. Several studies have tried to demonstrate its suitability in civil engineering application, such as in bituminous mixtures and cement-based materials, due to its good physical, chemical and mineralogical properties. Particularly the re-use as coarse aggregate for concrete production has been shown to be a promising valorisation, when physical and chemical stability is guaranteed. Additionally, EAF slags high mechanical strength makes it suitable for high-performance concrete production. In this work three EAF concretes, with various cement content and also with silica fume addition, were compared with a reference concrete, to identify a convenient mix design to reach a concrete strength class between C50/60 and C60/75. Mechanical strength was evaluated analysing compressive and tensile strength, and elastic modulus. A complementary microstructural analysis was performed after the failure of the specimens, with the aim of analysing the morphology of the interfacial transition zone. Results indicate that the use of EAF slag in concrete allows reaching higher compressive strength than with coarse natural aggregates. EAF slag application in structural concrete promotes also the reduction of cement content in the mix to reach the same strength class.

Cost analysis for maintenance and seismic retrofit of existing bridges

Abstract The work describes an extensive cost analysis for maintenance and seismic retrofit of typical existing road bridges, based on integrated procedures for assessment of state and seismic vulnerability. In particular, visual inspections to evaluate total sufficiency ratings and a simplified seismic assessment were carried out for each structure, according to procedures proposed in earlier works. The results were then used as input data for statistical analysis, to calibrate new unit maintenance, seismic retrofit and total cost equations. The procedure was applied to a stock of bridges in the province of Vicenza, north-east Italy. The results will allow public authorities and private managing companies to estimate economic indicators regarding the extent of resources required for bridge maintenance and retrofit in areas subject to seismic events.

Post-quake urban road network functionality assessment for seismic emergency management in historical centres

Abstract In this paper, a procedure for the evaluation of the interaction between existing buildings and urban roadway networks after a seismic event is proposed. This question is relevant in historical urban centres, where urbanisation typology has evidenced, in the past, lack of road networks’ residual connectivity in post-earthquake conditions. The present study proposes a method for the evaluation of the residual functionality in urban context, moving from the execution of building surveys, the application of probabilistic concepts and fuzzy logic with the aim to define probable urban road network damage scenarios. The methodology is applied to the Municipality of Conegliano (northeastern Italy) evaluating the potential seismic damage scenario to the historical urban centre and highlighting criticisms in the post-earthquake rescue operations.

Workability and Rheology of Fresh Recycled Aggregate Concrete

The use of recycled aggregates concrete (RAC) with coarse recycled concrete aggregates (CRCA) has been widely studied in literature. A number of works investigated both mechanical and durability-related properties of these concretes; however, fresh properties of RAC have not been extensively analyzed yet. Limited studies were focused on the influence of some recycled aggregate properties on slump, which is the most frequently used measure to evaluate workability. Since this measure is a single-value and it is often operator-sensitive, a more quantitative estimate can be derived in terms of fundamental physical quantities, such as plastic viscosity and yield stress. The higher heterogeneity in terms of experimental slump measure occurs indeed when recycled aggregate concrete is tested. In this chapter, a review of the existing experimental methods for the evaluation of fresh concrete workability is given. Additionally, the behavior of fresh concrete is explored, aiming to understand which physical phenomena govern the macroscopic rheological behavior, under some specific conditions, e.g. in terms of mix composition, casting conditions, etc. Some experimental results about fresh recycled concretes workability and rheology, collected from literature, are also discussed.

Reliability-Based Analysis of Recycled Aggregate Concrete under Carbonation

Durability represents a crucial issue for evaluating safety and serviceability of reinforced concrete structures. Many studies have already focused on carbonation-induced corrosion of natural aggregate concrete (NAC) structures, leading to several prediction models to estimate carbonation depth. Less research is devoted instead on recycled aggregate concrete (RAC), about which limited experimental works exist aimed at assessing the carbonation coefficient in accelerated tests. Additionally, deteriorating processes are subject to uncertainty, when defining materials, geometry, and environmental actions during the service life of structures. This work presents a reliability-based analysis of carbonation resistance of RACs, using experimental carbonation coefficients derived from the literature, and applied in the full-probabilistic method prosed in fib Bulletin 34. Results demonstrate how aggregates replacement ratio and w/c ratio influence the reliability of RAC carbonation resistance.

Bridge residual service-life prediction through Bayesian visual inspection and data updating

Abstract The paper describes an integrated procedure for evaluation of the service-life curve of existing bridges, calibrated with data derived from visual inspections and aimed at assessing the degree of deterioration of their structural/non-structural elements. Visual inspections allowed a total sufficiency rating for the bridges to be calculated, together with data collection, to be used in Bayesian updating of element deterioration curves. The results were combined with information from simulations of potential bridge deterioration scenarios to quantify mean trends and related uncertainties of the remaining service-life curves of existing bridges. The proposed procedure was applied to two bridge stocks and results are critically discussed. The method used may allow public authorities/private managing companies to optimise economic resources allocated to long/medium-term maintenance plans for the most critical structures.

Building damage assessment after the Riviera del Brenta tornado, northeast Italy

A tornado with severe intensity hit the municipalities of Pianiga, Dolo and Mira close to Venice, northeast Italy, causing damages on a wide number of residential and industrial buildings and destroying some historical villas. In this study, the authors show the results of the damage assessment survey performed in the first days after the occurrence of the extreme event. Limited literature deals with damage assessment of European building types due to wind actions, and the available one does not consider building vulnerability as key factor in the structural response of existing structures subject to tornado hazard. In this paper, structural damages surveyed in reinforced concrete frame structures and masonry buildings, representative of common Italian building types, are critically discussed. Additionally, this work provides a database of past tornado events in northeast Italy, evidencing how the analyzed area has been found to be quite prone to tornado hazard.

Effects of electric arc furnace dust (EAFD) addition on setting and strength evolutions of cement pastes and mortars

AbstractThe purpose of this work is to study the effects of including high dosage of electric arc furnace dust (EAFD) on both setting behaviour of cement pastes, and on strength evolution of eco-friendly mortars. Particularly, in this research, dust was taken in as-received conditions from the collection system of a carbon steelmaking factory. Setting time of blended cement pastes with varying EAFD content and water/binder ratios was monitored through Vicat test. In addition, physical and mechanical properties of fresh and hardened mortars including EAFD up to 20% on cement weight were investigated. Results indicate that the use of low w/b ratio is effective in shortening the setting time of blended cements, also at high EAFD content, limiting the setting time below 24 h in most of the analysed mixtures. Additionally, an improvement of fresh mortar properties is obtained using EAFD, whereas strength evolution is slightly delayed due to EAFD addition.

Recycled Aggregates for Concrete Production: State-of-the-Art

In the last decades, problems linked to industrial material landfill disposal has become more and more relevant to society, with cost increases for environment and municipalities. Waste reutilization is attractive to reduce economical costs and potential pollution problems, and preserve natural raw resources. In this context, the promotion of recycling in concrete industry may represent a valid route for sustainable development, preventing natural resources consumption, valorizing recycled materials, and avoiding the landfill of huge amount of materials. Nowadays, there are, among others, two significant possibilities to reduce natural aggregates exploitation: the use of recycled concrete from construction and demolition waste (C&DWs) and the use of slag from metallurgical industrial production. Additionally the use of supplementary cementing materials (SCMs) can reduce the great environmental emissions due to cement use. In this chapter, a review about the most commonly used recycled aggregates is given, i.e. recycled aggregates from C&DW and from metallurgical slag, with a special focus about the available codes and normative which regulate their use in structural concrete.