Autor(a/res): Caroline Santana Rangel, Romildo Dias Toledo Filho, Mayara Amario, Marco Pepe

Resumo: Although Recycled Concrete Aggregates, RCAs, derived from concrete waste, represent a potential sustainable solution for the structural concrete production, their heterogeneous composition is a feature that still prevents their large-scale use in the construction industry all around the world. In order to find a possible existing relationship between the source of residues and the resulting RCAs characteristics, a pilot scale case study was carried out, in which approximately 20 tons of concrete waste, derived from different origins, were processed to obtain granulometric fractions from coarse aggregates to powders. The RCAs fractions, obtained using a controlled processing procedure, were then thoroughly characterized to establish quality control parameters that could lead to a classification of different types of recycled aggregate generated. The results show that the source of concrete waste strongly influences the amount of each aggregate fraction produced during processing and, aggregate properties were dependent on the waste origin. Despite this, the presented analysis demonstrated, that by evaluating a fundamental parameter such as the Attached Paste/Mortar within the RCAs, a generalized quality-control classification can be proposed for the industrial upscaling of RCAs characterization. It is believed that such a classification could promote the integral and rational re-use of these secondary raw materials in different cement based products of the construction sector.

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Autor(a/res): Aline De Souza Oliveira, Jo Dweck, Eduardo de Moraes Rego Fairbairn e Otavio Gomes.

Resumo: Crystalline admixtures (CAs), categorized as permeability-reducing admixtures, are commercial products employed in low contents in cement-based materials either to improve concrete durability or to stimulate autogenous healing of cracks. This study investigated the effects on crystal formation promoted by CA presence in cementitious pastes by thermal analysis. X-ray diffraction was used as a complementary technique to identify the formed phases. The results indicated that the increment in CA content increased calcium hydroxide (CH) and monocarboaluminate (Mca) contents. However, it did not change the total combined water and calcium carbonate (CaCO3) contents. In fact, the increment of CA content prolonged the retarding of hydration reactions and decreased the dehydroxylation temperature of CH, suggesting the decreasing in crystallinity and purity degree. The primary action mechanisms of CA confirmed were the long-term ability for further hydration to occur, the CH recrystallization, and the conversion of lower to higher thermal stability phases. Chemical and physical mechanisms of CAs are related to their surface area increase and their chemical nature, mainly composed of limestone. These characteristics confer to CA the ability to act as a nucleation and precipitation stimulator to form new products.

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Autor(a/res): G Calcado, Lais Alves, E Vazquez e Romildo Dias Toledo Filho.

Resumo: Civil construction is responsible for the excessive consumption of natural resources and the generation of the largest share of solid urban waste. In this context, recycling of construction and demolition waste (CDW) is presented as an alternative to minimize the impacts generated by construction. This study aimed to evaluate the influence of recycled CDW aggregates on the behavior of Portland cement mortars with three distinct mixtures. In addition to the reference mixtures, mortars with three different substitution levels of the natural aggregate for recycled aggregate, which were submitted to physical and mechanical tests in the Laboratory of Structures and Materials (LABEST) - COPPE/UFRJ. The results showed that for some substitution levels there was no loss on the properties of the mortars. Therefore, their performance is a function of the mixture adopted and the substitution content of the natural aggregate for the recycled.

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Autor(a/res): Alex Neves Junior, Jo Dweck, Romildo Dias Toledo Filho e Brian R. Ellis.

Resumo: The concerns about greenhouse gas emissions have triggered investigations among the scientific community. The accelerated carbonation curing has been used as a tool to capture CO2 at early stages of cement-based material fabrication. In a previous study, the authors quantified the amount of CO2 captured in portland cement pastes by thermal analysis, at high relative humidity precure conditions. In the present work, the authors quantified the amount of CO2 captured in binary pastes derived from engineered cementitious composites (ECC), a family of composites worldwide used, whose one of their features is the precure at low relative humidity conditions. Two types of ECC pastes (1.2 and 2.2) were submitted to 4 h and 24 h of accelerated carbonation after 24 h of initial hydration. Using thermogravimetry and derivative thermogravimetry, the amounts of captured CO2 and respective carbonation degrees were quantified. The results showed that ECC paste 1.2 presented the highest values of captured CO2 and carbonation degree, considering all reactive components. In contrast, ECC paste 2.2 presented the highest values of these two parameters, when considering only portland cement as reactive component. For both pastes, the hydration degrees of the carbonated samples were higher than those of the non-carbonated references, indicating that in the used operating conditions, carbonation enhances ECC paste hydration.

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