Sérgio Cirelli Angulo

Chemical–mineralogical characterization of C&D waste recycled aggregates from São Paulo, Brazil

This study presents a methodology for the characterization of construction and demolition (C&D) waste recycled aggregates based on a combination of analytical techniques (X-ray fluorescence (XRF), soluble ions, semi-quantitative X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTG) and hydrochloric acid (HCl) selective dissolution). These combined analytical techniques allow for the estimation of the amount of cement paste, its most important hydrated and carbonated phases, as well as the amount of clay and micas. Details of the methodology are presented here and the results of three representative C&D samples taken from the São Paulo region in Brazil are discussed. Chemical compositions of mixed C&D aggregate samples have mostly been influenced by particle size rather than the visual classification of C&D into red or grey and geographical origin. The amount of measured soluble salts in C&D aggregates (0.15-25.4mm) is lower than the usual limits for mortar and concrete production. The content of porous cement paste in the C&D aggregates is around 19.3% (w/w). However, this content is significantly lower than the 43% detected for the C&D powders (<0.15 mm). The clay content of the powders was also high, potentially resulting from soil intermixed with the C&D waste, as well as poorly burnt red ceramic. Since only about 50% of the measured CaO is combined with CO(2), the powders have potential use as raw materials for the cement industry.

Separability studies of construction and demolition waste recycled sand.

The quality of recycled aggregates from construction and demolition waste (CDW) is strictly related to the content of porous and low strength phases, and specifically to the patches of cement that remain attached to the surface of natural aggregates. This phase increases water absorption and compromises the consistency and strength of concrete made from recycled aggregates. Mineral processing has been applied to CDW recycling to remove the patches of adhered cement paste on coarse recycled aggregates. The recycled fine fraction is usually disregarded due to its high content of porous phases despite representing around 50% of the total waste. This paper focus on laboratory mineral separability studies for removing particles with a high content of cement paste from natural fine aggregate particles (quartz/feldspars). The procedure achieved processing of CDW by tertiary impact crushing to produce sand, followed by sieving and density and magnetic separability studies. The attained results confirmed that both methods were effective in reducing cement paste content and producing significant mass recovery (80% for density concentration and 60% for magnetic separation). The production of recycled sand contributes to the sustainability of the construction environment by reducing both the consumption of raw materials and disposal of CDW, particularly in large Brazilian centers with a low quantity of sand and increasing costs of this material due to long transportation distances.

Resíduos de construção e demolição: avaliação de métodos de quantificação

In this paper, construction and demolition waste generation was estimated by two quantification methods, one direct and other indirect, regarding informal and formal generators. Construction area and transformation of the points of water and energy were applied for indirect quantification method. For the direct one, volume of dumping areas associated with informal and formal generators in different regions of municipality were quantified and the mass balance was applied. Indirect quantification of informal generators by transformation points of water is not precise. There are evidences that transformation points of energy can be more precise, avoiding costly direct construction and demolition waste quantification method.

Comminution and sizing processes of concrete block waste as recycled aggregates

Due to the environmental impact of construction and demolition waste (CDW), recycling is mandatory. It is also important that recycled concrete aggregates (RCA) are used in concrete to meet market demands. In the literature, the influence of RCAs on concrete has been investigated, but very limited studies have been conducted on how the origin of concrete waste and comminution processes influence RCA characteristics. This paper aims to investigate the influence of three different comminution and sizing processes (simple screening, crushing and grinding) on the composition, shape and porosity characteristics of RCA obtained from concrete block waste. Crushing and grinding implies a reduction of RCA porosity. However, due to the presence of coarse quartz rounded river pebbles in the original concrete block mixtures, the shape characteristics deteriorated. A large amount of powder (<0.15 mm) without detectable anhydrous cement was also generated.

Composição química de agregados mistos de resíduos de construção e demolição do Estado de São Paulo

Os Residuos de Construcao e Demolicao (RCDs) representam cerca de 50% dos residuos solidos de cidades brasileiras; a reciclagem e, portanto, desejavel, tanto do ponto de vista economico, como ambiental. Nesse trabalho sao apresentados resultados de estudos de caracterizacao quimica referentes a amostras de duas usinas de reciclagem do Estado de Sao Paulo. Verificou-se que a classificacao corrente do RCD, segundo criterios visuais (tipos cinza e vermelho), nao esta relacionada a composicao quimica destes, sendo esta influenciada, principalmente, pela granulometria. A composicao quimica dos RCDs varia em funcao dos conteudos de pasta de cimento, tipos dos agregados naturais (areia quartzosa ou granito), cerâmica vermelha e argila. Ainda, para a reciclagem dos residuos como agregados para concretos, sao necessarios dois estagios de britagem para atendimento as normas ABNT. A fracao miuda apresenta um enriquecimento nos teores de silica, indicando liberacao da pasta de cimento para os finos (< 0,15 mm). Os finos tem aplicacoes potenciais na industria de cimento.

Separação óptica do material cerâmico dos agregados mistos de resíduos de construção e demolição

A remocao de residuos de cerâmica vermelha dos agregados mistos procedentes de residuos de construcao e demolicao (RCD) deve ser priorizada para este material possa ser utilizado para a confeccao de concreto. Isso pode ser realizado por meio de diferentes tecnicas de processamento mineral, com principios de separacao, eficiencia, custos e impactos ambientais distintos. A principal vantagem da separacao optica e o uso reduzido de agua ou energia quando comparado com outros processos industriais. Este artigo tem por objetivo analisar os produtos obtidos por separacao optica de RCD mistos, com foco na remocao da cerâmica vermelha e conseguinte reducao da porosidade dos agregados reciclados para uso em concreto. A remocao da cerâmica vermelha viabiliza a obtencao de um agregado reciclado essencialmente composto de concreto, com menor porosidade e cuja absorcao de agua varia entre 4% e 7%. No Brasil, teores de ate 5% de cerâmica vermelha sao esperados no produto (agregado triado), e a producao de concretos de 20 a 30 MPa torna-se viavel com esse material.

Use of Fine Fraction

As an outcome of recycling the mineral part of construction and demolition waste significant quantities of the fine fraction, particle size below 4 mm in Europe, are generated. A common feature of the produced fine recycled aggregates is the high content of cement paste that could impair its quality. With the recent advances on the processing technologies improvement on the characteristics of the fine fraction of C&DW can be envisaged and new perspectives to their application arise.

Treatments on CDW Recycled Aggregates Surface Using Silane-Based Water Repellent

This study aims to investigate the properties of CDW recycled aggregates using silane-based water repellent agent in three different types of treatments: (a) immersion; (b) sprinkling; and (c) dripping; in order to improve the reduces quality of the material due to the high porosity. Wettability and water absorption were determined by apparent contact angle measurements, water absorption after 24h of saturation (standard method) and recording the variation of submerged mass during 24 hs. All treatment allowed reducing the water absorption and its kinetic. The contact angle measurements confirmed the effectiveness of the treatment: the surface resulted always hydrophobic. Comparing the treatments, immersion gave the best result in terms of absolute results and in terms of variability of measurements.

Building Design and Construction Process Influence in Construction Waste Generation

The amount of construction waste (CW) at building sites is highly variable, for instance the CW generation index ranges between 50-300 dm3 per square meters of gross floor area. Today there is still a lack of knowledge about variables (building design, construction process, construction technologies, etc.) affecting the CW generation. The objective of this paper is to analyse the influence of multi-storey building design and some construction processes on the CW generation indexes. The CW generation was analysed for two groups of buildings with two different construction processes; one with plumbing and electric services installed inside the masonry element and the other with plumbing and electric services installed onto the masonry element and covered with water-resistant drywall system (reducing the construction waste generation). The gross floor area directly affects the amount of executed construction works in a building site. Since the most important works (concrete, masonry and cladding) for CW generation is related to gross floor area, gross floor of buildings is also directly related to CW generation. For buildings with gross area varying from 20,000 to 80,000 m2, there is a reduction of approximately 18% of construction waste only changing the plumbing and electric services installation system, from embedded in the masonry element to installed onto the masonry element and covered with water-resistant drywall system.