Journal Sep 2019

Point of View : RECYBETON Jean-Marc Potier (France)

Concrete is the most important construction material in terms of volume and turnover. Its success comes, among other reasons, from its amazing versatility and its availability in most parts of this planet, being essentially a local material. However, this XXIst century sees humanity facing its most difficult challenge since its appearance on this planet: how to keep it livable for the next generations, with a population approaching ten billions of inhabitants, and a general shortage of non-renewable resources? Most informed people agree nowadays with the necessity of turning from linear to circular economy. Concrete cannot miss this major paradigm change.

Background to the BSI provisions for RCA in concrete Tom Harrison (UK)

The British Standards Concrete Committee wished to introduce provisions for recycled aggregates into its concrete standard (BS8500-2), but before it could do so a number of questions needed to be answered. Research undertaken at the University of Dundee provided answers to the questions raised by British Standards Institution (BSI) and this led to the introduction in 2002 of a full specification for the product and use of coarse recycled concrete aggregates (RCA) and a partial specification for other types of coarse recycled aggregates (RA).

The reason for the high use of RCA in the UK and the Netherlands is that the Governments took measures to make the use of RCA competitive with primary materials. One key measure was the introduction of landfill taxes. This would be an effective measure in India to reduce the volume of construction and demolition waste provided ‘fly tipping’ can be minimised.

Since 2002 the requirements for the use of coarse RCA and RA have only had very minor changes, but the requirements for the composition of the aggregate and the test method have been transferred from the BS8500-2 to the European aggregates standards.

The effect of the quality of construction and demolition waste on recycled aggregates concrete properties Miguel Bravo, Jorge de Brito, Luís Evangelist (Portugal)

Most studies have paid attention to the analysis of concrete with recycled aggregates (RA) that come from one source only. In some of them, recycled concrete aggregates (RCA) were used whereas in others RA from construction and demolition waste (CDW) were employed. However, in both cases, aggregates from different sources are not used, which does not allow evaluating the variation of the results.

With this research, one of the main objectives is to evaluate the variation of the properties of concretes when incorporating (fine and coarse) RA from five different CDW recycling plants.

Also, the properties of the natural and recycled aggregates used in the production of the concrete mixes are analyzed. For this purpose, composition, chemical and physical tests were performed.

In order to evaluate the concrete produced, compressive and tensile strength, modulus of elasticity, resistance to wear, immersion and capillary water absorption, resistance to chloride ions penetration and carbonation and shrinkage tests were carried out.

The analysis allowed concluding that the results significantly varied according to the RA family used, mainly when the fine aggregates were replaced. Furthermore, it was found that the great majority of the properties of recycled aggregate concrete (RAC) are lower than those of the corresponding (reference) natural aggregate concrete (NAC).

Use of recycled concrete aggregates – full scale demonstration Christian J. Engelsen, Jacob Mehus (Norway)

Several successful demonstration projects have been conducted in the past 20 years in order to verify the practical, technical and environmental applicability of recycled aggregates. One example is Sørumsand High School where 37% of the natural coarse aggregates were replaced by recycled concrete aggregates. The project was well-planned with solid documentation of the recycled materials as well as the fresh and hardened concrete properties. The experiences obtained were that the project was competitive to the regular project with natural aggregates with regard to costs, technical performance, practical handling and environmental properties. Furthermore, recycled aggregates are included for use in nearly all of the European (EN) aggregate standards, though at varying implementation level. In India, a large deficiency of treatment and recycling capacity of C&D waste exists. Recycling by the wet process technology seems to increase, due to the highly complex heterogenic waste received at the stationary plants. Heterogeneity should be tackled by increased source segregation, pre-mixing of feedstock materials and a daily control of the recycled products. Homogenous feedstock source of concrete waste is highly applicable to recycle into RCA.

A review on the valorization of marble dust/solids or slurry: classification, current trends and potentials Styliani Papatzani (Greece)

One of the challenges of concrete technology is to minimize cement clinker, responsible for 8% of the manmade CO2emissions globally and maximize other constituents emerging from waste, such as recycled aggregates, which belong to the construction, demolition and excavation waste (CDEW) stream or fly ash, which belongs to the industrial waste stream, according to European regulations. There is another form of waste, however, that has received limited attention, so far, and this is namely marble dust and solids. This waste stream is either derived from demolition and crushing of architectural parts made of marble and therefore belongs to the CDEW waste stream or it is produced during the cutting and shaping of marble in industrial units and can be found in the form of dust (water marble dust - WMD) or slurry. The present paper offers a new perspective of the waste stream classification and a review on the re-use and recycling methods and case studies suggested by scholars. Lastly, at the same time, potential extensions to the current state-of the-art in the field of valorization of the waste stream of marble dust, solids or slurry are discussed.

Effects of SCMs and nano- and ultrafine-materials on mechanical properties and carbon footprint of recycled aggregate concretes Faiz Uddin Ahmed Shaikh (Australia)

This paper presents the effects of supplementary cementitious materials (SCMs) (Fly ash, slag and silica fume) and emerging nano- and ultrafine-materials (nano silica and ultrafine fly ash) on mechanical properties of concrete containing 50% recycled coarse aggregate (RCA) as partial replacement of natural coarse aggregate. The RCA are mixed construction and demolition (C&D) waste consisted of concrete, masonry and other materials. In the first part, the effects of 50% slag or 50% fly ash as partial replacement of ordinary Portland cement (OPC) in concrete containing 50% RCA is evaluated, while in second part the effects of 5, 10 and 15% silica fume on above recycled aggregate concrete containing 50% slag or 50% fly ash are evaluated. In third part, the effects of 2% nano silica (NS) and 10% ultrafine fly ash (UFFA) on concrete containing 50% RCA are evaluated. The above results are compared with control concrete containing 100% and 50% natural coarse aggregate. Water-to-binder ratios of all concrete are kept constant, however, superplasticizer is added in the mixes containing silica fume, nano silica and ultra fine fly ash to improve the workability. The compressive and indirect tensile strengths of all concrete are measured at 7, 28, 56 and 91 days. The results show that due to addition of 50% RCA the compressive strength of concrete at all ages is reduced significantly compared to control concrete containing 100% natural coarse aggregates. The addition of high volume fly ash and slag further reduced the compressive strength of recycled aggregate concrete at all ages, where high volume fly ash shows more reduction in compressive strength than high volume slag. The addition of silica fume is, however, recovered the compressive strength reduction of both high volume fly ash and slag concretes containing 50% RCA. The addition of nano silica and ultrafine fly ash also improved the compressive strength of recycled aggregate concrete. Similar results are also observed in the case of indirect tensile strength. The carbon footprint of recycled aggregate concrete is slightly higher than the control concrete. However, the addition of SCMs reduced the carbon footprint significantly.

Heat Curing as a Means of Post-processing Influence on 3D Printed Mortar Specimens in Powder-based 3D Printing Pshtiwan Shakor, Shami Nejadi, Gavin Paul, Jay Sanjayan, Farhad Aslani (Australia)

Inkjet (Powder-based) three-dimensional printing (3DP) shows significant promise in concrete construction applications. The accuracy, speed, and capacity to build complicated geometries are the most beneficial features of inkjet 3DP. Therefore, inkjet 3DP needs to be carefully studied and evaluated with construction goals in mind and employed in real-world applications, where it is most appropriate. This paper focuses on the important aspect of curing 3DP specimens. It discusses the enhanced mechanical properties of the mortar that are unlocked through a heat-curing process. Experiments were conducted on cubic mortar specimens that were printed and cured in an oven at a range of different temperatures (40, 60, 80, 90, 100°C). The results of the experimental tests showed that 80°C is the optimum heat-curing temperature to achieve the highest compressive strength and flexural strength of the printed mortar specimens. These tests were performed on two different dimensions of the cubic specimens, namely, 20x20x20 mm, 50x50x50 mm and on prism specimens with dimensions of 160x40x40 mm. The inkjet 3DP process and the post-processing curing are discussed. In addition, 3D scanning of the printed specimens was employed and the surface roughness profiles ofthe 3DP gypsum specimens and cement mortar are recorded 13.76 µm and 22.31µm, respectively

Challenges and Prospects of Demolition Waste Recycling in India V. G. Ram, Rohit Prajapati, Manu K. Poulose (India)

Estimates of Construction and Demolition (C&D) waste generation in India range between 150 to 716 million tonnes/year. C&D debris recycling, one of the sustainable solutions for managing this sector of waste, is gaining popularity worldwide. However, very few recycling facilities are available in India presently to handle C&D debris. Several barriers, such as inadequate regulations, lack of incentives and awareness about recycling techniques, and unavailability of guidelines have been reported to hinder setting up recycling facilities in India. However, the influence of human factors, such as attitude and industry norms, have been overlooked in the existing literature. The primary objective of this paper is to evaluate the viability of a business model in the construction materials market in India for recycling operations and products. Different stakeholders of C&D waste recycling operations, such as construction & demolition contractors (waste generators), government engineers, architects and RMC producers were interviewed to understand their perspectives towards recycling and recycled products. A total of 67 open-ended semi-structured interviews across six major cities comprise part of the primary evidence. The customer discovery process of the lean startup methodology and related tools were employed to analyze the qualitative interview data. It was found that rewards in the industry for green products and services are negligible and inconsistent. The stiff competition offered by natural aggregate-based products necessitates price restrictions on any new entrants. Supply chain costs of waste acquisition and processing pose a big challenge owing to the lack of stringent regulations and enforcement. Quality concerns and usage restrictions might make direct selling of recycled aggregates unattractive. Value-added products, such as paver blocks made of recycled aggregates, present an attractive channel for recycled materials to enter the market. Challenges hindering the adoption of recycled aggregates and the ways in which government support could benefit recyclers by off-setting supply chain costs to make recycled products competitive are discussed.

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