1 Romildo Dias Toledo Filho
Professor and Head of Labest and Numats Laboratories for Sustainable Construction, Coppe/Universidade Federal do Rio de Janeiro, Brazil 2 Eduard Koenders
Visiting Professor, Coppe/Universidade Federal do Rio de Janeiro, Brazil; Associate Professor, Delft University of Technology, Delft, the Netherlands 3 Marco Pepe
PhD Student, University of Salerno, Italy
4 Guilherme Chagas Cordeiro
Associate professor, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Brazil
5 Eduardo Fairbairn
Professor, Coppe/Universidade Federal do Rio de Janeiro, Brazil 6 Enzo Martinelli
Assistant Professor, University of Salerno, Italy
1 2 3 4 5 6
The Brazilian construction industry is committed to delivering the venues and infrastructure of the Rio 2016
Olympic and Paralympic Games with zero increase in carbon dioxide emissions, reduced consumption of raw
materials, increased use of renewable materials and 100% local recycling of construction waste. This in turn
has led to significant research and development into using cement replacements – particularly sugar-cane ash
from local ethanol production – and recycled aggregates in concrete production. This paper reports on the initial
and promising results for ecological concrete mixes using up to 20% sugar-cane ash and 50% cleaned recycled
aggregates from demolition waste.
Rio 2016 sustainable construction commitments lead
to new developments in recycled aggregate concrete
1. Introduction
After hosting the United Nations Rio+20 conference on sustainable development in 2012, Rio de Janeiro has become Brazil’s key city for embodying sustainability in its widest form – but particularly for new and existing infrastructure (UNEP, 2007, 2013). Green cities, ecological concretes, supplementary cementitious materials for cement replacement and reusing aggregates from construction demolition wastes can all help to cut carbon dioxide emissions, reduce natural resource use and minimise conventional energy demands.
With the roll-out of new infrastructure for the 2014 FIFA World Cup Brazil (FIFA, 2012; World Cup Portal, 2013) and the Rio 2016 Olympic and Paralympic Games (Rio, 2013, 2016), Rio de Janeiro
aims to implement its sustainability agenda by setting new standards for future construction activities, including construction materials, energy use and operations. With the construction activities during the London 2012 games focusing on waste and sustainable construction management (Baird et al., 2011; Locog, 2012), Rio 2016 aims to set the standards even higher.
A sustainability management plan has been produced that contains the global issues and objectives to protect the city environment. For the construction industry, waste management and social responsibility are considered of major importance, as summarised in Table 1. A particular objective is for cooperative recycling programmes to be developed for 100% reuse of solid waste generated during the Rio 2016 games preparation and operation, including construction.
Carbon dioxide
neutral games Sustainable venue design/construction and noise pollution
• Implementation of strict Leed (Leadership in Energy and Environmental Design) guidelines (Leed, 2002) and certification of 100% of new buildings with reduced consumption of natural raw materials and use of renewable natural resources • Minimum distance criteria for material transport and reuse of demolition waste including relevant overlay materials Waste management
and social responsibility
Waste management • 100% of new buildings sending demolition waste to new recycling plants, introducing a new era for material reuse in Rio self-contained recycling plants for separate streams (recyclable and organic) in large venues to minimise waste forwarded to landfill and to lead to a zero waste approach
The vast extensions of road and railway infrastructure needed to prepare Brazil for the 2014 FIFA World Cup and Rio de Janeiro for Rio 2016 require the production of huge volumes of concrete. The Olympic Park alone will spread over 1·8 million m2 (Figure 1) and
large quantities of concrete are needed to facilitate all construction and infrastructure works planned to link the global events. An innovative vision for developing a sustainable solution to the vast amount of raw materials needed for concrete production is thus vital – both for the games and for the construction sector in general.
Since cement production is responsible for about 5% of global carbon dioxide emissions (Hendriks et al., 2004), many efforts are currently under way to search for alternative binders. Supplementary cementitious materials can be partly used to replace traditional Portland cement in concrete. These mostly originate as by-products from advanced industrial processes – such as steel slag, silica dust and fly ash – and have the chemical characteristics of a latent hydraulic binder. However, at the Labest laboratory for construction materials of Coppe–Universidade Federal do Rio de Janeiro (UFRJ) Graduate School for Research and Engineering in Rio de Janeiro, research has been conducted to examine the potential use of more natural pozzolans. These include sugar-cane bagasse (pulp) ash (Cordeiro, 2006), rice husk ash and ash from burned sewage sludge (Fontes,
2008), as well as marble and granite residues (Bacarji et al., 2013). The research has significantly increased knowledge in the field of using sustainable materials to replace traditional Portland cement. Combined with new knowledge on the application of recycled aggregates originating from construction demolition waste, the ingredients are now available to develop a far more ecological concrete.
This paper provides an overview of the potential replacements for cement and aggregates and reports on the first steps towards development of an ecological concrete utilising these materials for use in Rio 2016 infrastructure.
2. Replacements for cement
Sustainable construction materials are a major topic for enhanced research efforts on alternative binders and fillers such as pozzolans, but also on non-reactive fillers such as limestone, micronised sand, and marble and granite residues. Replacing large quantities of Portland cement by pozzolans or fillers is a strategy that contributes greatly to the reduction of traditional Portland cement in concrete and to a reduced environmental footprint.
Environmental impacts such as carbon dioxide emissions, natural resource usage, energy consumption and others will all be positively
Figure 1. Construction of the Rio 2016 Olympic Park and other new venues and infrastructure needs to achieve 100% local solid waste recycling (Courtesy of Aecom)
influenced when replacing Portland cement by either a supplementary cementitious material or a non-reactive filler. The challenge is to maintain equal performances for the cementitious composite, as well as to minimise the environmental footprint by a maximum reuse of waste-like residuals. An overview of cement replacements and non-reactive pozzolans is provided in Table 2 (Malhotra and Mehta, 1996).
When considering, for instance, the properties of sugar-cane bagasse ash, which is a by-product of the sugar-ethanol agro-industry, its pozzolanic reactivity has shown great potential to act as a cement
replacement. With its raw material used for ethanol production to replace petrol for cars (Cordeiro, 2006; Fairbairn et al., 2010), the burned fibrous remains of sugar cane turned out to be suitable to act as a pozzolanic material that can partially replace cement.
At the UFRJ, extensive research has been conducted to examine the properties of this class of cement replacements in terms of grinding, burning, reactivity, morphology, chemistry and mechanical properties, and also to evaluate its applicability in concrete (Cordeiro, 2006; Cordeiro et al., 2008, 2009; Fairbairn et al., 2010).
The morphological structure of such ashes has been investigated directly after burning and after 4 h of grinding (Figure 2). From these results the particle size distribution can be measured and its chemical composition characterised. Furthermore, the chemical results showed a silicon dioxide content of about 78% (24% of amorphous silicon dioxide), a density of 2530 kg/m3 and a specific surface (Blaine) of
196 m2/kg (Fairbairn et al., 2010). These properties show the potential
of sugar cane to act as a sustainable replacement material for cement. Compressive strength tests have confirmed this. Figure 3 shows the compressive strength of a high-performance concrete with a water/ cement (w/c) ratio of 0·35 and ash replacement ratios of 10%, 15% and 20% (Fairbairn et al., 2010). The results show that the replacement of cement by different percentages of ash leads to a similar strength capacity as the reference mixture.
The addition of sugar-cane ash also results in improvements in the rheology of fresh concrete (Cordeiro et al., 2008. In relation to durability, the results of chloride ion penetrability based on ASTM C1202-05 (ASTM, 2012) indicated that both conventional and high-performance concretes using ash reduce passed charges by around 30%. It was also proved, by a case study for the south-eastern region of Brazil, that sugar-cane ash can be used at an industrial scale, significantly reducing carbon dioxide emissions (Fairbairn et
al., 2010). The material can therefore be considered as a valuable
substitute for the development of more ecological concrete.
3. Replacements for aggregates
Reusing aggregates from construction demolition waste requires the development of an innovative mix design that deals with grading, hydration, strength, durability and replacement procedure. As partner in the European Encore project (see www.encore-fp7.unisa. it), research programmes are running at Coppe-UFRJ in the field of
80 70 60 50 40 Compr essive str ength: MPa 0 50 100 150 200 Reference concrete 10% sugar-cane ash 15% sugar-cane ash 20% sugar-cane ash
Curing time: days
Figure 3. Using sugar-cane ash as cement replacement has little effect on the strength of high-performance concrete (Fairbairn et al., 2010) Figure 2. Sugar-cane ash: (a) at initial state and (b) after 4 h of grinding (Courtesy of Cordeiro)
Cement replacements Waste stream Reactivity
Sugar-cane bagasse ash By-product of the sugar/ethanol agro-industry and is the
microporous matter that remains after burning the sugar cane Pozzolanic reactivity from amorphous SiO2 and Al2O3 Rice husk ash By-product of rice production and remains after burning the
hard protecting coverings of rice grains Pozzolanic reactivity from amorphous SiO2 Silica fume By-product of the induction arc furnaces in the silicon metal
and ferrosilicon alloy industries Pozzolanic reactivity from amorphous SiO2 Fly ash Fine residues generated in coal combustion of electricity
plants Pozzolanic reactivity from silicate glass containing Aland alkalis 2O3, Fe2O3 Sewage sludge ash Residual, by drying and burning the semi-solid material left
from industrial wastewater, or sewage treatment processes Pozzolanic reactivity from partially crystalline SiO2 and Al2O3 Granulated blast-furnace slag Obtained by quenching molten iron slag (a by-product of
iron- and steel-making) from a blast furnace in water or steam
Cementitious material from silicate glass containing mainly CaO, MgO, Al2O3 and SiO2
Marble and granite residues Residual waste product of the marble and granite industrial
production plants Non-reactive, acting as a filler material
Table 2. Cement replacement originating from primary waste streams
characterisation, mix design, workability and modelling of recycled aggregate concretes. The aim is to develop a mix design and an associated mix procedure for concretes with a partial replacement of natural aggregates by recycled aggregates.
Recycled aggregates can only be considered as a serious sustainable alternative for natural aggregates if their use leads to a concrete with predictable mechanical and durability properties, similar to those of ordinary concrete mixtures with natural aggregates. A controllable and predictable performance of recycled aggregates is therefore needed. Adding recycled aggregates to the concrete matrix may affect the bearing capacity of the aggregate grain structure as well as the morphological nature of the cementitious microstructure.
Recycled aggregates generally consist of construction demolition waste, typically crushed concrete. This means the aggregate contains both natural aggregate fractions but also remnants of the former cement paste microstructure, either as fully hydrated C–S–H gel or as anhydrous cement grains. These cement paste remnants are also partly responsible for the increased adsorption capacity of recycled aggregates, which can be attributed to the relatively higher porosity of recycled aggregates and the existence of surface and micro cracks that have the ability to accumulate water. Controlling the compressive strength of recycled aggregate concretes, therefore, boils down to the control of the mechanical properties, the adsorption capacity, the grading and morphology of the recycled aggregates.
The recycled concrete aggregates employed in this study were obtained from the demolition remnants of the hospital Clementino Fraga Filho in Rio de Janeiro (Figure 4). Materials from the demolition process were selected and analysed by Labest.
The recycled aggregates received from the demolished hospital were processed in the following steps
n particle homogenisation, with the objective to select homogeneous
samples from the demolition debris
n grinding and sieving, aimed at transforming the demolition
debris in aggregates of appropriate size classes
n autogenous cleaning, intended to remove the outer cement paste
layers residing on the aggregate surfaces.
The first two processes are generally performed on demolition waste to produce recycled aggregates. In addition, the third process was specifically carried out to see if it was possible to enhance the quality of recycled aggregates and, in association with this, the mechanical properties of the recycled aggregate concretes. Several experimental tests were thus performed on the samples to determine their key physical and mechanical properties and possibly compare
the results with the corresponding samples made from ordinary natural aggregates, characterised by water absorption, specific mass, grain size distribution and image analysis using photographs.
3.1 Selection, grinding and sizing
The first stage of the processing procedure carried out on the crushed concrete particles was based upon collecting and selecting such particles and debris by considering their predominant colour. Therefore, at the demolition site the debris was selected and subdivided into the following two fractions
n ‘grey’ fraction, consisting of particles mainly made of structural
concrete (and, in a minor portion, mortar) debris
n ‘red’ fraction, made of clay brick and other ceramic-based (i.e.
tiles) materials.
In this study the focus was mainly on the possible application of the grey fraction. In particular, the homogenisation process was carried out by means of the homogenising cells process (da Luz et
al., 2010), in which the raw material is distributed on a plastic sheet
in different homogeneous layers throughout the whole length of the sheet (Figure 5). In this way, the basic distribution of the raw concrete particles is equal over the length of the sheet and, starting with the middle section, the layered ‘cake’ of raw materials is subdivided into several sections called cells, leading to a homogeneous size distribution of particles.
Figure 5. Homogenisation of the ‘grey’ concrete-based demolition material
Figure 4. Demolition waste was investigated from the old hospital Clementino Fraga Filho in Rio de Janeiro (Courtesy of Eneraldo Carneiro – Coord COM/UFRJ)
The homogenised material was ground in a crusher, as shown (Figure 6). The machine was filled with the raw material from the top and during grinding the material was separated into two classes, namely coarse and fine aggregates.
For each sample of homogenised material, about 40% was obtained for coarse aggregates (nominal diameter bigger than
4·75 mm) and the rest was defined as fine aggregates. After grinding, the recycled aggregates were sieved to divide the material into the three size classes already defined.
3.2 Cleaning
To reduce the amount of fine material – mainly debris from cement paste and mortar – on the surface of recycled aggregates, an autogenous cleaning process was conceived and carried out (Figure 7). This involved rotating the particles in a mill drum to collide them against each other. The drum, with diameter of 30 cm and height of 50 cm, was one-third filled with raw recycled aggregates and rotated at 60 rpm. The efficiency of the cleaning process was then analysed by investigating its effect in terms of modification of the key physical properties of the particles for different durations of cleaning, ranging from 2 to 15 min.
Some preliminary trials were performed on raw concrete particles (not homogenised), which were subjected to water absorption capacity tests after different cleaning durations. Figure 8 shows the average values of the water absorption capacity measured from tests performed on recycled concrete particles, which were preliminarily classified according to the Brazilian standard NBR NM 53 (ABNT, 2003a) for coarse aggregates. The graph shown in Figure 8 demonstrates the significant decrease in terms of water absorption capacity observed from the recycled concrete particles when cleaning for durations of 2–15 min. These preliminary findings, therefore, determined the choice for the autogenous
Figure 7. Some of the recycled aggregate was ‘cleaned’ by rotating it in a mill drum
Figure 6. The demolition material was ground to form coarse and fine aggregate 6.0 5.5 5.0 4.5 4.0 3.5 3.0 Absorption water: % 0 5 10 15 Time: min
Figure 8. Increased cleaning times of raw demolition material resulted in lower water absorption
cleaning duration of the homogenised particles at 10 and 15 min. The first tests performed to measure the efficiency of the cleaning process on the concrete particles were carried out to determine water absorption and specific mass, performed according to NBR NM 53 for coarse aggregates (Brita 0, 4·74–9·5 mm dia., and Brita 1, 9·5–19 mm dia.). Table 3 reports the results of the water absorption tests. It can be seen from the table that the cleaning process led to a significant decrease in terms of water absorption, as a result of the removal of outer cement paste layers and fine mortar attached at the outer surface of raw concrete particles, and the consequent reduction of the voids percentage. The results highlight that after the cleaning procedure, the amount of absorbed water was reduced by 50% and 20% for Brita 0 and Brita 1 sizes, respectively. Other evidence of cleaning efficiency was obtained from the grain size distribution through the sieving analysis realised according to NBR NM 248 (ABNT, 2003b) Figure 9 shows surprisingly that the cleaning process produces an increase in the amount of fine particles, confirming that a significant part of the outer layers of the crushed concrete particles are actually removed. These can of course be graded and used as fine aggregate replacement.
A first assessment of shape change due to the cleaning procedure was obtained through a comparative visual analysis. Photographs of concrete particles taken after the three different durations of cleaning are shown in Figure 10. The pictures show that the cleaning process not only removes cement paste remnants but also modifies the shape and colour of recycled aggregate particles.
4. Recycled aggregate concrete
4.1 Mix designThe design of an ecological concrete with partial replacement of natural aggregates by recycled aggregates needs to take into account the basic material parameters of recycled aggregates. Controlling these parameters is considered indispensable for achieving a robust mix design with controllable and predictable mechanical and durability properties. The difference in chemical nature and mechanical properties between recycled and natural aggregates is the main reason for this potential deviation and scatter in concrete performance results.
Designing a concrete with a predefined percentage of natural aggregates replaced by recycled aggregates therefore requires a thorough examination of the different components used in the concrete, as well as the way the mixture is composed. From this point
100 90 80 70 60 50 40 30 20 10 0 Passing: % 0 1 10 Sieve opening: mm (a) (b)
RCA – 15 min cleaning RCA – 10 min cleaning RCA – no cleaning Natural 100 90 80 70 60 50 40 30 20 10 0 Passing: % 0 1 10 Sieve opening: mm
RCA – 15 min cleaning RCA – 10 min cleaning RCA – no cleaning Natural
Figure 9. Grain size distribution for natural and recycled aggregates (RCA) to Brazilian standards – cleaned aggregates have a higher proportion of fines, confirming that the process actually works: (a) Brita 0; (b) Brita 1
Figure 10. Recycled aggregates: (a) before cleaning; (b) after 10 min of cleaning; (c) after 15 min of cleaning; clear changes in shape and colour can be seen
Aggregate specification Size: mm Cleaning time: min Specific mass: kg/m3 Water absorption after
24 h: % Brita 0 4·75–9·5 0 2535 11·94 10 2566 6·06 15 2586 5·56 Brita 1 9·5–19 0 2268 4·94 10 2358 4·01 15 2328 4·09
Table 3. Water absorption and specific weight of recycled aggregates subject to different cleaning times
of view, four different mix compositions have been developed with the following variables considered (see Table 4).
n Mix 0: reference mix with natural aggregate, designed for
30 MPa strength at 28 days.
n Mix A: with uncleaned recycled aggregate
n A1 – 25% natural aggregates (Brita 1) replaced by recycled n A2 – 50% natural aggregates (Brita 1 and Brita 0) replaced
by recycled
n Mix B: with cleaned recycled aggregate
n B1 – 25% natural aggregates (Brita 1) replaced by recycled n B2 – 50% natural aggregates (Brita 1 and Brita 0) replaced
by recycled.
All the mixtures had a w/c ratio of 0·53 and contained 300 kg/ m3 of cement, while the aggregate grading was designed using the
particle packing model of De Larrard (1999). The extra amount of water added to the mixtures was based on the absorption capacity of the recycled aggregates and natural aggregates.
From the mix design it can be observed that the natural aggregates are replaced by recycled aggregates by 25% (A1 and B1) and 50% (A2 and B2), respectively. A research programme was then conducted to characterise the rheological, hydration and mechanical performance of the mixes.
4.2 Slump
Figure 11 shows the slump measured for all mixtures. From these results it can be observed that the slump values of the mixtures with 25% recycled aggregates are close to the reference mix, with 160 mm for both mix 0 and A1 and 190 mm for mix B1.
When replacing 50% of the aggregates by recycled material an increase in the slump was observed, to 24 mm and 22 mm for mixes A2 and B2 respectively. This could potentially be related to the amount of additional mixing water added to the mix to compensate for the absorption and to the rate the additional mixing water is absorbed by the recycled aggregates.
4.3 Compressive strength
The compressive strength development was measured by experimental testing after 2, 7, 14, 28 and 60 days of hardening and the results are shown in Figure 12. This shows that all results are
Mix Cement: kg/m 3 W ater: kg/m 3 Added water: kg/m 3 W ater/cement ratio Superplasticiser: kg/m 3
Natural aggregate: kg/m3 Uncleaned recycled
aggregate: kg/m3 aggregate: kg/mCleaned recycled 3
Sand Brita 0 Brita 1 Brita 0 Brita 1 Brita 0 Brita 1
0 (0% recycled aggregate) 300 160 31·4 0·53 4·02 952·6 439·9 470·2 — — — — A1 (25% uncleaned recycled aggregate) 45·4 951·7 439·5 — — 404·5 — — A2 (50% uncleaned recycled aggregate) 71·8 950·4 — — 346·6 404·0 — — B1 (25% cleaned recycled aggregate) 42·4 951·8 439·8 — — — — 415·3 B2 (50% cleaned recycled aggregate) 49·9 951·3 — — — — 403·1 415·1
Table 4. Details of concrete mixes
Figure 11. Slumps measured for the five mixes presented in Table 4 – higher slumps for the 50% recycled aggregate concrete could be attributed to different water absorption rates
40 35 30 25 20 15 10 5 0 fc : MPa Mix 0 23.36 28.44 30.43 33.02 36.97 2 days 7 days 14 days 28 days 60 days Mix A1 21.54 24.55 30.09 31.56 36.92 Mix A2 16.72 23.75 27.08 27.50 28.73 Mix B1 21.07 27.67 29.82 30.24 32.61 Mix B2 19.06 26.31 31.26 29.92 33.69 Figure 12. Compressive strength development for the five mixes presented in Table 4 – all but A2, with 50% uncleaned recycled aggregate, achieved 30 MPa strength within 28 days
Slump test
16 mm 16 mm 24 mm 19 mm 22 mm
relatively close to the reference mixture, except for mixture A2. This is the mixture that has 50% replacement of the natural aggregates by recycled aggregates, which have not been cleaned. The more porous, loose and weak parts of this aggregate have led to a weakening of the matrix and lower performance. The results of the other recycled aggregate mixtures, A1, B1 and B2, all achieved 30 MPa strength within 28 days.
It can be observed that there is almost no difference in the compressive strength capacity between the B1 and B2 mixtures, with respect to the reference mixture: this clearly confirms the potential of the cleaning process. It can also be observed that cleaning of recycled aggregates leads to very stable and robust results, even for 50% replacement.
5. Conclusions
The construction sustainability commitments of the Rio 2016 Olympic and Paralympic Games has led to significant research and development into using cement replacements and recycled aggregates in concrete production. A promising sustainable concrete design has been produced using recycled aggregate replacement.
Using recycled materials as a concrete constituent can reduce the demand for raw materials and increase sustainability of concrete production. Moreover, besides saving energy and reducing over-exploitation of natural resources, recycling and reusing materials avoids landfill disposal of large quantities of construction demolition waste.
Combining a recycled aggregate concrete with a pozzolanic binder such as sugar-cane bagasse ash will lead to an even smaller environmental footprint due to reduced use of Portland cement, cutting the carbon dioxide emissions of cement production.
The mechanical, hydration and rheological performance of the mixtures presented in this paper could be a blueprint for further development of ecological concrete. It also fits with the current Brazilian policy of aiming to develop a sustainable society where raw materials are used for more than their primary purpose only.
In addition it can lead to a change in materials usage, with recycled construction materials considered as a sustainable alternative with a long-term durability performance.
Acknowledgements
The mobility of some of the authors of this paper between the Federal University of Rio de Janeiro (Brasil) and the University of Salerno (Italy) was supported by the EnCoRe Project (FP7-PEOPLE-2011-IRSES No. 295283; www.encore-fp7.unisa.it) funded by the European Union within the Seventh Framework Programme.
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