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ABSTRACT: A number of studies on reusing and recycling of construction demolition waste (CDW) as well as the properties of building materials using recycled aggregates (RAs) have been carried out in many countries. In Vietnam, researchers are also interested in using RAs for the construction industry in order to develop sustainable construction and minimize environmental impact. This paper not only fo-cuses on the review and discussion about the research and application of recycled CDW in the world and in Vietnam. It also gives recommendations on researches and on recycling CDW technology as well as the applicability of recycled aggregate concrete (RAC) for sustainable construction in Vietnam.

1 INTRODUCTION

Cost of CDW disposal is becoming higher and difficult for demolition contractors. Due to environmental and technical factors, scientists around the world are trying to find ways to reuse (or reutilize) these mate-rials. It is not only bring significant economic, environment benefits but also demanding technical re-quirements for building. Table 1 and Figure 1 show the level of recycledg and landfilled rate of CDW in European countries [8] and Vietnam [25].

Table 1. Recycled and landfilled rate of CDW in Europe and in Vietnam

Countries ‘Hard’ CDW

(million tonnes) Recycled rate

(%) Landfilled or

incinerated (%) Landfill Tax for CDW

(€ per tonne) Germany 59 17 83 0 UK 30 45 55 2.9 France 24 15 85 6 Italy 20 9 91 1 Spain 13 < 5 > 95 0 Netherlands 11 90 10 23-90 Belgium 7 87 13 5.75-16 Austria 5 41 59 5.79 Portugal 3 <5 >95 0 Denmark 3 81 19 45 Greece 2 < 5 > 95 0 Sweden 2 21 79 30 Finland 1 45 55 19 Ireland 1 <5 > 95 0 Luxembourg 0 N/A N/A N/A Vietnam 1.9 0 100 N/A

Recycling construction demolition waste in the world and in Vietnam

Tong T. Kien1, Le T. Thanh2 and Phung V. Lu1

1National University of Civil Engineering , Hanoi, Vietnam 2Ministry of Construction, Vietnam  

The International Conference on Sustainable Built Environment for Now and the Future. Hanoi, 26 - 27 March 2013

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Figure 1. Rate of recycled and reused CDW in EU in periods of time [10]

Mixture of crushed bricks and portland cement to produce concrete products was first recorded in Ger-many in 1860 [9]. On behalf of RILEM technical committee 37DRC, Nixon prepared the first reports of recycled concrete aggregate for concrete in the period from 1945 to 1977. The 2nd Report of RAs and recy-cled aggregate concrete (RAC) was prepared by Hansen covering the period of 1978-1985 and the 3rd re-port was an updated version of the second state of art report covering the development in the period be-tween 1985 and 1989 [9]. In 1993, RILEM organised the International workshop on guidelines for demoli-tion and reuse of concrete and masonry waste [19]. In 2002, ACI Committee 555 reported information on evaluating and processing waste concrete as recycled concrete aggregates (RCA) to produce concrete con-struction [1]. In recent years from 1996 to 2011, many Chinese researchers are interested in the studying on nearly all aspects of mechanical properties and structural performance of concrete using RAC [39].

In Vietnam, the possibility of using recycled CDW aggregates substituting for natural aggregates (NAs) in concrete and mortar construction has been studied [20, 36]. A pilot plant to produce recycled aggregates from CDW was built [21]. Recycled CDW was used for road foundation layers [37].

To summerize all of those achievements, this paper is not only written primarily a state of art on recy-cling CDW in over the world and in Vietnam, but also to recommend further studies on recycled concrete for developing sustainable construction in Vietnam.

2 DEMOLITION AND RECYCLING CDW TECHNOLOGY

2.1 Demolition technology

Figure 2: Three construction and demolition waste pathways at a site

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During the 1950s and 1960s, the demolition contractors generally were limited to hand held breakers, jackhammers operated by compressed air, wrecking balls, etc. Only few demolition contractors can re-move whole structures. However, with the development of modern technology, good demolition equip-ment (devices) are now produced. They help us demolish constructions easily. ACI 555R [1] divides methods of demolition into: Demolition by hand tools, hand operated power tools, vehicle mounted equipment, explosive blasting, drills and saws, non-explosive demolition agents (mechanical or chemical separation methods).

The choice of demolition methods depends on many factors such as: financial; time limits imposed on a project; the strength and performance of concrete; the shape, size and accessibility of structure; the amount of demolished concrete; environmental concerns (including noise, dust, vibration and debris); worker safety and public safety; possible recycling of concrete and removal; transport and disposal of de-bris.

CDW sorting at demolition site depends on the method of demolition. Method of demolition also will affect the possibility of reused and recycled CDW. Some types of store and sort of CDW at a demolition site is shown in Figure 2 [4].

2.2 Recycled aggregate technology from CDW

Plants processing recycled CDW are similar to natural aggregate plants. Only minor variations for the removal of contaminants are found. . Currently, recycling technology can be divided into 3 levels as fol-lows [1]: - Level 1: Includes a mobile crusher with some classification screens. This technology is quite simple,

opten located at a demolition site and recycled materials for reconstruction at that site. It is suitable in developing countries, where low cost burial CDW.

- Level 2: Includes equipments of level 1 with adding a metal separation and classification system in-cludes many different sizes. This technology may be installed at fixity or mobile with bigger capacity.

- Level 3: The complete technology including equipments of level 2 and adding a separation to remove the large pieces of wood, foam, plastic, nylon, etc. This separation can be by hand or mechanical re-moval. Small impurities can be removed by dry or wet screening, washing with high pressure water, pressing sludge, etc. This technology is used for recycled plants with medium and large capacity or put on the closed landfills. Up to now, there is no recycling center in Vietnam. One trial recycling plant was built as the result

of a research project [21]. This plant can recycle 40 tonnes CDW per hour and is in level 2 according to ACI [1].

3 PROPERTIES AND TECHNICAL REQUIREMENTS FOR RAs

3.1 Characteristics of RAs

In general, RAs derived from crushed concrete consist of 65–80 vol.% of natural coarse aggregate and fine aggregate and 20–35 vol. % of old cement paste. The latter is often more porous than the former (make more precise). Consequently, RAs are less homogeneous, less dense and more porous than the NAs.

Both open and closed recycling system can produce RAs achieving specifications of ASTM C33 [1]. RAs quality also can meet the requirements without washing even when there are fine-grained particles on their surfaces [9]. Hansen assumed that aggregates from concrete rubbles (RCAs) generally angular and rougher than NAs. O'Mahony supposed that when RAs is crushed from masonry (RMA), content of the fine particles is much more than that from concrete. This leads to decrease workability and strength of concrete containing recycled fine aggregates (RFA) [28].

In general, specific density of RAs is smaller than that of NAs because of the cement paste in RA par-ticles. Hansen [9] concluded that 16-32mm aggregate particles of RAs have about 30 vol.% of old cement mortar (paste?). Corresponding figures are 40 vol.% for the 8–16 mm fraction and 60 vol.% for the 4–8 mm fraction. Fine recycled aggregate particles below 4 mm contain approximately 20 wt.% of old cement paste, while the filler fraction 0–0.3 mm may contain as much as 65 wt.% of old cement paste.

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Water absorption of both RCA and RMA are higher than that of NAs’. Water absorption of RCA is from 3 to 12%. Water absorption of RMA is from 20 to 25%, while water absorption of RAs is only 0.5- 1.2% [31]. Water absorption of recycled fine aggregates is significant higher than that of recycled coarse aggregates. Water absorption of RAs and NAs was summarised in Table 2 [20, 34, 36].

Table 2. Water absorption level of RAs and NAs

Water absorption value (%) of NAs Water absorption value (%) of RAs Researchers Fine fraction

(< 5mm) Coarse fraction

(= 5mm) Fine fraction

(< 5mm) Coarse fraction

(= 5mm)

Levy and Helene 0.8 1.8 10.3 (concrete) 13.0(masonry)

5.6(concrete) 7.9(masonry)

Poon et al 1.01* 1.25* 11.2-14.2* 4.19-7.60*

Zaharieva et al 2.0

Particle sizes 4mm-to-dust

0.2 20mm-to-6mm

12.0 4mm-to-dust

6.0 20mm-to-6mm

Topcu and Guncan 1.5 0.5 hour immersion

1.5 0.5 hour immer-

sion N/A

7.0 (concrete) 0.5 hour immer-

sion

Khatib 0.8* 4mm-to-dust

0.5* 37.5mm-to-5mm

6.2 (concrete) 14.8 (masonry) 5mm-to-dust

N/A

Sagoe-Crentsil et al N/A 1.0* N/A 5.6 (concrete)*

14 mm Salem et al N/A 0.3* N/A 4.7* Sri Ravindrarajah et al 0.63* 0.3* 6.2 (concrete)* 5.68 (concrete)* Shayan and Xu 0.59 0.5-1.0 6.3 (concrete) 4.7 (concrete)

Gutiérrez and Juan N/A 4.5 16mm-to-4mm N/A 7.0 (concrete)

16mm-to-4mm

Kien [36] 1.6* 5mm-to-0.14mm

0.53* 25mm-to-5mm

11.3 (concrete)* 19.7 (masonry)* 5mm-to-0.14mm

6.5 (concrete)* 14.3 (masonry)* 25mm-to-5mm

Hung [20] 1.2* 5mm-to-0.14mm

0.52* 25mm-to-5mm

11.2 (concrete)* 17.5 (masonry)* 5mm-to-0.14mm

6.4 (concrete)* 15.2 (masonry)* 25mm-to-5mm

* Aggregate was immersed in water for 24 hours to determine the water absorption ratio.

Khalaf [15] stated that the pores contained within the recycled aggregates vary in size over a wide range. The largest pores can be seen easily by a microscope or even with the naked eye. The smallest pores are usually larger than the size of the gel pores contained in the cement paste. Some of the aggre-gate pores are closed. Others are open on the surface of the aggregate particle.

Los Angeles Abrasion of RAs is higher than that of NAs but most of RCA (including the worst type) also meet the requirements of ASTM C33 (Los Angeles abrasion <50% for construction , <40% for roads infrastructure) [9].

One of the problems inherent in use of RAs for manufacture of new concrete mixtures is the possibility of contaminants in original CDW debris passing into new concrete mixtures. Contaminants may be clay balls, bitumen joint seals, expansion joint fillers, gypsum, periclase refractory bricks, chlorides, organic materials, chemical admixtures, tramp steel and other metals, glass, lightweight bricks and concrete, weathered or fire damaged particles, particles susceptible to frost or alkali reactions, etc. [9].

To improve properties of RAs, several techniques have been developed, such as removing loose parti-cles through an ultrasonic cleaning method [13], separating old mortar from virgin aggregate by ball-milling [24] or by heating first and then rubbing [35].

In Vietnam, there is no study on microstructure of RA particles, content and contribution of pores in RAs. A few research result on properties of RAs and RAC has been published [36]. The absorption and desorption of water by porous RAs has not yet been investigated in detail.

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3.2 Standards and specifications for RAs

Many countries allow using RAs for concrete and most of specifications in the same standard with NAs. However, some countries only allow using RCA like as: RILEM (1994), ACI 555R [1], BRE Digest 433, JIS technical report TRA 0006.

In Vietnam, technical standards and specifications for using RAs in concrete are not available. Guide-line for recycling CDW technology and using RAs for construction from the research project [21] is still not approved by Ministry of Construction of Vietnam.

4 RECYCLED AGGREGATE CONCRETE

Crushed brick concrete has been known since Roman time. The first application is concrete canals of Eif-fel in Cologne, Germany in 1860 [9]. Mixture of brick debris with Portland cement was used to produce concrete products.

After the 2nd World War, brick rubbles was around 400-600 million m3. Many recycling centers were built in the Federal Republic of Germany. At the end of 1955, they recycled approximately 11.5 million m3 of crushed brick aggregate for reconstructing of 175.000 housing units. By the end of 1956, about 85% of CDW was cleared in Germany [9].

4.1 Properties of Recycled Aggregate Concrete mixture

A comprehensive experimental work has been carried out by Zhang et al. [40]. It is found that, in general, the mix design procedure for RAC does not differ much from that for conventional concrete. However, more water is required to attain a similar workability due to the high water absorption of RAs.

Mulheron and O’Mahony [26] compared the use of recycled coarse aggregate from concrete and ma-sonry. The result indicated that workability of RAC with RCA is much lower than that of RAC with NAC but RAC mixture containing RMA has workability is similar to mixture containing NAC. They assumed that RMA particles were less angular and rounder than RCA particles. This revealed that shape and sur-face texture of aggregate particles have important effects on concrete workability.

Many researchers have proposed different ways to improve workability of RAC such as: Hansen [9] concluded that RAs should moistened before mixing, this is the same point of Etxeberria et al. [7]. How-ever Khaloo [17] said that deemed prewetting of recycled clay brick aggregates to be unnecessary. Neville (1996) [27] supposed should not moisten for any types of aggregates for concrete because the ag-gregate particles can become quikly coated with cement paste, preventing the further ingress of water necessary for saturation.

Hansen [9] concluded that the air amount of concrete mixture containing RCA is higher than that of NAC mixture. This leads to gravity density of RAC mixture decreased 5-15% compared to NAC mixture. Katz (2003) [14] suggested that the amount of air bubbles in RAC mixture is 4 to 5% higher than that of NAC mixture. This is cause of the higher porosity of RAs.

4.2 Properties of Recycled Aggregate Concrete

Akhtaruzzaman and Hasnat [2] carried out some researches using well-burned brick as a coarse aggregate in concrete. They found that it was possible to achieve high strength concrete using crushed brick. Khaloo [17] used crushed clinker bricks as a coarse aggregate in concrete. He reported that only 7% compressive strength of the concrete is decreased compared to concrete made with natural aggregates. And 9.5% unit weight reduction of crushed brick concrete is found. Jankovic (2002) [12] investigated the effect of poly-mer additives at 0, 4 and 8% (referred to cement) on concrete performance using recycled brick aggre-gates. It showed that compressive strength and tensile strength of this concrete do not change compared to non-polymer concrete. Its waterproof ability and frost resistance are better. Concrete containing recycled brick aggregates possesses smaller shrinkage and elastic modulus, higher creep compared to that of non-polymer concrete.

4.2.1 Compressive strength

Many researchers have conducted experiments on compressive strength of RAC. The results indicated that compressive strength of RAC decreases when the amount of RAs alternative for NAs increases [9,

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39]. The decrease in compressive strength of crushed brick aggregate is greater than RCA. When replac-ing 100% by RCA, the concrete strength at 28 days decreased 19% while by RMA down 35% compared with the concrete used NAs. This is resulted from the low strength of crushed brick aggregate as a result of Los Angeles abrasion [5]. The influences of sources and replacement content of RAs on compressive strength are shown in Figure 4 and Figure 5.

Figure 4. Compressive strength versus replacement level (%) of coarse aggregate with RCA or RMA

(W/C = 0.8 maintained in all mixes) [5]

Figure 5. Influence of RCA content on RAC compressive strength [39]

The use of recycled fine aggregate (RFA) has an greater adverse effect on compressive strength of RAC [6, 32]. Khatib [18] has studied this effect in a free water cement ratio of W/C= 0.5 when replacing natural sand by RFAs from masonry and concrete. The result indicated that there was not significant de-crease on compressive strength after 90-day curing in water. The same compressive strength was obtained in RAC with 50% RFA from masonry compare to NAC [38]. Khatib attributed that the cementitious na-ture of fine particles from masonry which contributed to enhancement of the long-term compressive strength.

4.2.2 Uniaxial and splitting tensile strength

The uniaxial tensile strength of RAC using recycled coarse aggregate and natural fine aggregate is equal or less than 10% compared to that of NAC [9]. In the case of using both coarse and fine recycled aggre-gates, this strength is reduced about 10-20% compared to the NAC. This was tagreed with Rao J. et al. results [31]. The bending tensile strength of concrete with 100% RCA also decreased by 15-20% when compared to NAC.

Neville [27] and Poon and Chan [30] believed that tensile strengths of concrete were primarily governed by the quality of the interfacial transition zone (ITZ) between aggregate and mortar, rather than byproperties of aggregates. This conclusion agrees with the finding of Dhir [5] who reported that aggregate properties have more effectiveness on compressive strength than tensile strengths of concrete. For instance, when 100% coarse aggre-gate was replaced by masonry-derived aggregate, the reduction of compressive strength was ap-proximately 40% , but the flexural strength of the concrete reduced only 25% [5]. According to Xiao Li et al. [39], the flexural strength of concrete using 100% RCA decreased 31% compared to conven-tional concrete. Effects of RCA content replacing natural aggregate on uniaxial and splitting tensile strength of concrete at different W/C are shown in Figure 6.

Figure 6. Uniaxial/Splitting tensile strength as a function of RCA replacement percentage

for RAC [39]

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4.2.3 Elastic modulus

The elastic modulus of RAC decreased as the RAs replacement percentage increased and the elastic modulus of RAC with 100% RCA was about 40% lower than that of conventional concrete (using present sentence). Figure 7 indicates that the elastic modulus decreases with the increase of the replacement per-centage of RCA. Most of studies on elastic modulus of RAC reported that elastic modulus decreases as increasing RAs content. It can be reduced to 30-50% when replacing 100% NAs by RAs. The large amount of old mortar with comparatively low modulus of elasticity in RAC results in this reduction of elastic modulus of RAC [29, 31, 39].

Figure 7. Elastic modulus as a function of RCA replacement percentage [39]

Figure 8. Effect of replacing coarse or fine RAs on the water absorption values of RAC [22]

4.2.4 Water absorption

Levy and Helene [22] reported a significantly higher water absorption level of RAC contaning recycled fine concrete aggregate compare to the RAC containing recycled coarse aggregate, see Figure 8. The cause is that the high water absorption value of recycled concrete dust in RFA compare to coarse aggregate.

According to Hansen (1992) [9], the degree of permeability of concrete using RAs with W/C of 0.5-0.7 is up to five times higher than that of NAC. Some other studies also indicate that the permeability of RAC can be improved by the use of mineral additives such as fly ash, silicafume, etc [23].

4.3 Durability of Recycled Aggregate Concrete

Carbonization of RAC increases from 1.3-2.5 times at the age of 6 months compared with NAC [22]. Ac-cording Building Contractors Society of Japan (BCSJ) the degree of carbonization of RAC is 65% higher than that of NAC [3]. Besides, using RAs also increases the corrosion of reinforcing steel in reinforced concrete. The reinforcing steel corrosion resistance of RAC can be improved by reducing W/C.

Due to the large amount of old mortar which is attached to original aggregate particles in recycled ag-gregates, drying shrinkage and creep of recycled aggregate concrete are always from 40% to 80% higher than that of corresponding control concretes which are made with conventional aggregates [9]. Drying shrinkage of RAC is improved by using conventional sand.

There is evidence to support the fact that when recycled aggregate concrete is produced with coarse re-cycled aggregate which originates from structural grade concrete, frost resistance of the recycled aggre-gate concrete will be as good as, or better than the frost resistance of the original concrete [9].

No study has been reported on the detriment of alkali silica reaction of RAC produced from RAs which are produced from original concrete that has been damaged by alkali silica reactions. The differ-ences in chloride penetration between RAC and NAC have not yet been published.

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5 CONCRETE BRICK BLOCK USING RAC

Khalaf and DeVenny [16] have studied the performance of concrete block using RA from crushed bricks at high temperatures. Normal concrete with compressive strength of 35-45 MPa or high strength of 50-65 MPa can be produced by using coarse aggregate from crushed bricks. Concrete using crushed brick ag-gregates has smaller density. Fire resistance of concrete blocks using crushed brick aggregates is similar or better than that of the used granite stone.

In 2010, Ismail and Yaacob researched properties of concrete blocks using recycled fine aggregates from masonry. Test results showed that the replacement of natural sand by recycled fine aggregates at the levels of 50% and 75% improves compressive strength of the blocks [11]. However, when natural sand is completely replaced by recycled fine aggregate, compressive strength of test samples is lower than that of control sample.

Soutsos et al. [33] investigated the use of stone aggregates taken from waste concretes and bricks to replace coarse and fine-stone aggregates. The maximum replacement levels for RCA were determined to be 60% for the recycled coarse concrete fraction and 20% for the fine concrete fraction, will not have significant detrimental effect on the compressive strength concrete blocks. While the maximum replace-ment levels for RMA were determined to be 20% for the coarse fraction and 20% for the fine fraction.

6 CONCLUSIONS AND RECOMMENDATIONS

- Until now, using RAs in Vietnam is not much meanwhile a huge volume of construction demolition waste is annually disposed. It strongly impacts on environment and cost of construction projects. Hence, research on characteristics of RAs and performance of concrete containing RAs is desirable.

- Further studies of the microstructure and micro mechanical properties of RACs are recommended in the world and in Vietnam. The interfacial zone between RAs surface and new cement paste are also studied urgently needed. No studies have been reported on the susceptibility to alkali reactions of recy-cled aggregate concrete produced from recycled concrete aggregates that has been damaged by alkali reactions. Such studies are also urgently needed

- Water absorption of RAs is much higher than NAs. It revealed that there is a interconnected open pore system in RAs. This lead to self-curing possibility of RAs during hydration of RAC mixtures. There has not been any researches in Vietnam on this issue.

- Furthermore, it is necessary to understand the influence of chemical and mineral additives (such as fly ash, blast furnace slag) on Compressive strength, tensile strength, elastic modulus, shingkage, autoge-neous of RAC.

7 ACKNOWLEDGEMENT

The authors would like to thank the project DELPHE 743 financing to this study.

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