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Evaluation of the durability of concrete made with crushed glass aggregates
Journal of Cleaner Production 41 (2013) 7e14
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Evaluation of the durability of concrete made with crushed glass aggregates Sara de Castro, Jorge de Brito* Department of Civil Engineering, Architecture and Geo-resources, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 May 2012 Received in revised form 25 August 2012 Accepted 16 September 2012 Available online 1 October 2012
Contrasting with previous studies that aimed to evaluate the mechanical properties of concrete made with glass, this one focuses on their durability performance. For this, water absorption by capillarity and immersion, carbonation resistance, chloride penetration and shrinkage tests were performed. Mixes containing 0%, 5%, 10% and 20% of glass aggregates (GA) as replacement of natural aggregates (NA) were prepared. Also analysed is the influence of the size of the replaced aggregates (fine and coarse, separately or simultaneously), in a total of 10 concrete mixes. It was found that the particle size strongly affects the workability of concrete. Due to the lower density of the glass aggregates, the mixes made with glass had a lighter fresh density than the reference concrete. Although there is a decrease in the compressive strength as the replacement rate increases, mixes with GA are totally feasible, even though there are some differences in performance as a function of the particle size of the GA used to replace the NA. It was found that in most cases the GA do not significantly alter the durability-related properties of concrete. In a few instances there is a variation from the reference concrete of 15%, which is well within the expectable scatter of the results from experimental research. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Concrete Glass aggregates Durability
1. Introduction The construction industry has been one of the largest and most active sectors in Europe (Torgal and Jalali, 2007). Since it is responsible for consuming around 40% of extracted natural resources (Angulo et al., 2003) solutions must be found to help minimise the environmental problems generated, because of both the adverse impact on the environment and the excessive use of non-renewable natural resources (Matias and de Brito, 2004). According to Shi and Zheng (2007), the first attempt to incorporate glass waste in concrete occurred in the 1960s but it failed. It was found that concrete suffered serious and extensive expansion that led to cracking and fractures and the consequent loss of structural safety after some years. This was due to the interaction between the silica in the aggregates and the alkaline cement paste. In the last 10 years and due to new environmental regulation, that taxes the dumping of waste by weight and type, efforts have been renewed to produce concrete incorporating recycled glass. As a consequence of the higher costs of dumping, the increase in the number of new constructions and demolitions and the low cost of acquiring waste, the viability of concrete/mortars where glass aggregates (GA) are used to replace either natural aggregates (NA) or cement is being discussed again. Contrasting with previous
* Corresponding author. Tel.: þ351 218443659; fax: þ351 218443071. E-mail addresses: [email protected], [email protected] (J. de Brito). 0959-6526/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2012.09.021
studies (Cazacliu and Ventura, 2010; Ling and Poon, 2012a,b) that mostly aimed to evaluate the mechanical properties of concrete made with glass, this one focuses on its durability performance. After an introductory literature review, 10 concrete mixes containing various contents and sizes of GA were characterised in this study in terms of water absorption by capillarity and immersion, carbonation resistance, chloride penetration and shrinkage. The results are presented and discussed to show the feasibility of concrete with GA compared with conventional concrete. Mayer and Baxter (1997, 1998) proved the feasibility of producing concrete with 100% GA, 80% of type III cement (ASTM), 20% metakaolin and superplasticizer. Kralj (2009) confirmed the viability of lightweight concrete with expanded GA as well as of using this concrete as recycled aggregates for new lightweight concrete with expanded GA. Su and Chen (2002) confirmed the added value of using glass in asphalt, given the similarity of its mechanical properties and those of asphalt without glass. After one year of on-site experience the authors concluded that glass reflects nocturnal light and so allows better night visibility, enhances traffic safety due to its higher friction coefficient and improves the permeability conditions. Arabani (2011) reached the same conclusions with respect to lowcost glass waste, since it reduced the costs of bituminous pavements and significantly improved their dynamic performance. The author stated that the incorporation of GA up to a limit of 15% increased the stiffness modulus of the pavements. The United States of America has a strong tradition of building urban, road and
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airport pavements with GA for over 50 years because of difficulties in getting rid of glass waste. Poutos et al. (2006) tested the effect of low and high temperatures, 20 C and 60 C respectively, on concrete with GA and concluded that it had great thermal stability due to the low specific heat and thermal conductivity compared with concrete with rock aggregates. The authors also concluded that this type of concrete is ideal for casting in buildings where thermal stability is paramount, and for cold climate casting. Studies on concrete and mortar with glass report a clear distinction in terms of performance, depending on the size of the aggregates replaced. There is some tradition of using glass to replace part of the cement or part of the fine, coarse and mixed aggregate and as a powder to mitigate the alkaliesilica reaction (ASR) between the cement paste and a reactive aggregate. The literature review is presented in terms of these different replacement options and the main conclusions of each study are mentioned. 1.1. Glass as fine aggregate Park et al. (2004) evaluated the consequences of incorporating fine recycled glass, replacing from 0% to 70% of sand, on the physical and mechanical properties of concrete. It was concluded that the slump and compaction efficiency decrease as glass is incorporated due to the irregular shape of the granules, which promotes friction between particles and encapsulation of air bubbles in the cement paste. The bond between the GA and the cement paste was weak, which caused significant losses in the mechanical properties analysed (compressive, tensile and flexural strength). Corinaldesi et al. (2004) determined the maximum size of the glass particles without ASR. They replaced 30% and 70% of the mass of sand. No detrimental effect of the glass particles (smaller than 100 mm) was detected, and in fact the compressive and flexural strength went up even though the water content increased. The images obtained using an electronic microscope revealed densification of the mortar structure. Lam et al. (2007) studied the application of coloured GA in nonstructural concrete. They first compared various contents of metakaolin and fly-ash to mitigate ASR and proved that fly-ash was more effective. It was concluded that it is not possible to make mixes with 100% GA without any ASR-mitigating addition. It was also concluded that it is necessary to incorporate at least 10% of flyash in mixes with GA incorporation above 25%. Increasing the glass content improves the 90-day compressive strength for the same fly-ash content and decreases the water absorption, regardless of the fly-ash content. Oliveira et al. (2008) evaluated the replacement of natural sand with glass waste in structural concrete, in amounts ranging from 0% to 100%. It was concluded that raising the glass content in mixes with 30% of fly-ash increases the compressive strength by around 25%. The finer fraction of the glass has a filler-like behaviour and leads to better packaging of the particles while its large specific surface engenders a better distribution of the cement paste. Therefore the mechanical strength of the specimens increases as the thickness of the paste between the aggregate particles decreases. Limbachiya (2008) evaluated the mechanical and durabilityrelated characteristics of concrete with replacement ratios of natural sand/coloured glass sand ranging from 0% to 50% by mass. Decreases in slump and mix stability were observed for ratios higher than 30%. Compressive strength did not suffer for ratios lower than 20%. Similar behaviour for water absorption and ASR was observed for ratios up to 15%. Wang (2008) studied the incorporation of glass sand in three mixes of varying strength, 21 MPa, 28 MPa and 35 MPa, in ratios
from 0% to 80%. It was found that compressive strength falls for replacement rates higher than 20%. In terms of durability it was found that electric resistance and resistance to sulphate attack both increase with glass incorporation and specimen age. This result was proven by the high ultra-sonic velocities found and the analysis of optical microscope and scanning electron microscope images. The existence of hydrated C-H-L composites on the interface of the aggregates with the cement paste, which favour the strength and durability of the mixes, was also checked. Ismail and Al-Hashmi (2008) analysed the potential for ASR when replacing from 0% to 20% of natural sand by glass sand. Losses of slump with higher ratios of glass incorporation were found, due to the irregular shape of the glass granules, but such losses were not significant. A pozzolanic effect was evident in 28-day compressive strength for a 20% replacement ratio. Wang and Huang (2010) evaluated the performance of selfcompacting concrete where natural sand was replaced with glass sand in amounts from 0% to 30%. It was found that the diameter in the flow table test increased for replacement ratios up to 30% and compressive strength decreased even though the ultra-sonic velocity indicated a denser inner structure. The finer fraction of the glass sand is responsible for filling the pores and creating this denser structure, which is less permeable and more resistant to the attack of sulphates and chlorides. 1.2. Glass as coarse aggregate Topçu and Canbaz (2003) studied the replacement of 4e6 mm gravel by crushed GA in ratios from 0% to 60%. Increasing the glass content resulted in a decrease in the slump, air content, and density and in increased workability in the flow table test and the vb test. The mechanical properties decline as more glass is incorporated in the mixes. After analysing the aggregate’s reactivity, the authors concluded that ASR must be taken into account when glass is used to make concrete. 1.3. Glass as fine and coarse aggregate Kou and Poon (2008) evaluated the performance of selfcompacting concrete when fine and coarse GA was incorporated in ratios from 0% to 45%. Adding glass to the mixes increased their slump, the blockage coefficient and air content. The mechanical properties and shrinkage decreased and resistance to chloride penetration improved. The authors found that ASR is efficiently suppressed by adding 33% (by mass) of fly-ash. 1.4. Glass as cement replacement Shao et al. (1999) analysed the performance of mortars made with glass partially replacing cement. They concluded that the particle size has a clear influence on mortar performance. Finer glass particles led to an increase in the reactivity of glass with lime, improved compressive strength and decreased shrinkage. Oliveira et al. (2008) determined the influence of crushed glass of various sizes on mortars. The mixes were made by replacing from 0% to 40% of the cement. They concluded that mortars made with 45e75 mm glass particles improve in terms of compressive strength, have a denser cementitious matrix and are less liable to expansive reactions such as ASR. Shwarz et al. (2008) developed a comparative study of the durability characteristics of concrete made with glass powder and fly-ash. Mechanical tests and observations were performed on the hydration process and it was found that 10% is the optimal replacement ratio of cement with glass powder. The glass powder led to higher initial compressive strength than fly-ash but at 90
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days the trend reverses, though the difference is only 5%. The chloride penetration test proved the densification of the inner structure of the mortars with glass. The ASTM C1260 test proved that for similar replacement ratios adding fly-ash is more efficient in terms of mitigating the expansion caused by ASR. Jain and Neithalath (2009) made a comparative study of the chloride-related performance of concrete with glass powder and fly-ash. In the accelerated penetration test the authors found a refinement of the cementitious matrix of concrete made with glass in the long-term and that, for the same replacement ratio, the behaviour of the mixes was similar for the two additions. In the non-stationary penetration test the addition of fly-ash proved to be more efficient. That was attributed to the formation of chloride composites because of the high alumina content, which results from the smaller pore size and the increase of tortuosity. 1.5. Glass as fine aggregate and as cement replacement Shayan and Xu (2005) carried out a study to evaluate the incorporation of glass sand and powder to replace natural sand and cement, respectively. They detected a pozzolanic reaction of glass with cement that contributed to the development of compressive strength. The densification of the inner structure also increases the concrete mixes’ resistance to chloride penetration. There was no expansive reaction related to the incorporation of glass sand. Taha and Nounu (2007a) studied the use of glass instead of natural sand and cement. They found fractures in the aggregate’s surface caused by the mechanical crushing of glass. The addition of glass to the mixes reduced their consistency and the bonding between the aggregates and the cement paste, due to their smooth surface and insignificant water absorption. This low absorption makes the concrete less permeable and promotes its durability by restricting water and ion migration within the matrix. Taha and Nounu (2007b) used pozzolanic glass powder to mitigate ASR in concrete with incorporation of fine recycled glass aggregates. The glass powder led to changes in the concentration of hydroxide ions (OH) in the matrix pores. This is considered to be the direct cause of the reduced risk of expansion due to ASR. Since the pozzolanic reaction occurs earlier than ASR, the alkaline content of the paste is consumed in the creation of hydrated CeHeS gels, and there are not enough ions in the later stages of cement hydration. Wang (2009) determined the physical and mechanical characteristics of low-strength concrete with glass sand from LCD panels. It was found that this addition leads to a decrease in compressive strength and an increase in ultra-sonic velocity. Even though the matrix becomes denser the contact surface between aggregates and cement impairs proportional strength increments.
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panels, washed and treated in a plant. The concrete was made with CEM II A-L 42.5 R cement and tap water. 2.2. Concrete mixes Ten concrete mixes were produced: the reference concrete (with no GA) and mixes with NA/GA replacement ratios of 5%, 10% and 20% of the overall volume of aggregates. In order to evaluate the influence of the size of the recycled aggregates, for each of these ratios mixes were made where only fine aggregates, only coarse aggregates and both aggregate sizes were replaced. The following mixes were thus produced: RC (reference concrete); B05C (coarse NA replaced by coarse GA at a ratio of 5% of the overall volume of aggregate); B10C (coarse NA replaced by coarse GA at a ratio of 10% of the overall volume of aggregate); B20C (coarse NA replaced by coarse GA at a ratio of 20% of the overall volume of aggregate); B05F; B10F; B20F (same for fine aggregates); B05FC; B10FC; B20FC (same fine and coarse aggregates). Table 1 presents the volume of fine and coarse aggregates replaced when 5%, 10% and 20% of the total aggregates volume is replaced, for each mix. It also presents the results of the water/ cement (w/c) ratio for each of the mixes in order to maintain the workability interval (RC 10 mm) for all the mixes. Fine aggregates here are those that pass through the 4 mm sieve and coarse aggregates are those retained in the same sieve. A maximum aggregate particle size of 22.4 mm was considered. However, in the case of the GA only aggregates with particle size below 11.2 mm were available. The replacement of NA with GA was done by sieve interval in order to guarantee that the aggregate’s size distribution in every mix of concrete with glass was the same as that of the reference concrete. No admixtures or additions were used in this research. Every mix has a slump of 127 10 mm, to compare equivalent concrete uses. 2.3. Aggregate testing The aggregates’ tests were conducted according to the following standards: size grading (sieving method) e EN 933-1 (2000); size distribution (test sieves, nominal size of the apertures) e EN 933-2 (1999); particle density and water absorption e EN 1097-6 (2003); bulk density and void content e EN 1097-3 (2003); Los Angeles wear test e LNEC E-237 (1970), and particle shape (shape index) e EN 933-4 (2008). 2.4. Fresh concrete tests
2. Experimental work
The fresh concrete tests were conducted according to the following standards: slump test (Abrams cone) e EN 12350-2 (2002), and density e EN 12350-6 (2002).
2.1. Materials
2.5. Hardened concrete tests
Natural aggregates (NA) and recycled glass aggregates (GA) were used in this research. The NA was coarse crushed gravel and limestone river sand. The GA came from building and car window
The hardened concrete tests were conducted according to the following standards: compressive strength e EN 12390-3 (2003); water absorption by capillarity e LNEC E-393 (1993); water
Table 1 Main characteristics of the concrete mixes analysed.
Overall replacement rate of aggregates (%) Fine aggregates’ replacement rate (%) Coarse aggregates’ replacement rate (%) Effective w/c ratio
RC
C05C
C10C
C20C
C05F
C10F
C20F
C05FC
C10FC
C20FC
0 0 0 0.55
5.00 0 9.07 0.55
10.00 0 18.15 0.55
19.60 0 35.57 0.55
5.00 11.14 0 0.55
10.00 22.27 0 0.57
20.00 44.54 0 0.58
5.00 5.57 4.54 0.55
10.00 11.14 9.07 0.55
20.00 22.27 18.15 0.57
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Table 2 Results of tests on aggregates. Sand
Oven dried particle density [kg/dm3] Saturated surface dried particle density [kg/dm3] Water absorption [%] Bulk density [kg/dm3] Los Angeles coefficient [%] Shape index [%]
Gravel 0.5
Fine
Coarse
2.579 2.582 0.1 1.500
2.624 2.625 0.05 1.550
e
e
Gravel
Fine fraction 2.659 2.683 0.9 1.440 34.2 18.6
absorption by immersion (at atmospheric pressure) e LNEC E-394 (1993); carbonation resistance e LNEC E-391 (1993); chloride migration coefficient (non-stationary test) e LNEC E-463 (2004), and shrinkage e LNEC E-398 (1993). 3. Results and discussion 3.1. Properties of aggregate As seen in Table 2 the particles density values of the GA are always lower than those of the other aggregates. As expected, the same was true for the bulk density. In terms of water absorption the hydrophobic behaviour of the GA is evident, leading to results close to zero in this test. The Los Angeles wear test reveals GA values that are higher than those for NA. This is due to the mechanical impact process that highlights the fragile and breakable characteristics of glass. The shape index values show that the various coarse natural materials have a similar geometry. However, the same index for the coarse glass particles is very high, denoting a significant percentage of elongated particles. This property greatly depends on the GA’s origin. In this study plane glass from building and car window panels was used and each particle of its coarse (over 4 mm) fraction exhibits the original plane surface, leading to this elongated shape. 3.2. Fresh concrete properties 3.2.1. Workability The objective was to reach an approximately equal slump value in all mixes, with a tolerance of 10 mm relative to the reference mix. As seen in Table 3 the slump of all mixes was restricted to the 127 10 mm range. The first conclusion drawn from this table and from Fig. 1 is that the behaviour of the mixes is highly dependent on the size of the aggregates replaced. While for coarse aggregates there is a slight increase in the slump value as that replacement ratio increases for a constant w/c ratio of 0.55, the opposite happens for fine aggregates. As the fines replacement ratio increases, the loss of workability means the w/c ratio has to increase to comply with the slump range. The mix of fine and coarse aggregates has an intermediate behaviour, leading to the w/c ratio increasing from 0.55 to 0.57 for an overall replacement of 20%.
Glass
Coarse fraction
1
2
2.654 2.686 1.2
2.648 2.682 1.3 1.430 30.8 17.9
2.649 2.675 1.0 1.430 31.9 12.0
Fine fraction 2.511 2.512 0.03 1.360 38.4 30.5
3.3. Hardened concrete properties 3.3.1. Compressive strength Even though the compressive strength of glass is around 1000 MPa, the strength of concrete decreases with increasing glass incorporation (Fig. 3). This is caused by the weak bond between GA and the cement paste and the higher w/c ratio of the mixes with fine GA. The performance of the mixes clearly differs with the size of aggregate replaced. The C20C mix (with GA only) is 3% lower than the RC while the C20F (with fine GA only) and C20FC (with fine and coarse GA) mixes decline by 14% and 22%, respectively. Further analysis of the compressive strength and other mechanical properties of these concrete mixes are presented in another paper, still unpublished.
Replacement ratio (%)
CF CC CFC
5
10
20
w/c
h [mm]
w/c
h [mm]
w/c
h [mm]
w/c
h [mm]
0.55
127
0.55 0.55 0.55
124.5 131.5 125.5
0.57 0.55 0.55
125 132.5 122.5
0.58 0.55 0.57
121.5 134.5 129.5
2.524 2.524 0.03
3.2.2. Density Fig. 2 and Table 4 show the density values of the concrete mixes. It can be stated that there is a clear reduction of the fresh density with the incorporation of GA. This trend is explained by the difference between NA and GA in terms of particles density. The changes in the mixes for which different sized aggregates are replaced are due to the replaced volume having changed. When incorporating fine GA a replacement of only 20% of the overall volume of aggregates corresponds to a replacement of 44.54% of all fines, but when incorporating coarse GA only and fine and coarse GA simultaneously it corresponds to a replacement of 35.57% of all coarse and 40.42% of all fines and coarse, respectively. Therefore, the smallest volume of NA is replaced in the case of coarse aggregates only, followed by the simultaneous replacement of fines and coarse and finally the replacement of fine aggregates only. Furthermore, the same order was followed in terms of extra water required to comply with the stipulated slump range. Therefore, the water addition causes an increase of the volume of voids and consequently greater porosity and lower fresh density.
Table 3 Abrams cone slump results.
0
Coarse fraction
Fig. 1. Slump test results.
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Fig. 2. Fresh density results. Fig. 4. Height of water absorbed by capillary action at 72 h compared with the reference mix.
Table 4 Fresh-state concrete density (kg/dm3). Replacement ratio (%)
CF CC CFC
0
5
10
20
2.365
2.348 2.365 2.336
2.348 2.337 2.350
2.339 2.298 2.319
3.3.2. Water absorption by capillarity Fig. 4 shows that the concrete mixes with GA perform well compared with the RC in terms of height of water absorption by capillary action: reductions between 9% and 18.4% (for any size of aggregates in up to 10% replacement ratios). In terms of water absorption (Fig. 5) there is again a reduction of 14e24% respectively for 5% and 10% of replacement of fines. Generally, there is a better relative performance for concrete mixes with a simultaneous incorporation of fine and coarse GA for all replacement ratios and mixes with fines and coarse aggregates for replacement rates up to 10%. The C20F mix was characterised by its high roughness and w/c ratio, which contributed to the increased porosity of its inner structure, leading to a poorer performance of this mix. 3.3.3. Water absorption by immersion Looking at Fig. 6 it is evident that the performance of the mixes with GA is very similar to that of the RC. The variations range from 1.3% to 9%, which results in an almost constant value. This may be due to the weak water absorption of the GA and the similar microstructure of the mixes. In the water absorption by immersion test the GA provided concrete with characteristics almost identical to those of the RC. However, the size of the replaced aggregates again has some influence on the results. The mixes with coarse GA
Fig. 3. Compressive strength results compared with that of the reference mix.
Fig. 5. Water absorbed by capillary action at 72 h compared with the reference mix.
only have the lowest water absorption, mostly because they had the same w/c ratio as the RC, for all replacement ratios. The opposite occurred in the mixes with fine GA only, which generally had higher water absorption values, also a result of the w/c ratio (in this case higher) and consequently higher open porosity of the microstructure. 3.3.4. Carbonation resistance Fig. 7 shows the carbonation depth values of all the concrete mixes at various ages, relative to the RC.
Fig. 6. Water absorption compared with the reference mix.
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Fig. 7. Carbonation depth compared with the reference mix.
Generally, the carbonation depth of the mixes with GA is similar to or lower than that of the RC at 91 days. The natural decrease of the carbonation depth for older concrete is also clear in every mix. There is therefore a progressive refinement of the cementitious matrix, which seems to be more significant in the mixes with GA than in the RC. However, the differences from the RC are relatively small and therefore it can be stated that the GA contribute to carbonation resistance in the same way as the NA. These conclusions are approximately the same as those for the water absorption by immersion test since these tests are influenced by the same factors. 3.3.5. Chloride penetration resistance Figs. 8 and 9 show the values for the depth of penetration of chlorides for all the concrete mixes at 28 and 91 days, relative to the RC. The results at 28 days are somewhat inconclusive and the absence of trends with GA ratio incorporation for any of the size ranges seems to indicate experimental problems connected with the environmental conditions of the dry chamber and with adjustment of the equipment. However, there is a general trend towards a decline of the chloride penetration-related performance with GA incorporation. At 91 days just the RC and the mixes with coarse GA only were tested. It is found that there is some stability of the results as the replacement rate increases, from which it is concluded that adding glass does not significantly alter the behaviour of concrete in terms of chloride penetration, which is mostly governed by the quality of the cement paste, and this is similar in the mixes analysed. Nevertheless, there is a slight trend towards increasing chloride penetration as the GA ratio increases.
Fig. 8. Chloride penetration at 28 days compared with the reference mix.
Fig. 9. Chloride penetration at 91 days compared with the reference mix.
However, due to the problems mentioned above this property needs further research. 3.3.6. Shrinkage Fig. 10 shows the values of shrinkage for all concrete mixes at 91 days, relative to the RC. Variations from the RC range from 10% to 22% (mixes C10FC and C10C respectively). Mixes where fine and coarse GA coexist have better characteristics for replacement ratios higher than 5%; for example, the C10FC mix varies by 10% and the C20FC mix by 5%. This positive trend concerns the properties of these mixes that lie between those of the mixes with fine GA only and those with coarse GA only. While the first have a higher w/c ratio because of loss of workability caused by the higher specific surface of the fine GA, the second are impaired by the weak bond between the aggregates and the cement paste, caused by the low porosity of glass and the lower specific surface of the coarse GA. The mixes with both fine and coarse GA thus seem to
Fig. 10. Shrinkage at 91 days compared with the reference mix.
S. de Castro, J. de Brito / Journal of Cleaner Production 41 (2013) 7e14 Table 5 Synopsis of the study in terms of the NA/GA overall replacement ratio and the size of the replaced aggregate. Test
Percentage change Increase of the NA/GA replacement ratioa
Increase of the size of the replaced aggregateb
2.7%
13.6%
5.3%
10.1%
5.0%
13.4%
Compressive strength (28 days)
Water absorption by capillarity
(m/m)
(g/mm2)
Water absorption by immersion (%) 1.28%
3.8%
16%
21.7%
20%
6.5%3
10%
7.4%
91-day carbonation depth (mm)
91-day chloride diffusion coefficient (m2/s)c
91-day shrinkage (m/m)
Notes. a Represented by the change between RC and C20C. b Represented by the change between C20F and C20C. c At 28 days due to lack of data at 91 days.
benefit simultaneously from the good bond of the fine GA to the cement matrix and the relatively low w/c ratio of the mixes with coarse GA. 4. Conclusions This research analysed the durability performance of concrete with glass aggregates (GA). The experimental results enabled the following conclusions to be drawn: 1. The workability of concrete with glass is strongly affected by the particle size, leading to an increase in the w/c ratio from 0.55 to 0.58 for the mix with the 20% incorporation of fine GA; 2. There is a clear loss of the concrete’s fresh density as glass is incorporated; this is caused by the lower particle density of the glass; 3. Generally, there was a fall in the 28-day compressive strength because of the weak interface between the glass aggregates and the hardened cement paste, for the mixes with fine GA only and the higher w/c ratio; 4. The mixes with simultaneous incorporation of fine and coarse GA perform better in terms of water absorption by capillarity for every replacement amount tested, as do the mixes with either fine or coarse GA for replacement amounts up to 10%; 5. The performance of concrete with GA in terms of water absorption by immersion is very similar to that of the reference
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concrete (RC); this may be due to the very low water absorption of the GA and the similarity of all the mixes in terms of microstructure; 6. There is a general improvement in terms of carbonation resistance of concrete with GA in the long-term (tests at 56 and 91 days); but at 7 and 28 days the carbonation depth is greater in these mixes than in the RC and grows with the replacement rate; it is thus concluded that the cementitious matrix of concrete with GA is much more refined for older ages; 7. The performance of mixes with any size and combination of GA proved to be similar but slightly worse than that registered by the RC in terms of chloride penetration; the low water absorption of the GA and the similarity of the microstructure of the various mixes probably underlie this result; however, results were not conclusive because of experimental problems; 8. The shrinkage of concrete with GA is similar to that of the RC; nonetheless the mixes with the lowest shrinkage are those with mixed fine and coarse GA. Generally concrete with GA is completely feasible, even though there are some differences in performance as a function of the particle size of the GA used to replace natural aggregates. It was found that in most cases the GA do not alter the durability-related properties of concrete. In a few instances there is a variation from the reference concrete of 15%, which is well within the expectable scatter of the results from the experimental research. Recycled glass aggregates may be used in the construction industry, thereby helping to reduce the extraction of primary resources and to meet nations’ goals in terms of waste recycling. The will of the industry to absorb glass waste that is otherwise difficult to get rid of becomes economically viable if it is coupled with heavy taxation of waste dumping and raw materials’ extraction. In terms of the threat of alkaliesilica reaction between the aggregates and the cement paste, the experimental results of Serpa et al. (2013), using the ASTM 1260 test, reveal that the aggregates used in this research are not reactive enough to raise concerns about their use in concrete production. Table 5 summarises the results obtained in all durability-related tests conducted on hardened concrete. It shows the trends when the NA/GA replacement ratio (up to 20% of the overall volume of aggregates) or the size of the replaced aggregate increases. It confirms that increasing the size of the GA is beneficial for compressive strength (13.6%), water absorption by capillarity and immersion (10.1% and 3.8%, respectively), carbonation resistance (21.7%) and shrinkage (7.4%). The main difference between the mixes with fine and coarse GA was the significant increase of the w/c ratio in the fine GA mixes to offset workability loss. The interstitial water increases the matrix voids, which leads to these mixes performing badly. Acknowledgements The authors acknowledge the support of the research centre ICIST (Instituto de Engenharia de Estruturas, Território e Construção), IST, Technical University of Lisbon and FCT (Foundation for Science and Technology). References Angulo, S., Kahn, H., John, V., Ulsen, C., 2003. Methodology of characterization of construction and demolition waste (in Portuguese). In: VI Seminar Sustainable Development and Recycling in Construction e Recycled Materials and Their Applications, São Paulo, Brazil. Arabani, M., 2011. Effect of glass cullet on the improvement of the dynamic behaviour of asphalt concrete. Construction and Building Materials 25 (3), 1181e1185.
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Cazacliu, B., Ventura, A., 2010. Technical and environmental effects of concrete production: dry batch versus central mixed plant. Journal of Cleaner Production 18, 1320e1327. Corinaldesi, V., Gnappi, G., Moriconi, G., Montenero, A., 2004. Reuse of ground waste glass as aggregate for mortars. Waste Management 25 (2), 197e201. Ismail, Z.Z., Al-Hashmi, E.A., 2008. Recycling of waste glass as partial replacement for fine aggregate in concrete. Waste Management 29 (2), 655e659. Jain, J.A., Neithalath, N., 2009. Chloride transport in fly ash and glass powder modified concretes e influence of the test methods in microstructure. Cement and Concrete Composites 32 (2), 148e156. Kou, S.C., Poon, S.C., 2008. Properties of self-compacting concrete prepared with recycled aggregate. Cement and Concrete Composites 31 (9), 107e113. Kralj, D., 2009. Experimental study of recycling lightweight concrete with aggregates containing expanded glass. Process Safety and Environmental Protection 87 (4), 267e273. Lam, C.S., Poon, C.S., Chan, D., 2007. Enhancing the performance of pre-cast concrete blocks incorporating waste glass e ASR consideration. Cement and Concrete Composites 29 (8), 616e625. Limbachiya, M.C., 2008. Bulk engineering and durability properties of washed glass sand concrete. Construction and Building Materials 23 (2), 1078e1083. Ling, T.-C., Poon, C.-S., 2012a. A comparative study on the feasible use of recycled beverage and CRT funnel glass as fine aggregate in cement mortar. Journal of Cleaner Construction 29e30, 46e52. Ling, T.-C., Poon, C.-S., 2012b. Feasible use of recycled CRT funnel glass as heavyweight fine aggregate in barite concrete. Journal of Cleaner Construction 33, 42e49. Matias, D., de Brito, J., 2004. Incorporation of admixtures in concrete made with crushed concrete recycled aggregates (in Portuguese). In: Congress Construction 2004. FEUP, Porto, Portugal, pp. 339e344. Mayer, C., Baxter, S., 1997. Use of Recycled Glass for Concrete Masonry Blocks. Final Report 97(15). New York State Energy Research and Development Authority, USA, Albany, New York. Mayer, C., Baxter, S., 1998. Use of Recycled Glass and Fly Ash for Pre Cast Concrete. Rep. NYCERDA, 98(15). New York State Energy Research and Development Authority, USA, New York. Oliveira, L.A., Castro-Gomes, J.P., Santos, P., 2008. Mechanical and durability properties of concrete with ground waste glass sand. In: 11th International Conference on Durability of Building Materials and Components, Istanbul, Turkey.
Park, S.B., Lee, B.C., Kim, J.H., 2004. Studies on mechanical properties of concrete containing waste glass aggregates. Cement and Concrete Research 34 (12), 2181e2189. Poutos, K.H., Alani, A.M., Walden, P.J., Sangha, C.M., 2006. Relative temperature changes within concrete made with glass aggregates. Construction and Building Materials 22 (4), 557e565. Serpa, D., Santos Silva, A., Santos, M., de Brito, J., 2013. Behaviour of glass in cementbased materials: its role on ASR. Materials Science Forum 730e732, 415e420. Shao, Y., Lefort, T., Moras, S., Rodriguez, D., 1999. Studies on concrete containing ground waste glass. Concrete and Cement Research 30 (1), 91e100. Shayan, A., Xu, A., 2005. Performance of glass powder as a pozzolanic material in concrete: a field trial on concrete slabs. Cement and Concrete Research 36 (3), 457e468. Shi, C., Zheng, K., 2007. A review on the use of waste glasses in the production of cement and concrete. Resources, Conservation and Recycling 52 (2), 234e247. Shwarz, N., Cam, H., Neithalath, N., 2008. Influence of a fine glass powder on the durability characteristics of concrete and its comparison with fly ash. Cement and Concrete Composites 30 (6), 486e496. Su, N., Chen, J.S., 2002. Engineering properties of asphalt concrete made with recycled glass. Resources, Conservation and Recycling 35 (4), 259e274. Taha, B., Nounu, G., 2007a. Properties of concrete containing mixed colour waste recycled glass as sand and cement replacement. Construction and Building Materials 22 (5), 713e720. Taha, B., Nounu, G., 2007b. Using lithium nitrate and pozzolanic glass powder in concrete as ASR suppressors. Cement and Concrete Composites 30 (6), 497e505. Topçu, I.B., Canbaz, M., 2003. Properties of concrete containing waste glass. Cement and Concrete Research 34 (2), 267e274. Torgal, F.P., Jalali, S., 2007. Sustainable construction. The case of construction materials (in Portuguese). In: Congress Construction 2007. Coimbra University, Coimbra, Portugal. Wang, H., 2008. A study of the effects of LCD glass sand on the properties of concrete. Waste Management 29 (1), 335e341. Wang, H.Y., 2009. A study of the engineering properties of waste LCD glass applied to controlled low strength materials concrete. Construction and Building Materials 23 (6), 2127e2131. Wang, H., Huang, W., 2010. Durability of self-consolidating concrete using waste LCD glass. Construction and Building Materials 24 (6), 1008e1013.
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Evaluation of the durability of concrete made with crushed glass aggregates Sara de Castro, Jorge de Brito* Department of Civil Engineering, Architecture and Geo-resources, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 May 2012 Received in revised form 25 August 2012 Accepted 16 September 2012 Available online 1 October 2012
Contrasting with previous studies that aimed to evaluate the mechanical properties of concrete made with glass, this one focuses on their durability performance. For this, water absorption by capillarity and immersion, carbonation resistance, chloride penetration and shrinkage tests were performed. Mixes containing 0%, 5%, 10% and 20% of glass aggregates (GA) as replacement of natural aggregates (NA) were prepared. Also analysed is the influence of the size of the replaced aggregates (fine and coarse, separately or simultaneously), in a total of 10 concrete mixes. It was found that the particle size strongly affects the workability of concrete. Due to the lower density of the glass aggregates, the mixes made with glass had a lighter fresh density than the reference concrete. Although there is a decrease in the compressive strength as the replacement rate increases, mixes with GA are totally feasible, even though there are some differences in performance as a function of the particle size of the GA used to replace the NA. It was found that in most cases the GA do not significantly alter the durability-related properties of concrete. In a few instances there is a variation from the reference concrete of 15%, which is well within the expectable scatter of the results from experimental research. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Concrete Glass aggregates Durability
1. Introduction The construction industry has been one of the largest and most active sectors in Europe (Torgal and Jalali, 2007). Since it is responsible for consuming around 40% of extracted natural resources (Angulo et al., 2003) solutions must be found to help minimise the environmental problems generated, because of both the adverse impact on the environment and the excessive use of non-renewable natural resources (Matias and de Brito, 2004). According to Shi and Zheng (2007), the first attempt to incorporate glass waste in concrete occurred in the 1960s but it failed. It was found that concrete suffered serious and extensive expansion that led to cracking and fractures and the consequent loss of structural safety after some years. This was due to the interaction between the silica in the aggregates and the alkaline cement paste. In the last 10 years and due to new environmental regulation, that taxes the dumping of waste by weight and type, efforts have been renewed to produce concrete incorporating recycled glass. As a consequence of the higher costs of dumping, the increase in the number of new constructions and demolitions and the low cost of acquiring waste, the viability of concrete/mortars where glass aggregates (GA) are used to replace either natural aggregates (NA) or cement is being discussed again. Contrasting with previous
* Corresponding author. Tel.: þ351 218443659; fax: þ351 218443071. E-mail addresses: [email protected], [email protected] (J. de Brito). 0959-6526/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2012.09.021
studies (Cazacliu and Ventura, 2010; Ling and Poon, 2012a,b) that mostly aimed to evaluate the mechanical properties of concrete made with glass, this one focuses on its durability performance. After an introductory literature review, 10 concrete mixes containing various contents and sizes of GA were characterised in this study in terms of water absorption by capillarity and immersion, carbonation resistance, chloride penetration and shrinkage. The results are presented and discussed to show the feasibility of concrete with GA compared with conventional concrete. Mayer and Baxter (1997, 1998) proved the feasibility of producing concrete with 100% GA, 80% of type III cement (ASTM), 20% metakaolin and superplasticizer. Kralj (2009) confirmed the viability of lightweight concrete with expanded GA as well as of using this concrete as recycled aggregates for new lightweight concrete with expanded GA. Su and Chen (2002) confirmed the added value of using glass in asphalt, given the similarity of its mechanical properties and those of asphalt without glass. After one year of on-site experience the authors concluded that glass reflects nocturnal light and so allows better night visibility, enhances traffic safety due to its higher friction coefficient and improves the permeability conditions. Arabani (2011) reached the same conclusions with respect to lowcost glass waste, since it reduced the costs of bituminous pavements and significantly improved their dynamic performance. The author stated that the incorporation of GA up to a limit of 15% increased the stiffness modulus of the pavements. The United States of America has a strong tradition of building urban, road and
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airport pavements with GA for over 50 years because of difficulties in getting rid of glass waste. Poutos et al. (2006) tested the effect of low and high temperatures, 20 C and 60 C respectively, on concrete with GA and concluded that it had great thermal stability due to the low specific heat and thermal conductivity compared with concrete with rock aggregates. The authors also concluded that this type of concrete is ideal for casting in buildings where thermal stability is paramount, and for cold climate casting. Studies on concrete and mortar with glass report a clear distinction in terms of performance, depending on the size of the aggregates replaced. There is some tradition of using glass to replace part of the cement or part of the fine, coarse and mixed aggregate and as a powder to mitigate the alkaliesilica reaction (ASR) between the cement paste and a reactive aggregate. The literature review is presented in terms of these different replacement options and the main conclusions of each study are mentioned. 1.1. Glass as fine aggregate Park et al. (2004) evaluated the consequences of incorporating fine recycled glass, replacing from 0% to 70% of sand, on the physical and mechanical properties of concrete. It was concluded that the slump and compaction efficiency decrease as glass is incorporated due to the irregular shape of the granules, which promotes friction between particles and encapsulation of air bubbles in the cement paste. The bond between the GA and the cement paste was weak, which caused significant losses in the mechanical properties analysed (compressive, tensile and flexural strength). Corinaldesi et al. (2004) determined the maximum size of the glass particles without ASR. They replaced 30% and 70% of the mass of sand. No detrimental effect of the glass particles (smaller than 100 mm) was detected, and in fact the compressive and flexural strength went up even though the water content increased. The images obtained using an electronic microscope revealed densification of the mortar structure. Lam et al. (2007) studied the application of coloured GA in nonstructural concrete. They first compared various contents of metakaolin and fly-ash to mitigate ASR and proved that fly-ash was more effective. It was concluded that it is not possible to make mixes with 100% GA without any ASR-mitigating addition. It was also concluded that it is necessary to incorporate at least 10% of flyash in mixes with GA incorporation above 25%. Increasing the glass content improves the 90-day compressive strength for the same fly-ash content and decreases the water absorption, regardless of the fly-ash content. Oliveira et al. (2008) evaluated the replacement of natural sand with glass waste in structural concrete, in amounts ranging from 0% to 100%. It was concluded that raising the glass content in mixes with 30% of fly-ash increases the compressive strength by around 25%. The finer fraction of the glass has a filler-like behaviour and leads to better packaging of the particles while its large specific surface engenders a better distribution of the cement paste. Therefore the mechanical strength of the specimens increases as the thickness of the paste between the aggregate particles decreases. Limbachiya (2008) evaluated the mechanical and durabilityrelated characteristics of concrete with replacement ratios of natural sand/coloured glass sand ranging from 0% to 50% by mass. Decreases in slump and mix stability were observed for ratios higher than 30%. Compressive strength did not suffer for ratios lower than 20%. Similar behaviour for water absorption and ASR was observed for ratios up to 15%. Wang (2008) studied the incorporation of glass sand in three mixes of varying strength, 21 MPa, 28 MPa and 35 MPa, in ratios
from 0% to 80%. It was found that compressive strength falls for replacement rates higher than 20%. In terms of durability it was found that electric resistance and resistance to sulphate attack both increase with glass incorporation and specimen age. This result was proven by the high ultra-sonic velocities found and the analysis of optical microscope and scanning electron microscope images. The existence of hydrated C-H-L composites on the interface of the aggregates with the cement paste, which favour the strength and durability of the mixes, was also checked. Ismail and Al-Hashmi (2008) analysed the potential for ASR when replacing from 0% to 20% of natural sand by glass sand. Losses of slump with higher ratios of glass incorporation were found, due to the irregular shape of the glass granules, but such losses were not significant. A pozzolanic effect was evident in 28-day compressive strength for a 20% replacement ratio. Wang and Huang (2010) evaluated the performance of selfcompacting concrete where natural sand was replaced with glass sand in amounts from 0% to 30%. It was found that the diameter in the flow table test increased for replacement ratios up to 30% and compressive strength decreased even though the ultra-sonic velocity indicated a denser inner structure. The finer fraction of the glass sand is responsible for filling the pores and creating this denser structure, which is less permeable and more resistant to the attack of sulphates and chlorides. 1.2. Glass as coarse aggregate Topçu and Canbaz (2003) studied the replacement of 4e6 mm gravel by crushed GA in ratios from 0% to 60%. Increasing the glass content resulted in a decrease in the slump, air content, and density and in increased workability in the flow table test and the vb test. The mechanical properties decline as more glass is incorporated in the mixes. After analysing the aggregate’s reactivity, the authors concluded that ASR must be taken into account when glass is used to make concrete. 1.3. Glass as fine and coarse aggregate Kou and Poon (2008) evaluated the performance of selfcompacting concrete when fine and coarse GA was incorporated in ratios from 0% to 45%. Adding glass to the mixes increased their slump, the blockage coefficient and air content. The mechanical properties and shrinkage decreased and resistance to chloride penetration improved. The authors found that ASR is efficiently suppressed by adding 33% (by mass) of fly-ash. 1.4. Glass as cement replacement Shao et al. (1999) analysed the performance of mortars made with glass partially replacing cement. They concluded that the particle size has a clear influence on mortar performance. Finer glass particles led to an increase in the reactivity of glass with lime, improved compressive strength and decreased shrinkage. Oliveira et al. (2008) determined the influence of crushed glass of various sizes on mortars. The mixes were made by replacing from 0% to 40% of the cement. They concluded that mortars made with 45e75 mm glass particles improve in terms of compressive strength, have a denser cementitious matrix and are less liable to expansive reactions such as ASR. Shwarz et al. (2008) developed a comparative study of the durability characteristics of concrete made with glass powder and fly-ash. Mechanical tests and observations were performed on the hydration process and it was found that 10% is the optimal replacement ratio of cement with glass powder. The glass powder led to higher initial compressive strength than fly-ash but at 90
S. de Castro, J. de Brito / Journal of Cleaner Production 41 (2013) 7e14
days the trend reverses, though the difference is only 5%. The chloride penetration test proved the densification of the inner structure of the mortars with glass. The ASTM C1260 test proved that for similar replacement ratios adding fly-ash is more efficient in terms of mitigating the expansion caused by ASR. Jain and Neithalath (2009) made a comparative study of the chloride-related performance of concrete with glass powder and fly-ash. In the accelerated penetration test the authors found a refinement of the cementitious matrix of concrete made with glass in the long-term and that, for the same replacement ratio, the behaviour of the mixes was similar for the two additions. In the non-stationary penetration test the addition of fly-ash proved to be more efficient. That was attributed to the formation of chloride composites because of the high alumina content, which results from the smaller pore size and the increase of tortuosity. 1.5. Glass as fine aggregate and as cement replacement Shayan and Xu (2005) carried out a study to evaluate the incorporation of glass sand and powder to replace natural sand and cement, respectively. They detected a pozzolanic reaction of glass with cement that contributed to the development of compressive strength. The densification of the inner structure also increases the concrete mixes’ resistance to chloride penetration. There was no expansive reaction related to the incorporation of glass sand. Taha and Nounu (2007a) studied the use of glass instead of natural sand and cement. They found fractures in the aggregate’s surface caused by the mechanical crushing of glass. The addition of glass to the mixes reduced their consistency and the bonding between the aggregates and the cement paste, due to their smooth surface and insignificant water absorption. This low absorption makes the concrete less permeable and promotes its durability by restricting water and ion migration within the matrix. Taha and Nounu (2007b) used pozzolanic glass powder to mitigate ASR in concrete with incorporation of fine recycled glass aggregates. The glass powder led to changes in the concentration of hydroxide ions (OH) in the matrix pores. This is considered to be the direct cause of the reduced risk of expansion due to ASR. Since the pozzolanic reaction occurs earlier than ASR, the alkaline content of the paste is consumed in the creation of hydrated CeHeS gels, and there are not enough ions in the later stages of cement hydration. Wang (2009) determined the physical and mechanical characteristics of low-strength concrete with glass sand from LCD panels. It was found that this addition leads to a decrease in compressive strength and an increase in ultra-sonic velocity. Even though the matrix becomes denser the contact surface between aggregates and cement impairs proportional strength increments.
9
panels, washed and treated in a plant. The concrete was made with CEM II A-L 42.5 R cement and tap water. 2.2. Concrete mixes Ten concrete mixes were produced: the reference concrete (with no GA) and mixes with NA/GA replacement ratios of 5%, 10% and 20% of the overall volume of aggregates. In order to evaluate the influence of the size of the recycled aggregates, for each of these ratios mixes were made where only fine aggregates, only coarse aggregates and both aggregate sizes were replaced. The following mixes were thus produced: RC (reference concrete); B05C (coarse NA replaced by coarse GA at a ratio of 5% of the overall volume of aggregate); B10C (coarse NA replaced by coarse GA at a ratio of 10% of the overall volume of aggregate); B20C (coarse NA replaced by coarse GA at a ratio of 20% of the overall volume of aggregate); B05F; B10F; B20F (same for fine aggregates); B05FC; B10FC; B20FC (same fine and coarse aggregates). Table 1 presents the volume of fine and coarse aggregates replaced when 5%, 10% and 20% of the total aggregates volume is replaced, for each mix. It also presents the results of the water/ cement (w/c) ratio for each of the mixes in order to maintain the workability interval (RC 10 mm) for all the mixes. Fine aggregates here are those that pass through the 4 mm sieve and coarse aggregates are those retained in the same sieve. A maximum aggregate particle size of 22.4 mm was considered. However, in the case of the GA only aggregates with particle size below 11.2 mm were available. The replacement of NA with GA was done by sieve interval in order to guarantee that the aggregate’s size distribution in every mix of concrete with glass was the same as that of the reference concrete. No admixtures or additions were used in this research. Every mix has a slump of 127 10 mm, to compare equivalent concrete uses. 2.3. Aggregate testing The aggregates’ tests were conducted according to the following standards: size grading (sieving method) e EN 933-1 (2000); size distribution (test sieves, nominal size of the apertures) e EN 933-2 (1999); particle density and water absorption e EN 1097-6 (2003); bulk density and void content e EN 1097-3 (2003); Los Angeles wear test e LNEC E-237 (1970), and particle shape (shape index) e EN 933-4 (2008). 2.4. Fresh concrete tests
2. Experimental work
The fresh concrete tests were conducted according to the following standards: slump test (Abrams cone) e EN 12350-2 (2002), and density e EN 12350-6 (2002).
2.1. Materials
2.5. Hardened concrete tests
Natural aggregates (NA) and recycled glass aggregates (GA) were used in this research. The NA was coarse crushed gravel and limestone river sand. The GA came from building and car window
The hardened concrete tests were conducted according to the following standards: compressive strength e EN 12390-3 (2003); water absorption by capillarity e LNEC E-393 (1993); water
Table 1 Main characteristics of the concrete mixes analysed.
Overall replacement rate of aggregates (%) Fine aggregates’ replacement rate (%) Coarse aggregates’ replacement rate (%) Effective w/c ratio
RC
C05C
C10C
C20C
C05F
C10F
C20F
C05FC
C10FC
C20FC
0 0 0 0.55
5.00 0 9.07 0.55
10.00 0 18.15 0.55
19.60 0 35.57 0.55
5.00 11.14 0 0.55
10.00 22.27 0 0.57
20.00 44.54 0 0.58
5.00 5.57 4.54 0.55
10.00 11.14 9.07 0.55
20.00 22.27 18.15 0.57
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Table 2 Results of tests on aggregates. Sand
Oven dried particle density [kg/dm3] Saturated surface dried particle density [kg/dm3] Water absorption [%] Bulk density [kg/dm3] Los Angeles coefficient [%] Shape index [%]
Gravel 0.5
Fine
Coarse
2.579 2.582 0.1 1.500
2.624 2.625 0.05 1.550
e
e
Gravel
Fine fraction 2.659 2.683 0.9 1.440 34.2 18.6
absorption by immersion (at atmospheric pressure) e LNEC E-394 (1993); carbonation resistance e LNEC E-391 (1993); chloride migration coefficient (non-stationary test) e LNEC E-463 (2004), and shrinkage e LNEC E-398 (1993). 3. Results and discussion 3.1. Properties of aggregate As seen in Table 2 the particles density values of the GA are always lower than those of the other aggregates. As expected, the same was true for the bulk density. In terms of water absorption the hydrophobic behaviour of the GA is evident, leading to results close to zero in this test. The Los Angeles wear test reveals GA values that are higher than those for NA. This is due to the mechanical impact process that highlights the fragile and breakable characteristics of glass. The shape index values show that the various coarse natural materials have a similar geometry. However, the same index for the coarse glass particles is very high, denoting a significant percentage of elongated particles. This property greatly depends on the GA’s origin. In this study plane glass from building and car window panels was used and each particle of its coarse (over 4 mm) fraction exhibits the original plane surface, leading to this elongated shape. 3.2. Fresh concrete properties 3.2.1. Workability The objective was to reach an approximately equal slump value in all mixes, with a tolerance of 10 mm relative to the reference mix. As seen in Table 3 the slump of all mixes was restricted to the 127 10 mm range. The first conclusion drawn from this table and from Fig. 1 is that the behaviour of the mixes is highly dependent on the size of the aggregates replaced. While for coarse aggregates there is a slight increase in the slump value as that replacement ratio increases for a constant w/c ratio of 0.55, the opposite happens for fine aggregates. As the fines replacement ratio increases, the loss of workability means the w/c ratio has to increase to comply with the slump range. The mix of fine and coarse aggregates has an intermediate behaviour, leading to the w/c ratio increasing from 0.55 to 0.57 for an overall replacement of 20%.
Glass
Coarse fraction
1
2
2.654 2.686 1.2
2.648 2.682 1.3 1.430 30.8 17.9
2.649 2.675 1.0 1.430 31.9 12.0
Fine fraction 2.511 2.512 0.03 1.360 38.4 30.5
3.3. Hardened concrete properties 3.3.1. Compressive strength Even though the compressive strength of glass is around 1000 MPa, the strength of concrete decreases with increasing glass incorporation (Fig. 3). This is caused by the weak bond between GA and the cement paste and the higher w/c ratio of the mixes with fine GA. The performance of the mixes clearly differs with the size of aggregate replaced. The C20C mix (with GA only) is 3% lower than the RC while the C20F (with fine GA only) and C20FC (with fine and coarse GA) mixes decline by 14% and 22%, respectively. Further analysis of the compressive strength and other mechanical properties of these concrete mixes are presented in another paper, still unpublished.
Replacement ratio (%)
CF CC CFC
5
10
20
w/c
h [mm]
w/c
h [mm]
w/c
h [mm]
w/c
h [mm]
0.55
127
0.55 0.55 0.55
124.5 131.5 125.5
0.57 0.55 0.55
125 132.5 122.5
0.58 0.55 0.57
121.5 134.5 129.5
2.524 2.524 0.03
3.2.2. Density Fig. 2 and Table 4 show the density values of the concrete mixes. It can be stated that there is a clear reduction of the fresh density with the incorporation of GA. This trend is explained by the difference between NA and GA in terms of particles density. The changes in the mixes for which different sized aggregates are replaced are due to the replaced volume having changed. When incorporating fine GA a replacement of only 20% of the overall volume of aggregates corresponds to a replacement of 44.54% of all fines, but when incorporating coarse GA only and fine and coarse GA simultaneously it corresponds to a replacement of 35.57% of all coarse and 40.42% of all fines and coarse, respectively. Therefore, the smallest volume of NA is replaced in the case of coarse aggregates only, followed by the simultaneous replacement of fines and coarse and finally the replacement of fine aggregates only. Furthermore, the same order was followed in terms of extra water required to comply with the stipulated slump range. Therefore, the water addition causes an increase of the volume of voids and consequently greater porosity and lower fresh density.
Table 3 Abrams cone slump results.
0
Coarse fraction
Fig. 1. Slump test results.
S. de Castro, J. de Brito / Journal of Cleaner Production 41 (2013) 7e14
11
Fig. 2. Fresh density results. Fig. 4. Height of water absorbed by capillary action at 72 h compared with the reference mix.
Table 4 Fresh-state concrete density (kg/dm3). Replacement ratio (%)
CF CC CFC
0
5
10
20
2.365
2.348 2.365 2.336
2.348 2.337 2.350
2.339 2.298 2.319
3.3.2. Water absorption by capillarity Fig. 4 shows that the concrete mixes with GA perform well compared with the RC in terms of height of water absorption by capillary action: reductions between 9% and 18.4% (for any size of aggregates in up to 10% replacement ratios). In terms of water absorption (Fig. 5) there is again a reduction of 14e24% respectively for 5% and 10% of replacement of fines. Generally, there is a better relative performance for concrete mixes with a simultaneous incorporation of fine and coarse GA for all replacement ratios and mixes with fines and coarse aggregates for replacement rates up to 10%. The C20F mix was characterised by its high roughness and w/c ratio, which contributed to the increased porosity of its inner structure, leading to a poorer performance of this mix. 3.3.3. Water absorption by immersion Looking at Fig. 6 it is evident that the performance of the mixes with GA is very similar to that of the RC. The variations range from 1.3% to 9%, which results in an almost constant value. This may be due to the weak water absorption of the GA and the similar microstructure of the mixes. In the water absorption by immersion test the GA provided concrete with characteristics almost identical to those of the RC. However, the size of the replaced aggregates again has some influence on the results. The mixes with coarse GA
Fig. 3. Compressive strength results compared with that of the reference mix.
Fig. 5. Water absorbed by capillary action at 72 h compared with the reference mix.
only have the lowest water absorption, mostly because they had the same w/c ratio as the RC, for all replacement ratios. The opposite occurred in the mixes with fine GA only, which generally had higher water absorption values, also a result of the w/c ratio (in this case higher) and consequently higher open porosity of the microstructure. 3.3.4. Carbonation resistance Fig. 7 shows the carbonation depth values of all the concrete mixes at various ages, relative to the RC.
Fig. 6. Water absorption compared with the reference mix.
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S. de Castro, J. de Brito / Journal of Cleaner Production 41 (2013) 7e14
Fig. 7. Carbonation depth compared with the reference mix.
Generally, the carbonation depth of the mixes with GA is similar to or lower than that of the RC at 91 days. The natural decrease of the carbonation depth for older concrete is also clear in every mix. There is therefore a progressive refinement of the cementitious matrix, which seems to be more significant in the mixes with GA than in the RC. However, the differences from the RC are relatively small and therefore it can be stated that the GA contribute to carbonation resistance in the same way as the NA. These conclusions are approximately the same as those for the water absorption by immersion test since these tests are influenced by the same factors. 3.3.5. Chloride penetration resistance Figs. 8 and 9 show the values for the depth of penetration of chlorides for all the concrete mixes at 28 and 91 days, relative to the RC. The results at 28 days are somewhat inconclusive and the absence of trends with GA ratio incorporation for any of the size ranges seems to indicate experimental problems connected with the environmental conditions of the dry chamber and with adjustment of the equipment. However, there is a general trend towards a decline of the chloride penetration-related performance with GA incorporation. At 91 days just the RC and the mixes with coarse GA only were tested. It is found that there is some stability of the results as the replacement rate increases, from which it is concluded that adding glass does not significantly alter the behaviour of concrete in terms of chloride penetration, which is mostly governed by the quality of the cement paste, and this is similar in the mixes analysed. Nevertheless, there is a slight trend towards increasing chloride penetration as the GA ratio increases.
Fig. 8. Chloride penetration at 28 days compared with the reference mix.
Fig. 9. Chloride penetration at 91 days compared with the reference mix.
However, due to the problems mentioned above this property needs further research. 3.3.6. Shrinkage Fig. 10 shows the values of shrinkage for all concrete mixes at 91 days, relative to the RC. Variations from the RC range from 10% to 22% (mixes C10FC and C10C respectively). Mixes where fine and coarse GA coexist have better characteristics for replacement ratios higher than 5%; for example, the C10FC mix varies by 10% and the C20FC mix by 5%. This positive trend concerns the properties of these mixes that lie between those of the mixes with fine GA only and those with coarse GA only. While the first have a higher w/c ratio because of loss of workability caused by the higher specific surface of the fine GA, the second are impaired by the weak bond between the aggregates and the cement paste, caused by the low porosity of glass and the lower specific surface of the coarse GA. The mixes with both fine and coarse GA thus seem to
Fig. 10. Shrinkage at 91 days compared with the reference mix.
S. de Castro, J. de Brito / Journal of Cleaner Production 41 (2013) 7e14 Table 5 Synopsis of the study in terms of the NA/GA overall replacement ratio and the size of the replaced aggregate. Test
Percentage change Increase of the NA/GA replacement ratioa
Increase of the size of the replaced aggregateb
2.7%
13.6%
5.3%
10.1%
5.0%
13.4%
Compressive strength (28 days)
Water absorption by capillarity
(m/m)
(g/mm2)
Water absorption by immersion (%) 1.28%
3.8%
16%
21.7%
20%
6.5%3
10%
7.4%
91-day carbonation depth (mm)
91-day chloride diffusion coefficient (m2/s)c
91-day shrinkage (m/m)
Notes. a Represented by the change between RC and C20C. b Represented by the change between C20F and C20C. c At 28 days due to lack of data at 91 days.
benefit simultaneously from the good bond of the fine GA to the cement matrix and the relatively low w/c ratio of the mixes with coarse GA. 4. Conclusions This research analysed the durability performance of concrete with glass aggregates (GA). The experimental results enabled the following conclusions to be drawn: 1. The workability of concrete with glass is strongly affected by the particle size, leading to an increase in the w/c ratio from 0.55 to 0.58 for the mix with the 20% incorporation of fine GA; 2. There is a clear loss of the concrete’s fresh density as glass is incorporated; this is caused by the lower particle density of the glass; 3. Generally, there was a fall in the 28-day compressive strength because of the weak interface between the glass aggregates and the hardened cement paste, for the mixes with fine GA only and the higher w/c ratio; 4. The mixes with simultaneous incorporation of fine and coarse GA perform better in terms of water absorption by capillarity for every replacement amount tested, as do the mixes with either fine or coarse GA for replacement amounts up to 10%; 5. The performance of concrete with GA in terms of water absorption by immersion is very similar to that of the reference
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concrete (RC); this may be due to the very low water absorption of the GA and the similarity of all the mixes in terms of microstructure; 6. There is a general improvement in terms of carbonation resistance of concrete with GA in the long-term (tests at 56 and 91 days); but at 7 and 28 days the carbonation depth is greater in these mixes than in the RC and grows with the replacement rate; it is thus concluded that the cementitious matrix of concrete with GA is much more refined for older ages; 7. The performance of mixes with any size and combination of GA proved to be similar but slightly worse than that registered by the RC in terms of chloride penetration; the low water absorption of the GA and the similarity of the microstructure of the various mixes probably underlie this result; however, results were not conclusive because of experimental problems; 8. The shrinkage of concrete with GA is similar to that of the RC; nonetheless the mixes with the lowest shrinkage are those with mixed fine and coarse GA. Generally concrete with GA is completely feasible, even though there are some differences in performance as a function of the particle size of the GA used to replace natural aggregates. It was found that in most cases the GA do not alter the durability-related properties of concrete. In a few instances there is a variation from the reference concrete of 15%, which is well within the expectable scatter of the results from the experimental research. Recycled glass aggregates may be used in the construction industry, thereby helping to reduce the extraction of primary resources and to meet nations’ goals in terms of waste recycling. The will of the industry to absorb glass waste that is otherwise difficult to get rid of becomes economically viable if it is coupled with heavy taxation of waste dumping and raw materials’ extraction. In terms of the threat of alkaliesilica reaction between the aggregates and the cement paste, the experimental results of Serpa et al. (2013), using the ASTM 1260 test, reveal that the aggregates used in this research are not reactive enough to raise concerns about their use in concrete production. Table 5 summarises the results obtained in all durability-related tests conducted on hardened concrete. It shows the trends when the NA/GA replacement ratio (up to 20% of the overall volume of aggregates) or the size of the replaced aggregate increases. It confirms that increasing the size of the GA is beneficial for compressive strength (13.6%), water absorption by capillarity and immersion (10.1% and 3.8%, respectively), carbonation resistance (21.7%) and shrinkage (7.4%). The main difference between the mixes with fine and coarse GA was the significant increase of the w/c ratio in the fine GA mixes to offset workability loss. The interstitial water increases the matrix voids, which leads to these mixes performing badly. Acknowledgements The authors acknowledge the support of the research centre ICIST (Instituto de Engenharia de Estruturas, Território e Construção), IST, Technical University of Lisbon and FCT (Foundation for Science and Technology). References Angulo, S., Kahn, H., John, V., Ulsen, C., 2003. Methodology of characterization of construction and demolition waste (in Portuguese). In: VI Seminar Sustainable Development and Recycling in Construction e Recycled Materials and Their Applications, São Paulo, Brazil. Arabani, M., 2011. Effect of glass cullet on the improvement of the dynamic behaviour of asphalt concrete. Construction and Building Materials 25 (3), 1181e1185.
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