Recycled glass replacement as fine aggregate in self-compacting concrete

Abstract

With increasing environmental pressure to reduce solid waste and to recycle as much as possible, the concrete industry has adopted a number of methods to achieve this goal by replacement of waste glass with concrete composition materials. Due to differences in mixture design, placement and consolidation techniques, the strength and durability of Self Compacting Concrete (SCC) may be different than those of conventional concrete. Therefore, replacement of waste glass with fine aggregate in SCC should deeply be investigated compared to conventional concretes. The aim of the present study is to investigate the effect of glass replacement with fine aggregate on the SCC properties. In present study, fine aggregate has been replaced with waste glass in six different weight ratios ranging from 0% to 50%. Fresh results indicate that the flow-ability characteristics have been increased as the waste glass incorporated to paste volume. Nevertheless, compressive, flexural and splitting strengths of concrete containing waste glass have been shown to decrease when the content of waste glass is increased. The strength reduction of concrete in different glass replacement ratios is not remarkable, thus it can be produced SCC with waste glass as fine aggregate in a standard manner.

Keywords

Self Compacting Concrete (SCC) / recycle glass / fine aggregate / fresh and hardened properties

Introduction

Self Compacting Concrete (SCC) is considered as one of the best high performance concrete in recent years. SCC is a concrete which can be placed and compacted under its self weight without vibration effort. It is able to fill reinforcement spaces and voids, even in heavily reinforced concrete members, and it flows without segregation. SCC not only reduces noise due to a vibration free environment, but also increases the quality of concrete as a result of minimizing of human participation in workability works. Recently, this concrete has gained wide use in many countries for different applications. Although the use of SCC has many technical advantages, its supply cost could be two or three times higher than that of conventional concrete depending upon the composition of the mixtures and quality control of concrete produced [1,2].

Therefore, the attempt is to decrease the cost of SCC production by replacement of the composition of the material mixtures by cheaper materials especially waste compositions. Besides, many countries are witnessing a rapid growth in the construction industry which involves the use of natural resources for the development of the infrastructure. This growth is jeopardized by the lack of natural resources that are available. Natural resources are depleting worldwide while at the same time the generated wastes from the industry are increasing substantially. The sustainable development for construction involves the use of non-conventional and innovative materials, and recycling of waste materials in order to compensate the lack of natural resources and to find alternative ways for conserving the environment.

For SCC, it is generally necessary to use super-plasticizer in order to obtain high mobility. Adding a large volume of powdered material can eliminate segregation. The powder materials are fly ash, silica fume, lime stone powder, glass filler, quartzite filler and ground granulated blast furnace slag that can be added to increase the slump of the concrete mix and also to reduce the cost of SCC. Fly ash is a byproduct of thermal power plants or a fine organic material with pozzolanic properties has been reported to improve the mechanical properties and durability of concrete when used as a cement replacement material [3]. Thus, the use of supplementary cementing materials have become an integral part of Portland cement concrete production, and the research on new materials with supplementary cementing potential, including waste or recycled materials is receiving considerable attention from the scientific community.

Glass is one of the wastes that needed to be recycled and is made in different forms. It can be in forms of packaging or container glass, flat glass, bulb glass, and cathode ray tube glass. Hence, glass need to be reused in order to avoid environmental problems. There are a number of applications of using waste glass in the construction industry over the world. The application of using waste glass in asphalt concrete, normal concrete tiles, masonry blocks, paving blocks and other decorative purpose, but practical applications of using waste glass in structural concrete specially SCC are limited [4-12]. Glass is hydrophobic; added to concrete, it can reduce water absorption and dry shrinkage [13]. With the use of high content glass aggregates in concrete, a serious alkali silica reaction (ASR) maybe induced which resulted in a lower strength and durability of concrete. The main problem with the use of waste glass as aggregate replacement is the alkali-silica reaction that occurs between the waste glass and the alkalis produced by the cement during hydration. This reaction leads to cracks in the concrete [13]. Meyer et al. [14] report some of the possible measures to mitigate ASR, which include grinding glasses to a particle size less than 300 µm, using mineral admixtures, using alkali resistant glass, sealing concrete to keep it dry, or using low alkali cement. Besides, The ASR results indicated that deleterious expansions and cracks might occur if the glass content was more than 45% [15]. In other study by Miao Liu [16] it is reported that by using low-alkali cement and ASR suppressants such as silica fume, metakaolin, fly ash and GGBS, the ASR adverse effect can be mitigated. Here, the maximum amount of recycled glass has been selected as 50%, and also the ASR expansion of all the SCC specimens can be significantly reduced by the use of fly ash a part of binder.

Several studies have been conducted on the reuse of waste glass as fine aggregate in production of SCC, recently [15-21]. Totally, they found that replacement of waste glass with sand, decreased the hardened properties and consequently was increased the flowability. The objective of the present study is to examine the production of SCC, with replacing the fine aggregate with flat waste glass. This type of glasses is used in buildings construction.

Experimental program

Materials

Cement

Ordinary Portland cement was used for preparing concrete mixes. The chemical and mechanical properties of the used cement as determined by laboratory tests showed its suitability for concrete works. Chemical and mechanical properties of used cement are given in Table 1.

Silica fume

Silica fume is a byproduct in electrical core functions in the production of silicon. The chemical and physical properties of silica fume are given in Table 2.

Aggregate

Locally available sand from natural sources was used in the present experimental investigation. Table 3 shows the physical properties of coarse and fine aggregates.

Waste glass

The crushed waste glass used in the current work is shown in Fig. 1. The chemical and physical properties of used waste glass are shown in Table 4. The sieve analysis of the waste glass is also presented in Table 5.

Admixture

Super plasticizer is a powerful water reducing operative in concrete mixture. The super plasticizer which has been used in this work is Viscoz 1. The properties of super plasticizer are presented in Table 6.

Mixing water

Drinking water as recommended in codes provision has been used for mixing.

Mix proportions

A total of six SCC mixes were made and their detailed mix proportions are presented in Table 7. These included one control mix (Mix 1), and five mixes (Mix 2-6) made by replacing fine aggregates with 10%, 20%, 30%, 40%, and 50% of waste glass. For all SCCs the amount of cementations used was generally maintained at approximately 365 kg/m³.

Coarse and fine aggregates contents were maintained at 690 kg/m³ and 850 kg/m³, respectively. The W/C ratio was 0.52 for all mixes.

Casting and curing of specimens

For each proportion, required quantities of materials were weighed. Cement and silica fume were mixed in dry state as well as aggregates. After adding water, all materials were mixed together to obtain the homogeneous mix. Several initial tests conducted on fresh concrete to investigate the workability and rheology of concrete paste. The measured fresh tests were slump flow, L-box, V-funnel and J-ring. The aforementioned test methods have been described in following sections. For each concrete mix, 12 (100 mm × 100 mm × 100 mm) cubes were cast to determine the compressive strength at 3, 7, 14 and 28 days. Three (150 mm × 300 mm) cylinders were cast for determination of indirect tensile strength at 28 days. Three beams of dimensions (100 mm × 100 mm × 500 mm) were cast to determine the flexural strength at 28 days (Fig. 2).

After casting, all the cast specimens were covered with plastic sheets and water-saturated burlap and left in the laboratory at 25°C for 24 h. The specimens were then demolded and transferred to a standard water curing tank at 27°C until the age of testing.

Test methods

Fresh properties methods

Various tests have been used in present experimental study to investigate the fresh properties for mixes compositions. So far no single method or combination of methods has achieved universal approval and most of them have their adherents. Hence, each mix design should be tested by more than one test method for different workability parameters. Slump flow, L-box, V-funnel and J-ring will perform for determination the fresh self-compatibility properties. Brief descriptions of the tests are presented in the subsequent paragraph.

Slump-flow test procedure is a combination of Abrams’ cone settling test. After lifting a filled and previously moistened metal cone, the final diameter of the circle formed by the spreading concrete is measured. The permissible diameter is 650-800 mm, (Table 8) (Fig. 3a) [22]. In V-funnel test, the funnel is filled with concrete and the flow time, that is between opening the orifice and the first daylight appearing when looking vertically down through the funnel recorded and then filled the funnel after 5 min and recorded the time. The permissible time for V-funnel test is between 6 to 12 s (Table 8) (Fig. 3(b)). L-box test consists of the L shaped box, of a rectangular cross section, with a horizontal and vertical parts separated by the movable partition in front of which vertical rebars are arranged. The vertical compartment is filled with concrete, and then the partition is removed to allow the flow of concrete at the end of the horizontal part and of the remaining concrete in the vertical part is measured. That is an indicator of the capacity of concrete to pass through the rebars, and it should be as close to one as possible (the lowest permissible value is 0.8) (Table 8) (Fig. 3(c)) [22]. J-ring investigates the blocking behavior of SCC. Step of J-ring, indicates passing ability of SCC (Table 8) (Fig. 3d) [22].

Hardened properties methods

In this study compressive, flexural and indirect tensile (split) strength tests were carried out on hardened concrete. Compressive, flexural and tensile strengths of SCC specimens were measured using a compressive machine with a loading capacity of 300 ton. To evaluate concrete compressive strength at test ages of 3, 7, 14 and 28 days, cubes specimens 100 mm-100 mm-100 mm were tested. The flexural standard beams 100 mm-100 mm-500 mm was tested to evaluate concrete flexural strength at the age of 28 days. The splitting tensile standard cylinders, 150 mm diameter and 300 mm long, was obtained to evaluate concrete splitting strength at the age of 28 days (Fig. 4).

Results and discussions

Fresh concrete properties

As it can be seen from Table 9, the flowability of fresh concrete will increase with an increase in waste glass replacement. Slump flow is over 650 mm for all of the mixes. It was seen an increase in slump flow as the waste glass content is increased in concrete paste similar reported results by previous literatures [18-21]. This trend can be attributed to low water absorption of glass sand and smooth surface. Therefore, the results show an indication of good deformability. As reported by Wang and Huang [18], the higher slump flow at higher glass replacements ratios could be also due to higher compactness of concrete granular skeleton. Because the glass grains are finer than the sand, it can fill better the porosity of the course aggregates, and has a low water absorption and smooth surface.

As shown in Table 9, the L-box ratio varied from 0.82 to 0.94. These results indicate that the waste glass mixes prepared here achieved adequate passing ability and maintained sufficient resistance to segregation around congested reinforcement area. It is obvious from Table 9 that with an increase to replacement of sand by glass the L-box ratio is decreased. This is also similar to the related previous reports [18-21]. This can be attributed to the sharp granule of glass that makes it difficult to pass the reinforcement easily.

To evaluation the concrete viscosity and resistance to material segregation, the required time for concrete to flow down through a funnel named V-funnel test is employed. As it can be found from Table 9, the V-funnel times are decreased by increasing the amount percentage of waste glass. According to the European specification [22] (Table 8), V-funnel time of SCC should be between 6 and 12 s. There is an improvement in flowability for the SCC mixes incorporating glass. This can be attributed to smooth surface of glass which made the concrete flow down easier and sooner. Moreover, low water absorption of glass sand and smooth surface with constant ratio of water to cement for all specimen mixes made the specimens more flowability with incorporating glass. The J-ring spread has been also tabulated in Table 9.

Hardened concrete properties

Compressive strength

The experimental test results of the compressive strength of the control and recycled glass SCC specimens (RG-SSC) at 3, 7, 14 and 28 days are tabulated in Table 10. Each given value is the average of three measurements. It can be found from Table 10 that using recycled glass as fine aggregate in SCC made compressive strengths to be decreased compared to control mixes (Mix 1) in a negligible manner. This result is similar the previous literatures [18-21]. It should be noted that compressive strengths decreasing behavior of RG-SCCs was expected but the differences in the strengths is not such of the related previous scientific reports. This trend can be seen from Figs. 5 and 6 where the compressive strengths of RG-SCCs have no remarkable decreasing in compared with control mix. As shown in Fig. 6, the reduction after 28 days compressive strength of recycled glass SCC mixes are 2.93%, 0.36, 2.735, 1.3% and 3.17%, respectively. This is same as the other concrete age. As it was expected, the compressive strength of each mix has been increased as aging (Fig. 7). It can be concluded that the compressive strengths of RG-SCCs are approximately equal to the mix without waste glass content for practical applications. Therefore, replacement of waste glass as sand below the 50% gives reasonable results in term of compressive strength. It can be found that addition of 50% of waste glass to SCC as fine aggregate caused a decrease of 8% in compressive strength, compared with its control mixture.

It is suitable to compare the results of concrete made with recycled concrete aggregate (RCA) with those made of RG-SCC. Li et al. [23], Tang [24], Jin et al. [25] and Kou et al. [26] had conducted experiments on the compressive strength of recycled aggregate concrete (RAC). The results indicate that the amount of RCA has remarkable influence on the compressive strength of concrete. It can be found from these studies that, in general, the concrete compressive strength decreases with the increase of the RCA content. However, if the RCA content is less than 30%, the influence on the compressive strength is not obvious. This is completely match with the results obtained from this paper and can be seen from Fig. 6.

Flexural strength

The results of the flexural strength after 28 days of the RG-SCCs are presented in Table 10. Each strength value is the average of three measurements. As it is evident from Fig. 8, the flexural strengths tend to decrease with the increase of the percentage of waste glass replacement in concrete mix compared with the control mixture, except Mix2, that contained 10% glass replacement. Maybe adding a little volume glass as sand make a more adhesion between the glass and cement past, but by increasing replacement of sand with glass, the high smoothness of glass decrease the bond strength between the cement paste and glass. Based on the flexural results, replacement of 50% of sand with recycled glass in SCC caused a decrease of 15% in flexural strength compared with its control mixture (Mix 1). Decreasing of flexural strength is completely slight.

Xiao and Li [27], and Hu [28] found that the RCA replacement percentage has only marginal influence on the flexural strength of RAC. Similar results were also obtained by Cheng [29]. Topçu and Sengel [30] found that as the RCA replacement increased, the flexural strength of RAC decreased. Whereas Ravindrarajah and Tam [31] concluded no significant difference existed in the flexural strength of conventional concrete and RAC made with RCA, which is similar of the results of this paper.

Splitting strength

The results of the indirect tensile strength at 28 days of the RG-SCCs as well as previous mentioned results are presented in Table 10. Same other each given value is the average of three measurements. Figure 9 Shows the splitting strength after 28 days, which are also tend to decrease. This figure showed a slight decrease in splitting strength for mixes containing more than 20% waste glass replacement as sand. According to the test results, the 28 days splitting strength is observed to decrease of 5% by 50% replacement of sand by recycled waste glass, compared with its control mixture.

Cheng [29], Shi et al. [32] and Zhou et al. [33] investigated the influence of RCA on the splitting tensile strength of RAC. In their tests, cube specimens were used. The test results are presented and compared. It is evident that the splitting tensile strength reduces as the RCA content increases. Ravindrarajah et al. [34] reported that the splitting tensile strength of RAC was consistently 10% lower than that of conventional concrete. Tabsh and Abdelfatah [35] reported that about 25%-30% drop in the tensile strength was observed in concrete made with RCA. It may be concluded that in most cases there is somewhat difference in tensile strength between RAC and conventional concrete. It should be mentioned that all of the results on RAC brought from the paper of Xiao et al. [36].

It is evident from Table 10 that the density of the RG-SCCs decreased with the increase in waste glass content. This can attributed to the differences in densities between the recycled glasses and natural sand. In other words, the glass sand unit weight is lower than that of sand, thus leading to a reduction in concrete unit weight.

Concluding remarks

The present study treats the feasible employing of recycled glass to production of SCC. This experimental paper demonstrates the replacement of fine aggregate with recycled glass to 50%. Based on the experimental results the following conclusions have been drawn:

1) The slump flow spread of recycled glass SCC mixes has been increased with the increase of recycled glass content. But the L-box ratio and V-funnel decreased by increasing of replacement of sand by recycled glass. It can be found from the fresh results that flowability is increased and makes the concrete suitable for construction of many normal structures, such as walls and columns. The V-funnel test results indicate that the viscosity or segregation resistance of RG-SCCs has been decreased; therefore, the segregation parameter will be a dominant factor for this type of concrete. Finally the passing ability of RG-SCCs have been decreased.

2) The compressive strength, flexural strength and splitting strength of RG-SCCs have been decreased, but decreasing was negligible. Mix 2 in which the proportion of recycled glass was 10% of fine aggregate was found to give more flexural and split strengths compare with the control mix. May be replacement about 5-15% sand with glass causes a more adhesion between the glass particles and cement paste, which made a more flexural and tensile strengths. However, in the context of hardened strengths, all of the RG-SCCs could be considered to be satisfactory for structural applications. The density decreased with the increase in the content of recycled glass.

3) Based on the obtained results it can be used recycled glass as sand to construction SCC, without remarkable decreasing in hardened strengths. May be the fresh properties of RG-SCCs is needed to examined in terms of segregation and viscosity.

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