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ANALYSIS OF THE PHYSICAL-MECHANICAL CONCRETE PROPERTIES WHEN CONCRETE WASTE ADDITIVES ARE USED IN THE MIXTURES

Olga Finoženok1, Ramunė Žurauskienė2 Rimvydas Žurauskas3

1Vilnius Gediminas technical university, Saulėtekio ave. 11, LT-10223 Vilnius, Lithuania. E-mail: 1olga.finozenok@vgtu.lt; 2 ramune.zurauskiene@vgtu.lt 3 rimvydas.zurauskas@vgtu.lt

Abstract. Most often construction waste in Lithuania is used for road construction. 78 % of construction waste con-sists of concrete waste, bricks and tiles. Concrete waste can be used for the production of higher quality products, and this waste can be returned to the production technological cycle. In the research the variation of the properties of con-crete samples is analysed when concrete waste aggregates are used. Concrete waste with various fractions was used as coarse aggregate in the research, as well as filler aggregates from the crushed concrete waste were used. Physical-mechanical properties of the samples were analysed by comparing with reference samples where typical aggregates were used. Sectional analysis of the samples, produced by using coarse aggregates from concrete waste, is carried out during the research and covering areas of every integrated phase are calculated.

Keywords: normal weight concrete, demolition waste, concrete waste, recycled aggregate, filler aggregate.

Introduction

Demolition and construction waste consists of the following waste materials: wood, concrete, bricks and blocks, gypsum, metal, asphalt concrete, plastics, glass and packing. The amounts of these waste materials are different in various regions. In some regions the major part of waste materials consists of wood waste, in other – concrete waste. The amounts of waste materials vary depending on the former construction traditions and on local natural resources of these regions. Main problem of demolition waste management is waste sorting. Only sorted waste materials can be used for the production of high quality products.

Over the past decade the problems of concrete waste reprocessing problems are intensively investigated worldwide. Reprocessing amounts of concrete and demo-lition waste in particular countries differ considerably. For instance, in Taiwan (Hsiao et al. 2002), starting from 2002 to 2009 year the reprocessing of this waste had to be increased from 50 % to 100 % in order to avoid the over-load of dumps. Other researcher from Hong Kong (Tam 2009a) notes that in the overall amount of construction and demolition waste in the region up to 70 % is concrete waste, and the utilisation of this waste is very important.

Utilisation of crushed concrete waste is analysed worldwide. It was determined that this waste can be used not only as a breakstone for road construction, but also for the production of paving-tiles (Poon and Chan 2007).

However, researchers also provide the recommendations to carry out investigations in every country and determine the conditions for the utilisation of crushed concrete waste to produce new products, because in a particular country products are affected by different climatic condi-tions.

In Lithuania most often construction waste is used for road construction, as secondary breakstone. The com-position of this waste depends on the type of building to be demolished and demolishing technologies imple-mented. When buildings are demolished after they wear out morally and constructively, demolition waste consists of the following materials: concrete, wood, metal, plaster boards, oils, chemical materials and roof coverings (78 % of waste is composed of concrete waste, bricks and tiling (Uselytė et al. 2007)). When buildings that are in con-struction phase are demolished, demolition waste consists of concrete and metals. Currently, in Lithuania the amount of second type buildings (not exploited) is the same as the amount of first type buildings. These not exploited buildings are skeleton constructions of public purpose, their construction works were not completed due to various reasons and they are demolished (Figure 1). Demolition works consist of the following technological operations: crushing, sorting, metal separation, initial sieving, milling, metals separation, sieving.

In Europe, 1/3 of secondary breakstone is produced in the stationary systems at especially equipped sites and 2/3 is produced in mobile systems at construction sites.

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Following the feasibility study, prepared by “Ekokonsul-tacijos” UAB (Uselytė et al. 2007), over the period from 2002 and 2006 year, the reprocessing of construction waste in Lithuania has increased 8 times and this amount reached 50 % of overall waste. In 2007 year (Uselytė et al. 2008) the amount of construction waste in Lithuania was 700 thousand tonnes, and 470 thousand tonnes were reprocessed. However, in recent years, after the slow-down of realty market and suspension of constructions of new buildings, over 30–50 % of buildings (with uncom-pleted skeleton) were left non-commissioned. After the market recovers, these buildings could be demolished, and during the demolition huge amount of concrete and metal waste, that is not polluted by other construction waste, would be created.

Fig 1. Demolition works of non-commissioned building

“Lina” UAB PN can be studied as one of Lithuanian

companies, which works on the reprocessing of construc-tion waste. In 2009 year this company put on the market the following products, produced from construction waste: concrete breakstone and brick-concrete breakstone (with fractions of 0–16, 8–32, 16–45, 32–45, 0–45 mm), as well as crushed small concrete and brick-concrete particles of 0–5 mm fraction. These products are pro-duced in mobile mills, with sorting line, where container type waste is sorted. In main regions of Vilnius, Kaunas and Klaipėda, other similar construction waste reprocess-ing companies carry out their activities as well.

In accordance with the directive 2008/98/EB ap-proved at 19-11-2008 by European Parliament and Coun-cil, the following waste reprocessing targets, related to construction waste, were determined up to 2020 year: at least 70 % of nonhazardous construction and demolition waste must be prepared for secondary usage and reproc-essing. According to development priorities measures for the reprocessing of secondary waste within the period of 2009-2013, the markets for the products, manufactured from the secondary raw materials, must be established, the support for secondary raw materials’ sorting, wash-ing, reprocessing projects must be ensured. Creation of high quality reprocessing capabilities and development of existing ones must be preferred.

Considering the determined priorities, new products produced from construction waste should be developed, analysed and popularized. Utilisation of currently sup-

plied products produced from construction waste is lim-ited to their usage for road construction. However, this waste can be reprocessed and used for the production of higher quality products. Based on these priorities this research was carried out.

Research materials

During the research the following raw materials were used to prepare concrete:

Cement: limestone Portland cement CEM II/A-L 42.5 N, complying with the requirements of standard LST EN 197-1. This cement is moderately aluminous, its physical-mechanical properties are provided in Table 1. Table 1. Physical-mechanical properties of the cement

Parameter Value Early compressive strength after 2 days, N/mm2 21

Standard compressive strength after 28 days, N/mm2 47

Initial set, min. 155 Final set, min. 288 Specific surface, cm2/g 3100 Specific particles’ density, g/cm3 2.75 Bulk density, g/cm3 1.02

Fine aggregate: natural sand, the maximal size of the particles thereof is smaller than 5 mm, bulk density 1.64 g/cm3, particles’ density 2.41 g/cm3, module of coarseness 2.1.

Coarse aggregate: gravel breakstone and used crushed concrete waste. The main characteristics of these materials are provided in Table 2. View of crushed con-crete waste is provided in Figure 2. Table 2. Characteristics of coarse aggregate

Parameter and its value Coarse

aggregate Bulk density, g/cm3

Particles’ den-sity, g/cm3

Hollow-ness, %

Crushed gravel 5–20 mm

1.44 2.47 42

Crushed gravel 10–20 mm

1.43 2.42 41

Concrete waste 5–10 mm

1.10 2.03 46

Concrete waste 5–20 mm

1.13 2.26 50

a b

Fig 2. View of crushed concrete waste: a – 5–10 mm fraction; b – 10–20 mm fraction

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Filler aggregate: crushed concrete waste, with parti-cles’ size smaller than 0.125 mm, most of this aggregate pass the sieve with the mesh size of 0.063 mm, the re-maining part <10 %, according to the standard LST EN 12620:2003+A1:2008. Bulk density of the filler aggre-gate is 0.95 g/cm3, particles’ density 2.13 g/cm3.

Compositions of the mixture analysed

During the research 4 concrete mixtures with the markings A, B, C, D were prepared. Concrete composi-tion was estimated in accordance with the characteristics of raw materials by applying volume method used most often and described in the literature. Compositions of concrete mixtures are provided in Table 3. The selected compressive strength class of the concrete is C30/37, slumping factor – 3 cm.

Coarse aggregates with 5–20 mm particles’ size were used in the research. Only in first and fourth con-crete mixtures (A and D) crushed gravel was used as coarse aggregate, in second (B) – mixture of crushed gravel and crushed concrete waste, in third (C) – only crushed concrete waste. During the preparation of the mixture consisting of gravel breakstone and crushed con-crete waste (B) the optimal ratio for the mixture fractions was followed: when two mixture’s fractions are used and maximal allowed diameter of the particles of coarse ag-gregate is 20 mm, then the amount of aggregate of 5–10 mm fraction is 35 %, and 10–20 mm fraction – 65 %.

Concrete waste was crushed with jaw crusher and sieved out with the laboratory sieves. The fractions be-longing to coarse aggregates, fine aggregates and filler aggregates were separated. In the research the crushed concrete waste with the particles larger than 5 mm and concrete waste particles, belonging to the group of filler aggregates, were used. In mixture D, 8 % of cement mass was replaced by filler aggregate. In accordance with LST 1577:1999, the ratio between the masses of filler aggre-gate and CEM II A Portland cement, should not exceed 15 %. During the research half of this amount was se-lected to add.

All concrete mixtures were mixed manually at labo-ratory. The prepared concrete mixture of the required consistence was poured into the moulds. Samples were thickened by vibrating them on the laboratory vibrating plate for approximately 1 min. Samples were hardened in the moulds for 24 hours, then they were taken from the moulds and immersed into the water with temperature of 20ºC ± 2ºC, as it is specified in LST EN 12390-2 2003. In these conditions samples were stored until the tests of mechanical properties. Five samples (100×100×100 mm)

were taken from each concrete batch (three batches in total) produced at laboratory conditions.

Research methodology

Compressive strength of concrete samples was esti-mated after 28 days of hardening. Main physical and mechanical properties were determined by applying stan-dard methods: density of the samples was determined according to LST EN 12390-7, compressive strength – according to LST EN 12390-3, samples were compressed by using hydraulic press “ALPHA 3-3000” complying with the requirements of standard LST EN 12390-4.

Scanned view of the sample B was analysed by us-ing image processing software. 800 dpi resolutions were set for the scanning. Adobe Photoshop CS2 software was used for image processing. In this software the following phases were indicated with different colours: white – pores, light grey – cement stone with fine aggregates, dark grey – cement stone with fine aggregates produced from crushed concrete waste and black – coarse aggre-gate produced from crushed concrete waste (rock).

X-ray diffraction analysis of the filler aggregate was implemented by using diffraction meter DRON–2 (Cu anode, Ni filter, monochromator, gaps 1:8:0.5 mm). Op-erating conditions of the pipe of diffraction meter are as follows: U = 30 kV, I = 10 mA. The recorded diffracto-gram was encoded, by comparing the obtained experi-mental values of the interplanar distances d and relative integral intensity I/I0 of the lines with the corresponding values in ASTM card file.

According to the results of water absorption (after 72 h, after vacuuming) the following parameters were calculated: effective porosity (WE, %), total open porosity (WR, %), reserve of pore volume (R, %), degree of struc-tural inhomogeneity (N), and capillary rate of mass flow at normal conditions (g, g/cm2), capillary rate of mass flow in vacuum towards freezing direction (G1, g/cm2) and capillary rate of mass flow in vacuum perpendicular to freezing direction (G2, g/cm2) (Mačiulaitis 1996). Con-sidering these structural parameters, the forecasted ex-ploitation frost resistance (after the beginning of fragmen-tation, in cycles) was calculated.

Experimental results and discussions

X-ray diffraction analysis for the filler aggregate was carried out. Figure 3 shows X-ray pattern of the filler aggregate. From this pattern it can be noticed that the main minerals of this raw material are as follows: quartz Q SiO2 (0.137, 0.138, 0.154, 0.167, 0.182, 0.198, 0.213,

Table 3. Composition of concrete mixtures A, B, C and D

Composition Coarse aggregate, kg/m³

Concrete marking Cement,

kg/m³ Concrete waste Crushed gravel Fine aggre-gate, kg/m³

Water, l/m³ Filler aggre-gate, kg/m³

Water / cement ratio

A 440 – 1288 356 189 – 0,43 B 440 408 758 356 189 – 0,43 C 440 991 – 556 189 – 0,43 D 405 – 1288 356 189 35 0,47

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0.208, 0.245, 0.335, 0.425 nm), calcite K CaCO3 (0.152, 0.160, 0.162, 0.187, 0.191, 0.209, 0.208, 0.249, 0.304, 0.385 nm), dolomite D CaMg(CO3)2 (0.178, 0.180, 0.201, 0.219, 0.240, 0.266, 0.288 nm). Other minerals, such as Portlandite P Ca(OH)2 (0.169, 0.192, 0.263, 0.490 nm), feldspars L (0.216 0.318 0.324, 0.370 nm), cement min-erals C 3CaO SiO2 (0.254, 0.278 nm), dominate as well. Mica Ž 0.999 nm and chlorites X 0.706 nm passed to the filler aggregate from the granite aggregates, existed in the concrete before crushing.

Considering the results of X-ray diffraction analysis of the filler aggregate it can be assumed that the minera-logical composition of the filler aggregate depends on the composition of cement stone of initial material used for the crushing and partially on the type of coarse aggre-gates existed in the concrete. Cement minerals, that could not react before the crushing, could remain in the crushed cement stone, as well as calcium hydroxide, created dur-ing the reaction.

Concrete block C (100×100×100 mm) was cut after 28 days of hardening and visual recognition of composite materials in the block was carried out. View of the cut block after the scanning is shown in Figure 4.

In Figure 4 we can see how crushed concrete waste is distributed in the sample. During visual recognition it was noticed, that half of the coarse aggregate lost contact with the cement stone during the crushing, and half of the grains in the mixture are bonded firmly with the cement stone. Coarse aggregates in the concrete are distributed evenly and in all areas they are separated by newly mixed cement paste with the fine aggregates.

Part of the coarse aggregates from the crushed con-crete waste are composed from solid particles and cement stone parts adhered to one or several sides. Scientists, after the microstructure analysis (Tam et al. 2005; Tam et al. 2009b), assume that the cracks (created during the crushing of concrete waste) in this cement stone, adhered to the solid particle, could influence the compressive strength of the concrete products. Additionally, suffi-ciently large amount of pores could exits in this cement stone, and this amount depends on the porosity of con-struction waste.

Fig 4. View of concrete sample C

Scanned image was analysed by using computer

graphic software. Individual phases composing the sam-ple are specified in different colours. Analysed view is provided in Figure 5.

By applying special features it was possible to calcu-late how much area each colour in Figure 5 covers. It was estimated that pores, indicated in white colour, cover 1.43 % area (for calculations were used those pores that are marked and which diameter is ≥ 0.9 mm), cement stone, indicated in light grey colour, covers 46.63 % area and coarse aggregate from the crushed concrete waste, indicated in dark grey and black colours, covers 50.95 % (coarse aggregates indicated with black colour cover 27.07 %, and old crushed cement stone with fine aggre-gates, indicated in dark grey, covers 23.88 %). When phases’ arrangement (of obtained area in Figure 5) in a plane is compared with phase volumes in overall area of the concrete samples, it would be noticed that coarse aggregates cover 47 % area of overall concrete volume. It can be assumed that coarse aggregates from the crushed concrete waste are arranged evenly in overall area of the concrete sample.

Fig 3. X-ray pattern of filler aggregate: Q – quartz; K – calcite; D – dolomite; P – Portlandite; L – feldspars; C – tricalcium silicate; Ž – mica; X – chlorites

Inte

nsit

y

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Fig 5. View of concrete sample C: white colour is used to indicate pores; light grey – newly created cement stone with fine aggregate; dark grey and black – con-crete waste (dark grey – cement stone with fine aggre-gates and black – coarse aggregates)

Density of the produced concrete samples is shown

in Figure 6. All concrete samples comply with density requirements applicable for the normal concrete samples, their density is in the range from 2.0 g/cm3 to 2.6 g/cm3.

2,05

2,1

2,15

2,2

2,25

2,3

2,35

A B C D

Samples' marking

Den

sity

, g/c

m3

Fig 6. Results of density estimation for concrete sam-ples

Compressive strength of the concrete samples was

determined (Figure 7). It can be noticed that when the amount of concrete waste is increased in the mixture, the compressive strength decreases: compressive strength of concrete samples B is 91 % comparing to the compres-sive strength of reference samples (marking A). Accord-ing to the researchers (Batayneh et al. 2007), compressive strength of the concrete samples decreases by 12 % when 20 % of crushed concrete waste is used for the mixture. However, in this case concrete mixture had much larger water/cement ratio – 0.56. As it is described also by the researchers (Tabsh and Abdelfatah 2009), when the crushed concrete waste is used for the concrete mixture, the slumping factor of the concrete changes, because concrete waste requires more water. The measured slumping factor of concrete mixture B was 2 cm, concrete mixture C – 1 cm. Slumping factor of the concrete mix-ture D, where instead of a part of cement the filler aggre-

gates from the crushed concrete waste were used, was the same – 3 cm. According to the data provided in the references (Batayneh et al. 2007), concrete’s bending strength and spalling strength remains the same when the amount of crushed concrete waste increases.

During the analysis of the change of compressive strength, for the case when all aggregates are replaced by crushed concrete waste, it can be noticed that compres-sive strength decreases by 18 % (when waste materials are used) comparing with the compressive strength of reference samples. Researchers (Tabsh and Abdelfatah 2009) describe that when crushed concrete only with considerably larger strength is used for the coarse aggre-gates, it is possible to produce concrete stone of the same strength as concrete stone with the natural coarse aggre-gates.

When part of the cement in the concrete mixture was replaced by filler aggregate from the crushed concrete waste, compressive strength of the concrete decreased by 32 %, although concrete’s density decreased by only 6 % comparing to the reference concrete samples.

Compressive strength of the concrete decreases as well when other filler aggregates, such as fly ash, are used. Researchers (Kosior-Kazberuk and Lelusz 2007) describe the tests where compressive strength decreases by 12 % when 30 % of the cement is replaced by fly ash. During the analysis of the influence of filler aggregates on the properties of concrete samples, each particular case must be investigated comprehensively and the analy-sis must be implemented to find out how one or other aggregate influences mechanical properties of the final product, because the usage of fine mineral additives in the cement grout causes physical, chemical and micro-structure effects (Boudchicha et al. 2007), which must be analysed.

0

10

20

30

40

50

60

A B C D

Samples' marking

Com

pres

sive

str

engt

h, M

Pa

Fig 7. Results of the estimation of compressive strength of concrete samples

Researchers (Zaharieva et al. 2004), who analysed

the durability of the concrete, produced by using concrete waste, according to the frost resistance, had found that the important parameter for this characteristic – water/cement ratio of concrete mixture, must be lower than 0.55, and the selection of the method for the estimation of frost resistance is very important as well. Additionally, it was found that theoretical methods for the estimation of fore-

Samples’ marking

Samples’ marking

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casted frost resistance cannot be based only on the results of changes of mechanical properties.

The forecasted frost resistance of constructional concrete can be estimate through physical and structural characteristics (Nagrockienė et al. 2004). Based on the recommendations of the scientists (Mačiulaitis 1996 and Nagrockienė et al. 2007), the structural characteristics of the concrete samples were determined (Table 4) and fore-casted exploitation frost resistance of the concrete sam-ples was calculated according to the beginning of frag-mentation.

From the results of the analysis (Table 4) it can be noticed that the general porosity of all three concrete samples is similar. Authors (Lelusz and Malaszkiewicz 2004) state that general porosity of the sample by 90 % depends on the amount of water used for the mixing, and this amount in our analysed mixtures is the same.

Referring to the structural characteristics of the sam-ples, the forecasted exploitation frost resistance of the concrete samples was calculated according to the begin-ning of fragmentation. Considering this parameter, it can be noted that the maximal forecasted exploitation frost resistance exists in the concrete samples that were pro-duced by using natural aggregates. This parameter is smaller when crushed concrete waste is used, as well as for the samples, for which production the filler aggregate from the crushed concrete waste was used. Table 4. Structural characteristics and forecasted exploitation frost resistance of the samples

Marking of concrete samples Parameter

A C D Effective porosity WE, (%) 7.94 10.25 9.06 General sample’s porosity WR, (%)

13.81 14.61 13.57

Reserve of pore volume R, (%) 42.48 29.84 33.22 Conditional width of the wall of pores and capillaries D

6.24 5.84 6.40

Structure’s directional irregu-larity factor N

2.72 3 3.67

Capillary rate of mass flow in vacuum towards freezing direc-tion G1, (g/cm2)

1.24 0.76 1.28

Capillary rate of mass flow in vacuum perpendicular to freez-ing direction G2, (g/cm2)

1.24 0.52 1.28

Capillary rate of mass flow at normal conditions g, (g/cm2)

0.62 0.19 0.67

Forecasted exploitation frost resistance according to the beginning of fragmentation, (cycles)

203 166 142

In order to effectively forecast very important char-

acteristics of the concrete – frost resistance in future, it is necessary to implement more investigations, including estimation of structural and mechanical properties, as well as to carry out comparative analysis on frost resis-tance values obtained during the tests.

Conclusions

Considering the priorities of reprocessing of secon-dary raw materials, demolition and construction waste, created in the construction sector, especially concrete slabs, should be used for the production of new, good quality, products.

Crushed concrete waste can be used as coarse ag-gregates for the production of concrete products. When this waste is used in the mixtures as replacement of the coarse aggregate, this waste evenly distributes in overall concrete mass, and the properties of produced samples are as follows: density 2.2 g/cm3, compressive strength 46.2 MPa, general sample’s porosity 14.61 %, and the calculated forecasted exploitation frost resistance accord-ing to the beginning of fragmentation is 166 cycles.

After the part of coarse natural aggregate was re-placed by crashed concrete waste, concrete’s density decreases only by 2.8 %, and strength decreases by 9 %.

When filler aggregates from the crushed concrete waste were used, we estimated that with this additive smaller density, smaller strength of concrete stone is reached and the calculated forecasted exploitation frost resistance according to the beginning of fragmentation is smaller comparing to the reference concrete samples produced without filler aggregates.

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