Comparative Tests of Beams and Columns Made of Recycled

Journal of Advanced Concrete Technology Vol. 5, No. 2, 259-273, June 2007 / Copyright © 2007 Japan Concrete Institute 259

Technical report

Comparative Tests of Beams and Columns Made of Recycled Aggregate Concrete and Natural Aggregate Concrete Andrzej B. Ajdukiewicz1 and Alina T. Kliszczewicz2

Received 6 October 2006, accepted 14 March 2007

Abstract The tests concerning use of concrete with recycled aggregates (RAC) presented in different countries were focused on material properties. Very few serial tests were done on structural reinforced-concrete members with RAC to be com-pared with similar members with natural aggregate concrete (NAC). Such tests are necessary because it is difficult to predict the influence of differences in particular properties on the overall behaviour of reinforced concrete members made of various mixtures of recycled aggregate concrete. The aim of the tests presented in the paper was to determine differences in behaviour of simple reinforced concrete members made of RAC, with different contribution of recycled aggregates, in comparison with members made of concrete with natural aggregate (NAC) only. The results of replacing by recycled aggregate the coarse and fine aggregate or the coarse aggregate only were particularly taken into considera-tion. 16 series of beams and 5 series of columns have been selected for tests. The comparison of results showed similar bearing capacity of members in the series, and significantly greater deformations of concrete in members with recycled aggregate concrete. Differences in load-bearing capacity could be neglected in practice, but the differences in deform-ability should be considered carefully at beam deflection assessment, as well as at columns shortening analysis.

1. Introduction

Recycling of concrete has been introduced into practice many years ago and from the beginning it has been con-sidered in two main environmental aspects: solving the growing waste disposal crisis and protection of depleted natural sources of aggregates. In the last decades it has also become an economical problem, as the prices of good natural aggregates, as well as costs of wastes stor-age, have significantly increased in many regions. In the European Union the mass of 500 kg of demolition waste correspond annually to each citizen (Oikonomou 2005). Recycling of concrete became the crucial point of the strategy of sustainable building all over the world, and is growing as an important factor of sustainable devel-opment, particularly in Japan (Tamura et al. 2002), and in Poland too (Ajdukiewicz 2005).

Formerly, the quality of aggregates derived from con-crete structures was relatively low and consequently the applications were of secondary importance (Frondistou-Yanns 1977; Nixon 1978; Hansen 1986; Lauritzen 1992; RILEM 1994). Nowadays, the necessity of demolition of reinforced-concrete or prestressed-concrete structures originally made of strong, sometimes very strong con-crete, like building frames, bridge beams, airport run-ways, or rejected members in precast plants, creates the huge sources of recycled aggregates that have quite rea-

sonable quality (Grübl 1998, Limbachia et al 2000, Ka-wano 2002, fib No 28 Bulletin 2004). Such a situation is particularly typical for developing countries where the long-term programs of modernization started for roads, bridges, municipal and industrial structures. Sometimes it is necessary to demolish relatively young structures, for instance ten or less years old, because the functional features do not fit with the new projects (Collins 1996; Dal Zio Palutan et al. 1996; Di Maio 2004; Kliszcze-wicz 2004).

For recycled aggregates, apart from the obvious envi-ronmental aims of concrete recycling, has been found a new economical aspect. Concrete originally mixed with large amount of cement retains some binding abilities, particularly when the carbonated zone is not too deep. It may be activated with silica fume or fly ash admixtures. This may lead to some savings in cement consumption to be obtained in this way (Cava et al. 1993; Moon et al. 2002; Katz 2003).

The results of tests undertaken to explain the way how to obtain good quality structural concrete using aggregates from demolished structures made of for-merly medium- or high-strength concrete, and to deter-mine what properties could be obtained in such concrete by introduction of silica fume and superplasticizers were presented in (Ajdukiewicz, Kliszczewicz 2000, 2002a).

The early investigations on the use of RAC in rein-forced-concrete beams were published in Japan (Mukai, Kikuchi 1988), and since then the general indications have been proposed (e.g. Di Niro et al. 1998).

The large serial tests of the structural members with RAC started in Poland in 1998. Some partial results of the tests on beams and columns have been presented

1Professor, Dr. Department of Structural Engineering, Silesian University of Technology, Poland. E-mail:[email protected] 2Dr. Department of Structural Engineering, Silesian University of Technology, Poland.

260 A. B. Ajdukiewicz and A. T. Kliszczewicz / Journal of Advanced Concrete Technology Vol. 5, No. 2, 259-273, 2007

since 2002 (Ajdukiewicz, Kliszczewicz 2002b, 2006). The test results from the period 1998-2006 are presented here for the first time in the complete set.

2. Experimental program

The main aim of the tests was determination of differ-ences in behaviour of simple structural reinforced con-crete members – simply supported beams and axially loaded columns – made of RAC, with different contri-bution of recycled aggregate, in comparison with mem-bers made of concrete with natural aggregate (NAC) only. The results of replacing by recycled aggregate the coarse and fine aggregate, or the coarse aggregate only, were particularly taken into account. It was a conse-quence of the results of wide range tests concerning differences in properties of concrete with various con-tributions of recycled aggregates used in concrete mix-tures (Ajdukiewicz, Kliszczewicz 2000, 2002b).

2.1 Characteristics and notation of concretes used in members The members for the tests were manufactured with con-cretes of different strength class and made with different kind of aggregates. To identify the series of members and particular elements in series the following notation was introduced.

In general, the series of members (beams or columns) were made of concrete with three kinds of coarse aggre-gates: • rounded (river) gravel, mainly quartzite - symbol O, • crushed granite - symbol G, • crushed basalt - symbol B.

In each series of three members prepared for tests the concrete mixture was almost the same, but the aggregate differed in particular elements according to various con-tribution of recycled aggregate: • natural aggregate – new coarse aggregate and new

fine aggregate - symbol NN, • recycled coarse aggregate and new fine aggregate -

symbol RN, • recycled coarse and fine aggregate - symbol RR. • Concrete of three different classes of compressive

strength were used: • low-strength concrete: class designed C20/25 - signed

“l”, • medium-strength concrete: class designed C35/45 -

signed “m”, • high-strength concrete: class designed C80/95 -

signed “h”. For instance, the notation identifying concrete used in

particular members may be as follows: ONNl – low strength concrete with new (natural) round gravel as coarse aggregate, and new sand, GRNm – medium strength concrete with recycled coarse aggregate (original concrete made with crashed granite aggregate), and new sand, BRRh – high strength concrete with recycled coarse and fine aggregate, both obtained from crushed concrete originally made with basalt as coarse aggregate.

In addition, the members are identified with symbol “b” for beams and symbol “c” for columns. Because two reinforcement ratios were used in beams, the nota-tion “1” or “2” was introduced. All the columns were made with the same reinforcement, so, this additional notation was not necessary. Finally, the notation for beams was used, e.g: GNNm-b1 or GRNm-b2, while for columns: BRRh-c.

2.2 Recycled aggregates and concrete mixtures Six kinds of recycled aggregate were used to make the test. All kinds were obtained from crushed prefabricates and accompanying specimens made originally in the period 1995-1998. The recipes and properties of con-crete were known. The laboratory jaw crusher was used and the aggregate was divided into four grades (0÷2 mm, 2÷4 mm, 4÷8 mm and 8÷16 mm). Properties and mix proportions for six kinds of original concrete are pre-sented in Tables 1, 2 and 3.

For concrete mixture proportions the composition with natural (new) aggregate was the basis. The recipes of mixtures with partial or full use of recycled aggre-gates were almost the same. Aggregate grading curves were kept very similar in the series. The data for the concrete in the beams and in columns are presented in Tables 4, 5 and 6.

Table 1 Composition and properties of original concrete (with rounded gravel coarse aggregate) used after crushing as recycled aggregate.

Mixture components [kg/m3] Compressive strength [MPa]

Elastic modulus

[GPa]

Bulk density

[kg/dm3]Sand Rounded gravel

aggregate

Mix (concrete mixture)

fcm(28) fcm Ecm(28) ρcm

Cement CEM I 32.5

Water

0÷2 2÷8 8÷16

“A” 32.8 45.1 - 2.27 310 220 2040 “B” 25.2 30.5 26.0 2.27 335 201 794 265 706

”A” – in beams ORNl –b1 and ORRl –b1; “B” – in beams ORNl –b2 and ORRl –b2, ORNm–b1 and ORRm–b1, ORNm–b2 and ORRm–b2, as well as in columns ORNm–c and ORRm–c.

A. B. Ajdukiewicz and A. T. Kliszczewicz / Journal of Advanced Concrete Technology Vol. 5, No. 2, 259-273, 2007 261

Table 2 Composition and properties of original concrete (with granite coarse aggregate) used after crushing as recycled aggregate.


Modulus [GPa]

Bulk density

[kg/dm3]Sand Crushed granite

aggregate

Mix fcm(28) fcm Ecm(28) ρcm

CementCEM I

Water

0÷2 2÷5 5÷8 8÷11 11÷16

SF SP

”C” 44.1 60.5 26.9 2.39 300* 148 600 300 400 350 350 - - ”D” 66.0 73.1 28.7 2.42 571** 145 530 212 285 315 315 29 36

* CEM I 32.5; **CEM I 52.5; SF – silica fume; SP – superplasticizer. ”C” – in beams GRNl –b1 and GRRl –b1, GRNl –b2 and GRRl –b2, GRNm–b1 and GRRm–b1, GRNm–b2 and GRRm–b2, as well as in columns GRNm–c and GRRm–c; ”D” – in beams GRNh–b1 and GRRh–b1, GRNh–b2 and GRRh–b2. Table 3 Composition and properties of original concrete (with basalt coarse aggregate) used after crushing as recycled aggregate.


Elastic modulus

[GPa]

Bulk density

[kg/dm3]Sand Basalt

aggregate

Mix fcm(28) fcm Ecm(28) ρcm

CementCEM I

Water

0÷2 2÷8 8÷16

SF SP

“E” 46.6 72.4 39.2 2.52 300* 149 653 653 871 - - “F” 84.8 110.1 48.3 2.61 500** 123 565 444 1008 50 15

* CEM I 32.5; ** CEM I 42.5; SF – silica fume; SP – superplasticizer. ”E” – in beams BRNl-b1 and BRRl-b1, BRNl-b2 and BRRl-b2, BRNm-b1 and BRRm-b1, BRNm-b2 and BRRm-b2, as well as in columns BRNm-c and BRRm-c; ”F” – in beams BRNh-b1 and BRRh-b1, BRNh-b2 and BRRh-b2, as well as in columns BRNh-c and BRRh-c. Table 4 Composition of concrete mixtures with rounded gravel coarse aggregate used in beams and in columns (recycled aggregate kind “A” and “B”, according to Table 1), in [kg/m3].

Water Sand (new)

Natural gravel aggregate

Recycled gravel aggregate

Concrete in beam

or column

Cement CEM I

design added 0÷1 0.8÷2 2÷8 8÷16 0÷2 2÷4 4÷8 8÷16ONNl 300* 148 - 364 243 708 708 - - - - ORNl 300* 148 33 329 220 - - - 183 366 732 ORRl 300* 148 76 - - - - 530 177 353 706

ONNm 500** 180 - 314 209 611 611 - - - - ORNm 500** 180 12 288 192 - - - 160 320 639 ORRm 500** 180 38 - - - - 462 154 308 617

*CEM I 32.5; **CEM I 42.5. Table 5 Composition of concrete mixture with granite coarse aggregate in beams and in columns (recycled aggregate kind “C” and “D”, according to Table 2), in [kg/m3].

Natural aggregate (new) Recycled aggregate Water Sand Granite Granite

Concrete in beam

or column

Cement CEM I

design added 0÷1 0.8÷2 2÷5 5÷8 8÷11 11÷16 0÷2 2÷4 4÷8 8÷16 SF SP

GNNl 300* 148 - 360 240 300 400 350 350 - - - - - - GRNl 300* 148 21 338 225 - - - - - 187 375 750 - - GRRl 300* 148 66 - - - - - - 548 183 365 731 - -

GNNm 500** 180 - 314 210 262 349 306 306 - - - - - - GRNm 500** 180 - 295 196 - - - - - 164 327 655 - - GRRm 500** 180 27 - - - - - - 478 159 319 638 - - GNNh 455** 126 - 331 220 276 368 321 321 - - - - 15 45GRNh 455** 126 - 310 207 - - - - - 172 344 689 15 45GRRh 455** 126 7 - - - - - - 503 168 336 671 15 45

*CEM I 32.5; **CEM I 42.5; SF – silica fume; SP – superplasticizer.


To maintain the same consistency of concrete mixture, some water addition was necessary and it was experi-mentally assessed. This additional water amount was indicated in Tables 4, 5 and 6. 2.3 Tests of reinforced concrete beams Sixteen series of beams were tested. The dimensions of beams, supports and loading systems were the same in all members, as shown in Fig. 1. There were three beams in each series prepared with the same reinforce-ment and from concrete of almost the same composition but – as mentioned above in p. 2.1 – mixed with differ-ent contribution of natural and recycled aggregate.

The recycled aggregate for beams was obtained from elements made in 1995 and 1998. Properties and mix-ture proportions of original concretes A, B, C, D, E and F are presented in Tables 1, 2, 3 while data for concrete in the beams are presented in Tables 4, 5, 6.

The reinforcement was changed in series of beams to obtain different shape of failure – flexural or shear (Fig. 1). The flexural reinforcement was made in all beams of ribbed bars with characteristic strength fyk = 410 MPa and with diameter ∅12 mm (in beams signed 1) or ∅16 mm (in beams signed 2), while secondary and shear reinforcement was of plain bars of ordinary steel (fyk = 210 MPa).

The following 16 series of beams (3 elements in each series) were prepared and tested: • two series (ONNl-b1, ORNl-b1, ORRl-b1) and

(ONNl-b2, ORNl-b2, ORRl-b2) with low-strength concrete made of rounded gravel as coarse aggregate,

• two series (GNNl-b1, GRNl-b1, GRRl-b1) and (GNNl-b2, GRNl-b2, GRRl-b2) with low-strength concrete made of granite as coarse aggregate,

• two series (BNNl-b1, BRNl-b1, BRRl-b1) and (BNNl-b2, BRNl-b2, BRRl-b2) with low-strength concrete made of basalt as coarse aggregate,

• two series (ONNm-b1, ORNm-b1, ORRm-b1) and

(ONNm-b2, ORNm-b2, ORRm-b2) with medium-strength concrete made of rounded gravel as coarse aggregate,

• two series (GNNm-b1, GRNm-b1, GRRm-b1) and (GNNm-b2, GRNm-b2, GRRm-b2) with medium-strength concrete made of granite as coarse aggregate,

• two series (BNNm-b1, BRNm-b1, BRRm-b1) and (BNNm-b2, BRNm-b2, BRRm-b2) with medium-strength concrete made of basalt as coarse aggregate,

• two series (GNNh-b1, GRNh-b1, GRRh-b1) and (GNNh-b2, GRNh-b2, GRRh-b2) with high-strength concrete made of granite as coarse aggregate,

• two series (BNNh-b1, BRNh-b1, BRRh-b1) and (BNNh-b2, BRNh-b2, BRRh-b2) with high-strength concrete made of basalt as coarse aggregate. All beams were tested as simply supported, under two

equal forces of F (see Fig. 1). At each 5 kN increment of force the following data were measured: • deflections of beams, by means of inductive gauges, • concrete strains, by means of electro-resistance

gauges, • location and width of cracks, particularly in the level

of main reinforcement, • approximate load at cracking, Fcr, • load accompanying the flexural reinforcement yield-

ing, Fy, • ultimate load, Fu.

The beam prepared for tests on the testing stand is shown in Fig. 2. 2.4 Tests of reinforced concrete columns Five series of three columns each were prepared and tested: • one series (GNNl-c, GRNl-c, GRRl-c) with low-

strength concrete made of granite as coarse aggregate, • one series (ONNm-c, ORNm-c, ORRm-c) with me-

dium-strength concrete made of rounded gravel as coarse aggregate,

Table 6 Composition of concrete mixture with basalt coarse aggregate in beams and in columns (recycled aggregate kind “E” and “F”, according to Table 3), in [kg/m3].

Natural aggregate (new) Recycled aggregate Water Sand Basalt Basalt

Concrete in beam or column

Cement CEM I

design added 0÷1 0.8÷2 2÷8 8÷16 0÷2 2÷4 4÷8 8÷16 SF SP

BNNl 300* 148 - 327 327 653 871 - - - - - - BRNl 300* 148 - 291 291 - - - 194 388 776 - - BRRl 300* 148 30 - - - - 575 192 383 767 - -

BNNm 500** 180 - 285 285 570 760 - - - - - - BRNm 500** 180 14 255 255 - - - 170 339 679 - - BRRm 500** 180 34 - - - - 503 168 335 671 - - BNNh 455** 108 - 310 310 620 827 - - - - 45 8 BRNh 455** 108 - 277 277 - - - 185 369 738 45 8 BRRh 455** 108 13 - - - - 547 182 365 729 45 8

*CEM I 32.5; **CEM I 42.5; SF – silica fume; SP – superplasticizer.


• one series (GNNm-c, GRNm-c, GRRm-c) with me-dium-strength concrete made of granite as coarse ag-gregate,

• one series (BNNm-c, BRNm-c, BRRm-c) with me-dium-strength concrete made of basalt as coarse ag-gregate,

• one series (BNNh-c, BRNh-c, BRRh-c) with high-strength concrete made of basalt as coarse aggregate. The recycled aggregate for columns was obtained

from elements made in 1997 and 1998. Properties and mixture proportions of original concretes B, C, D, E and F are presented in Tables 1, 2, 3 while data for concrete in the columns are presented in Tables 4, 5 and 6.

All the columns were prepared with the same dimen-sions and reinforcement (Fig. 3). The main reinforce-ment was made of ribbed bars with characteristic strength fyk = 410 MPa (4 ∅12 mm), while the stirrups were of plain wires of ordinary steel fyk = 210 MPa (∅4.5 mm) - Fig. 3a.

The columns were tested to the half-scale under axial load in the testing machine of 3000 kN capacity (Fig. 3c). For each column the program of testing started with three initial cycles of loading and unloading. This was done to control the axial action in machine and proper service of gauges. The force increased in steps of 50 kN, and the level of initial loading was approximately equal to 1/3 of predicted ultimate load. Fourth cycle was done up to failure, with static loading in steps 50 kN. At each loading step the concrete strains were measured by

means of electro-resistance gauges – see arrangement of gauges in Fig. 3b. The final load capacity was measured automatically. In the last stage of testing the cracks pat-tern, as well as final shape of failure was recorded. 3. Test results

3.1. Reinforced concrete beams All important results of tests on the beams are presented in Tables 7 and 8. There are also placed the results from testing of properties on specimens of concrete used in the beams: mean compressive strength, fcm, mean tensile (splitting) strength, fctm, mean values of modulus of elas-ticity, Ecm, Poisson’s ratio, νcm, density of hardened con-crete, ρcm. The results measured in the tests of beams are gathered as a second group: • load at first cracking, 2Fcr, • load accompanying yielding of flexural reinforce-

ment, 2Fy, • ultimate load, 2Fu, • comparable deflection of beams at midspan, a70 (for

the beams with reinforcement 4∅12) or a110 (for the beams with reinforcement 4∅16), measured at the chosen load 2F = 70 kN or 2F = 110 kN,

• summarized width of cracks, Σw70 or Σw110, meas-ured on both sides of the beams along the reinforce-ment, at the chosen load 2F = 70 kN or 2F = 110 kN,

• maximum concrete strains measured on the top sur-face of beams, εc,max.

Fig. 1 Dimensions, reinforcement and loading system for beams used in the tests.

Fig. 2 View of the beam on the testing stand.


a)

b) c)

Fig. 3 Data for columns in the tests: a) dimensions and reinforcement arrangement, b) localization of electro-resistance gauges, c) view of the column on testing stand.

Table 7 Properties of concrete and results of tests on beams with bottom reinforcement 4Ø12 mm.

Results of concrete tests Results of beam tests fcm fctm Ecm νcm ρcm 2Fcr 2Fy 2Fu a70 Σw70 εc,max

Beam symbol

MPa MPa GPa - kg/dm3 kN kN kN mm mm ‰ ONNl-b1 37.7 2.9 31.9 0.16 2.35 40 126 129 3.21 0.85 2.84ORNl-b1 34.6 2.6 25.9 0.16 2.25 40 117 128 3.63 1.15 3.11ORRl-b1 29.2 2.5 21.0 0.17 2.20 30 115 121 4.20 1.40 3.28

ONNm-b1 57.9 3.5 35.6 0.16 2.38 40 130 160 3.37 0.80 4.20ORNm-b1 56.4 3.3 31.8 0.17 2.31 30 126 156 3.93 1.20 4.77ORRm-b1 55.5 2.9 26.2 0.17 2.22 20 124 155 4.37 1.33 4.73GNNl-b1 39.8 3.2 27.3 0.16 2.39 30 135 156 3.61 0.66 3.33GRNl-b1 40.1 2.9 24.3 0.16 2.31 30 135 163 3.57 0.81 4.00GRRl-b1 36.2 2.6 22.6 0.17 2.23 30 131 162 3.65 0.73 3.51

GNNm-b1 58.3 4.4 32.5 0.18 2.39 40 130 140 2.40 0.55 2.52GRNm-b1 60.2 4.3 28.5 0.19 2.29 40 127 136 2.94 0.62 2.70GRRm-b1 54.2 3.9 26.1 0.20 2.21 30 120 133 3.48 0.85 3.31GNNh-b1 89.9 6.1 36.2 0.18 2.45 40 130 164 2.74 0.48 3.62GRNh-b1 85.3 5.3 35.3 0.19 2.34 40 130 158 3.41 0.56 3.30GRRh-b1 84.3 4.9 30.4 0.21 2.29 30 128 142 3.36 0.75 2.89BNNl-b1 40.1 3.4 36.2 0.19 2.55 40 134 151 3.84 0.51 3.15BRNl-b1 35.3 3.0 31.7 0.19 2.40 40 132 150 3.90 0.79 2.75BRRl-b1 31.0 2.8 26.0 0.19 2.30 30 129 157 4.61 1.06 3.07

BNNm-b1 61.8 4.5 41.9 0.21 2.53 40 127 146 2.58 0.49 3.25BRNm-b1 57.6 3.7 35.9 0.20 2.43 40 124 143 2.74 0.65 3.45BRRm-b1 55.5 3.4 31.3 0.22 2.36 30 124 141 3.46 0.88 3.54BNNh-b1 103.0 6.7 51.9 0.21 2.61 60 141 165 1.69 0.13 3.08BRNh-b1 105.3 6.0 43.5 0.20 2.49 50 140 166 2.59 0.49 2.83BRRh-b1 97.7 5.2 39.3 0.22 2.42 40 136 165 3.52 0.77 3.34


In majority the failure was of flexural type (Table 7), with reinforcement yielding, and with small damage of compressed concrete in the final phase. The cases of shear failure are indicated in the Table 8.

The results of σcm - εcm relations for concrete in se-lected four series of beams are presented in Fig. 4. In Fig. 4a the results of medium-strength concrete testing

(BNNm, BRNm, BRRm) are presented. These concretes were used for two series of beams (BNNm-b1, BRNm-b1, BRRm-b1) and (BNNm-b2, BRNm-b2, BRRm-b2). In Fig. 4b the results of high-strength concrete testing (BNNh, BRNh, BRRh) are presented. These concretes were used in two series of beams (BNNh-b1, BRNh-b1, BRRh-b1) and (BNNh-b2, BRNh-b2, BRRh-b2).

Table 8 Properties of concrete and results of tests on beams with bottom reinforcement 4Ø16 mm.

Results of concrete tests Results of beam tests fcm fctm Ecm νcm ρcm 2Fcr 2Fy 2Fu a110 Σw110 εc,max

Beam symbol

MPa MPa GPa kg/dm3 kN kN kN mm mm ‰ ONNl-b2 38.2 3.4 37.3 0.16 2.35 40 214 227 4.40 0.86 3.14ORNl-b2 36.6 2.9 28.1 0.15 2.28 30 214 236 4.91 0.79 3.89ORRl-b2 30.5 2.5 21.5 0.18 2.20 20 210 226 5.52 1.55 3.79

ONNm-b2 59.1 3.6 37.4 0.17 2.36 30 214 234 4.06 0.81 3.22ORNm-b2 58.3 3.2 31.8 0.18 2.29 40 214 237* 4.37 1.26 3.45ORRm-b2 57.5 3.0 28.0 0.19 2.24 20 214 248 4.72 1.34 4.10GNNl-b2 38.7 3.1 28.5 0.16 2.39 40 210 217* 4.23 0.93 2.88GRNl-b2 39.3 3.0 25.5 0.17 2.31 30 200 233* 4.59 1.11 3.69GRRl-b2 35.8 2.7 22.1 0.19 2.24 20 210 226* 4.79 1.61 3.82

GNNm-b2 63.7 4.4 31.8 0.20 2.39 40 215 238 3.89 1.25 3.38GRNm-b2 59.6 4.1 30.1 0.21 2.29 30 218 237* 4.59 1.33 3.17GRRm-b2 59.2 3.8 26.4 0.20 2.23 30 210 251 4.64 1.38 3.81GNNh-b2 93.4 5.9 37.1 0.18 2.45 50 200 250* 5.62 0.79 1.15GRNh-b2 89.1 5.1 34.4 0.19 2.35 40 194 242* 5.60 0.94 1.67GRRh-b2 82.2 4.8 30.2 0.21 2.28 30 210 255* 6.60 1.03 3.02BNNl-b2 39.6 3.5 37.4 0.20 2.55 50 213 231 3.96 0.75 4.15BRNl-b2 35.8 3.2 33.4 0.19 2.44 45 214 241 4.13 0.85 3.96BRRl-b2 31.4 3.0 27.5 0.19 2.36 30 213 220 4.69 0.96 3.83

BNNm-b2 60.8 4.1 41.5 0.20 2.52 50 210 238* 3.59 0.51 3.25BRNm-b2 59.6 3.6 35.7 0.19 2.42 60 212 238* 3.90 0.69 3.37BRRm-b2 57.6 3.3 30.8 0.20 2.36 50 217 236* 4.13 0.93 3.45BNNh-b2 100.9 7.2 51.9 0.21 2.62 65 221 262* 3.37 0.33 3.59BRNh-b2 107.8 6.3 43.5 0.20 2.46 50 220 261* 3.86 0.64 3.32BRRh-b2 100.5 5.1 39.3 0.22 2.41 50 223 256* 4.20 0.70 3.28

*shear failure.

a)

0

20

40

60

80

100

120

0 0,5 1 1,5 2 2,5 3 3,5

εcm [o/oo]

cm [M

Pa]

BNNmBRNmBRRm

b)

0

20

40

60

80

100

120

0 0,5 1 1,5 2 2,5 3 3,5

εcm [o/oo]

cm [M

Pa]

BNNhBRNhBRRh

Fig. 4 Relations σcm-εcm for the concrete used in beam series.

σ cm

[MPa

]

σ cm

[MPa

]


a)

0

20

40

60

80

100

0 10 20 30 40 50 60

deflection [mm]

F [k

N]

BNNm-b1BRNm-b1BRRm-b1

b)

0

20

40

60

80

100

0 10 20 30 40 50 60

deflection [mm]

F [k

N]

BNNh-b1BRNh-b1BRRh-b1

c)

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60deflection [mm]

F [k

N]


d)

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60

deflection [mm]

F [k

N]


Fig. 5 Comparison of deflection/load relation at midspan section for four beam series.

a)

0

20

40

60

80

100

0 0,5 1 1,5 2 2,5 3 3,5εc [o/oo]

F [k

N]


b)

0

20

40

60

80

100

0 0,5 1 1,5 2 2,5 3 3,5εc [o/oo]

F [k

N]


c)

0

20

40

60

80

100

120

140

0 0,5 1 1,5 2 2,5 3 3,5

εc [o/oo]

F [k

N]


d)

0

20

40

60

80

100

120

140

0 0,5 1 1,5 2 2,5 3 3,5

εc [o/oo]

F [k

N]


Fig. 6 Comparison of strains in concrete, εc, recorded on the top surface of beams in series.


The differences in deformability in both groups of concretes (medium- and high-strength) depend on the origin of aggregate used in concrete mixtures, despite using in all cases basalt as a coarse aggregate. The greater contribution of recycled aggregate the lower modulus of elasticity is evident.

Some results from the tests on series of beams are presented in Fig. 5, 6 and 7. In particular, two groups of relation are showed: deflection/load at midspan section and development of strains in concrete on the top sur-face of the beams. Both relations are very similar in the members, just as results of comparison of summarized width of cracks measured along the main reinforcement (Fig. 7).

In general, the differences in behaviour of beams sub-jected to short-term loading were very small, but the beams made with fully recycled aggregate should be assessed as a bit worse from the structural point of view, taking into account the flexural stiffness. The tests pre-sented here confirmed the initial analysis presented ear-lier (Ajdukiewicz, Kliszczewicz 2002b, 2006). In the beams made with high-strength concrete and with a smaller flexural reinforcement (4∅12), the mean value of destructive load (recorded as yielding of reinforce-ment) was 11.2 % greater in comparison with the same beams made of medium-strength concrete. However, in the beams with stronger reinforcement (4∅16), the mean difference in the similar comparison was 3.9 % only.

The behaviour of beams at failure differed, but all the beams in each series showed very similar pattern of

cracks and shape of failure (compare Fig. 8 and 9). In the beams made with RAC the first cracks were ob-served at one step of loading earlier than in beams made with natural aggregate concrete. In all cases initial cracks occurred along the stirrups. At more advanced levels of loading many branched cracks of small width were observed. It was the evidence of proper bond of reinforcement and such situation was observed up to the failure.

All the beams in series with flexural reinforcement 4∅12: (ONNl-b1, ORNl-b1, ORRl-b1); (ONNm-b1, ORNm-b1, ORRm-b1); (GNNl-b1, GRNl-b1, GRRl-b1); (GNNm-b1, GRNm-b1, GRRm-b1); (GNNh-b1, GRNh-b1, GRRh-b1); (BNNl-b1, BRNl-b1, BRRl-b1); (BNNm-b1, BRNm-b1, BRRm-b1); (BNNh-b1, BRNh-b1, BRRh-b1) showed the flexural shape of failure and yielding of main reinforcement as the main reason of failure.

In all the beams made with high-strength concrete and with stronger reinforcement - 4∅16: (ONNl-b2, ORNl-b2, ORRl-b2); (ONNm-b2, ORNm-b2, ORRm-b2); (GNNl-b2, GRNl-b2, GRRl-b2); (GNNm-b2, GRNm-b2, GRRm-b2); (GNNh-b2, GRNh-b2, GRRh-b2); (BNNl-b2, BRNl-b2, BRRl-b2); (BNNm-b2, BRNm-b2, BRRm-b2); (BNNh-b2, BRNh-b2, BRRh-b2) the shear failure was finally dominating (see Table 8). In Fig. 8 and Fig. 9 the cracks decisive at failure are signed with thicker line.

The selected beams at the final stage of testing are presented in Fig. 10, 11 and 12.

a)

0

20

40

60

80

100

0 5 10 15 20 25 30

Σ w [mm]

F [k

N]


b)

0

20

40

60

80

100

0 5 10 15 20 25 30

Σ w [mm]

F [k

N]


c)

0

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100

120

140

0 5 10 15 20 25 30

Σ w [mm]

F [k

N]


d)

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60

80

100

120

140

0 5 10 15 20 25 30

Σ w [mm]

F kN

]


Fig. 7 Comparison of summarized width of cracks, Σw, measured along the reinforcement for the beam series.


Fig. 8 Final patterns of cracks in beam series BNNh-b1, BRNh-b1, BRRh-b1 (flexural failure).

Fig. 9 Final patterns of cracks in beam series BNNh-b2, BRNh-b2, BRRh-b2 (failure by shear).

Fig. 10 Beam BRNh-b1 at the stage of advanced cracking.


3.2. Reinforced concrete columns The results of testing of properties of concrete used in columns are presented in Table 9 similarly as before for beams. The second part of Table 9 contains the main test results for columns: • load at the first horizontal cracks, Fcrx, • load at the first vertical cracks, Fcry, • ultimate load, Fu, • the greatest horizontal strains in concrete, εcx,max,

• the greatest vertical strains in concrete, εcy,max re-corded during testing columns up to the failure. The comparison of characteristics σcm-εcm for me-

dium-strength concretes used in columns (ONNm, ORNm, ORRm; GNNm, GRNm, GRRm; BNNm, BRNm, BRRm) with various contribution of recycled aggregate is presented in Fig. 13a÷c, while for high-strength concretes (BNNh, BRNh, BRRh) in Fig. 14a.

Some selected results from column tests are presented

Fig. 11 Middle part of the beam BRNh-b1 in the final step of loading before flexural failure.

Fig. 12 Beam BRNh-b2 in the final step of loading before failure by shear.

Table 9 Properties of concrete and results of tests on columns.

Results of concrete tests Results of column tests fcm fctm Ecm νcm ρcm Fcrx Fcry Fu εcx.max εcy.max

Column symbol

MPa MPa GPa - kg/dm3 kN kN kN ‰ ‰ GNNl-c 40.2 3.3 28.3 0.18 2.40 950 1000 1051 1.25 2.77 GRNl-c 38.7 3.3 24.1 0.18 2.30 500 800 950 1.43 3.03 GRRl-c 34.3 2.8 22.4 0.20 2.22 400 800 905 2.42 3.16

ONNm-c 50.9 3.5 35.6 0.16 2.38 800 1300 1300 1.18 2.80 ORNm-c 51.5 3.2 31.8 0.18 2.29 950 1500 1506 1.23 2.91 ORRm-c 57.5 3.6 28.0 0.19 2.24 700 1500 1352 1.00 3.41 GNNm-c 60.2 4.4 34.6 0.20 2.39 1000 1400 1445 1.24 3.61 GRNm-c 63.7 4.1 31.8 0.21 2.31 850 1406 1406 2.14 3.13 GRRm-c 59.2 3.8 26.4 0.20 2.24 850 1350 1459 2.71 3.91 BNNm-c 55.7 4.3 39.4 0.20 2.55 800 950 1297 1.85 1.92 BRNm-c 61.1 3.7 37.3 0.20 2.43 800 800 1252 2.40 2.52 BRRm-c 55.5 4.3 32.8 0.22 2.39 400 600 1203 2.83 2.31 BNNh-c 90.8 5.8 51.3 0.22 2.60 700 2000 2401 1.25 2.66 BRNh-c 102.5 6.1 48.2 0.21 2.50 800 2100 2402 0.74 2.43 BRRh-c 94.7 4.7 40.3 0.21 2.46 800 2000 2302 0.86 2.81


in Fig. 13d÷f, and in Fig. 14b on diagrams of the verti-cal strains in concrete, εcy, and for horizontal strains in concrete, εcx. The differences in deformability are visi-ble, but much smaller than those recorded for specimens of concrete with various contribution of recycled aggre-gate. The strains in columns with RAC are slightly greater. It should be emphasized that the difference of strains in concrete specimens with fully recycled aggre-

gate (e.g. ORRm, GRRm, BRRm, BRRh – Fig. 13a÷c and Fig. 14a) are significantly greater than the strains measured in columns made of this concrete (e.g. ORRm-c, GRRm-c, BRRm-c, BRRh-c – Fig. 13d÷f and Fig. 14b). The presence of reinforcement is a crucial factor for equalizing the behaviour of concrete in col-umns in comparison with specimens.

The behaviour of all columns at failure was very

a) d)

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80

-3,5-3-2,5-2-1,5-1-0,500,511,5

ONNmORNmORRm

εcx [o/oo] εcy [o/oo]

σc [MPa]

0

500

1000

1500

-3,5-3-2,5-2-1,5-1-0,500,511,5

ONNm-cORNm-cORRm-c

F [kN]

εcx [o/oo] εcy [o/oo] b) e)

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-3,5-3-2,5-2-1,5-1-0,500,511,5

GNNmGRNmGRRm


σc [MPa]

0

500

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1500

-3,5-3-2,5-2-1,5-1-0,500,511,5

GNNm-cGRNm-cGRRm-c


F [kN]

c) f)

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20

40

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-3,5-3-2,5-2-1,5-1-0,500,511,5

BNNmBRNmBRRm


σc [MPa]

0

500

1000

1500

-3,5-3-2,5-2-1,5-1-0,500,511,5

BNNm-cBRNm-cBRRm-c


F [kN]

Fig. 13 Results of strains measured in concrete specimens in column made of medium-strength concrete: a÷c) comparison of relation σc - εc recorded at testing specimens ∅150x300 mm,d÷f) diagrams of vertical strains, εcy, and horizontal strains, εcx, in the middle part of column height.


similar – at relatively low level of loading the first hori-zontal cracks were observed, while the vertical cracks appeared just before the failure. In all cases the direct reason of failure was rapid crash of concrete, and in the parts of concrete failure the buckled reinforcement was visible (Fig. 15).

4. Conclusions

In general, behaviour of reinforced concrete beams sub-jected to bending and shear, as well as columns sub-jected to axial compressive loads, depends on properties of materials and constructional features. Considering similar elements made from concrete of the same mix-

a) b)

0

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-3,5-3-2,5-2-1,5-1-0,500,511,5

BNNhBRNhBRRh

σc [MPa]

εcy [o/oo]εcx [o/oo]

0

500

1000

1500

2000

2500

-3,5-3-2,5-2-1,5-1-0,500,511,5

BNNh-cBRNh-cBRRh-c

εcx [o/oo]

F [kN]

εcy [o/oo] Fig. 14 Results of strains measured in concrete specimens and in column made of high-strength concrete: a) comparison of relation σc - εc recorded at testing concrete specimens ∅150x300 mm, b) diagrams of vertical strains,

εcy, and horizontal strains, εcx, in the middle part of column height.

Fig. 15 View of the columns BNNh-c, BRNh-c, BRRh-c after failure.

BNNh-c BRNh-c BRRh-c


ture proportions, but using different aggregates, it is difficult to predict properly their failure shape, load-bearing capacity, deflection etc. Such a situation was found at the introduction of recycled aggregate con-cretes (RAC). Despite the wide range of tests concern-ing differences in properties of concrete made with use of particular recycled aggregates, the assessment of global result may be done more or less roughly only on the basis of standard methods of analysis.

The test results and observations may be concluded as follows: (1) differences in behaviour of reinforced-concrete members made of new, partially recycled and fully re-cycled aggregate were relatively small within a particu-lar series as regards failure, but quite significant when strains have been analyzed,

(2) load-bearing capacity of the beams made of recy-cled aggregate concrete was somewhat smaller, in av-erage 3.5 %, in cases of flexural failure (beams with relatively small reinforcement), while in beams with stronger reinforcement (shear failure) the capacity was a bit greater,

(3) in the tests of specimens was recorded the greater deformability in those made of RAC and this resulted in greater deformation of beams (deflection) and col-umns (shortening); nevertheless, the presence of rein-forcement moderated this influence,

(4) deflections (immediate) of beams made of RAC were always greater than of comparable beams made with natural (new) aggregate, and the range of differ-ences varied from about 18 % to 100 % at a probable service load (see a70 in Table 7 and a110 in Table 8),

(5) in the tests of columns no difference was observed in the behaviour under load up to failure, but itself phe-nomenon of failure was less rapid in case of columns made of RAC; this is a result of greater ductility of RAC recorded in specimens.

The results of tests on reinforced-concrete members confirmed the full possibility of use of good quality recycled aggregates in structural members made of me-dium- or high-strength concrete. This is a general con-clusion from the tests under instantaneous loading. The use of RAC in beams should be more careful when limi-tation of deflection is important. Consequently, investi-gations on beams and columns behaviour under long-term load are necessary to clarify the influence of rela-tively large differences in creep and shrinkage recorded in recycled aggregate concrete (RAC) in comparison with natural aggregate concrete (NAC).

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Documents

Comparative Tests of Beams and Columns Made of Recycled