Use of concrete road recycled aggregates for Roller Compacted Concrete

Construction and Building Materials 24 (2010) 390–395

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Use of concrete road recycled aggregates for Roller Compacted Concrete Luc Courard, Frédéric Michel *, Pascal Delhez University of Liege, ArGEnCo Déparment, GeMMe Building Materials, Belgium

a r t i c l e

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Article history: Received 2 April 2009 Received in revised form 7 July 2009 Accepted 5 August 2009 Available online 7 October 2009 Keywords: Rigid pavement Concrete Compaction Recycling Roller Compacted Concrete Recycled aggregate Design Vibration Weighing Test

a b s t r a c t Construction waste management is a quite important economical and environmental deal for our societies. More than 2 million tons demolition and construction wastes are annually produced only in Wallonia, Southern Region of Belgium; recycling has clearly to be promoted. Roller Compacted Concrete (RCC) is a special dry concrete made of aggregates, water and low quantity of cement, laid down and compacted like a soil, for the construction of massive structures like dams or large horizontal surfaces like road foundations. The topic of this research is the replacement of natural aggregates by concrete road recycled aggregates in the mix design of concrete. Characteristics of aggregates are of prime importance for the quality of the concrete: Los Angeles, water absorption and specific gravity. It has been observed that RCC with natural and concrete road recycled aggregates are similar for solid compactness, while no major influence of cement content – when around 200 kg – may be detected. However, compressive strength is higher for RCC with natural aggregates. This study clearly shows the opportunity of using concrete road recycled aggregates for RCC in basements. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Roller Compacted Concrete (RCC) has the same basic ingredients as conventional concrete [1–3]: cement, water, sands and aggregates. But unlike conventional concrete, it is a drier mix—stiff enough to be compacted by vibratory rollers [4]. Typically, RCC is constructed without joints. It needs neither forms nor finishing, nor does it contain dowels or steel reinforcing. If well designed [1,5], the RCC will develop high compressive strength and good durability, i.e. 40 N/mm2 at 3 days for a cement content of 300 kg/m3 and a W/C ratio of 0.35 [6]. Moreover, this type of concrete is less sensitive to cracking in relation with drying shrinkage. In road construction, RCC is generally laid down in 20 cm thick by means of motor graders that will insure the flatness and uniformity of the surface. Compaction is assured by pneumatic-tyred rollers and finishing rollers. Belgian Guidelines [7] define the minimum requirements for such a type of concrete used in road foundations: BSC 20 and BSC 30 samples (100 cm2 cores), with a cement content of minimum 200 kg/m3 and 250 kg/m3, respectively, must reach an average compressive strength of 20 and 30 N/mm2, respectively, at the age of 90 days. Today, RCC is used for any type of industrial or heavy-duty pavement. The reason is simple. RCC has the strength and performance of conventional concrete with the economy and simplicity of asphalt.

* Corresponding author. Address: University of Liege, Chemin des Chevreuils, 1, 4000 Liege, Belgium. Tel.: +32 4 366 92 37; fax: +32 4 366 95 20. E-mail address: [email protected] (F. Michel). 0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2009.08.040

On the other side, production of recycled aggregates coming from construction, renovation and demolition is increasing. Due to the large variety of their performances and origin, recycled aggregates offer variable properties, which may bridle reuse [8– 10]. Concrete road recycled aggregates generally present more constant properties due to the relative homogeneity of the source: hydraulic and bituminous concretes are the two main types of road recycled materials. They are consequently easier to reuse and qualify: common applications are road foundations, with or without cementitious binders. Limitations are usually coming from wear, attrition or low strength due to cement paste content. The aim of this research project is the study of the use of concrete road recycled aggregates as raw material for the design of RCC. 2. Description of materials 2.1. Recycled aggregates Recycled concrete aggregates are coming from industrial plant and originally come mainly from bituminous road pavements. Different tests have been performed in order to characterize their physical, chemical and mechanical properties. Visual observation (Fig. 1) shows there are mainly composed of concrete aggregates, with some parts of bitumen, clinkers pavements and steel fibres, smaller recycled aggregates could also greatly affect the mechanical properties of RCC due to larger amount of cementitious mortar. Sieve analysis is necessary to design concrete; it has been

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Fig. 1. Recycled aggregates in delivery state (a) and recycled aggregates after drying and water washing (b).

measured on the material in its delivery state and after a dry mixing procedure (30 min). It shows (Fig. 2) that the majority of the grains are greater than 10 mm. Before mixing, only 5.87% in mass are lower than 10 mm, while this percentage grows up to 13.53% after mixing. That means also that the aggregate is more close to 10/20 than 2/20. The analysis of the passing though 80 lm sieve has also been realized to evaluate the potential surface activity of fine particles (clay, organic materials, ferrous hydroxides), according to the measurement of the methylene blue value (NBN B11-210); density is also fundamental, particularly in relation with material porosity. Finally, water absorption coefficient (NBN B 11-255) is determined in order to evaluate the quantity of water that could be removed during hydration process (Table 2). This water absorption is only determined on granulometry fractions from 7 to 20 mm. Methylene blue values are very low, which means that the aggregate is acceptable for use in concrete. Specific and bulk densities are quite high and very close to natural aggregates, which is again a label of quality. Finally, resistance to fragmentation has been evaluated according to NF P 18-573 and Los Angeles coefficient has been calculated; values that are obtained for 10/14 and 14/20 fractions show again an excellent behavior. On the base of mean values of water absorption of the different calibres, and taking into account the composition of the mix, a

Passing (%)

100 80 60 40 20 0 0.01

0.10

1.00

10.00

100.00

Sieving diameter (mm) Fig. 2. Granulometry of recycled aggregate before (N) and after mixing (j).

Table 1 Principal physical characteristics of recycled aggregates. Test

Results

Value of methylene blue (g/kg) As delivered After dry mixing Bulk density (kg/m3) Specific gravity (kg/m3) Water absorption coefficient (%) Los Angeles coefficient

12.4 6.2 2609 2634 4.58 25

Table 2 Water absorption results for different aggregate calibres (d/D) in mm. Calibre (mm)

Sampling

m1 (g)

m2 (g)

Absorption coefficient (%)

14/20 14/20 10/14 10/14 7,1/10 7,1/10

1 2 1 2 1 2

317 312 348 296 142 131

302 297 334 284 133 122

5.14 4.97 4.27 4.51 6.82 6.55

mean coefficient (Table 1) has been calculated. Water absorption remains largely greater than for natural aggregates; porous nature of concrete will consequently induce the use of higher quantities of water for mix design. 2.2. Other materials Blast Furnace Slag cement CEM III/A 42.5 N LA was selected for its low hydration rate and a longer workability of the mix. The granulometry of the granular skeleton has been completed with a limestone crushed sand 0/2.5. 2.3. Mix design The main objective is to optimize the compactness [11,12], in order to obtain a resistant and durable material. Design methods include concrete consistency tests, soil compaction method, optimal paste volume method and solid suspensions model [5,6]. These methods are always proceeding by trials and errors: they usually tend to minimize cement content, with regard to water and aggregates. Main design methods are however based on compacity concept [13], as used for soil compaction. Specifically, solid compaction model [6] helps to take into account consistency and compacity of the mix. Consequently, the vibratory compaction energy appears to be very important for RCC and largely contributes to the quality of the operations: Proctor Modified Test is usually performed for this reason [5]. Another procedure (Fig. 3) was however developed and allowed to directly cast £160 mm and h320 mm cylinders. The main advantage of this alternative method is the possibility of reuse of the cylinder prepared by compaction (‘‘non destructive technique”). The entire mix procedure is described hereafter: 1. introduction of aggregates and sand in the mixer and mixing for 2 min; 2. resting for 1 min; 3. addition of cement and mixing for 2 min; 4. addition of water and mixing for 2 min;

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Fig. 3. (a) Material necessary for Vibration Weighing Test. (b) Principle of the Vibration Weighing Test.

5. fulfilling of the mould fixed on the vibrating table (2 layers); 6. vibration for 1 min. The compactness is evaluated on samples of about 7.5 kg; a weight of 20 kg produces a pressure of 10 kPa during the vibration (150 Hz). The volume of concrete really cast is measured and compactness is deduced from the relation Vsolid/Vtotal, where Vsolid is corresponding to the volume of solid after vibration and Vtotal the volume of the mould. 3. Optimization of the mix The mix is based on the requirements defined in the Belgian Guidelines [7] and the design of the concrete according to Faury theory [11], for optimizing the granular skeleton on the base of reference curves. Due to the lack of grains between 2 and 10 mm, a first mix was designed with too much quantity of sand [11]. We have consequently worked in order to optimize the sand to aggregates ratio and the water content in such a way we obtained the highest compactness (Vibration Weighing Test, Fig. 3). The optimized granular skeleton is finally given in Table 3. Table 3 Optimal composition of the granular skeleton of the mix. Raw material

Quantity (kg/m3)

Cement CEM III/A 42.5 Limestone sand 0/2.5 Recycled aggregates 2/20

250 735 1190

The quantity of water is then optimized by measuring compactness for different water contents (Table 4). The mix proportions must take into account the water absorption coefficient of recycled aggregates in order to define the quantity of water that is needed (Wtot) and the water that is really efficient in the hydration process of cement (Weff). The compactness £ of the material is given by the ratio between the volume of material (solid or water) and the total volume (1 m3): that means, specifically, that £solid represents the volume of solid vs total volume, £water efficient the volume between aggregates fulfilled with water vs total volume, £water absorbed the volume inside aggregates fulfilled with water vs total volume and £solid-efficient = £solid + £water absorbed. Fig. 4 shows that solid compactness optimum is relatively wide spread, for total water content between 140 and 160 l/m3. The compressive strength after 7 days (Table 4) remains constant for water content between 140 and 170 l/m3, while it is hardly decreasing (Fig. 5) when lower quantities of water (120– 130 l/m3): in this case, concrete becomes too dry and unbonded. The final composition of concrete is selected, corresponding to a water content of 150 l/m3. This allowed the concrete to be laid down and compacted in good conditions, and to obtain quite excellent mechanical performances. Durability tests (freeze–thaw cycles and porosity) have also been performed on RCC with recycled aggregates (Table 3). Freeze–thaw cycles (NBN B05-203) have been realized on 100  100  100 mm samples (Fig. 6). The loss of mass is lower than 0.03% and there is almost no variation between samples (Table 5). Some debonding are however observed for aggregates covered with bituminous layer (Fig. 7). Moreover, resonance

Table 4 Water content and compactness of mixes with identical granular skeleton. Mix

Total water (l/m3)

Efficient water (l/m3)

(W/C)eff

£solid

£water

1 2 3 4 5 6 7

170 160 150 145 140 130 120

115.5 105.5 95.5 90.5 85.5 75.5 65.5

0.46 0.42 0.38 0.36 0.34 0.30 0.26

0.799 0.807 0.811 0.810 0.814 0.789 0.757

0.115 0.106 0.096 0.091 0.086 0.074 0.062

efficient

£solid-efficient

fcm 7 days (N/mm2)

0.853 0.862 0.866 0.865 0.869 0.843 0.808

20 20 21 20 20 16 13

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L. Courard et al. / Construction and Building Materials 24 (2010) 390–395

0.84 0.82 0.80 0.78 0.76 0.74 0.72 0.20

0.30

0.40

0.50

(W/C) eff

f0 at 7 days (N/mm²)

Fig. 4. Solid compactness vs (W/C)eff for optimum s/g ratio.

25 20 15 Fig. 7. Debonding on the edge of a concrete road recycled aggregate.

10 0.740

0.760

0.780 0.800 Solid compactness

0.820

Fig. 5. Compressive strength at 7 days vs solid compactness.

frequency was evaluated before and after freeze-haw cycles (NBN B 15-230). Once again, it shows very small variation, which is not discriminant. The material should consequently have a good behavior in winter conditions. 4. Parameters optimization

aggregates. The granulometry of the natural RCC was adapted to the one of the recycled aggregate, which leads to a composition of 7/14 and 14/20 crushed limestone aggregates (Table 6). Solid compactness for both RCC is in the same range (Table 7). Efficient solid compactness are however quite different, due to the higher water absorption coefficient of recycled aggregates. We observe that the compressive strength is higher for natural aggregates RCC, mainly due to the better quality of aggregates (static compression, LA coefficient). Moreover, performances are increasing after 7 days (around 5 N/mm2) for both mixes. 4.2. Test conditions

4.1. Comparison with natural aggregates A concrete with natural aggregates was designed and cast in order to compare the relative performances of RCC with recycled

In order to compare the results to classical references, a Proctor Modified Test has been performed on one mix. This test is used in geotechnical engineering to evaluate the relationship between the water content and the dry density of a soil, for a specified energy of compaction: a hammer (4.5 kg) falls down (457 mm) several times (56) on the material cast in 5 layers in a CBR mould. After arising, the moisty density qh is measured. The dry density qd is evaluated according to Eq. (1):

qd ¼



qh

w þ 100



 100

ð1Þ

Table 6 Mix design of RCC with natural and recycled aggregates.

Fig. 6. RCC sample after 14 freeze–thaw cycles.

Table 5 Resonance frequency variation and loss of mass after freeze–thaw cycles. Sample reference

Resonance frequency before freeze/thaw (Hz)

Resonance frequency after freeze/thaw (Hz)

1 2 3 2H 2M 2B 3H 3M 3B

2335 2326 2341 2327 2339 2343 2331 2331 2346

2391 2382 2383 2402 2411 2409 2421 2422 2410

(D = 2.40%) (D = 2.41%) (D = 1.79%) (D = 3.22%) (D = 3.08%) (D = 2.82%) (D = 4.72%) (D = 3.90%) (D = 2.73%)

Mix design

RCC (recycled)

RCC (natural)

Cement (kg/m3) Sand (kg/m3) 2/20 recycled (kg/m3) 7/14 Limestone aggregates (kg/m3) 14/20 Limestone aggregates (kg/m3) Water (l/m3)

250 735 1190 – – 95,5

250 735 – 810 420 95,5

Loss of mass (%) 0.02 0.03 0.02 0.02 0.02 0.03 0.03 0.002 0.06

Table 7 Compactness and compressive strength of RCC with natural and recycled aggregates.

Solid compactness Efficient solid compactness Compressive strength (7 days) Compressive strength (28 days)

RCC recycled aggregates

RCC natural aggregates

0.809 0.864 23 28

0.820 0.820 41 46

L. Courard et al. / Construction and Building Materials 24 (2010) 390–395

where w is the water content of the concreteCompaction curve (qd vs w) present a clock-shape, with a maximum value corresponding to the optimal value of water content for the higher dry density of the concrete mix (Fig. 8). Optimum Proctor is obtained for water content between 6.46% and 7.39%; these are corresponding to a total volume of water between 140 l/m3 and 160 l/m3. In order to be able to compare the two procedures, it is necessary to determine the specific gravity of the dry material coming from the concrete cylinders by using Eqs. (2) and (3):

M0 qh ¼ 0 V

ð2Þ

where M0 is the mass and V0 is the volume of concrete

qd ¼

qh

ð3Þ

ð1 þ wÞ

where w is the water content of concrete The two curves (Fig. 8) present the same shape and optimum for the same water content, which clearly means that Vibration Weighing Test is relatively selective: this procedure is more interesting because it gives cylinders that can be used for further classical investigations and evaluation of concrete. (see Table 8). 4.3. Cement content Based on the optimized composition of RCC, mixes were realized with lower cement content, in order to analyze the sensitivity of the mix to this parameter. The voids ratio is increasing when cement content decreases and becomes quite excessive for 150 kg/ m3. This is due to the decreasing quantity of water, which is replaced by air (Table 9). While solid compactness remains constant between 250 and 175 kg/m3, the compressive strength (Fig. 9) after 7 days is naturally decreasing (43%); if this criteria is the most discriminating, cement content should not be less than 200 kg/m3.

Density of dry material (kg/m³)

2300 2250 2200 2150 2100 2050 2000 4%

5%

6%

7%

8%

9%

Water content (%) Fig. 8. Comparison of Proctor Modified (j) and Vibration Weighing Tests (N).

Table 8 Bulk density of the RCC mix, according to Proctor Modified and VWT. Water content, w (%)

Proctor Modified Test, qd (kg/m3)

Vibration Weighing Test, qd (kg/m3)

7.85 7.39 6.93 6.46 6 5.54

2190 2224 2229 2227 2204 2124

2225 2246 2245 2244 2167 2068

Table 9 Solid compactness and compressive strength vs cement content of RCC mixes. Cement content (kg/m3)

/Solid

Compressive strength at 7 days (N/mm2)

250 200 175 150

0.809 0.803 0.800 0.773

23 20 13 12

0,820

Solid compactness

394

0,810 0,800 0,790 0,780 0,770 0,760 100

125

150

175

200

225

250

275

300

Cement content (kg/m³) Fig. 9. Evolution of solid compactness with RCC cement content.

5. Conclusions The following conclusions may be reached from the present investigations concerning the optimization of Roller Compacted Concrete with recycled concrete aggregates:  Recycled aggregates may present very good performances for use in RCC: very small content of fine particles, specific gravity of 2634 kg/m3, absorption coefficient of 4.58% and LA coefficient equal to 25;  Water content optimum is spread on a large range of values, which is very profitable on site. If environmental conditions are moving (temperature, relative humidity), the induced water content modification has no major impact on working conditions and final properties;  Vibration Weighing Test (VWT) gives similar results than Optimum Proctor Modified Test. This is very useful, considering the opportunity to cast samples needed for compressive strength evaluation;  RCC with natural and recycled concrete aggregates are similar for solid compactness. However, compressive strength is higher for RCC with natural aggregates;  Cement content has no major impact on solid compactness when varying between 250 and 175 kg/m3. However, sensitivity of compressive strength to cement content tends to limit this minimum value to 200 kg/m3. This study clearly shows the opportunity of using bituminous road pavements for recycling. Quality and constancy of supplying are fundamental for further use. But this is common for every work; even if it is sometimes more critics for recycling. References [1] Ouellet E. Design and study of the mechanical behaviour of Roller Compacted Concrete. Master Thesis 1998, Université Laval (Qc), Canada; 1998 [in French]. [2] Use of Roller Compacted Concrete for roads, Technical committee for concrete roads, PIARC, France; 1993. [3] Guerinet M. Roller Compacted Concrete, Ecole Nationale des Ponts et Chaussées. Ponts formation édition; 1997. p.17–29 [in French]. [4] Burns Cecil D, Saucier Kenneth L. Vibratory compaction study of zero-slump concrete. ACI J 1978;75(3):86–90. [5] Tremblay S. Design methods for Roller Compacted Concrete and effect of Air Entraining Agents on Consistency. Master Thesis 1997, Université Laval (Qc), Canada; 1997. p. 16–80 [in French].

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