USE OF CONCRETE RECYCLED AGGREGATES IN ROLLER COMPACTED CONCRETE

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1 USE OF CONCRETE RECYCLED AGGREGATES IN ROLLER COMPACTED CONCRETE P. Delhez, X. Willem, F. Michel and L. Courard University of Liège, GéomaC Department, Research Unit in Building Materials, Belgium Abstract Construction waste management is a quite important economical and environmental deal for our societies. More than 2 million tons are annually produced in Wallonia, South Region of Belgium, and numerous valorisations have been already promoted. Roller Compacted Concrete 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 recycled aggregates in the composition of the concrete. Characteristics of aggregates are of prime importance for the quality of the concrete: Los Angeles, water absorption and specific gravity are measured. Design method, type of hydraulic binder and proportions have to be adapted. Final and long term properties have also been evaluated. Keywords: Roller Compacted Concrete, recycled aggregate, cement content, sand content, water content. 1. ROLLER COMPACTED CONCRETE The Roller Compacted Concrete (RCC) is made of the same constituents than ordinary concrete [1,2,3]: cement, water, sands and aggregates. It is however more dry, with zero slump [4], which requires a higher compacting energy than ordinary concrete, in order to be well consolidated. 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 Moreover, this type of concrete is less sensitive to cracking in relation with drying shrinkage. In road construction, RCC are generally laid down in 20cm 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. The Belgian Guidelines RW99 [6] define the minimum requirements for such a type of concrete used in road foundations : BSC 20 and BSC 30, with a cement content of minimum 200kg/m³ and 250kg/m³, respectively, must reach an average compressive strength of 20 and 30 N/mm² respectively (90 days, 100 cm² cores). 675

2 The aim of this research project is the use of 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 are referred JMV2/20. Different tests have been performed in order to characterize their physical, chemical and mechanical properties [7,8,9]. Visual observation (Fig.1) shows there are mainly composed of concrete aggregates, with some parts of bitumen, clinkers pavements and steel fibres. Figure 1: recycled aggregates in delivery state (a) and recycled aggregates after drying and water washing (b) Granulometry analysis is necessary to design concrete; it has been established 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 10mm. Before mixing, only 5.87% in mass are lower than 10mm, while this percentage grows up to 13.53% after mixing. That means also that the aggregate is more a 10/20 than a 2/20 material. Passing (%) ,01 0,10 1,00 10,00 100,00 Sieve (mm) Figure 2 : Granulometry of recycled aggregate before ( ) and after mixing ( ) 676

3 The analysis of the passing though 80µm 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 because this material is porous. Finally, water absorption coefficient (NBN B ) is determined in order to evaluate the quantity of water that will be removed during hydration process. This water absorption is only determined on granulometry fractions from 7 to 20mm. Table 1: Principal physical characteristics of recycled aggregates Test Results Value of methylene As delivered 12.4 blue (g/kg) After dry mixing 6.2 Bulk density (kg/m³) 2609 Specific gravity (kg/m³) 2634 Water absorption coefficient (%) 4.58 Los Angeles Coefficient 25 Methylene blue values are very low, which means that the aggregate is acceptable for using in concrete. Specific and bulk density 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 and Los Angeles coefficient has been calculated; values that are obtained for 10/14 and 14/20 fractions show again an excellent behaviour. 2.2 Other materials A blast furnace slag cement CEM III/A 42.5 N LA has been selected for its low hydration rate and a longer maniability of the mix. The granulometry of the granular skeleton has been completed with a limestone crushed sand 0/ Mixing procedure The main objective of designing concrete is to optimize the compactness [10,11], in order to obtain a resistant and durable material. For RCC, the vibratory compaction energy is very important and will contribute to the quality of the job. Proctor Modified Test are usually performed [6]; we have chosen another procedure (Fig.3) that permitted us to directly cast Ø160mm and h320mm cylinders. The entire procedure is described hereafter: 1. introduction of aggregates and sand in the mixer and mixing for 2 minutes 2. resting for 1 min 3. addition of cement and mixing for 2 min 4. addition of water and mixing for 2 min 5. fulfilling of the mould fixed on the vibrating table (2 layers) 6. vibration for 1 min 677

4 Figure 3a: material necessary for Vibration Weighing test Figure 3b: principle of the test The compactness is evaluated of samples of about 7.5kg; a weight of 20kg is inducing a pressure of 10kPa during the vibration (150Hz). The volume of concrete really cast is measured and compactness is deduced from the relation Vsolid/Vtotal. 3. OPTIMIZATION OF THE MIX The mix is based on the requirements defined in the Belgian Guidelines RW99 [3] and the design of the concrete according to Faury theory [11], which optimize the granular skeleton. Due to the lack of grains between 2 and 10mm, a first mix was designed with too much quantity of sand [11]. We have consequently worked on the optimization of the sand to aggregates ratio and the water content corresponding to the highest compactness. The optimized granular skeleton is finally given in Table 2. Table 2: composition of the granular skeleton of the mix Raw material Quantity (kg/m³) Cement CEM III/A Limestone sand 0/ Recycled aggregates JMV2/ The quantity of water is then optimized by measuring compactness for different water contents (Table 3). 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 (W tot ) and the water that is really efficient in the hydration process of cement (W eff ): Ø is the volume 678

5 of material (solid or water) vs the total volume (1m³): it represents the compactness of the material. Table 3: water content and compactness of mixes with identical granular skeleton Mix Total water (l/m³) Efficient water (l/m³) (W/C) eff Ø solid Ø water efficient Ø solidefficient f cm 7days (N/mm²) The fig.4 shows an optimum of solid compactness relatively wide spread, for a total water content between 140 and 160l/m³. Solid compactness 0,840 0,820 0,800 0,780 0,760 0,740 0,720 0,20 0,25 0,30 0,35 0,40 0,45 0,50 0,55 (W/C) eff Figure 4: Solid compactness vs (W/C) eff for optimum s/g ratio The compressive strength after 7days (Table 3) remains constant for water content between 140 and 170l/m³, while it is hardly decreasing (Fig.5) when lower quantities of water ( l/m³); in this case; concrete becomes too dry and unbonded. The final composition of concrete is given with a water content of 150l/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 shown [11] that the material should have a good behavior in winter conditions. 679

6 f 0 at 7 days (N/mm²) ,750 0,760 0,770 0,780 0,790 0,800 0,810 0,820 Solid compactness Figure 5: compressive strength at 7 days vs solid compactness 4. OPTIMIZATION OF PARAMETERS 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 aggregates. The granulometry of the natural RCC was adapted to the one of the recycled aggregate, which lead to a composition of 10/14 and 14/20. (Table 4 ). Table 4: Composition of RCC with natural and recycled aggregates Composition RCC RCC Recycled Natural Cement (kg/m³) Sand (kg/m³) /20 recycled (kg/m³) /14 Limestone aggregates (kg/m³) /20 Limestone aggregates (kg/m³) Water (l/m³) 95,5 95,5 Solid compactness for both RCC are in the same range (Table 5). 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, due to their better quality (static compression, LA coefficient) and an increasing after 28 days (± 5 N/mm²) for the both mixes. Table 5: Compactness and compressive strength of RCC with natural and recycled aggregates RCC Recycled aggregates RCC Natural aggregates Solid compactness Efficient solid compactness Compressive strength (7 days) Compressive strength (28 days)

7 4.2 Test conditions 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 (4.5kg) falls down (457mm) several times (56) on the material cast in 5 layers in a CBR mould. After arising, the moisty density h is measured. The dry density d is evaluated according to equation (1): ρh (1) ρ d = x100 where w is the water content of the concrete w+ 100 Compaction curve ( ρ d vs w) has 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.6). Optimum Proctor is obtained for a water content between 6.46% and 7.39%; these are corresponding to a total volume of water of 140 l/m³ to 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 equations (2) and (3): ρ h = M V' ' where M is the mass and V the volume of concrete (2) ρh (3) where w is the water content of concrete 1+ w ρ d = ( ) The two curves (Fig. 6) present the same shape and optimum for the same water content, which clearly means that we made a good choice with Vibration Weighing Test: this procedure is more interesting because it gives cylinders that can be use for further classical investigations and evaluation of concrete. Table 6: Bulk density of the RCC mix, according to Proctor Modified and VWT Proctor modified Test Vibration Weighing Test w (%) ρ d (kg/m³) ρ d (kg/m³) ,

8 2300 Volumic mass of dry material (kg/m³) % 5% 6% 7% 8% 9% Water content (%) Figure 6: Comparison of Proctor Modified ( ) and Vibration Weighing Tests ( ) 4.3 Cement content Based on the optimized composition of RCC, mixes are 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 150kg/m³. This is due to the decreasing quantity of water, which is replaced by air (Table 7). Table 7: Solid compactness and compressive strength vs cement content of RCC mixes. f cm at 7 jours Cement (kg/m³) φ Solid (N/mm²) 250 0, , , , While solid compactness remains constant between 250 and 175kg/m³, the compressive strength (Fig.7) after 7 days is naturally decreasing (43%); if this criteria is the most discriminate, cement content should not go under 200kg/m³. 0,820 Solid compactness 0,810 0,800 0,790 0,780 0,770 0, C (kg/m³) Figure 7: Evolution of solid compactness with RCC cement content. 682

9 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 presented quite good performances for such use : 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) give 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, due to the excellent quality of them ; - Cement content has no major impact on solid compactness when varying between 250 to 175 kg/m³. However, sensitivity of compressive strength to cement content tends to limit this minimum value to 200 kg/m³ ; REFERENCES [1] Ouellet E., Formulation et étude du comportement mécanique des bétons compactés au rouleau, Mémoire de maîtrise ès sciences, Université Laval (Qc), Canada (1998). [2] Emploi du béton compacté dans les chaussées, Comité Technique des Routes en Bétons, Association Internationale Permanente des Congrès de la Route, France, [3] Guerinet M., Le béton compacté au rouleau, Ecole Nationale des Ponts et Chaussées, Ponts formation édition (1997), pp [4] Burns Cecil D., Saucier Kenneth L., Vibratory Compaction Study of Zero-Slump Concrete, ACI Journal, March [5] Tremblay S., Méthodes de formulation de Bétons Compactés au Rouleau et effet des agents entraîneur d air sur la maniabilité, Mémoire de maîtrise ès sciences, Université Laval (Qc), Canada (1997), pp [6] Cahier des charges-type RW 99, Clauses administratives et techniques applicables à l exécution des routes et autoroutes situées en Région Wallonne. [7] Oikonomou Nik.D., Recycled concrete aggregates, Cement and Concrete Composites, 2004 (under press). [8] Levy Salomon M., Helene Paulo, Durability of recycled aggregates concrete : a safe way to sustainable development, Cement and Concrete Research, 2004 (under press). [9] Gomez-Soberon J., Porosity of recycled concrete with substitution of recycled concrete aggregate, An experimental study, Cement and Concrete Research 32 (2002), pp [10]de Larrard F., Marchand J., Pouliot N., Sedran T., Prédiction de la compacité des bétons compactés au rouleau à l aide d un modèle d empilement granulaire, Bulletin des Laboratoires des Ponts et Chaussées, 233, Juillet-Août 2001, REF 4370, pp [11]Delhez, P., Formulation d un Béton Compacté au Rouleau à partir de granulats recyclés pour l utilisation dans le domaine routier, Master Thesis, Université de Liège, Faculté des Sciences Aplliquées, Juin 2004, 125p. 683