C16/20 CONCRETE STRENGTH CLASS DESIGN WITH RECYCLED AGGREGATES

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1 ISSN: / e-issn: ART.NO. 156, pp C16/20 CONCRETE STRENGTH CLASS DESIGN WITH RECYCLED AGGREGATES Ofelia Corbu a, *, A. Puskás b, Henriette Szilágyi c, Cornelia Baeră c a Central Laboratory of the Faculty of Civil Engineering, Technical University of Cluj-Napoca, 28 Memorandumului Street, Cluj-Napoca, Romania, ofelia.corbu@staff.utcluj.ro b Structures Department of Faculty of Civil Engineering, Technical University of Cluj-Napoca, 28 Memorandumului Street, Cluj-Napoca, Romania, attila.puskas@dst.utcluj.ro c National Research & Development Institute for Building, Urban Planning and Sustainable Spatial Development URBAN- INCERC, Cluj-Napoca Branch, 117 Calea Floreşti Street, , Cluj-Napoca, Romania, henriette.szilagyi@incerc-cluj.ro, cornelia.baera@incerc-cluj.ro Received: / Accepted: Revised: / Available online: KEY WORDS: concrete waste, recycled aggregates, new aggregate/concrete ABSTRACT: The present paper describes the mix design and experimental tests carried out on C16/20 concrete strength class with recycled aggregates. The developed research reveals favourable results in order to militate for using of recycled concrete aggregate in regular concrete strength classes respectively for common structural elements, mainly for infrastructural elements and slabs. River sand (0/4 mm) and coarse aggregates (4/8 mm and 8/16 mm from natural sources and from recycled concrete were alternatively used in several concrete mixes. Use of recycled aggregates in concrete composition is reducing its ecological impact by saving large amounts of natural aggregates resources, making this type of concrete environmentally friendly. Concrete recycling means also waste reduction and economy; giving up both: waste transportation and storage taxes, which are becoming increasingly expensive. 1. INTRODUCTION Since 1945 several studies related to recycled aggregate concrete resulting from construction and demolition waste were performed in Romania by researchers Steopoe (Steopoe,1945) and institutes like Technical University of Civil Engineering Bucharest and National Research & Development Institute for Building, Urban Planning and Sustainable Spatial Development URBAN-INCERC, Cluj-Napoca Branch. Also researches on usual and lightweight concrete made by recycled concrete aggregates have been undertaken (Szilagyi, 2005); while in the Technical University of Cluj-Napoca, concrete roads mixes with waste glass or recycled concrete aggregates were tested (Corbu, 2013a) (Corbu, 2014). Concrete recycling process (Iacoboaea, 2009) was carried out in several countries, sources and requirements for recycled aggregate concrete are shown in Table 1 and Table 2 (Goncalves, 2010). Country/ Recycled Aggregate Maximum Organisation Aggregate (Type/Name/ Classification) Genre RCA Substitution (a) NR RCA RCA United 20% Kingdom LCAgg LCAgg NR RA RA - Australia Class 1A RCA 30% Class 1B RCA 100% USA LCA LCAgg 100% (b) 25% 60% (c) RCAC Type I RA 100% RILEM RCAC Type II RCA 100% RCAC Type III RCA 20% Korea - RCA 30% 30% (c) Germany Type 1 35% RCA Type 2 25% Portugal ARB1 25% RCA ARB2 20% Hong Kong - RCA 20% 100% Table 1. Maximum RCA substitution in new concrete (Goncalves, 2010) * Corresponding author 13

2 (a) Percentages are of coarse aggregate fraction unless otherwise stated; (b) Assumes leftover concrete aggregate separated by strength class; (c) Coarse and fine fraction; NS - Non-structural concrete; RCA - Recycled concrete aggregate (Predominantly from demolition waste concrete); LCAgg - Leftover concrete aggregate (Aggregate processed from hardened leftover concrete of known composition that has not been in use and has not been contaminated in storage); RA - Recycled aggregate (Predominantly demolition waste including concrete, masonry and asphalt); NR - No restriction. Country/ Organisation United Kingdom Australia USA RILEM Korea Germany Portugal Hong Kong Maximum Recycled Aggregate Concrete 28 Day Cylinder Strength Other Restrictions 40 MPa RCA and LCAgg. No chlor. exp. No freeze thaw. Designated concrete 20 to 40 MPa NR - 16 MPa Only mild exposure 40 MPa - 25 MPa - 20 MPa 50 MPa NS Concrete 16MPa Masonry Aggregate. Exposure restrictions 50MPa NR 27 MPa - 21 MPa 25 MPa In dry or low humidity environments 30 MPa 35 MPa - 40 MPa 35 MPa - 20 MPa NS Conc. Table 2. Strength properties and restrictions for recycled aggregate concrete in different countries (Goncalves, 2010) The mandatory elements for the new approach of the construction domain are the energy and natural resources saving tendency respectively the large use of waste (Corbu, 2010) (Corbu, 2013b). Concrete remains the most widely used building material, having the advantage of its resources (traditional or innovative) as well as the long service life of concrete structures. Concrete civil infrastructure is highly promoted also due to its sustainability benefits, including thermal capacity and the potential use of waste and by-products (Guidelines Sibiu, 2011), (Iacoboaea, 2009). The environmental impact and the huge consumption of natural aggregates are substantially reduced through the use of recycled aggregates (Poteras, 2006) (Corbu, 2010). 2. METHODS AND MATERIALS 2.1. Materials Conventional materials used in concrete mixtures are delivered by local producers and correspond to the national and European standards requirements. Recycled aggregate are resulting from hardened leftover concrete with known composition that has not been contaminated in storage (LCAgg), representing concrete samples of a large local producer of concrete elements. Usually companies pay high fees for removal, transportation and disposal of this kind of waste to landfill as inert solid waste (Poteras, 2006) Cement: CEM I 42,5 N with normal strengths (SR EN 197-1: 2011) was used in the composition of experimental concrete mixes Aggregates: natural sand (0/4 mm) as fine aggregate, crushed river aggregate and recycled aggregate processed from hardened leftover concrete, as coarse aggregate (SR EN A1: 2008). The concrete waste was originated from concrete specimens, crushed, sieved and sorted in several fraction, resulting recycled concrete aggregate (4/8 mm and 8/16 mm) same size as crushed, natural aggregate, in order to be able to substitute it in new concrete. Concretes are designed to meet the requirements of concrete normative (NE 012: 2007). In this context the grading limits for the total aggregates were chosen for C16/20 concrete strength class with 16 mm maximum aggregate size (SR EN 933-1: 2012). Passing percentages for each aggregate fraction, representing there grading curves are shown in table 3 (0/4 mm, 4/8 mm and 8/16 mm natural aggregates) and table 4 (4/8 mm and 8/16 mm recycled concrete aggregates). 14

3 composition and it also constitute the variable compound of the mixes. Table 3. Grading curves for (NA) of control concrete (CC) mix Table 4. Grading curves for (RA) of Concrete with Leftover Concrete Aggregate (CLC RAgg ) mix The total grading aggregate curve satisfies the conditions of inferior and superior limits recommended by mix design principles, presented in Table 5. The control concrete mix design (CC) made with natural aggregates, currently used in concrete mixtures, represents the first step in this research. The next step was developing three more alternative mixes by partial or total replacement of natural crushed aggregates with recycled crushed ones (4/8 mm and 8/16 mm types). Natural sand, 0/4 mm, was maintained in each mixture in order to ensure a better concrete workability, by the means of the round shape of the natural aggregate particles. The following aggregates proportions (volume percentages) were kept constant for all mixtures: % - for 0/4 mm; % - for 4/8 mm; % - for 8/16mm (Table 5). In the same time, the water/cement ratio was constant for all mixes, in order to observe the concrete workability variation function to the nature of aggregates used in concrete mixes. Table 5. Total grading aggregate curve and admissibility conditions Recycled aggregate composition should be well evaluated in order to produce high quality concrete (Yong-Huang, 2004). Several studies demonstrated that 4/8 mm recycled aggregate fraction has the largest amount of adhered mortar layer, resulting that aggregate size have a high effect on water absorption and concrete resistance (Yadav 2009), (Hansen, 1983). 4/8 mm recycled aggregate fraction has 6% water absorption and 8/16 mm recycled aggregate fraction has 5% Mix design Mix design of concrete composition was performed in the present study considering a careful analysis of aggregates properties, especially the used recycled aggregates characteristics (Ilker, 1995), and also taking into account an algorithm for proportions optimisation, thus the mix compositions meet the Romanian regulation requirements, in force, for execution of concrete structures (NE 012-1:2007). Special attention was paid to the aggregate, considering the fact that it represents around 70% of the concrete mix The concrete mixtures constituent proportions reported to the cement amount, considered as the unit, are presented in table 6. Cement Fine aggregate: 0/4 mm Coarse aggregate: 4/8 mm Coarse aggregate: 8/16 mm Water [kg/m³] [kg/m³] [kg/m³] [kg/m³] [kg/m³] 1 2,82 1,13 1,93 0,60 Table 6. C16/20 concrete strength class constituents The following concrete mixtures were designed and tested in this study: 1. Control Concrete (CC) with natural aggregate (NA). 2. Concrete with Leftover Concrete Aggregate (CLC RAgg4/8 ) with recycled aggregate (RA) 4/8 mm. 3. Concrete with Leftover Concrete Aggregate (CLC RAgg8/16 ) with recycled aggregate (RA) 8/16 mm. 4. Concrete with Leftover Concrete Aggregate (CLC RAgg4/8; 8/16 ) and recycled aggregate (RA) 4/8 and 8/16 mm. 3. RESULTS AND DISSCUSION Control concrete (CC) mixture design fulfils the Romanian standard requirements for preliminary mixtures, where the acceptable value of mean 15

4 compressive strength is obtained by adding a value ranging from 6 to 12 units (MPa) to the characteristic strength f ck corresponding to each concrete strength class (f c = f ck + (6 12) (MPa)), according to National and European norms (Table 7). Table 8 contains the testing results available at this stage of research, for four types of concrete mixtures (CC, CLCR Agg 4/8, CLCR Agg 8/16, CLCR Agg 4/8; 8/16 ), both in fresh and hardened state; experimental tests were performed in accordance to and harmonized European norm series, all in force at this moment. Source (fib Bulletin 42) (NE 012-1: 2007) Mathematical relation (cylinders with H/ Φ- 300/150 or cube with l = 150 mm) a) f cm = f ck + Δf, Δf = 8 MPa b) f cm = f ck + (6 12) MPa Maximum class C120 / 140 C100 / 115 Table 7. Relations for mean compressive strength f cm The mean values of compressive strength test at 28 days, presented in Table 9, proves the fulfilment of even the most sever condition of regulations imposed by the Romanian norm (NE 012: 2007), which requires 32 MPa ( = 32 MPa) for C16/20 concrete strength class insurance. Mixture fcm cube28 fck cube Concrete class [MPa] [MPa] at initial testing CC C16/20 CLCR Agg 4/ C20/25 CLCR Agg 8/ C20/25 CLCR Agg 4/8; 8/ C25/30 Table 9. Establishing concrete classes 3.1. Concrete workability Tests performed on fresh concrete mixtures show a decrease of slump values, for the three recycled aggregate concrete mixes in comparison with the control concrete mix. CC mixture workability was established as S3 slump class, admissible values ranging from 100 mm to 150 mm. Table 8. Characteristics of fresh and hardened concrete 8/16 mixtures value with respect to the CC mixture compressive property. These results contradict other relevant studies upon the matter, which imply decrease of compressive performances of recycled concrete aggregate mixes (Frondistou, 1977) (Hansen, 1983) (Olorunsogoa, 2002) (Sami W. Tabsh, 2009). A possible explanation for the increase of compressive strength of studied mixture could derive from the good quality of raw materials, respectively increased performance of the recycled aggregates processed from a hardened leftover concrete (good resistance to fragmentation and good resistance to wear) Modulus of elasticity Modulus of elasticity values, determined for each concrete mixtures (CC, CLCR Agg 4/8, CLCR Agg 8/16 and CLCR Agg 4/8; 8/16 ) presented in Table 7 satisfy the requirements of European norms (Eurocod 2 SR EN :2004). 4. CONCLUSIONS 3.2. Compressive strength Compressive strength tests results show a sensitive increase of CLCR Agg 4/8, CLCR Agg 8/16 and CLCR Agg 4/8; Concrete with Leftover Concrete Aggregate mixes workability suffered serious decreases comparatively with the control concrete, mixtures optimization could be done by the following adjustments: the water/cement ratio increases respectively 16

5 supplementing the water dosage with (10 20)%, or the admixture percentage increases with the cement amount decreases. The last option would be an economical efficient solution. The compressive strength of RCA mixes shows a significant increases, up to two strength classes comparatively to the CC class, strength conferred by the particularly good properties of Leftover Concrete Aggregate. It is highly important to know the main physical and mechanical properties of the recycled aggregates and also their source in order to have a proper control and prediction over the designed concrete mix performances. Further studies on recycled concrete aggregates will demonstrate the importance of resistance to fragmentation (Los Angeles coefficient) and resistance to wear (Micro Deval coefficient). These properties are considered to be essential in establishment of optimum water/cement ratio for designed mixes of recycled aggregate as raw materials for new concrete. Present research shows that recycle concrete aggregate replaced successfully the non-renewable natural aggregate, conditioned by a quality control, which has confirming the aggregate properties and representing a pillar in concrete mixtures optimization. 5. ACKNOWLEDGEMENTS This paper was supported by the Post-Doctoral Programme POSDRU/159/1.5/S/137516, project cofunded from European Social Fund through the Human Resources Sectorial Operational Program REFERENCES Corbu, O., Economia de energie la realizarea betoanelor performante, (Economia de energie la realizarea betoanelor performante) Volumul Conferinţei Ştiinţa Modernă şi Energia, Ediţia 29, pp Corbu, O., 2013a. 13th SGEM GeoConference on Nano, Bio And Green Technologies For A Sustainable Future, SGEM2013 Conference Proceedings, ISBN / ISSN , June 16-22, pp , Albena, Bulgaria. Corbu, O., 2013b. Reciclarea deşeurilor şi reutilizarea acestora în sectorul construcţiilor (Recycling and reuse in construction), Volumul Conferinţei Ştiinţa Modernă şi Energia, Ediţia 32, pp (Modern Science and Energy Conference Volume, Issue 32, p ). Multidisciplinary Scientific GeoConference & EXPO-SGEM, pp , Albena, Bulgaria. Eurocod 2 SR EN :2004. Design of Concrete Structures. fib Bulletin, Constitutive Modeling of High Strength / High Performance Concrete. Bulletin 42, CEB-FIB, France. Frondistou-Yannas, S., Waste Concrete as aggregate for new concrete, ACI Journal, Proc., Vol. 74, No.8, Aug., pp Goncalves P., Recycled Aggregate Concrete (RAC) comparative analysis of existing specifications, Magazine of Concrete Research, ICE Publishing, Volume 62(5), London, UK, pp , Ghid Ghid privind gestionarea deşeurilor din construcţii şi demolări, Sibiu, România (Guidelines on the management of construction and demolition waste), Hansen, T.C., Recycling of Demolished Concrete and Masonry, report of Technical Committee 37-DRC, RILEM Report 6. Hansen, T.D., Strength of recycled concrete made from crushed concrete coarse aggregate, ACI, Concrete International, Design and Construction, Feb., pp Iacoboaea, C., Reciclarea deşeurilor din construcţii şi demolări - o necesitate? (Recycling of construction and demolition waste - is a need?) Volumul 12, The Romanian Economic Journal, Bucharest, i:33, pp Ilker B.T., Using Waste Concrete as Aggregate, Cement and Concrete Research, Vol. 25, No. 7. pp NE 012: Code of Practice for execution of concrete, reinforced concrete and prestressed concrete. Part 1: Concrete Production. Olorunsogoa, F.T., Performance of recycled aggregate concrete monitored by durability indexes, Cement and Concrete Research, Vol Poteras, G., Reciclarea Materialelor Provenite Din Demolări şi Dezafectări (Recycling Materials resulting from demolition and decommissioning) - Revista Salubritatea nr.1 (17). SR EN 1008: Mixing water for concrete. Specification for sampling, testing and assessing the suitability of water, including water recovered from processes in the concrete industry, as mixing water for concrete SR EN A1: Aggregates for concrete, SR EN 197-1: Cement composition. SR EN 933-1: Grading curves of aggregates. Corbu, O., Recycling and waste recovery in the construction field, Proceedings of the 14th International 17

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