STUDY ON ARC'S AGGREGATE UTILIZATION RECYCLED OF CONCRETE

Transcription

1 STUDY ON ARC'S AGGREGATE UTILIZATION RECYCLED OF CONCRETE MENDES, Thiago Melanda (1) ; MORALES, Gilson (2) ; CARBONARI, Gilberto (3) (1) UEL, Brazil (2) Dep. of Civil Construction, State University of Londrina, Brazil (3) Dep. of Structures, State University of Londrina, Brazil Abstract This assignment studied some properties of the aggregate recycled of concrete, and some properties of the concrete produced with RCA in the fresh state and in the hardened state. The aggregate was gathered close to the Dump Recycling Plant of Londrina city and submitted to physical tests, absorption rate, maxim absorption and unitary mass. In the fresh concrete was measured the density, workability and consistency. The hardened concrete was submitted for test of density, compressive strength, modulus of elasticity and creep and to assume the creep property, reinforced concrete beams with conventional concrete and with recycled aggregates were rehearsed. Keywords : recycled concrete aggregates, structural concrete, modulus of elasticity, creep in beams. 1. INTRODUCTION The use of concrete structures is a practice very spread in Brazil, however due to age of these buildings or because of its depreciation, some of this constructions are demolished resulting in a lot of rubbish ( CDR - construction and demolition residues). With an adequate treatment this material can be applied in the production of recycled aggregates obtaining a great quality of recycled aggregates, like the recycled concrete aggregates (RCA) which can be applied in new concrete structures. Despite yet do not there be any Brazilian code that conditions the utilization of aggregate recycled for the concrete production with structural function, some international rules and many researches showed great results and parameters for RCA s utilization in the production of structural concretes. Based on previous experiences and some rules recommendations and specifications, it was opted to the partial substitution of the coarse aggregate for RCA, this used in the condition of previous wetting or partially saturated. 629

2 2. OBJECTIVE 2.1 MAIN OBJECTIVE The main objective of this assignment was the study of some important properties of the concrete produced with the substitution of part of the natural aggregate for RCA to make possible its use in the construction business SPECIFIC OBJECTIVES To study some RCA's properties to make possible its use in concretes production: - Unitary mass; - Absorption rate; - Maxim absorption; To study of the concrete produced with partial substitution of natural aggregate for RCA and compare it with the conventional concrete. Here follow some properties: - Workability; - Consistency (Slump); - Density of the fresh concrete; - Density of the hardened concrete; - Compressive strength; - Modulus of elasticity; - Creep in beams; 3. HEADINGS 3.1 ARC It was gathered about 100 kilograms of aggregate recycled of concrete close to the recycling Plant of Londrina, a sample of this material was submitted to unitary mass test and classification by particle size, afterwards were droughts in drying ovens to 100ºC for 24h so that it was measured its natural humidity. After this, it was submitted to absorption test were measured in the following period: 1,2,5,10,15,30 minutes and 1 and 24 hours. With these results it was possible to calculate the absorption rate of the RCA. 3.2 Concrete With the absorption rate results it was made 4 mixtures with RCA in the condition of previous wetting or partially saturated. The absorption water of RCA was added with mixed water. Both waters and coarse aggregate remained together for a period of 5. This is the time that the RCA needs to achieve its maximum absorption (almost98%). The first three mixtures were produced with RCA to achieve compressive strength of 20,25 and 30 MPa in 28 days, and the last mixture was produced with conventional concrete to achieve compressive strength of 25 MPa in 28 days. The mixtures that used and water/cement ratios adopted are described in the Table 01. Table 01 Mixes design, water/cement ratio and general mix design (1:m) Mix design w/c (x) 1:m (cement:aggregates) ARC fc20 0,57 1:4 ARC fc25 0,60 1:6 ARC fc30 0,50 1:5 Reference fc25 0,66 1:6 630

3 It was measured, the workability, the consistency (slump -test) and the density in all mixtures. Then five specimens (150mm diameter x 300mm long) were made for each mixtures. The specimens were cured in the concrete curing system for 28 days, after this period the compressive strength, modulus of elasticity and specific mass of the hardened concrete were measured. 3.3 Creep in beams They were rehearsed beams of manufactured reinforced concrete as much with conventional concrete as with concrete manufactured with aggregate recycled of concrete. Both with the concretes produced to have compressive strength of 25MPa. The beams used in the rehearsal own transversal section of 8 cm (base) for 12 cm (height), and 1,90 m of length. The concentrated load of creep is applied in the middle of the span of the isostatics beams, two times-supported, after a cure of 28 days in concrete curing system, whose value corresponds to a normal tension in the more compressed fibre of the central section of about 35% of the compressive strength of the concrete, obtained in the specimens rupture rehearsal in the day of the application of the creep load (age of 28 days). Moreover, in the creep load age of the beams, the modulus of elasticity measured in the concrete specimens was used in the calculation of the instantaneous vertical displacements and compared with models of modulus of elasticity. The vertical displacements measured during this period will serve for the obtainment of the long term curves of the creep coefficients through the no lineal regression, using a hyperbolic function suggested by CEB. 4 RESULTS 4.1. ARC Table 02 Unitary mass, natural humidity and maxim absorption. Specimen Unitary mass Natural humidity Absorption ARC 1,25 g/cm3 1,94% 5,30% Absorption x time Absorption (%) 6,00% 5,00% 4,00% 3,00% 2,00% 1,00% 0,00% Time (min) Figure 01 Absorption rate 631

4 4.2 Concrete Fresh concrete Table 03 Workability, consistency (slump) and density of the fresh concrete. Mix design Workability Slump (mm) Density (g/cm3) ARC fc20 Great 80 2,52 ARC -fc25 Excellent 150 2,51 ARC - fc30 Great 80 2,51 C.C. - fc25 Excellent 200 2, Hardened concrete Table 04 Hardened concrete density. Mix design Density (g/cm3) ARC -fc20 2,49 ARC -fc25 2,46 ARC - fc30 2,47 C.C. - fc25 2,48 Table 05 Compression strength (MPa) - fc, Modulus of elasticity (GPa) E fc20 - ARC fc25 - ARC Fc E fc E 21,86 26,63 26,68 31,21 fc30 - ARC fc25 - REF. Fc E fc E 29,80 30,85 25,77 28,68 632

5 Table 06 Modulus of elasticity models (GPa) and measured modulus of elasticity (GPa) Rules Models rules ARC fc20 ARC fc25 ARC fc30 C.C. fc25 ACI-318 Ec = 4,73 fc 1/2 22,11 24,43 25,82 24,01 Norueguesa Ec = 9,5 fc 0,3 23,96 25,44 26,30 25,18 Francesa Ec = 12 fc 1/3 33,55 35,85 37,20 35,44 Britânica Ec = ,8 fc 1/2 35,09 36,46 37,28 36,21 EC-2 Ec = 9,5 fc 1/3 26,56 28,38 29,45 28,06 CEB-90 Ec = 9,98 fc 1/3 27,90 29,82 30,94 29,47 NB-1/1978 Ec = 6,6 fc 1/2 30,85 34,09 36,02 33,50 NB-1/2001 Ec = 5,6 fck 1/2 22,42 27,08 28,26 25,40 Measured - 26,63 31,21 30,85 28,68 The creep coefficient is obtained by the equation: Ö = Total Displ. (t) Inst. Displ.(to) (Equation 01) Inst. Displ.(to) Creep coefficient x Time Creep Coefficientö 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0, Reference Concrete ARC Concrete t (days) Figure 02 Creep coefficient Ö of the beams. 633

6 5. ANALYSIS OF THE RESULTS The recycled aggregate (RCA) absorbed about 98% of the maxim absorption in about five minutes and the maxim absorption value of the aggregate is inside the expected values taking as researches reference accomplished by other authors and inside the limits established in some international rules. All the concretes presented a workability satisfactory, and the concrete with recycled aggregate behaves like the conventional concretes, when RCA is used in the condition previous wetting. The partial substitution of natural aggregate for ARC doesn t present a big difference in the modulus of elasticity and models of the module that more approached the module measured experimentally were the CEB-90 and EC-90, see table 06. The creep coefficients indicated that a concrete produced with RCA introduces vertical displacements of creep greater than the concrete produced with natural aggregate. One of the factors that justify this is the fact that ARC is a porous aggregate, summed to the emptiness let by the drying of the concrete that are compressible. 6. CONCLUSIONS RCA s utilization in the production of plastic concretes with structural function should be proceeded with an absorption rate and maximum absorption rehearsal so that it can determine the absorption water and time of absorption making possible the use of this aggregate. The partial substitution of this aggregate in the condition previous wetting doesn t influence the properties of the fresh concrete. However, the same can t be tell for the hardened concrete properties, dispite the specific mass of hardened concrete and the modulus of elasticity don t present a significant difference, the partial substitution of natural aggregate for RCA introduced an increase in the creep coefficient what is of great importance in relation to structural concretes, the recommendation of the Dutch code (CUR) says have an increase of 10% of one of the dimensions of the section of the piece is totally pertinent, once that would compensate vertical creep displacements the biggest introduced by the concrete with ARC. 634

7 REFERENCES [1] CARBONARI, G.. Comportamiento mecánico instantáneo y differed Del hormigón of high strength. Doctorate thesis. ETSECCPB Universitat Politècnica de Catalunya Departament D Enginyeria de La Construcció, Barcelona, Spain, December, pp. 198,1996. [2] CARBONARI, G.; BALLAROTTI, C.; RIBAS, H.S.. Simple system and Load Practiser in Experimental Rehearsals of Beams. Ransack Engineering, Science and Technology, v.6, nº 1, pp , janeiro/fevereiro [3] BUTTLER, Alexandre Marques. Concrete with great aggregate recycled of influence concrete of the recycling age in the properties of the aggregate and recycled concrete. Engineering school of São Carlos (Structures Department) University of São Paulo ( Dissertation of Mestrado). São Carlos [4] Levy, Salomon Mony. Contribution to the study of the concretes durability, produced with concrete and masonry residues. Polytechnic school of the University of São Paulo.(Department of Civil Construction). University of São Paulo (Doctorate Thesis). São Paulo [5] Leite, Mônica Batista. Concretes mechanical properties evaluation produced with aggregate recycled of construction and demolition residues. Engineering school of the Federal University of Rio Grande do Sul. UFRG Thesis of Porto Alegre Doctorate [6] ÂNGULO,Sergio Cirelli. Concrete production of recycled aggregates. Londrina,1997. course Technology and Urbanization Civil Engineering Center conclusion work, State University of Londrina. p [7] PINTO, T.P., Recycling in the costs environmental responsibility works and reduction flowerbed. technical article Technology Magazine of the Construction TÉCHNE. PINI.N. 49. São Paulo: November. [8] RILEM RECOMMEDATION. Specification for concrete with recycled aggregates. Materials and Structures.n27,p ,