Page 21 - New Trends in Green Construction

HIGH PERFORMANCE SELF-COMPACTING CONCRETE WITH RECYCLED AGGREGATES FROM THE PRECAST INDUSTRY
Tiago Barroqueiro, Pedro Raposeiro da Silva, Jorge de Brito
Keywords: high performance self-compacting concrete, recycled aggregates, precast industry 1. Introduction
In this short paper we present the results of an experimental campaign whose final objective was to produce high performance self-compacting concrete (HPSCC) using recycled aggregates (RA) from the precast industry (PI). This work intended to evaluate the potential of self- compacting concrete with RA to achieve similar performance as high- performance concrete. We present the results of the tests, which were carried out on six concrete mixes, wherein the first one corresponds to a mix using natural aggregate (NA) only (100% NA) and the remaining five mixes in which the percentage of fine recycled aggregate (FRA) and coarse recycled aggregate (CRA) in the concrete composition varies, namely: 1st FRA/CRA%: 25/25% (25% RA); 2nd FRA/CRA %: 50/50% (50% RA); 3rd FRA/CRA %: 100/100% (100% RA); 4th FRA/CRA %: 0/100% (100% CRA); 5th FRA/CRA %: 100/0% (100% FRA).
The cement replacement percentage with mineral additions was kept constant in all the mixes and included 5% of limestone filler (LF) and 30% of fly ash (FA) (instead of cement). The amount of silica fume (SF) and cement (C) was also kept constant in all mixes: 10% SF (relative to the cement weight) and 450 kg/m3 of C. The a/c ratio of all the mixes was 0.44. A value of the ratio, in absolute volume, between the total amount of fine material (cement and additions) and fine aggregates in the mixes (Vp/Vs) was set. According to the results obtained by Silva et al. (2011), a value Vp/Vs=0.80 was considered.
2. Material and methods
The fine natural aggregate used in all the mixes was silica sand, in two sizes: fine sand (0- 2 mm) and coarse sand (0-4 mm). Two types of limestone CNA were used: medium gravel (Dmax = 11.2 mm) and coarse gravel (Dmax = 22.4 mm). The RA came from crushed precast concrete elements of 65 MPa class strength. Type I cement of class 52.5R, limestone filler and fly ash (used as a partial replacement for the cement) were used in ternary mixes. A high- performance superplasticizer was used as admixture.
3. Results and conclusions
Table 1 shows a summary of the results obtained, where a negative sign corresponds to a decrease and a positive sign to an increase in the value of the property under analysis. The commparisons are made in relation to the 100% NA mix. The results in Table 1 show that the 25% RA mix performs best, with losses of less than 10%. The mixes with 50% RA and 100% CRA present similar performances even though the first one tends to have worse results than the second one. The 100% RA mix shows the highest losses. The registered differences may be justified by the nature of the CRA and the water absorbed by them.
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New Trends in Green Construction