Page 55 - New Trends in Green Construction

FROM 150 mm CUBIC TO Փ150 mm X 300 mm CYLINDRICAL COMPRESSIVE STRENGTH OF COARSE RECYCLED AGGREGATE CONCRETE SPECIMENS
João Pacheco, Jorge de Brito, Carlos Chastre, Luís Evangelista
Keywords: recycled aggregate concrete, laboratory testing, compressive strength, size effects 1. Introduction
The compressive strength (𝑓 ) is arguably the most tested and relevant concrete property, serving 𝑐
as the basis for quality control and conformity testing. Structural design codes specify most load- bearing and serviceability clauses as directly dependent on 𝑓 .
The acceptance of recycled aggregate concrete (RAC) by designers, clients, and contractors requires solid knowledge of its 𝑓 , the proper constitutive modelling of RAC properties, and the
𝑐,𝑐𝑦𝑙
This paper concerns a factor (K) that converts 𝑓 to 𝑓 , by comparing laboratory experiments 𝑐,𝑐𝑢𝑏𝑒 𝑐,𝑐𝑦𝑙
in which the 𝑓 is tested simultaneously on cubes and cylinders (Eq. 1). K is analysed for natural 𝑐
aggregate concrete (NAC) and coarse recycled aggregate concrete (CRAC) whose recycled aggregates were sourced from concrete.
𝐾=𝑓 /𝑓 (1) 𝑐,𝑐𝑢𝑏𝑒 𝑐,𝑐𝑦𝑙
2. Ethodology and database
This paper concerns CRAC produced with total replacement of natural aggregates (NA) with
recycled coarse aggregates sourced from concrete. Recycled aggregates produced from other
sources of waste have been tested less often, especially in what concerns the simultaneous testing
of 𝑓 and 𝑓 ; the same is valid for intermediate incorporation ratios of NA by coarse 𝑐,𝑐𝑢𝑏𝑒 𝑐,𝑐𝑦𝑙
recycled concrete aggregates. A database was built from all publications known to the authors and statistical analyses were performed. The publications were the following: Gull (2011); Kheder & Al-Windaw (2005); Muhammad & Sankaranarayanan (2016); Paul (2011); Pedro et al. (2014); Rao & Desai (2014); Santos et al. (2017).
The K values obtained from the database were compared with those resulting from the 𝑓 and 𝑐,𝑐𝑢𝑏𝑒
𝑓 of the strength class definitions of EN206 (2000) / Eurocode 2 (2008). Coefficients of correlation 𝑐,𝑐𝑦𝑙
between K and other parameters (binder content, w/b ratio, and 𝑓 ) were calculated. Since K is also 𝑐
intended for reliability analyses, a probabilistic version of the K factor is proposed. This required probability goodness-of-fit tests.
3. Results and conclusions
Fig 1. plots K vs. the 𝑓 and binder blend. Two observations are noteworthy: the K values of 𝑐,𝑐𝑢𝑏𝑒
NAC are closer to EN206 (2000)/Eurocode 2 (2008) assumptions than those of CRAC, and if the
underlying conversion of EN206 (2000)/Eurocode 2 (2008) is used to convert 𝑓 to 𝑓 of 𝑐,𝑐𝑢𝑏𝑒 𝑐,𝑐𝑦𝑙
CRAC specimens, the CRAC cylinder strength is overestimated.
𝑐
definition of specific code clauses for RAC applications. Since RAC has been mostly tested in 150 mm cubes (𝑓 ) and codes define 𝑓 as the compressive strength of Փ150 mm x 300 mm
𝑐,𝑐𝑢𝑏𝑒 𝑐
cylinders (𝑓 ), research on the conversion of 𝑓 to 𝑓 of RAC specimens is needed.
𝑐,𝑐𝑦𝑙 𝑐,𝑐𝑢𝑏𝑒
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𝑐
New Trends in Green Construction