A simple mix design method for structural lightweight aggregate concrete
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ORIGINAL ARTICLE
A simple mix design method for structural lightweight aggregate concrete J. Alexandre Bogas • Augusto Gomes
Received: 5 September 2012 / Accepted: 14 February 2013 RILEM 2013
Abstract Current design methods for structural lightweight aggregate concrete (SLWAC) are usually only valid for a limited range of concrete compositions that have previously been subjected to trial tests. The SLWAC mix design is more complex than that of normal weight concrete as more parameters need to be determined. Taking this into account, a simplified design method is proposed for SLWAC made with natural sand. The major advantages of the proposed method are that it is easy to apply and it can be generalized to any type of lightweight aggregate (LWA). For this, three additional design parameters are needed: the strength of LWA in concrete; the limit strength; the SLWAC potential strength. At most, two experimental mixtures are needed to determine these parameters. A biphasic model to estimate the strength of SLWAC is evaluated and high correlations are obtained. The good performance of the suggested method is demonstrated by examples of practical application and by the comparison with experimental results reported by the authors and other investigators. Keywords Lightweight aggregate Lightweight aggregate concrete Mix design Limit strength Potential strength
J. A. Bogas (&) A. Gomes DECivil/ICIST, Instituto Superior Te´cnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal e-mail: [email protected]
1 Introduction Today, there is still no comprehensive design method for structural lightweight aggregate concrete (SLWAC) that can take into account different types of lightweight aggregates (LWA) and a wide range of strength and density levels. In general, current design procedures are only valid for a limited range of compositions, with a particular type of concrete that has been subjected to prior experimental tests [1–6]. According to some authors SLWAC can be formulated with the same basic principles adopted for normal weight concretes (NWC), just with some specific aspects of its behaviour and nature being taken into account [6–11]. Maage et al. [8] report that the water absorbed by LWA and the increased risk of segregation due to the lower density of aggregates are the main additional factors that must be considered. Density is an additional requirement for the SLWAC design that must be also taken into account [11, 12]. Lightweight concrete design optimization is therefore more difficult since it must respect different properties that are partially conflicting such as durability, strength, workability, density and thermal properties. For example, a concrete with higher strength and durability is usually associated with higher density and lower insulation properties. In addition to the mortar strength (w/c ratio) and quality of the transition zone aggregate-paste, the SLWAC strength depends on the volume and properties of LWA [13–15]. Design methods based on the
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