Uniformity of in situ properties of self-compacting concrete in full-scale structural elements Wenzhong Zhu * , John C. Gibbs, Peter J.M. Bartos Department of Civil Engineering, Advanced Concrete and Masonry Centre, University of Paisley, High Street, Paisley, Scotland PA1 2BE, UK Received 17 April 2000; accepted 28 September 2000 Abstract Inadequate homogeneity of the cast concrete due to poor compaction or segregation may dramatically lower the performance of mature concrete in situ. To ensure adequate compaction and facilitate placement of concrete in structures with congested rein- forcement and in restricted areas, self-compacting concrete SCC) has been developed. Considering the highly ¯owable and self- levelling nature of the SCC, there are general concerns that segregation and settlement may occur during its transport and placing. ThisstudywasdesignedtoprovideinformationonuniformityofinsitupropertiesofSCCmixesinpracticalstructuralcolumnsand beamsandtocompareresultswiththoseofproperlycompactedconventionalconcrete.Theinsituconcretepropertieswereassessed by testing cores for in situ strength, pull-out of pre-embedded inserts and rebound hammer number for near-surface properties. The results indicated that there were not signi®cant dierences in uniformity of in situ properties between the SCC mixes and the corresponding well compacted conventional mixes. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Self-compacting concrete; In situ properties; Uniformity; Structural elements 1. Introduction Self-compacting concrete SCC), ®rst developed in Japan 10 years ago, and adopted in Europe and the rest of the world more recently, represents one of the most signi®cant advances in concrete technology for decades. It can ¯ow and compact in a mould or formwork under its own weight without the need for vibration. Use of SCC oers substantial bene®ts in enhancing construc- tion productivity, reducing overall cost, improving working environment and in sustainability [1±4]. Con- sidering the highly ¯owable and self-levelling nature of the SCC, however, there are general concerns that seg- regation and settlement may occur during its transport and placing. Standard, separately cast specimens that are easy to compact cannot reliably indicate substan- dard, poorly compacted concrete placed in situ, so it is essential to verify that SCC cast in situ can provide similar uniformity in key properties to that obtained with traditional vibrated concrete. Work carried out by Khayat et al. [5,6] has shown that variations of in situ strength along the height of experimental walls and columns were similar for the SCC and conventional non-SCC mixtures. However, structural elements used in their investigation were rel- atively small, i.e., 950 200 1500 mm 3 for the exper- imental walls and 235 235 1400 mm 3 for the columns. The aim of the current research was to inves- tigate the uniformity of in situ strength and near-surface properties of SCC and corresponding reference con- ventional concrete mixes in full-scale 3-m columns and 3.8-m beams. The work reported here was carried out as part of the Brite EuRam research project: ``Rational productionandimprovedworkingenvironmentthrough using SCC'' [7]. The main goals of the project were: · Development and optimisation of SCC mixes, and veri®cation of their fresh, hardened and in situ prop- erties; · Development of production, transport and casting methods suitable for SCC. The University of Paisley was responsible for Task 4 of this research programme: ``properties of hardened concrete'', and a major part of this task was the inves- tigation of in situ properties and their variations in practical structural elements. Cement & Concrete Composites 23 2001) 57±64 www.elsevier.com/locate/cemconcomp * Corresponding author. Tel.: 44-141-848-3578; fax: 44-141-848-3275. E-mail address: wenzhong.zhu@paisley.ac.uk W. Zhu). 0958-9465/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0958-946500)00053-6