A methodology to assess robustness of SCC mixtures Sandra Nunes a , Helena Figueiras a , Paula Milheiro Oliveira b , Joana Sousa Coutinho a , Joaquim Figueiras a, ⁎ a LABEST / FEUP– Department of Civil Engineering, University of Porto, Portugal b CEC / FEUP– Department of Civil Engineering, University of Porto, Portugal Received 5 January 2006; accepted 1 October 2006 Abstract The present paper highlights the importance of a robust SCC mixture for the successful introduction of this innovative technology in the concrete industry. A methodology to quantify SCC mixture robustness is also proposed. A central composite design was carried out to mathematically model the influence of five mixture parameters and their coupled effects on deformability, passing and filling abilities and compressive strength of SCC mixtures. The target SCC mix composition, to be applied during full-scale tests in a precast factory, was selected to be the central point in the factorial design. The mixture parameters suggested by the Japanese SCC-designing method were adopted. The derived models were used to estimate SCC properties while mixture parameters variations were simulated, based on daily fluctuations inherent from production process. SCC robustness was assessed by measuring how frequently the properties of simulated mixes fall inside the acceptance intervals. © 2006 Elsevier Ltd. All rights reserved. Keywords: Self-compacting concrete; Robustness of SCC mixtures; Statistical factorial design; Bootstrap technique 1. Introduction Self-compacting concrete (SCC), initially developed in Japan [1], is an innovative type of concrete which main characteristic is to fill the forms and consolidate without the need of vibration. In the last years, there has been a growing interest on SCC technology among constructors and construc- tion industry in several countries. The principal reasons for this interest concern the ease of placing this type of concrete in heavily reinforced areas difficult to access, the reduced effort in accomplishing some of the casting tasks and the significant reduction of the construction period. Along with these advantages, in terms of environment, this technology will enable a considerable reduction of the acoustic noise levels and the use of secondary raw materials. Until now, in Portugal, many mixtures have been developed and tested in the laboratory but the experience of producing SCC on site is limited. Within a national research project, “BACPOR” [2], which covered a wide range of applications and materials, some problems occurred on site during full-scale tests [3]. Variations in cement or mineral additives due to changes in the production process as well as changes in aggregate type, e.g. from one sand pit to another, were observed to cause large variations on properties of fresh SCC. Therefore it is of great importance to have a robust mixture, which is minimally affected by external sources of variability. In “The European Guidelines for Self-Compacting Concrete” the robustness checking is recognized as an important step in the SCC design process [4]. Since variability of most constituent materials can be translated by a change in water requirement, it is suggested in [4] that compositions with plus and minus 5 to 10 L of the target water content be tested and the respective changes in fresh state properties be measured. A robust SCC should tolerate these deviations, i.e. should maintain its fresh properties inside the specified limits [4]. But this approach seems too simplistic because it does not take into account the specific characteristics of the production center like the existing level of quality control, equipment performance, skills and knowledge of the personnel involved. Cement and Concrete Research 36 (2006) 2115 – 2122 ⁎ Corresponding author. Departamento de Engenharia Civil, Faculdade de Engenharia da Universidade do Porto, Rua do Dr. Roberto Frias, 4200-465 Porto, Portugal. Tel.: +351225081948; fax: +351225081835. E-mail address: jafig@fe.up.pt (J. Figueiras). 0008-8846/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2006.10.003