Title:
Multi-Electrode Conductivity Method to Evaluate Static Stability of Flowable and Self-Consolidating Concrete
Author(s):
Kamal H. Khayat, Yannick Vanhove, Trimbak V. Pavate, and Carmel Jolicoeur
Publication:
Materials Journal
Volume:
104
Issue:
4
Appears on pages(s):
424-433
Keywords:
bleeding; conductivity; segregation, stability
DOI:
10.14359/18833
Date:
7/1/2007
Abstract:
The Segregation of coarse aggregate in cement-based materials can lead to heterogeneous properties of the hardened material with direct implication on mechanical properties and durability. The control of segregation is especially critical in flowing and selfconsolidating concrete (SCC), as well as in concrete made with supplementary cementitious materials or fillers used as partial replacement of cement. In the present study, an attempt was made to develop a rapid methodology for estimating segregation during the dormant period of cement hydration, using electrical conductivity to monitor changes in the local composition over a specimen height, as a function of time. The results of the multi-pair electrode conductivity method were compared with those obtained by studying the actual segregation determined on hardened concrete samples. This was done by an image processing technique of tracing and counting aggregate particles along hardened cylindrical sections. In total, nine concrete mixtures having slump values of 70 to 240 mm (2.76 to 9.45 in.) and five SCC mixtures with slump flow values ranging between 650 mm and an excessive value of 880 mm (25.6 to 34.7 in.) were tested. A high degree of correlation between the results of the electrical conductivity and image analysis methods was established. Data obtained from the electrical conductivity approach after 20 minutes of testing are shown to correlate well with bleeding, segregation, and homogeneity indexes determined from electrical conductivity approach at peak conductivity typically greater than 3 hours as well as with the segregation index determined from image analysis. The conductivity approach can then be used as a nondestructive method for evaluating the static stability following concrete placement.