Self-Consolidating High Performance Concrete – SCC – Self-Compacting & Highly Flowable Concrete

Other test methods that can evaluate the segregation for SCC in a hardened state were also developed at UIUC. In the image analysis method, a concrete cylinder is cut lengthwise into two, and a digital photo is then taken of the cut surface. Image analysis software is used to calculate and compare the percentages of coarse aggregates in different levels of the cut cylinder. Due to the large amount of work needed to prepare and analyze the image, this method is good for the purpose of laboratory study. Another method, called visual stability rating method, was developed for both the field and laboratory testing. In this method, the SCC cylinder is cut lengthwise, and the cut surface is then used to observe the distribution of the coarse aggregates. A Hardened Visual Stability Index (HVSI) is used to assess the stability.

For fresh SCC, besides the segregation probe test, eddy current test was also introduced by researchers at UIUC. In this method, a concrete covermeter is used to monitor the position of a metallic aggregate, which is designed to have similar size and density to normal coarse aggregate. This method has a high requirement on the instrument. It measures the position of a single metallic aggregate. However, this method can monitor the settling process in most kinds of suspensions, which may help to understand the segregation mechanism.

A multi-pair electrode conductivity approach was also introduced by Khayat, et. al at Université de Sherbrooke, who is a partner of ACBM. The method relies on measuring the differences in electrical conductivity measured at different depths, and as a function of time. The variations in electrical conductivity throughout the sample as a function of time are used to interpret the material homogeneity. Good correlations were established between the stability of concrete determined from physical testing (external bleeding and homogeneity of coarse aggregate distribution along hardened concrete samples) and the bleeding, segregation, and homogeneity indices evaluated from the conductivity approach, as illustrated in Fig.12. The electrical conductivity approach can even be used for quality control on the job site. Variations in electrical conductivity after 20 min of testing can be related to the various indices determined from the conductivity approach, as illustrated in Fig. 13. Thus, the method provides with the reliable measurement on the stability of concrete.

Fig. 12 Relationship between segregation index from image analysis and homogeneity index

from electrical conductivity approach

Fig. 13 Variation of segregation index determined from image analysis and coefficient of variation of conductivity values after 20 min of testing (30 min of age)

Khayat et al. developed a pressure filter test to evaluate the ability of SCC to retain its mix water. The test involves the placement of approximately 5 kg of concrete sample in a pressure vessel measuring with compressed air of 700 kPa. The forced bleed water is monitored for 10 minutes to determine the water permeability of the fresh concrete using Darcy's law. The test was shown to be effective in differentiating between the stability of SCC made with different binder contents, w/cm, and VMA concentrations and can be suitable for quality control of SCC in the field.