Self-compacting concrete (SCC) is prized for its ability to flow and consolidate under its own weight, eliminating the need for vibration. Ensuring this crucial property requires robust testing methods. One such method is the V-funnel test, a relatively simple yet informative procedure developed in Japan by researchers like Ozawa et al. This article details the V-funnel test, including its standard procedure and a variation performed at T5 minutes, highlighting its interpretation and limitations.
Equipment for Flowability Assessment
The V-funnel test utilizes a specifically designed apparatus consisting of a V-shaped funnel (Fig. 1). An alternative design, known as the O funnel with a circular shape, is also employed in some regions. The equipment is straightforward, requiring minimal components: a V-funnel, a bucket capable of holding approximately 12 liters, a trowel for leveling, a scoop for handling concrete, and a stopwatch for accurate time measurement.
Limitations in Interpretation
While the V-funnel test is designed to measure flowability, it’s important to acknowledge that the results can be influenced by factors beyond just the concrete’s inherent ability to flow. The inverted cone shape of the funnel can amplify any tendency for the concrete to block, particularly if there’s an excessive amount of coarse aggregate. High flow times may also indicate low deformability due to a high paste viscosity or increased inter-particle friction within the mix. Furthermore, the precise effect of the funnel’s angle and potential wall effects on the concrete’s flow remain areas for further investigation.
Procedure: Standard Flow Time Measurement
The standard V-funnel test requires approximately 12 liters of normally sampled concrete. The procedure is as follows:
- Setup: Position the V-funnel on firm, level ground.
- Preparation: Moisten the inside surface of the funnel to prevent adhesion. Ensure the trapdoor allows any surplus water to drain freely. Close the trapdoor and place a bucket directly beneath the funnel’s outlet.
- Filling & Flow: Fill the apparatus completely with concrete, avoiding compaction or tamping. Simply strike off the concrete level with the top of the funnel using a trowel. Open the trapdoor within 10 seconds after filling and allow the concrete to flow out under gravity. Simultaneously start the stopwatch when the trapdoor is opened.
- Measurement: Record the time for complete discharge, defined as the point at which light can be seen from above through the funnel. The entire test must be completed within a 5-minute timeframe.
Procedure: Flow Time Measurement at T5 Minutes (T5)
This variation of the V-funnel test provides additional insight into the concrete’s stability and segregation potential. The key difference lies in the observation period before flow measurement.
- No Preparation: Crucially, do not clean or moisten the inside surface of the funnel again after the initial flow time measurement.
- Refill & Repeat: Close the trapdoor and immediately refill the V-funnel with another 12 liters of concrete, following the same filling and leveling procedure as before. Place a bucket underneath.
- Delayed Flow: Open the trapdoor exactly 5 minutes after the second fill. Simultaneously start the stopwatch when the trapdoor is opened and record the time for complete discharge (defined as light visible from above).
Interpreting the Results: What Do the Times Tell Us?
The V-funnel test provides a valuable indication of concrete’s ease of flow; shorter flow times generally correlate with greater flowability. For SCC, a flow time of 10 seconds is considered an appropriate benchmark, indicating good self-compacting characteristics. Prolonged flow times in the standard test can suggest a susceptibility to blocking due to factors like excessive coarse aggregate or high paste viscosity.
The T5 minute variation offers further insights. A significant increase in flow time after the 5-minute settling period suggests segregation within the concrete mix. This indicates that the concrete’s internal cohesion is compromised, and it’s losing its homogeneity over time – a critical concern for SCC performance.
Conclusion
The V-funnel test, both in its standard form and with the T5 minute variation, remains a valuable tool for assessing the flowability and stability of self-compacting concrete. While acknowledging its limitations regarding other influencing factors, it provides a relatively simple and cost-effective method for evaluating mix designs and ensuring SCC meets performance requirements.