apparatus, the time for the SCC to spread to 500mm (20 inc.), T50 and the final slump flow diameters as shown in Figure 3 can be measured. According to ACI 237R-07, [29] a common range of slump flow for SCC is 450–750mm (18–30 inc.). J-ring test as shown in Figure 4 was also performed based on ASTM C1621 (Standard Test Method for Passing Ability of Self-Consolidating Concrete by J-Ring). [30] This test method provides a procedure to determine the passing ability of concrete by using a J-Ring in combination with the slump flow test. The J-Ring is placed outside the slump cone so that the concrete flows through the legs of the ring when the cone is lifted. The slump flow with and without the J-Ring is measured. A difference of less than 25mm (1 inch) generally indicates good passing ability. A difference greater than 50mm (2 inc.) generally indicates poor passing ability.[29] In additional to slump flow and J-ring test, visual stability index (VSI) test was also used to determine the stability of SCC mixture. The test was performed according to ASTM C1611, which involves the visual examination of the SCC slump flow spread. A VSI number of 0, 1, 2, or 3 (referring to highly stable, stable, unstable, and highly unstable respectively) is usually given to the spread to characterize the stability of the mixture based on the observation of segregation, bleeding, and consistence of the spread. Example of mixtures with different VSI rating can be found in Figure 5. A VSI rating of 0 or 1 are indications of stable SCC mixture and a VSI rating of 2 or 3 generally indicate unstable and possible segregation.
L-box test was used to investigate the passing ability of the SCC. As shown in Figure 6, the equipment consists of an Lshape box of a rectangular cross-section, with a horizontal and vertical part separated by the movable portion (exit) in front of which vertical rebars are arranges. With the L-box, the height of concrete in the vertical part, h1, the height of concrete in the horizontal part h2, and the time for concrete to reach the end of the horizontal part T final can be measures. The ratio of h2/h1 is usually defined as blocking ratio. According to EFNARC, [31] when the blocking ratio is larger than 0.80, SCC generally has good passing ability.
V-funnel test as shown in Figure 7 measured the total time Tv for concrete to flow through the V-shape funnel, which is to evaluate the fluidity of concrete and ability of concrete to change its path and to pass through a constricted area. The purpose of V-funnel test was to measure the flowability and passing ability of fresh concrete. According to EFNARC, [31] a typical SCC should have Tv between 6 and 12 s.
Major acceptance criteria of abovementioned tests for SCC based on ACI and EFNARC are summarized in Table 4. It should be noted that most of the above-mentioned methods are empirical test methods used to indirectly reflect SCC behaviors through simulation of flow of concrete under different situations, and many times the results were either not
well correlated to each other or not able to accurately reflect SCC properties.
2.4.2. Concrete rheology test
In addition to conventional tests measuring SCC flowability, passing
ability, and stability, an ICAR concrete rheometer was used to measure the rheological behavior of concrete in order to better understand fundamental concrete behavior in fresh state.[32] It is generally agreed that the flow behavior of fresh concrete can be represented by a twoparameter relationship known as the Bingham model, which requires the determination of yield stress s0 and plastic viscosity l as shown in Equation (1):
τ ＝ τo＋μY (1)
The parameter of Y is the shear strain rate and the parameter of τ is shear stress. The yield stress generally represents the shear stress required to initiate flow and the plastic viscosity reflects the resistance to flow after the yield stress has been surpassed. These two parameters, which define the flow curve, provide a complete description of the flow behavior of the concrete mixtures. A flow curve test was used to measure the relationship between shear stress and shear rate, and to compute the Bingham parameters of yield stress and plastic viscosity. As shown in Figure 8, the ICAR Rheometer is composed of a container to hold the fresh concrete, a driver head that includes an electric motor and torque meter; a four-blade vane that is held by the chuck on the driver; a frame to attach the driver/vane assembly to the top of the container; and a laptop computer to operate the driver, record the torque during the test, and calculate the flow parameters. The container contains a series of vertical rods around the perimeter to prevent slipping of the concrete along the container wall during the test. The vane used in this study is 63.5mm (2.5 inc.) in diameter and 127.0mm (5 inc.) in height, and approximately 18.9 L (20 quarts) of fresh concrete is used for each test. In this study, a flow curve test is used to determine the dynamic yield stress and the plastic viscosity. Test procedure of the flow curve consists of a pre-shear period and test period as shown in Figure 9(a). The flow curve test begins with a pre-shear period in which the vane is rotated at a speed at 0.5rev/s for 20 s, which is to breakdown any thixotropic structure that may exist and to provide a consistent shear history before measuring the Bingham parameters. Following the pre-shear period, the flow curve is immediately started with a series of testing points in descending order. The speed dropped from the initial speed (0.50 rps) to the final speed (0.05 rps) with seven different speeds which equally distributed between the initial and final speed. Each of the speed ran for 5 s. During each step the speed is held constant and the average
speed and torque are recorded. Theplot of the average torque and average vane rotation measured during seven steps of decreasing vane speed is generally called flow curve. A typical result from flow curve test is shown in Figure 9 (b), which can be used to compute both relative and fundamental units related to concrete rheology. The software computes a best-fit line to the data and reports the intercept and slope as relative parameters. The intercept is denoted as yield value (Nm) and the slope is donated as the viscosity value (Nm.s). The software then computes the Bingham parameters: dynamic yield stress and plastic viscosity based on geometries of vane and container. The yield value and viscosity value are proportional to, but not equal to the two fundamental units of yield stress and plastic viscosity.[32] Detailed information of the conversion can be found in the manual of device. [33] It should be noted that due to this method used to calculate the yield value and yield stress, i.e. estimated from an extrapolation of the shear rate vs. Shear stress curve to zero shear rate, negative yield stresses are sometimes observed in highly flow mixtures. Since all these mixes should have very small yield stresses, the negative values have no real physical meaning.[34]
2.4.3. Hardened concrete test
After all fresh concrete tests, concrete was poured into 100mm×
200mm (4 inc.×8 inc.) cylinders without any form of consolidating, i.e. action of rodding or vibration. The concrete cylinders were placed in a standard curing room confirmed to ASTM C192 [27] right after casting. All specimens were demolded after 24 h and cured in the curing room till compressive strength test. The 28 days compressive strength of all concrete mixtures were tested with a Test Mark CM 400 compression testing machine based on ASTM C39 (Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens).[35] One specimen was randomly selected from each of the mix was cut through the middle to examine the coarse aggregate distribution in vertical direction of cross-section, which was used to evaluate the segregation resistance. In addition to compressive strength test, free drying shrinkage test based on ASTM C157 (Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete) [36] was used to evaluate the effect of FRCA on drying shrinkage of concrete. Three specimens with dimension of 76×76×265mm (3×3×10 inc.) were prepared for the drying shrinkage test. After removed from the curing room following 28 days of curing, the initial length of each specimen was measured using a digital length comparator with sensitivity of 0.0025mm (0.0001 inc.). The specimens were then moved to a room with temperature of 23 ± 2°C (73 ± 3°F) and a relative humidity of 50 ± 4% as shown in Figure 10. 7 days, 28 days, 56 days, and 112 days shrinkage change rate were measured with the length comparator.
Figure 3. Slump flow test setup. Figure 4. J-ring test setup.
Figure 5. Example of concrete with different VSI indexes
Figure 6. L-box test setup. Figure 7. V-funnel test setup. Table 4. General acceptance criteria of SCC (ACI 2007; EFNARC 2002).
Typical range of values Test method Reference Unit Minimum Maximum Slump flow ACI 2007 mm (inc.) 450 (18) 760 (30) T50 ACI 2007;EFNARC 2002 s 2 5 L-box blocking ratio ACI 2007; EFNARC 2002 % 0.8 1.0 VSI ACI 2007 – 0 1 V-funnel, Tv EFNARC 2002 s 6 12
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