Frequently Asked Questions about SCC

Q: What is Self-Consolidating Concrete (SCC) and how is it tested?

A: Self-Consolidating concrete (SCC) is a high-performance concrete that can flow easily into tight and constricted spaces without segregating and without requiring vibration. The key to creating self-consolidating concrete (SCC), also referred to as self-compacting, self-leveling, or self-placing concrete, is a mixture that is fluid, but also, stable, to prevent segregation.

To achieve the desired flowability a new generation of superplasticizers based on polycarboxylate ethers works best. Developed in the 1990s, they produce better water reduction and slower slump loss than traditional superplasticizers. The required level of fluidity is greatly influenced by the particular application under consideration. Obviously the most congested structural members demand the highest fluidity. However, element shape, desired surface finish, and travel distance can also determine the required fluidity.

Generally, the higher the required flowability of the SCC mix, the higher the amount of fine material needed to produce a stable mixture. However, in some cases, a viscosity-modifying admixture (VMA) can be used instead of, or in combination with, an increased fine content to stabilize the concrete mixture.

Test Methods
SCC is characterized by its unique fresh concrete properties. Therefore, new test methods are being developed to characterize SCC properties. See table for test methods approved or under consideration at ASTM:

Test Method	Description
Slump Flow	ASTM C1611 Test is performed similar to the conventional slump test (ASTM C143) using the Abrams cone (use of inverted cone possible). However, instead of measuring the slumping distance vertically, the mean spread of the resulting concrete patty is measured horizontally. This number is recorded as the slump flow. Additional information can be obtained about the mixture by measuring the time it takes for the pat to reach 500 mm (20 in.). This is called the T50 value and is a measure of the viscosity. A final visual observation of the pat can be compared to an index called the Visual Stability Index, which rates the degree of segregation during the test. Measured characteristic: Filling ability (deformability), viscosity, & stability
J-Ring	ASTM C1621 The J-Ring consists of a ring of reinforcing bar such that it will fit around the base of a standard slump cone. The slump flow with and without J-Ring is measured, and the difference calculated. An index, called the Visual Blocking Index, is available to rate the segregation of the mixture during the test, however, this is not part of the ASTM standard. Measured characteristic: Passing ability
Column Segregation	ASTM C1610 Test evaluates static stability of a concrete mixture by quantifying aggregate segregation. A column is filled with concrete and allowed to sit for awhile after placement. The column is then separated into three or four pieces. Each section is removed individually and the concrete from that section is washed over a No. 4 sieve and the retained aggregate weighed. A non-segregating mix will have a consistent aggregate mass distribution in each section. A segregating mix will have higher concentrations of aggregate in the lower sections. Measured characteristic: Stability

There are many other accepted test methods for SCC that have not been standardized within ASTM. The following table summarizes some of the more recent or commonly used methods:

Test Method	Description
L-Box	Test evaluates the passing ability of the mixture. Concrete is placed inside the vertical portion of the testing apparatus. A grill placed at the entrance of the horizontal portion simulates reinforcement. Once the concrete has flowed to a resting position, the heights of concrete in the vertical portion (H1) and the end of the horizontal portion (H2) of the apparatus are measured. The ratio H2/H1 is used as a measurement of passing ability. Values of 0.75 and higher are considered acceptable. Measured characteristic: Passing ability  (photo courtesy of BASF Construction Chemicals)
V-Funnel	The V-Funnel consists of a V-shaped apparatus with an opening at the bottom. The time taken to empty the funnel is regarded as a measure of the viscosity of the mixture. Measured characteristic: Viscosity (photo courtesy of BASF Construction Chemicals)
Segregation Probe	The segregation probe test is a quick and easy test that measures the thickness of the mortar layer on the surface. A standard 150 mm by 300 mm (6 in. by 12 in.) cylinder is filled in one lift and allowed to sit for two minutes. A wire ring with a graduated stem is then placed on the top surface of a cylinder and allowed to settle for one minute before the depth of penetration is recorded. Penetration values range from less than 4 mm (1/6 in.) for very stable mixtures to morethan 25 mm (1 in.) for highly unstable mixtures. Measured characteristic: Stability

Additional Resources:

Szecsy, R. and Mohler, N., "Self-Consolidating Concrete," IS546, Portland Cement Association, Skokie, Illinois, 2009, 24 pages.

Order Self-Compacting Concrete: Bibliography of Resources (2nd ed.)
PCA Library Bibliography Series No. 6 (LB06.02) Portland Cement Association, c2004
for an extensive list of SCC references.

 

More Reading

McGovern, M., "Going with the Flow," Concrete Technology Today, CT022, Portland Cement Association, Skokie, Illinois, July 2002, pages 1, 2, and 8. Click here to download article.

Interested in Self-Consolidating Grout? 
Read Masonry Today, Vol. 14, No. 2, Winter 2004/2005,

Flow with Show: Self-Consolidating Concrete Offers New Opportunities for Architectural Concrete

ACBM, Self-Consolidating Concrete, RP440, Advanced Cement-Based Materials Center, Evanston, Illinois, 2007, 42,pages.