The mini-slump test is one component of a protocol to identify incompatible combinations of concrete materials outlined in the new FHWA TechBrief.
CTLGroup The mini-slump test is one component of a protocol to identify incompatible combinations of concrete materials outlined in the new FHWA TechBrief.
The CTLGroup has recently completed a comprehensive Federal Highway Administration (FHWA) study of material incompatibility issues and developed a testing protocol to prevent problems before construction.

The comprehensive research project, which began in 1998-99, had several goals: gain a clearer understanding of the chemistry of reactive materials in concrete; develop a pre-construction laboratory testing regimen to detect problematic interactions and incompatible mix designs; correlate lab and field test methods to facilitate quality assurance during construction; and recommend field tests to confirm concrete quality and allow for needed adjustments onsite.

The research results made clear that properties of both plastic and hardened concrete can be changed by even slight adjustments in mix design or environmental conditions. The preconstruction test protocol allows for the evaluation of this sensitivity in a particular mixture, and the selection in advance of alternative materials or action plans to be implemented if such changes are observed in the field.

Suppliers of cement, SCMs, and chemical admixtures can use the protocol to test the products in various combinations and conditions and confirm their compatibility and performance characteristics. For contractors, the protocol provides tools to help prevent problems from occurring and guidance on alleviating problems that do occur.

FHWA has issued a TechBrief, Publication No. FHWA-HRT-06-082 “Protocol to Identify Incompatible Combinations of Concrete Materials,” to help publicize the information. The six page TechBrief, is available online at www.fhwa.dot.gov/pavement/concrete/06082/06082.pdf