Use of Thermal Measurements to Detect Potential Incompatibilities of Common Concrete Materials

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Title: Use of Thermal Measurements to Detect Potential Incompatibilities of Common Concrete Materials

Author(s): V.T. Cost and G. Knight

Publication: Special Publication

Volume: 241

Issue:

Appears on pages(s): 39-58

Keywords: aluminates; calorimetry; cement-admixture interaction; exotherm; hydration heat; incompatibility; retardation; silicates; sulfates.

Date: 4/1/2007

Abstract:
Abnormal early hydration resulting from "incompatibilities" of common concrete materials can result in erratic set and strength gain behavior and associated finishing, curing, and cracking issues. Contributing influences include high temperatures, cement sulfate levels, Class C fly ash content, chemical admixture use, and design approaches for retardation of hot-weather concrete. Simple, expedient test methods are needed to identify potentially incompatible materials and conditions and to verify appropriate modifications to concrete proportions. Thermal measurements of the early heat development of materials mixtures in the laboratory (semi-adiabatic calorimetry) have been shown very useful toward this end. Abnormal set and strength development of field concrete was reproduced in laboratory paste and mortar mixtures and studied using thermal measurements, verified by parallel mortar cube strengths. Sensitivities of various contributing influences were documented in extensive testing. Changing one or more of the key material or mixture characteristics was usually successful in restoring normal behavior. Recommendations are presented for avoiding related field issues and for the use of calorimetry testing programs for diagnosis of such problems.