Title:
Influence of Mixing Time on Fresh and Hardened Concrete Characteristics
Author(s):
David Trejo and Jiaming Chen
Publication:
Materials Journal
Volume:
112
Issue:
6
Appears on pages(s):
745-753
Keywords:
compressive strength; diffusivity; extended mixing; freezing and thawing; mixing time; modulus of elasticity; modulus of rupture; tensile strength; workability
DOI:
10.14359/51687396
Date:
11/1/2015
Abstract:
Most specifications for ready mixed concrete (RMC) limit the time of mixing to 90 minutes before discharge. These specifications have been in place for many years with the objective of ensuring the quality and performance of the finished concrete product. However, limited research has been performed to determine the validity of these limits. Because of the significant changes in the concrete industry, these limits were first implemented by ASTM International in 1935; research is needed to determine if these limits are still applicable. Results from this research indicate that extended mixing times (longer than current specification) have no detrimental effects on the mechanical properties and durability characteristics of concrete as long as the concrete exhibits adequate workability to be properly cast. Results also indicate that different mixtures exhibit a wide range of slump and slump-loss values and the 90-minute discharge limit could not be validated in this research.