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.
Related References:
AASHTO M 157-11, 2013, “Standard Specification for Ready Mixed Concrete,” American Association of State Highway and Transportation Officials, Washington, DC, 14 pp.
ACI Committee 304, 2000, “Guide for Measuring, Mixing, Transporting, and Placing Concrete (ACI 304R-00),” American Concrete Institute, Farmington Hills, MI, 41 pp.
American Petroleum Institute, 2002, Specification 10A, “Specification for Cements and Materials for Well Cementing,” API, Washington, DC, 46 pp.
ASTM C94/C94M-13, 2013, “Standard Specification for Ready-Mixed Concrete,” ASTM International, West Conshohocken, PA, 14 pp.
Barnett, S. J.; Soutos, M. N.; Millard, S. G.; and Bungey, J. H., 2006, “Strength Development of Mortars Containing Ground Granulated Blast-Furnace Slag: Effect of Curing Temperature and Determination of Apparent Activation Energies,” Cement and Concrete Research, V. 36, No. 3, pp. 434-440. doi: 10.1016/j.cemconres.2005.11.002
Beaufait, F., and Hoadle, P., 1973, “Mix Time and Retempering Studies on Ready Mixed Concrete,” ACI Journal Proceedings, V. 70, No. 12, Dec., pp. 810-813.
Beitzel, H., 1981, “Effect of the Mixing Time on the Quality of the Mixing,” Precast Concrete, V. 12, pp. 403-408.
Bouzoubaâ, N.; Zhang, M. H.; and Malhotra, V. M., 2000, “Laboratory-Produced High-Volume Fly Ash Blended Cements: Compressive Strength and Resistance to the Chloride-Ion Penetration of Concrete,” Cement and Concrete Research, V. 30, No. 7, pp. 1037-1046. doi: 10.1016/S0008-8846(00)00299-4
Kırca, Ö.; Turanlı, L.; and Erdoğan, T., 2002, “Effects of Retempering on Consistency and Compressive Strength of Concrete Subjected to Prolonged Mixing,” Cement and Concrete Research, V. 32, No. 3, pp. 441-445. doi: 10.1016/S0008-8846(01)00699-8
Lobo, C., and Gaynor, R., 2006, “Chapter 45: Ready-Mixed Concrete,” in: Lamond, J., and Pielert, J. (eds.), “Significance of Tests and Properties of Concrete and Concrete-Making Materials,” ASTM International, West Conshohocken, PA, pp. 533-547.
Nehdi, M., and Al-Martini, S., 2009, “Coupled Effects of High Temperature, Prolonged Mixing Time, and Chemical Admixtures on Rheology of Fresh Concrete,” ACI Materials Journal, V. 106, No. 3, May-June, pp. 231-240.
Ravina, D., 1975, “Retempering of Prolonged-Mixed Concrete with Admixtures in Hot Weather,” ACI Journal Proceedings, V. 72, No. 6, June, pp. 291-295.
Ravina, D., 1996, “Effect of Prolonged Mixing on Compressive Strength of Concrete with and without Fly Ash and/or Chemical Admixtures,” ACI Materials Journal, V. 93, No. 5, Sept.-Oct., pp. 451-456.
Trejo, D., and Chen, J., “Effects of Extended Discharge Time and Revolution Counts for Ready-Mixed Concrete,” Final Report, Washington Department of Transportation, Olympia, WA, 2014, 349 pp.
Trejo, D., and Prasittisopin, L., 2015, “Effects of Mixing Variables on Hardened Characteristics of Portland Cement Mortars,” ACI Materials Journal, V. 112, No. 3, May-June, pp. 399-408