Title: Effects of Mixing Variables on Hardened Characteristics of Portland Cement Mortars

Author(s): Lapyote Prasittisopin and David Trejo

Publication: Materials Journal

Volume: 112

Issue: 3

Appears on pages(s): 399-408

Keywords: chloride diffusivity; compressive strength; hardened characteristics; microstructure; mixing time; number of mixer revolutions; porosity

DOI: 10.14359/51686973

Date: 5/1/2015

Abstract:
Specifications and guidelines for ready mixed concrete (AASHTO M 157, ACI 304R, and ASTM C94) place limits on placement time, concrete temperature, number of truck drum revolutions, or a combination of the three. These limits should correlate with concrete performance—that is, if the limits are exceeded, it would be expected that an inferior product would be produced. An earlier paper investigating the effects of mixing time and number of mixer revolutions on cement pastes and mortars concluded that increased mixing time and mixer revolutions resulted in decreased flows, altered setting times, and increased shrinkage. This paper assesses the influence of mixing time and number of mixer revolutions on the hardened characteristics of lab-made mortars. Results indicate that increasing mixing time leads to higher 1-day compressive strengths but lower 28-day strengths. Results also indicate that an increased number of mixer revolutions can result in increased porosity, leading to decreased strength.