Improving PCC Mix Consistency and Production by Mixing Improvements (TR-505, Proj. 11)

Project Details
STATUS

Completed

START DATE

10/01/03

END DATE

09/30/05

RESEARCH CENTERS InTrans, CP TECH, CTRE
SPONSORS

Federal Highway Administration
Iowa Highway Research Board
PCC Center Sponsored Research Fund

Researchers
Principal Investigator
Vern Schaefer

Interim Director, CEER

Co-Principal Investigator
Scott Schlorholtz

Faculty Affiliate

Co-Principal Investigator
Kejin Wang

PCC Engineer, CP Tech

About the research

A two-stage mixing process for concrete involves mixing a slurry of cementitious materials and water, then adding the slurry to coarse and fine aggregate to form concrete. Some research has indicated that this process might facilitate dispersion of cementitious materials and improve cement hydration, the characteristics of the interfacial transition zone (ITZ) between aggregate and paste, and concrete homogeneity.

The goal of the study was to find optimal mixing procedures for production of a homogeneous and workable mixture and quality concrete using a two-stage mixing operation. The specific objectives of the study are as follows: (1) To achieve optimal mixing energy and time for a homogeneous cementitious material, (2) To characterize the homogeneity and flow property of the pastes, (3) To investigate effective methods for coating aggregate particles with cement slurry, (4) To study the effect of the two-stage mixing procedure on concrete properties, (5) To obtain the improved production rates. Parameters measured for Phase I included: heat of hydration, maturity, and rheology tests were performed on the fresh paste samples, and compressive strength, degree of hydration, and scanning electron microscope (SEM) imaging tests were conducted on the cured specimens. For Phases II and III tests included slump and air content on fresh concrete and compressive and tensile strengths, rapid air void analysis, and rapid chloride permeability on hardened concrete.

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