00212601

Component

http://onlinepubs.trb.org...rbbulletin/355/355-001.pdf

DEVELOPMENT OF HIGH EARLY STRENGTH IS DESIRABLE TO THE MANUFACTURERS OF PRECAST AND PRESTRESSED CONCRETE UNITS, WHICH OFTEN REQUIRE EXPENSIVE FORMS OR STRESS BEDS. STEAM CURING ACCELERATES THE GAIN IN STRENGTH AT EARLY AGES, BUT THE UNCONTROLLED USE OF STEAM MAY SERIOUSLY AFFECT THE GROWTH IN STRENGTH AT LATER AGES. THE RESEARCH DESCRIBED IN THIS REPORT WAS PROMPTED BY THE NEED TO ESTABLISH REALISTIC CONTROLS AND SPECIFICATIONS FOR THE STEAM CURING OF SUCH UNITS MANUFACTURED IN CENTRAL PLANTS. THE PURPOSE OF THE LABORATORY INVESTIGATION WAS TO DETERMINE SOME OF THE RELATIONSHIPS BETWEEN DEVELOPMENT OF CONCRETE STRENGTH AND VARIOUS DETAILS OF THE STEAM CURING PROCEDURE, SUCH AS THE INTERVAL BETWEEN MIXING OF THE CONCRETE AND BEGINNING OF STEAM CURING, THE RATE OF TEMPERATURE RISE OF THE CONCRETE DURING STEAM CURING, THE HIGHEST TEMPERATURE ATTAINED BY CONCRETE, LENGTH OF STEAM CURING PERIOD, AND RATE OF TEMPERATURE DECREASE. CONCLUSIONS INCORPORATED IN THE STANDARD SPECIFICATIONS OF THE IOWA STATE HIGHWAY COMMISSION INCLUDE: (1) INITIAL TEMPERATURE OF THE CONCRETE SHALL NOT BE RAISED ABOVE 100 F FOR A MINIMUM OF 2 HOURS AFTER THE UNITS HAVE BEEN CAST, (2) THE RATE OF INCREASE AFTER THE 2 HOUR PERIOD SHALL NOT EXCEED 25 F PER HOUR AND THE MAXIMUM TEMPERATURE ATTAINED SHALL NOT EXCEED 150 F, (3) THE MAXIMUM TEMPERATURE SHALL BE HELD FOR A PERIOD SUFFICIENT TO DEVELOP THE REQUIRED STRENGTH (4500 PSI FOR PRESTRESSED UNITS), (4) RATE OF DECREASE IN TEMPERATURE SHALL NOT EXCEED 20 F PER HOUR, AND (5) IN ALL CASES UNITS SHALL BE KEPT COVERED FOR A MINIMUM OF 24 HOURS AFTER CASTING. /AUTHOR/

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01410733

pp 1-26

1962

Highway Research Board Bulletin

41st Annual Meeting of the Highway Research Board

Digital/other

Figures (16) ; Tables (13)

Atmospheric pressure; Concrete mixing; High early strength cement; Laboratory studies; Portland cement; Precast concrete; Prestressed concrete; Specifications; Steam curing; Strength of materials; Temperature measurement

Highways; Materials

TRIS, TRB, ATRI

Jun 3 1994 12:00AM

• AN OCCURRENCE OF ALKALI-REACTIVE CARBONATE ROCK IN VIRGINIA