ACCELERATED CONCRETE STRENGTH TESTING IN HIGHWAY DEPARTMENT OPERATIONS

ENSURING USE OF CONCRETE OF ADEQUATE STRENGTH IS IMPORTANT TO EVERY HIGHWAY AGENCY. STRENGTHS MUST BE SUCH THAT TRAFFIC LOADS NOT OVERSTRESS THE CONCRETE CAUSING DAMAGE TO THE HUGE INVESTMENT IN PAVEMENTS AND STRUCTURES. THE FACT THAT THE STRENGTH OF CONCRETE VARIES WITH ITS AGE AND THAT A SUBSTANTIAL RANGE OF ULTIMATE STRENGTHS MAY BE ATTAINED DEPENDING UPON MIX PROPORTIONS, INGREDIENT CHARACTERISTICS, AND TREATMENT AT THE JOB SITE PROVIDES A BEWILDERING NUMBER OF VARIABLES WITH WHICH TO COPE. ONE OF THE MOST TROUBLESOME ASPECTS OF CEMENT AND CONCRETE STRENGTH TESTING AND ONE WHICH IS ENTIRELY OUT OF TUNE WITH THE RAPIDITY OF PRESENT-DAY CONSTRUCTION IS THE CLASSICAL DEPENDENCE UPON 28-DAY STRENGTHS FOR DESIGN AND ACCEPTANCE PURPOSES. AT LEAST TWO DISTINCTLY DIFFERENT REMEDIES FOR THE INTOLERABLE 28-DAY TIME LAG EXIST: 1. BASE DESIGN AND ACCEPTANCE UPON STRENGTHS AT AGES EARLIER THAN 28 DAYS. 2. DEVELOP TECHNIQUES TO PREDICT 28-DAY STRENGTHS AT EARLIER AGES. VERY SLOW PROGRESS HAS BEEN MADE WITH RESPECT TO ITEM 1; HOWEVER, IN 1942 ASTM DID SPECIFY THAT LABORATORY ACCEPTANCE TESTING OF PORTLAND CEMENT ITSELF WAS TO BE BASED UPON STRENGTHS AT 3 AND 7 DAYS UNLESS OTHERWISE PRESCRIBED BY THE PURCHASER. HOWEVER, 28-DAY REQUIREMENTS ARE CARRIED BY ASTM TO THIS DAY IF THE PURCHASER WISHES TO INVOKE THEM. STRUCTURAL DESIGNERS HAVE SHOWN LITTLE ENTHUSIASM FOR BASING DESIGNS ON OTHER THAN "ULTIMATE" STRENGTHS, USUALLY CONSIDERED SYNONYMOUS WITH 28-DAY STRENGTHS. THIS IS UNDERSTANDABLE SINCE THE LONG-TERM LIFE OF THE CONSTRUCTION IS OF MAJOR CONSEQUENCE, AND SHORT-TERM STRENGTHS, I.E. DURING THE FIRST FEW HOURS OR DAYS, ARE MORE OF A DETAIL OF FABRICATION CONVENIENCE INVOLVING REUSE OF FORMS, CONSTRUCTION SAFETY, ETC. ALSO, THE DESIGNER IS AWARE THAT THE STRENGTH-GAIN PATHWAY BY WHICH THE CONCRETE REACHES ITS ULTIMATE STRENGTH CAN BE SUBSTANTIALLY ALTERED TO SUIT JOB CIRCUMSTANCES BY USE OF INTEGRAL ACCELERATING ADMIXTURES, RETARDERS, MODIFIED CURING TECHNIQUES, ETC. THE PRESENT INVESTIGATION EXPLORES IN BEHALF OF THE DEPARTMENT ITEM 2 ABOVE, I.E. PREDICTION OF 28-DAY POTENTIAL STRENGTH FROM MEASUREMENTS OF ONLY A FEW HOURS DURATION. IT SHOULD BE EMPHASIZED THAT THE PRESENT PROGRAM DOES NOT ATTEMPT ASSESSMENT OF IN-PLACE STRENGTH OF JOB CONCRETE; ATTENTION IS CONFINED ONLY TO SUCH STRENGTH THAT THE CONCRETE IS CAPABLE OF ATTAINING UNDER STANDARD CONDITIONS. OTHERS ARE ATTACKING THE PROBLEM OF IN-PLACE STRENGTH OF JOB CONCRETE, AND IT APPEARS PROBABLE THAT FURTHER EXTENSIVE RESEARCH IN THIS REGARD MAY BE FUNDED SOON BY AASHO FOR AN NCHRP RESEARCH PROGRAM. /AUTHOR/

  • Supplemental Notes:
    • Rept No 335150-2-F 6 APP
  • Corporate Authors:

    University of Michigan, Ann Arbor

    Department of Civil Engineering
    Ann Arbor, MI  United States  48109
  • Authors:
    • Legg, F E
  • Publication Date: 1971-11

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 26 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00214273
  • Record Type: Publication
  • Report/Paper Numbers: Final Rept
  • Files: TRIS
  • Created Date: Mar 15 1974 12:00AM