Click for next page ( 23

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 22
22 CHAPTER 5 TESTING OF FRESH AND HARDENED CONCRETE Testing of fresh and hardened EOT concrete is required to air-void size distribution, total air content, and specific sur- monitor the construction process as well as ensure that desir- face from which a spacing factor can be calculated. Although able concrete properties are achieved. Routine standard tests the use of this device for large paving projects might be jus- for fresh concrete include workability, air content, and matu- tified, it seems unlikely that the device will be used exten- rity. The most common, and often the only, testing of hard- sively to monitor field installations of EOT concrete. The ened concrete is measuring compressive strength and/or flex- device, however, might be useful in the laboratory during ural strength. Other tests of hardened concrete that could be mix design to verify the sufficiency of the air-void system. considered include methods to assess volume change, dura- Another fresh concrete test that will see increasing use in bility in freeze-thaw environments, absorption/permeability, EOT concrete applications is maturity (ASTM C 1074). The and microstructural characterization. A number of tests are maturity concept relates the time-temperature relationship recommended for evaluation of EOT concrete mixtures. directly to strength gain for a given mixture. It is an excellent way to determine the time to opening. The relatively new use of wireless technology has eliminated the need for wires and 5.1 TEST METHODS continual recording of data common in older maturity meters. As wireless technology continues to develop, it is foreseeable 5.1.1 Testing Fresh Concrete that each repair will have a wireless maturity gauge installed that reports to a hand-held unit, which in turn computes the Testing of fresh EOT concrete entails measuring worka- time to opening based on stored mix design information. bility, air content, and maturity. Workability is most often assessed through the slump test (AASHTO T 119), with a desired range in slump for EOT concrete often specified 5.1.2 Testing Hardened Concrete between 50 and 150 mm (2 to 6 in.). The time of setting (AASHTO T 131) can also be used to establish the time in Strength Testing which the mixture is workable. This time should be sufficient to provide time for mixing, placing, and finishing the EOT Strength testing is an integral part of the mixture design concrete. process and construction monitoring for EOT concrete. Com- Air content of the fresh concrete is measured as an indirect pressive strength (AASHTO T 22), measured on cylindrical indication of the air-void system in the paste. In a freeze-thaw specimens, is often specified to be at least 13.8 MPa (2,000 psi) environment subjected to deicer use, the air content for con- at time of opening (FHWA 2003). Some agencies prefer the crete mixtures containing coarse aggregates with a nominal use of a flexural strength (AASHTO T 97) opening criterion. maxium size of 1 in. (25 mm) or less should range from Testing is conducted on beam specimens with common cri- 6 to 7.5 1.5 percent depending on coarse aggregate size, as terion of 1.7 MPa (250 psi) for third-point loading and 2.1 recommended in Table 3. Air contents are commonly mea- MPa (300 psi) for center-point loading. The minimum required sured using the pressure method (AASHTO T 152), compressive or flexural strength is commonly raised for the although the volumetric method (AASHTO T 196) is slower-setting 20- to 24-hour concrete mixtures. also used. For construction monitoring, early strength testing is often The AVA is currently being used for the analysis of paving not conducted because of the short time available. If logistics concrete (Price 1996). The AVA measures changes in buoy- preclude strength testing prior to opening, the use of the ancy using a special buoyancy recorder that captures bubbles maturity concept is recommended. Strength-maturity relation- as they rise from the concrete through a viscous medium. ships established for a given mixture can be used during con- Since larger bubbles rise more quickly, monitoring the change struction to ensure that adequate strength has been achieved in buoyancy as a function of time provides a measure of the prior to loading.