NCHRP Web Doc 14 Laboratory Determination of Resilient Modulus for Flexible Pavement Design Final Report (1997) / Chapter Skim
Currently Skimming:
4 Significant General Findings
4 Significant General Findings
Pages 251-277
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 251... ...
The broad aspects of resilient modulus testing are examined in this chapter and put into perspective from a practical viewpoint. OPTIMUM RESILIENT MODULUS TESTING SYSTEM For production resilient modulus testing, a completely automated, modern' electro-hydraulic loading and data acquisition system is a necessity to maximize the number of tests performed am to minimize the poter~fi~fortestiingan~data reduction errors.
|
From page 252... ...
;,. ~ icky F3~ai ~9 Data Acquisition System Figure 123.
|
From page 253... ...
Consider, for example,the average coefficient of variation for Me repeated load biaxial test resilient moduli obtained for five 0.
|
From page 254... ...
Adequate transducer sensitivity is often a problem in resilient modulus testing. Data Reduction Large quantities of data are obtained from a full resilient modulus test sequence using a data acquisition system.
|
From page 255... ...
SET UP AND OPERATION OF NEW TAXIING SYSTEM Laboratories have significant problems in properly setting up and making operational the resilient modulus test including testing equipment, data acquisition apparatus, specimen preparation methodology, specimen set-up and data reduction. Several factors including He sophistication of the testing system electronics and difficulty to visually observe specimen behavior mean a greater level of care is required to obtain meaningful resilient modulus test results Man for most other tests.
|
From page 256... ...
Conclusions. The following general conclusions are made concerning resilient modulus testing of asphalt concrete specimens: I. Resilient modulus decreases when testing is repeated on an axis mutually perpendicular to the axis initially tested.
|
From page 257... ...
As a result the haversine load pulse is recommended for resilient modulus testing. The loading time significantly affects the MR values.
|
From page 258... ...
The following configuration of test apparatus is recommended for use in resilient modulus testing: Load Device: A device comparable to the SHRP EG device, possibly with the following modifications: I Reduction of the upper plate weight using high strength, light weight materials and thus elimination of the counterbalance weights, 2.
|
From page 259... ...
The complete proposed test procedures are given in Appendix lo. Major Issues - Dee foRowzag major msdient modulus test issues completely overshadow other test details which usually have relay rely minor influence on the measured resilient modulus: (~)
|
From page 260... ...
POS~ T292-911 TR46 (ED.1) GENERAL TESTING SYSTEM not "pecitied electro-hydraulic fully-automated, electro-hydraulic DATA ACQUISITION strip chart or not specif fed AID Data computer Acquisition Sy$.
|
From page 261... ...
STRESS STATES (PSI) Repr - entatives CIj; ~-6,~,2; t5 ~'.
|
From page 262... ...
Cohesive Soil Test Method -- An unconfined repeated load test is proposed for both undisturbed and compacted cohesive subgrade specimens. The considerably more complicated biaxial test is specified by bow the AASHTO and SHRP test procedures.
|
From page 263... ...
Because of capillary tension, a tested specimen compacted at optimum moisture content and then air dried gives significantly higher resilient moduli than if dry aggregate is used in preparing He specimen [1071. Later, during a wet period, He dry base or subgrade material often reaches a high degree of saturation with the resilient modulus being as small as 10% or less of the value in a very dry condition (Figure 124~.
|
From page 264... ...
Influence of environmental cycle on resilient modulus of aggregate base specimen 264
|
From page 265... ...
Sickness due to resilient modulus testing error is less than about 5.5% of the required thickness considering variability from other sources (Figure 125~. The reason for He small effect of asphalt concrete resilient modulus variation on Sickness is that the structural coefficient is relatively insensitive to variation in resilient modulus in He vicinity of 400,000 psi.
|
From page 266... ...
Influence of lab variability on full Kept A.C. pavement thickness for Monte CarIo analysis 60 50 ~ 40 7 c, ~z Y c' > ~ 20- .
|
From page 267... ...
Change in thickness determined by the AASHTO type reliability analysis due to resilient modulus testing errors, however, are about one-half of the ~ to 14% increase in total equivalent base thickness (i.e., no A.C.) typically predicted using the Monte CarIo analysis.
|
From page 268... ...
Influence of lab variability on base thickness for AASHTO reliability analysis: Base MR = 3D,000 psi 268
|
From page 269... ...
Variation of asphalt concrete structural coefficient with resilient modulus used in reliability analysis 269 l
|
From page 270... ...
Variation of base structural coefficient with resilient modulus used in reliability analysis Table 60. Approximate relative effect on pavement thickness of resilient modulus test variabiliny of each layer (l,2)
|
From page 271... ...
161. Also, both Monte CarIo and AASHTO type reliability analyses, using He 1986 AASHTO Design Guide, indicate modest errors in evaluating resilient moduli as large as 10 to 15% of He mean MR value have in general a relatively small effect on He overall required pavement thickness.
|
From page 272... ...
As a result, a table of design resilient moduli can be prepared based on laboratory testing of the base and subbase materials used by a particular agency. In areas where marginal materials of variable quality commonly are encountered, caution must be exercised including performing periodically resilient modulus tests.
|
From page 273... ...
The permanent deformation behavior of asphalt concrete can be evaluated using a loaded wheel tester or else as an extension of the repeated load diametral test. A loaded wheel tester could perhaps also be used to evaluate the permanent deformation behavior of aggregate base and subgrade materials although this has apparently not been done in He past.
|
From page 274... ...
Correlation between predicted and measured resilient moduli for Georgia subgrade soils (after reference 120)
|
From page 275... ...
25 30 Figure 131. Moisture sensitivity corrections for resilient modulus for cohesive Texas soils (after reference 119)
|
From page 276... ...
Layered theory should, therefore, be used to develop generalized tables or charts for estimating the stress state to use in selecting design resilient moduli for each layer. Development of these tables or charts must be carried out as an integral part of He development of He design procedure.
|
From page 277... ...
One of He weakest links in He design process, however, is how He AASHTO approach utilizes the resilient modulus in flexible pavement design. The resilient modules concept was added during He 1986 revision, and it does not appear to mesh very well with the overall design process.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.