SPA Application: Forensics
Identifying the cause of premature failure of pavements is not an easy task. Proactive highway agencies, such as the Texas Department of Transportation ( TxDOT ), conduct forensic studies on projects so that they do not repeat mistakes. Seismic tests with the SPA technology have been a part of such forensic studies on many occasions. The SPA technology provides a directly measured property, not a backcalculated one. The SPA technology provides more accurate information about the variation in mechanical properties within the pavement layers, which is typically difficult to obtain from other nondestructive testing methods.
Case Studies for Forensics
Quality Management of Base and
Subgrade Materials with Seismic Methods
S. Nazarian, D. Yuan,
The University of Texas at El Paso, El Paso, TX 79968,
Materials and Tests Section, Texas Department of Transportation, 125 East 11th Street, Austin, TX 78701
The acceptance criteria for compacted geo-materials (such as base and subgrade) are typically based on adequate inplace density. Unfortunately, the design of a given project is based on the engineering parameters, such as strength and stiffness. A procedure based on seismic techniques to measure the modulus layer-by-layer shortly after placement is presented. The major advantage of seismic methods is that similar results are anticipated from the field and laboratory tests as long as the material is tested under comparable conditions. This unique feature of seismic methods in material characterization is particularly significant in quality control and quality assurance for ground treatment prior, during and after construction.
Simplified field and laboratory tests are suggested that can be rapidly and nondestructively performed and interpreted so that problem materials can be identified before construction and in order that any problems during the construction process can be adjusted. The field and laboratory methods are incorporated in a manner in which the results can be readily reconciled without any scaling or simplifying assumptions. The simplified laboratory tests can be used to develop the ranges of acceptable properties for a given material. Nondestructive field tests are performed to determine whether the contractor has achieved the minimum specified stiffness.
This paper provides a concept on using seismic nondestructive testing technology in the evaluation of compacted materials and describes the equipment and setups that have been developed for implementing the technology in both field and laboratory tests. The methods have shown promise as practical tools for use by highway and construction industry. Currently, the procedure is being implemented on the trial basis by the Texas Department of Transportation.
A Methodology for Optimizing Opening of PCC Pavements to Traffic
Deren Yuan, Ph.D.
Soheil Nazarian, Ph.D., P.E.
Anitha Medichetti, BSCE
The Center for Highway Materials Research
The University of Texas at El Paso
El Paso, TX 79968-051
Due to difficulties associated with the maintenance of highways constructed
in urban settings, the expedited construction of durable portland cement
concrete (PCC) pavement has become a necessity. To obtain a durable PCC pavement,
a number of parameters should be considered. One important parameter is the
adequate curing of a proper mix before opening the road. Since most urban
roads experience excessive traffic, the tendency of highway agencies is to
open a newly constructed highway to traffic as soon as possible. A rational
assess the minimum time required to gain a desired strength before opening it to traffic is proposed here. Two reliable and easy-to-use test methods, maturity method and seismic method, are combined to improve the determination of the readiness of a road to be opened to traffic.
Optimizing Opening of PCC Pavements
Integrated Maturity and Nondestructive Tests
S. Nazarian, D. Yuan and A. Medichetti
Center for Highway Materials Research
The University of Texas at El Paso
El Paso, TX 79968
A paper presented to the
Emerging Technologies for Expediting Construction Session
2003 Annual TRB Meeting
In this paper the use of seismic testing technique combined with maturity concept to monitor and predict the strength gain of Portland cement concrete is described. In this process, the dynamic modulus of elasticity of a given mix obtained from its stress wave velocity can be related to the strength parameters and static modulus of the mixture using the same specimens used in the calibration process commonly carried out for maturity tests. When these relationships are combined with the maturity parameters, the predictive power is significantly improved. In this investigation, the lab tests on molded specimens and cores were carried out with the simplified free-free resonant column method and the field tests on concrete slabs were performed with a hand- held device called the portable seismic pavement analyzer. Based on these experiments, relationships between the dynamic modulus and the strength parameters as well as the maturity are proposed. The technique has shown to be a rapid, simple and economic means for optimizing concrete mix design, quality control/quality assurance of concrete construction and determining the time required before a repaired or newly constructed structure is ready for use.
Use of Seismic Pavement Analyzer in Forensic Studies in Texas
Mark McDaniel, Deren Yuan, Dar Hao Chen and Soheil Nazarian
Seismic nondestructive testing technology has been incorporated in two newly developed devices: the Seismic Pavement Analyzer (SPA) and its hand-portable version (PSPA). Shortly after a prototype of the SPA was built and tested under a SHRP contract, the Texas Department of Transportation (TxDOT) acquired a second prototype SPA and several PSPAs. Each of the two devices can rapidly carry out a suite of seismic tests to evaluate pavement condition. A few short-term projects were conducted to learn when and where the use of seismic technology is feasible. The usefulness of the test methods involved in SPA and PSPA has been to some extent evaluated. In their present
states, the SPA and PSPA seem to be emerging as valuable tools for forensic studies and the day-to-day operation of TxDOT. The devices have been helpful in understanding some of the complex mechanisms encountered under accelerated pavement testing with the Texas Mobile Load Simulator, and have provided useful information to the engineers in a few TxDOT projects. More experience is needed to fully understand the potential and weaknesses of the devices, and further development of their software is required.
Geomedia SPA Application: Forensics