Meeting the Code of Federal Regulations (CFRs) for construction acceptance using ICT is a national issue but a worthwhile endeavor to ensure the ICT produces quality data for construction acceptance decisions. MoDOT is among the leading DOTs working towards satisfying the requirements to implement ICT. This project's main objective is to advance MoDOT's efforts to obtain data QA solutions for ICT.
In recent years, modulus-based compaction QA of unbound materials is gaining attention, as it can not only result in a better constructed product but also provide the engineering properties critical for better understanding of the connection between pavement design and long-term pavement performance. Moisture content is one of the main factors influencing soil modulus and should also be performed concurrent with field modulus measurement. However, existing LWDs do not have the function to measure moisture content.
In this study, a national survey on acceptance of LWD and a substantial literature review were firstly carried out to study the current status of LWD application. Then, four types of representative soils from two projects provided by MoDOT were selected to investigate the implementation of LWD for construction acceptance of unbound materials. Four LWD devices including three Zorn ZFG 2000 and one Zorn ZFG lab 3.0, were used in laboratory and field tests. Furthermore, two moisture content analyzers including Aggrameter and Ohaus MB120 were chosen to evaluate their practicability of quick moisture content measurement in the field. Based on the results of considerable laboratory and field tests, it was concluded that the modulus-based construction quality assessment method using LWD and moisture content analyzer Ohaus MB120 worked well at four construction sites. In addition, a guideline was created for the use of the modulus-based method in the appendix.
The results showed that the deterioration patterns for structures generally had an inflection point at CR 5, where deterioration rates increased as compared with CR 6,7, and 8. The results also demonstrated that the application of salt to the roadway to prevent icing had a significant impact on the deterioration of all structures, and its impact was commonly at least twice that of any other parameter studied. It was also found that increasing span length increased the rate of deterioration. Traffic volume as measured by Average Daily Traffic (ADT) and Average Daily Truck Traffic (ADTT) did not have a statistically significant effect on the deterioration of bridges. It was also found that the deterioration of bridge decks was different in different districts, and reliability curves were developed for each district to aid engineers in decision-making regarding maintenance and repair.
Recommendations from the research included increasing the use of preservation strategies to maintain bridges in CR 6,7, and 8, where deterioration rates are lower as compared with CR 5, 4, and 3. Actions to prevent exposure to deicing chemicals, many of which are already applied in some cases, were described. Looking forward, research results should be considered as one factor in the selection of materials and geometry for new bridges.
The study included a review of experience from previous research and project applications as well as collection of new data from a MoDOT project application. Together, the previous studies and the new research indicate TIP and CSL are generally complementary, with TIP more effective for identifying defects outside the reinforcing cage and weak concrete defects and CSL more effective for identifying defects within the reinforcing cage and soft bottom conditions. However, the results of this study indicate soft bottom conditions may be detectible with TIP methods, especially if temperature versus time records at the bottom of the shaft are evaluated.
This research also included implementation of fiber optic methods for collecting TIP data. Laboratory and field results indicate fiber optic methods result in similarly accurate temperature results compared with conventional TIP, although practical limitations generally mean the fiber optic methods do not produce as complete of a time record. Cost data was also analyzed, indicating conventional TIP may result in cost savings compared to CSL, which is primarily a result of savings associated with remote data collection for many TIP projects. Finally, recommended specifications for MoDOT implementation of TIP methods were developed. The proposed specifications are included as an appendix.
Test results showed that the incorporation of fibers enhanced the mechanical properties (compressive and flexural strengths) of CCP mixtures when proper compaction was provided, as in the case of cast-in field samples. Also, fibers changed the flexural failure mode of saw-cut and cast-in-field CCP samples from brittle to ductile failure. The incorporation of fibers had a restraining effect on the drying shrinkage of CCP mixtures. The use of fibers did not have a significant effect on the performance of CCP mixtures, as shown from the falling weight deflectometer (FWD), truck loading tests and curling and warping. This can be mainly related to the extremely dry consistency of the CCP mixtures (Vebe consistency > 60) that can hinder bond strength in the interfacial transition zone with the matrix. This was more accentuated in the saw-cut samples from the paved CCP as the paving process in the field did not provide enough compaction. As for the size of slabs, results showed that the size of CCP slabs was more effective in the curling and warping measurements. The slab with longer length (15 ft) showed higher variations in curing and warping along the diagonal, transverse and longitudinal lengths over time.
Therefore, the use of fibers in CCP can be recommended provided that the CCP mixture has adequate workability and sufficient compaction energy applied during construction.
