CRACK ANALYSIS OF CFRP REINFORCED CONCRETE BEAMS UNDER SECONDARY LOADING

The paper established the calculation formulas on the average crack spacing and the maximum crack width of CFRP（Carbon Fiber Reinforced Polymer）reinforced concrete beam under the secondary loading. Conversion of CFRP plate area into the reinforcement ratio of the reinforced beam, the calculation formula on the average crack spacing of CFRP reinforced concrete beam under the secondary loading was established. On basis of the calculation formula on the maximum crack width of concrete beam, the calculation formula on the maximum crack width of CFRP reinforced concrete beam under the secondary loading was established. The average crack spacing and the maximum crack width calculated by the formulas in the paper were compared with the test data, it was verified that the formula is correct.

Continuously Reinforced Concrete Pavement Cracking Patterns and Properties with Internal Curing and Active Cracking

Transverse cracking in continuously reinforced concrete pavement (CRCP) develops over time and may exhibit irregular patterns such as cluster cracks, Y-shaped cracks, and divided cracks. These undesirable cracking patterns can increase the probability of premature spalling and punchouts. Ideally, a uniform transverse cracking pattern with small crack widths leads to favorable long-term performance in CRCP. An experimental field project was constructed with internally cured concrete and active cracking to control crack initiation timing, patterns, and properties. Prewetted fine lightweight aggregate was used for internal curing, and edge notches of 2 in. depth and 2 ft length every 4 ft along the test section were sawcut for active crack control. The three experimental CRCP sections in Illinois were monitored for crack spacing, crack width, and formation of undesirable cracks over a 4-year period. Internally cured concrete significantly reduced the undesirable crack patterns relative to the control section. Internally cured concrete coupled with active crack concrete produced superior crack patterns and properties, that is, uniform crack spacing of 3.6 ft without cluster cracks, 0.2 mm surface crack width, and only a small number of undesirable cracks. Active crack control produced a higher number of transverse cracks near the terminal joint (last 150 ft) compared with the control section. Moisture and temperature management with active crack control during construction of the CRCP provided a desirable crack pattern and properties that should increase the overall service life of a pavement.

Enhanced CRCP Backcalculation Procedure and Interface Bond Assessment: Volume 3

Falling weight deflectometer (FWD) testing is effective in evaluating the structural response of in-situ concrete pavements through the backcalculated pavement layer parameters. Since Continuously Reinforced Concrete Pavement (CRCP) has closely spaced transverse cracks, the traditional backcalculation assumption of an infinite slab can lead to significant errors in the backcalculated results. In this study, solutions for backcalculated k-value, elastic modulus of concrete (E), and effective thickness (heff) for different crack spacing have been derived from 2-D finite element analysis for both interior- and edge-loaded CRCP. AASHTO sensor configuration (0, 12 in, 24 in, 36 in.) was recommended for CRCP with crack spacing greater than or equal to 6ft, and an alternative solution for crack spacing of 4 and 5ft was proposed with AREA24. Crack load transfer efficiency (LTE) across transverse cracks had limited impact on backcalculated results if the LTE was greater than 80%. According to the sensitivity study, both positive and negative temperature differentials less than 16oF had limited impact on backcalculated parameters. As expected, the backcalulation values were very sensitive to the load plate’s longitudinal position relative to the transverse crack especially for crack spacings smaller than 8ft. For edge-loaded condition, it is important to drop within a 2-inch lateral offset from edge in order to achieve accurate backcalculated results. In addition, the over width of the base provided extra support to CRCP slab resulting in higher backcalculated heff. The proposed backcalculation procedure system was applied to the Tollway field CRCP test section with different crack spacing, reinforcement ratio, and base types. Finally, a procedure for evaluating the slab-base bonding condition using simplified friction model along with backcalculated heff was extended and applied to one of the CRCP test section on Illinois Tollway near Itasca and one on Interstate 57 near Effingham. Based on the analysis of friction coefficient from measured deflection basin, cement treated base (CTB) was shown to provide good support to CRCP slab given the interface bonding condition between slab and base is stable in the long-term (more than 20 years). The combination of warm mix asphalt (WMA) and CTB also has good performance, even though the dynamic modulus of asphalt changes with the temperature causing decreased interface bonding condition in the summer.

Cost-Effective Construction Innovations/Improvements for CRCP: Volume 5

This volume addresses key factors such as cracking behavior of CRC pavement, end movements at terminal and header joints, and interfacial bond and erosion damage between the slab and the base layer as it may pertain to punchout development and the performance of CRCP. This volume also addresses measures to reduce initial cost of CRC pavement construction through modification of base types, pavement and jointing configuration, and transverse crack spacing variability.

Analysis on cracking of structure layer of cement stabilized graded macadam

Because of its strong bearing capacity, good stability and easy control of construction technology, cement stabilized graded macadam was widely used in highway pavement structure. In order to solve its characteristics of easy cracking, relevant researchers have carried out systematic studies on it, but such studies did not involve the large volume and large scope of the structural layer, and only carried out research on the specimen and small scope. Based on engineering project, the influence of dust content and cement content on the cracking was studied by adjusting the parameters and paving the test section during the production process. At the same time, the cracks in the project were counted, and the influences of exposure time, structural level, traffic load and construction level on the cracks in the cement stabilized graded macadam were analyzed. The relationship between crack spacing and exposure time is established, and through comparative analysis, it is found that construction level is the most important factor affecting crack spacing.