Design And Reliability Of Damaged Cement Concrete Pavement Renovation

Based on the reconstruction project of cement concrete pavement (CCP) of the national highway 321 (from Gaoyao to Fengkai in Guangdong province), the major problems in the renovation work were studied. Because of this state, the following were investigated. The crack distribution of the damaged CCP was statistically analyzed. A new type of modified asphalt was prepared and tested in laboratory. An alternative measurement method to determine the pavement mechanical properties was studied. Finally, the mechanical response of the damaged CCP, asphalt concrete (AC) surface and semi rigid base overlay renovation were calculated, and the influence of parameters' variation on the pavement structure mechanical response was analyzed. In this disertation, the new test and monitoring system and improved asphalt are presented for the improvements in the reliability and economy of renovation work .Futhermore, the renovation design theory of the damaged CCP is enhanced through the mechanical analysis.Initially the pavement slabs in the test road are numbered and pavement crack damage was investigated. The location and size of every crack in each pavement slab was measured and drawn in a plan. Through the statistical analysis of crack distribution in every pavement slab, the average crack distribution of the pavement under stochastic vehicle and environmental load is obtained. The physical mechanisms causing the cracks are discussed. With the crack distribution determined from the analysis, the design theory of new-constructed CCP, as well as of the maintenance and renovation of damaged CCP is developed and improved.One of the key problems in AC pavement overlay on the damaged CCP is the reflective crack. STRATA stress absorbing interlayer is one of the effective solutions. Based on its retarding and resisting reflective crack principle, the A-70 asphalt was modified with epoxy resin and rubber powder. Different samples of the modified asphalt were tested, varying the quality and the proportions of the additives for the penetration index (P25℃,100g,5s), softening point (TR&B) and ductility (D25℃,5cm/min), which are the three basic asphalt property indexes. At the same time, the low temperature ductility D5℃,5cm/min and torsion resilience were also tested. A new type of modified asphalt with good high and low temperature property was prepared at laboratory. Further testing of this modified asphalt mixture was carried out in the laboratory. These experiments demonstrated the good stability under high and low temperature regimes, good anti-fatigue properties and limiting the water-induced damage of the modified asphalt mixture.The present loading bearing capacity index—surface deflection has limitions when different materials was used for the pavement design. A new measurement and monitoring method, based on vibrating wire strain gauges (VWGS), was used for the testing. VWGS were embedded in the laboratory concrete beams and field CCP, then the relative mechanical experiments in and out of doors and long term monitoring in field of the concrete pavement were done. The suitability of the application of VWGS to test the mechanical properties of the CCP is proved by these experiments. Based on the VWGS, long-term automatic wireless and semi-automatic monitoring systems are suggested. The mechanical parameters of various layers of the AC pavement overlay on the damaged CCP can be measured with these VWGS and temperature sensors installed at various depths in the test road. The temperature range and the strain field at different depths in the pavement structure under random traffic and environmental loads are also able to be measured. This system allows for the mechanical response of pavement to be measured and also provides a basis to check on the design and performance of the renovated CCP.According to the actual pavement structure and investigation in the test road, a finite element model was developed, In the model the actual geometrical dimensions of the test road is taken into account. Parameters such as the influence of concrete slab with different boundary conditions, traffic loads at different positions, various ground modulus and surface thicknesses, different void dimensions and traffic load on the response of the damaged CP was calculated and discussed. The bearing capacity of the test road was measured at different time, and then the two important factors accelerating the damage, the stability of the shoulder and the drainage of the pavement structure are obtained. In order to enhance the reliability of the damaged CP renovation, these two factors should be given serious consideration.The mechanical response of the AC and semi-rigid base overlay on the damaged CP was also calculated with the finite element method. The damaged CP is treated by a break & seat procedure or grouting & seat procedure. The comparison between theoretical and measured values are presented, then based on these calculated results and the measured strain and surface deflection results from the VWGS and Benkelman beam, are used to support the validity of the calculation model and method. Using this method, the influence of the old cement concrete slab thickness and the influence of the break dimensions on the mechanical response of the composite pavement, under different traffic and temperature loads, are calculated. The influence of base thickness of the cement concrete slabs that were treated by break &seat procedure, the AC surface modulus and the traffic load on the mechanical response of the composite pavement are further presented.