Investigation Of Early Shrinkage And Cracking Resistance Of High Performance Highway Pavement Cement Concrete Containing Ultra-fine Fly Ash

Untral-fine Fly Ash (UFA) has been used in civil engineering field because of its good performance and UFA high-performance concrete has been produced, which displayed tremendous role in some important structures and big basic buildings such as high-rise building, bridge, highway, hydro-structure and harbor work, etc.In this paper, high-performance concrete used for pavement was produced with UFA replaced equivalent cement. According to the data analysis in a series of experimental studies, the early shrinkage and cracking resistance of UFA high-performance highway cement-base materials and concrete were studied synthetically. The research contents include that the early chemical shrinkage of cement paste, the early autogenous shrinkage of UFA highway concrete, the early plastic shrinkage, the early thermal shrinkage and all age dry-shrinkage.On the basis of the shrinkage experiment, the early shrinkage and thermal stress of UFA high-performance concrete were analyzed by introducing the finite-element theory, and the UFA-FG special admixture using in shrinkage reducing and crack resisting, which was applied to the production of highway concrete, was attempted and developed. Moreover, the fuzzy comprehensive evaluation system about the early cracking resistance of UFA high-performance highway concrete was developed by making use of the fuzzy mathematics theory. In the end, UFA was used in the field pavement construction and UFA highway concrete was produced. The early and long-term cracking resistance of UFA high-performance highway concrete was tracking observed. Meanwhile, the correspondent construction technical requirements were generalized.The following are the main achievements in this paper:1. The research results of UFA powder technology effects proved that UFA spherical shape particle has good effects of dense packing, water reducing and strength increasing in cementitious materials, and the packing structure of UFA+cement particle is closer to "Horsfield packing" than that of the pure cement particle. Meanwhile, under thecondition of obtaining the same flow, UFA mortar can reduce 10—15% of water demand, and 28-days strength is higher than the reference cement mortar.2.The early chemical shrinkage of UFA cement paste is first tested systematically by experimental device of chemical shrinkage, which was designed and improved by the author. The results indicate that UFA can reduce the chemical shrinkage of cement hydration. The more UFA added, the less chemical shrinkage will be. On the other hand, the reducing-shrinkage mechanism and the shrinkage model of UFA cement paste were analyzed and researched. It supplied the correspondent theoretical supports for UFA'S reducing-shrinkage effect.3. The autogenous shrinkage test device was improved by introducing the inductance frequency-modulation type micro-displacement transducer, and the early autogenous shrinkage (before 7-days) of UFA high-performance highway concrete is tested with the improved test device. The results indicate that UFA can reduce the autogenous shrinkage of concrete. Meanwhile, the early internal autogenous desiccation degrees of the UFA cement paste and reference cement paste were compared according to the pore water calculating of hardened cement paste. It can be seen that the addition of UFA reduce the internal autogenous desiccation degree of hardened cement paste, which proved that UFA can reduce the autogenous shrinkage of concrete.4. The early plastic shrinkage, thermal shrinkage and dry-shrinkage of UFA high-performance concrete were tested systematically. It can been seen that the addition of UFA reduce the early plastic shrinkage and thermal shrinkage. UFA can depress dry-shrinkage effectively when the content of UFA is less than 40% of binding materials, but the dry-shrinkage increases with the growth of UFA content when the content of UFA is more than 40% of binding materials. On the basis of the dry-shrinkage test, the mutual relation of autogenous shrinkage and dry-shrinkage was studied, and the relation was compared systematically under the condition of fix and variable water-binding material ratio. At last, the total shrinkage prediction empirical model of UFA highway concrete was developed, and the playback of shrinkage test proved thatthe predictive value and empirical value is anastomotic well.5. The early shrinkage and thermal stress of UFA highway concrete desk were calculated with Ansys software by introducing the finite element theory, and two kinds of stress were coupled. The results proved further that the addition of UFA enhances the early ability of concrete against cracking compared to the reference concrete.6. Regarded UFA as the main body material and Fluoro Gypsum (FG) as the modifying material, UFA-FG special admixture using in shrinkage reducing and crack resisting was researched and developed according to the orthogonal test. The early shrinkage of concrete was reduced effectively and the cracking resistance of concrete was improved by making use of the shrinkage-compensated effect of UFA-FG.7. The fuzzy comprehensive evaluation system, which was developed by the fuzzy mathematics theory, can appraise the early cracking resistance of UFA high-performance highway concrete effectively. The system removes the "exclusive" evaluating of the ordinary evaluation methodology, which make the evaluation outcome more scientific. Moreover, it was used in the cracking resistance evaluating of the actual pavement project, and the evaluation outcome showed that the early cracking resistance of pavement is "excellent", which agreed to the practical observed outcome.8. UFA high-performance highway concrete was used in the field test pavement project successfully, which belongs to the 18th contract section of ChangNing interconnection, "HengZao" highway. And the construction technical requirements and quality monitoring technique used in the pavement construction process were generalized. From the actual project application it can be seen that the mechanical performance of UFA high-performance highway concrete meets the design requirement, the fractural strength of highway concrete, which is produced in the winter (<5°C), meets the requirement of 7-day opening traffic. The concrete's workability is well, and the quality is stable. Moreover, the early cracking resistance of highway concrete is good, so the flaw can't be discovered. Meanwhile the long-term performance is well. All in all, we can draw a conclusion that it is less in China that thelarge volume UFA which is used in the pavement project achieves success.9. The cost of concrete can be reduced effectively when UFA is added into concrete, In fact, the cost is cut down about 12.7% compared to the ordinary concrete pavement. Meanwhile, the addition of UFA can utilize waste materials, save energy, thus the environment benefits are obvious.