Application Of Low-heat Portland Cement In Marine Engineering Concrete

With the development of construction technology,various large-scale marine projects are continuously being built,which leads to an increase of the application of mass concrete.Crack control is a key issue in the construction of mass concrete.Cracks of concrete structure may cause serious influence on concrete durability.A potential solution for this problem is the application of low-hydration heat cement,which can help a lot in crack control and durability.Compared with ordinary Portland cement,the main advantages of low-heat Portland cement(PLH)include lower heat release at the early age and better strength development at later age,which may lead to a wide application of PLH in marine structures.The material property and hardening performance of PLH system were studied in this paper.Influences of fly ash and slag on workability,mechanical properties,durability and shrinkage of PLH concrete were characterized.The preparation technology of high performance marine concrete with the application of PLH was obtained.Finally,the cracking risk of structure made with PLH was modeled and evaluated.Main contents and results of this work are concluded as follows.Influences of fly ash and slag on rheology,hydration heat,strength and hardening process of PLH system were researched.The results show that the low-heat Portland cement slurry belongs to B-H fluid.With the increase of shear rate,the cement paste exhibited shear thinning characteristics.The application of fly ash and slag didn't change the rheology model of the paste,but increased the plastic viscosity and decreased the yield stress.The PLH has a later heat release peak than ordinary PO.Fly ash and slag can reduce the hydration heat during the whole period.The effect of fly ash is more significant.The workability,mechanical properties,durability and volume stability of PLH concrete were studied.The influences of slag and fly ash on the properties were also studied.It shows that PLH concrete has satisfied workability and encapsulation.Compared with PO,the early strength(7d)of PLH concrete is low.However,the strength of PLH concrete increased significantly at the later age.At the age of 56 d and 90 d,the compressive strength of PLH concrete are 103.7% and 116.4% of the PO respectively.The early age strength of PLH concrete with fly ash or slag is low.However the strength increased obviously at the later age.When 10%fly ash+20%slag powder are compounded,the work performance and strength of the concrete are improved.The chloride diffusion coefficient PLH concrete is higher than PO at early age,but it is much lower at late age.The use of fly ash and slag improved the chloride resistance and volume stability of PLH concrete obviously.When fly ash and slag were incorporated doubly,the pore structure of PLH concrete was refined significantly.The PLH concrete was applied in the construction of a marine lock project.The temperature revolution and crack risk of the concrete structure were simulated and monitored.The results show that the simulated and monitored center temperature of the structure built with PLH concrete are 44.8? and 42.0? respectively,while they are 54.2? and 55.2? for structure built with PO.Compared to the PO structure,the center to surface temperature difference is about 9~13? lower for the PLH structure.The crack risk safety coefficient k of PLH structure is much higher than PO structure at the all ages.The actual application results reveal that the crack resistance of PLH concrete is satisfied.The use of PLH in mass marine concrete projects is expected.