This paper investigates the causes of excessive long-term deflection of PC bridge viaducts by using 3D integrated material-structural analyses to take into account the coupled chemo-physics at various scales from the molecular size of water to the structural members. The excessive deflection observed at site is found to be rooted in the deformation of cement paste stemming from both externally applied loads and internal stresses driven by capillary surface tension and disjoining pressures in micro-pores. Not only the former but also the later effect is focused in the serviceability control of PC viaducts. It is found that the nonlinear, long-term deflection of the bridge viaduct can be approximately separated into the components of deflections provoked by external mechanistic and internal thermodynamic actions, even though each component is nonlinearly associated with the thermodynamic states of moisture in micro-pores of cement hydrates.
This paper reports the results of laboratory investigations into the time history of the shrinkage of fibre reinforced high-performance concrete with 0.25%, 0.50% and 0.75% by volume of longer IRI 50/30 or shorter IRI 50/16 steel fibres or polypropylene fibres. To allow suitable comparisons, measurements of the shrinkage of a comparable plain concrete were also performed. The results of the measurements of the autogenous shrinkage of the tested composites and of the comparable plain concrete at early and later ages of the specimens are presented. The results of the performed laboratory tests show that the use of steel fibres is more effective for the reduction of early autogenous shrinkage than that of dry polypropylene fibres. For the reduction of later autogenous shrinkage, the polypropylene fibres are almost as effective as the steel fibres. The least drying and total shrinkage of the composites at later ages occur in the case when polypropylene fibres are used.
A comprehensive study is presented on the effects of pulverised fly ash (PFA) and ground granulated blast furnace slag (GGBS) on early-age engineering properties of Portland cement (PC) systems. It has been found that partially replacing PC by PFA or GGBS resulted in longer setting times but better workability with PFA exhibiting more prominent effect than GGBS. As the replacement level increased, the setting of both PFA and GGBS pastes further delayed but workability of concrete was enhanced. PFA concretes exhibited consistently lower compression and splitting tensile strengths than PC ones. As the replacement level increased, strengths decreased. At the replacement level up to 30% by mass, GGBS concrete exhibited higher splitting tensile strength than PC concrete. However, as the replacement level further increased, it developed lower strength than PC concrete up to 21 days. Then, it managed to gain higher splitting tensile strength than PC concrete at the replacement levels up to 70% by mass at 28 days. Both PFA and GGBS can reduce drying shrinkage and the reduction effects became more significant as replacement level increased with GGBS performing better than PFA. Adding fibres into PFA concrete increased its splitting tensile strength and further reduced its drying shrinkage.
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