2D,3D chloride ion concentration at the edge and corner zones were systematically investigated for fly ash concretes made with different cement replacement percentage by fly ash (0%,10%,20%,40%,60%),water to binder ratios (0.3,0.35,0.4),and curing ages (28 d,90 d).An interaction effect caused by 2D and 3D diffusion could obviously be observed through the comparison with 1D testing results.In order to quantify the interaction effect,2D and 3D diffusion interaction coefficients was proposed in this paper.Finally,the changes of 2D and 3D interaction coefficients with the change in the free chloride ion concentration were given.The above research provide an insight into chloride ion attack on the edge and corner reinforcing bars of concrete structures in the field of civil engineering.
The applicability of ultrasonic pulse velocity(UPV) method to in-situ monitor setting and hardening process of foamed concrete(FC) was systematically investigated. The UPVs of various FC pastes were automatically and continuously measured by a specially designed ultrasonic monitoring apparatus(UMA). Ultrasonic tests were performed on FC mixtures with different density(300, 500, 800 and 1 000 kg/m3), and different fly ash contents(0%, 20%, 40% and 60%). The influence of curing temperatures(20, 40, 60 and 80°C) was also studied. The experimental results show that three characteristic stages can be clearly identified during the setting process of an arbitrary FC paste: dormant stage, acceleration stage, and deceleration stage. Wet density, fly ash content, and curing temperature have great impact on setting behavior. A stepwise increase of the wet density results in shorter dormant stage and larger final UPV. Hydration reaction rate is obviously promoted with an increase in curing temperature. However, the addition fly ash retards the microstructure formation. To aid in comparing with the ultrasonic results, the consistence spread test and Vicat needle test(VNT) were also conducted. A correlation between ultrasonic and VNT results was also established to evaluate the initial and final setting time of the FC mixtures. Finally, certain ranges of UPV with reasonable widths were suggested for the initial and final setting time, respectively.
Single and multiple dynamic impacts tests were conducted on ultra-high performance cementitious composite (UHPCC) with various volume fractions of steel fibers (0, 1%, 2%, 3%, 4%) by using the split hopkinson pressure bar (SHPB). Besides, the ultrasonic velocity method was used to test the damage on specimens caused by dynamic impacts. For single dynamic impact, the data suggest that UHPCC obviously presents dynamic strength enhancement. With increasing of strain rate, the peak stress and peak strain increase rapidly. For multiple dynamic impacts, the results show that addition of steel fibers can obviously enhance the properties of UHPCC to resist the repeated dynamic impacts. Firstly, the number of impacts sharply increases with the increasing of volume fraction of steel fibers. Secondly, the energy absorption ability linearly increases with addition of steel fibers. Thirdly, the steel fibers can prevent the disruption phenomenon and maintain the integrity of specimen.
