The alkaline activator has a significant effect on the microstructure and mechanical properties of fly ash-based alkali activated products. This paper aims to identify the reaction products of fly ash (FA) activated with alkaline activators of different concentrations of Na2O and different SiO2/Na2O ratios. NaOH solution (NA), a mixture of NaOH and sodium silicate solution (MIX) and sodium silicate solution (LG) were used to activate fly ash.
Different techniques were used to characterize the reaction products of activated fly ash including X-ray diffraction (XRD) with Rietveld refinements, attenuated total reflectance Fourier transformer infrared (ATR-FTIR), 29Si dipolar-decoupling (DD) magnetic angel spinning/nuclear magnetic resonance (29Si MAS/NMR) and 27Al MAS NMR, field emission scanning electron microscopy (FE-SEM) attached with energy-dispersive X-ray (EDX) analyzer. Also, the fly ash-based alkali activated products were indentation tested using a Vickers indenter.
The results revealed that the main reaction product of alkali activation of fly ash is a sodium aluminosilicate gel (geopolymer) with high Si/Al ratio when sodium silicate was used as alkaline activator, while zeolite appeared as minority phase when fly ash was activated with NaOH solution or a mixture of NaOH and sodium silicate solution. Moreover, Na2O content and SiO2/Na2O ratio in the activator solution influence on the amount of amorphous phase and Q4(mAl) units formed in the alkali activated materials and that reflect on the mechanical properties.
An investigation on the scatter of code-type constitutive models that relate compressive strength (fc) with tensile strength (fct) and Young’s modulus (Ec) of standard concrete specimens is presented. The influence of the mix design on the accuracy of the fc vs. fct and fc vs. Ecrelationships is discussed, with emphasis on the lithological type and morphology of the coarse aggregates. The uncertainty of the constitutive models is analysed in probabilistic terms and random variables that model the uncertainty of the fc vs. fct and fc vs. Ec relationships are proposed for reliability analyses of serviceability limit states. The suitability of the models proposed is assessed through preliminary conservative estimates of their design values.
To explore flexural behaviors of ecological high ductility cementitious composites (Eco-HDCC) for bridge deck link slab under severe service conditions, interaction experimental schemes of freeze-thaw cycles and carbonation were designed. Factors such as interaction cycle and preloading stress level were considered. Carbonation front and pore structure of Eco-HDCC were analyzed. The results show that ultimate flexural strength and ultimate deflection of Eco-HDCC decrease when interaction cycle or preloading stress level increases. Besides, all flexural load-deflection curves exhibit four stages: linear elastic, non-linear, deflection hardening and deflection softening stage. In addition, carbonation front of Eco-HDCC increases when interaction cycle or preloading stress level increases. With the same depth range in Eco-HDCC, pore structure deteriorates as interaction cycle increases, and deterioration degree of pores decreases as depth increases. For general consideration, after interaction cycles of 15, flexural property of Eco-HDCC with preloading stress level of 0.5 can be adopted for bridge deck link slab design with the aim to safety.
A building was severely damaged during the 2011 Tohoku Earthquake in spite of having been strengthened before the event and having withstood a comparable event before with only minor damage. An experimental study was conducted to test the hypothesis that damage to the building may have been triggered by cone breakout failure of anchors installed during the strengthening program leading to a strain concentration at the third story. Specimens were tested which represented portions of shear wall boundary columns either before or after the strengthening program. Observed damage in the specimens representing the boundary columns after strengthening was similar to the damage observed in the building after the 2011 Tohoku earthquake. Projections of the test results suggest that the strengthening program may have reduced the drift capacity of the building.