The Mechanical Properties And Transport Properties Under Loading Of Alkali-activated Slag Concrete

Alkali-activated slag?AAS?material is an ideal alternative to ordinary Portland cement,due to its high strength,excellent durability and fire resistance and environmental friendliness.There is still a long way to go for this material to be popularized in engineering application,and related researches need to be further improved,especially for the study of the performance under load.In practical engineering,concrete structures always work under loads,therefore,it is meaningful to investigate mechanical properties and transport resistance under load of AAS concretes.It is also essential for predicting its service life.This thesis studies the effect of short-term compressive loading or long-term flexural loading on mechanical properties,capillary sorptiviy and chloride diffusivity,and the influence of mix proportion,activator types,activator alkalinity,modulus of water glass and whether fly ash is blended,is also took into account.Meanwhile,morphology and pore structure are investigated by scanning electron microscope?SEM?,mercury intrusion?MIP?and Brunauer-Emmett-Teller?BET?.The important conclusions are summarized in the following:1.Activator type,content of Na₂O and SiO₂,fly ash/slag ratio influence the mechanical properties of AASC.Among these influenced factors,the variation of activator types,altering from NaOH to water glass,have the greatest impact on mechanical strength.2.Fracture area can reflect the amount of micro cracks induced directly,but if it is applied to different concrete types,it does not work well,because compaction cannot be taken into account in this method.The volumetric change makes up for the disadvantages of the previous method,and also evaluate the loading damage through the extent of volumetric expansion.By contrast,the method of elastic modulus is able to capture the cracks sensitively,especially under low stress level.Through damaged characterization,the results show that loading damage of concrete corresponds closely to stress levels.Critical stress exhibits at around 0.85.Besides,the increase of activator alkalinity benefits to resistance to loading damage.3.There is obvious compaction phenomenon in water glass-activated specimens under axial compressive load,which does not happen in NaOH-ones.It is related to the shrinkage cracking of different activator-type of concretes.4.The enhancement of alkalinity of activator is beneficial to improve resistance to transportation.For water glass-specimens,the resistances to chloride diffusion,capillary water absorption and water adsorption are lower than that of NaOH-ones,which is contrast to the results of strength and porosity.Actually,the comparison of porosity between them cannot correspond to their comparison of transport resistance,due to the majority of pores falling in extremely small diameter,below 100nm,which has little effect on transport.Besides,shrinkage cracking in water glass-specimens is severe,which decreases resistance to transportation.5.The internal load damages the concrete and increases transport rate.Chloride diffusion rate of water glass-specimens decreases because of compaction by load when the stress level is low.But this phenomenon isn`t observed in the test of capillary sorptivity.It is due to that some new cracks are induced even by 0.35 stress level and capillary sorptivity is more sensitive to cracking than chloride diffusivity.6.For water glass-specimens,the resistance to flexural loading is stronger than NaOH-ones,while substitution of fly ash decreases this performance.The increase in load level accelerates chloride transport and its influence increases with the increase of exposed time.