Composition Design And Basic Properties Of Alkali-activated Underwater Non-dispersible Concrete

With the extensive development of marine resources,there are more and more marine buildings,which leads to higher and higher requirements for the underwater pouring of concrete.Therefore,the study of underwater non-dispersible concrete?NDC?is important particularly.However,the current cement-based NDC generally has some problems,for example,low mechanical strength,poor compatibility between cement and anti-dispersant,rapid loss of fluidity over time and long setting time and so on,which greatly restricts application of NDC in underwater engineering.Therefore,finding a new cementing material to solve many problems encountered in NDC at this stage is of great significance to the promotion and application of NDC in engineering.This article intends to use alkali-activated slag cementing materials which instead of cement-based materials to prepare NDC.It has done exploratory and innovative work in the following aspects:?1?Study on the adjustment and control of the coagulation of the fresh alkali-activated cementitious materialsBy changing the stimulus modulus,Na₂O content and anti-dispersant dosage,the onshore initial settling time,onshore final settling time,underwater initial settling time and underwater final settling time of the alkali-activated paste were measured.The influence of the several factors on the setting time of alkali-activated paste was analyzed.Cement-based slurries with the same anti-dispersant content were formed on land and under water as control groups and the effect of anti-dispersant on the setting time of two materials was compared and analyzedThe results show that the order of the influence of various factors on the different coagulation time of the alkali-activated slurry is as follows:activator modulus>anti-dispersant content>Na₂O content.?2?Study on the workability of alkali-activated cementitious materialsThrough the changes of the fluidity of the slurry and the spread of the concrete slump,the effect of the amount of anti-dispersant on the workability of the alkali-activated cementitious material was studied.At the same time,the cement-based paste with the same content of anti-dispersant was formed as control group and the similarities and differences of the influence of the anti-dispersant on the workability of the two materials were compared and analyzed.The research results show that with the increase of the anti-dispersant content,the fluidity of cement-based materials decreases greatly,while the fluidity of alkali-activated slurry decreases less.And a new type of NDC vibration pouring device was designed.?3?Study on Anti-dispersion of fresh alkali-activated cementitious materialsThe effects of the amount of anti-dispersant on the dispersion resistance of alkali-activated cementitious materials were studied by the changes of plastic viscosity and yield stress of the paste and the change of the suspension of the water sample after the concrete was poured into water.Cement-based concrete with the same amount of anti-dispersant was formed and the effect of anti-dispersant on the dispersion resistance of the two materials was compared and analyzed.Furthermore,rheological indexes of the base-excited base slurry under different anti-dispersant dosages were measured,the change of the interaction force and the agglomeration state of the particles within the slurry through the changes of plastic viscosity and yield stress was studied.The research results show that the dispersion resistance of alkali-activated concrete is significantly better than that of cement-based concrete under the same amount of anti-dispersant.When the content of anti-dispersant is 1%,the alkali-activated concrete can obtain good anti-dispersion.?4?Study on mechanical properties of alkali-activated NDC3d,7d and 28d compressive strength of the alkali-activated concrete with different anti-dispersant content,molding method,Na₂O content and water-binder ratio were measured and the influence of these factors on the mechanical properties of alkali-activated concrete was analyzed.At the same time,cement-based concrete with the same amount of anti-dispersant formed was formed and the effect of anti-dispersant on the mechanical properties of the two materials was compared and analyzed.The results of the study show that the strength grades of cement-based NDC under all anti-dispersant dosages in this paper have not reached C30,while the strength grades of alkali-activated NDC have reached C40,and the mechanical strength of alkali-activated NDC is much higher than that of cement-based NDC.The test method of underwater concrete pouring designed in this experiment greatly reduces the adverse effect of the underwater pouring method on the mechanical strength of concrete.The optimal Na₂O content of the alkali-activated underwater non-dispersible concrete is 8%,and the optimal water-binder ratio is between 0.45-0.475.?5?Study on reaction mechanismThe influence of the change of anti-dispersant content on the hydration process of the alkali-activated slurry was studied with the help of heat of hydration.The effects of anti-dispersant content and different molding methods on the microstructure and macroscopic defects of alkali-activated slurry were studied with the help of video microscope and scanning electron microscope.Finally,the inherent mechanism of the alkali-induced gelling material's setting time,working performance,anti-dispersion and mechanical strength changes was analyzed.The mechanism of action of the anti-dispersant on the two materials was compared and analyzed.The research results show that the action mechanism of the anti-dispersant is different between cement-based materials and alkali-activated materials.In the cement slurry,polyacrylamide adsorbs a large amount of cement particles.And the molecular chain forms a bridge between the cement particles,which connects the cement particles together to form a stable network structure.The network structure wrapped on the surface of the cement delays the hydration process of the cement and plays a similar effect as a retarder.Polyacrylamide absorbs a part of the unhydrolyzed water glass micelle in the alkali-activated material,which increases the viscosity of the concrete mixture,stabilizing the dispersed gelation system,instead of forming flocs to wrap the slag.So it has little effect on the hydration process.The paper has 37 pictures,35 tables,and 77 references.