Effect Of Melamine-based Superplasticizer And Naphthalene-based Superplasticizer On The Workability Of Alkali-Activated Fly Ash Cementitious Materials

With the increasing emphasis on environmental protection in recent years,the development of alkali-activated fly ash cementing materials can not only reduce the amount of cement and fill the gap in the cement industry after eliminating outdated production capacity,but also effectively expand the use of fly ash resources in China and provide new possibilities for solving fly ash disposal problems.The performance of alkali-activated fly ash cementitious materials is inferior to Portland cement,which is one of the main obstacles restricting its popularization and application.This paper draws on the important work performance improvement methods in cement concrete,studies the role of various water-reducing agents in alkali-activated fly ash cementitious materials,obtains the most effective water-reducing agent varieties and optimizes their mixing ratio,and studies their The effect of alkali excitation on the compressive strength of the fly ash cementitious material test block.The micro-testing methods such as rheological test,zeta potential test and infrared spectroscopy are used to analyze the action mechanism of water-reducing agent in the alkali-excited fly ash paste and the compositional changes with time,temperature and other factors to provide support for the macro test data.The comparison test results of various water-reducing agents show that melamine-based water-reducing agents and naphthalene-based water-reducing agents have the most significant effect on the performance of alkali-activated fly ash cementitious materials.Melamine-based water-reducing agent can significantly improve the initial fluidity of alkali-activated fly ash paste,but the fluidity loss is large over time,and naphthalene-based water-reducing agent significantly reduces the fluidity of alkali-activated fly ash paste.During the test,it was found that the effect of the melamine-based water-reducing agent in the alkali-excited fly ash paste has obvious temperature-sensitive characteristics.This paper further studies the effect of melamine water reducer on the initial fluidity and time loss of alkali-activated fly ash paste at an ambient temperature of 10 ?-40 ?.It is found that the effect of melamine water reducer on improving fluidity varies with as the temperature rises,it weakens.When the ambient temperature is 10 ?,the melamine water-reducing agent can increase the initial fluidity of the alkali-activated fly ash paste and maintain it for a certain period of time.After the alkali-activated fly ash is mixed with water for 60 minutes,it can still maintain a fluidity of 142 mm.As the ambient temperature rises,the viscosity reduction effect of the melamine-based water-reducing agent on the alkali-excited fly ash paste is gradually lost.At higher temperatures,the yield stress of the alkali-excited fly ash paste increases significantly with time,resulting in alkali-activated pulverized coal the loss of ash fluidity increases rapidly with time.According to the infrared spectroscopy test results,the naphthalene-based water-reducing agent produced hydrate after 1h in the alkaline solution,and its molecular structure itself did not change significantly;after the melamine-based water-reducing agent was present in the alkaline solution for 1h,there was free The hydroxyl group means that the molecular structure of the melamine water-reducing agent has changed and the hydroxyl group has been removed,which may be the reason for its weakening effect.At higher temperatures,it can synergistically use the melamine-based water-reducing agent to increase the initial fluidity and the naphthalene-based water-reducing agent to reduce the fluidity loss over time,to improve the performance of alkali-activated fly ash paste.When the ambient temperature is 30 ?,the sodium hydroxide content is 15 wt.%,And the water-cement ratio is 0.24,the two water-reducing agents are compounded in the proportion of melamine-based water-reducing agent 0.75 wt.% And naphthalene-based water-reducing agent 0.25 wt.%.When mixed,the initial fluidity of the alkali-activated fly ash paste is the largest at145 mm,and also has the smallest fluidity loss over time.After mixing with water for 60 minutes,it still maintains a fluidity of 130 mm.The combination of melamine-based water-reducing agent and naphthalene-based water-reducing agent can maximize the improvement and maintenance of the workability of water-reducing agent on alkali-activated fly ash paste.When the ambient temperature is 10 ?,the effect of the two water reducing agents mixed in the above proportion is still the best.Compared with the single blending of two water reducers with the same dosage,the optimal compounding ratio has a smaller viscosity and yield stress,and the absolute value of zeta potential is higher,indicating that its viscosity reduction effect is better.The particle surface has better adsorption effect.The melamine-based water-reducing agent and naphthalene-based water-reducing agent with an amount not exceeding 2 wt.%Have almost no adverse effect on the compressive strength of the alkali-excited fly ash.The XRD test found that the two water reducers used alone or in combination had no effect on the hydration products of alkali-activated fly ash paste.