The Influence Mechanisms Of Strongly/Weakly Alkaline Activators On The Microstructure And Property Of Supersulfated Cement Concrete

The implementation of the carbon peaking and carbon neutrality goals put new requirements on the carbon emissions of the cement industry,and improving the utilization rate of solid waste has become an emphasis for the present cement research.Supersulfated cement,generally shortened to SSC,is a low-carbon cementitious material,that is composed of a thimbleful of cement clinkers and massive industry by-products,e.g.: gypsum and slag.However,the SSC concrete has low strength,weak carbonation resistance and poor frost resistance.In this thesis,the influences of strongly/weakly alkaline activators on the mechanical properties and durability of SSC concrete were systematically researched.Further,the mechanisms of lactate and lactic acid on the hydration behavior and microstructure of SSC were revealed.The main conclusions are as follows:(1)The weakly alkaline activator(lactate)can significantly improve the compressive/flexile strengths of SSC concrete and reduce the carbonation depth,it is also conducive to the improvement of frost resistance.However,as sodium hydroxide was added,the compressive strength of concrete increased slightly in the early stage but decreased in the later stage.Meanwhile,sodium hydroxide showed no improvement effect on durability.(2)The hydration process of SSC could be finely controlled through lactates for two opposite mechanisms.At the early stage,the presence of lactates decreases the release of hydration heat and delays the hydration of SSC,which is beneficial to maintaining workability.In the long term,lactates stably adsorb on the slag surface and strongly attract Ca ions,gradually weakening the structural integrity of geopolymer components in the slag matrix.As a result,the dissolution of slag is accelerated,and thus more hydration products and higher mechanical properties are obtained for SSC.(3)Lactic acid significantly improved the fluidity and setting time of SSC.In addition,lactic acid exerted a double-sided tuning effect on the hydration process of SSC.At the early stage,the hydration heat release decreased and fewer hydration products were generated,which led to a lower mortar strength.However,a greater number of hydration products formed after long-term curing that included a compact microstructure with less porosity,which contributed to the strength.In this thesis,methods for improving the mechanical and durability of SSC concrete were put forward,which will establish some technical bases for the application of low carbon cementitious material;Meanwhile,the double-sided tuning effect of lactate and lactic acid on the hydration process of SSC was revealed,which provide a theoretical basis for the efficient utilization of activators in SSCs.