Influence Mechanism Of Lithium Compounds On Hydration Process Of Sulphoaluminate Cement Based Material

Sulfoaluminate cement-based grouting materials have been used in many in engineering,and their main components include C₄A₃（?）,CaSO4 and CaO.In order to ontain the high working performance,a high water to binder ratio is adopted which makes the early hydration of sulphoaluminate cement slow.Lithium admixtures such as lithium carbonate are often used to promote hydration,but the total amount of heat release from hydration increases at low content of lithium carbonate,while the total amount of heat release from hydration decreases with high content of lithium carbonate.In our previous research work,it was found that nano-lithium aluminum hydrotalcite can improve the hydration heat release rate and the total hydration heat release of sulphoaluminate cement-based grouting material.The influence mechanism of two lithium compounds（Li₂CO₃and LiAl-LDH）on the hydration process of sulphoaluminate cement is still not clear.Hydration heat,thermogravimetric analysis（TG）,XRD and ICP techniques were used to characterize the composition changes of solid and liquid phases during hydration.The influence mechanism of Li₂CO₃and LiAl-LDH hydrotalcite on cement hydration was proposed.The synthesized LiAl-LDH was packed into semi-permeable membranes by isolation hydration method and placed into the suspension of C₄A₃（?）-CaSO₄-CaO system.The nucleation effect of LiAl-LDH was studied by measuring the solid mass and composition of the semi-permeable membranes.The concentration of lithium ion or carbonate in slurry solution was measured or calculated,and their influence on solid phase composition of sulphoaluminate cement-based materials was studied.The specific conclusions are as follows:（1）Both Li⁺and CO₃^2-in lithium carbonate can affect the hydration process of sulphoaluminate cement-based materials.In C₄A₃（?）-CaSO₄-CaO system,the content of lithium carbonate is 0.1 mol/L,when there is C₄A₃（?） in the system,Li⁺mainly consumes Al³⁺and OH^-to form lithium aluminum amorphous compounds.Therefore,Li⁺can promote the dissolution of C₄A₃（?） and increase the production of hydration products.In addition,CO₃^2-can consume Ca²⁺to form calcium carbonate,the decrease of Ca²⁺leads to the dissolution of calci-containing compounds,thus promoting the dissolution of C₄A₃（?）.When the hydration of C₄A₃（?） is fully hydrated and Li⁺is left in the solution,Li⁺continues to consume the Al³⁺,causing ettringite to decompose.On the other hand,the presence of CO₃^2-consumes Ca²⁺in the solution and causes AFt to decompose.（2）The hydration of sulphoaluminate cement-based materials is influenced by the synergistic effect of crystal nucleus,released lithium ion and carbonate.LiAl-LDH can selectively provide nucleation sites for hydration products.In the C₄A₃（?）-CaSO₄-CaO system,LiAl-LDH provides AFt nucleation sites.In the C₄A₃（?） single ore solution,the LiAl-LDH provides the nucleation site for AFm.Small amounts of Li⁺and CO₃^2-are released from the precipitation and dissolution equilibrium of LiAl-LDH,and small amounts of Li⁺and CO₃^2-promote the hydration of C₄A₃（?） in the early stage of hydration.The influence mechanism of Li₂CO₃and LiAl-LDH on hydration process of sulfoaluminate cement-based grouting materials material was elucidated,which laid a theoretical foundation for developing new type of sulphoaluminate cement material admixture.