Effect Of Light Burned Magnesia On The Physical Mechanics Performance And Shrinkage Properties Of Alkali-activated Slag Cement

Compared with ordinary Portland cement,Alkali-activited slag cement(AAS)made with alkali activated granulated blast furnace slag(GGBS)has good mechanical properties and durability,and is a low-carbon、energy-saving and environmentally friendly building material.However,the cracking caused by large shrinkage and deformation of AAS hinders its development.Therefore,correct understanding of the main causes of the cracking of AAS and reducing the shrinkage of AAS are problems that need to be solved urgently in the future development and application of AAS.Light-burned MgO was mixed into AAS to study the influence of light-burned MgO on the physical and mechanical properties and shrinkage behavior of AAS.Discussed the content of light-burned MgO,the activity of light-burned MgO,the modulus of water glass,and the ratio of water-binder to the effect of light-burned MgO-alkali slag(AASM)physical and mechanical properties,drying shrinkage and chemical shrinkage.XRD and SEM were used to analyze the influence of the content of light burned magnesium oxide on the hydration products and microstructure of AASM,as the same time,the hydration mechanism of AASM gel system was discussed.the setting time of AASM pastes increases with the decrease of water glass modulus,the increase of water-binder ratio and the decrease of light-burned MgO.When other parameters are fixed,the setting time of AASM is the shortest,when the content of light burned magnesium oxide is 20%,and the setting time is the longest when the content of light burned magnesium oxide is 30%.The fluidity of AASM decreases with the increase of the content of light burned magnesium oxide,the decrease of water glass modulus,the decrease of water-binder ratio,and the increase of light burned magnesium oxide activity.The compressive strength of the AASM increases with the increase of the content of light-burned MgO,the decrease of water glass modulus,the decrease of water-binder ratio,and the increase of light-burned MgO activity.When the curing age is 56 days,the water-binder ratio is 0.4,the water glass modulus is 1.0,and the content of high-activity light-burned magnesium oxide is 40%,the compressive strength of the AASM is as high as 90.2MPa,which is as high as the compressive strength of the benchmark group,increased by 30.5MPa.The drying shrinkage of AASM decreases with the decrease of the content of light-burned MgO,the increase of water glass modulus,the decrease of water-binder ratio,and the decrease of light-burned MgO activity.When the curing age is 30 days,the water-binder ratio is 0.4,the water glass modulus is 1.0,and the high-activity light-burned magnesium oxide content is 30%,the chemical shrinkage of the AASM is the smallest,and the shrinkage value is 0.6mm~3/100g,which is the benchmark The group’s chemical shrinkage value of 5mm~3/100g decreased by more than 8 times.When the content of light burned magnesium oxide is 40%,the influence on the mass loss of the AASM is the most significant,and the mass loss rate is 0.17%.The hydration process and hydration products of AASM are affected by the activity and content of light-burned MgO.Within a certain range,when the same curing age,with the increase of the activity and content of light-burned MgO,the higher hydration degree and the more M-S-H and Ht hydration products are produced.light-burned MgO has three functions in AASM:First of all,it accelerates the disintegration and dissolution of slag.Secondly,the OH~-ions formed by hydrolysis make the slag accelerate the early hydration process.Finally,it participates in the hydration reaction to generate M-S-H and Ht.To sum up,the addition of light-burned MgO can reduce the degree of polymerization of calcium silicate hydrate(C-S-H)and increase the Ca/Si ratio of AASM,and generate hydration products such as M-S-H and Ht.These factors are the primary cause to restrain the cracking of AASM.