Study On The Preparation And Chemical Corrosion Performance Of Alkali-activated Slag Grouting Material

Ordinary Portland Cement grouting materials were widely used in infrastructure fields including bridge pile foundation,subgrade for roadways and tunnel surrounding rocks.Along with the implementation of Western Development and the construction of new west land-sea passages,the highways,railway bridges,roadbeds,tunnels and other underground projects will pass through saline-alkali land and karst areas inevitably.As the hydration products of traditional cement grouting materials,hydrated calcium silicate（C-S-H）and calcium hydroxide（CH）could react with carbonate ions and sulfate ions,followed by the decrease of strength and structure crackings.Alkali-activated slag grouting material（AASGM）has three-dimensional network zeolite structure,which composed of silicon-oxygen tetrahedrons,and aluminum-oxygen tetrahedrons,It is a ideal grouting material for the reinforcement of infrastructure in special rocky soil areas due to its advantages of environmental friendly,fast hardening,early strength,and acid/salt corrosion resistan.At present,the chemical corrosion of AASGM was seldom being reported.In this paper,cement grouting materials were used as the experimental control group,slag and water glass were adopted as the main raw materials to prepare AASGM.After the sample was demolding,AASGM were directly immersed into sulfate or carbonate solution,the alkalinity of Na₂O%（4%,5%,6%）,erosion ages,different concentrations of sodium sulfate and sodium carbonate were systematically studied on the ersion effect.The mechanical properties,hydration products and microstructure changes of AASGM after immersing in sodium sulfate and sodium carbonate solutions with different erosion ages were determined and analyzed.The main conclusions are as follows:（1）After 360 d of immersion in sodium sulfate solutions,AASGM samples maitained a complet structure,the mass of the samples increased the most after immersing in 4 wt%Na₂SO₄ solution,the maximum increase was 1.8%.The expansion rate of the samples reduced with the increase of alkalinity.The flexural strength of the samples immersed in the sodium sulfate solution increased firstly and then decreased,and the compressive strength decreased slightly with the increase of immersion time.The benchmark cement samples also had a complete apperance after immersing in sodium sulfate solution,but cracks found inside.The change of mass and expansion of were larger than the AASGM,and the compressive strength decreased significantly with the maximum drop of more than 25%.（2）After immersing in sodium sulfate solutions,ettringite,gypsum and other products which are responsible for the cracks were found in the cement,but were not observed in AASGM samples.The pore size center changes of AASGM were changed from 10 nm to 3 nm.On the other hand,the pores around 2nm were full filled in,the standard cement sample,but the pores size around 10 nm were unchanged.（3）AASGM samples were soaked in sodium carbonate solution,calcium carbonate formed on the surface.The mass was greatly affected by the alkalinity increases,the smaller the change in mass and expansion.Both the flexural and compressive strength increased after soaked in sodium carbonate solution,with the maximum flexural strength and compressive is 8.5 MPa,and 100 MPa respectively.The expansion and mass changes of the cement samples in sodium carbonate solution were greater than that of the AASGM,and the compressive strength was lower than AASGM.（4）Calcium carbonate was generated on the surface layer of AASGM in the sodium carbonate solution,while calcium carbonate was found in each layer of the cement samples.After immersing in sodium solution,the center of the pore in AASGM changed from 9-10 nm to about 3-4 nm,and the pore size became smaller.In cement system,the pores with a pore size center of about 2 nm were filled,while the pores with a pore size center of about 10 nm were essentially unchanged.