On Special Ready-mixed Mortar Based Sulphoaluminate Cement

Sulphoaluminate cement mortar (SACM) has the characteristics of high early-agestrength, high strength, high corrosion resistivity, low alkalinity and slight expansion. It canbe widely used in fields like salt-alkali region, cold area, marine projects, and fast repairingwork. However, the difficulty in the control of the setting, the contradiction of the setting timefor placing and a high early-age strength, especially the one-hour strength, the incapability ofthe mortar with modifying agents, etc. have blocked its application. Meanwhile, it can benoticed that the ready-mixed mortar has become the development direction of mortar due tothe easy control of the product quality and its eco-friendly features. However, no report on theready-mixed SACM has been documented thus far, and it is the goal of this work to develop aspecial type of ready-mixed SACM with stable quality and high corrosion resistivity.After studying the effects of the retarding agent BR and early-strengthening agent LA onthe setting time and strength development of sulphoaluminate cement, modification study onSACM was carried out by using starch ether, HPMC, composites, starch and bentonite clay.And then the anti-corrosion properties of SACM and ready-mixed SACM were analyzed. Themajor conclusions can be drawn as follows:(1) The initial setting time of sulphoaluminate cement can be effectively regulated by thecomposite retarding agent of BR and LA, which greatly shortens the time gap between initialand final setting and improves the strength, as well as eliminates the reduction of strength atlater ages. It also showed that the dosage of LA should not be greater than0.1%. XRD andhydration heat results indicated that the hydration of sulphoaluminate cement has beenchanged by the set-regulating agents.(2) Modifying agents like HPMC has great effect on the workability of SACM. Itshowed that the2h-slump loss of the mortar can be remarkably reduced and a significantimprovement of the permeability can be seen. When comparing with the HPMC of highviscosity, the one with low viscosity can better improve the properties of the mortar. And anoptimal dosage of HPMC with a viscosity of100thousand of0.1%was determined.(3) Orthogonal design was preformed to study the effect of HPMC, starch ether、re-dispersible polymer powder and bentonite clay on the workability of mortars through investigation of the range and regression analysis. Results showed that water reducing agentof polycarboxylic type has a better compatibility with modified mortar to naphthalene type,while re-dispersible polymer powder and bentonite clay have bad compatibility with waterreducing agents. The properties of A2B2C1D1modified mortar can be significantly improvedby polycarboxylic plasticizer and its saturation dosage is0.15%with a water-reducing agentof12.9%.(4) The anti-corrosion property of SACM was evaluated by the strength developmentand Ca2+dissolution in the solutions of MgSO4, MgCl2, Na2SO4and NaCl. It revealed that theflexure strength of most SACM can be improved to some extent, while the compressivestrength can be lowered and the compressive strength decreases with the concentration of thesolution increasing. The anti-corrosion coefficients of flexure and compressive strength arebetween0.92~1.51and0.81~1.06, respectively. Studies on the dissolution of Ca2+ion ofSACM suggested that in a certain solution, the severity degree of corrosion under differentconcentrations follows the order of10.0%＜3.0%＜0.3%＜0%, while for a certainconcentration of the solution, the corrosion degree under different solution types follows theorder of H2O＞MgSO4＞MgCl2＞Na2SO4＞NaCl. A Ca2+ion concentration of mortar of28dold lies in0.02~0.08mg/ml. More AFt crystallines are formed in SACM samples cured incorrosion solutions.(5) The flexure and compressive strength of ready-mixed SACMs cured in corrosionsolution can be increased to some extent. The anti-corrosion coefficients of flexure andcompressive strength are between0.90~1.66and0.87~1.21, respectively. The Ca2+ionconcentration in each corrosion solution is lower than that of purified water and the rate of thedissolution of Ca2+becomes smaller with age. Studies on the dissolution of Ca2+ion ofready-mixed SACM revealed that in a certain solution, the severity degree of corrosion underdifferent concentrations follows the order of10.0%＜3.0%＜0.3%＜0%, while for a certainconcentration of the solution, the corrosion degree under different solution types follows theorder of H2O＞MgSO4＞MgCl2＞NaCl＞Na2SO4. XRD results also suggested that more AFtis formed in ready-mixed SACM samples that have been corroded.Through the study of this work, an SACM with a controllable setting, a good workabilityand a high anti-corrosion performance that can be applied in situ was prepared, and it is hoped that this work can thrive the application of ready-mixed SACM in special engineeringprojects.