Durability Study On Rapid Repairing Magnesium Phosphate Cement-based Composite Material For Cement Concrete Pavement

As a new type of inorganic cementing material characterized with rapid setting and high strength growth,magnesium phosphate cement(MPC)provides an alternative for engineers to rapidly repair distresses of cement concrete pavement.Based on magnesium phosphate cement formula(mole ratio of borax and phosphate to magnesium are 0.05 and 0.25,respectively),an optimized mix proportion of magnesium phosphate cement was obtained and its performance was evaluated in the scales of paste and mortar.Guiding by the technical specification for construction of cement concrete pavement(JTG F30-2003),the mix proportion of MPC concrete was conducted and the durability of both MPC mortar and concrete were then evaluated.Additionally,combining with the scientific project of manufacturing,education&Research in Gruangdong province,i.e.,Research and products of multiple functionable rapid repairing material for cement concrete pavement,this dissertation mainly includes the following aspects:1.Fly ash,gypsum,ordinary portland cement and sodium polyphosphate were blended to improve the performance of MPC.Based on the experimental results of setting time and strengths,their influences on reference MPC paste were analysed and the optimum dosage of fly ash,gypsum,ordinary portland cement and sodium polyphosphate was 10%,10%,5%and 0.3%,respectively.2.The durability of the reference and optimized MPC mortar was comprehensively evaluated,i.e.,freeze-thawing resistance,water damage resistance and chemical agent resistance.The results indicated that the optimized MPC mortar was superior to the reference one,indicated particularly by less 30%reduction of flexural strength loss after soaking in water for 7 days.In addition,the MPC mortar made from potassium dihydrogen phosphate demonstrated better durability than that from ammonium dihydrogen phosphate.3.The mix proportion of MPC concrete was carried out.The optimum gradation type was determined.The results also showed that the MPC had the highest strength when the compacted density of aggregate was the highest.Moreover,the influence of the mechanical performance of aggregate on compressive strength of MPC concrete was analysed.The results indicated that granite was superior to limestone in terms of compressive strength of MPC concrete.4.The workability test of MPC concrete was carried out and the results indicated it favorable for construction.Based on the environmental simulation,various types and dosages of water-proof agents were added to improve water resistance of MPC concrete and the results indicated that both silica sol and HEA water-proof agent could positively influence the water resistance of MPC concrete.The shrinkage test results showed that MPC concrete made of granite had lower shrinkage than that of limestone.5.The penetration resistance and chemical attack resistance of MPC(sulfate attack and chloride attack)concrete were evaluated.Atomic absorption spectrophotometer and mercury injection apparatus were used to explore the degradation mechanism of the MPC concrete performance.6.The MPC paste,mortar and concrete were used to repair the distresses of cement concrete pavement of S267 in Guangdong province.The field performance indicated the MPC material was favorable both for construction operations and durability.