Study On Hydration Temperature Rise Inhibition Technology For Cast-in-situ Concrete Of Railway Engineering

The cast-in-situ concrete of railway engineering has the characteristics of complex section structure,mutual restraint among different structures,high hydration and heat release of medium and high strength concrete.High hydration temperature rise concrete is liable to crack under restraint.Cracking of cast-in-situ concrete structure in railway engineering not only affects the mechanical properties and durability of concrete,but also causes the insulation of track circuit and other problems in ballastless track concrete of high-speed railway.There is an urgent need to study the hydration temperature rise inhibitor for the cracking of cast-in-situ concrete of railway engineering.In this paper,three types of hydration temperature rise inhibitors are selected based on different mechanisms of action,aiming at reducing concrete hydration temperature rise,to add as hydration temperature rise inhibitors into the concrete.The hydration inhibition mechanism of hydration temperature rise inhibitors and the thermodynamic properties,workability,mechanical properties,durability and shrinkage properties of cement-based materials with hydration temperature rise inhibitors are studied.The main conclusions are drawn as follows:(1)Hydration temperature rise inhibitors can significantly reduce the heat release rate of cement hydration,with a reduction of 29.7%~77.6%,delay the peak time of the heat release rate of cement hydration,with a delay of 3.2h~16.4h,and a decrease of 24.6%~62.2% in the cumulative released heat of cement hydration for 72 hours.Protein hydration temperature rise inhibitors form a stable solvated water film on the surface of cement particles by association of hydroxyl group and water molecule,which delays the hydration reaction of cement.Ammonia hydration temperature rise inhibitors absorb heat released by cement hydration through endothermic reaction and inhibit cement hydration.(2)The hydration degree of cement decreased slightly by temperature rise inhibitor,with the highest decrease of 3.1% for 7d and 2.8% for 28 d.From the rate curve of cement hydration exothermic rate and the phase and morphology analysis of hydration products,it can be seen that the hydration temperature rise inhibitor will not change the process of cement hydration exothermic,and will no effect on the type and morphology of hydration products.Ammonia hydration temperature rise inhibitors can increase the content of calcium carbonate in hydration products,because the carbonate produced by the reaction of ammonia hydration temperature rise inhibitors with water will react with calcium hydroxide of cement hydration products to produce calcium carbonate.(3)Hydration temperature rise inhibitors all have a certain water reducing effect.The standard consistency of cement paste with hydration temperature rise inhibitor can be reduced by 1.5%~37.3%.The ammonia hydration temperature rise inhibitor has the most obvious water reducing effect,which can reduce the water consumption of the standard consistency of the cement paste by 37.3%.And the hydration temperature rise inhibitor can delay the setting time of the cement paste.The initial setting time of cement paste mixed with hydration temperature rise inhibitor can be delayed by 33 minutes to 267 minutes,and the final setting time can be delayed by 48 minutes to 238 minutes.Compound and protein hydration temperature rise inhibitors have similar and relatively large delaying effect on setting time of cement paste,while ammonia hydration temperature rise inhibitors have the least effect on setting time.Hydration temperature rise inhibitors can increase the plastic viscosity of cement paste,because adding hydration temperature rise inhibitors in cement paste will increase the medium viscosity of paste.(4)Hydration temperature rise inhibitors can reduce the early(3d,7d)flexural strength and compressive strength of cement mortar in varying degrees.By the age of 28 days,the compressive strength and flexural strength of mortar mixed with 5%~10% ammonia hydration temperature rise inhibitor can reach the 90% of the flexural strength of the reference group.Ammonia hydration temperature rise inhibitors have the least influence on the compressive strength and flexural strength of mortar at all ages.Considering the influence of hydration temperature rise inhibitors on hydration heat release and mortar strength,the recommended dosages of compound,protein and ammonia hydration temperature rise inhibitors are 0.8%~1.0%,0.05%~0.10% and 5%~10%,respectively.(5)Hydration temperature rise inhibitor can significantly reduce the adiabatic temperature rise of concrete,the decrease range is 3.02? to 15.75 ?.And the dry shrinkage of concrete with hydration temperature rise inhibitor at all ages is smaller than that of the reference group.Hydration temperature rise inhibitor can improve the workability of concrete,which can increase the slump of concrete by 5.3%,but will not effect on the air content of concrete.Hydration temperature rise inhibitor can improve the frost resistance and chloride ion penetration resistance of concrete.The chloride ion migration coefficient of base group concrete can be increased from grade RCM-I to grade RCM-V,and the frost resistance level can be increased from F450 to above F500.However,the hydration temperature rise inhibitor will delay the setting time of concrete and reduce the early compressive strength of concrete.The appropriate amount of hydration temperature rise inhibitor and the demoulding time of concrete should be selected in practical application.