Experimental Study On Properties Deterioration Of Early Frozen Roller Compacted Concrete

Concrete construction in winter often faces the problem of early frost damage.At early age,the internal structure of the concrete has not been fully formed.Early freezing damage will cause damage to the properties of the concrete to a certain extent,and it may not be able to fully recover even after the positive temperature is restored in the later period.For roller compacted concrete(RCC)containing a large amount of fly ash,its early strength growth is slow.If it encounters early frost damage,it will cause more serious damage to the properties of RCC.Aiming at the problem of properties deterioration of RCC after early freezing,this paper selects the combination of pre curing time and interlayer interval time,designs the test scheme and specific implementation method of RCC under early freezing,studies the deterioration law of macro and micro properties of RCC under early freezing environment,and reveals the damage mechanism of RCC under early freezing,The calculation model between pore structure fractal dimension and macroscopic property damage of RCC in early frost environment is established.The main conclusions are as follows:(1)Through the compression test and direct shear test,the mechanical property damage characteristics of RCC after early freezing are analyzed.The results show that the damage degree of pre curing time on the strength of RCC after early freezing is as follows:12h>>24h>48h>72h>7d.The damage of shear strength after early freezing is more serious than that of compressive strength.The shorter the pre-curing time,the more serious the strength damage of RCC;as the pre-curing time increases,the properties of RCC after restoration of positive temperature curing is closer to that of standard-cured RCC.The influence of interlaminar interval time on compressive strength loss of early frozen RCC is shown as body specimen>layer specimen,and the influence of shear strength loss is shown as 24h>>12h>4h>body.With the increase of interlayer interval,the shear strength loss of RCC increases after early freezing.(2)The durability of RCC after early freezing was tested by quick freezing method.The results show that the apparent damage of the RCC after early freezing during the freeze-thaw cycle is more serious,and the deterioration rate of the shear strength is also faster.With the increase of freeze-thaw cycles,the peak shear strength,residual shear strength and friction shear strength of RCC decrease,and the residual shear strength and friction shear strength are close gradually.The shorter the pre curing time,the longer the interval between layers,the more serious the shear strength decrease after the freeze-thaw cycle.(3)The pore structure characteristics of RCC after early freeze-thaw cycles were studied by nuclear magnetic resonance(NMR).The test results show that the porosity of RCC increases and the proportion of harmful pore and multi harmful pore increases after early freezing.The shorter the pre curing time,the higher the proportion of pores and macropores,and the faster the damage under freeze-thaw cycles;The longer the pre curing time is,the higher the proportion of cementitious pores is,and the damage is delayed under the freeze-thaw cycle.The pore structure of the layer specimen deteriorates faster than that of the bulk specimen under freeze-thaw cycles.(4)Based on the fractal theory,the damage characteristics of RCC pore structure are quantitatively described by fractal dimension,and the calculation model between the fractal dimension of RCC pore structure and macro properties damage in early freezing environment is established.The results show that the shorter the pre curing time,the smaller the fractal dimension of pore structure,the more serious the compressive strength,shear strength and pore structure damage caused by early freezing,and the faster the shear strength decreases after the freeze-thaw cycle in the later stage.The results show that the pore structure of the layer specimen deteriorates faster under the freeze-thaw cycle,the fractal dimension decreases faster,and the shear strength deteriorates faster after the freeze-thaw cycle.This paper uses a combination of experimental research and theoretical analysis to study the properties degradation characteristics of early-frozen roller compacted concrete.The research results are of great significance to enrich the theoretical research of early-frozen roller compacted concrete and prevent the construction of roller compacted concrete.The early freezing damage of the period has certain reference value.