Effect Of Aggregate On Frost Resistance Of Hydraulic Concrete And Its Mechanism

The scope of concrete freeze-thaw damage is extremely wide.Especially for hydraulic concrete in over-water buildings,it is in a state of water absorption saturation,and it is easy to freeze-thaw damage after a large temperature alternating.Serious freezing and thawing damage will adversely affect the function and structural safety of concrete buildings and structures,thus reducing the service life of concrete structures.At present,research on the antifreeze performance of concrete mainly focuses on water-cement ratio and pore structure.As an important part of concrete,the research on the anti-freezing performance of concrete is relatively rare,and it is mainly concentrated on recycled aggregates,and does not form a systematic theory.Therefore,this paper takes aggregate as the entry point,and tests the effect of aggregate on the frost resistance of concrete,and analyzes its mechanism of action.(1)Applying the fractal geometry theory,the fractal calculation of coarse aggregate grading is carried out,and the coarse-grain grading-formed concrete anti-freeze standard test piece obtained by fractal calculation is used,and the freeze-thaw cycle test is carried out.The test results show that the anti-freezing performance of the concrete specimens under different aggregate grading is from D=2.5,D=2.3,D=2.1 and D=2.7.Under the premise of ensuring the slump and gas content are basically the same,the difference in the frost resistance of concrete specimens under different fractal dimensions is the difference of the bubble spacing coefficient of different aggregate grade hardened concrete.(2)Comparing the difference of frost resistance between secondary and fourth grade concrete,the effect of size effect of aggregate on the frost resistance of full grade concrete was studied.The test results show that due to the increase of aggregate size,the internal structure non-uniformity of the concrete increases,and the defects and weak links increase,which causes the micro-cracks in the internal transition zone of the fully-graded concrete to develop faster and the damage is more serious during the freeze-thaw cycle.(3)Selecting five different lithological aggregates of granite(HGY),tuff(NHY),sand slate(SBY),limestone(HY),and pebbles(LS),comparing bones in different particle sizes The frost resistance of the formed concrete and the difference of the hardened bubble parameters,combined with the nanoindentation,element clustering and phase distribution,reveal the microstructural characteristics of the aggregate-cement-based transition zone and the mechanism of anti-freezing effect..The test results show that the anti-freezing performance of concrete specimens is from HGY>HY>LS>NHY>SBY,the gas content of HGY specimens is the highest,the average chord length of bubbles is the smallest,and the bubble spacing coefficient is the smallest.Therefore,the HGY specimens are the smallest.The best antifreeze performance.The bubble spacing coefficient from small to large is HGY>HY>LS>NHY>SBY,which is completely consistent with the frost resistance of the test piece.The total amount of hydration products in the interfacial zone is less than that of the slurry zone,resulting in a lower modulus of elasticity and hardness of the interfacial transition zone than the slurry zone,and increasing along the direction of the slurry until it stabilizes.The frost resistance of concrete is mainly affected by the internal pore structure of concrete.The difference of interface transition zone is not obvious for the frost resistance of concrete specimens.