Freeze-thaw Damage Laws and Model of Hydraulic Fully Graded Concrete

On the basis of previous research results, the frost resistance of fully graded concrete and small wet sieving concrete specimens was compared and analyzed, and the characteristics and rules of freeze-thaw damage of hydraulic fully graded concrete after freeze-thaw cycles were analyzed through freeze-thaw test, impact-echo test, mechanical test and so on. Meanwhile, the damage characteristics of concrete in the salt and water freezing environment were compared. Through the mechanical test, it is found that the mechanical properties of both fully graded concrete and wet sieving concrete decreased to varying degrees after freeze-thaw cycles. The laws of uniaxial compression and tensile strength of concrete varying with the number of freeze-thaw cycles were obtained. The life of concrete after freeze-thaw cycles was predicted, and it is concluded that the life of concrete in the salt freezing environment was only 0.8 times that in the water freezing environment, proving once again that the damage of concrete in the salt freezing environment was more serious than that in the water freezing environment. Therefore, the grade of frost resistance should be improved appropriately for concrete engineering with salt solution. Finally, based on the damage theory and Lemaitre strain equivalence principle, the freeze-thaw damage evolution equation suitable for fully graded concrete was obtained.

Experimental Study on the Degradation of Hydraulic Fully Graded Concrete under Freeze-thaw Cycles

In recent years,the winter temperature in southern China decreases year by year,and the phenomenon of freeze-thaw damage is also wide-spread in hydraulic buildings.In this paper,the freezing-thawing cycle tests of fully graded concrete specimens and corresponding wet sieving suitable for climate conditions in southern China were carried out,and the effects of freezing-thaw cycles on the appearance,mass loss,relative dynamic elastic modulus,internal temperature and strain of fully graded concrete and wet sieving concrete were studied.The splitting tensile strength test of concrete specimens with specified salt freezing cycles was carried out,and the relationship between the strength reduction of fully graded concrete and wet sieving concrete specimens and the number of freeze-thaw cycles was analyzed.The results show that with the increase of freeze-thaw cycles,the properties of fully graded concrete and wet sieving concrete degraded,and the degradation of compressive strength was the most significant,followed by the splitting tensile strength.In the initial stage of the freeze-thaw cycles,the degradation of each property was not obvious,and the deterioration rate of each property increased significantly after 100 freeze-thaw cycles.Besides,the relationship between the splitting tensile strength of fully graded concrete and wet sieving concrete and the internal wave velocity after freeze-thaw cycles was established.The test results can provide theoretical basis for the design,repair,maintenance and life prediction of dams and offshore platforms in southern China.

Finite Element Analysis of Shrinkage in the Interface of Functionally Graded Concrete Segment Used in Shield Tunneling

In functionally graded materials (FGM), the problem of interface stability caused by the volume deformation is commonly regarded as the key factor for its performance. Based on test results, in terms of finite element method (FEM) this paper analyzed problems in the shrinkage of functionally graded material interface of shield concrete segment, which was designed and produced by the principle of functionally graded materials. In the analysis model, the total shrinkage of concrete was converted into the thermal shrinkage by means of the method of 'Equivalent Temperature Difference'. Consequently, the shrinkage stress of interface layer was calculated and compared with the bond strength of interface layer. The results indicated that the volume deformation of two-phase materials of functionally graded concrete (FGC) segment, which were the concrete cover and the concrete structure layer, showed better compatibility and the tension stress of interface layer, which was resulted from the shrinkage of concrete and calculated by ANSYS, was less than the bond strength of interface layer. Therefore, the interface stability of functionally graded concrete segment was good and the sliding deformation of interface layer would not generate.

Compressive and Flexural Strength Property Enhancement for Fibre Reinforced M30,M50 and M80 Grade Concrete Using Foundry Sand(FS)and Crushed Concrete Waste(CCW)

Nowadays,many research works are carried for all grades of concrete to make the concrete most economical and durable there by adding the supplementary cementitious materials and alternative replacement aggregates.In this research work deals with the experimental investigation of mechanical properties of the M30,M50 and M80 grade concrete by replacing the fine and coarse aggregate by foundry sand and crushed concrete waste respectively.Mix design procedures were followed as per IRC44:2017 guidelines and recommendation.Proper dosage of super plasticizer(SP)was maintained in the concrete to make it better performed.In this present investigation,a Poly Propylene fibre(PPF)of 0.3%by weight of the cement is used.Mechanical properties such as Compressive strength and Flexural Strength were determined by preparing the respective mould sizes for specific test and are cured for 7,14 and 28 days and result obtained for respective days were tabulated and discussed.

Energy Absorption in Functionally Graded Concrete Bioinspired by Sea Urchin Spines

Functionally Graded Concrete （FGC） is fabricated at the Institute for Lightweight Structures and Conceptual Design （ILEK） by using a layer-by-layer technique with two different technological procedures： casting and dry spraying. Functional gradations are developed from two reference mixtures with diametrically opposed characteristics in terms of density, porosity, compression strength and elasticity modulus. In this study the first mixture consists of Normal Density Concrete （NDC）, with density about 2160 kg·m^-3 while the second mixture helps to obtain a very lightweight concrete, with density about 830 kg·m^-3. The FGC specimens have layers with different alternating porosities and provide superior deformability capacity under bulk compression compared to NDC specimens. In addition, the FGC specimens experienced a graceful failure behaviour, absorbing high amounts of energy during extended compression paths. The porosity variation inside the layout of tested specimens is inspired by the internal structure of sea urchin spines of heterocentrotus mammillatus, a promising role model for energy absorption in biomimetic engineering.

Manufacturing technique and performance of functionally graded concrete segment in shield tunnel

The quality of segment is very important to the service life of shield tunnel.Concerning the complex engineering environment of the Wuhan Yangtze River Shield Tunnel,the principle of functionally graded materials was introduced to design and produce the functionally graded concrete segment(FGCS).Its key manufacturing technique was proposed and its performance was tested.