C30 Concrete Research Articles

Study on dynamic compressive mechanical properties of freeze-thaw concrete

In this paper, the split Hopkinson pressure bar (SHPB) equipment was adopted to investigate the dynamic compressive mechanical properties of C40 concrete under various loading speeds after freeze–thaw cycles. The range of freeze–thaw times was 0 to 125 times. The range of loading speed was 4 to 10 m/s, and the tested peak strain rate ranged from 39.87 to 163.35 s−1. During the experiment, pulse shaper and lubricating oil were applied to make the test results more accurate. Based on the obtained results, this paper discussed two fundamental assumptions of one-dimensional wave propagation and dynamic stress equilibrium. A general equation was developed to express the dynamic compressive strength in dependency of the freeze–thaw times. The test results showed that the dynamic compressive strength of concrete increased first and then decreased with the increase of freeze–thaw times. The dynamic compressive strength also increased gradually with the increase of loading velocity. In addition, this paper discussed the difference and relationship between failure patterns of specimens and revealed the changing rules of stress versus strain curve, dynamic compressive strength, and dynamic impact factor (DIF). Two influence coefficients were introduced to quantify the effects of freeze–thaw damage and hydration on the dynamic compressive strength. Theory of statistical damage and Weibull distribution were employed to establish a constitutive model of freeze–thaw concrete. The results showed that the model can effectively describe the dynamic compressive mechanical responses of freeze–thaw concrete under impact loading, and gave some suggestions to concrete structural design, structural health detection, structural performance evaluation and so on in cold areas.

Raw materials selection method based on the durability of the concrete for bridge

To enhance the durability of the cement concrete of the bridge, C40 and C50 concretes with different raw materials have been made. A method of optimal selection method for raw materials has been put forward. For different raw materials from different plant, based on the orthogonal experimental design, certain raw materials groups are gained. By the same C40 and C50 concrete mix proportion but different raw materials groups, the specimens have been made for testing the performance of the compressive strength, carbonization and anti-chloride penetration. By range analysis, the best raw material group of the concrete with higher compressive strength, lower chloride penetration coefficient and lower carbonization depth has been selected.

Influence of contact friction in compression tests of concrete samples

This paper presents an experimental assessment of the influence of the boundary conditions and geometry of the specimen in unconfined compression tests, employing two concrete types. For such purposes, an experimental program was designed, dividing the samples into cylinders with height h = 20 cm and diameter b = 10 cm, prisms with height h = 20 cm and square 10 cm base and 10 cm sides cubes. Concrete traces resulting in 50 MPa (C50) and 30 MPa (C30) nominal strengths were used. The compression tests were carried out under five different boundary conditions on the loaded planes: Grease, Teflon and Brush plate, as anti-friction means. For reference, standard tests and increasing the lateral restraint employing Glued sheets, in order to maximize the interface friction, were also performed. The strength difference between height/base ratios (h/b) = 2 and (h/b) = 1 prisms varies on average from 15% for C50 and 35% for C30 concretes. No significant difference was found between cylindrical and prismatic specimens with the same h/b ratio. In specimens provided with anti-friction devices, the strength variation for the different geometries and h/b ratios was almost totally eliminated, as well as the post-peak softening of the tests. The reported results prove that the post-peak softening is not a characteristic of the material but a consequence of the interface friction in the tests. Cubic specimens provided with grease to eliminate friction led to the same compressive strength than cylinders or prisms with the same cross-sectional area and therefore offer the unquestionable advantage of allowing the assessment of the influence of the orientation of casting.

Experimental study on the influence of mixing time on concrete performance under different mixing modes

Abstract To study the influence of different mixing times on the performance of concrete under vibration mixing and conventional mixing, C40 and C60 are selected in this paper to verify the influence of mixing time of 60, 75, 90, 105, and 120 s on the compressive strength and durability of concrete comparing vibration mixing and common forced mixing. The results show that the early strength of concrete is more significantly improved in 3 and 7 day; the strength with vibration mixing for mixing 105 s in each age is higher than that of conventional mixing at 120 s; under the condition of guaranteed strength, the mixing time of at least 15 s can be reduced. The strength of C40 concrete with vibration mixing has a peak value with the corresponding mixing time of 105 s, and the rapid growth stage of compressive strength is 15 s earlier than that of conventional mixing. For all mixing time, the electric flux of vibrated concrete is significantly smaller than that of forced concrete, and the change rate is generally above 10%; compared with conventional mixing for 120 s, the durability of C40 and C60 concrete increases by 11.8 and 11.1%, respectively, at the time of vibration mixing for 105 s. It was found that under the same mixing time, the compressive strength of concrete with vibration mixing method is higher than that of conventional mixing. In a certain range, the durability of concrete can be improved by prolonging the mixing time.

Experimental study on river sediment incorporation in concrete as a full aggregate replacement: Technical feasibility and economic viability

The reuse of river sediments as aggregates is a sustainable management technique that reduces waste from dredging operations and offers the potential to realize economic benefits. This research aims to evaluate the technical feasibility and economic viability of producing C30 class concrete made from sediments. Sediment from the Seine River Basin is characterized from a physical, environmental and mineralogical perspective before its incorporation into concrete as full substitute for conventional aggregates. The physical, mechanical and durability properties as well as the leaching of these concretes are then investigated. Sediment characterization shows that the physical properties (i.e. density, water absorption, and particle size) are close to those of conventional aggregates. The environmental and mineralogical characterization has proven that the studied sediments are inert and are mainly silico-calcareous materials. Experimental results reveal that a slight increase in cement dosage (less than 5%) yields a sediment concrete possessing properties similar to those of the control specimen with any effects remaining only marginal. Leaching tests indicate that the rate of pollutants released by the sediment-based concrete is of the same order of magnitude as that released by the control specimen. The economic viability study has found that the production of a C30 concrete based on sediment is 41 % less expensive. In-situ use of sediments in concrete prevents the carbon footprint of aggregate transport, which offsets that of additional cement for sediments-based concrete.

Recycling used engine oil in concrete design mix: An ecofriendly and feasible solution

Used engine oil (UEO) accumulation increases the risk of urban environment through soil contamination and water pollution. Incorporating UEO into concrete as chemical admixtures is a feasible approach for its disposal, since it can serve similar functions to water reducing agents and air entraining admixtures in developing sustainable and durable concrete. However, the dosage levels of UEO that can be incorporated into concrete are restricted to approximately 0.3–0.5% by weight of cementitious materials due to UEO's poor dispersion. In this study, a typical superplasticizer was employed to achieve good dispersion of UEO in ternary blended concrete with fly ash and silica fume. The workability performances and mechanical properties of concrete admixed with UEO were investigated through slump and compression tests. The experimental results reveal that ternary blended concrete containing a high dosage of UEO (5% by weight of cementitious materials) compared favorably to ordinary concrete without sacrificing workability and compressive properties. C60 concrete with a 2% dosage level of UEO exhibited the maximum improvement in compressive strength by 4.4%. In addition, a scanning electron microscope was used to reveal the microstructural origins behind the alterations in the mechanical properties. Microscale images demonstrate that the addition of UEO aids in the microstructure densification of concrete. The findings in this paper not only provide a clean and innovative UEO disposal approach but will also contribute to developing sustainable concrete in the construction industry.

Microstructure and life prediction model of steel slag concrete under freezing-thawing environment

Abstract The goals of this paper are to study the frost resistance of steel slag concrete (SSC), research the damage mechanisms, and predict the service life of SSC in cold regions. First, the stability of steel slag (SS) was tested, and then SS samples with different treatment dosages were used as aggregates to replace natural aggregates of equal volumes in the preparation of C40 concrete. The microstructures of concrete and micro properties of cement hydration products were investigated in nanospace in this research. In addition, rapid frost resistance durability tests were carried out under laboratory conditions. The results revealed that the ordinary concrete (OC) exhibited a more serious damage phenomenon, and the mass loss and relative dynamic elastic modulus of OC were changed by 5.27 and 62.30%, respectively. However, with increases in the SS content, the losses in mass were lowered. Furthermore, the relative dynamic elastic modulus decreased less, and the frost resistance of the specimens was stronger. The range of mass loss rate was between 2.233 and 3.024%, and the relative dynamic elastic modulus range was between 74.92 and 91.09%. A quadratic function with a good fitting degree was selected to establish a freezing-thawing damage calculation model by taking the relative dynamic elastic modulus as the variable. Then, the freezing-thawing durability lifespan of concrete in the colder regions of northern China was successfully predicted by using the damage calculation model. The results of SSC20–60 showed the better frost resistance durability when the content of SS sand was 20% and the dosage of SS stone was 60%. Its frost resistance lifespan was more than twice that of OC, which demonstrated that SS as an aggregate could effectively improve the frost resistance lifespan of concrete to a certain extent.

Experimental and numerical research on seismic performance of S-RC-SRC composite frame

The hysteretic behavior of upper steel-beam-to-column and lower RC-beam-to-SRC-column (S-RC-SRC) composite frame was investigated experimentally and numerically in this paper. Two 1:3 scale-reduced three-layer frame specimens (KJ-1 and KJ-2) were manufactured and tested under low cyclic loading. Both the KJ-1 and KJ-2 failed due to the plastic hinge (weld fracture) at the beam end of 2nd-layer. The hysteretic curves were smooth and plump, which indicated that the S-RC-SRC composite frames possessed excellent energy dissipation capacity. The seismic performance index, e.g. ductility coefficient, strength and stiffness degradation and energy dissipation coefficient were analyzed and the results showed that KJ-2 had larger initial elastic stiffness (2.37kN⋅mm) and slower strength degradation. Experimentally validated finite element models were established and parametric analysis was performed on three factors: strength grade of concrete (M − 1 series), axial compression ratio (M − 2 series) and slenderness ratio (M − 3 series). Ten finite element method (FEM) models were analyzed and the results showed that M-14's (FEM model with C60 concrete) horizontal load-carrying capacity and initial elastic stiffness had limited promotion (all lower than 9%) comparing with the benchmark M − 11 (FEM model with C30 concrete), but M − 2 and M − 3 series varied obviously. Finally, a practical skeleton curve model and hysteretic rule were proposed on basis of the modified angular displacement equation. The theoretically analyzed results were in good agreement with test and FEM results with an average error of 4.90% and 2.59%.

High Tensile Bollard Structure Using Macro Synthetic Fiber

The usage of bollard is very important in protecting buildings. It can prevent vehicles from passing through the building. But the public now is less sensitive about the use of bollards. They assume the use of bollard is wasteful and for aesthetic only. Therefore, most buildings did not install bollards to protect the building. Besides that, there are also mounted bollards installed that are inappropriate to that place. For example, some bollards installed around buildings are not concrete type that can withstand strong impacts. Furthermore, some important and historic buildings need to install an explosive-proof type of bollard as building protection. The methods used for this research were non-destructive test and destructive test. Non-destructive test is slump test and destructive tests are compression test, tensile test, flexural test, and air blast test. Seven mix were used and tested in this research. From the compression test result, it shows that concrete mixed with 0.5% of macro synthetic is much stronger than control sample and other mixtures. From the tensile test, it shows that the control sample of the concrete achieved tensile strength of 3.48 N/mm2 while the mixed concrete with 0.5 % mix of macro synthetic fiber gave higher tensile strength. The flexural test shows that the concrete mixed with percentage ratio of 0.5%, 1.0%, and 1.5% of macro synthetic fiber gave higher strength than the control sample which is only 2.77 N/mm2. Based on experiments that have been carried out, it can fulfil objective one, which is to evaluate the type of blast safety for building envelope with the concrete bollard grade 30. Quality of concrete in terms of strength, tensile, and flexure of the proposed material with 0.5% of macro synthetic fiber can produce the same quality and meets the quality grade C30 concrete.

Experimental Study on the Mechanical Properties and Durability of High-Content Hybrid Fiber-Polymer Concrete.

Polymer-modified concrete and fiber concrete are two excellent paving materials that improve the performance of some concrete, but the performance of single application material is still limited. In this paper, polymer-modified concrete with strong deformation and fiber concrete with obvious crack resistance and reinforcement effect were compounded by using the idea of composite material design so as to obtain a high-performance pavement material. The basic mechanical properties of high-content hybrid fiber–polymer-modified concrete, such as workability, compression, flexural resistance, and environmental durability (such as sulfate resistance) were studied by using the test regulations of cement concrete in China. The main results were as follows. (1) The hybrid fiber–polymer concrete displayed reliable working performance, high stiffness, and a modulus of elasticity as high as 35.93 GPa. (2) The hybrid fiber–polymer concrete had a compressive strength of 52.82 MPa, which was 31.2% higher than that of the plain C40 concrete (40.25 MPa); the strength of bending of the hybrid concrete was 11.51 MPa, 191.4% higher than that of the plain concrete (3.95 MPa). (3) The corrosion resistance value of the hybrid fiber–polymer concrete was 81.31%, indicating its adjustability to sulfate attack environments. (4) According to cross-sectional scanning electron microscope (SEM) images, the hybrid fiber–polymer concrete was seemingly more integrated with a dense layer of cementing substance on its surface along with fewer microholes and microcracks as when compared to the ordinary concrete. The research showed that hybrid fiber–polymer concrete had superior strength and environmental erosion resistance and was a pavement material with superior mechanical properties.

Study on Quasi-Static Mechanical Property of SFRSCC

Steel fiber reinforced self-compacting concrete (SFRSCC) inherits the advantages of self-compacting concrete (SCC) characterized by sound fluidity and self-compaction. Meanwhile, the addition of steel fiber has enhanced the roughness and ductility of substratum. This paper designs SCC of two different strength grades, including C40 and C60, and conducts SFRSCC quasi-static mechanical property test and split tensile test. Uniaxial tensile test is carried out through the design of a dedicated damper to obtain SFRSCC quasi-static uniaxial tensile strength and relational expressions about SFRSCC uniaxial tensile strength and eigenvalue of steel fiber content. It is discovered from SFRSCC split tensile test that, for the concrete with strength grade of C40, its split tensile strength rises by about 36% when the fiber content increases from 0.5% to 2%. For the concrete with strength grade of C60, in addition to the concrete with 1% fiber, the overall variation trend of split tensile strength is the same as that of C40 concrete, but the variation range is relatively small. The damage morphology of specimens indicates that steel fiber can effectively improve the tensile strength and roughness of SFRSCC and help it fully take in the energy before being damaged.

Consolidated effect of fiber-reinforcement and concrete strength class on mechanical performance, economy and footprint of concrete for pavement use

The advancement in the tensile strength and ductility of plain concrete can minimize the quantity of materials required per unit strength to build eco-friendly structures. This paper compares the compressive and flexural behavior of different strength classes (C20, C30, and C45) of concrete with the varying volume fractions of hooked steel fiber (HSF) considering the application of concrete road. The performance of each strength class was evaluated and compared based on the compressive and tensile testing results. Using the mechanical properties of concrete mixtures; the design thickness, cost, and global warming potential of concrete pavement were calculated and compared between different mixes under the same traffic loadings. The results showed that the maximum utilization of HSF was observed in the high-strength C45, whereas HSF showed comparatively low efficiency in low-strength C20. At 0.25% volume of HSF, low strength C20 concrete showed higher residual strength and flexural toughness than that of the plain high strength C45 concrete. The analysis of design thickness of pavements revealed that low-strength C20 at 0.25–0.5% HSF can provide cost-effective and eco-friendly pavements compared to a plain high strength C45 for the same design loadings. The results of this study provide useful insights on the selection of strength class and concentration of steel fiber for pavement application.

Mechanical properties of fiber nano-modified rubber concrete in high temperature

The purpose of this study is to explore the mechanical properties of fiber nano-modified rubber concrete in high temperature. In this study, ordinary C30 concrete was used as the test benchmark, and 10% by volume of five kinds of rubber particles were used to replace fine aggregate to prepare rubber concrete (RC). On this basis, steel fibers with a volume ratio of 0%, 0.5%, 1.0%, 1.5% and 2.0% were added to make fully mixed steel fiber rubber concrete (SFRRC), according to the completely mixed steel fiber rubber concrete (SFRRC) Compression test, split tensile test, 4-point bending test, and fatigue test of steel fiber rubber concrete (SFRRC) with three stress levels, studied the fully mixed steel fiber rubber concrete (SFRRC) machinery of various steel fiber mixed materials Properties and the effects on the fatigue life, fatigue probability distribution law and damage progression law of steel fiber rubber concrete. The test results show that the combination of steel fiber and nano-silica can increase the crack resistance of 600-degree high-temperature concrete to 57.19% and the maximum separation tensile strength to 269.09%.

Effect of Iron Tailings and Slag Powders on Workability and Mechanical Properties of Concrete

Tailings are one of the largest solid wastes in stock at present. In order to improve the comprehensive utilization rate of tailings, especially to solve the problems of fine-grained tailings treatment, the concrete composite admixture was prepared by using iron tailings powder and slag powder. In order to study the influence of iron tailings powder on the workability and long-term mechanical properties of concrete, C30 and C50 concrete with different iron tailings powder dosages were prepared, and the slump, expansion, flexural strength, splitting tensile strength, and compressive strength of concrete at different ages were tested. The results showed that the proper addition of iron tailing powder is beneficial to the working performance of concrete and can effectively reduce the time-loss of concrete fluidity. When the content of iron tailings powder in the composite admixture is 50%, the 1080d long age strength of C30 and C50 concrete can reach 50.3 and 80.7 MPa. Based on the 28d compressive strength, the relative strength-age prediction model of iron tailings powder concrete was established. The calculation and experimental results show that the model can accurately predict the compressive strength of micro-powder concrete of iron tailings at long age, and the error rate is less than 1%. The results lay a theoretical foundation for the utilization of iron tailings in concrete.

Shear fracture performance of the interface between ultra-high toughness cementitious composites and reactive powder concrete

This study used unnotched compression tests and digital image correlation technology to analyze the influence of two different casting intervals and three different roughness conditions on the fracture toughness of the interfaces between ultra-high toughness cementitious composite (UHTCC) and reactive powder concrete (RPC). UHTCC exhibits pseudo-strain-hardening responses and multi-cracking behaviors, and the most notable characteristic of RPC is its dense microstructure. The results show that the complete interfacial shear fracture process included three stages: crack initiation, steady crack propagation and unsteady crack propagation. A double-K crack propagation criterion for interfacial shear fracture of composite structures was proposed by introducing two parameters: initial and unstable fracture toughness. After introducing interfacial roughness via the scratch method, the unstable fracture toughness decreased. The 24-h casting interval group had a lower initial fracture toughness and higher unstable fracture toughness than the 2-h group. The unstable fracture toughness of all the composite specimens exceeded that of C60 concrete, indicating that they had excellent resistance to interfacial shear fracture.

SIMILAR MATERIALS FOR QUASI-STATIC SCALED TESTS OF FAULT-CROSSING TUNNELS

The design of similar materials is one of the key links to ensure the matching of the physic-mechanical properties between the prototype and the test specimens. Based on the prototype of the Xianglu mountain tunnel of the water diversion project in the central Yunnan province, China, the scaling relationship of the physical quantities in the quasi-static scaled test of a fault-crossing tunnel is derived in this study according to the similarity theory and dimensional analyses. The similar materials of concrete and rock mass used in the test are developed with barite powder and sand as the aggregates and with gypsum and lime as the cementing material. The effects of each component on the physic-mechanical properties of the similar materials are investigated through orthogonal tests. The test results indicate that the strength, elasticity modulus and density of the similar materials can be significantly changed by the overall content of the high-strength gypsum and water-gypsum ratio. Small variation of the strength of the similar material is found when the sand-gypsum ratio is between 0.8 and 1.2, but the strength significantly decreases when the sand-gypsum ratio is between 3 and 12. The elastoplastic performance and the brittle failure mode of Grade C30 concrete can be well simulated by the similar material made of high strength gypsum, low strength gypsum, barite powder and sand. The tensile splitting and the diagonal shear failure modes of rock mass of Grade IV and V can be well simulated by the proposed similar material made of high strength gypsum, lime and sand. The development process and ratios of similar materials can provide important reference for model test and numerical simulation.

Mechanical properties and freeze-thaw resistances of bronze-concrete composites

Studies in the literature show that the physical and mechanical properties of concrete could be improved by the incorporation of different kinds of industrial waste, including waste tire rubber and tire steel. Recycling of waste is important for economic gain and to curb environmental problems. In this study, finely ground CuAl10Ni bronze is used to improve the physical and mechanical properties, and freeze-thaw resistances of C30 concrete. The density, cold crushing strength, 3-point bending strength, elastic modulus, toughness, and freeze-thaw resistances of concrete are determined. In addition, the Schmidt Rebound Hammer (SRH) and the ultrasonic pulse velocity (UPV) tests, which are non-destructive test methods, are applied. SEM/EDX analyses are also carried out. It is noted that a more compacted structure of concrete is achieved with the addition of bronze sawdust. Then higher density and strength values are obtained for concretes that are produced by bronze addition. In addition, concretes including bronze sawdust generally show higher toughness due to high plastic energy capacities than pure concrete.

Influence of stone powder content in machine-made sand on mortar concrete

The paper mainly studies that Influence of stone powder content in machine-made sand on mortar concrete. By changing the amount of stone powder in the machine-made sand, the ratio of cement to water and sand to grout, the change in the tensile value of the steel bar in concrete can be found. After a lot of test data to prove that the content of stone powder is 6%, the mortar ratio is 1: 2.5, the water-cement ratio is 0.40, the content of water-absorbent resin is 0.20, and the performance of the C40 concrete is good.

Experimental Study on Pipe Strength and Field Performance of Pipe Jacking TBM in Deep-Buried Coal Mines

To study the strength of steel rebar-reinforced jacking pipes under the loading of deep-buried coal mine strata, this paper proposed a specially designed triaxial pipe loading system and a set of similitude model tests are conducted. The mechanical behaviors of pipes under triaxial loading conditions are analyzed and the configuration parameters of pipe prototypes are determined based on test results. The test results show that the loads are mainly undertaken by concrete rather than steel rebars and the strength of pipes can be increased more efficiently using higher grade concrete. Compared with increasing reinforcement ratio, using C60 concrete to fabricate pipes can increasing the ultimate bearing capacity to 2420 kN. The pipe jacking TBM penetrated 138 m in underground coal mine with a buried depth of 600 m and a maximum jacking force of 7042.58 kN. The construction methods and the performance of pipe jacking in deep-buried coal mine are illustrated. The monitoring data of jacking force and deviations are recorded and analyzed. The working experiences obtained from engineering practices are summarized. In addition, the suitability of pipe jacking in underground coal mines is examined.

Study on the JH-2 Model Parameters for Metro Shield Cutting Reinforced Concrete Pile

In order to investigate the application of JH-2 (Johnson-Holmquist-2) constitutive model in concrete, a series of parameters study have been conducted to evaluate the JH-2 model in C30 concrete. The finite element analysis software ABAQUS is utilized to simulate the compression test of the three-dimensional standard concrete test based on the ALE adaptive mesh and the damage failure criterion of element deletion function. The numerical analysis of 3D concrete pile foundation and simplified shield machine cutter head to simulate shield cutting pile is established. Analyzing the numerical simulation and construction data, the key points of the shield machine cutting pile are illustrated. Research shows that: (1) JH-2 constitutive model can be used to simulate the concrete cutting. (2) The better damage parameters have been represented and verified against the results of experiments, which are D1 = 0.6 and D2 = 0.1 in the JH-2 model of C30 concrete. (3) In the simulation example of concrete compression and cutting pile, the failure form of concrete is brittle failure, and the non-linear characteristics of concrete has been observed. (4) The simulated torque vibration of the cutter head is relatively large than actual pile cutting, and the actual shield machine cutting pile construction should have a low rotation speed and low propulsion speed.