Experimental Study on Mechanical Properties of Concrete at Super-Early Age

Abstract

Few studies have reported the cohesion and friction angle of concrete at a super early age. However, these two mechanical parameters are necessary to study the influence of engineering vibration on super-early-age concrete. In view of this, the mechanical properties of the super-early age-concrete are investigated in this work by direct shear testing. Firstly, the shear strength of the super-early-age concrete is measured by the direct shear experiment under different normal pressures at different times. Secondly, the cohesion and friction angle of the super early age concrete are calculated according to the Mohr–Coulomb criterion of failure. To overcome the great discreteness and randomness in the measured data, a new robust regression analysis algorithm is presented to replace the traditional regression analysis method to obtain more reliable and reasonable mechanical parameters. According to the experimental and theoretical analysis results, it is found that the friction angles of the super early age concrete are located in the interval of [50°, 70°]. The cohesion of the concrete is about 78.7 kPa at the initial setting state and about 190.9 kPa at the final setting state, respectively. It has been shown that the cohesion of the concrete at a super-early age tends to increase rapidly with time. The method and test results of this work can be used as a reference for relevant engineering practice. Specifically, the proposed regression method can be extended to the data analysis of other mechanical parameters of concrete, as well as other brittle materials such as rock. The test results of early concrete cohesion and friction angle can be used to analyze the adverse effects of vibration on newly cast concrete members in pile driving and blasting engineering.

Mathematical Model for Early-Aged UHPFRC Compressive Strength Changes

“…Equation (1) indicates that the advantage of the exponential model is that the function is It is clear that the proper mathematical curve model is the key to determining whether such methods can be implemented successfully. This section first reviews several of the existing mathematical models of changes in concrete compressive strength with time, discusses the advantages and disadvantages of these models, and then proposes a new compressive strength-time mathematical model.…”

“…In Equation (1), x 0 and x 1 denote two non-negative fitting parameters that should be obtained by curve fitting based on the strength test data of concrete at an early age. Equation (1) indicates that the advantage of the exponential model is that the function is an increasing function. s(t) increases with an increase in t, which conforms to the law that the strength of concrete increases with its age in engineering practice.…”

“…Concrete is widely used in bridge structure, beam, slab, column, and pile foundation engineering in building construction [1][2][3][4]. In recent years, ultra-high performance fiber reinforced concrete (UHPFRC) has become an important development direction of cementbased composites due to its ultra-high strength and excellent durability.…”

General Curve Model for Evaluating Mechanical Properties of Concrete at Different Ages

“…The mechanical properties of concrete, such as compressive strength and elastic modulus, exhibit dynamic growth patterns after pouring and remain stable until 28 days later. Evaluating the early mechanical properties of concrete can effectively guide the early construction and design of concrete engineering [1][2][3][4], such as prestressed tensioning or formwork removal. For example, in the production of large-volume concrete for bridge box girders, steel reinforcement prestressing should be applied as early as possible to prevent concrete cracks.…”

Study on Soil Corrosion Resistance Reinforced with Reactive Powder Concrete in Chloride Environment

“…Kočí [12] proposed that the compressive strength of RPC can usually reach 200 MPa and it can maintain the integrity of the structure for a long time. In this regard, reactive powder concrete (RPC) [13][14][15], which has the characteristics of ultra-high strength, high toughness, and durability, may become the key to solving these problems.…”