Abstract
The standard methods used to determine the mechanical properties of single aggregate particles have shortcomings. Indeed, methods that are commonly used to measure the strength of irregular particles do not provide their elastic modulus and are also only semi-quantitative. The aim of this work is to determine more accurately both the tensile strength and the elastic modulus of single coarse aggregate particles using the point load test fitted with tungsten carbide semi-spheres and coupled with a linear transducer. In the experiment, the poles of the particles are made flat and parallel at the points of contact with the semi-spheres of the apparatus, allowing to estimate the elastic modulus of aggregates in accordance to Hertz contact theory. Glass particles of different shapes (spheres, cubes, and prisms) were used as reference material to validate the experimental method and establish the optimal conditions to conduct the test. These conditions consisted of a deformation rate of 0.2 mm/min, a blunt 4.0-mm diameter cylinder piston for spherical particles, while two 14.0-mm diameter semi-spheres in the case of rectangular particles (cubes/prisms). It is also hereby proposed to measure the tensile strength of irregularly-shaped particles by a modified version of Hiramatsu and Oka’s formula using the equivalent core diameter. The proposed method was then applied to measure the strength and modulus of coarse granite aggregate particles (25.0 to 9.5 mm). It demonstrated that the variability of the elastic modulus and tensile strengths of the individual aggregate particles was quite significant, confirming the importance of using the proposed improved method to qualify materials for structural (high strength) concrete, or to simulate/predict the mechanical behavior of concrete.
Highlights
Coarse aggregates represent about 45% of the volume of the concrete. They influence the structural performance of concrete, with an impact in the elastic modulus and the compressive strengths of concretes higher than 50 MPa [1,2,3,4]
Tests were used to qualify particles of many rock types for geotechnical applications [15,16,17], railway ballast [18, 19], or coarse aggregates used in concrete [20]
The objective of the work is to determine the tensile strength and elastic modulus of single coarse aggregate particles using Point Load Test (PLT) coupled with an Linear Variable Differential Transducer (LVDT), without the need to assume that irregularly-shaped particles are spheres
Summary
Coarse aggregates represent about 45% of the volume of the concrete They influence the structural performance of concrete, with an impact in the elastic modulus and the compressive strengths of concretes higher than 50 MPa [1,2,3,4]. According to the theory of elasticity, the strength of a particle can only be defined when the state of stresses generated by loading is known [23]. Analyzing the maximum stress theoretically for a spherical particle, the authors [20] proposed estimating the tensile strength (rt) using Eq 1, considering only the breakage force (Fb) and the distance between the points of application of the compressive loads (D): rt 1⁄4 0:9Fb D2 ð1Þ. Several experimental studies have shown that even when particles with homogeneous composition, such as glass, are tested, their breakage strength is very scattered [9, 12, 26]
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