Abstract
The paper reports on measurements and analysis of the measurements during hardening and drying of specimens using selected acoustic nondestructive testing techniques. An integrated approach was created for better understanding of the relations between the lifetime cycle and the development of the mechanical properties of concrete. Acoustic emission, impact echo, and ultrasonic techniques were applied simultaneously to the same mixtures. These techniques and results are presented on alkali-activated slag mortars. The acoustic emission method detects transient elastic waves within the material, caused by the release of cumulated stress energy, which can be mechanical, thermal, or chemical. Hence, the cause is a phenomenon which releases elastic energy into the material, which then spreads in the form of an elastic wave. The impact echo method is based on physical laws of elastic stress wave propagation in solids generated by mechanical impulse. Ultrasonic testing is commonly used to find flaws in materials or to assess wave velocity spreading.
Highlights
Concrete is one of the most widely used building materials with global consumption rate approaching 25 gigatonnes (Gt) per year, which corresponds to over four tones per person annually [1]
When a material is subjected to loading and when cracks occur, which lead to a sudden release of strain energy from the material, an elastic stress wave is created which travels from the point of origin to the boundary of the material [9]
Evaluation during spontaneous drying was focused on the relative loss of weight, measuring of specimens weighting, ultrasonic velocity, impact echo response and acoustic emission activity were used [21,22,23]
Summary
Concrete is one of the most widely used building materials with global consumption rate approaching 25 gigatonnes (Gt) per year, which corresponds to over four tones per person annually [1]. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone, and the paste is water and usually Portland cement [2]. Alkali-activated concrete is a new generation of alternative building materials; the main difference from traditional Portland cement concrete is the use of a relatively alkalirich, clinker-free binder matrix such as alkali-activated slag or geopolymer. Concrete is known as a heterogeneous material containing various constituents (sand, aggregates, cement, etc.). The dimensions and geometry of the constituents are different and their locations are randomly distributed in the body of concrete
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