Thermal properties of concrete C25/30 with partially replaced gravel by recycled materials measured by pulse and step-wise transient methods

Abstract

Concrete is one of the most widely used building materials and is an artificial material, as it is not naturally occurring. We cannot imagine any construction without them. Currently, new concrete mixtures have been developed for various innovative purposes. In principle, they are composite materials containing different types of cement, fillers and stone aggregates. Concrete is produced by mixing cement, water, and aggregates as sand, gravel or crushed stone. In certain cases, some additives and admixtures can be added to improve its physical and mechanical properties. Cement concrete materials produced in the Ladce cement plant are increasingly used in the production of all engineering and earthworks, such as roads, buildings, foundations, bridges, modern construction of single-family houses and even airport runways. In all applied fields, there is a basic need to know all their properties.
The observed physical and mechanical properties of concrete are: tensile, shear and compressive strengths, the strength under dynamic load, waterproofing, resistance against the various effects like frost, salt, wear, chemicals, etc. Special classes of interest include thermophysical properties, i.e., the thermal conductivity, thermal diffusivity and specific heat capacity. The derived parameters are the thermal resistance (R-value specific to the thickness of the material divided by thermal conductivity), and the U-value, which is a measure of thermal transmittance. The experimental measurement of thermophysical properties aims to compare not only the properties of the given materials, but also their change and mutual comparison. Thermophysical parameters were measured by the Pulse Transient and Step-Wise Transient methods. The article explains the methodology of how we can handle parameter estimation in such conditions and optimise experimental conditions. The concrete samples were labelled as follows: the Reference samples 29, C25/30, and 31-Tritech C25/30 + admixture. Recycled Brick Waste was used as regenerated natural clay. Such materials can be used in concrete-based materials as artificial recycled aggregate or as an additive to Pozzolanic Type II. The differences in both types of concrete are discussed. Measurements of thermophysical properties performed on concretes with different compositions were performed using transient methods.