PSI - Issue 28

Chbani Hamza et al. / Procedia Structural Integrity 28 (2020) 430–439 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

431

Bolomey (1935), Faury (1958), Dreux and Festa (1998)... etc. In view of this multiplicity and diversity, the method of Dreux Gorisse was chosen, since it is relatively recent and gives optimal results Dreux and Festa (1998). Nomenclature �������� Absolute density C Cement dosing ���� Real density E Water dosing ��� Coefficient of absorption M FG Fineness modulus � Apparent density Ks Additional correction term Coefficient of compactness K Correction Term Aggregates weight ������ Cement weight per cubic metre Apparent volume of aggregates ������ Volume of cement per cubic metre D Mould diameter � Aggregate volume per cubic metre � Distance between shims and piston in empty mould ����� ��� Volume of sand per cubic metre � Distance between shims and plunger in filled mould ������ ��� Volume of gravel 3/8 per cubic metre cm Average resistance ������ ���� Volume of gravel 3/8 per cubic metre ��� Target characteristic resistance ����� ��� Weight of sand per cubic metre G Dimensionless granular coefficient ������ ��� Weight of gravel 3/8 per cubic metre �� Cement class ������ ���� Weight of gravel 8/16 per cubic metre D max Size of the largest aggregate 2. Characterization of aggregates The characterization of the aggregates is based on two main tests. The first test consists of measuring the density and water absorption coefficient, while the second is a measure of the compactness of the aggregates. This characterization is essential to define the formulation of the concrete since the standard NF EN 206 (2014) to take into account the real volume occupied by the aggregates and the quantity of water they contain. 2.1. Density and water absorption Over time, aggregates can absorb water as much as the liquid penetrates the rock, causing an increase in weight. This process is called absorption. The absorption can vary to a very large extent depending on the nature of the aggregate. The water absorption of the aggregates during concrete production must be taken into account (San Nicolas 2011). At the beginning of the test, a sample (according to NM 10.1.703 (2008) and NM 10.1.710 (1999)) of 1500g of aggregates was immersed in the pycnometer filled with water at (22 C° ± 3) and occluded air is removed by gently rotating and oscillating the pycnometer in an inclined position. After drying the outside of the pycnometer, we weigh it with a 0.01g precision balance, the weight found is noted M2 (Fig. 1. (a)). The aggregates are removed from the water. Afterwards, the pycnometer is filled again with water and the lid is put back on as before, the weight of the {Pycnometer +Water} assembly is noted M3. The aggregates extracted from the pycnometer are dried by a heat source (Fig. 1. (b)) until the visible water has disappeared, these aggregates however keep a wet appearance, their weight is noted M1. At the end, the sample of the superficially dry aggregates is dried again in a ventilated oven at a temperature of 105°C ± 5 to a constant weight denoted M4, i.e. until two successive weightings separated by 24 hours do not differ by more than 0.05%. The absolute and real densities are given respectively by the equations (1) and (2). The coefficient of absorption is expressed by equation (3).