Search

The purpose of this paper is to propose a methodology to optimise the granular skeleton assembly of cementitious materials containing non-spherical aggregates. The method is general and can be applied to any granular skeleton whatever the aggregate shape, size, or composition because it is simply based on the direct minimisation of the intergranular porosity to consequently increase the skeleton's compactness. Based on an experimental design approach, this method was applied to and validated for bio-based oyster shell (OS) mortar with 100% aggregate replacement. First, the best combination of seven crushed oyster shell particle classes was determined and compared with a standardised sand skeleton (0/4 mm) and three other non-optimised OS gradings in terms of intergranular porosity. In particular, it is shown that simply mimicking a reference grading curve initially designed for spherical particles with non-spherical particles led to poor performances. Then, different mortars were cast with the standardised sand skeleton, the optimised OS grading, and the three other non-optimised OS gradings by keeping the water-to-cement ratio (0.5), the aggregate bulk volume, and the cement paste content constant. Mechanical tests in compression confirmed the higher performance of the optimised OS mortar, validating the global optimisation approach. However, the high elongation of the oyster shell aggregates led to high skeleton intergranular porosities—even after optimisation—and the cement paste content needed to be adapted. For a given granular skeleton and for a constant aggregate bulk volume, the increase of the cement paste content led to an increase of both the filling ratio and the mechanical properties (compressive and flexural strengths). Finally, it is shown that the proposed skeleton optimisation and a cement paste content adjustment allowed recovering good mechanical properties for an oyster shell mortar with 100% aggregate replacement, especially in flexural tension. [ABSTRACT FROM AUTHOR]

The paper compares the effect of different compaction procedures on the porosity and mechanical characteristics of earthen materials. In a first series of tests, a very high static pressure, up to 100 MPa, is applied to the soil for a sufficient period of time to allow consolidation (hyper-compaction). This method produces materials with very high densities up to 2300 kg/m3 and good mechanical properties, which are suitable for the construction of masonry structures. In a second series of tests, the soil is compacted according to the standard Proctor method, which is the reference compaction procedure for the design of geotechnical fills such as dams and embankments. In the Proctor method, the soil is dynamically compressed by means of a much lower effort compared to hyper-compaction. All specimens are equalized under identical hygro-thermal conditions and subjected to unconfined compression tests to measure stiffness and strength. It is shown that hyper-compacted specimens exhibit physical and mechanical properties that are comparable with those of traditional building materials for masonry structures. Finally, mercury intrusion porosimetry tests are performed to study the effect of the compaction method on the pore structure of the material.

High performance concrete (HPC) is an innovative concrete used widely in modern construction. New techniques of formulating and designing HPC have made it possible to obtain remarkable mechanical performance and durability compared to the conventional concrete. The main advantages of HPC are related to its low porosity, very high mechanical resistance, and excellent durability. The ease of HPC application is obtained by the combined use of superplasticizer and mineral addition, which results in a significant increase in the compressive strength while improving workability and durability. The Algerian steel industry in North Africa generates very large quantities of slag which are currently little or not used for the formulation of hydraulic binders in the field of construction materials. In the current economic climate, research on high-performance concretes in Algeria is mainly focused on their formulations with a view to producing cement-based concretes composed of better strengths and more durable. The objective of this work is to optimize a formulation of HPC based on a ternary binder integrating granulated Algerian blast furnace slag as a cement substitute. This can partially solve an environmental problem by recycling waste and by-products from the steel industry. The manufacture of a HPC with less cement could lead to both environmental benefits thanks to a reduction in CO2 emissions and financial benefits through a lower construction cost and build more sustainable structures. [ABSTRACT FROM AUTHOR]