Characterization and Geotechnical Classification of Soils and Lateritic Gravelly Materials along the Songololo-Lufu Road Axis (Kongo Central Province, DR Congo)

This study aims to characterize from a geotechnical point of view, the soils as well as the lateritic gravels along the Songololo-Lufu road route in the Kongo Central Province in the Democratic Republic of Congo (DRC). Ten soil samples and eight lateritic gravel samples were analysed and tested in the laboratory. For each sample, identification parameters were determined such as particle size analysis, natural water content, Atterberg limits (plasticity index and consistency index), but also compaction and lift parameters such as optimal water content, maximum dry density and CBR lift index. All materials and soils have been classified according to the Congolese Road Standard (NRC) and according to the American HRB classification. The test results show us that clay soils almost always contain between 70% and 90% fine fraction;the grained fraction represents less than 30% in clay samples. For lateritic gravels soils, the percentage of fine elements varies between 35% and 15%;in sand around 20%;the gravelly fraction represents a little more than 50% of the soil. The majority of soil facies encountered define a plasticity index lower than 15. As for the consistency index, we obtained values greater than 1, both for clayey soils and for gravelly soils. The classification according to NRC defined for these soils the types Ae1 and Ae2 for the clayey facies and the types GL1 and GL2 for the gravelly soils, while that of the HRB identified the classes and subclasses A-6 and A-7-6 for clayey soils, and subclass A-2-6 for gravelly soils. The optimal water content values obtained range between 10.2% and 23.10%;the maximum dry densities are between 1.66 and 2.07 t/m3 and the CBR index is between 6 and 26. As for the lateritic gravels materials of the Songololo region, the percentage of fine elements generally remains between 12% and 31%;the plasticity index is between 8 and 18;the optimal dry density is around 2 t/m3;the optimal water content is between 9.8% and 14.5% and the CBR index is between 27 and 82. The Songololo-Lufu lateritic gravels are characteristic of laterites in the savannah region, with a high gravel fraction at the expense of the fine fraction, but low parameters such as the liquid limit and plasticity index.

Production of an Eco-Cement by Clinker Substitution by the Mixture of Calcined Clay and Limestone, Songololo (DR Congo)

Ordinary Portland Cement (OPC) is by mass the largest manufactured product on Earth, responsible for approximately 6% - 8% of global anthropogenic carbon dioxide emissions (CO2) and 35% of industrial CO2 emissions. On average 0.8 to 0.9 ton of CO2 is emitted to produce one ton of OPC. In this paper, partial substitution of clinker (30% - 35%) by the calcined clay-limestone mixture was investigated in order to produce an eco-cement (LC3). Analyzes by XRF, XRD and ATG/ATD have characterized different components, determined the calcination temperature and selected the right clay which can act as effective Supplementary Cementitious Material (SCM). Mechanical tests on mortar carried out over a period of 90 days. The WBCSD/WRI “Greenhouse Gas Protocol” methodology then allowed the calculation of CO2 emissions into the atmosphere. Three types of clay are available in the Songololo Region. The kaolinite is the principal clay mineral and its content varies from 27% to 34%. The sum of kaolinite and amorphous phase which enable clay to react with cementitious material ranges from 57% to 60%. The SiO2 content ranges from 33% to 76%, the Alumina content from 12% to 20% so that the ratio Al2O3/SiO2 is on the higher side (0.17 - 0.53). The calcination window is between 750°C and 850°C and the best clay which can act as SCM identified. The clinker’s substitution reduced CO2 emissions from 0.824 ton of CO2 for one ton of OPC to 0.640 ton of CO2 for one ton of LC3, means 22% less emissions. The compressive strengths developed by LC3 vary from 8.91 to 57.6 MPa (Day 1 to Day 90), exceed those of references 32.5 cement and are close to 42.5 cement. In view of the results, LC3 cement can be considered for industrial trials.