Physical and mechanical characterization of pyroclastic materials in Baleng area (Bafoussam, West-Cameroon): implication for use in civil engineering

Abstract

Bafoussam, like other regions along the Cameroon Volcanic Line has huge pyroclastic resources. These materials are widely used in civil engineering works and result from different volcanic activities and therefore display locally different geotechnical properties. Thus, pyroclastic rocks in the Takouche quarry (Baleng-Bafoussam) were subjected to physical and mechanical analysis in order to determine their suitability and to optimize their use in civil engineering. Results indicate that the Takouche pyroclastic rocks are organized in five strata according to their color, structure and grain size. Except the stratum 2 with a water content of 14.4%, the others and the mixture of all strata displayed a low water content (> 7%) and therefore a low percentage of fine particles and are suitable for the production of concretes and realization of pavement bases. Based on absolute density (2.53–2.75 t/m3), pyroclastic materials of Takouche are common aggregates of the ungraded sand type and can be used for road construction and concrete works. The sand equivalent (69.0–92.8%) and the absorption coefficient (0.01–0.14%) reveal that these materials are very clean sands and contain poorly accessible pores. However, materials of stratum 2 with a sand equivalent of 69.0% and absorption coefficient of 0.14% allow the formation of concretes, exclusively with the use of Portland cement. The optimal dry density (1.83–2.07 t/m3) and optimal water content (8.0–12.5%) which are Optimum Proctor Modified parameters evidenced that materials from stratum 2 require treatment/correction before their use in road embankments. Meanwhile, materials from the remaining strata and the mixture of strata can be directly used and need to be improved only as base layer for heavy traffics T4 and T5. Referring to the 95% CBR values which range from 25 to 98, materials of stratum 1 and the mixed strata can be used as base layers for T3 traffic. In the mean-time, materials from stratum 3 and stratum 4 can be used as base layers for roads with a low volume of traffic. Nevertheless, materials from stratum 2 with a 95% CBR value of 25 need to be improved before their use as base layer. Moreover, the particle size distribution curves of materials extracted from stratum 1 to stratum 4, and the mixture of all strata do not belong to any particle size grading of sand for concrete. This study suggests proposals with the aim to improve the quality of the studied materials for their better use as concrete sand and backfill material. The correction involves the addition of fine volcanic ash to the pyroclastic rocks collected near the Takouche quarry. The resulting gains in compressive strength of concrete are quite considerable and vary from 52.87% to 97.23%, compared to the strength of concrete usually formulated by local users. The CBR coefficient after correction increases significantly with the maximum value of 115. Finally, the corrected aggregates provide good characteristics for their better use in road construction and concrete formulation.