Evaluation of Performances of Calcined Laterite and Oyster Shell Powder Based Blended Geopolymer Binders

This work consisted in characterizing of calcined laterite and oyster shell powder based blended geopolymer binders. To do this, raw laterite taken from Soa in the city of Yaoundé and oyster shells extracted from Mouanko in the Sanaga-Maritime were initially air-dried, then dried at 105 °C, before being calcined at 500 °C and 200 °C respectively for 2 hours. These samples were subjected to preliminary studies, i.e. determination of their chemical and mineralogical compositions, particle size distributions, densities, as well as thermal analysis for the synthesis of geopolymer binders. X-ray diffractometry, thermal and gravimetric analysis were carried out on the oyster shell powder and laterite, in order to elucidate the time and degree of calcination of the two samples, the evolution of the linear shrinkage, the setting time as well as the compressive and flexural strengths of the geopolymer binders. The results obtained show that oyster shells are rich in CaCO3 and contain crystalline phases, while laterite is rich in silica, iron (FeCO3) and alumina (Al2O3). The geopolymer samples: Lat + 0% oyster shells have a setting time between 125 and 168 min for a compressive strength of about 47 MPa. The peak strength is observed around 15% addition of oyster shell powder, i.e. 53.5 MPa at 28 days with an increased setting time. This strength was decreased from 25 % of addition of oyster shells, despite the increase observed in the setting time. It appears from this study that the addition of 15% oyster shell increases the compressive strength of the geopolymer, but also leads to a considerable decrease in absorption rate. Above this rate, the compressive strength decreases drastically and concomitantly the setting time increases

The viability of calcined clays and volcanic scoria from western Cameroon as Supplementary Cementitious Material (SCM)

peer reviewedIn order to promote the use of calcined clays and volcanic scoria from the western Cameroon as Supplementary Cementitious Material (SCM), the physical, chemical and mechanical properties of fresh and hardened cements were investigated. The cement was formulated by substituting 10, 20, 30, and 40% of clinker by calcined clays from Mayouom (Mkm) and Balengou (MKb), and volcanic scoria from Foumbot (PNf). For each of the three raw materials, the loss on ignition is less 1%, the sum %SiO2 + %Al2O3 + %Fe2O3 is greater than 70%, amorphous phase is present and pozzolanic reactivity with the Chappelle test is greater than 80% of Ca(OH)2 consumed. This makes it possible to classify MKm, MKb and PNf among the pozzolanic materials. The addition of calcined clay to the clinker, result to an increase in the water to cement ratio, unlike the Foumbot pozzolan, which does not really affect this ratio. The three raw material act as setting retarders, with PNf having a greater retarding effect than MKm and MKb. The compressive strengths of the cements formulated in this study shows that with 10% clinker substitution, cements of class 42.5 can be obtained, and that from 20% onwards, the cements obtained are of class 32.5. However, an addition of more than 20% PNf in the clinker produces cements with strength less than 30 MPa at 28 days. Calcined clay from Balengou and Mayouom could be used as a viable alternate source of SCM for cement production with better performances compared to volcanic scoria from Foumbot