Bernadin Kenne Diffo

This study formulates an efficient, affordable, and low-carbon binder based on locally excavated earth from Yaoundé, offering sufficient mechanical strength and water resistance for rendering applications. Through material characterization, a binary binder composed of Portland cement (PC) and calcined laterite (CL) was developed, reducing the PC content by up to 30%. The mortar used laterite sand with varying fine particle contents in place of river sand, and its mechanical strength and water absorption via capillarity action were evaluated. Due to the porosity of the laterite fines, all mixes were prepared at equivalent workability. The mechanical strength was the same as if the binder solely consisted of PC and reached 11 MPa when the laterite sand contained no fine particles. As the fine particle content increased, the mechanical strength decreased to a minimum value of 4 MPa when raw laterite was used, and the coefficient of water absorption via capillarity action decreased. Overall, the formulated class Wc2 mortar is suitable for rendering applications. The valorization potential of fine particles and coarse aggregates of the crushed mortar was assessed: the crushed mortar fines had pozzolanic properties and could serve as supplementary cementitious materials; the largest particles are suitable for lime stabilization.

An efficient and affordable low carbon binder, based on Yaoundé local excavation earth, that achieves sufficient mechanical strength and water resistance for rendering applications has been formulated. Blends of Portland cement (PC) and laterite calcined at 750∘C (CL) with varying weight ratios were investigated. The pozzolanic reaction was detected when replacing up to 70% PC by CL. The research investigated laterite sand mortar formulations, with varying proportion of fine particles. The strength of mortar pastes containing 40% and 100% PC in the binder reached the same level. The compressive strength increased with decreasing proportion of fine particles, and reached the maximum value of 10.2 MPa when the laterite sand grain size is larger than 100μm. The water absorption tests by capillarity showed that the formulation belongs to class Wc2 mortar, for all the laterite sand granulometries. The water absorption by capillarity coefficient decreased with increasing fines proportion : the highest value of 0.051kg/(m2.min0.5) was obtained when the laterite sand contains no fine particles. Furthermore, the study explored the reuse potential of the grinded mortar : the fines showed pozzolanic properties and can be used as supplementary cementitious material, and the largest particles are suitable for lime stabilization.

Kaolin samples of the same mass were treated at 700°C for the same duration of 30min by varying the rate of calcination (1, 2.5, 5, 10, 15 and 20°C/min) in order to obtain metakaolins which were used to produce geopolymers. Depending on the nature of each type of material, kaolin, metakaolins and geopolymers were characterized using thermal analysis, chemical analysis, XRD, FTIR, particle size distribution, specific surface area, bulk density, setting time and compressive strength. FTIR and XRD analyses showed that metakaolins except at 1°C/min contained residual kaolinite whose quantity increased with the rate of calcination of kaolin and which influenced the characteristics of geopolymers. Thus as the rate of calcination of kaolin increased, the setting time increased (226min (rate of 1°C/min)–773min (rate of 20°C/min)) while the compressive strength reduced (49.4MPa (rate of 1°C/min)–20.8MPa (rate of 20°C/min)). From the obtained results the production of geopolymers having high compressive strength along with low setting time requires that the calcination of kaolin be carried out at a low rate

The aim of this work is to valorize volcanic scoria by using them as starting material for geopolymers production. Nevertheless, volcanic scoria possesses low reactivity. Various amounts of metakaolin (5%, 10%, 15%, 20% and 25%) were added into two volcanic scoria (ZD and ZG) in order to improve their reactivity. Two alkaline solutions were used to activate the aluminosilicate materials. The starting materials were characterized by particle size distribution, specific surface area, chemical and mineralogical composition. The geopolymers were characterized by the setting time, XRD, FTIR, SEM and compressive strength. The results indicated that volcanic scoria have low specific surface area (2.3m2/g for ZD, 15.7m2/g for ZG), high average particle size (d50=13.08μm and 10.68μm for ZD and for ZG respectively) and low glass phase contents. Metakaolin have a smaller average particle size (d50=9.95μm) and high specific surface (20.5m2/g). The compressive strength of geopolymers increased in the ranges of 23–68MPa and 39–64MPa for geopolymers from ZD–MK and ZG–MK respectively. This study shows that despite the low reactivity of volcanic scoria it can still be used to synthesize geopolymers with good physical and mechanical properties