Marbles and schists from Bidzar (North Region of Cameroon) : characteristics and the use of schists as additives in blended cement production

Abstract

Abstract This work presents the petrography et major element composition of marbles and schists found at the Bidzar CIMENCAM marble quarry (North Region, Cameroon). Part of the studied rocks were selected and combined with other characterized raw materials to process schist-blended cements. Marbles are white, yellow, pink, light to dark-grey, or dull yellow, pure or impure, calcitic, dolomitic or transitional type; with CaO (32–57 wt.%), MgO (0.49-24 wt.%), and SiO2 (0.09–8.4 wt.%). Schists are bluish-green chlorite schist, chlorite-bearing dark-grey schist, and yellowish-green sericite schist with SiO2 (26-47.3 wt.%), Al2O3 (11–16 wt.%), Fe2O3(8–15 wt.%), CaO (3–26 wt.%), and MgO (4–15 wt.%). The used cement raw materials include: clinker, gypsum, marble additive, low CaO bluish-green chlorite schist and low CaO chlorite-bearing dark-grey schist. Clinker, gypsum, and marble are all good for cement production. The two groups of manufactured blended cements are mainly composed of CaO (64.2–64.6 wt.%), SiO2 (18.0-18.5 wt.%) with significant and variable Al2O3, Fe2O3, MgO, SO3, and Na2O + K2O contents; all within the range in ASTM standard, and some reference cements. The LSF (1.11–1.15), HM (2.6–2.8), SAR (4.6–5.1), SR (2.8–3.1), and AR (1.5–1.7) varying from one group of cements to another, fall within the range of some reference OPC. The proportion of free lime (0.92–1.25%) in both processed cements, is within the range 0.8–2.25% for reference cement Multi X (CEMIX32.5R). The proportion of SO3 (1.6 to 2.3%,), LOI (8.9–13.8%), and IR (1.3-6.0%) in bluish-green schist-blended cements, range from 1.7 to 2.2%, 8.9 to 13.7%, and 1.3 to 10.6%, in dark-grey schist-blended cements. Part of these values are within those of reference cement and other OPC. The BSSA (4794 to 5794 cm2/g) and proportion of retained sieved fractions (4.13 to 11.1%) place the processed cements within high fineness type. The setting time (130–245 min) seem to satify cement standards. The compressive strength tests show a decrease in strength with the increase in proportion of schist; which could be due to the mineralogical composition of the used cements and their high IR.