Canola meal as a by-product from the vegetable oil production provides a protein-rich material which is available This study investigated the potential of Burkina Faso’s local kaolin clay in formulation of geopolymer bricks. The formulation used a mixture of raw clay and activator alkaline solutions with varying concentrations. Prismatic molds were used to shape geopolymerized adobes. The physicochemical characteristics of the samples, including water absorption, linear shrinkage, density, porosity and spray test, were determined after 28 days. According to the standard NF P 15-471 mechanical analyses revealed that the geopolymer, formulated from locally sourced clay and a (NaOH + sand) solution with 10M concentration, exhibited favorable performance characteristics essential for civil engineering construction. These include a maximum linear shrinkage of 5.31%, a density ranging from 1.607 g.cm-3 to 1.900 g.cm-3, porosity of 29.90%, acceptable mass loss following a rain erosion test of 0.56%, and excellent compressive strength of 28 MPa. Mineralogical characterization results demonstrated that all formulated bricks contain quartz, kaolinite, goethite and a novel phase Na2(AlSiO4)6(OH)2.2H2O.
The paper investigates the differences in the chemical composition of the selected Cem 1 cement brands in Kenya and their effect on mechanical properties of concrete. It also investigates if the differentiation in mechanical properties of concrete prepared from different cement brands affects its service life. Currently, there are nine cement manufacturers in Kenya, the majority of whom produce Cem 1 cement along with other grades. To achieve the desired objective, three cement brands; Cem A, Cem B and Cem C of Cem 1 were used in preparation of concrete samples for testing. Other concrete constituent materials; fine and coarse aggregates and steel were obtained from the local Kenyan market suppliers. The physical and chemical properties of the materials were investigated to ensure compliance with relevant applicable standards. Concrete of characteristic strength of 25N/mm2 derived from the DOE method was used. Concrete materials were batched by weight and mixed by a lab electric pan concrete mixer in batches of 0.009 m3 . The concrete batches were tested for consistency by the slump and compaction factor tests. For each brand of cement 9 cubes of 150mmx 150mm x 150mm for compression test, 9 cylinders of 150mm x 300mm for tensile strength were cast. After 24 hours the cast specimens were demolded and immersed in curing tanks for 27 days. Specimens for compression and tensile test were tested at 7,14 and 28 days. From the results in the research, the different Kenyan selected cement brands affect the compressive strength which influences the rate of infiltration of corrosion agents affecting the service life of reinforced concrete. The variation in chemical composition must be taken into account when formulating the concrete mix design for specific structural purposes.
Silicon multilayer thin films consisting of alternating amorphous SiOx (a-SiOx) and nanocrystalline silicon (nc-Si) layers were fabricated on p-type silicon substrates using a sol-gel spin-coating method. Boron-doped silicon powders, prepared through prolonged grinding, were mixed with a TEOS–ethanol sol-gel solution, and two nc-Si layers embedded in a-SiOx were sequentially deposited. The as-grown films were annealed at 100–400 °C and characterized using Raman spectroscopy, GXRD, FTIR, SEM, Resistivity and UV spectroscopy to analyze their structural, chemical, optical, and electronic properties. Annealing progressively enhanced crystallinity and increased the <111> and <110> grain sizes to ~11 nm and ~12 nm, respectively. Films annealed at higher temperatures showed a minimum mobility of ~37.5 cm²/V·s, maximum resistivity of ~7.35 Ω-cm, and a decreasing optical bandgap. Enhanced nanocrystal growth, reduced defects, and improved structural ordering intensified the 520 cm⁻¹ Raman peak. The multilayer architecture further strengthened these effects by offering additional nucleation sites, controlled nanocrystal confinement, defect-relaxing interfaces, improved phonon transport, and enhanced Si diffusion, resulting in superior crystalline quality.
The Larson–Miller constant (C) of martensitic steel, which is used as the Larson–Miller parameter, is considerably larger than the typically used value of 20 for many types of heat-resistant steels. To provide better understanding regarding this fact, an analytical formulation for the Larson–Miller constant is developed using a model based on interactions between moveable dislocations and elastic singularities in a system. To verify the proposed equation, eight types of Grade 91, 92, and 122 steels are used, whose maximum rupture life exceeds 1E5 h. Creep data are classified into 257 groups by temperature, stress, and strain or time. C values are obtained by applying multiple-regression analyses to time parameters that obey the exponential law, assuming a thermally activated process. C and Ccal are calculated for each data group based on an exponential law and a proposed equation, respectively. The statistical values for C and Ccal are as follows: ̄C=32.41, Cmin=7.87, Cmax=64.88, and (Ccal⁄C)=99.3%. Although (∆C)̄=(Ccal-C) ̅=0.02 is extremely low, the standard deviation of ∆C is large, i.e., 1.27. Results confirmed that the proposed equation can estimate wide-ranging C values, although the equation is expected to be improved. A major component of C for C>15 is an increase in the entropy change caused by elastic interactions between moveable dislocations and elastic singularities in a system.
The leading cause of deterioration in reinforced concrete structures is the corrosion of steel bars embedded in concrete in the aggressive environment. This includes carbonation of concrete due to high CO2 concentration, chloride rich regions such as in marine environments from the sea water or airborne chloride and the corrosive industrial zones. In the recent past, nano-materials have risen to lime-light as one of the promising class of materials providing good corrosion protection to reinforced concrete structures. This class of materials include nano-silica, nano-alumina, carbon nano-tubes, nano-clays, graphene oxide, nano-coatings, nano-inhibitors as well as nano-particles of metal oxides. The mechanism of action for these nano-materials depends on the type of material used. For instance, some may refine the pore structure of concrete and reduce the permeability of concrete. Others may enhance the interfacial transition zone between the steel reinforcement bars and concrete. All this helps to limit the ingress of harmful substances including moisture, chloride ions, carbon dioxide and oxygen. Yet some other types of nano-materials may provide a protective layer or barrier through absorption, adsorption or reaction with the steel rebar surface and/or improvement in the passive layer. Nanomaterials have a multi-functional role and may also improve the mechanical properties along with the improvement in corrosion related durability. They may also influence the electrical resistance and may provide a self-healing behavior as well. Despite all the advantages, some challenges remain to be overcome such as dispersion, long term effect, impact on environment, scale and cost-benefit ratio.
