Uchechi G. Eziefula

Closed-form solutions simplify the design of thick orthotropic plates, but their accuracy for plates with a free edge is unknown. This study developed one-term closed-form and multi-term series solutions of Alternative 1 Theory, with three-dimensional (3D) constitutive relations, for uniformly loaded rectangular orthotropic plates with a free edge. Ten support combinations, with the free edge parallel or perpendicular to the stiff direction, were analysed in 1,200 cases (E₁/E₂ = 5–40, a/t = 4–20, b/a = 0.5–3.0). A 3D Ritz solution, with deflections within 0.08% of exact, Lévy-type, and finite element solutions, served as the reference, and the series separated shape error from theory error. The converged series underestimated the 3D deflection by 4–19% at a/t = 4 and by up to 10% at a/t = 20. Its error was largest where the stiff direction spans between a clamped and a simply supported edge; there, it also overestimated the clamped-edge moment by up to 129%. Free-edge orientation governed the response. Plates with the free edge across the stiff direction deflected up to 1,050 times as much as their quarter-turned counterparts, and the one-term solution underestimated their deflection by 11–95% for b/a ≥ 1.0. The one-term formulas were within 10% of 3D elasticity in 319 cases, half of them for four plates with a/t ≤ 5 and b/a ≥ 1.0, partly through a cancellation of shape and theory errors. In thick plates, 3D face stresses at the free edge exceeded the linear values by up to 110%.

Classical plate theory (CPT)¹ is the default model for the bending of thin orthotropic plates, yet the span–thickness ratio beyond which it can be trusted is typically taken from isotropic experience. This study determines this ratio from three-dimensional (3D) elasticity for the 21 distinct orthotropic rectangular plates with clamped, simply supported, and at most one free edge, under uniformly distributed loading. A Ritz solution of 3D elasticity, validated against exact and finite-element solutions, was compared with CPT over 3,360 cases (E₁/E₂ = 5–40, aspect ratios 0.5–3, span–thickness ratios 4–100). The ratio needed for CPT to be within 5% of the 3D deflection ranges from 10 to 90, and the common threshold of 20 fails in 76% of the 420 combinations. For aspect ratios of 1.5 or more and the 15 plates whose fibres end on supported edges, the limit depends only on those two edges and scales with the square root of E₁/G₁₃. These limits follow a Timoshenko beam strip spanning the fibres, which is first-order shear deformation theory in cylindrical bending: the group averages agree within 0.3% and individual plates within 4.5% (9% in one case). This yields a closed-form rule: the square of the limit equals 0.96, 2.65, or 4.80 times E₁/(εG₁₃) for simply supported, propped, and clamped strips, where ε is the tolerance. The rule holds within 1.2% for graphite–epoxy, glass–epoxy, and glulam plates, and soft simple supports increase the limits by at most 3%. Plates with a free edge across the fibres and no clamped edge opposite it carry the load across the fibres and follow √(E₂/G₂₃) instead. Deflection governs the limit in 88% of cases; moments govern mainly when a free edge crosses the fibres.

This study evaluated the strength properties of concrete produced with palm bunch ash–calcined anthill clay (PBA-CAC) as pozzolans. Two groups of palm bunch ashes were produced: ashes generated by burning only palm bunches (PBA) and ashes obtained by blending palm bunches and anthill clay at elevated temperatures (PBA-CAC). The PBA and PBA-CAC satisfied the requirements of Class C pozzolans. The concrete constituents were batched by mass, and the cement–fine aggregate–coarse aggregate ratio was 1:2:4. The cement content was partially substituted with PBA and PBA-CAC at 5%, 10%, 15%, 20%, and 25%, with the 0% specimen serving as the control. The concrete cubes were cured for 7, 14, 28, 56, and 90 days, whereas the concrete cylinders and beams were cured for 7, 28, 56, and 90 days. The 28th day strength values of the control specimens exceeded those of the PBA and PBA-CAC concrete specimens. By the 90th day of curing, the strength values of the specimens produced with 5% PBA and 5% PBA-CAC exceeded those of the control specimen. The PBA-CAC specimens generally had higher values of compressive strength, splitting tensile strength, and flexural strength than PBA specimens containing the same amount of pozzolan.

Experimental investigation of behaviour of concrete mixed and cured with Nembe seawater

The inelastic buckling behaviour of different rectangular thin isotropic plates having a free edge is studied. Various combinations of boundary conditions are subject to in-plane uniaxial compression and each rectangular plate is bounded by an unloaded free edge. The characteristic deflection function of each plate is formulated using a polynomial function in form of Taylor–Maclaurin series. A deformation plasticity approach is adopted and the buckling load equation is modified using a work principle technique. Buckling coefficients of the plates are calculated for various aspect ratios and moduli ratios. Findings obtained from the investigation are found to reasonably agree with data published in the literature.

This study compared the physical and mechanical properties of river sand concrete with quarry dust concrete. The constituent materials were batched by weight. The water-cement ratio and mix ratio selected for the experimental investigation were 0.55 and 1:2:4, respectively. The specimens were cured for 7, 14, 21 and 28 days. Slump, density and compressive strength tests were carried out. The results showed that river sand concrete had greater density and compressive strength than quarry dust concrete for all curing ages. At 28 days of curing, river sand concrete exceeded the target compressive strength by 36%, whereas quarry dust concrete was less than the target compressive strength by 12%. Both river sand concrete and quarry dust concrete for the selected water/cement ratio and mix ratio are suitable for non-structural applications and lightly-loaded members where high strength is not a prerequisite.

Comparative analysis of mechanical properties of palm kernel shell concrete with periwinkle shell concrete is presented in the paper. The binder and fine aggregate were Ordinary Portland cement and river sand, respectively, while potable water was used for mixing and curing. The constituent materials were batched by weight. Concrete mix ratio was 1:2:4 and water/cement ratio was 0.5. Three groups of concrete mixes containing different coarse aggregates were tested: 100% palm kernel shells, 100% periwinkle shells, and 100% granite as control. Tests were carried out for bulk density and compressive strength of the concrete cubes at 7, 14, 21, and 28 days curing, respectively. The results revealed that for all curing ages, palm kernel shell concrete had lower bulk density and lower compressive strength than periwinkle shell concrete. The bulk density and compressive strength of the 28-day palm kernel shell concrete were 1840 kg/m3 and 14.02 N/mm2, respectively, those of periwinkle shell concrete were 1936 kg/m3 and 16.90 N/mm2, while those of granite concrete were 2496 kg/m3 and 25.95 N/mm2, respectively. Both palm kernel shell concrete and periwinkle shell concrete satisfied the bulk density and compressive strength requirements for lightweight aggregate concrete.

Concrete is the most popular man-made construction material in the world. However, there is a growing need to use sustainable recycled materials as replacement of conventional aggregate in concrete due to environmental and economic considerations. A possible solution to the waste management problem of agricultural and aquaculture by-products is to use them as an alternative aggregate in concrete. Agricultural and aquaculture by-products such as palm kernel shell, coconut shell, date seed, rubber shell, corn cob, rice husk, periwinkle shell, mussel shell, oyster shell, cockle shell and scallop shell have been used in experimental investigations as partial or full replacement of conventional aggregate in concrete. This paper is a literature review of recent developments in the utilisation of agricultural and aquaculture by-products as aggregate in concrete. Physical and mechanical properties of the by-products, as well as properties of by-product aggregate concrete in fresh and hardened states, are discussed. Trends, developments and possible barriers in using agricultural and aquaculture by-products as aggregate replacement materials in concrete are highlighted. It is recommended, among others, that detailed research on durability properties of concrete containing agricultural and aquaculture by-product aggregates should be carried out.