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The article presents the results of testing models of rigid pavements for agricultural airfields from hexagonal slabs in laboratory conditions. Models of slabs were made of concrete on the basis of Portland slag cement grade 300. The optimal composition of concrete was chosen. For this, samples were made, having the shape of a cube, with dimensions of 10 x 10 x 10 cm. They were tested for compressive strength at ages 1; 3; 7 and 28 days. The results of three series of experiments with three groups of samples are presented. The first group was made from concrete without the introduction of plasticizing additives into it, the second-from concrete with the addition of calcium chloride (CaCI2), and the third with the addition of the superplasticizer naphthalene-formaldehyde type (C-3). It was found that the highest compressive strength have samples in which additives of superplasticizer C-3 were introduced. Models of slabs were made of concrete with this additive. Relations between the parameters of a hexagonal plate and the parameters of its model are established on the basis of existing modeling methods. The results of tests of five models of plates are presented. Two of them were loaded with a central load, and the other three with a load applied in a corner. The analysis of the nature of the destruction of models under different loading methods is carried out. It has been established when the plate model is loaded with a central load, radial cracks first appear in it. However, they did not lead to the loss of the bearing capacity of the model, and the load could be increased further. With a further increase in the load, the formation of ring cracks occurred. This led to the complete destruction of the plate model. When testing plate models for an angular load, only ring cracks appeared on their upper surface. As a destructive load, such a load was taken at which the first hairline crack appears on the surface of the model. It is concluded the destruction of the centrally loaded model of the slab occurs at a load exceeding on average 1.2÷1.3 times the breaking load when loading the corner of the model. [ABSTRACT FROM AUTHOR]

This work presents the results of the evaluation of Sesame Stalk Ash (SSA) used as partial replacement for Ordinary Portland Cement (OPC) in concrete. SSA was used to replace OPC by weight ranging from 0 to 20% at intervals of 5% replacement using the concrete mix ratio (1:2:4). Experimental tests such as setting times, consistency, soundness, XRF and slump were carried out to determine the properties of SSA-cement paste and fresh concrete respectively. Likewise, compressive strength test was carried out on 100mm cubes after 7, 14 and 28 days curing. However, from the result obtained it indicates that both the Initial and Final Setting Time increases with an increase in the percentage of Sesame Stalk Ash (SSA). The values of soundness obtained at each replacement levels falls within the acceptable limit specified by BS EN 196-3 (1995). Also, XRF conducted on SSA indicate that the content of Silica (SiO2) is 11.636 %, Aluminium oxide (Al2O3) is 3.005 % and Ferrous oxide (Fe2O3) is 0.982 % sums up to (15.623 %) which is less than the minimum value for a good Pozzolanic material. Therefore, SSA is of low Pozzolanic reactivity (ASTM C618, 2008). It was also confirmed from the research that the compressive strength of concrete decreases with an increase in SSA content. On the other hand, it increases as the curing age increases. The 5, 10, 15 and 20 % replacement of cement with SSA respectively gives a compressive strength of 15.55N/mm², 9.08N/mm², 6.00N/mm², and 5.50N/mm² at 28 days of curing. However, the 5 % replacement gives the optimum compressive strength of 15.55N/mm². [ABSTRACT FROM AUTHOR]