Proportions Of Different Sizes Research Articles

Developing a novel mix design methodology for slow hardening composite cement concretes through packing density approach

In the recent decades, partial replacement of Ordinary Portland Cement (OPC) with pozzolanic materials gained more importance compared to plain OPC due to several advantages in terms of performance and sustainability. However, it is well known that the replacement of pozzolans in OPC, results in delayed strength particularly, at early ages due to slow pozzolanic activity compared to cement hydration. However, in case of pozzolanic concrete mixes, a better packing of aggregates is found to improve the compressive strength apart from the beneficial properties in terms of durability and sustainability. In this study, Composite cement (CC), a ternary blended cement with replacement of fly ash (FA) and granulated blast furnace slag (GBFS) is used in design of concrete mixes. The amounts of OPC, FA and GBFS in CC were optimized based on packing density and compressive strength results. Four mixes of CC concrete were prepared with different values of packing densities of aggregates (0.80, 0.75, 0.70 and 0.65) with two combinations each having coarse and fine aggregate dominant and with three water to binder ratios (0.45, 0.50 and 0.55). It was identified that at the same level of packing density, with variation in proportions of different sizes of aggregates within the domain of extreme size range, the difference in compressive strength was found to be insignificant. Hence, a tri-relationship between compressive strength, water to binder ratio and packing density of aggregate system is established for proposing a new concrete mix design approach. Compressible Packing Model (CPM) is used in proportioning the coarse and fine aggregates to achieve the required packing density. As increase in the compactness of aggregate system results in low workability, the correlations were established between the parameters influencing the workability of concrete such as water to binder ratio, coarse to fine aggregate ratio, packing density, binder to aggregate ratio and dosage of superplasticizer. Packing density of aggregate system was found to have a strong positive correlation with compressive strength (R2 = 0.957) and strong inverse correlation with workability of concrete (R2 = 0.815) compared to other parameters. A relationship between workability and packing density is established for different water to binder ratios for designing CC concrete mixes. This approach was found to be more flexible and provides different possible alternatives of packing density, water to binder ratio and workability for the same target compressive strength useful for the concrete designer. Efforts are made to understand the influence of proportioning of different sizes of aggregates in designing the concrete mix. The binder paste content is determined by the volume of voids present in between the aggregates. Tests on slump and compressive strength were carried out on concrete mixes. The concrete mixes having higher aggregate packing densities were found to give higher compressive strength at all ages of curing with lesser binder consumption. Since, the packing density decreases the binder content per unit compressive strength, it was found to have a strong correlation with binder intensity index with R2 = 0.944. It was also noticed that, at 90 days, the compressive strength of all the CC concrete mixes has increased between 1.2 and 1.3 times of 28 days compressive strength due to slow pozzolanic action.

Cataloging Cowries: A Standardized Strategy to Record Six Key Species of Cowrie Shell from the West African Archaeological Record

Two species of the cowrie shell, Monetaria moneta (Linnaeus, 1758) and Monetaria annulus (Linnaeus, 1758), repeatedly occur in archaeological contexts across West Africa. Despite their archaeological and ethnographic importance, these shells remain poorly and inconsistently reported in the archaeological literature. The absence of standardized data on species composition, size, and condition of cowrie assemblages, and whether and how the shells were modified, make it difficult to examine their significance in a regional and chronological framework. To address this problem, we propose a set of standardized criteria and coding system for recording cowrie assemblages—in particular, species, size, condition, and state of modification. We aim to enable nonshell specialists within the wider archaeological community to securely identify intact or modified specimens of M. annulus and M. moneta, showing how these can be distinguished from four cowrie species native to West Africa—Luria lurida (Linnaeus, 1758), Zonaria zonaria (Gmelin, 1791), Zonaria sanguinolenta (Gmelin, 1791), and Trona stercoraria (Linnaeus, 1758). We demonstrate how accurate species identification and the assessment of proportions of different sizes of shells within suitably large assemblages can provide insight into their provenance. This information can enhance our appreciation of the exchange networks within which these shells moved. We also identify five different strategies documented in the archaeological record that were used to modify cowries, detailing how these can be differentiated and classified. The aim here is to suggest a recording strategy that will enable comparisons of the use and value of cowries in West Africa and elsewhere.

Impacts of natural polymer derivative neutral polysaccharide Jag S and cationic hydroxypropyl polysaccharide Jag C162 on rainfall infiltration on an experimental loess hillslope

ABSTRACT Developing effective measures to improve soil structure and increase soil infiltration in the Loess Plateau located in arid and semiarid areas is important for soil and water conservation. Simulated rainfall experiments were conducted to determine the effects of two new natural polymer derivatives, namely neutral polysaccharide (Jag S) and cationic hydroxypropyl polysaccharide (Jag C162), on rainfall infiltration and their underlying mechanisms. The proportions of different sizes of water-stable soil aggregates were analyzed after spraying four different concentrations (0, 1, 3, and 5 g m−2) of Jag S and Jag C162 under rainfall intensities of 1, 1.5, and 2 mm min−1 and a slope gradient of 15°. Treatments with Jag S and Jag C162 significantly improved the rainfall infiltration rates (IRs) compared with the control. Moreover, applying 1 and 3 g m−2 Jag S effectively increased the IRs by 22.81% and 13.69%, respectively. Treatment with Jag C162 also increased the rainfall IRs by 39.47%, 46.59%, and 46.50%. Furthermore, the content of >0.25 mm water-stable soil aggregates increased from 27.19% to 90.42% before rainfall and from 9% to 50% after rainfall. Compared with Jag C 162, treatment with Jag S was less effective on improving rainfall infiltration and aggregate content. In particularly, application of 5 g m−2 Jag S improved the soil aggregate content but weakened rainfall infiltration because of the higher viscidity and consistency of the Jag S solution. Overall, spraying appropriate amounts of Jag C162 and Jag S on the loess slope surface can increase the water-stable soil aggregate content, resulting in improved rainfall infiltration and reduced soil erosion. Thus, application of two new natural polymer derivatives is a possible alternative conservation practice in the Loess Plateau.

Comparing size‐limit strategies for exploitation of a self‐thinned stream fish population

There is increasing evidence that territorial stream fish populations exhibit some degree of self‐thinning. Four size‐limit strategies were examined, under which a size‐structured model population exhibiting self‐thinning was exploited. The effects of: (1) increased minimum‐size limits; (2) protection of spawners; (3) decreasing maximum‐size limits; and (4) slot limits (prescribe lower and upper size limits of fish that must be released) were analysed in terms of population size and mean body size in the population after harvest. Biomass and numbers harvested, mean size of fish taken and proportions of different sizes in the population after harvesting were also analysed. Combinations of high exploitation rates and high minimum‐size limits maximized both the number and biomass harvested while it favoured post‐harvest abundance and the proportion of larger sizes in the population. When harvest rates and minimum‐sizes were increased, the combinations of these that maintained or increased yield were successively narrowed. Protection of spawners and slot limits did not come close to reaching the levels of post‐harvest abundance, yield, positive size structure and endpoints of harvest rates that were obtained with a high minimum size applied to the fishery. Maximum‐size limits favoured the abundance of smaller size‐classes. The results emphasize the advantages of setting the largest sizes of fish in the population as a minimum size that can legally be retained.

Foraging behaviour of Carcinus maenas on Mytilus edulis: the importance of prey presentation

The manner in which mussels, Mytilus edulis, are presented to Carcinus maenas significantly influences crab prey-selection, resulting in different foraging behaviour. Handling techniques, breaking and handling times, percentage flesh eaten and prey value curves were compared when mussels of the following size-classes, 5–10, 10–15, 15–20, 20–25, 25–30 mm shell length, were presented singly and when they were presented as part of a group to crabs of 30–55 mm carapace width. When prey were presented singly, crabs used four size-specific opening techniques; outright crushing and directed crushing were used on smaller prey whilst boring and edge-chipping were used on larger, more resistant mussels. However, when mussels were presented as part of a group, boring and edge-chipping were never observed since larger mussels were not consumed. Handling time increased exponentially with mussel size irrespective of how mussels were presented, but, when crabs fed on mussels presented as part of a group, handling times tended to be shorter than when they fed on similar-sized mussels presented singly. The median percentage of flesh left uneaten in discarded shells ranged between 9.58 and 25.25% and was significantly greater than the median percentage of flesh left in the shells of mussels presented singly, which ranged between 4.66 and 14.70%. All resultant prey value curves were convex in shape, but the predicted optimal prey size altered with modifications in prey presentation. Similarly, when crabs of 30–65 mm carapace width were presented with groups of mussels comprised of different proportions of different sizes of mussels, size-class vulnerability was not fixed but altered significantly with the relative proportions in which these were presented. Thus, when the relative number of mussels in the smaller size groups were increased so was their vulnerability, indicating that prey size preference is flexible and not fixed.

The number and size of axons in the thoracic connectives of the desert locust, Schistocerca gregaria forsk.

1. EM mosaics have been built up to give transverse sections of the connectives between the suboesophageal and prothoracic ganglia, pro- and mesothoracic, meso- and metathoracic, and metathoracic and first abdominal ganglia of the desert locust. 2. The number of axons in each connective, and the proportion in each of 5 size categories are given. The meso/metathoracic has the most, about 8000, and the metathoracic/abdominal the fewest, about 2500. The proportions of different sizes are approximately constant. About 60% of all axons are less than 1 micron in diameter, and a further 25% less than 2 microns; less than 5% exceed 5 microns. 3. There is a “small axon area” on the periphery containing most of the smallest fibres (nearly half the axons in the connective) and occupying less than 5% of the cross section. 4. No evidence was found of branching axons, synaptic areas or neurosecretion. 5. The components of the connectives are compared with those of insect ganglia. There are no big differences. The perineurium is continuous, but thinner, and the extracellular space reduced. There are no tracheoles.