Effect of paste volume on the performance of UHPC under the optimum grading of Yellow River sand

This study was undertaken in Kitui South in Kitui County in the south eastern parts of Kenya. The main objective of the study was to develop a spatial model that can be used for selection of suitable sites for sand dam in Kitui South. The study also assessed the spatial variation of sand grain sizes and how these determine the suitability of sites for the sand dams. Data analysis was done using three approaches. The first approach involved the use of the Remote Sensing (RS) technique where data was preprocessed and analyzed using Erdas Imagine software and Geographical Information Systems (GIS) for spatial modelling. The distribution of sand particle-sizes was based on sieve analysis on the sand samples collected from seasonal rivers in the study area. The seasonal rivers that were investigated in this study included Mwila, Kakya, Wiitu, Nguni, Ngunyumu, Muvuko, Kanzilu, Masaa, Katiliku, Ngulungu, Nzeeu, Koma and Katitika. Statistical analysis was done to establish the relationships between the various spatial components affecting sand particle distribution. The results from the spatial model which integrated all factors shows that 16% of the studied sites along the seasonal rivers in Kitui South were fairly suitable for construction of sand dams while 79% were classified as suitable and 5% are categorized as very suitable. Several sites in the central and the entire eastern parts of Mutha Ward were found not suitable for sand dam construction due to poor conditions such as the lack of suitable sand particles, lack of bedrock exposure on the riverbeds, flat terrain, very shallow stream banks, and weak soils on the riverbanks. Suitable sites for sand dams were found on the western and central areas of Kitui South where production and high accumulation of coarse sands was observed along the seasonal rivers. The areas near Mutomo hills and the rocky areas in Ikanga wards were found to be characterized by few excellent sites for sand dams. The optimum accumulation of different grades of sand in the seasonal rivers was found on streams with slope of between 1.5 and 6% that were dominated with 0 to 40% coarse sands, 0 to 30% fine gravels, 0 to 20% fine sands, and 20 to 80% medium sands. The accumulation of fine gravels was found to be closely related to the distribution of D30, D60 and D90 sand particle-sizes (0.4-4 mm) while accumulation of coarse sands showed good relationship with the distribution of the medium size sand (0.2-0.4 mm). The accumulation of medium sands was equally high when the occurrence of coarse sands was minimal. Different grades of sand were found to be strongly influenced by the changes in the elevation of the stream especially with regard to the accumulation of the medium sands (r=0.76) and coarse sands(r=0.75). Out of 80 investigated sites, 59% of them were dominated with uniform sands (Cu 5). The study also found that 86% of the sites along the seasonal streams were dominated with medium sands while 10% were dominated with fine sands and the rest (4%) dominated by coarse and gravelly sands. From the results this study concludes that 59% of the 80 sites that were investigated in this study have a high potential for providing suitable sites for sand dams in Kitui South.

Conventional engineered cementitious composites (ECCs) are produced with low-volume and expensive ultrafine silica sand (maximum size 250 µm), which imposed negative influence on dry-shrinkage, cost and the practical application of ECC. In this study, an economical ultra-high ductile engineered cementitious composite featuring large-particle and high-volume ordinary river sand (RS) is developed. The gradation of ordinary river sand is consistent with that of fine aggregate in traditional concrete and its maximum size (4750 µm) is almost 20 times that of ultrafine silica sand (USS) in traditional ECC. Price of RS is about 1/30 of that of USS. The experimental results show that all river-sand ECCs (RS-ECC) present the strain-hardening and multiple-crack phenomena. Especially, the average tensile strain of RS-ECC with maximum sand size of 4750 µm and a sand/binder ratio of 0.55 is over 9%. Meanwhile, the cost of composites is reduced by more than 10%. The pseudo strain-hardening (PSH) indices of RS-ECCs are more than 30, which indicates that replacing USS with high-volume and large-particle RS in ECC is sufficient to meet the requirement of the ultra-high ductility although the use of RS increases the fracture toughness and decreases the fiber bridging complementary energy.

Recently, interest grew on the quality of aggregates following the diminution of primary resources from river as to grow construction demand and the low grade of nature sand like sea sand. following, need is to diversify the supply sources of fine aggregates which are excessively relying on sea sand and urgency is to find as soon as possible aggregate resources that can substitute sea sand. On the other hand, various fine aggregates we utilized to produce concrete in the domestic construction fields. However, few studies have been systematically investigated on the effects of such fine aggregates on concrete properties. Therefore, this study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the shrinkage, durability and watertightness of concrete. Results revealed that drying shrinkage increases, and durability and watertightness degrades for concrete using crushed sand than natural fine aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting bad grain shape and grade was larger adverse effect on the quality of concrete. In addition, appropriate adjustment of the grain shape and grade during the blending of crushed sand exhibiting bad grain shape and grade with natural aggregates appeared to enhance the shrinkage and durability of concrete.

Ball grid array solder joint reliability is known to be dependent on the shape of solder joints after reflow. To ensure good solder joint formation and prevent solder bridging, it is critical to understand the amount of paste volume needed during assembly and reflow. The final shape of the solder joint is a function of surface tension, wetting area, gravity, and applied forces. In this paper, a new methodology to simulate solder joint shape is presented. Large deformation viscoplastic finite element analysis is used to simulate incompressible fluid flow. A numerical model for surface tension is outlined and validated with closed-form solutions. The results of the numerical model are compared to other known solder joint shape prediction methods. The effects of package weight, coplanarity, warpage, paste volume, pad misregistration, and joint construction on solder joint shape are then analyzed. Recommendations are provided on ways to maximize standoff height and avoid bridging. Finally, the formation of leadless solder joints is studied and compared to experimental data.

SAC (Sn-Ag-Cu) solder joints are frequently exposed to thermal cycling, leading to microstructural evolutions that accelerate thermal fatigue. During thermal cycling, the coarsening of Ag<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>Sn precipitates and recrystallization occur, impacting the reliability and microstructure of solder joints. To enhance the high-temperature performance of lead-free alloys, dopants such as Bismuth (Bi), Antimony (Sb), and Indium (In) have been proposed by leveraging the solid solution and dispersion-strengthening mechanisms. However, limited studies have investigated the impact of varying paste volumes of third-generation alloys on thermal cycling reliability and the resulting microstructural evolution. This study examines the thermal cycling reliability of three CABGA208 components mounted on a printed circuit board (PCB) using three different paste alloys, namely SAC305, SAC-Bi, and SAC-Bi-Sb, while maintaining fixed 18-mil SAC305 solder balls. Three paste volumes were printed to achieve paste-to-sphere-volume ratios of 0.1, 0.3, and 0.5. The PCB was plated with Electroless Nickel Immersion Gold (ENIG) and Organic Solderability Preservative (OSP) surface finishes. Thermal cycling tests were conducted between -40 °C and +125 °C, with a dwell time of 15 minutes and a ramp rate of 10°C/min. Weibull analysis revealed that doped alloys outperformed SAC305, with SAC-Bi exhibiting the highest reliability. A higher paste-to-sphere volume ratio generally improved reliability, except for SAC-Bi-Sb, where larger voids formed at higher paste volumes. The ENIG surface finish provided better performance than OSP, likely due to the beneficial effect of the Ni layer. Microstructural analysis showed that higher paste volume in SAC-Bi and SAC-Bi-Sb significantly reduced Ag<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>Sn coarsening. Additionally, increased paste volume resulted in a thinner intermetallic compound (IMC) layer and less evolution.

Experimental and mesoscopic investigation of self-compacting rubberized concrete under dynamic splitting tension

The Yellow River basin is an important economic zone and an important ecological barrier in China. The ecological environment protection of the Yellow River basin is an important direction for the development of ecotourism. Promoting the ecological protection and high-quality development of the Yellow River basin through ecotourism can realise the rational utilisation of ecological resources development and environmental protection functions. This paper takes wetland scenic spots as the main research object, and under the guidance of high-quality development theory, environmental education theory, education evaluation and other related theories, conducts field research on the current situation of eco-tourism environmental education in wetland scenic spots in the Yellow River basin. Based on the expert opinions and literature analysis, the evaluation index system of ecotourism environment of wetland scenic spots in the Yellow River basin is constructed. The Yellow River estuary and sand lake ecotourism scenic spots are selected as the case sites, and the entropy weight fuzzy comprehensive evaluation method is used for comprehensive evaluation, and the reasons for the evaluation results are analysed. This model has laid a theoretical foundation for the research on the high-quality development of ecotourism along the middle and lower reaches of the Yellow River in the context of big data.

Compared with the river sand, manufactured sand’s particle type and gradation is relatively poor and the surface is mat .The manufactured sand also has a big effect on the workability of concrete. In this paper,the Equivalent powder paste’s volume of manufactured sand concrete was determined according to Mehta and Aitcin’s ideas for the preparation of HPC,at the same time,the equivalent powder paste volume is assumed as the cement paste volume in the experiment. The influence of polypropylene fiber on Manufactured sand concrete’s workability and Compressive strength were researched in the case of fixed powder paste .

The disposal of the huge volume of glass waste is one of the significant environmental issues that need to be addressed. One of the efficient ways to solve this problem is to incorporate ground glass waste in concrete mixtures. However, its inherent surface smoothness and microcracks within the glass particle harm the hardened properties of concrete. Minimizing the particle size and controlling the amount of cement in the mixture can reduce the adverse effect of using glass in concrete. This study utilized ground glass waste (850 μm) as aggregate filler in a concrete mix. More specifically, this study investigated the effect of paste volume (Vp) on the properties of fresh and hardened concrete with ground glass waste as aggregate filler. Based on the test results, ground glass waste as aggregate filler negatively affects the workability of fresh concrete, but increasing the amount of paste can mitigate it. Vp values in terms of void volume (Vv) in the aggregates of 1.6Vv and 1.8Vv achieved satisfactory consistency of fresh concrete. In addition, the concrete compressive strength increased when increasing Vp. The test results have shown that ground glass waste has the potential to be utilized as aggregate filler in concrete mixtures.

Mechanical and durability properties of sisal-Nylon 6 hybrid fibre reinforced high strength SCC

Multi-layer casting of self-consolidating concrete: Influence of mortar rheology and casting parameters on the inter-layer bond strength

PurposeSolder paste printing is the most common method for attaching surface mount devices to printed circuit boards (PCB), and it has been reported that a majority of all assembly defects occur during the stencil printing process. It is also recognized that the solder paste printing process is wholly responsible for the solder joint formation of leadless package technologies such as land grid array (LGA) and quad-flat no-lead (QFN) components and therefore is a determining factor in the long-term reliability of said devices. The aim of this experiment is to determine the acceptable lower limit for solder paste volume deposit tolerances during stencil printing process to ensure both good assembly yield and reliability expectations.Design/methodology/approachStencils with modified aperture dimensions at particular locations for LGA and QFN package footprints were designed to vary the solder paste volume deposited during the stencil printing process. Solder paste volumes were measured using solder paste inspection system. Low volume solder paste deposits were generated using the modified stencil designs to evaluate assemble yield. Accelerated thermal cycling (ATC) was used to determine the reliability of the solder joints. Failure analysis was used to determine if the failure was attributed to the low paste volume locations.FindingsSolder joints formed with nominal paste volume survived longer in ATC compared to intentionally low volume joints. Transfer efficiency numbers for both good assembly yield and good reliability are reported for LGA and QFN devices. A lower volume limit is reported for leadless devices that should not significantly affect yield and reliability in thermal cycling.Originality/valueVery little literature is available on solder paste volume tolerance limits in terms of assembly yield and reliability. Manufacturers often use ±50 or ±30 per cent of stencil aperture volume with no evidence of its effectiveness in determining yield and reliability of the solder joints.

Uneven surfaces of sand particles provide ideal opportunities, under arid conditions, for runoff to be stored in the voids of sandy riverbed of ephemeral river. Series of laboratory experiments were performed to study major controlling parameters of sedimentation in sand water storage in order to optimize storage potential. Analysis was based on coefficient of uniformity of grain size distributions of deposited sediments. Ideally, desirable sediment grade for optimal water storage in sand reservoir is uniform sand grade with coefficient of uniformity less than 5. The results can be used to determine height of weir given required grade of sand and the flow conditions. Key words: Floodwater harvesting, sedimentation, sand river, groundwater storages.

Understanding the source‐to‐sink relationship of a large river‐marginal sea system is key to using marginal sea sediments to infer terrestrial erosion/weathering variations. The Zambezi River, the largest river in the southern African region, has been transporting large amounts of sediments to the southwestern Indian Ocean since the Cretaceous, which have been often used to infer river integration history and uplift of the southern African region. Thus, characterizing the geochemical features of different parts of the river is the key to correctly interpreting terrestrial sediment signals in the southwestern Indian Ocean drill cores. Here we present the first provenance study based on Sr‐Nd‐Hf isotopic results of river sands from mainstream and tributaries of the Zambezi River. We find that the isotopic signatures of the river sediments are largely consistent with its underlying basements of the different reaches, which suggests the local geology control of the river sedimentary provenance. This result is in line with the studies of the provenance of the Yellow and Yangtze Rivers, which suggest that sediments transported by the upper reaches of large rivers draining interior continents are primarily stored in sedimentary basins on land instead of marginal seas. This study suggests caution must be taken in using sediments of marginal seas to infer erosion history of the hinterland mountain uplift and exhumation.

The present study focus on the systematic design methodology for producing a self-compacting concrete (SFRSCC) consisting of steel fibre reinforcements. It is intended to achieve a self-consolidating concrete which can yield dual benefit of self-consolidating properties as well as toughness of the composite. Experimental modelling consisted of designing the mortar phase using manufactured sand (M-sand) as fine aggregate using systematic mix design methodology based on particle packing concept. Optimisation of aggregates was arrived based on packing density concept by conducting slump cone studies. Powder combinations consisting of cement and ground granulated blast furnace slag (GGBFS) were selected by conducting paste consistency test. Finally, superplasticizer dosage was fixed based on Marsh cone studies and volume fraction of steel fibres from slump flow studies. The workability of standard and high strength concrete is affected by the inclusion of steel fibre dosage and the fresh properties revealed the importance of maintaining a high paste volume for better flow ability. Based on the proposed mix design methodology with M-sand a high strength self-compacting concrete was achieved upto 70MPa. Experimental investigations were reported on the other assessment made from fresh and hardened properties of designed self-compacting steel fibre concrete mixes. Also, the outcome of test results revealed the possibility of using M-sand as an alternative for complete replacement of river sand.