Sand Volume Research Articles

Sustainable Alternatives for Green Mortar: Quarry Waste and Ultra high fly ash utilization

The use of waste materials from different industries as a replacement of cement has gained much attention all over the world. In addition, many attempts have been done to replace partially or totally one of the ingredients from the mix design to lower the negative impacts of construction industry. In this study, quarry waste and fly ash were used as two different sustainable approaches to replace the maximum volume of natural alluvial sand and cement, respectively, in the traditional mortar matrix. The quarry waste is a by-product of quarries characterized with a large volume of fines, whereas, fly ash is the by-product of coal-fired electric generation plants. The performance of the green mortars containing the maximized volume of quarry waste and fly ash were evaluated with regard to the mechanical properties. The results have clearly indicated the beneficial use of the quarry waste and fly ash as a substitute for siliceous sand and cement respectively in preparation of green mortars. In addition, the cost and parametric analysis was also performed for a multi-story reinforced concrete building using the designed quarry sand and fly ash as concrete ingredients.

Shake Table Test of Scaled Masonry Structure Using Rubber Tire Crumbs Mortar

The existence of masonry walls in structures is very useful in increasing the structure's resistance to lateral loads. The role of the walls is more important in providing adequate stiffness and damping than in resisting axial forces. The use of rubber tire crumbs (RTC) mortar on masonry walls is to increase the ductility and damping capacity of the wall. This study examines the application of RTC mortar on masonry walls, in particular for increasing the damping ratio of the wall. This study aims to determine the optimum RTC content in mortar by observing its dynamic properties using the shake table test. The specimens were 4 scaled models with mortar containing 10%, 20%, 30%, and 40% RTC. The prototype is a 3D half-brick wall 2.5 m high and a 2.5 x 2.5 m² plane, with a scale of 2 to provide a miniature model. There are 2 types of loads, namely sinusoidal loads and Yogya earthquake loads. The sinusoidal load has an amplitude of 0.1g with a frequency range between 4 Hz and 20 Hz, while the Yogya earthquake load has an amplitude between 0.1 g and 0.9 g. The results showed that the use of RTC mortar on the masonry wall structures can increase the damping capacity of the walls and reduce the drift ratio. This study recommends that the optimum RTC content is 30% of the sand volume.

Effect of alongshore sediment supply gradients on projected shoreline position under sea-level rise (northwestern Portuguese coast)

Shoreline changes are associated with natural and anthropic factors, such as sea-level rise, sediment budget, and beach fills. Shoreline retreat is mainly related to sediment deficit and sea-level rise. Some studies show that by the end of the 21st century some beaches may be lost, with the erosion of sandy beaches becoming predominant across the globe. The main purpose of this work is to model the shoreline evolution for 2050 and 2100 along a sandy coastal stretch in the NW Portugal, considering different scenarios of sea-level rise, to evaluate the influence this parameter and sediment budget have on shoreline displacement, as well as estimate the nourishment volume necessary to hold the shoreline in case of shoreline retreat. For this, we applied the stochastic version of the Random Shoreface Translation Model (RanSTM), in four cross-shore topo-bathymetric profiles, which are representative of alongshore coastal compartments. The overall results indicate that the key drivers in shoreline migration along the coastal stretch are not the same for the different profiles; in areas with a sediment supply deficit, shoreline recession increases, and hence the volume of sand required to hold the shoreline position in those zones is much greater. In contrast, positive sediment budgets can mitigate or reverse the erosion caused by sea-level rise.

Wood ash versus expanded clay aggregate as internal curing water reservoirs in high performance concrete

The performances of expanded clay aggregate and wood ash as internal curing water reservoirs were studied in the mortar phase of a hypothetical high performance concrete with a low water-to-binder ratio. The two materials substituted the 15 and 30% of the sand volume. Two different binders, Portland cement and high-volume fly ash blended cement, were used. The compressive strength and the volume stability of the mortars in sealed and air-drying conditions were studied. Furthermore, the desorption capacity of the internal curing water reservoirs and the internal humidity inside the mortars during the first days after casting were analysed. The results shown that the reduction in the self-desiccation shrinkage was higher when the expanded clay aggregate was used, even in air-drying curing conditions, due to its higher desorption capacity in low-relative-humidity environments in comparison to that of the wood ash. However, wood ash had a stronger beneficial effect on early age autogenous shrinkage without significantly increasing the drying shrinkage. The two alternative aggregates influenced the strength moderately. Considering the technical, economic, and environmental implications of using the two lightweight aggregates, wood ash is recommended.

An experimental insight into dynamic characteristics and wear of centrifugal pump handling multi-size particulate slurry

The river water has a high sand content and the characteristics of mixed distribution of sand particles with different diameters. The effect of sand particles on the dynamic characteristics and wear of centrifugal pumps is an important issue when handling particulate slurry. The objective of this work is to establish the effect of flow rate and sand volume concentration variation on pump energy performance, outlet pressure pulsation, pump body vibration, and pump impeller wear. Experiments were conducted in a pilot plant test rig with five flow rates and three particle concentrations based on multi-size particulate slurry. It was observed that the head and efficiency of the centrifugal pump decrease with the increase of sand concentration, whereas the effect of small sand concentration on the energy performance of the pump is weak. The larger the flow rate of centrifugal pump, the lower the pressure pulsation and vibration intensity of pump body, but the more serious the impeller wear. When the sediment concentration increases, the pressure pulsation at the pump outlet and the vibration intensity of the pump body increase, and the impeller wear is more serious. In addition, with the increase of pump operation time, the outlet of blade pressure surface, the middle area of blade suction surface and the outlet area of impeller back shroud passage are seriously worn, and the outlet of blade pressure surface is the most serious.

Climate-driven dinoflagellate cyst stratigraphy of the Oligocene-lower Miocene turbidite succession of the Lower Congo Basin (offshore NW Angola)

Biostratigraphic studies of cuttings from wells located in the Lower Congo Basin, offshore northwestern Angola, document with unprecedented wealth of data the organic-walled dinoflagellate cyst (dinocyst) assemblages of the Malembo Formation. The identification of a series of dinocyst events (highest and lowest occurrences, influxes and acmes) recurring in the same stratigraphic position in different wells and cross-calibrated by calcareous nannofossil data, provides a tool for age control and correlation of the Oligocene and lower Miocene in the equatorial and South Atlantic region.Proceeding downwards in the stratigraphy of the examined succession, the lowest occurrence of Pyxidinopsis pastilliformis, detected within the CN3 nannofossil Zone, approximates the Langhian-Burdigalian boundary, whereas the lowest occurrences of Sumatradinuim druggii and Sumatradinium hispidum occur at the base of the CN2 nannofossil Zone in the Burdigalian. The lowest occurrences of Sumatradinium soucouyantiae and Barssidinium taxandrianum fall within the Zone of acme of Hystrichokolpoma rigaudiae at the Burdigalian-Aquitanian transition, and immediately above the acmes of Cribroperidinium tenuitabulatum and Systematophora-Cleistosphaeridium group that are supposed to reflect climate cooling pulse Mi-1a. The presence of Chiropteridium spp. and Membranophoridium aspinatum is limited to the upper part of the Chattian. An influx of Tuberculodinium vancampoae, possibly related to a warmer interlude during a period of overall climate cooling, occurs in proximity of the Chattian-Rupelian boundary. The nearly synchronous highest occurrences of Gerdiocysta conopeum, Eocladopyxis peniculata and Heterosphaeridium sp. provide a robust infra-Rupelian biohorizon. Further down in the Rupelian, the influxes of Pentadinium laticinctutm and Distatodinium paradoxum are interpreted as responses to cooling pulses. The lowest occurrence of G. conopeum, detected in the basal part of the NP23 nannofossil Zone, corresponds to the global first appearance of this excellent Rupelian marker. Genera Deflandrea and Wetzeliella are noticeably missing in the studied material just as they lack in some coeval dinocyst assemblages reported in the literature from low paleolatitude Atlantic sections.The recorded alternation of influxes and acmes of Gonyaulacoid dinocyst taxa indicative of cooler and warmer water conditions was probably climate-driven, i.e. paced by cooling pulses and relatively warmer interludes characterizing the climate evolution during the Oligocene and early Miocene. Indeed, the lack of acmes of Peridinioid cysts suggests that climate, rather than constantly elevated nutrient levels ensured by the Congo River discharge, was the discriminant factor triggering the observed blooms of Gonyaulacoid cyst-forming taxa.The delivery of large volumes of sands into deepwater settings via gravity-driven fluxes was favored by sea-level drops and is ultimately associated with pulses of climate cooling and Antarctic ice-sheet growth, finally reflected by the composition of the dinocyst assemblages. In addition to paleoecological factors, hydraulic fractionation resulting from sedimentary processes that transported palynomorphs down the slope as part of turbidite fluxes, contributed to shape the palynological assemblages observed in this study.

Evaluation of Lithological Influence on Seismic Wave Velocity in Part of Niger Delta, Nigeria

This study is aimed at evaluating the influence of lithology on seismic wave velocity in part of Niger Delta. A suite of geophysical well log comprising of gamma ray, sonic and density logs in Log Ascii Standard (LAS) format from two exploratory wells (OKO 5 and OKO 7) within the study area was used for this study. Gamma ray log was used to identity and delineate the lithology into shale and sand units, seismic wave velocity was categorized into compressional wave velocity Vp and shear wave velocity Vs. The former was computed from interval transit time while the later from compressional wave velocity. The results of this study show that seismic wave velocity is very much affected by difference in the lithology of formation. Compressional wave velocity (Vp) is higher than shear wave velocity (Vs) in shale and sand lithologies in the two wells. The values of the compressional wave velocity, shear wave velocity, percentage volume of shale and percentage volume of sand ranges from 3485 to 6620m/s, 2159 to 3932m/s, 2682 to 5323m/s, 1736 to 3161m/s, 11 to 60%, 13 to 59%, 40 to 89% and 29 to 87% for the two wells respectively. The knowledge of this study can be applied in civil engineering and engineering geophysics activities like foundation for high rise buildings, dams, bridges and road construction.

Mechanical behaviour of sandy soils embankments treated with cement and reinforced with discrete elements (fibres)

It is well known that the reinforcement of the Soil is considered as a solution to its stability problems. This technique ameliorates the mechanical and physical comportment of the soil. Based on this, this research paper aims at investigating the behaviour of a specific type of dried-cemented-sandy soil reinforced with discrete elements such as polypropylene fiber basically through experimental tests. The latter are a series of consolidated drained triaxial tests which were carried out on samples of sand that are prepared with 0, 3 and 6% of cement, reinforced with 1% of polypropylene fiber (12, 18 mm) randomly distributed. Furthermore, those contents are measured by the volume of dry sand. In addition to these tests, a parametric study has also been conducted on a road embankment using a finite element program such as Plaxis 2D in order to observe the variation of different parameters like safety factor and the displacements (Ut, Ux, Uy). The test results showed that the addition of cement and polypropylene fiber of different accommodations increased both cohesion and friction angle of sands while the numerical results indicated that the presence of these additions improved the safety factor and decreased significantly the displacements.

Experimental Investigation on the Fracture Conductivity Behavior of Quartz Sand and Ceramic Mixed Proppants.

In this paper, a series of fracture conductivity experiments were designed and conducted by an American Petroleum Institute (API) standard fracture conductivity evaluation system. The mixing proportion of quartz sand and ceramic was optimized. By the evaluation of the proppant breakage rate and sphericity analysis of mixed proppant with different sand volume proportions (PS), the proppant mixture conductivity evolution behavior was analyzed. Results of this study showed that the conductivity of mixed proppant was between that of pure ceramic proppant and pure quartz sand proppant under the same conditions. For 20/40 mesh mixed proppant, a small amount of ceramic (25%) in mixed proppant could obtain 1.27–3 times higher conductivity than pure sand, while 40/70 mesh mixed proppant required the addition of 50% or more ceramic. The crushing resistance of mixed proppant determined the decrease of conductivity with the increase of effective closure stresses. A logarithmic empirical model was further derived from the results, which could be used to forecast the performance of fracture conductivity at different effective closure stresses and sand volume proportions.

Mortar’s rheological property and workability investigation based on morphology impact factor for graded sand particles

The morphology of sand particles strongly influences mortar rheology properties. A characterizing method for the morphology indicator of graded sand particles was proposed by morphology testing and analyzing. Then, taking sand volume fraction as the weight of the morphology indicator of the graded sand particles, the morphology impact factor was put forward to characterize the comprehensive effects of morphology and quantity of graded sand particles on the mortar performance. The effects of morphology impact factor on mortar rheology properties, workability and strength were explored by rotational rheometer, slump flow, anti-segregation and strength testing. The results show that the proposed morphology impact factor is capable of characterizing morphology effects of graded sand particles, well correlated with yield shear stress and slump flow of the mortar, and the slump flow can be predicted in terms of the yield shear stress of the fresh mortar; when the morphology impact factor is between 0.86 and 1.08, the fresh mortar possesses good fluidity and anti-segregation performance. This research, based on rheology, contributes a new way to the mortar and concrete design manner.

Calculation of the Rub’ al Khali Sand Dune Volume for Estimating Potential Sand Sources

The Rub’ al Khali desert (or Empty Quarter) is the largest and perhaps most significant sand sea in the world. Located on the southern Arabian Peninsula, the dune field has remained largely unexplored owing to the harsh clime and difficult terrain. This study takes advantage of geospatial technology (interpolations, supervised classification, minimum focal statistic) to extract information from the data contained in global Digital Elevation Model (DEM)s, satellite imagery. The main objective here is to identify and map different dune forms within the sand sea, estimate the volume of sand and explore probable sources of sand. The analysis of dune color strongly suggests that the sand is not completely reworked and intermixed. If this is true, a spatial variability map of the mineral composition of the sand could be very revealing. The red sand is quite pronounced, the largest volume of sand (~36%) is associated with the yellow color class. Yellow sand covers most of the western part of the dunes field and seems to be a transitional color between red and white sand in the eastern part of the dune field. This suggests that the yellow sand might be derived from both local and regional sources, or it might be less oxidized, reworked, or have a different composition that represents a combination of red and white sand.

Factors Controlling Storm-Induced Morphology Changes at an Erosional Hot Spot on a Nourished Beach, Sand Key Barrier Island, West-Central Florida

Cheng, J. and Wang, P., 2022. Factors controlling storm-induced morphology changes at an erosional hot spot on a nourished beach, Sand Key barrier island, west-central Florida. Journal of Coastal Research, 38(4), 750–765. Coconut Creek (Florida), ISSN 0749-0208. Beach nourishment has become the dominant sandy shore protection method over the past 40 years. The performance of nourished beaches and therefore the design of renourishment projects are significantly controlled by the presence of erosional hot spots and storm impacts. Based on 5.5-year bimonthly beach profile surveys, along a nourished beach spanning an erosional hot spot, this study examines the hydrodynamic conditions of extratropical (winter) and tropical (summer) storms that cause significant morphology changes. The sand volume loss above the short-term closure depth averaged along the 1.8-km stretch erosional hot spot was 178 m3/m over the 5.5 years after the nourishment. A large portion of this volume loss was caused by several extratropical storms and Hurricane Irma in 2017, when the high, northerly approaching waves were associated with a depressed water level. The northerly approaching waves induced a large longshore sediment transport gradient along the generally north-south trending coast due to wave refraction over a nearby ebb tidal delta. The energetic Hurricane Irma induced a large negative surge and also transported sediment seaward beyond the short-term closure depth. On the other hand, during the passages of typical tropical storms, the southerly approaching waves superimposed on elevated water levels caused substantial beach volume loss above the mean sea level. The eroded sediment deposited on the nearshore sandbar, resulting in conserved sand volume above the short-term closure depth. Understanding the different beach response to extratropical and tropical storms would benefit beach management, especially under the circumstance of increasing storm activities due to climate change.

Field experiments of different fracturing designs in tight conglomerate oil reservoirs

Mahu oilfield is currently the largest tight conglomerate reservoir in the world, where Ma-131 and Ma-18 plays are the first two commercially developed reservoirs. In order to reduce the cost and explore the best fracturing parameters, field experiments have been conducted in these two plays since 2017. Types of proppant and fracturing fluid, the slickwater ratio, and the fracture spacing are mainly changed for comparison, and fracturing effects are evaluated to establish a reference for developing neighboring plays in the Mahu oilfield. This paper summarizes the fracturing parameters and production histories of 74 wells in Ma-131 and Ma-18 plays during four years of field operations. Firstly, results indicate that silica sands perform similar to ceramics in the Ma-131 play where the reservoir depth is smaller than 3300 m; however, in the Ma-18 play where the reservoir is deeper than 3500 m, increasing the sand volume by 1.1–1.2 times still cannot reach the production in wells using ceramics. Secondly, when the fracture spacing is reduced, both oil production and water flowback become even smaller in wells using sands than those using ceramics; this is due to the increase of closure pressure and decrease of fluid volume per cluster respectively. Thirdly, when the crosslinked guar is replaced by the slickwater, no obvious change in oil production is noticed even though the volume of fracturing fluid is almost doubled; limited lengths of propped fractures due to the poor proppant-carrying ability of slickwater likely offset the production enhancement from the decrease of formation damage by slickwater. This paper summarizes learnings from the field experiments during the four-year development of the Mahu oilfield, and help guide the optimization of hydraulic fracturing parameters for future wells.

About the self-sensing behavior of smart concrete and its interaction with the carbon fiber percolation status, sand connectivity status and grain size distribution

The addition of conductive fibers to ordinary cementitious matrix permits to reduce its electrical resistivity, and consequently create its self-sensing behavior. This guarantees to the smart concrete a multifunctional behavior, where it satisfies the structural and self-sensing expectations simultaneously.This study intends to provide a better understanding of the self-sensing behavior of smart concrete function of the connectivity of carbon fibers, sand particles structure and its grain size distribution. The results showed that for cement paste, over carbon fiber volume fraction range, sensibility presented two local peaks. For mortar, in presence of diluted sand and partially connected sand, local peaks persisted. In presence of 50 % of sand volume fraction, sensibility to external compression forces was significantly reduced.

EFFECT OF METAL FIBERS ON THE PROPERTY OF WELL CEMENT

Nowadays more oil and gas fields are developed in unconsolidated sandstone. When the formation consists of poorly cemented rocks, the connections between the rock particles are broken under the influence of forces acting in the bottomhole during oil production (wells), and the rock skeleton is intensively disintegrated and brought to the well by fluid flow. The sand production is considered undesirable product and the control of sand production is considered as one of the main concerns of production engineers. It can damage downhole, and surface production facilities, also increasing the risk of catastrophic failure. Choosing a method for preventing formation sand production depends on different reservoir parameters. The analysis of the production wells, where measures are taken to prevent the sand production, showed that the most effective method is to cover the bottom hole with various mortar materials. However, the current methods of bottomhole strengthening with cement mortars have a number of technological shortcomings which can include limited ductility and little resistance to cracking. According to the results, the efficiency of bottomhole reinforcement in the Absheron field is 40-50%. The reason for the low efficiency of this method is mainly the presence of lithostatic pressure and dynamic (perforation, sliding and lifting) loads applied to the cement barrier in the wellbore area. It is known that the weakest part of cement stone, prone to collapse and wear, is the perforation holes. During the oil production, the volume of sand increases that brought to the well, and around the perforation holes that on the cement stones are formed the collapses and fractures. Due to its low deformation and crack resistance, it cannot withstand these impact loads. Hence there is a need to reinforce the property of cement. The article presents the results of experimental studies of fiber-reinforced cement recommended for improving the quality of bottomhole coverage in increasing dynamic impact intervals. One of the promising directions to increase the resistance of the cement barrier under dynamic loads is its strengthening against compression and bending, using the principle of composition, which provides the compression resistance of the cement matrix. The most important properties of cement stone can be effectively regulated by using metal fibers, which allow implementation of the principle of composition in cement barrier. The main physical and mechanical properties of the cement burrier formed as a result of increasing the fiber concentration in the tampon solution change. Reinforcing metal fibers, uniformly distributed in the matrix and having different directions, received forces in any direction, preventing the formation and development of cracks in the cement stone. The metal fibers are randomly oriented and uniformly distributed throughout the volume, work together with the matrix due to the adhesion forces, and form a compact shape. When fiber adhesion is disrupted, the fibers prevent the growth and development of cracks by maintaining the integrity of the cement stone. Based on this principle, a new dispersion-enhanced buffering material consisting of a mixture of quartz sand and metal fibers was developed. Experiments were carried out to improve the physical and mechanical properties of the cement system (strength, fluidity, setting time, etc.) in the laboratory. Studies have taken a certain proportion of the water-cement mixture. Metal fibers of different quantities and lengths were added during the experiments to determine the mechanical properties of the cement stone. The test period, day and the curing temperature performed at different intervals according to the mixtures. The article shows the positive effect of fiber on the main properties of buffering solutions and the resulting stone, both theoretically and experimentally. The choice of the optimal method of cement stone reinforcement is the result of laboratory experiments. Following the results obtained, recommendations were given for the optimization of cement compositions. Keywords: cement stone, cement barrier, well area, dynamic loads, fiber, reinforcement, destruction, deformation, expansion.

Agglomerative clustering to improve the resolution of pseudo well stochastic seismic inversion: A case study

The Monte Carlo rejection and Monte Carlo Markov Chain methods are two common sampling techniques in Bayesian seismic inversion. Conventional methods of pseudo well stochastic seismic inversion for reservoir properties uses Monte Carlo rejection sampling of pseudo-wells to select those that best match seismic traces. The selected pseudo-wells do not influence the selection/rejection of subsequent pseudo-wells. The process requires a very large number of prior pseudo-wells to draw a reasonable outcome, which consumes a major part of the computation time. In conventional methods, the best-matched pseudo-wells often have dissimilarly shaped volume of shale logs, which can degrade the resolution of the outcome. Though Agglomerative clustering is well-known but the idea of grouping pseudo-wells based on similarly shaped volume of shale logs in pseudo well stochastic seismic inversion is unique. We propose an agglomerative clustering technique to group the prior pseudo-wells according to the shape of their volume of shale logs, before matching to seismic. The centroids of the pseudo-well clusters summarize the large number of prior pseudo-wells. The best-matched pseudo-well cluster centroid with seismic gives the most likely outcome while the two next best-matched cluster centroids give alternative results. The alternative results are useful to understand the uncertainty in the outcome. It has been observed that, the proposed method has reduced computation time (50–55% less than conventional pseudo well stochastic inversion). Meanwhile, the quantification of sand volume from the proposed method shows improvement over the conventional method. A comparison between the proposed and the conventional method has been shown on a synthetic wedge model and real seismic. In the wedge model (volume of sand is 0.65), the resultant volume of sand predicted in the modified method (0.7) is better than that predicted using the conventional method (0.8). The modified pseudo-well stochastic seismic inversion method has been applied on seismic data from deepwater Krishna-Godavari basin. The result shows an improvement in the characterization of thin shale layers within the reservoir.

Determination of shielding Effectiveness of Concretes with different Aggregate and cement composition

The shielding effectiveness of concretes with different aggregate and cement composition was determine by shielding Co-60 gamma radiation source at center for energy research and training (CERT), Ahmadu Bello University Zaria with block concretes that contain aggregate 5.00 mm, 10.00 mm and 15.00 mm respectively. A concrete with thickness of 0.0762 m with dimension of 0.30 m x 0.30 m was formed from each of the aggregates with equal volume of sharp sand and cement. The result revealed the calculated mean free path (MFP) with values within a range of (0.033 to 0.070) m for samples DG (Dangote) and BU (BUA), mass attenuation coefficient (MAC) and half value layer (HVL) values within a range of (1.9 to 2.75) x 10-3 m2/kg and (0.023 to 0.049) m respectively. This shows that samples DG1, DG2 and DG3 have better shielding ability due to its lower MAC, MFP and HVL compared to samples BU1, BU2 and BU3.

Equal Volumes of Sand and Gravel Concrete Mix Ratios in Cameroon and Its Effect on Concrete Compressive Strength

In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive test results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm2 for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m3 of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.

Headcut erosion characteristics revealed through simulated rainfall and scouring experiments in the gully region of the Loess Plateau

Headcut erosion is the main sediment source that may cause severe damage to the ecological environment and agricultural production. The study of headcut erosion characteristics, such as gully headcut morphological evolution and sediment particle transport processes, is essential for understanding the mechanism of gully erosion. A series of simulated rainfall combined scouring experiments with constant rainfall intensity (0.8 mm min^–1) and variable flow discharge (3.6, 4.8, 6.0, and 7.2 m³ h^–1) were conducted to illustrate the headcut erosion process in the gully region of the Loess Plateau. The results showed that gully width and gully depth increased as time and flow discharge increased. The headcut retreat length increased exponentially with experiment time. The gully head heights decreased by 10, 13, 21, and 26 cm at different flow discharges after 180 min. The contents of clay and silt in eroded sediment particles decreased by 7.97% to 16.59% and 7.98% to 15.34%, respectively, whereas the sand volume fraction increased by 9.33% to 20.04% compared to that of the original soil. The enrichment rates of clay and silt sediment were 0.83 to 0.92 and 0.85 to 0.92, while the enrichment rate of sand sediment was 1.09 under different flow discharges. The critical particle size was 0.0326 mm. The fractal dimension of the eroded sediment particles was 2.61 to 2.67 and showed good agreement with the clay volume fraction, with a coefficient of determination (<i>R</i>²) of 0.93. These results provide a basis for headcut erosion model establishment, ecological management, and soil and water conservation in the gully region of the Loess Plateau.

Cyclic behaviour of beam-column joints made of crumb rubberised concrete (CRC) and traditional concrete (TC)

Crumb rubberised concrete (CRC) is a sustainable material that recycles rubber particles from end-of-life tyres as partial fine aggregates in concrete. To promote the applications of CRC in building structures, this paper presents an experimental study on the cyclic behaviour of beam-column joints from both CRC and traditional concrete (TC) frame structures. CRC with 15% rubber content by sand volume was employed. Three full scale CRC joint samples and one full scale TC sample were tested. Varying axial loads were applied on the top of columns and anti-symmetrical low-frequency cyclic loads were applied at the two beam ends. The failure modes, hysteretic behaviour, stiffness degradation, bearing capacity degradation, shearing capacity, displacement ductility and strain response of CRC and TC joints were investigated and compared. Both CRC and TC joint samples reached their ultimate loads due to shear failure. When CRC and TC were with similar strengths, the first crack loads, yielding loads, ultimate loads and ultimate displacements for TC and CRC joints at the same axial compression ratios were comparable with slight differences within 5%. However, CRC joints exhibited an improved energy dissipation ability by up to 10.4% over TC samples.