River Sand Characterization for Its Use in Concrete: A Revue

Despite the gradual professionalization of the construction sector as well as the abundance of sand mining sites offered by the North Kivu, Democratic Republic of Congo Region, ignorance of materials by local builders persists. This is the case of quarries extracting river sand used to make concrete and mortar. However, the dosages of the various constituents are most often chosen on the basis of experience without any prior characterization of this material. This paper presents a comprehensive review of the characterization of river sand for its use in concrete in DRC. The origin and global use of river sand in construction are presented in percentage terms to highlight the importance of river sand as a construction material. The physical properties of river sand, including particle size distribution, bulk density, absolute density, and cleanliness are discussed in detail. The paper examines the effect of variations in river sand properties on concrete behavior, including density and compressive strength. Overall, this paper emphasizes the need to properly characterize river sand before using it in construction to ensure durable, high-quality structures. This will avoid the problems that are observed in particular a bad behavior of the coating on the walls;cracks and crumbling of the beams, lintels, posts and even the ruin of the structures.

Assessment of Bholari River Sand for Its Geotechnical Characterization as Fine Aggregate

Present study is aimed at assessment of Bholari river sand for its geo­technical characterization and suitability as fine aggregate which is being quarried in Jamshoro district,Sindh,Pakistan.For this purpose,sand samples(n=11)were collected from quarry sites and main river channel.Physical properties reveal that Bholari sand is mainly coarse to fine in size(0.2 mm-5 mm).Average values of fineness modulus,specific gravity,bulk density and void content of collected samples are 2.58,2.56,1659.90 kg/m^(3) and 35.12%respectively which varied within the corresponding permissible ranges of ACI(American Concrete Institute).Carbonate content of about 57.59%is also in agreement with corresponding range for fine aggregate.Petrographic examination revealed that Bholari River sand mainly compris­es of quartz and rock fragments with subordinate limestone fragments.As per classification of Dott(1964),Bholari sand is lithic arenite where quartz(50%)occurs as main mineral followed by rock fragments(30%),feldspars(15%)and other opaque minerals(5%).Texturally,the sediments are angu­lar(77%)to sub-round(33%).All these physical properties lie within the range set by National Highway Authority(NHA)and American Standard of Testing Material(ASTM).It is concluded that Bholari River sand is suita­ble for use in concrete mixed with cement and asphalt.

Sand mining disturbances and their effects on the diversity of arbuscular mycorrhizal fungi in a riparian forest of Iran

The major objective of this study was to evaluate the effects of sand mining disturbances on the diversity of arbuscular mycorrhizal fungi（AMF）. In addition, the proportional changes in the diversity of AMF to the distances from riverbanks were assessed. For this purpose, the riparian forest of the Maroon River, Iran was divided into three locations with a 200-meter wide zone in between. Thus, the locations studied were named Distance I（riverbank）, Distance II（intermediate）, and Distance III（farthest from riverbank）. In each of these distances, 10 Tamarix arceuthoides and Populus euphratica of each species were randomly selected. At the same time, soil and root samples were collected from the rhizosphere of the tree species studied. Results indicated that totally 13 AMF species were observed in T. arceuthoides and 19 AMF species were recorded in P. euphratica rhizosphere belonging to 6 genera and 6 families. In these AMF species, Glomus segmentatum, G. geosporum, G. rubiforme, G. nanolumen, G. spinuliferum, Claroideoglomus drummondii, Gigaspora gigantea and Acaulospora paulinae appeared only in P. euphratica rhizosphere, while G. multiforum and Claroideoglomus claroideum were observed only in T. arceuthoides rhizosphere. Moreover, Distance II had the least AMF species both in T. arceuthoides and in P. euphratica rhizospheres, and also the least spore density and root colonization rate. Our results are important in that they provide a list of resistant AMF species that could be used in the conservation of biodiversity.

Grinding Properties of Abandoned Concrete

The grinding properties of abandoned concrete, which consists primarily of hardened cement, limestone aggregate and river sand, are studied. Theoretical models of grinding are used to explain the experimental observation. The results show that 1) The principle disintegration mechanism of hardened cement and river sand is volumetric grinding, although at later stages grinding of cement becomes difficult because of its flaked structure; 2) The lime- stone grinding process can be divided into two steps. First, volumetric grinding, with an obvious component of surface grinding, followed by primarily surface grinding as the micro-particle content increases; 3) Initially, the principle mechanism of grinding limestone and river sand is volumetric grinding, albeit less efficient grinding than if these components were ground separately, and; 4) After 10 to 20 min of grinding the grinding bottleneck phenomenon ap- pears and after 20 min of grinding the content of micro-particles is large and surface grinding is the main mechanism while the particle size of the mixture is smaller than that of separately ground river sand and cement but bigger than that of separately ground limestone.

Agglomeration Characteristics of River Sand and Wheat Stalk Ash Mixture at High Temperatures

The agglomeration characteristics of river sand and wheat stalk ash mixture at various temperatures are investi- gated using a muffle furnace. The surface structural changes, as well as the elemental makeup of the surface and cross-section of the agglomerates, are analyzed by polarized light microscopy, scanning electron microscopy （SEM）, and energy dispersive X-ray （EDX）. Multi-phase equilibrium calculation is performed with FactSage in identifying the melting behavior of the river sand-wheat stalk ash mixture at high temperatures. No indication of agglomeration is detected below 850~C. At a temperature of 900-1000~C, however, obvious agglomeration is observed and the agglomerates solidify further as temperature increases. The presence of potassium and calcium enrichment causes the formation of a sticky sand surface that induces agglomeration. The main component of the agglomerate surface is KEO-42aO-SiO2, which melts at low temperatures. The formation of molten silicates causes particle cohesion. The main ingredient of the binding phase in the cross-section is K20-SiO2-Na20- Al2Oa--CaO; the agglomeration is not the result of the melting behavior of wheat stalk ash itself but the compre- hensive results of chemical reaction and the melting behavior at high temperatures. The multi-phase equilibrium calculations agree well with the experimental results.

Impact assessment of river sand resource shortage under different policy scenarios in China

More than half of the annual global concrete materials were produced in China due to the rapid developing construction industry,which partly led to the shortage of river sand.However,mining rate exceeds the natural replenishment rate of river sand recently,resulting in depletion of natural river sand accumulation.The increasing demand of river sand influences lots of aspects including altered landforms,increasing carbon emissions,ecological deterioration,international trades and disputes.To face the river sand resource shortage in China and to propose possible coping strategies,the data of river sand for construction in China and other related data were collected,and it is suggested that effective policy measures should be taken right now to protect river sand and strictly manage sand mining.Professional solutions for river sand shortage can be summarized as“5Rs”principle,which includes reduce,recycle.reuse,replace and recover.System dynamic model is established to predict the trend of river sand shortage and it was predicted that the gap between river sand supply and demand will come up to 63%.The impact of three policy scenarios is tested in the model,and the gap can be reduced to 35%by single policy scenario,while the scenario with all policy measures is able to reduce the contradiction between supply and demand to 4%.Suggestions are proposed from the aspects of structural and material technology,policy measures and international alliances.Attention should be paid to the shortage of river resources,to realize the sustainable development of the construction industry and other related industries,and to promote the harmonious coexistence of human and nature.