News

Industry Information

Sand and gravel market

Policies and regulations

What are the different requirements for mechanism sand and river sand or river sand in construction engineering?

What are the different requirements for mechanism sand and river sand or river sand in construction engineering?

Basically, there is no difference. The particle shape of the mechanism sand has more edges and corners than the river sand, and the bonding ability with the cement slurry is better, but it is not good for pumping concrete. Machine-made sand mainly detects stone powder content, river sand detects silt content, and other detection indicators are basically the same. Sand as a floor material, generally using local materials, as long as the crushing value meets the requirements, grading is not too big problem, stone powder content does not exceed the standard can be used. River sand is less and less. Machine-made sand was not allowed to be used on high-speed railways before, but now it is included in the standard. Machine-made sand will be used more widely in the future. Extended information: Current situation of river sand and mechanism sand use In recent years, with the continuous development of various construction undertakings, the demand for concrete is increasing, and sand, as an essential part of concrete production, also has a more important impact on the performance of concrete. The main types of sand used in the field of engineering construction are river sand and machine-made sand. As a resource, river sand is mainly distributed in the river basin. With a large number of uncontrolled mining, the use of natural river sand is generally faced with the problems of mining difficulty, large investment in river sand procurement cost and continuous reduction of resources, which have a negative impact on the implementation of engineering construction projects. In addition, due to the high mud content and poor quality of some river sand, the strength and stability of concrete are affected. Facing the lack of river sand resources, high price and difficult quality control, looking for its alternative materials has become the focus of research on concrete sand. In concrete for the application of river sand replacement is mainly machine-made sand. Machine-made sand refers to crushed stone particles with a particle size of less than 5.00mm obtained through mechanical crushing and screening of crushed stone.

20

2023

/

09

How many kinds of river sand

How many kinds of river sand

River sand is mainly divided into three types: coarse sand, medium sand and fine sand. Nowadays, coarse sand for interior decoration is rarely used, and medium sand is mostly used. The porosity of sand depends on the matching degree of sand particle size at all levels. The well-graded sand can not only save cement, but also improve the compactness and strength of concrete and mortar. When configuring concrete, medium sand shall be preferred. When coarse sand is used, the sand ratio should be increased and sufficient cement dosage should be maintained; when fine sand is used, the sand ratio should be appropriately reduced. The sand for masonry mortar shall meet the technical property requirements of sand for concrete. Due to the thin mortar layer, the maximum particle size of sand should be limited. For rubble masonry, the maximum particle size shall be less than 1/4 to 1/5 of the thickness of the mortar bed. For brick masonry, medium sand is suitable, and the particle size shall not be greater than 2.5mm. Fine sand shall be used for smooth plastering and jointing mortar.

12

2021

/

11

Controlled Mining and Rational Utilization of River Sand

Controlled Mining and Rational Utilization of River Sand

Overview of 1. River The main stream of the middle and lower reaches of the Yangtze River starts from Yichang and ends at the mouth of the river, with a total length of 1893km, flowing through 6 provinces and municipalities including Hubei, Hunan, Jiangxi, Anhui, Jiangsu, and Shanghai. The area along the Yangtze River is economically developed, with a high level of urbanization and rich water resources. It is the essence of the Yangtze River Basin and an important economic zone in my country. After the Yangtze River leaves the Three Gorges, it enters the middle and lower reaches of the plain area. The main stream of the Yangtze River is controlled by the regional geomorphology and geological structure, and belongs to the alluvial plain river. Yichang-Hukou is an alluvial plain in the middle reaches of the Yangtze River, located in a neotectonic subsidence zone, with low terrain, small ground slope, gentle water flow, and connected with many lakes. The landform on both banks below the lake mouth is floodplain along the river and lake area, and there are large and small lake waters. The bank slopes of the middle and lower reaches of the Yangtze River can be divided into bedrock (gravel) bank slopes, sandy bank slopes and soil bank slopes according to their material composition, with sandy bank slopes and soil bank slopes being the main ones. The general trend of riverbed composition along the course is from coarse to fine. The section from Yichang to Zhicheng is mainly composed of fine sand, medium sand and sandy pebbles. The upper Jingjiang river bed is medium sand and pebbles, and the lower Jingjiang river bed is fine sand. The riverbed below Chenglingji is basically composed of fine sand. The bed sand in the Yangtze River estuary is very fine sand and silt. The plane shape of the river is composed of micro-bend single type, meandering type and branching type, and the branching type river is the main type. The Yangtze River is a river with small sediment concentration but large sediment transport. The sediment in the middle and lower reaches of the Yangtze River mainly comes from the inflow of the main and tributaries above Yichang and the tributaries and lakes on both sides of the middle and lower reaches of the Yangtze River. * When the sediment-carrying capacity of the river is unsaturated, the flow will pick up sediment from the riverbed and transport it to the downstream. According to statistics, the average annual sediment discharge of Yichang station and Datong station is 0.501 billion t and 0.433 billion t respectively. Since 1990, due to the construction of reservoirs in the main and tributaries and the water and soil conservation projects in the upper reaches of the Yangtze River, the annual average sediment discharge at Yichang and Datong stations has decreased compared with the annual average sediment discharge. At present, the annual deposition of suspended sediment larger than 0.1mm in the Yichang-Datong section of the middle and lower reaches of the Yangtze River is about 25.8 million t, and the average annual deposition of sandy load is 2.7 million t. Suspended sediment greater than 0.1mm passes through the large cross section about 30 million t per year. After the initial impoundment of the Three Gorges Project in June 2003, the change of sediment greater than 0.1mm in the Yichang-Datong River section was greatly affected by the age of the reservoir and the composition of the river bed. At the initial stage of reservoir operation (11~20 years), only the section from Wuhan to Datong is slightly silted up, with an average annual rate of about 20 million t. With the trend of scouring and silting in the river reach, the amount of sediment larger than 0.1mm entering the river reach below Datong every year is close to that before the construction of the reservoir. These sediments provide abundant sediment resources for sand mining in the Yangtze River.

12

2021

/

11

Overview of sand mining in river channel

Overview of sand mining in river channel

Sand mining in the Yangtze River has a long history, but mechanical sand mining began in the late 1970 s and gradually formed a trend of large-scale mining in the late 1980 s. In the 1990 s, with the rapid development of the construction of the Yangtze River Economic Belt, the demand for construction sand and gravel increased greatly, and the price of sand rose. Driven by considerable economic interests, various sand mining vessels flocked to the middle and lower reaches of the Yangtze River. The chaotic situation of indiscriminate mining and digging has a serious impact on the stability of the middle and lower reaches of the Yangtze River, flood control safety, navigation safety, and national economic and social development. Sand mining in the middle and lower reaches of the Yangtze River is mainly distributed in the reach of the Yangtze River in Hubei, Jiangxi, Anhui, Jiangsu and other provinces. According to incomplete statistics, before the ban on mining, the provincial water administrative departments approved a total of 44 sand mining areas, with a total annual sand mining volume of more than 5300 million t. Due to unscrupulous illegal sand mining, the amount of sand mining in the middle and lower reaches of the Yangtze River is far greater than the above figures. Indiscriminate mining of river sand has aggravated the collapse of the Yangtze River bank, affected the stability of the river regime, endangered the safety of flood control and navigation of the Yangtze River, and seriously threatened the economic development and people's lives and property along the Yangtze River. To this end, in June 2000, the General Office of the State Council issued a circular requiring the people's governments of the provinces (municipalities directly under the Central Government) in the middle and lower reaches of the Yangtze River to take immediate and effective measures to comprehensively control and rectify the sand mining activities in the Yangtze River within their provinces (municipalities directly under the Central Government) and completely ban illegal sand mining activities. In February 2001, the middle and lower reaches of the Yangtze River began to ban river sand mining. In order to straighten out the management system of sand mining in the Yangtze River, clarify the management responsibilities, intensify the crackdown on illegal sand mining, and standardize and establish a normal sand mining order, the State Council promulgated the "Regulations on the Management of Sand Mining in the Yangtze River" on October 25, 2001 (State Council Decree No. 320), which came into effect on January 1, 2002. At this point, the Yangtze River sand mining and its management began to enter the legal track.

09

2021

/

11

The Necessity of Controlling the Exploitation of River Sand

The Necessity of Controlling the Exploitation of River Sand

1. The need to maintain the stability of the river In the long-term evolution of the middle and lower reaches of the Yangtze River, a relatively stable riverbed pattern has been formed through the interaction between the sand-laden flow and the riverbed. Large-scale and disorderly illegal sand mining has destroyed the riverbed morphology and river regulation project, changed the balance of sediment transport in local river sections, caused local changes in river regime and bank collapse, and adversely affected the stability of river regime in local river sections. 2. The need for flood control safety The middle and lower reaches of the Yangtze River are the focus of flood control, and dikes are the ancient and basic flood control facilities in the middle and lower reaches of the Yangtze River. As the middle and lower reaches of the Yangtze River embankments are built on the Quaternary alluvial plain, and the embankment construction is mostly phased and cultivated, the embankment body soil joint is poor, resulting in poor quality of the embankment body, soil complex, there are still many embankment section is not up to standard. Indiscriminate mining of river sand will bring more adverse effects on the originally weak embankment project, and its possible impact on flood control safety is mainly as follows: mining of river sand near the river embankment makes the deep bank stick to the bank, the relative height of the embankment increases, the bank slope becomes steep, which easily causes the collapse of the bank and endangers the safety of the embankment; exploitation of river sand near water conservancy projects such as culvert gates, pumping stations and revetment projects seriously threatens the safe operation of water conservancy projects. 3. The need to ensure the safety of navigation The Yangtze River is a well-developed river in my country's inland waterways. It is a major water channel between Southwest, Central and East China and to the sea. It is called the golden waterway. The middle and lower reaches of the Yangtze River are the golden section of this golden waterway. To ensure the safety of navigation is of great significance to promote the economic and social development of the areas along the Yangtze River. The impact of indiscriminate mining and excavation on the navigation safety of the Yangtze River is mainly manifested in: crowding out the main channel, prone to sea damage accidents.

09

2021

/

11

< 12 >