A shocking news, according to CNBC reported a few days ago, the world is facing a shortage of sand, in the past 20 years, the use of sand in the world has increased twice, reaching 400 to 50 billion tons per year, and the natural production rate of sand is far lower than the current growth rate of use.
As early as 2019, the United Nations has put the crisis of sand shortage on the agenda, but there is still a lack of plans for sustainable sand mining, and the demand for sand will explode due to the massive increase in population and urbanization in the future!
Where did the sand come from? What are the requirements for construction sand?
Sand or sand can be, generally is a very fine rock, the scale is between 0.0625 mm and 2 mm, the larger one is called gravel (2 to 64 mm), the finer one is called mud, the simple touch is the feeling of rust when rubbing is sand, and the powder feeling is mud.
The composition of sand is usually silica, usually in the form of quartz, but the composition will vary depending on different rock types, usually formed after the rock has been weathered or eroded, such as the most common is the river washed stone formation. Generally on the coast or on the inside of the river is an area of sand accumulation, it is easily carried by the current, and when the flow rate is reduced, a sandbar or beach is formed.
What kind of sand can be used for construction
The composition of concrete in modern buildings is sand, cement and water, which will vary according to the proportion of concrete requirements, but generally require particle sizes of less than 4.75 mm, and there are two sources of sand for construction:
Natural sand: Sand dominated by quartz granules in rivers, lakes and seas
Mechanical sand: Unwinded rock is mechanically broken to meet the specifications of sand for construction
Mechanism sand
In addition to the natural sand in the rivers, lakes and seas, there are also a large amount of sand in the ancient river channel, so you often hear that the sand of the ancient river channel of the Yellow River is excavated, resulting in environmental damage, etc., because the ancient river channel has been covered with mud and formed vegetation, and the sand of the ancient river channel will lead to environmental disasters, such as lower groundwater level, ground cracking and large-scale vegetation destruction, resulting in a reduction in cultivated land area.
Mechanism sand production process
Why dig up the sand of the ancient river channel, isn't there a lot of sand on the beach?
The sand we use is mainly from river sand, sea sand can also be used as a building, but because the sea sand contains sulfides and sulfates and sodium chloride and other substances, it will form a primary battery, destroy the passivation film of the steel bar, cause the steel bar to rust, form a gap between the steel bar and cement, and then reduce the strength, accelerate oxidation, and finally the concrete cracks, shorten the life, and the function of the building is terminated.
Of course, sea sand can also reduce the chloride content by washing, as long as the chloride content meets the requirements (a class of sand is less than 0. 01%; Class II sand is less than 0. 02%, three types of sand below 0. 06%) can be used as the corresponding standard of the building, but such an operation will greatly increase the cost, so many unscrupulous builders will use simple water washing (the standard is soaked in fresh water for at least 24-48 hours) for processing, and fresh water may also be used repeatedly, simply can not meet the standard!
Buildings that use these sands are not visible in the early days, but smashing the cement will find that the steel bars inside have rusted, which will cause a reduced service life over time, and the building will be retired from service prematurely.
Sea sand contains salt and cannot be used, there is so much sand in the desert, why not use it?
Sea sand is salty, to corrode steel, everyone can understand, but there are so many deserts in the world, a Sahara Desert sand can make tens of billions of people around the world have a house per person to live, but also worry about not enough sand?
The difference between sand in the desert and sea sand and river sand is that the desert sand has not been repeatedly washed by water, so the desert sand has a high alkali content, what will be the consequences? Slightly damp will be alkaline, that is, combined with the carbon dioxide in the air to form calcium carbonate, volume expansion, that is, the ground becomes white and white hair, and even exaggerated like a layer of hair on the ground, the painted wall skin is up, and it will also corrode the steel bar, reduce the strength and so on.
So the desert sand wants to use for construction, it is also very troublesome, so Dubai in the desert, but to import construction sand, is not a very ironic thing, but this is no way, desert sand can not be used. According to data released by the United Nations, the UAE imported $456 million worth of sand and gravel in 2014.
In March 2018, a team at Imperial College London developed a building material called "Finite", which uses desert sand to make concrete and achieve the same strength as river sand, and "Finite" can also reduce carbon dioxide emissions, because about 5% of the world's carbon dioxide now comes from concrete.
The use of sand is quite large, in addition to construction sand, there is also the semiconductor industry also use sand, of course, mainly all kinds of buildings, in March 2017 in the Netherlands held a summit, Dutch designer Atelier NL said:
"Sand is the most consumed resource on Earth after fresh water."
Whether there is sand available in the future depends on whether modern technology can transform desert sand into a usable resource!