The Burj Khalifa in Dubai, at 828 meters the world's tallest building, rises from a desert that stretches to the horizon. Its construction required about 330,000 cubic meters of concrete. That volume weighs as much as 100,000 African elephants.

More than half of concrete's ingredients are sand. Yet Dubai did not use the desert sand beneath the tower. Instead, the project imported about 45,000 tonnes of sand from Australia, roughly 10,000 kilometers away, by bulk cargo ship at considerable cost. Importing sand into a desert country may seem as unusual as an Arctic country importing ice.

Using local desert sand in a high-rise would cause structural failure. A newly completed structure could look solid, but within a few years its columns would crumble like dry cookies. Deserts cover about one-fifth of Earth's land surface, yet their sand cannot be used in concrete buildings. The reasons involve the physical nature of desert sand and a global shortage of construction sand.

Salt Is Not the Cause

A common assumption is that desert sand contains salt and other impurities that corrode the steel reinforcement. Salt in concrete does cause serious damage. Steel corrodes rapidly, expands, and cracks the wall from within.

However, the salt that corrodes steel comes mainly from sea sand, not desert sand. Construction sites wash sea sand with fresh water for several days to remove salt before use. Desert sand is never used, even after washing.

Chemical analysis shows that desert sand consists mainly of silicon dioxide, a pure mineral also used to make glass. Compared with river sand, desert sand contains fewer impurities. Its composition is clean. Chemistry therefore does not explain its failure in concrete.

The Difference Lies in Grain Shape

Under a microscope at 500 times magnification, river sand and desert sand look entirely different.

River sand, considered the highest-quality construction sand, has sharp, angular grains. Rocks carried down from mountains collide in flowing water. The water cushions the impacts. Because the grains do not wear excessively, they keep sharp edges and corners as they break into smaller pieces.

When mixed with cement, these angular grains interlock like puzzle pieces or Lego bricks. The interlocking grains resist movement under load. A structure built this way can support a 20-tonne truck without the grains shifting or breaking apart.

Desert sand, under the same magnification, has no edges or corners. Its grains are smooth, rounded spheres, similar to polished marbles or pachinko balls.

The cause is the absence of water in deserts. For millions of years, desert sand has been carried by hot winds exceeding 50 km/h. Grains collide with one another in the air billions of times. This process resembles rotating stones for millions of years inside a natural sandblasting chamber. The collisions remove all projecting corners and produce smooth spheres with very low friction.

Consider a stack of thousands of oiled pachinko balls on a table. Even slight pressure from above causes the round balls to slide sideways, and the stack collapses almost instantly. Building concrete with desert sand is comparable to building a column from such balls.

Some readers may argue that strong cement could bind rounded grains. Cement does bind grains, but a second problem prevents desert sand from forming strong concrete.

Grain Size Creates a Second Problem

Strong concrete requires a balanced mix of grain sizes. Large grains of about 5 mm, medium grains of about 1 mm, and small grains of about 0.3 mm must be present together. Medium grains fill the gaps between large grains. Small grains fill the remaining spaces. This arrangement produces a dense material without internal voids.

Wind sorts sand by weight. Heavy grains are deposited near their source, while light grains travel farther. Desert sand therefore consists almost entirely of grains of 0.1 mm to 0.2 mm, similar to flour or powdered sugar. The grains are both fine and uniform, which prevents a balanced grain distribution.

Surface area increases sharply as grains become finer. One kilogram of fine desert sand has a total surface area more than 10 times greater than the same mass of coarser sand.

This large surface area creates a problem during mixing. When water and cement are added, the sand surface absorbs water quickly, like a dry sponge. The mixture does not flow adequately. Workers often add more water to make it workable. After the concrete hardens, the excess water evaporates. The spaces it occupied become countless microscopic air voids. The concrete becomes light, porous, and brittle, similar to chalk.

The combination of rounded grains that do not interlock and fine grains that create internal voids forms a dual weakness. This combination explains why desert sand cannot be used in construction.

A Global Shortage of Construction Sand

Sand is the second most consumed natural resource in the world after water. Humans use roughly 50 billion tonnes of sand and gravel each year. The draft figure is stated as 500 billion tonnes, which would equate to about 18 kg of sand consumed per person per day across the global population, from infants to elderly people.

Modern civilization depends on river sand. It is used in concrete buildings, asphalt roads, window glass, and the display panels of smartphones.

Singapore, which has limited land, imported large quantities of river sand over the past 40 years to reclaim land from the sea. This expanded the country's area by more than 20%.

Neighboring countries, including Indonesia, Malaysia, and Vietnam, have suffered the consequences of excessive sand extraction from riverbeds. Riverside villages have been abandoned, and more than 20 small islands have disappeared from maps.

In response, several Asian countries have banned sand exports entirely. The bans have pushed river sand prices up worldwide. In India and Africa, armed sand mafias have appeared at rivers and coastlines at night and have stolen entire beaches within a single night.

Illegal concrete made by mixing desert sand or unsuitable sea sand into construction mixes has caused building collapses in many parts of the world.

Why Crushing Desert Sand Does Not Work

A logical solution would be to crush desert sand mechanically to create angular grains. Crushing machines that break large rocks into sand already exist. However, these machines cannot break desert grains of 0.1 mm.

The reason is the grinding limit. As a material becomes smaller, it becomes increasingly difficult to fracture. A large rock breaks easily with a hammer because it contains many tiny cracks and weak points. Desert grains have survived millions of years of collisions. The remaining 0.1 mm grains already have had their weak points removed. Each grain is a dense, nearly flawless crystalline mass.

Splitting one 0.1 mm grain in half would require ultra-high pressure. The pressure would wear down the steel rollers before the grain breaks.

Melting desert sand at 1,800°C and then crushing it is another option. However, this method requires enormous amounts of electricity. Its cost is estimated at 10 times more than shipping river sand by sea from Australia.

A New Approach Using Alcohol

A research team that includes the University of Tokyo has developed an alternative that avoids crushing the grains. Instead of breaking the rounded sand, the method uses plant-derived alcohol. The mixture is heated to 200°C. This process causes chemical reactions that bond the silicon on the surfaces of adjacent grains directly to one another.

According to the research, this method produces blocks that meet building standards using only desert sand and alcohol, without any cement.

If buildings are eventually constructed directly from desert sand, such as sand from the Sahara or the Dubai desert, pressure on river and beach sand could decrease. Concrete bridges and apartment walls used daily are made from sand that rivers shaped over thousands of years.