This article is from WeChat official account:Bring science home (ID: steamforkids), author: seven Jun, from the title figure: vision China
People often see cement construction work on construction sites. Children know that after a period of time, cement will harden and take shape. But what you don’t know is that if you sprinkle sugary drinks on the cement that hasn’t dried yet, or sprinkle sugar directly, you will cause an accident.
Before explaining the principle, let’s take a look at an accident that happened 6 years ago.
In January 2014, the control room on the Victoria Line of the London Underground was flooded with concrete, and passengers could not travel on the subway. It turned out that the construction founder was filling an elevator shaft with cement, but he did not expect the cement side to leak into the adjacent control room.
Concrete flooded control room on the Victoria Line of the London Underground
The fast-hardening concrete, which seems to harden in just a few hours, covers important wires and switches. It is becoming stiff step by step. If it is not blocked, the entire control room will be buried and can no longer be operated.
At this moment, the repair workers rushed to a nearby convenience store, bought bags of white material, and then poured it into the cement that had not hardened and kept stirring.
Contrast between the control room (left) and before it was flooded (right) on the Victoria Line of the London Underground flooded with concrete. Image source: telegraph
After adding this magical substance, the relieved workers can scoop the cement away like porridge, and my mother is no longer afraid that I have an excuse to be late for school.
The white substance that can be bought in convenience stores is sugar. Many city dwellers who have lived in cement forests for generations do not know that in addition to mixing potato mash, sugar can also be used to mix cement so that the cement cannot harden.
White sugar, that is, sucrose is a simple sugar, but it is also a concrete retarder and is sometimes used to control the setting time of cement.
You can clearly see that after adding sugar, the cement on the right did not harden after 60 minutes, while the cement on the left did not harden.The sugar cement has hardened, and the metal rod used for testing cannot be penetrated——
As long as a small amount of sugar, the stiffness time of cement can be significantly slowed down. For example, adding 0.04% sugar can double the setting time of cement that takes 1 hour and 18 minutes to harden.
Although there are commercial retarders on the market, the price of sugar is lower than that of them. In hot climates, in order to prevent the cement from hardening too quickly, the workers will use sugar as a retarder to slow down the solidification of the concrete, which can prevent hardening too fast and buy time for construction.
During construction, workers sometimes spray sugar water on the surface of the cement that has not solidified, and then wash off the surface to expose the gravel underneath, creating a rough matte effect.
The more powerful thing about sugar is that as long as you add too much, that is, add more than 1%, the cement can be turned into a puddle of waste mud, and even if it dries in the end, it loses its compressive strength. Therefore, sugar is often called the cement destroyer(cement destroyers).
Many cement mixer trucks also have a bag of sugar to prevent the cement from solidifying when encountering traffic jams and other accidents. Generally about 7 kilograms of white sugar can turn 8 cubic meters of cement into waste. Of course, the cement is useless after putting too much sugar, but the mixer truck can keep it.
During World War II, French resistance activists surreptitiously mixed sugar in German cement to give German military buildings and mud.
From April to June 1989, French anti-government activists used this trick to hinder the government from building prisons in places such as Les Milles in southern France. They used one-thousandth of (1 ton of cement plus 1 kilogram of sugar) mixed white sugar into the cement, and the cement used to build the prison became The mud that can’t stick to the wall.
So, why can sugar prevent cement from hardening?
The main components of common Portland cement, which is Portland cement, are limestone, clay, gypsum, and sand. After adding water, the concrete will undergo hydration reaction, and finally form hydrated calcium silicate (C-S-H). Calcium silicate hydrate is the embodiment of the power of cement.
Cement body-calcium silicate hydrate crystals
Although in the field of cement research and practical operation, the retarder effect of white sugar is well-known to everyone, its principle has not been fully understood.
For the role of sugar, the general theoretical explanation is that sugar can adsorb tricalcium silicate, the main component of cement before hydration.(C3S) The particles eliminate the hydrated calcium silicate crystal nuclei on the particle surface and prevent the formation of hydrated calcium silicate, that is, the cement body.
In addition to white sugar (sucrose), raffinose (a common Trisaccharides, found in cottonseed and sugar beets, are formed by the combination of galactose, fructose and glucose), the retarder that is the culprit that makes you fart after eating beans is also very effective. But some sugars are completely useless, such as α-methyl glucoside.
In short, now you should know to invite workers to drink milk at the construction siteBe careful when making tea and happy water.
The girl is made of water, the boy is made of mud, and the sweetness of the girl and the boy will turn into waste cement.
This article is from WeChat official account:Bring science home (ID: steamforkids), author: seven Jun