What happens when Sugar is Added to Concrete?

What happens when Sugar is Added to Concrete?


Principle Behind Sugar in Concrete


The Basic Principle followed is the glucose catalytic principle.According to its formula, it belongs to the polyhydroxy group and its surface has strong polarity. This will result in solid-liquid adsorption. Hence the molecular hydroxy group slows the hydration process by hindering the crystal contact and delays tricalcium silicate hydrate reaction.


Remarkable Effect of Sugar on Concrete


The authors elaborated the positive influence and principle of sugar ( ordinary table sugar ) on concrete retarding, liquidity, density, hydration heat, strength and other aspects, introduced good effect, adding ratio and issues needing attention of adding sugar in the process of concrete construction, highlighted advantages of being easy to obtained and with low cost, comparing with other additives, reached the conclusion that sugar is a kind of good additive to be used in concrete construction [Yang Chen, Nanjing University of Technology].

Functions of Sugar in Concrete


The function are:

  • Retarding action on Concrete
  • Increase in Flowability and Compactness
  • Reduction in Hydration Heat and Temperature Cracks
  • Reduction in Hydration Heat and Temperature Cracks
  • Increase in Later Strength of Concrete



Retarding on Concrete

The retarding effect of sugar actually has something to do with the glucose catalytic principle. According to the molecular formula of sugar, it belongs to the polyhydroxy compound. Its surface has strong polarity, thus resulting in solid-liquid adsorption, molecular hydroxyl groups in the cement surface hindered cement hydration process, crystal contact between is shielded, hinders the crystallization of continued growth, changes the structure of the forming process, main changes to delay and delay of three calcium silicate hydrate crystal transformation, following table is the retarding time of concrete mixed with ordinary Portland cement by sugar according to the experimental data from laboratory and field application, in the daytime maximum temperature 31 degrees Celsius on average temperature of 26 degrees Celsius:

Sugar amounts
Retarding time ( h )
Notice
0.1%
7
Tested outside the lab, nature environment
0.2%
11
Tested on the site
0.3%
35
Tested outside the lab, nature environment


Increase The Flowability and Compactness


In terms of concrete pouring construction, concrete is often too viscous (with bad flowability) to be put into formwork operation, such as thin wall slide framework, thin wall concrete board, concrete water pool and etc.. As well as that, in these thin concrete projects, construction quality will be influenced by bad flowability and hard flap. The bad effects are even more serious to water pools with the anti-permeability requirement, grain silos and cement silos with air tightness requirement. If we handle this issue by increasing water amount to increase collapsed slump, it is inevitable that this method does harm to concrete strength and anti-permeability. Instead, we can solve this problem by adding the appropriate amount of sugar.  


Reduction in Hydration Heat and Temperature Cracks


In mass concrete construction, temperature cracks often appear due to the uncontrollable temperature difference between inside and outside mainly resulting from the heat hydration of cement. While retarding effect of sugar delays and postpones the conversion of tricalcium silicate crystal hydrates, delays heat hydration of cement. And reduces hydration heat peak, then reduces the cracks of concrete caused by temperature difference. It is proved by practice that in term of mass concrete construction without adding sugar, its center temperature peaked at 70 degrees Celsius. Whereas, by adding sugar (2% of the cement amount ),its center temperature peaked at 55 degrees Celsius. Obviously, sugar not only can retard concrete but also can reduce its hydration heat.


Increase in Later Strength of Concrete


water will be segregated on the concrete (with sugar) surface. This reflects sugar has water reducing rate as an additive. In this way, the late strength of concrete will be improved. The authors did an experiment like this. By adding sugar (0.1%of the cement amount), and reducing 12% of the concrete water consumption, concrete collapsed slump of concrete with sugar and that without sugar are basically the same. Adding sugar (0.1% of the cement amount) leads to about 10% water reduction. While adding 0.3%, the concrete water consumption is theoretically reduced by 15%, therefore, sugar as a water reducing agent can improve the late strength of concrete like other water reducing agent (but early strength is rather low).

Points To Remember while Adding Sugar to Concrete


Above all, the amount of sugar added in concrete cannot be excessive. 


Although sugar is inexpensive and efficient, the dosage should be determined by strict tests. When sugar amount is close to or surpass 0.3% of cement amount, collapsed slump will not be increased, on the contrary, it will continue to decrease as the sugar amount increased, even occurs segregation, but regarding time will increase continuously. In conclusion, sugar amount should be less than 0.2% of cement amount. Usually, 0.1% can achieve a good construction effect. 


A subsequent factor is that the speed of water segregation is fast. 


The concrete surface will continue with water seeping after adding sugar. This is equivalent to submerge of concrete aggregate. Thus, stationary concrete is prone to sugar uneven and condense. If concrete is still for a long time (normally two hours), the concrete will be difficult to vibrate compactly. Furthermore, the viscosity of concrete will be decreased. So, after adding sugar, the concrete should be used up within 2 hours. Otherwise, segregation phenomenon will appear. At the time of being pumped, we should be cautious that after concrete is pumped into the delivery pump bucket, stagnation time ought to be less than 1 hour. Workers have to stir all the time, otherwise, it would sink and block the pump. 


Suggestion on sugar adding method.


In order to let the sugar add into concrete evenly, sugar should configured solution and plus to stirring material. (The concrete water consumption needs to consider the amount of water in the sugar solution.) In addition, sugar can directly add in the stirring water of concrete

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