60 Concrete Questions Part 2 -- Let Nicoo Concrete Manufacturers answer all your concrete questions.

21. What is the adiabatic temperature rise of concrete?

The cement in the concrete will release heat in the hydration process, and the heat release is related to the cement variety and the amount of cement. Assuming that the concrete is in an adiabatic state where the heat can not be emitted up and down, the temperature in the concrete will continue to rise with the cement hydration, and when it rises to the highest, it will reach the highest adiabatic temperature rise.

22. How to calculate adiabatic temperature rise?

The adiabatic temperature rise of cement hydration heat is calculated as follows:

Tmax = mq/cρ

In the formula: Tmax-cement hydration adiabatic temperature appreciation (℃) m- per cubic meter of concrete cement dosage (kg), Q-cement hydration heat, specific heat of C-concrete (0.96j/K), ρ-concrete density (2400 kg/cubic meter).

23. What is the heat of hydration of cement?

All kinds of cement hydration heat can refer to the table.

Heat of hydration Q per Kg cement (Kj/Kg)

24. What are the rules of concrete temperature rise?

General mass concrete pouring 2-3 days after the heat peak. For example, the bottom plate of a project is 2 meters thick and is prepared with 42.5 grade cement of 360 kg/m3. In summer, the mold temperature is 32℃ in the construction site. Its central temperature can be as high as 80℃ or so. After 4 days, most of the heat energy of cement hydration has been consumed, and the internal temperature gradually drops. This temperature may last for more than ten to thirty days, and the hydration and heat dissipation process of some large volume concrete of hydraulic engineering may be much longer. Master this law, the temperature control of mass concrete should be focused on a week after pouring, especially the 2-3 days.

25. What happens when the raw material cannot be stopped immediately and the supply of concrete cannot be interrupted?

When contacting raw material suppliers, special personnel should be assigned to control the mixing water consumption and monitor the fluidification of concrete on site to prevent the site from adding water by itself. When necessary, control the water binder ratio unchanged and increase the amount of cement appropriately to increase the fluidity of concrete. Generally, every increase of 1cm collapse, every 1m3 concrete needs to increase the cement slurry volume of 1.5%~2.5%.

26. What matters should coarse and fine aggregate pay attention to?

The grain size, gradation, grain shape, stone powder content and clay content of coarse aggregate should be controlled. Each vehicle shall be inspected at a macro level, and unqualified vehicles shall not be unloaded. In addition, according to the specification requirements, according to the batch inspection indicators.

Fineness modulus, mud content and clay lump content should be controlled for fine aggregate. Carry out macroscopic inspection on each car, do not unload if unqualified; The same should be in accordance with the specification of batch inspection.

27. Why should the coarse aggregate particle size be controlled at 5-25mm?

The coarse aggregate particle size is restricted by the concrete pumping pipe diameter and pumping height, and the maximum particle size that can be pumped decreases with the increase of pumping height. If the pumping height is less than 50m, the ratio between the maximum particle size of coarse aggregate and the conveying diameter is less than 1:3; When the pumping height is 100m, the ratio will be reduced to 1:5, otherwise it is easy to block the pipe.

28. Why should the needle flake content of coarse aggregate be controlled in pumping concrete?

When its content is high, the flexural strength of acicular coarse aggregate is relatively low, and the bond strength between coarse aggregate decreases, resulting in the decline of concrete strength. For ready-mixed concrete, the high needle-flake content will make the coarse aggregate particle shape is not good, thus reducing the concrete fluidity. Meanwhile, the needle-flake aggregate is easy to be blocked in the pipeline, resulting in pump blockage or even pipe explosion. Therefore, the needle content of pumped concrete is less than 10%, and the requirement of high strength concrete is higher.

29. What kind of sand do you need for ready-mixed concrete?

Medium sand is required for ready mix concrete. In addition to the grading, mud content and clay lump content of sand according to the code requirements, it should be noted that no less than 15% sand should pass through the 0.315mm sieve hole. This has a great impact on the pumpability of concrete, the value is too low easy to block the pump, and the concrete water retention is poor, easy to bleed water.

30. What is the effect of fine sand?

The sand is too fine, the concrete water demand rises, and the concrete prepared with fine sand is very poor in pumpability and plasticity, the concrete strength will decline, easy to crack.