In the past, concrete was rarely used in buildings, but now it is different. Concrete is widely used in any building now. With the widespread use of concrete, a large number of old concrete will appear when demolishing houses.

In the past, this kind of concrete was directly classified as construction waste. However, with the increasing amount of old concrete, people wonder whether they can reuse these things. After all, their ingredients are very good. Stones, cement and sand are solidified together. Their hardness should be very high. It is a pity to directly use them as construction waste. Can't it be crushed and reused?

Indeed, can the concrete made of stone, cement and sand be used as sand after being crushed?

In fact, sand plays a very important role in architecture. We don't think it is remarkable, but its role is actually irreplaceable. Sand is the best aggregate in concrete and mortar, which can't be compared with anything else that can be used as aggregate.

So the old concrete can't be reused? In fact, this is not the case. It can be reused, but its scope of use is limited.

The old concrete can be turned into aggregate after crushing and screening. However, what we need to distinguish is that although these old concrete is composed of cement, stone and sand, when it is broken and sieved as aggregate, its role is completely incomparable with that of new sand.

After this kind of concrete is crushed, its strength is very low. When we crush it and wash it, we will get some sand and gravel. Where can the sand be used? Some remote commodity mixing plants will be used as aggregates. However, the commercial ash mixed with this kind of aggregate is not used anywhere. It is generally used for pavement, that is, pavement hardening.

We can see that now many places are hardening the road surface, as well as the hardened Hutong. If we have the intention, we can take these hardened commercial ashes to test. Its composition is different from the commercial ashes used in ordinary buildings. Of course, the use of old concrete crushing materials is only a small part of the mixing plant, and not all hardened pavement will use these materials, but there is a certain probability.

In addition, there is no problem for these aggregates to be used on hardened pavement. Hardened pavement and building are two completely different concepts, so they can not be compared. However, the requirements for hardened pavement are completely different from those for buildings.

The primary guarantee of hardened pavement is to harden and wear-resisting, improve the ground strength and prevent sand and dust. Hardening and wear resistance can be achieved after concrete solidification, but some things need to be added, such as curing agent. The curing agent can also prevent sand and dust.

But these requirements, the sand and gravel after the old concrete is crushed and screened can be fully competent, and its force can not be used up in this respect. Therefore, the old concrete can be broken and reused. It can be used to pave the hardened pavement. In terms of strength, it can fully reach the qualified level without quality problems.

Someone will ask, can it be reused in buildings? This is also what we will talk about next.

Some people say, after I crush the old concrete, can I mix it in mortar to build the wall? Can you mix it in concrete to cast the roof? Can you paint the wall? In fact, these are all possible, but at the same time they are not.

What we can say here is that it can also be used if it is forced to be used. But if it is required to be qualified, it is defective. In other words, it can not be reused in buildings. Whether it is the mortar for building walls or the concrete for pouring roofs, it is unqualified to replace the sand with the sand crushed by the old concrete.

We all know that in buildings, whether mortar or concrete, they all need aggregates, and sand is the preferred aggregate. What is the disqualification of the crushed old concrete sand?

There are three aspects: small particle size, large moisture content and poor strength. Let's talk about it separately.

First, the particle size is small. It seems that there is no difference in sand, but sand is actually divided into big sand and small sand. Small sand is mostly used for building walls, and big sand is mostly used for painting and pouring concrete. Why divide these? It is because there are differences in the particle size of sand, and the particle size of sand is also an important reason why it cannot be replaced.

The sand is used as aggregate. What is aggregate? That is, it seems to be very small, but in fact it plays the role of bones. If concrete is compared to the flesh and blood of buildings, then steel bars are its bones. When it comes to subdividing, cement is the flesh and blood of concrete, and sand is its bone.

Therefore, aggregate is very important. The crushed concrete can not meet the requirements of sand particle size. The crushed concrete sand and gravel should be finer than the small sand, which is not qualified for wall building, let alone for painting and concrete pouring.

Secondly, the water content is large. The high water content here does not mean that it contains high water content, but that it has strong water absorption when used in buildings. No matter in building walls or painting, or in pouring concrete, the most afraid thing is that the water is absorbed too quickly. If the water is absorbed too quickly, the setting shrinkage time will be shortened, resulting in unstable setting and even concrete cracking. Therefore, the bricks shall be wetted when building the wall, and the wall shall also be wetted when painting. After pouring the concrete, it shall be watered for maintenance. All of these are to prevent the water from losing too fast and causing unstable solidification.

However, the sand and gravel after the old concrete is crushed will absorb water especially due to its too small particle size, resulting in the decrease of setting force.

Finally, the strength difference. Since it absorbs too much water, it will cause damage to its firmness, which is connected as a whole. For example, we need to spray water to maintain the concrete after pouring, but we must not stay in the water all the time. That will cause the concrete not to solidify for a long time. After the concrete finally solidifies, its firmness has also been seriously damaged. When the firmness is damaged, the strength is naturally poor.

These are the three reasons why old concrete can not be used as building materials after being crushed. It can be used to pave roads, but it is inappropriate or even impossible to use it on buildings for a second time.

In fact, if it is necessary to reuse these things in buildings, it will certainly lead to the opposition of the construction unit. The commercial ash mixing plant specially used by these construction units will never dare to use it privately. This is a very serious matter. There are strict regulations for the normal mixing plant, whether it is batching or mixing, and the concrete produced is absolutely qualified.

As a kind of widespread construction waste, it is a pity to directly treat old concrete as garbage. Therefore, the technology of secondary utilization will certainly become more and more perfect in the future, and these things will be generally reused.