Zhang Jiashi did not strictly understand the research and development of cement, but in the education he received before the crossing, he had been exposed to the corresponding information of cement. Small $ %^ says ^ family ^

In these materials, Zhang Jiashi basically forgot the proportion of cement. But he still remembers the two main materials, clay and lime.

However, even if the corresponding proportion of cement was obtained, after testing, the cement did not work accordingly.

It's not that these cements don't work, but what Zhang Jiashi doesn't understand is that cement is easy to solve, but cement and concrete are strictly two different things.

This is because even if it is not reinforced concrete, cement alone is unlikely to make concrete with good bonding.

Because in addition to cement, there is another material that is very important for concrete, and that is aggregate.

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Aggregates, i.e., granular loose materials that act as a skeleton or filling in concrete. As the main raw material in concrete, aggregate plays a role as a skeleton and support in buildings.

In the relevant division of later generations, aggregates with a particle size greater than 4.75mm are called coarse aggregates, commonly known as stones. There are two commonly used types: gravel and pebble. Crushed stone is a natural rock or rock made by mechanical crushing and screening, and the particle size is greater than 4.75mm. Pebbles are rock particles with a particle size greater than 4.75 mm that are formed by natural weathering, water flow transportation and sorting, and accumulation. Pebbles and gravel particles are needle-like particles if the length is greater than 2.4 times the average particle size of the corresponding particle size, and flake particles are less than 0.4 times the average particle size. The pebbles and gravel used in construction shall meet the technical requirements of the national standard GB/T14685-2001 "Pebbles and Gravel for Construction".

Aggregates with a particle size of less than 4.75mm are called fine aggregates, commonly known as sand.

Sand is divided into two categories: natural sand and artificial sand according to the source. Natural sand is formed by natural weathering, water flow transportation and sorting, and accumulation, and the particle size is less than 4.75mm, but it does not include soft rock and weathered rock particles. Natural sand includes river sand, lake sand, mountain sand and desalinated sea sand. Artificial sand is a general term for machine-made sand and mixed sand that have been desoiled.

The four standards for aggregates are roughly as follows:

1. The fine aggregate should be hard, clean and well graded, and the fineness modulus of artificial sand should be in the range of 2.4~2.8, and the fineness modulus of natural sand should be in the range of 2.2~3.0. The use of mountain sand and coarse sand should be tested and demonstrated.

2. In the mining process, the alkali activity of fine aggregates should be tested regularly or according to a certain amount of mining, and corresponding measures should be taken during the potentially harmful period, and special tests and demonstrations should be carried out.

3. The moisture content of fine aggregate should be kept stable, and the moisture content of artificial sand saturated surface should not exceed 6%, and accelerated dehydration measures should be taken if necessary.

As the main raw material in concrete, aggregate plays a role as a skeleton and support in buildings.

When mixing, when the cement is stirred with water, it becomes a thin paste, if the aggregate is not added, it will not be formed, and it will be unusable.

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Zhang Jiashi faced this problem and did not find a corresponding solution in the Qingyu Spirit Book, which made him a little helpless.

But just because you haven't killed a pig doesn't mean you haven't seen how to kill a pig.

In his later life, Zhang Jiashi has seen many times that when some cement buildings are being built, there are not only a large number of bricks and stones, cement bags, but even piles of sand.

After many reminiscences, Zhang Jiashi thought of this matter, and he knew very well that these sand must be a very critical existence.

It's just that for him, who doesn't have experience in this area, Zhang Jiashi can only think about how the sand works.

After a long time of reminiscing, Zhang Jiashi tried to have some personnel add cement and sand to water to mix.

And the result of this practice is that Zhang Jiashi is very excited, because this method can indeed be concrete. But again, these concretes are prone to spalling and even have a poor ability to bond to stone.

The problem must be solved step by step, which Zhang Jiashi knows very well.

So in his free time, Zhang Jiashi gradually recalled some details, hoping to get a solution to this problem.

But time has passed a long time, he has been in this world for more than ten years, and many memories before crossing over are a little blurred.

It's just that during an accidental inspection of Weishui, Zhang Jiashi saw a net hanging on a small fishing boat, and he suddenly remembered something.

True, he remembered seeing some construction workers next to the sand, and then throwing a shovel of sand onto some gridded iron net.

Chances are, that's the real key.

Thinking of this problem, Zhang Jiashi ordered the soldiers to make several iron bars with fairly small holes, and then used them to conduct corresponding tests.

And after several improvements, Zhang Jiashi finally got the concrete that can be said to be a passing grade for him.

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In later generations, concrete is referred to as "concrete": refers to the general term of engineering composite materials that cement aggregates into a whole by cementitious materials. The word "concrete" usually refers to the cement concrete that is used as cementitious material, sand and stone as aggregate, and the cement concrete obtained by mixing with water in a certain proportion, also known as ordinary concrete, which is widely used in civil engineering.

The history of concrete is shorter than that of cement, probably because the construction needs of the time were met by the bonding of cement itself:

In 1900, the Universal Exposition demonstrated the use of reinforced concrete in many ways, causing a revolution in the field of building materials. The French engineer Ernabic was inspired to apply the material to houses when he saw Monier's pots, bathtubs, and cisterns made of barbed wire and concrete at the Paris Exposition in 1867.

In 1879, he began manufacturing reinforced concrete floor slabs, which were later developed into complete buildings using concrete structural beams reinforced with reinforced hoops and longitudinal rods. Only a few years later, in the construction of his apartment complex in Paris, he used reinforced concrete main columns, beams and floor slabs that had been improved and still commonly used today.

In 1884, a German construction company purchased Monier's patent and carried out the first scientific experiments on reinforced concrete, studying the strength and fire resistance of reinforced concrete. The adhesion of steel bars to concrete.

In 1887, the German engineer Coren first published the calculation method of reinforced concrete, the Englishman Wilson applied for a patent for the reinforced concrete slab, and the American Heyt conducted experiments on concrete beams.

From 1895 to 1900, the first bridges and sidewalks were built in France with reinforced concrete.

In 1918, Abram published his famous theory of water-cement ratio, which calculates the strength of concrete. Reinforced concrete began to become an important material to change the landscape of this world.

Concrete can be traced back to ancient times, and the cementitious materials used are clay, lime [2], gypsum, volcanic ash, etc. Since the emergence of Portland cement in the 20s of the 19th century, the concrete formulated with it has the strength and durability required by the project, and the raw materials are easy to obtain, the cost is low, and especially the energy consumption is low, so it is extremely versatile

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At the beginning of the 20th century, some people published theories such as water-cement ratio, which initially laid the theoretical foundation for the strength of concrete. Later, light aggregate concrete, aerated concrete and other concrete appeared one after another, and various concrete admixtures also began to be used.

Since the 60s, superplasticizers have been widely used, and high-efficiency superplasticizers and corresponding fluidized concrete have appeared, polymer materials have entered the field of concrete materials, polymer concrete has appeared, and a variety of fibers have been used to disperse and reinforce fiber concrete. Modern testing techniques are also increasingly being applied to the study of concrete material science.

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Compared with the more primitive concrete proportions obtained by Zhang Jiashi, the data of concrete production in later generations can be said to be quite detailed:

When preparing concrete, first of all, according to the requirements of the project for workability, strength, durability, etc., the raw materials should be reasonably selected and their matching ratio should be determined, so as to achieve the purpose of economic application. The design of the concrete mix is usually carried out according to the requirements of the water-cement ratio law. The amount of material used is mainly calculated using the assumption bulk density method or the absolute volume method.

1. Determination of water-cement ratio:

The calculation of the water-cement ratio of high-strength concrete can not use the formula of the strength of ordinary concrete, and the relationship between the strength of concrete and the water-cement ratio should be proposed according to the test data, and then used as a diagram or calculation method to find the water-cement ratio corresponding to the strength of the concrete.

When a plurality of different mixtures are used for concrete strength testing, one of them should be the benchmark mix ratio, and the water-cement ratio of the other mix ratios should be increased and decreased by 0.02~0.03 respectively compared with the benchmark mix ratio.

2. Aggregate dosage:

The amount of crushed stone per cubic meter of G0 high-strength concrete is 0.9~0.95m3, then the mass of crushed stone per cubic meter is: G0=VS× loose bulk density of crushed stone:

The amount of sand per cubic meter S0S0=[G0/(1-QS)]QSQS-sand rate should be determined by the test, and it is generally controlled in the range of 28~36%.

3. Water consumption:

When calculating the mix ratio of high-strength concrete, the water consumption can be modified by the water reduction rate method on the basis of the water consumption of ordinary concrete. The water consumption of concrete without admixture is deducted from the water consumption calculated according to the water reduction rate of the admixture, which is the water consumption of concrete when mixed with water reducer. At this time, it should be noted that the water reduction rate of the admixture must be determined by the test.

4. Cement dosage:

In the production of high-strength concrete, the amount of cement is crucial, which directly affects the adhesion between cement mortar and aggregate. In order to increase the proportion of colloidal binder in the mortar, the cement content should be relatively high, but it should be noted that the amount of cement should not be too high, otherwise it will cause problems such as too fast exothermic rate or too large shrinkage during hydration. The amount of high-strength concrete cement should generally not exceed 550kg/m3.

5. Test mix adjustment:

The calculated mix ratio results should be verified by trial matching and test mixing. Compulsory mixers must be used to mix high-strength concrete, and high-frequency pressure vibrating should be used to ensure the compactness of the mixture. It should be noted that the test mixing amount should not be less than 1/4 of the rated amount of the mixer, and the mixing method of concrete and admixture should be consistent with the method used in actual production.

6. Determination of mix ratio:

When the absolute value of the difference between the measured density of the mixture and the calculated value does not exceed 2% of the calculated value, it can not be adjusted. When it is greater than 2%, it shall be adjusted accordingly according to the provisions of JGJ55-2000 of the "Design Regulations for Ordinary Concrete Mix Ratio".

After the concrete mix ratio is determined, the mix ratio should be verified by no less than 6 repeated tests, and its average value should not be lower than the strength value of the preparation to ensure its stability.

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The main characteristics of concrete are as follows:

Workability: The most important property of concrete mixtures. It mainly includes three aspects: fluidity, cohesion and water retention. It comprehensively represents the consistency, fluidity, plasticity, resistance to stratification and segregation of water secretion and easy plastering of the mixture.

Strength: The most important mechanical property of concrete after hardening refers to the ability of concrete to resist compression, tension, bending, shear and other stresses. The water-cement ratio, cement variety and dosage, aggregate variety and dosage, as well as mixing, forming and curing all directly affect the strength of concrete.

Deformation: Concrete will be deformed under load or temperature and humidity, mainly including elastic deformation, plastic deformation, shrinkage and temperature deformation. The elastic deformation of concrete under short-term load is mainly expressed by the elastic modulus. Under the action of long-term load, the phenomenon of constant stress and continuous increase of strain is creep, and the phenomenon of constant strain and continuous decrease of stress is relaxation. The volumetric deformation due to cement hydration, carbonization of cement stone, and water loss is called shrinkage.

Durability: The ability of concrete to resist the action of various damaging factors during use. The durability of concrete determines the life of concrete engineering. It is an important property of concrete, so it has been highly valued for a long time.

In general, concrete has good durability. However, in cold areas, especially in engineering sites where water levels change and when subjected to frequent freeze-thaw alternation in a saturated state, concrete is prone to damage. For this reason, there are certain frost resistance requirements for concrete. When used in impervious works, concrete is required to have good impermeability and corrosion resistance. Impermeability, frost resistance, and erosion resistance are concrete durability.

And concrete itself has conditions such as restrictions on its use:

The purpose of curing is to create appropriate temperature and humidity conditions to ensure or accelerate the normal hardening of concrete. Different curing methods have different effects on concrete properties. Commonly used maintenance methods include natural curing, steam curing, dry, wet and thermal curing, autoclaving curing, electrothermal curing, infrared curing and solar curing. The time that the maintenance experience is called the maintenance cycle. For the sake of comparison, it is specified that specimens for determining concrete properties must be cured under standard conditions.

The curing of concrete includes natural curing and steam curing.

During the curing of concrete, the humidity and temperature control of concrete should be strengthened, the exposure time of surface concrete should be minimized, and the exposed surface of concrete should be closely covered in time (tarpaulin, plastic sheet, etc.) should be used to prevent surface moisture evaporation. Before the initial setting of the concrete of the exposed surface protective layer, the covering should be rolled up, and the surface should be rubbed with a trowel at least twice to make it smooth and covered again, and it should be noted that the covering should not directly touch the concrete surface until the concrete is finally set.

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