In some cases, the construction of the object is impossible without the use of this equipment. For example, when installing structures in cramped conditions or during the pouring of densely reinforced structures.

The most popular types of concrete pumps today are techniques with a mechanical or hydraulic type of drive. Models are piston, rotary and screw. All of them have their pros and cons, so the choice of technique should be approached especially carefully.

There are different types of concrete pumps, each of which has its own features and scope of application. For example, there are not only stationary, but also auto concrete pumps.

How the concrete pump works

In most cases, the principle of operation of the concrete pump will be as follows:

• Due to the movements of the hydraulic cylinders, the mortar enters the inside of the transport cylinder from the receiving hopper.
• The mixture is pumped into the concrete conveyor.
• The pumping speed is regulated by using different amounts of oil (oil-hydraulic models).

It should be noted that the device and operation of the concrete pump are not always the same. Some types of equipment are designed for periodic delivery of concrete, while others – for continuous pouring. Each of the options has found its application in construction:

Continuous mix delivery is needed to fill large structures in their entirety. As a rule, rotary models are used for this purpose.

Intermittent pouring will be an advantage if it is necessary to pump concrete into small segments of formwork of different structures. For this purpose, piston-type equipment is best suited.

The principle of operation of the autoconcrete pump should be considered separately, since it differs from that of stationary equipment:

• The concrete mixture is unloaded from the mixer of the concrete truck into the receiving hopper.
• The pumping station pumps the solution into the system.
• The mortar is conveyed through pressurized pipes.
• The mixture is subsequently unloaded at the end point.

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Pouring the concrete mixture into the formwork is not the end of concrete work, as previously written poured concrete requires further care, to acquire the required strength in a certain period of time. Increase in the strength of concrete at the initial stages is fast and concrete prepared on Portland cement already on 7 – 10 days after pouring, gaining 60-70% of its design strength, which comes on 28 days. After that, the rate of strength gain slows down. Under optimal conditions of hardening concrete is best to gain strength at t=20 C and humidity of at least 80%) and it is especially important to maintain such conditions during the first 3-5 days. For more information about concrete care and its necessity, please see “Why Concrete Care?”.

Uncracking

To disassembly work can begin after the concrete has gained 70-80% of its design strength, under normal curing conditions, this occurs on the 7th day. But this is for general monolithic works including massive structures, in private construction, in private construction, in compliance with the technology of concreting and subsequent care for the laid concrete, depending on the massiveness of the structure, decompression can be carried out on 4-5 days.

Formwork removal, disassembling

The formwork should be carefully dismantled in order to avoid the destruction of the formwork and concrete structures. The surfaces of the formwork, which will still be used, should be cleaned with metal brushes and scrapers from the remains of concrete mixture and lubricated with a special emulsion. In case of large sinks and spalls on the concrete surface, it can be cleaned and grouted with cement-sand mortar. Remove the formed concrete surface buildup with a trowel.

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Concrete cutting tips

1) Allow the saw to cut evenly

The diamond cutter should always move naturally in a straight line, as any misalignment can affect the result. The cutting process should take place in a controlled environment. If you want to do it right, it is best to draw a straight line where the cut will go and then allow the saw to pass the material without adjusting halfway through.

2) Avoid bends

A fairly common mistake when diamond cutting concrete occurs when a novice cutter tries to make a smooth angle.

3) Use the right diamond disks

Choosing the right cutting disks is also important for smooth cuts. Poor quality cheap blades will give you wobbles. Always use only quality blades for diamond cutting concrete!

4) Think about safety

This is an important tip to consider when cutting concrete. It is essential to have the proper safety gear to ensure your safety while cutting concrete.

Believe it or not, it actually helps when cutting as it helps you better focus on the process rather than how to save your limbs.

5) Plan ahead

Planning is paramount when it comes to cutting concrete. By planning ahead, the right steps to take, you can save a lot of time and actually achieve the best possible result.

6) Turn to the professionals

The best guarantee of quality is always the professionalism of the craftsman. While achieving smooth concrete edges requires precision and the use of the right equipment, it is also important to seek professional help whenever possible.

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Covering with PVC sheeting: provides additional insulation and protection from low temperatures. This method is effective at moderate frosts.

Heat guns: are installed to maintain heat at the construction site. are used to create a thermal “tent” using polyethylene over the poured concrete surface. This allows concrete to harden quickly even at extreme low temperatures (concrete will set in 1-2 days).

Anti-freeze fillers: added to the concrete mix to prevent water in the mortar from freezing. They are used in frost and winter concrete.

Paving concrete in winter

Paving concrete in winter requires additional steps to preserve its qualities
To prepare concrete mix in winter conditions and preserve its qualities, the following recommendations should be considered:

• Heating of aggregates and water: this is achieved by heating the aggregates to 60°C and the water to 90°C. The cement is not heated, which ensures a final mix temperature of about 35-40°C.
• Filling the mixer drum with water: the drum is first filled with water and then the mix is added, ensuring more even heat distribution.
• Extending the mixing time: extending the mixing time by 1.2-1.5 times contributes to more efficient uniform heating.
• Transportation in insulated closed containers: to prevent cooling of the prepared mortar during transportation.

The base on which the concrete will be placed is heated to positive temperatures and thoroughly cleaned of ice and snow. The reinforcement may also need to be heated if its temperature is below 10°C. The concreting process is carried out at a rapid pace so that each previous layer of concrete has time to set before the temperature inside drops significantly.

Many builders wonder at what temperature concrete can be poured in winter and our experts have the answer: winter concrete can be poured at temperatures from +5°C to 0°C, frosty M5 – from 0°C to -5°C and frosty M10,15 – from -10°C to -15°C. That is, depending on the temperature regime, you can lay concrete from 0 to -15 ° C, the main thing is to choose the right material.

Temperature during concreting in winter

The use of electric heating of concrete is usually justified on large construction projects with powerful transformers. However, its cost makes it ineffective for private buildings in the current state of domestic power grids.

The most reasonable and affordable method to protect concrete from freezing is its covering, which is effective in the temperature range from +3 to -3 °C. Simple covering of concrete with polyvinylchloride film or other heat-insulating material allows preserving the heat released by cement when it interacts with water. Creating an artificial greenhouse effect also provides good results, but requires immediate covering of the fresh construction. However, covering is effective only in certain temperature conditions, and with a sharp drop in temperature to -5 or -15 ° C, becomes impractical, requiring the transition to the use of gas or electric heat guns.

When heating with heat guns, it is also necessary to use PVC film or other insulation for temporary shelter, providing sufficient conditions for rapid achievement of concrete strength within 3 days.

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What is the mobility of concrete

Recall, we are not interested in grade, frost resistance, strength and other properties, since almost any concrete can have mobility, labeled from M1 to M5.

The formal definition is as follows: “Mobility (hereinafter M of concrete mortar is the ability to spontaneously spread under the action of its own weight or under slight impact”.

Again, formally, water is of key importance: the more of it there is, the more mobile the mixture will be. Hence the incorrect conclusion that only the amount of water determines the mobility characteristic, although in fact the physics of the process is much more complex.

To appreciate how this looks in construction, let’s take a simple example. If you pour out of a dump truck a low-mobility compound (M1), it will remain lying in a heap, which will have to be raked with shovels. Poured out of the mixer (such mortars are not taken by dump trucks) very plastic mixture (M5) will spill out a large, uniform spot. As you understand, a large fluidity will not allow to solve some problems, and too dense mass – others, so the characteristic directly affects the applicability.

Mobility is also known as plasticity, workability or stiffness. It does not change the essence of the matter, we are talking about the same thing – the density, viscosity or, scientifically speaking, the degree of cohesion of the mortar. Simply put, it is nothing but the viscosity of the finished cement-sand mass with filler.

What affects the mobility, on what it depends and what is it like

When mixing concrete according to the recipe, components are added, including water, which really has a decisive effect on the P. But this is not all. The indicator is affected by the internal frictional forces of the particles, so other factors are also important:

• Cement grade (the final density of the cement dough);
• The ratio of water to cement;
• Size and shape of sand and fillers;
• The overall ratio of all components;
• Purity of water (minimum impurities and inclusions, ideally distilled water);
• Fineness and uniformity of cement grinding, the higher the uniformity the better;
• Purity of sand and aggregate, washed material refers to the benchmarks;
• Additives and modifiers.

Another factor rarely mentioned is thoroughness of mixing. A poorly mixed concrete mix will be stiffer than a well-mixed one. It is for this reason that the mortars prepared on site in a concrete mixer are always inferior in quality and standards to factory mixes.

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What reduces the quality characteristics of mixtures

Shaking, vibration and downtime significantly degrade the “maturity” and condition of the mortar. When factory logistics chooses the transportation, which will deliver concrete to the site, factors are taken into account, of which the customer does not even suspect.

Distance

Taking into account the quality of the road surface sets the allowable delivery time and places restrictions on dump truck delivery.

• During transportation by dump truck, vibration and shaking on a bad road will cause rapid stratification, the mixture will be divided into fractions (heavy components will settle down, cement milk will be on top). It is impossible to lay such a mortar without additional mixing after arrival on site.
• Open surface. With even traffic or stops on the way, after about an hour, the mortar will begin to set. This greatly reduces delivery by dump truck, especially in hot weather;
• Under difficult conditions (heat, traffic congestion, etc.) overloading is prohibited during open haul transportation. Unloading is required in a hopper where the mixture can be mixed to restore homogeneity.

Shipping

With mixers, transportation is more gentle:

• The mixer will provide constant mixing and maintain uniformity, maximizing distance and delivery time;
• Unloading can be delayed for some time if the mixer will stir the mortar periodically;
• No contact with air and mixing eliminates the onset of setting.

In any case, how the transportation will be organized, decide the technologist and logistician, making a roadmap. Therefore, do not be surprised when, when placing an order, our manager “inquires” the details of access, the possibility of travel by roundabouts, etc. Concrete mortar must be delivered to the site on time, without losses in terms of characteristics. This activity requires a responsible attitude.

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The minuses of prefabricated foundations are manifested where they should not be used
First of all, strip foundations should be considered not as monolithic structures. This is a frequent mistake of private developers, in civil and industrial construction this feature is taken into account separately.

How a single block works in a load-bearing serious load-bearing structure can be understood by several examples:

• Insufficient preparation. Unprepared base can differently “subside” when exposed to loads, hence – uneven shrinkage of the entire perimeter;
• Errors during installation (lack of proper dressing, wrong choice of cement mixture grade, too large distances between blocks, etc.);
• Improperly assessed soil, especially if the water table is high, will lead to the fact that FBS will “sag”, if not immediately after installation, then over time;
• In the absence of a reliable foundation, each block will experience separate loads, practically not participating in the unloading of load-bearing walls and floors.

At the same time, most of the durable blocks can be installed without preliminary preparation, it is enough to backfill with crushed stone (preferably gravel). But there are limitations. If you do not want to get a skewed box of erected walls, it makes sense to remember where prefabricated foundations should not be used:

• Weak soils with a high level of groundwater without additional protection measures and organization of a drainage system;
• Areas with a relief that does not allow the pouring of a reliable foundation;
• Houses in which one load-bearing wall is 3 or more meters higher than the other (load-bearing);
• For objects with a construction volume of more than 1,500 m3 in coastal areas.

If we take into account the scope of use of strip bases from FBS with the listed restrictions, the disadvantages will be excluded. The positive aspects of ready-made reinforced concrete products in this case will greatly simplify life, because every developer is interested in the delivery of the object in the shortest possible time.

If we talk about construction, the blocks have only pluses

Let’s not argue for a long time, just list the main advantages that give the use of FBS blocks, prepared for installation at the construction site:

• The block foundation is ready for wall erection 2-3 days after completion of installation. The reinforced concrete at the factory has gained strength, it is enough to wait for the cementitious mortar to set;
• The work goes quickly. While the crane puts the next block, the delivered FBS blocks can be tied together and the laying of mud bricks can begin;
• Waterproofing and drainage system can be carried out at the same time as installation, there is no need to wait for the formwork to gain strength and dismantle it;
• The size of the perimeter can be any size, it is enough to choose the appropriate size of the block. When laying out bay windows, corner joints can be poured with concrete or made of bricks;
• While the poured concrete is gaining strength (28 days), it is possible to erect walls. The technology of installation of prefabricated foundations allows you to significantly accelerate the construction of both private homes and industrial buildings.
• Therefore, if you take into account the soil on the site, prepare the support zone, excluding installation errors, the block foundation will be the leader in terms of strength, reliability and durability.

However, the disadvantages of such foundations should be taken into account, they are few, but they are there.

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About what the composition and labeling will tell

In terms of classification, concrete is divided into two main groups:

• General building (structural), used most widely.
• Special, which has additional properties and characteristics in connection with the specific purpose.

In both groups there is a division based on the weight of the solidified monolith:

• Heavy (density more than 2000 kg/m3);
• Light (density less than 2000 kg/m3).

Additional characteristics are also taken into account in the classification, among them there is a division by composition:

• By type of binder (cement, slag, gypsum or lime);
• According to the structure after gaining strength (large-porous, cellular, porous and dense);
• By type of filler (dense, porous or specialty).

The above factors provide differences within a single brand, but there are not so many. For example, M250 can be light or heavy, but not porous. At the same time, there are frost-resistant varieties and waterproof, which means that the brand can have a special purpose.

Hence another addition in the classification by additional properties:

• Frost resistance. The number of complete freeze-thaw cycles that the material can withstand without deformation and destruction. It is denoted by the letter F, the number is the number of cycles (for example, F50);
• Water resistance. It is denoted by W, the larger the number, the more the material resists water. Special hydraulic concrete is labeled W200, and generally does not interact with water.

Thus, the marking of BSG M250 B20 B20 P1 F200 W6 can be read, making a complete picture of the permissible application:

• Ready-mix concrete (BSG);
• Monolithic strength 250 ksi/cm2 (M250), guaranteed strength 20MPa (B20);
• The mobility (otherwise called plasticity) P1 (sometimes P1) characterizes the workability. In this case, the mixture is “very viscous”;
• High frost resistance (F200) guarantees in the climate of Ukraine hundreds of years of operation without destruction and defects;
• Medium water resistance (W6) will require mandatory waterproofing.
• The detailed description will indicate the type of filler. The usual choice is granite crumbs or crushed stone.

The ability to read the markings will help to choose the required concrete.

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Types of shrinkage and the time during which it occurs

Non-experts believe that, given the quality and strength, thanks to which concrete of all grades has become the most popular building material, it is initially a “monolith”. In fact, concrete mortars have three “life cycles”, each of which is accompanied by a natural decrease in volume. This is called “concrete shrinkage”, which according to GOST should not exceed 3%.

The main causes of shrinkage are three: the presence of water in the ready-mix mortar, the process of hydration (formation of cement stone), and density gain (not to be confused with strength gain). Hence the three stages of volume reduction, shrinkage.

Plastic

From the moment water is added, it begins to bind to the cement, evaporate, flow away, etc. Before and after the concrete is placed. The higher the plasticity of the ready-mix concrete (more water), the greater the volume loss will be. In any case, moisture will be removed from the volume, so all grades of concrete are subject to shrinkage without exception.

This stage lasts 6-8 hours (primary setting) and gives the largest shrinkage ~4 mm per linear meter.

Autogenous

It starts from the moment of transition of primary hydration to the formation of strong cement stone. At this time, water binds, compaction begins (carbonization processes take place), excess moisture is forced out through capillaries to the outside or dries inside the monolith.

This stage lasts approximately 5-9 days, depending on the concrete grade. The total volume loss is ~1 mm per 1 p.m.

Contraction

Depending on the concrete grade and reinforcement, the rate varies between 0.2-0.8 mm per 1 p.m. It is associated with the natural compaction of the material, the departure of residual moisture and the final formation of cement stone. This is the final stage of the final set of strength and density of the concrete monolith, which lasts from a year to a year and a half.

Given the above, shrinkage processes and volume loss are not “force majeure”, but a predictable and calculated value that should be taken into account when ordering the required amount of mix.

How to calculate losses and reduce the shrinkage percentage

Let’s dispense with the intrigue, the practical value of the “additive” to the calculated volume of concrete mix is 8-10%. For the foundation – less, for the site – more. The reserve will take into account losses in transportation and pouring on site, as well as errors in the maintenance of the poured monolith, which is better to avoid.

In general, the calculation is based on plasticity and prediction of water loss. Therefore, the higher the plasticity index (mobility, maximum P5), the greater the shrinkage will be. But there are other ways to reduce volume loss:

• Reinforcement. The thicker it is, the less shrinkage there will be;
• Vibratory paving. Primary compaction during paving will reduce losses, even simple “poking” and tamping of the poured mixture will reduce them;
• Adding plasticizers and additives to the finished concrete mix to reduce volume loss;
• Reducing the amount of cement or sand (will affect strength);
• Using special grades of concrete that are not subject to shrinkage.

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For any body, density is directly related to strength, the most dense natural material is osmium (platinum group). The strength characteristics of this metal are exceeded only by artificially created materials. Do not confuse the relationship between density and hardness, the hardest element is diamond, which is related to the crystal lattice. At the same time, its density is 3,500 kg/m³, while osmium has 22,590 kg/m³, hence its super-high strength.

Despite the direct connection, the weight-volume characteristics of concrete are not paid enough attention, especially by private builders.

What is the density index and how it affects the properties of the monolith
In fact, the characteristic, sometimes called “specific gravity”, speaks about the amount of material in the volume under consideration. The ratio is always less than 100%, that is, there are air pores in a given volume that are not filled with the components of the concrete mixture. A denser monolith also has a stronger structure.

However, the indicator affects not only the strength.

• When air replaces other components in the structure, the overall strength of the monolith is reduced; displacement of pores increases it.
• The denser the concrete, the higher its thermal conductivity, especially heavy grades practically do not retain heat, and light, porous types of concrete are also used as heat insulators.
• Compacted monolith practically does not absorb moisture, does not react with it, which makes it possible to produce compositions for hydraulic engineering works. At the same time, frost resistance increases. Since there is no moisture in the volume, no defects occur during the “freeze-thaw” cycle.
• The denser the internal structure, the greater the resistance to tensile and bending loads. At the same time, the characteristic of compressive resistance (standard strength marking) can coincide with lighter concretes.
• It is clear that, as a result, the weight affects a wide range of properties, so the grade indicated in the documents for the batch is not decisive when choosing a mortar. Note that the weight of a cubic meter of mixture is a manageable value.

Increase the density can be increased during pouring, which will increase the strength of structures, by the following methods:

• Poking with shovels, rebar, etc. Air escapes from the pierced volume and the mixture is compacted. Suitable for small formworks;
• Application of vibrators. The mortar not only fills the reinforced space better, but is also deprived of air bubbles;
• Heating the monolith in the process of laying or pouring. The measure is not easy, but allows you to remove almost all pores from the volume.

These are technological measures that we recommend to carry out even when pouring typical concrete mixes on a private plot, even if you are pouring an ordinary floor screed.

It is easy to find out the density of the resulting solution. Weigh a liter jar, remember the weight, fill it with the mixture, stir it with a rebar and weigh it again. From the resulting figure, subtract the weight of the jar and divide by its volume (1000 cm³). Get the value in g/cm³. This will be the density of the resulting solution.

For example, the jar weighs 300 grams, and with concrete 2400. Simple calculation: 2400 – 300 = 2100, divide by 1000 = 2,1 g/cm³ or 2100 kg/m³. If the capacity is exactly 1 liter, you can simply take the difference in grams.

If the measures in laying allow a slightly higher specific gravity, a wider range of values is managed in production.

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