1. Overview of concrete construction materials

Concrete is a type of artificial stone, formed by mixing ingredients: coarse aggregate, fine aggregate, binder, ... in a certain ratio (called concrete mix). In concrete, the binder (cement + water, asphalt, additives ...) plays the role of binding coarse aggregate (stone, gravel, ... sometimes using synthetic materials in lightweight concrete) and fine aggregate (usually sand, crushed stone, crushed stone, ...) and when solidified, makes all into a hard block like stone.

There are common types of concrete: ready-mixed concrete, asphalt concrete, Asphalt concrete, Polymer concrete and other special types of concrete.

In terms of physical strength, concrete has good compressive strength but not very good tensile strength. Therefore, in construction works, materials with good tensile strength (such as steel) are arranged to be placed inside the concrete block, acting as a load-bearing frame to improve the tensile strength of the concrete.

This type of concrete with a steel core is called reinforced concrete. Other effects such as freezing or water seeping into the concrete can also cause damage to this material.

Concrete is widely used in the construction of architectural structures, foundations, unburnt bricks or blocks, pavements, parking structures, fences, electric poles and even boats.

2. General technical requirements when pouring concrete

2.1 Technical requirements for hand-mixed concrete
For hand-mixed concrete, the input materials must meet technical requirements. Sand and stone must meet TCVN 7570:2006, Aggregates for concrete and mortar - technical requirements. Cement must meet TCVN 6260:1997, Portland cement blend - technical requirements.

Materials:

• When cement is imported to the construction site, the engineer and the supervisor will check the quality certificate of the cement batch and make a record of material acceptance. Note that the cement in the warehouse must be arranged according to the principle of "first in, first out".

• When a source of sand and stone is imported to the construction site, the engineer and the supervisor will check the quality against the submitted sample. The parties will make a record of sampling to send for testing to determine the technical specifications of the materials.

• In addition, the construction water must meet technical requirements. TCVN 4506-87, Water for concrete and mortar - Technical requirements.

• The testing unit is an independent consulting unit submitted by the construction unit and approved by the supervising consultant or investor. When conducting the test, there must be full monitoring of all parties.

• Based on the test results, determine whether the source of sand and stone imported to the project is used for the project or not and establish the mix ratio.

Mix ratio and mixing method:

• Based on the results of sand and stone testing, the laboratory will design a mixing table for each type of concrete grade.
• Calculate the conversion of concrete mix according to the batch (bag of cement) and submit it to the supervisor for approval.
• Post the mixing table at the mixing locations.
• Measure sand and cement according to the calculated volume (cement according to the bag, sand is determined by a 20-liter plastic barrel or depending on the case, calculate the appropriate conversion).
• Use a mortar mixer;
• Mixing time: 5~10 minutes per batch.

2.2 Technical requirements for pouring fresh concrete

• Fresh concrete when imported to the construction site must ensure the technical conditions of concrete grade, slump, temperature, time from leaving the factory to arriving at the construction site.
• Time: The factory time recorded on the form and the time of pouring concrete into the structure must not exceed 120 minutes.
• Concrete grade: Compare with the design of the structure and the delivery note.
• Slump: Test the concrete slump against the delivery note. Concrete is poured into the slump cone 3 times, each time compacting 15 times with a round steel bar of diameter 14, then flatten and withdraw the test cone within 5+-2s, using a ruler to check the slump.
• Concrete temperature: The concrete temperature at the time of pouring should not exceed 30 degrees.
• Sampling: Take concrete samples (3 blocks of 15x15x15cm) for each batch of 20m³; there is a separate symbol to mark on the sample and the concrete pouring area on the drawing.
• The symbol requires sufficient information.

3. Joints between concrete pouring areas

When pouring concrete on a large area, it is necessary to calculate the pouring area so that the joints between the areas in the same pouring batch do not have the case of "the area of ​​concrete poured before has begun to set (concrete begins to dry) but the area of ​​concrete poured after has not been poured in time". This depends largely on the direction of concrete pouring and the division of concrete pouring areas in the same batch.

• In the case of pouring floors with multiple pumps, the pumps and concrete pouring directions must be arranged reasonably; if the floor area is too large, depending on the situation, the concrete pouring stop joint can be divided.
• The waiting time for the joints of the pouring area should not exceed 60 minutes and also depends on the weather when pouring concrete.
• Refer to standard 4453-1995, Monolithic concrete and reinforced concrete structures - Construction and acceptance standards.

Tamping: The concrete pouring process must be tamped continuously and evenly throughout the pouring position so that the concrete does not have holes.

• Columns, walls: Pour at the base of the column; 1 layer of wall base 30cm-40cm high, compact thoroughly then continue pouring and compacting each layer 60cm-80cm until the stopping elevation. When compacting the layer just poured, the rammer is inserted into the previous layer 20cm. When the concrete water floats evenly on the column and wall section, stop compacting and pour the next layer. Avoid compacting too much, causing the concrete to stratify and affect the formwork.
• Floor beams: For floor beams with large heights, concrete must be poured and compacted in layers; the floor must be scraped and compacted evenly (scraping the concrete to where it is compacted).
• Stairs: This is a structure that is very prone to pitting, so care must be taken when pouring and compacting. When compacting concrete, it must be combined with scraping and smoothing the concrete to limit concrete flow. When the concrete is stable, it is necessary to combine using a hammer to knock on the formwork surface.

Concrete surface: correct elevation, even surface

• For columns and walls, the pouring height must be marked on the steel or formwork.
• For the floor to check the height during the concrete pouring process using a level and a spatula. When the concrete has been scraped on the surface, the person holding the spatula marks an area (diameter 20cm) of the position that needs to be marked with a trowel; use the spatula to place on the marked position and read the index compared to the standard height. Adjust the height until reaching the standard height; the distance between the areas marked with hooks is usually 2m in both directions.
• The concrete surface must be covered when it rains. In case of heavy rain, the concrete pouring must be stopped; it is necessary to consider the location of the stop joint; ask for the supervisor's opinion and refer to TCVN 4453-1995.

Concrete curing: Curing the concrete for 7 days
Under normal conditions, immediately after pouring 4 hours, if it is sunny, we must cover the surface to avoid the phenomenon of 'white surface' of the concrete, which greatly affects the strength.

• In the first 3 days, water must be watered regularly to keep it moist, about every 3 hours; at night at least 2 times, the following days water 3 times a day.
• Watering by spraying (artificial rain) with a spray bottle; do not water directly on the surface of newly solidified concrete. Water used for maintenance must satisfy the technical requirements as water used to mix concrete.
• For roof floors that can be maintained by building concrete, pump 1 meter of water for maintenance. During the maintenance process, do not let the concrete dry out.
• Do not impact the newly poured concrete structure such as throwing equipment on the floor...

4. Standard concrete floor pouring construction method

• Taking the floor level

Taking the floor level is done according to the current standard water level measurement method. The floor needs to have a minimum level of 0 according to the local standard level.

• Pouring concrete

Pour concrete according to the grade and thickness according to the design. Depending on the type of ready-mixed concrete (fresh concrete) or batched concrete; we will get floors with different levels of stability. Fresh concrete is mixed according to the standard ingredient ratio; and mixed in one block, so the mortar stability is higher than hand-mixed concrete in small batches. Fresh concrete mortar has high stability; sufficient water content, reducing foaming on the concrete surface. After leveling; wait until the mortar surface can be walked on (needle penetration hardness of about 1mm); then proceed to smooth - level with a grinder.

During the leveling process, avoid sprinkling high-grade cement sand mixture; or unmixed cement because it can increase the surface concrete grade, reducing the paint permeability of the concrete surface. For hand-mixed concrete; Due to the unstable water/cement/sand ratio, it is easy to cause cracks between blocks; excess water - foaming, and deviation of the foundation. At that time, it is necessary to pour a layer of mortar to level the surface.

5. Floor surface mortar scraping in concrete pouring construction techniques

In case of having to pour manually, due to the different proportions of concrete components; it is difficult to ensure uniformity, so after tamping with a rammer and a table; we wait for the concrete block to partially harden and then proceed to level the mortar (cement/sand = 1/3 to 1/4); use a manual trowel or a trowel machine. However, before proceeding to leveling, it is necessary to check the hardness of the leveled mortar.

Avoid leaving too much water; or leveling when the floor surface is still wet, which will cause the cement to float, causing the surface grade to be too high; or burning the cement locally; both cases will cause poor absorption of paint on the concrete surface. The leveled mortar layer can be constructed within 24 hours after pouring the concrete to ensure the structure between the layers. In case the previously poured concrete layer has reached maximum hardness (after 28 days); it is necessary to use an adhesive additive to ensure the bond between the new mortar layer and the old concrete.

Concrete floor maintenance
After pouring, it is necessary to conduct curing for 28 days (without additives); or shorter if using fast-hydrating additives. In case of old floors, pour an additional layer of mortar; the waiting time for hydration is about 1 week to 10 days. During the curing period; it is possible to grind and level (wet or dry) with a grinding stone or sandpaper. Avoid using heavy machines or strong impacts on the surface. In case the surface is not smooth enough; a patching mixture can be used to level it.

6. Introducing a reputable design & construction consulting service provider

The importance of construction units is undeniable, their reputation will ensure the quality and aesthetics of your project. Nowadays, there are many units providing construction design services to meet the increasing construction needs in our country. Therefore, finding a reputable unit is not easy and requires you to spend time researching. In the selection process, you need to research carefully and make sure that the accompanying unit must have high expertise, many years of experience, have a clearly signed contract, transparent costs, ... To help customers save time searching, Công ty TNHH Đầu tư Xây dựng Hưng Nghiệp Phú confident that it will be the best choice for you.

Hung Nghiep Phu Construction Investment Co., Ltd. with the mission of providing the best solutions and services, building a prosperous community with customers, Hung Nghiep Phu is gradually affirming its brand through sincere cooperation, with a team of leaders with ethical capacity, creativity, expertise and strategic vision. Hung Nghiep Phu owns a team of skilled, highly qualified employees who will bring customers the best quality technology.

Hung Nghiep Phu Construction Investment Co., Ltd. - specializes in constructing civil and industrial works. We look forward to accompanying our valued customers in construction projects as well as continuous procedures such as planning diagrams, applying for construction permits, completing procedures, applying for fire prevention and fighting certificates, ... If you have any questions or are in need of design, completing procedures, please contact us immediately for free consultation!

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Source: Internet Collection