Types of foundations There are a large number of different types of foundations, but they all have one thing in common. Almost everywhere, concrete mortar is used as a binding material. It is this that gives the foundation the necessary strength and reliability, but it takes some time for it to gain the necessary parameters.
It is this period that is considered key in the construction of any foundation, therefore it is strictly prohibited to build load-bearing walls on a raw foundation. First, you need to wait some time until the concrete gains its original strength, and this depends on the type of solution, the amount of water in it, even climatic conditions and pouring technology.
Therefore, it is quite difficult to say exactly how long it takes for concrete to harden.
The design and characteristics of concrete foundations provide for the necessary moment - this is the time until the concrete hardens. During this time, a chemical reaction occurs between cement and water, releasing a large amount of heat. Therefore, even in standard climatic conditions with a large number of warm days, concrete dries for at least a week, but during this time the average strength of the concrete base is achieved.
But the final strength of the structure is achieved in a much longer time, and an important factor here is the conditions for its hardening.
Under standard drying conditions, the duration of this process can be up to four weeks, sometimes even longer if the base is thick enough and consists of several separate balls (monolithic foundation). And if a columnar or strip structure is used, then the time will be significantly less.
Polymerization of concrete
Concrete hardening is carried out due to hydration - a special chemical reaction that occurs between binder components and water. The process is intended to convert the base raw material (cement-sand mixture with crushed stone and sand) into calcium hydrosilicate. At the end of the hardening period, a monolithic base with increased strength properties is created.
The hardening time of concrete is determined by the following factors:
- Brand of cement mixture.
- Proportions and ratio of components in the solution.
- Indicators of atmospheric humidity.
- Production technology.
- Ambient temperature.
- Thickness and density of concrete pouring.
- Compliance with the rules for caring for the solution during the hardening process.
For complete polymerization, two stages are involved:
- Grasping.
- Set of declared strength.
When determining how long concrete takes to dry, it is important to consider the brand of cement that was used when mixing the mixture. The M500 model is characterized by the greatest reliability, and the M100 has the minimum strength.
The hardening time of concrete is determined by the proportions of the components and the presence of various fillers in the composition. The more sand or gravel there is in the solution, the faster the excess liquid will come out of it. If you use a large amount of expanded clay and slag, the water will begin to evaporate more slowly.
If the placement density is not observed, the strength properties of the concrete mixture will be reduced. When constructing industrial facilities, concrete is additionally compacted using vibrocompression. At home, the procedure is replaced by simple compaction with hand tools.
To retain moisture in the mixture, it must be covered with a waterproofing film. It can be polyethylene or bitumen mastic. The purpose of such materials is to enhance hydration and protect the solution from rapid loss of liquid.
This effect is also achieved by periodically wetting the solution with water. It is applied by spraying or spraying.
Grasping
Setting of concrete is the first stage of its polymerization and takes no more than 1-2.5 hours. The exact interval is determined by the temperature conditions under which the work is performed:
- If the ambient temperature is +20°C, the chemical reaction will start 100-120 minutes after pouring the mixture into the formwork. Then the composition will dry for another hour.
- At a temperature of +1...+19°C, setting will occur in 3-5 hours.
- At zero temperature, the reaction begins 7-10 hours after mixing. In this case, the drying time will be 16-20 hours.
If there is a negative temperature at the construction site, the components of the mixture will no longer enter into the process of hydration with water, and the mixture will not be able to dry. It will remain inert until temperatures rise above 0°C. To get rid of this phenomenon, you can add special fillers to the concrete composition that accelerate hydration, or build insulated formwork.
If it is hot enough outside (above +30°C), the setting time of the concrete will be reduced, but the quality of the final product will decrease. This is due to the rapid evaporation of moisture and deterioration of the strength properties of concrete products.
During hot periods, special fillers are added to the mixture, which increase the hardening time of concrete.
Among them:
- Acid NTF.
- Sugar feed molasses.
- Sodium gluconate.
- Complex compositions.
- Other additives.
How long it takes concrete to dry and how long it takes to set depends on a lot of factors. Hydration refers to the process of converting raw materials into calcium hydrate, i.e. the cement base begins to mineralize and becomes monolithic.
Curing time
After setting, the concrete hardening process begins. It consists in the occurrence of a chemical reaction between cement granules and the liquid from the solution. The best hydration rates are observed at air humidity of 75% and at a temperature of +15...20°C.
If the temperature remains below +10°C, special anti-frost components will need to be added to the composition. Otherwise, the concrete will not receive its design strength.
Conditions for high-quality hardening
The main conditions for high-quality hardening of concrete are:
- temperature above zero (optimal indicator - 18-22 degrees);
- air humidity is 90% and above.
If these conditions are not created, it is necessary to provide them artificially. The best option is to use moistened sand, a special chamber or sawdust. Being in a humid environment, the quality and speed of concrete hardening will be higher. If you leave the solution to harden in the open air, otherwise there is a risk of moisture evaporating from it. This will lead to reduced strength.
Premature drying does not have the best effect on the hardening of concrete. The thing is that all the grains of the mixture are not able to quickly react with the liquid medium. Therefore, it is recommended to use polyethylene films to create an obstacle to the evaporation of moisture.
Caring for concrete after pouring
Any concrete mixture requires proper care after pouring. First of all, it is necessary to provide suitable conditions for a normal chemical reaction between water and binder components. If the basic rules are followed, the solution becomes strong and solid. The specifics of care directly depend on the time of year when the installation was performed.
Experts do not recommend carrying out construction work in the heat, so it is better to start it in the morning or evening, after sunset. If pouring is done during the day, it is necessary to provide good protection from ultraviolet radiation by covering the layer with roofing felt, slate sheets or other covering material.
Aftercare is to protect the surface from erosion and holes. When performing independent mixing, it is necessary to adhere to the requirements of SNiP and not allow long pauses between activities. In summer, the mixtures dry quite quickly, so any downtime is contraindicated. Otherwise, the solution will become unusable.
In hot weather, the mixture must be regularly moistened with water and adhere to technological standards that prevent the evaporation of the liquid.
If the outside temperature is more than 15°C, water must be added to the composition every 10-12 hours. In windy weather - after 2-3 hours.
There are no special difficulties in caring for the poured base. The main thing is to maintain optimal humidity and temperature during the setting and hardening stage of the mixture.
Weather affects opening times
In hot, dry weather, especially if you're pouring under the hot sun, heat can quickly draw water out of wet concrete, reducing pouring time to 30 minutes, so it's best to pour on a day when the temperature is between 15 and 25 degrees Celsius . If you do have to work in hot weather, the following tips will help extend your pour time:
- Use cold water to mix the solution.
- Before pouring, wet the sand in the molds. This will prevent the dry soil from drawing water out of the concrete too quickly.
- Store bags of concrete in the shade - the hot sun will increase the temperature of the dry mix.
- Plan to work early in the morning when temperatures are cooler.
- Hire more workers because pouring concrete is a labor-intensive process.
Strengthening stages
Hardening of concrete until it reaches grade strength takes about 28 days, but it is possible to determine exactly how long the material hardens only at the construction site.
The whole process is carried out in two stages:
- The first is the setting of the mixture, when all its components are combined into one whole.
- The second involves a set of strength properties and hardening.
To clarify how long it takes for concrete to set, you can first focus on the generally accepted value of 1 day from the moment of pouring. The exact time depends on temperature conditions. If it is warm enough outside (above 20°C), the process will take no more than 5 hours.
The mixture begins to set within 2-3 hours from the moment the components are mixed. In autumn this can last more than a day. At the same time, construction work continues in cold weather.
During the first stage, the mixture remains in a mobile state, so the user can make changes to the shape of the future structure. To reduce viscosity, the thixotropy mechanism is used.
The next step is to harden the mixture. Brand strength characteristics appear after four weeks, but finishing properties are achieved after a couple of years. The curing time of concrete depends on temperature and humidity conditions.
The first 5-6 days from the moment of pouring are characterized by the maximum intensity of hardening, so during this period the material already has 30% strength. After 90-10 days, the indicator will be 20% higher than the brand value.
During the first week, concrete must be exposed to temperature, moisture, heat and waterproofing.
Particular attention should be paid to maintaining optimal humidity. At a temperature of +25...+30°C, concrete is loaded within 7 days from the moment of pouring.
Don't forget to take into account the completion time
When pouring concrete, plan to spend half your working time on the pouring process and the other half on the finishing process. If the concrete mix has approximately one hour of labor time, plan to spend no more than 30 minutes on the pouring and screeding process itself so that you have enough time to finish finishing the slab.
To begin the finishing process, it is necessary to screed the surface. Screeding is the process of removing excess concrete by leveling the top level of the slab. Whatever tool you use (ruler, level or block), it should be larger than the width of the area you are filling. One pass in each direction is usually sufficient to achieve the desired result.
Finishing fresh concrete involves floating the surface with a concrete float, hand finishing the edges where a straight edge doesn't reach, using an edging tool to create rounded edges, adding texture with a broom to reduce slip, and then using a groove tool to create control joints. The larger the slab, the longer it will take to finish, so take this into account and work quickly and seek additional help if necessary. If the concrete begins to harden, skip the control joints and work on smoothing and cleaning the surface and smoothing the edges. Control joints can always be cut the next day with a concrete saw.
Dependence of strength gain time on concrete grade
The intensity of strength gain also depends on the grade of concrete. The lower the grade of concrete, the higher the strength characteristics will be. Compositions under the M15-M150 brands are characterized by a critical strength of up to 50%.
Structures made from M200-300 grade materials have a value of 40% of the grade. At the same time, the safe indicator allowed by standards is 50%, and construction work can begin only after receiving marks of 72% of the specified values.
To assess the strength properties of a concrete mixture, you can use two methods:
- Destructive. Involves crushing a cube using a press.
- Non-destructive. In this case, the properties of the material are determined without destructive effects.
The second technology is more in demand and is based on the use of elastic rebound devices, ultrasonic equipment or impact devices.
With the help of modern portable devices, you can quickly and accurately determine the degree of strength.
They are:
- Electronic. They are highly accurate and capable of storing up to 5 thousand measurements per diagnostic.
- Mechanical. They are used to determine the strength properties of concrete of different classes.
- Ultrasonic. Designed to assess transfer and tempering strength during solidification. The propagation speed of ultrasound exceeds 4500 m/s.
Filling time is limited
For most concrete mixes, you can expect about an hour of labor time to get the concrete loaded into the molds and leveled before the mixture begins to harden. During this time, it is vital that everyone working on the project knows what their job is and that everyone works as quickly as possible. You won't have time to run out and buy an extra bag of cement, so make sure you have enough construction materials before you start pouring, as well as all the necessary tools (shovels, concrete rakes, screed, construction floats, spatulas, broom).
Impact factors
To find out how long concrete takes to dry, it is necessary to take into account a number of conditions that affect the rate of concrete hardening.
Seasonality
The key factors that determine how long concrete hardens are the environment and the period of the year when construction work is carried out. This group includes indicators of outdoor temperature and air humidity.
If in summer the composition can harden in a few days, then in the cold period hardening will take more than a month. The specifics of strength gain under favorable concrete hardening conditions are as follows:
- 1-3 days - no more than 30% brand strength.
- 7-14 — 60-80%.
- 28 — 100%.
If you want to make the foundation mortar quick-hardening, you need to add special additives to its composition.
Tamping
Tamping has an even greater influence on the drying time of concrete. The better this procedure is carried out, the better the reaction of water with astringent components will be. In the industrial production of concrete solutions, vibration equipment is used, but at home you can get by with bayoneting.
A dense screed does not tolerate cutting and drilling after compaction, so for such work it is necessary to use diamond drills. A simple tip will quickly fail.
Compound
How long the concrete hardening process can take depends on its composition. So, if it contains a large amount of porous additives, such as slag and expanded clay, water will linger in the solution for a long time. If the mixture contains sand or gravel, the liquid will come out faster.
To reduce the intensity of moisture evaporation and increase the strength characteristics of the composition, it is diluted with additional components. It can be bentonite or a soap composition. The introduction of such additives increases the overall cost of the work, but prevents the problem of early drying out of the solution.
How long does it take for concrete to harden?
graph of the strength of concrete as a percentage of a day depending on the ambient temperature.
A strip foundation made from concrete blocks or stone should dry for no more than a month, although the drying time depends on specific climatic conditions.- The monolithic foundation dries out for a long time, because there are several horizontal layers. Therefore, the average drying time is one and a half to two months.
- The prefabricated block structure, given the complexity of construction, also takes about a month to dry.
- A pile-screw foundation does not require waiting, because it uses ready-made factory structures on which a grillage or load-bearing walls are already installed;
- Pile-grillage foundations take several weeks to dry, because the grillage is open on each side, so there is an excellent level of ventilation.
Hardening
The hardening process of concrete begins immediately after thickening and setting. At this time, the substance gains its strength. Despite the specified 28 days, the process continues later. This period is standardized for certain grades of concrete. But in the first weeks and months, the hardening of cement stone proceeds more dynamically.
This stage cannot be accelerated. If water evaporates too quickly, the hydration process stops and the characteristics and performance of the final cement stone product decrease. The norm is considered to be up to 2 weeks with sufficient water.
Concrete poured into a mold or formwork should not be touched for at least a week, otherwise the integrity of the structure will be compromised. As it hardens, the volume of the cement mixture decreases. Concrete hardens from the outside to the inside, shrinking. If the conditions for hardening are not suitable, then cracks may appear on the surface, which indicate uneven heating of the substance. As a result, the cement stone turns out to be fragile and short-lived.
