Curing Of Concrete – How & why

Definition

Curing of concrete is defined as providing adequate moisture, temperature, and time to permit the concrete to gain the specified properties for its intended use. In other words watering the concrete to make it stronger. The more the better.

Concrete derives its strength by the hydration(releasing heat after reaction of cement with water) of cement particles. The hydration of cement is not a momentary action but a process continuing for a long time. Of course, the rate of hydration is fast to start with, but continues over a very long time at a decreasing rate. The quantity of the product of hydration and consequently the amount of gel formed depends upon the extent of hydration. It has been mentioned earlier that cement requires a water/cement ratio about 0.23 for hydration and a water/cement ratio of 0.15 for filling the voids in the gel pores. In other words, a water/cement ratio of about 0.38 would be required to hydrate all the particles of cement and also to occupy the space in the gel pores. Theoretically, for a concrete made and contained in a sealed container a water cement ratio of 0.38 would satisfy the requirement of water for hydration and at the same time no capillary cavities would be left. However, it is seen that practically a water/cement ratio of 0.5 will be required for complete hydration in a sealed container for keeping up the desirable relative humidity level. 

In the field and in actual work, it is a different story. Even though a higher water/cement ratio is used, since the concrete is open to the atmosphere, the water used in the concrete evaporates and the water available in the concrete will not be sufficient for effective hydration to take place particularly in the top layer. The drying behaviour of concrete. If the hydration is to continue unabated, extra water must be added to replenish the loss of water on account of absorption and evaporation. Alternatively, some measures must be taken by way of provision of impervious covering or application of curing compounds to prevent the loss of water from the surface of the concrete. Therefore, the curing can be considered as creation of a favourable environment during the early period for uninterrupted hydration. The desirable conditions are a suitable temperature and ample moisture. 

Curing can also be described as keeping the concrete moist and warm enough so that the hydration of cement can continue. More elaborately, it can be described as the process of maintaining a satisfactory moisture content and a favourable temperature in concrete during the period immediately following placement, so that hydration of cement may continue until the desired properties are developed to a sufficient degree to meet the requirement of service. 

 

Curing is being given a place of increasing importance as the demand for high quality concrete is increasing. It has been recognized that the quality of concrete shows all round improvement with efficient uninterrupted curing. If curing is neglected in the early period of hydration, the quality of concrete will experience a sort of irreparable loss. An efficient curing in the early period of hydration can be compared to a good and wholesome feeding given to a new born baby. 

 

A concrete laid in the afternoon of a hot summer day in a dry climatic region, is apt to dry out quickly. The surface layer of concrete exposed to acute drying conditions, with the combined effect of hot sun and drying wind is likely to be made up of poorly hydrated cement with inferior gel structure which does not give the desirable bond and strength characteristics. In addition, the top surface, particularly that of road or floor pavement is also subjected to a large magnitude of plastic shrinkage stresses. The dried concrete naturally being weak, cannot withstand these stresses with the result that innumerable cracks develop at the surface Fig, shows plastic shrinkage cracks on concrete surface due to quick drying and inadequate early curing. The top surface of such hardened concrete on account of poor gel structure, suffers from lack of wearing quality and abrasion resistance. Therefore, such surfaces create mud in the rainy season and dust in summer.

Quick drying of concrete is bad

The quick surface drying of concrete results in the movement of moisture from the interior to the surface. This steep moisture gradient causes high internal stresses which are also responsible for internal micro cracks in the semi-plastic concrete. Concrete, while hydrating, releases high heat of hydration. This heat is harmful from the point of view of volume stability. If the heat generated is removed by some means, the adverse effect due to the generation of heat can be reduced. This can be done by a thorough water curing. Fig, shows the influence of curing by ponding and wet covering.

Curing methods

Curing methods may be divided broadly into four categories:

(a) Water curing 

(b) Membrane curing 

(c ) Application of heat 

(d) Miscellaneous

When to Start Curing and how Long to Cure

Many a time an engineer at site wonders, how early he should start curing by way of application of water. This problem arises, particularly, just in case of weather concreting. In an arid region, concrete placed as a road slab or roof slab gets dried up during a very short time, say within 2 hours. Often questions are asked whether water are often poured over the above concrete within two hours to stop the drying. The associated problem is, if water is applied within say two hours, whether it’ll interfere with the water/cement ratio and cause harmful effects. In other words, question is how early water are often applied over concrete surface in order that uninterrupted and continued hydration takes place, without causing interference with the water/cement ratio. the solution is that first of all, concrete shouldn’t be allowed to dry fast in any situation. Concrete that are susceptible to quick drying is required to be covered with wet gunny bag or wet hessian cloth properly squeezed, in order that the water doesn’t drip and at an equivalent time, doesn’t allow the concrete to dry. This condition should be maintained for twenty-four hours or a minimum of till the ultimate setting time of cement at which duration the concrete will have assumed the ultimate volume. albeit water is poured, after this point , it’s not getting to interfere with the water/cement ratio. However, the simplest practice is to stay the concrete under the wet gunny bag for twenty-four hours then commence water curing by way of ponding or spraying. Of course, when curing compound is employed immediately after bleeding water, if any, dries up, the question of when to start out water curing doesn’t arise in the least .Many a time an engineer at site wonders, how early he should start curing by way of application of water. This problem arises, particularly, just in case of weather concreting. In an arid region, concrete placed as a road slab or roof slab gets dried up during a very short time, say within 2 hours. Often questions are asked whether water are often poured over the above concrete within two hours to stop the drying. The associated problem is, if water is applied within say two hours, whether it’ll interfere with the water/cement ratio and cause harmful effects. In other words, question is how early water are often applied over concrete surface in order that uninterrupted and continued hydration takes place, without causing interference with the water/cement ratio. the solution is that first of all, concrete shouldn’t be allowed to dry fast in any situation. Concrete that are susceptible to quick drying is required to be covered with wet gunny bag or wet hessian cloth properly squeezed, in order that the water doesn’t drip and at an equivalent time, doesn’t allow the concrete to dry. This condition should be maintained for twenty-four hours or a minimum of till the ultimate setting time of cement at which duration the concrete will have assumed the ultimate volume. albeit water is poured, after this point , it’s not getting to interfere with the water/cement ratio. However, the simplest practice is to stay the concrete under the wet gunny bag for twenty-four hours then commence water curing by way of ponding or spraying. Of course, when curing compound is employed immediately after bleeding water, if any, dries up, the question of when to start out water curing doesn’t arise in the least.

Incidentally, it’s seen that test cubes cast at site are allowed to dry without covering the highest with wet covering. they’re allowed to dry within the hot sun. Such cubes develop cracks and show low strength when crushed. it’s usual that they complain about poor quality of cement or concrete. 

Regarding how long to cure, it’s again difficult to line a limit. Since all the desirable properties of concrete are improved by curing, the curing period should be as long as practical. For general guidance, concrete must be cured till it attains about 70% of specified strength. At lower temperature curing period must be increased. 

Since the speed of hydration is influenced by cement composition and fineness, the curing period should be prolonged for concretes made with cements of slow strength gain characteristics. Pozzolanic cement or concrete admixed with pozzolanic material is required to be cured for extended duration. Mass concrete, heavy footings, large piers, abutments, should be cured for a minimum of 2 weeks.

Drying of Concrete

Drying of concrete is defined as providing the right conditions to permit the concrete to realize a moisture condition appropriate for its intended use. The moisture condition of a concrete slab is of serious importance for the appliance of moisture sensitive floor finishes like vinyl composition tile, linoleum, wood flooring, and non-breathable coating like epoxy.

Industrial engineering methods to improve administrative processes

This article focuses on the development of administration processes using the tactic of commercial engineering. It highlights the most differences between manufacturing and administrative processes. Then, it shows the potential that would be found within the administrative processes. the most goal of this text is to introduce the work procedure using the executive processes, during which the economic Engineering methods are getting used . the utilization of this procedure will make companies achieve better leads to the efficiency of administrative processes.

Introduction

Nowadays, we encounter the utilization of commercial Engineering methods, especially within the production spheres. Concurrently, an enormous potential use of those methods is simply in administration processes. With the assistance of their application to administrative processes, companies can still increase the efficiency and competitiveness of the business and reduce their costs.
The aim of this text is to introduce industrial management methods to enhance administrative processes and show a procedure how we will work with these processes.

MANUFACTURING COMPANIES AND ADMINISTRATIVE PROCESSES

Present state of administrative processes

Current status of administrative processes points that these processes significantly contribute the value to the businesses . it’s obvious that it depends on the corporate . However, estimations normally show 60-80 percent to be assigned to administrative processes. Surveys made by API (Figure 1) (Mašín et al. 2007) show that:

  • over 100 years, the labor productivity of labor in production processes has been raised by 1000 percent. On the opposite hand, the productivity in administrative processes has been raised by 150 percent only. 
  • Only 30 percent of complaints are caused by production processes and therefore the rest “70p” is said to the event , services and administration.
  • Administrative processes render 50% of continuous-time of order (Košturiak et al. 2006).

Comparison of manufacturing and administration processes

Based on the surveys, which were conducted in manufacturing companies, the subsequent problems in administration process are defined:

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Figure 1. Causes of complaints in non-manufacturing
and manufacturing processes.

  • Administrative processes aren’t dedicated the maximum amount attention on manufacturing processes.
  • Administrative processes generate 25–60% of costs on order, sometimes more.
  • Many people performing at administrative processes don’t know the concepts and methods of commercial engineering.
  • Seldom within the administration process, one can find a worker who is liable for the security , quality, shipping and price of this process.
  • For workers performing administrative processes, changing their thought patterns are often difficult.
  • People who work on administration aren’t familiar with performing at predetermined intervals.

In the above-mentioned lists, we will find a few of samples of the issues that occur in administration processes.
This status shows during which critical conditions the administration processes are being found. And there’s an excellent potential to extend the company’s efficiency and reduce their costs. From now of view, the corporate should start working with their administrative processes within the same way, as they’re working with their production processes.

THE WORK PROCEDURE WITH THE ADMINISTRATIVE PROCESSES

Identification of objectives of methodology

Initially, during the creation of working methods using the executive processes, it had been necessary to define the objectives which will be achieved. These objectives were supported long-term analysis and requirements from daily practice. The analysis found that the most important problem is that companies aren’t ready to identify the issues in their administrative processes. meaning if companies cannot identify their problem, then they will also not remove away this problem. This fact defined the primary objective:
1. the issues identified within the administration processes.
Based on the primary aim, the second aim was set:
2. Find solutions to spot waste removal in these processes. First, 81 sorts of waste were defined in these processes. it’s the best-known and most occurring sorts of waste in administrative processes. These 81 sorts of waste were divided into 8 areas of waste, because it is within the case of producing processes. Individual sorts of waste were determined and adjusted supported a survey that was conducted by the corporate Fraunhofer IPA, and therefore the book was written by Košturiak (Košturiak et al. 2006), and by identifying waste within the administrative processes consistent with Lareau (2012). All eight areas including the amount and kinds of waste in each area are detailed in Table 1.
In the second step, it had been necessary to seek out a tool to get rid of waste in these processes. Here, we decided to use the methods of commercial engineering because it is in production processes. One method of commercial engineering was assigned to every sort of waste, which should eliminate waste. In total, 20 methods were identified for the removal of waste from these processes in Table 2.

Methods were assigned on the subsequent basis:
1. the tactic was assigned supported its utilization for an equivalent problem in practice, i.e. its usage “regarding the given problem” is already verified in practice.
2. the tactic was assigned supported the assignment method for solving the issues consistent with Mašín et al. (2007).
3. Method was assigned on the idea of an assessment team of experts on methods of commercial engineering at the Department of commercial Engineering.

The methodology for improving administrative processes, using industrial engineering methods

The whole process is divided into three phases. These phases are handled individually, but in sequence. To achieve the desired outcome, it is necessary to go through all the three phases of the methodology.
3.2.1 Preparatory phase Preparation phase can be described as the actual state in which the company is located. The worker, who performs the implementation at this stage, will develop a complete picture of a company’s administrative processes and get an idea of the condition of the processes. Also, he will know whether it will be necessary to implement any of the methods of industrial engineering.
The second step of this phase is to determine the region and deadline for creating the questionnaires. The area is defined as follows: the number of employees who will fill out the questionnaire. These workers must perform the same administrative processes. The questionnaire must be evaluated individually for each different position in the administrative processes. The distribution and filling out of the questionnaire are the last step of this phase.
3.2.2 Calculation phase This phase is used to obtain calculated data, based on data input. Defined problematic processes are based on the evaluation questionnaires. The next step is the measurement of these problematic processes. It is the most important part of the first two phases, because the final result depends on the accuracy of data input. It is necessary to know the value of the problematic process before it is improved. Evaluation in the next step allows us to obtain the necessary feedback on the changes. For the evaluation of these problematic processes, it is recommended to use the following tools.
1. Method Value Stream Design in indirect Areas (VSDiA)
2. Method and tool for modeling ARIS
3. Method Activity-Based Costing
4. Motivational interviewing
5. Method Visual Office Kaizen
These tools will help us obtain the necessary input information about problematic processes.
3.2.3 Evaluation phases
At this stage, they are implemented methods of industrial engineering at problematic processes. As mentioned above, for each type of problem, one method is assigned, which will help remove the problem. That means after the identification of the problem, we assign a method for elimination based on the given table.
The next step is to present the results of the implementation of the employees. The evaluation step of the implementation is very important for the company. The management of the company will receive the information about what kinds of implementation methods are applied.
• How much time was reduced in this process (time).
• How many of funds were spared (finance).
• How to increase the efficiency of the process.
• How the number of workers has changed in these processes.
• The time spared for individual workers at this process (time).
• How to reduce the cost of office supplies (CZK).
Thanks to this information; in this way, we get the feedback on the real changes. Evaluation of the process after the implementation of the methods must be through with an equivalent tools as finished the problematic process at the second phase. The last step of this phase is permanent control and improvement of of these processes at company. Phases and main steps are outlined in Table 3.

EXAMPLES OF USING THE METHODS OF INDUSTRIAL ENGEENEERING

In the below section, two simple examples are shown about the utilization of methods of commercial engineering in administrative processes. 

4.1 Use of the tactic 5S within the office
At the auto company , the tactic 5S is implemented to all or any secretariats (Figure 2). an equivalent system was introduced to every of the secretariats due to fungibility. Furthermore, within the context of implementing this method, the system for print was found out . it had been determined which documents should be printed and which documents should be saved on the shared disk.
There was a saving of up to 50 bales of paper per month. Of course, office supplies were reduced. 

4.2 Use of the tactic kanban in office
Kanban within the office are often used, for instance , for ordering of office supplies (Figure 3). the most important advantage is that it are often used when the corporate has not saved funds for office supplies. Another advantage is that the staff have always the office supplies they have and it doesn’t extend their work. Responsibility is just too designated for these needs.

Figure 3. Area of the printer before implementation of
the Kanban method.

Figure 4. Implementation of the Kanban system.

An example is given below for the ordering of paper using the Kanban method. so as to save lots of the employer’s decision that thanks to the very fact that color printing isn’t as frequently used, there’ll be just one printer for the whole department located within the corridor. Every office will have just one monochrome printer. After the implementation of the colour printer, these two situations arise:
1. round the printers, packages of papers were scattered, which were ordered by the secretary.
2. Paper for printers wasn’t available
Neither of those situations is clearly not desirable. Therefore, the Kanban system was implemented (Figure 4). As a part of the introduction of the Kanban system for office supplies, the worth of office supplies was reduced by about CZK 150 000 at the department.

CONCLUSIONS

This article discussed the utilization of commercial engineering methods in administrative processes. The samples of waste occurring in administrative processes were mentioned. Then, a comparison between the executive and manufacturing processes was made. because it are often seen, these processes still have the potential to be improved. When companies begin to affect all its processes, they will increase the efficiency of their processes, reduce their costs and increase their competitiveness completely. Therefore, they ought to start and improve their administrative processes as soon as possible, even using industrial management methods, as noted within the above examples.
This article gives only an overview of how companies can work with their administrative processes and the way they will achieve their improvements. the chances and therefore the use of commercial engineering methods in administrative processes require further research.

Earth architecture: An eco-compatible solution for future green buildings

Earth architecture: An eco-compatible solution for future green buildings

 Earth materials, including minerals, rocks, soil and water, are the oldest and are the foremost widely used construction materials since quite 9000 years. This earthen architecture has stood the test of your time and proved that it can represent quite 2500 years just like the Arg-e-Bam Citadel in Iran (the world largest sun-dried brick structure). Earth as a artifact has almost disappeared during the 20th century thanks to the international development of the commercial concrete. this type of architecture made up of mud is until recently considered primitive, not suitable for our contemporary lifestyle, and typically described because the architecture for low-income societies. during this research, i will be able to demonstrate that the unbaked mud isn’t only a durable construction material, but also the proper construction material for all because it can answer the sustainability challenges they face in terms of energy efficiency, comfort and eco-compatibility.

EARTHEN ARCHITECTURE

Unfired-mud construction may be a widely present traditional architecture. it’s quite easy to note the presence of traditional mud architecture that’s still standing and having an interesting weathering resistance despite the time span. Obvious examples like the traditional city Arg-e-Bam Citadel in Iran show the resistance and therefore the potential to use this product of nature. Many adobe buildings are recognized as having a historical and architectonic value. Unfired-mud construction may be a widely present traditional architecture. it’s quite easy to note the presence of traditional mud architecture that’s still standing and having an interesting weathering resistance despite the time span. Obvious examples like the traditional city Arg-e-Bam Citadel in Iran show the resistance and therefore the potential to use this product of nature. Many adobe buildings are recognized as having a historical and architectonic value.

 

About one-third of the worldwide population lives within the unbaked-mud buildings (Minke 2006). it’s impressive to ascertain how it might be an efficient solution to the 21st century energy problem for local communities. Mud is one among the few building materials which will be recycled indefinitely; it also can be found in most parts of the planet with low transportation, processing and pose cost. additionally , unlike the conglomerate concrete whose process of production alone is liable for almost 13% of worldwide CO2 emissions (Benghida 2015), the method of mud brick making has near zero emissions. Brick is, indeed, the most cost effective , most practical and convenient sustainable construction material. With the good value of bricks and their architectural technology, architects and other professionals should keep bricks within the race.

STRENGTH AND WEAKNESS OF MUD BRICKS

The great thickness of earthen walls acts as a buffer to the warmth , holding it while the wall temperature rises. However, this process is merely slowing down the warmth transmission and deferring it later for several hours during the night on the other side after the sunset, after the thick wall warms up. The night-natural ventilation also can be an efficient passive technology (courtyards) to dwell the thermal temperature during summer (Steele 2009). due to its low-cost and low aesthetics options, earthen architecture is perceived as a symbol of poverty (Sheweka 2011). But this image of mud architecture doesn’t do justice thereto since it’s the potential of making contemporary houses (Figure 1). Table 1. Comparison of various construction material properties (Fernandes et al. 2014). Material Thermal conductivity λ-value (W/m.ºC) Thermal storage capacity (Wh/kgºC) Heat transfer delay (250 mm thickness) hour global warming Potential (kg CO2/m3) Rammed earth/ adobe 1.00–1.20 0.23–0.30 10 / 9 38 Stone 2.30–3.50 0,22–0.24 5.5 26 Concrete 1,80 1.10 7 264 Hollow bricks 0.39–0.45 0,26 6 357 Figure 1. The perch, a rammed earth architecture project, Sedona Arizona, 2008, by courtesy of the engineering and construction Zone. Brick may be a popular and distinctive choice thanks to its advantages over other construction materials. Table 2 summarizes why it’s appealing to homeowners and architectural professionals, and what disadvantages could be contributing to its dropping popularity (Benghida 2015, Revuelta-Acosta 2010).

Comparison of indoor and outdoor air temperature fluctuation within 24 h period for the prefabricated concrete test model, for the mud-brick test model (Fathy 1986).

CONCLUSIONS

Earth brick is a superb example of eco-compatible construction material because the worldwide availability and therefore the in place production make it cost-effective with low embodied energy. Its high thermal resistance makes it the favourite material, especially for decent dry climate populations, because it provides a high standard of indoor comfort. Brick has few weaknesses, which may be fixed through the acceptable use of sustainable technologies to stay this material 100% eco-compatible and responsive. By educating architects about this traditional material, by implicating engineers and by improving the mechanical properties of the mud bricks against weathering and moisturizing, earth architecture will thrive within the near future, notably for its intrinsic advantages at reducing CO2.

AKNOWLEDGMENT

This work was supported by the Dong-A University research fund.