CONCRETE CRACKS Table of Crack types in Reinforced Concrete Structures A) Structural Cracks This type of crack results from the tensions that the structure must carry due to its function. They take place in structures without projects, and when the ground problem is not solved, and are very dangerous; they have nothing to do with the concreting and the concreting conditions. In such cases you must certainly consult the relevant authorities (engineering office, university etc.).
No such problem is witnessed when the structure is engineered properly and when there is no overloading. These types of cracks occur vertically to the tensile strengths in reinforced concrete agents. Cracks occurring in the middle of a simple girder interval or on a corbel bearing are of this type. B) Application Based Cracks This type of crack is seen in fresh concretes or over aged concretes. 1. Fresh Concrete Cracks Fresh concrete cracks occur within the first 30 minutes to 5 hours following the placement of the concrete to the formwork, generally in concretes with wide surfaces such as floor concretes. The depth of these cracks can reach 10 cm and their length can vary from a few centimeters to 2m. Deep and long cracks can be very harmful to the concrete in terms of its strength and durability. The two most significant reasons for fresh concrete cracks are settlement differences and plastic shrinkage. Settlement Cracks These cracks occur in newly poured concretes in which concrete cover is forgotten, cure isn’t applied and excessive water is added, in reinforced concrete agents with voids, in areas having too many reinforcements, on the reinforcements close to the surface, and when the placement isn’t done properly.
The Essay on Fferent Types Of Bridges
The quest for travel has always been one that man has tried to conquer. First, he traveled on foot, and then developed methods of transportation such as boats, but one of the first obstacles that he had to overcome was getting across rivers, waterways, and canals. Today, bridges have become a part of everyday life; hence without them, people would have a much more difficult time going from one ...
In fresh concrete, the water containing cement particles rise up to the surface, while the big aggregate grains sink to the bottom. The girders and floor reinforcements close to the surface resist this replacement and the fresh concrete can not settle completely in these regions. The unsettled concrete cracks throughout the steel. There is less settlement in flooring due to its fineness and so cracks aren’t seen very often. There is more settlement in girders due to their depth, and the map of the steel rods is seen on the concrete surface; the cracks make the reinforcement places visible. As the water content of the concrete increases, the amount of settlement increases. The settlement, and thus the cracks, increases unless the concrete is placed, compacted and vibrated properly. The way to prevent these cracks is to use concrete in normal consistency (12 cm slump), avoid concretes to a high consistency with excessive water, and apply good vibration to the concrete. Plastic Shrinkage Cracks This type of crack, randomly spread in various sizes, may occur especially on concretes (floor, ground, road, port etc.) poured on windy days, with low humidity, and high temperature. The crack width is usually less than 1 mm and it is on the surface, not deep. It is not dangerous in terms of the building’s safety.
When floor concrete is poured, the water in the upper surface starts to vaporize. It leaves the concrete and rises into the air. In place of this water, the water inside the concrete comes up to the surface. If the speed of vaporization is higher than that of the water coming up to the surface the surface starts to dry, and therefore to shrink and crack. The same cracks may result from the absorption of the concrete water by other materials such as briquettes in hollow-tile floor slabs or moisturized concretes. Factors increasing the vaporization speed are: Air Temperature: The higher the temperature, the more the vaporization. The increase of the temperature increases the vaporization approximately twofold. If the concrete is hotter than the air, the vaporization speeds up. The Humidity of the Air: The less the humidity in the air, the more and the easier the vaporization. The vaporization increases fivefold when the relative humidity decreases from 90% to 5%. The Speed of the Wind: The more the wind, the faster the vaporization. The vaporization increases fourfold when the wind speed increases from 0 to 20 km/h. Sun Rays: If the concrete surface is open to direct sunlight, the temperature of the concrete and therefore the speed of the vaporization increases.
The Essay on Water Surface Rock Process
ENVIORMENTAL SCIENCE REVIEW SHEET 1) Mutation- a random change in one or more genes of organisms. Mutations may occur spontaneously in nature, but exposure radiation and / or other chemicals vastly increase their number and degree. 2) Natural selection- the process whereby the natural factors of environmental resistance tend to eliminate those members of the population that are least well adapted ...
The two main factors affecting the water desorption speed of the concrete are the compactness of the concrete and the granulometry of the aggregates. The less voids in the aggregate granulometry, the higher the strength in the concrete, however since there aren’t too many voids, it gets harder for the desorption water to go up; it delays and the desorption speed decreases. As long as the desorption water can’t replace the vaporization water, the concrete surface dries and cracks. In ready-mixed concrete, there are more shrinkage cracks because the granulometry is well adjusted so that desorption becomes difficult. These are the precautions to be taken in order to decrease shrinkage and the cracks caused by shrinkage: Avoid the formwork agents absorbing the concrete water and speed up concrete’s desiccation by moisturizing the formwork and the reinforcement bar. Protect the concrete from the sun (by pouring at night), and the wind (by means of a wind screen).
Avoid water vaporization (by covering with wet burlaps, nylon blankets or by sprinkling cure materials).
Pour concrete very quickly by using a sufficient number of quality workers, apply surface finishing and start the cure as soon as possible, and continue the cure for at least 3 days. Plastic shrinkage cracks may occur in 30 – 45 minutes, which is even before the concreting is completed. Therefore the desiccation precautions should be taken for the poured parts while the concreting still goes on. These precautions can be taken step by step as the surface finished pieces are covered with wet burlaps, nylon blankets and sprinkled with cure materials. Otherwise, the concrete cracks in different amounts, varying according to the temperature, humidity and wind conditions. It is in your power to reduce and minimize these cracks.
The Essay on Water 5
Thesis Statement: Water is the most crucial part of life its self, and must never go unnoticed. I. People frequently overlook the importance of water in the body. In order to keep the body healthy, people must consume water. A healthy body is a well-hydrated body. Without the constant consumption of water the body becomes dehydrated. Perhaps people overlook waters importance, simply because its ...
2. Overaged Concrete Cracks This type of crack may be seen in concretes of different age groups (from few week old concretes to 30 year-old concretes).
The cracks are chemical or physical based. These cracks seem like hairlines at the beginning but then they grow and combine. Stripping, outpouring and bursting occur following the crack formation. If no precautions are taken, the reinforced concrete agents fall completely into ruin as time passes. Among the reasons of these types of cracking, freezing – thawing, alkali -active silica reaction, carbonation, corrosion of the reinforcements and reactions caused by harmful materials such as sulphate, acids and salts can be counted.
