In urgent need of 30 weekly internship diaries for road and bridge data clerks, more than 200 words each

According to the school arrangement, I went to the Wuhan State-owned Enterprise Project Department of the Fourth Construction Enterprise in Wuhan on June 25, 2004 for a construction internship. This was an opportunity for me to understand the construction site. A good opportunity for me to have a deeper understanding of the difference between theory and reality.

1: Project Introduction

This project is a single apartment building developed by Wuhan Donghu Gaoxing State-owned Enterprise Investment Company. The construction company is the fourth construction company in Wuhan

, respectively Buildings 5 ??and 6, and the Golf Fitness Building. The foundations were constructed by Asthma Fourth

Pile Foundation Company. Designed by Beijing Weston Design Institute. It adopts frame shear wall structure and the columns are heterosexual columns. It is a commercial and residential building with an area of ??13,000 square meters and consists of 3 buildings. It has a cast-in-place reinforced concrete six-story frame-shear structure.

Second internship content

1: Carpentry

1) Types and production methods of formwork;

2) Installation of various structural formwork Quality standards;

3) Quality standards for installation of cast-in-place structural formwork;

4) Time and sequence of removal of cast-in-place structural formwork;

5) Precautions for dismantling formwork;

6) Methods and regulations for cleaning, stacking and maintenance of formwork;

2: Steel bar workers

1) Types of steel bars and appearance characteristics;

2) Welding methods and quality requirements of steel bars;

3) Methods and processes of cold working of steel bars;

4) Binding of steel bars Methods and quality requirements;

5) Overlap length requirements for steel bar binding;

6) Control methods for the thickness of protective layers of various components;

7) Master the recording methods and main contents of concealed projects;

3: Concrete construction

1) Types, specifications, and mixing principles of mixers;

2) Vibration Types of equipment and scope of application;

3) Conversion of construction mix ratios and content of signboards;

4) Setting and treatment of construction joints;

5) Concrete maintenance methods and regulations;

6) Causes of concrete surface defects and preventive treatment methods;

7) Quality inspection content of concrete projects;

Three Gains and Experiences

First of all, internship is a familiar and unfamiliar word to me, because I have been a student for more than ten years

I have experienced many internships, but this one is so different. He will comprehensively test my abilities in various areas: study, life, psychology, body, mind, etc. It is like a touchstone to test whether I can apply the theoretical knowledge I have learned into practice. It is related to whether I can successfully establish myself in this challenging society in the future. It is also the key to building my confidence. Therefore, my investment in it is also 100%! A tense month of internship life is over, and I still have a lot of gains in this more than a month. After the internship is completed, it is necessary to summarize it. First of all, through more than a month of internship, I learned a lot of practical knowledge through practice. The so-called practice is the only criterion for testing truth. By standing on the sidelines, I observed the entire house construction process at close range and learned a lot of practical and practical details. Construction knowledge, this knowledge is often something I rarely come into contact with and pay little attention to in school, but it is very important and basic knowledge.

For example, the cause and treatment of cracks in concrete is a very complicated issue, so let me share my

opinion:

1 Reasons for cracks

There are many reasons for cracks in concrete, mainly changes in temperature and humidity, brittleness and unevenness of concrete

as well as unreasonable structure and failure of raw materials. (such as alkali aggregate reaction), formwork deformation, foundation

uneven settlement, etc.

During the hardening of concrete, the cement releases most of the heat of hydration, and the internal temperature continues to rise, causing tensile stress on the surface.

In the later cooling process, due to the constraints on the foundation or old concrete, tensile stress will appear inside the concrete. The decrease in temperature will also cause large tensile stresses on the concrete surface. When these tensile stresses exceed the concrete's ability to resist cracking, cracks will occur. The internal humidity of many concretes changes very little or slowly, but the surface humidity may change greatly or drastically. If the maintenance is not done well, it is dry and wet, the dry shrinkage deformation of the surface will be restrained by the internal concrete, which often leads to cracks. Concrete is a brittle material. The tensile strength is about 1/10 of the compressive strength, which is the limit during short-term loading. The tensile deformation is only (0.6~1.0)×104, and the ultimate extension deformation during long-term loading is only (1.2~2.0)×104. Due to uneven raw materials, unstable water-cement ratio, and segregation during transportation and pouring Phenomenon, the tensile strength of the same piece of concrete is uneven, and there are many weak parts with very low tensile strength and prone to cracks. In reinforced concrete, tensile stress is mainly borne by steel bars, while concrete only bears compressive stress. If tensile stress occurs in the structure at the edge of plain concrete or reinforced concrete, it must be borne by the concrete itself. Generally, the design stipulates that no tensile stress or only a small tensile stress will appear. However, during construction, the concrete is cooled from the highest temperature to the stable temperature during operation, which often causes very large tensile stress inside the concrete. Sometimes the temperature stress can exceed the stress caused by other external loads, so understanding the changing rules of temperature stress is extremely important for reasonable structural design and construction.

2 Analysis of temperature stress

According to the formation process of temperature stress, it can be divided into the following three stages:

(1) Early stage: from the beginning of concrete pouring to The cement heat release is basically completed, usually about 30 days. Two characteristics of this stage are: first, the cement releases most of the heat of hydration, and second, the rapid change in the elastic modulus of concrete. Residual stresses develop within the concrete during this period due to changes in the elastic modulus.

(2) Mid-term: from when the heat release effect of the cement is basically completed to when the concrete cools to a stable temperature. During this period, the temperature stress is mainly caused by the cooling of the concrete and changes in the outside temperature. These The stresses are superimposed on the residual stresses formed in the early stages, during which the elastic modulus on the concrete does not change much.

(3) Late stage: the operation period after the concrete is completely cooled. Temperature stress is mainly caused by changes in external temperature, and these stresses are superimposed on the residual stresses of the first two types. It can be divided into two categories according to the causes caused by temperature stress:

(1) Self-generated stress: a structure without any constraints on the boundary or a completely static structure. If the internal temperature is non-linearly distributed, the structure itself will constrain each other. The temperature stress that occurs. For example, the structure size of a bridge pier is relatively large. When the concrete cools, the surface temperature is low and the internal temperature is high. Tensile stress appears on the surface and compressive stress appears in the middle. .

(2) Constraint stress: The stress caused by

all or part of the boundary of the structure being constrained by the outside world and not being able to deform freely. Such as box beam roof concrete and guardrail concrete.

These two temperature stresses often work together with the stress caused by the drying shrinkage of concrete.

It is a relatively complicated task to accurately analyze the distribution and magnitude of temperature stress based on known temperatures.

In most cases, it is necessary to rely on model tests or numerical calculations. The creep of concrete causes a very large relaxation in temperature stress. When calculating temperature stress, the influence of creep must be considered. The specific calculation will not be discussed in detail here.

3 Temperature control and measures to prevent cracks

In order to prevent cracks and reduce temperature stress, we can start from two places: controlling temperature and improving constraint conditions.

Measures to control temperature are as follows:

(1) Improve the aggregate gradation, use dry hard concrete, add mixtures, add air-entraining agents or plasticizers, etc.

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Measures to reduce the amount of cement in concrete;

(2) Add water when mixing concrete or cool the gravel with water to reduce the pouring temperature of concrete;

( 3) When pouring concrete on hot days, reduce the pouring thickness and use the pouring layer to dissipate heat;

(4) Bury water pipes in the concrete and pass in cold water to cool down;

(5) Provide for reasonable demolition During molding time, surface insulation should be carried out when the temperature drops sharply to avoid

sharp temperature gradients on the concrete surface;

(6) Surfaces of concrete pouring blocks or thin-walled structures exposed for a long time during construction , take insulation measures in the cold season

;

Measures to improve the constraints are:

(1) Separate seams and blocks reasonably;

(2) Avoid excessive fluctuations in the foundation;

(3) Reasonably deploy the construction process to avoid excessive height differences and long-term exposure of the sides;

In addition, improve the concrete performance, improve crack resistance, strengthen maintenance, and prevent surface dry shrinkage, especially

Ensuring the quality of concrete is very important to prevent cracks. Special attention should be paid to avoid penetrating cracks, resulting in

< p>It is very difficult to restore the integrity of the structure after it is discovered, so the construction should focus on preventing the occurrence of penetrating cracks

.

In concrete construction, in order to increase the turnover rate of the formwork, it is often required that the newly poured concrete be removed as early as possible

The formwork. When the concrete temperature is higher than the air temperature, appropriate consideration should be given to the form removal time to avoid early cracks on the concrete surface. Removal of the formwork in the early stage of new pouring will cause a large tensile stress on the surface and cause a "temperature shock" phenomenon.

In the early stage of concrete pouring, due to the dissipation of hydration heat, the surface causes very large tensile stress. At this time, the surface temperature is also higher than the air temperature. At this time, the formwork is removed and the surface A sudden drop in temperature will inevitably cause a temperature gradient, thus

A tensile stress will be added to the surface, which will be superimposed with the hydration thermal stress. Coupled with the shrinkage of the concrete, the tensile stress on the surface will reach a very large value. There is a risk of causing cracks, but if the surface is covered in time after removing the formwork

A light insulation material, such as foam sponge, etc., is very effective in preventing excessive tensile stress on the concrete surface

It has a significant effect.

Reinforcement has little effect on the temperature stress of mass concrete because the reinforcement ratio of mass concrete is extremely low. iEt Worry-free Training Network

Only affects general reinforced concrete. Under the conditions where the temperature is not too high and the stress is lower than the yield limit,

the various properties of steel are stable and have nothing to do with stress state, time and temperature. The linear expansion coefficient of steel is very different from that of concrete. When the temperature changes, only a small internal stress occurs between the two. Since the elastic modulus of steel is 7 to 15 times the elastic modulus of concrete, when the internal concrete stress reaches the tensile strength and cracks, the stress of the steel bar will not exceed 100 ~200kg/cm2.. Therefore, it is difficult to use steel bars to prevent the occurrence of small cracks in concrete. However, after reinforcement, the cracks in the structure generally become more numerous, smaller in spacing, and smaller in width and depth. And if the diameter of the steel bars is small and the spacing is close, it will have a better effect on improving the crack resistance of concrete. Fine and shallow cracks often occur on the surface of concrete and reinforced concrete structures, most of which are shrinkage cracks. Although such cracks are generally shallow, they still have a certain impact on the strength and durability of the structure.

In order to ensure the quality of concrete projects, prevent cracking and improve the durability of concrete, the correct use of admixtures is also

one of the measures to reduce cracking. For example, when using a water-reducing and anti-cracking agent, the author summarizes its main functions in practice as follows:

(1) There are most capillary channels in concrete. After water evaporates, capillary tension is generated in the capillary tubes, making the concrete < /p>

Soil shrinks and deforms due to drying.

Increasing the capillary pore size can reduce capillary surface tension, but will reduce the strength of concrete.

This surface tension theory has been confirmed internationally as early as the 1960s.

(2) The water-cement ratio is an important factor affecting the shrinkage of concrete. The use of water-reducing and anti-cracking agents can reduce the water consumption of concrete by

by 25%.

(3) The amount of cement is also an important factor in the shrinkage rate of concrete. Concrete mixed with water-reducing and anti-cracking agents can reduce the amount of cement by 15% while maintaining

the strength of the concrete. Its volume is supplemented by increasing the amount of aggregate.

(4) Water-reducing and anti-cracking agents can improve the consistency of cement slurry, reduce concrete bleeding, and reduce settlement deformation.

(5) Improve the bonding force between cement slurry and aggregate and improve the crack resistance of concrete.

(6) When the concrete shrinks, it is restrained to produce tensile stress. When the tensile stress is greater than the tensile strength of the concrete, cracks will occur.

Cracks will occur. Water-reducing and anti-cracking agents can effectively increase the tensile strength of concrete and significantly improve the anti-cracking performance of concrete.

(7) Adding admixtures can make concrete denser, effectively improve the carbonation resistance of concrete and reduce

carbonation shrinkage.

(8) The retarded setting time of concrete after adding water-reducing and anti-cracking agent is appropriate. On the basis of effectively preventing the rapid hydration and heat release of cement,

avoids the consequences caused by long-term non-setting of cement. The plastic shrinkage increases.

(9) Concrete mixed with admixtures has good workability, the surface is easy to smooth, and forms a microfilm, which reduces water evaporation and

drying shrinkage.

Many admixtures have the functions of retarding setting, increasing workability, and improving plasticity. We should conduct more experimental comparisons and research in this area in engineering practice, rather than simply relying on improving external conditions. , may be simpler and more economical.

4 Early maintenance of concrete

Practice has proved that most of the common cracks in concrete are surface cracks of different depths, and the main reason is temperature

Rapid temperature drops in cold areas caused by gradients also tend to form cracks. Therefore, the insulation of concrete is particularly important to prevent early cracks on the surface.

From the perspective of temperature stress, thermal insulation should meet the following requirements: iEt Wuyou Training Network

1) Prevent the temperature difference between the inside and outside of the concrete and the gradient of the concrete surface to prevent surface cracks.

2) To prevent concrete from being super-cooled, we should try our best to ensure that the lowest temperature during the construction period of the concrete is not lower than the stable temperature during the service life of the concrete.

3) Prevent old concrete from being overcooled to reduce constraints between new and old concrete.

The main purpose of early curing of concrete is to maintain appropriate temperature and humidity conditions to achieve the effect of two places. One place protects the concrete from unfavorable temperature and humidity deformation, and prevents harmful cold shrinkage and Shrinkage. One place allows cement hydration to proceed smoothly in order to achieve the designed strength and crack resistance. Suitable temperature and humidity conditions are interrelated. Insulation measures on concrete often also have a moisturizing effect. From a theoretical analysis, the moisture contained in newly poured concrete can fully meet the requirements for cement hydration. However, water loss often occurs due to evaporation and other reasons, thereby delaying or preventing the hydration of cement. Surface concrete is most easily and directly affected by this adverse effect. Therefore, the first few days after concrete pouring are the critical period for curing, and should be paid attention to during construction.

Therefore, we must handle these incidents carefully during construction and handle them differently according to different situations.

These issues should be paid attention to during construction. What kind of cement should be used during construction and the amount should be paid attention to

as well as the early maintenance of concrete.

There is also template design:

(1) Construction preparation

1. Basic work before template installation:

1) Place Line: First, the side columns and wall axis of the building are measured, and each axis is drawn using this axis as the starting point. When laying out the formwork, use ink lines to pop up the center line and side lines of the formwork according to the construction drawing. Wall formwork should pop up the side lines and outer control lines of the formwork to facilitate installation and correction of the formwork.

2) Use a level to measure the building horizontal elevation directly to the template installation location

according to the actual elevation requirements.

3) The bottom part of the formwork should be leveled in advance and the debris should be cleaned up to ensure the correct position of the formwork and prevent

slurry leakage at the bottom of the formwork or root rot after the concrete is formed.

4) The foreman determines the assembly design plan of the formwork in advance and makes a complete disclosure of technology, quality, and safety

to the construction team.

5) The template should be painted with release agent. There are many other things to note, which I won’t list here.

I firmly believe that through this period of internship, the practical experience gained will benefit me throughout my life and will be continuously verified in my actual work after graduation

I will continue to

In my future work, I will continue to apply the theoretical knowledge and practical experience I have learned to real work,

< p>Fully demonstrate your personal value and life value. Work hard to realize your ideals and bright future.