Crack prevention and control technology
(1) the main technical content
Concrete cracks have become a common disease of the quality of concrete projects, how to prevent and control concrete cracks is a technical problem that engineers and technicians are eager to solve. However, the prevention and control of concrete cracks is a systematic project, including design, materials, construction of each technical aspects. This technology mainly describes some key techniques to prevent and control cracks, improve the crack resistance of concrete, so as to achieve the purpose of preventing and controlling concrete cracks. The main content of this technology includes: the design of the construction measures, the selection of concrete raw materials (cement, admixture, fine aggregate, coarse aggregate), concrete ratio factors affecting crack resistance, crack-resistant concrete ratio design and crack-resistant concrete ratio optimization design methods and some technical measures in construction.
(2) Technical indexes
For how to evaluate the concrete thick material and concrete crack-resistant performance, this technology provides the corresponding test methods and evaluation indexes to make it operable.
(3)Scope of application
This technology is applicable to the design of concrete structures with high crack resistance requirements, the selection of raw materials, the design and construction of crack-resistant concrete ratios, and the evaluation of the crack resistance of concrete.
(4) Typical projects that have been applied
It has been applied in pilot projects with good results. And specific engineering examples are given.
Self-compacting technology
(1)Main technical contents
The homogeneous concrete that can fill the whole mold cavity without leaving any void under the action of self-weight and without any compacting and molding measures is called self-compacting concrete. This technology provides the main technical content: the technical requirements of the concrete raw materials, the design of self-compacting concrete, namely, fluidity, filling, segregation resistance, and plasticity and self-compacting concrete proportion design.
(2) Test Methods and Evaluation Indexes
This technology gives the corresponding test methods and evaluation indexes, and gives the specific provisions for controlling the performance of self-compacting concrete mixes in the construction site.
(3)Scope of use
It is applicable to the casting of concrete which is difficult to be mechanically vibrated. Due to the large content of fine powder in self-compacting concrete, more attention should be paid to the anti-cracking properties of concrete. In the case of anti-cracking measures, the anti-cracking performance of self-compacting concrete is relatively poor. It is not suitable for continuous wall and large area floor slab pouring.
(4) Application examples
This technology gives an example of the application of self-compacting concrete in the steel pipe concrete of Shenzhen Saige Plaza. It describes the whole process of self-compacting concrete technology from the selection of concrete raw materials, concrete ratio design, concrete mix verification test, on-site simulation test to the on-site construction, and formulates the "Self-Compacting Concrete Quality Standards", "Production Technical Regulations" and "Construction Technical Regulations" to ensure the quality of self-compacting concrete construction.
Durability Technology
(1)Main Technical Contents
In the previous design of concrete proportion, the main consideration is the strength index, and less consideration is given to durability. High-performance concrete is characterized by high workability, high strength and high durability, distinguishing it from ordinary concrete. For marine projects, highway and bridge projects sprayed with icing salts, and projects in salty areas, the intrusion of chloride salts into the concrete leads to corrosion of reinforcing steel and causes expansion and cracking of the concrete, which seriously affects the service life of the building. The most important technical measure to improve its durability is to use high-performance concrete with high resistance to chloride ion permeability, which fundamentally improves the reinforcing bar protection performance of concrete itself. The use of conventional materials, conventional technology can be formulated at room temperature resistance to chloride ion permeability and freeze-thaw resistance are strong high-performance concrete. The key to the preparation is to choose a high-efficiency water-reducing agent that matches the cement, and under the condition that the water-cement ratio is not greater than 0.35, the use of fly ash, ground slag powder, silica fume, and other mineral admixtures to replace part of the cement as a cementitious material. These finely ground mineral admixtures exert a filling effect and volcanic ash reaction in the mixed concrete, making the concrete denser and thus reducing the permeability of the concrete. Reducing the water consumption of the concrete mix and using a low water-to-cement ratio is the key to improving the durability of concrete.
(2) Technical indicators
The test of durability of high performance concrete against chloride salt pollution should be in accordance with the relevant provisions of the current water transport industry standard, "Quality Control Standards for Concrete in Water Transportation Projects" JTJ269, and the flux characterizing the permeability of chloride ions should not be greater than 1,000 coulombs. China's industry standard "seaport engineering concrete structure anti-corrosion technical specifications" JTJ27 5-2000 on seaport engineering concrete structure requirements of high-performance concrete put forward the following technical indicators:
Concrete mix hardened concrete
Water-cementitious ratio Total amount of cementitious material (kg/m3) Slump (mm) Strength class Anti-chlorine ion permeability (C)
≤0.35 ≥400≥120≥C45≤1OOO
The concrete raw materials also put forward the corresponding technical requirements. The water reduction rate of water reducing agent is not less than 20%. Admixtures should be selected with fineness not less than 4000 cm2/g of ground blast furnace slag, I, II fly ash and silica fume. The fineness modulus of fine aggregate is between 2.6-3.2. The maximum particle size of coarse aggregate should not be larger than 25mm, and the anti-chlorine ion permeability index should reach the specified requirements by reducing the water-cement ratio and adjusting the mixing amount of admixtures in the mixing ratio design. Concrete mixing should use forced mixer, mixing time should be longer than the conventional concrete more than 4Os. The concrete should be covered immediately after plastering. After final setting, the top surface of concrete shall immediately begin continuous moist curing, at room temperature, at least 15d.
(3)Scope of application
Applicable to marine engineering, highway and bridge engineering in winter spreading de-icing salts, salty areas and shore buildings closer to the sea, and other buildings and structures in the chlorine and salt contaminated environment.
(4)Typical projects that have been applied
The technology is cost-effective, raw materials are easy to obtain, and the preparation process is simple. So in recent years has been in the north and south of all kinds of ports and cross-sea bridge project application. Such as Shanghai Yangshan Deep Water Harbor Project, East China Sea Bridge, Hangzhou Bay Bridge, Yantian Port Container Terminal, aid to Pakistan Gwadar Terminal Project.
The use of chlorine salt contamination of high-performance concrete than ordinary concrete unit price increase is quite limited, but its durability life doubled compared to the effect of greatly reducing the service life of the building costs, economic and social benefits are very significant, the application of a very broad prospect.
Clear water concrete technology
Clear water concrete refers to the structure of the concrete after hardening is no longer on the surface of any decoration, to the concrete color directly as the building's exterior finish. With fair-faced concrete as a decorative surface, there are high requirements for aesthetics, color difference, surface bubbles, etc. Therefore, corresponding measures should be taken in concrete preparation, production, construction, maintenance and other aspects.
(1)Main technical content
①Concrete preparation
Concrete should use the same raw materials and the same proportion, the concrete mix should have good compatibility, no segregation, no water secretion.
Mineral admixture as an indispensable component of concrete, in consideration of the activity of the admixture at the same time, make full use of the different particle sizes of the various admixtures, the formation of a tight filling inside the concrete, to enhance the densification of the concrete, in the admixture should pay further attention to solving the adaptability of admixtures and cement, to reduce the rate of urination of the concrete, to reduce the slump of the concrete loss of the time.
In addition to the different water-cement ratio will lead to changes in the color of the hardened concrete, the impact of aggregates on the appearance can not be ignored, so the same visual surface of the concrete project, the same type of aggregate should be used.
②Concrete template
In order to make the surface of the concrete smooth and bubble-free, according to different strength levels of concrete should be selected from different materials of the template, while the mold release agent in addition to play the role of mold release, should not affect the appearance of the concrete.
③Concrete construction
When pouring concrete, the distance between the concrete discharge port and the pouring surface should not be too large, otherwise the concrete will be easy to segregate, and it is suitable to make slurry on the surface of the concrete when vibrating, and at the same time, it should be avoided to miss vibration and over vibration.
④Concrete maintenance
Concrete maintenance should ensure that the surface of the concrete is not contaminated, adequate and reasonable maintenance is to ensure that the surface of the concrete after hardening and the key to the internal quality.
(2) Technical indicators
①No cracks on the surface of the concrete, no obvious bubbles, no obvious color difference, no clear honeycomb surface.
②The concrete surface is flat and smooth, and the axial and body dimensions are accurate.
3 large cross-section, variable cross-section of the structure of regular lines, corners and angles.
④The joints of beams and columns are smooth, without clear hew marks.
(3) Scope of use
Watertight concrete adds a unique decorative effect to the building with its simple and steady, natural and pure texture. Generally used in municipal, transportation, water conservancy, aviation and other projects, and gradually adopted in residential construction.
(4) has been applied to the typical projects
①Yangpu and Nanpu Bridge main tower of concrete
②Shanghai Broadcasting Television Tower sloping cylinder concrete
③Maglev train project pier part of the concrete
④Oriental Pearl Tower
⑤Pudong International Airport and the Capital International Airport, the new terminal building.
Ultra-high pumping technology
Ultra-high pumping concrete technology generally refers to the modern concrete pumping technology with a pumping height exceeding 2,00m.
Since the reform and opening up, high-rise ultra-high-rise buildings have reached thousands of teaching, ultra-high pumping concrete technology has become an indispensable aspect of ultra-high-rise building construction technology, and has become a development trend by the engineering community in various countries.
(1)Main technical content
①Raw material quality
Formulation of ultra-high pumping range concrete, its raw materials than the general pumping concrete has a big difference. As the most basic cementing material - cement, in addition to the amount of cement, should also give full consideration to the rheology of cement, that is, the compatibility of cement and high-performance water reducing agent, the two compatibility is good to obtain low water consumption and large mobility, and slump through the time of loss of the effect of small. For the fine aggregate, its quality should be in line with the "sand quality standards and test methods for ordinary concrete" (JGJ52), in addition to different strength levels of concrete should be used in different modulus of fineness of the sand. Admixtures as an important component of high-performance high pumping range concrete need to be balanced from the activity, particle composition, water reduction, heat of hydration, pumping performance and other aspects of the choice. As an admixture, a single component of the admixture has not been able to play its role well, and purely for the purpose of water reduction admixture can not achieve the purpose of ultra-high pumping range of the use of concrete, admixture multi-component composite, as well as for the specific requirements of specific projects formulated admixture has become an important aspect of the admixture manufacturer to strengthen the field service.
②Concrete preparation
Ultra-high pumping range of concrete preparation at the same time also need to study the fresh concrete integrity, fluidity and pumping interrelationship. To study the direct measurement of concrete pumpability.
3 pumping equipment
Pumping concrete can not be separated from the concrete pump, so high pressure, large displacement, wear-resistant, adaptable pumping equipment is also a must. In addition to the design of the pumping pipe, how to reduce resistance, shorten the route is also an aspect of pumping technology research.
(2)Technical indicators
①Concrete pumping height >200m.
②Hardened concrete performance meets the design requirements.
③Concrete extension degree >600mm, inverted cone method concrete falling time <2OS
(3)Scope of application
Ultra-high pumping range of concrete is suitable for pumping height greater than 200m in various super-high-rise buildings.
(4)Typical projects that have been applied
① Jinmao Tower. Pumping height of 382.5m, a pumping 174m3.
②Hang Lung Plaza. Pumping height of 288m, the standard floor of the main building more than 1000m3 of concrete per floor.
Pavement construction technology
(1) the main technical content
① in the proportion design: the use of asphalt concrete proportion design and charting computer-aided system, automatic calculation of the mineral ratio, generation and adjustment of grading curve; automatic drawing of Marshall test indicators and asphalt dosage of the relationship between the map, the calculation of the optimal asphalt dosage; to provide the sand screening Record table and sieving curve diagram. Calculation speed is more than 20 times higher than manual.
②construction technology and construction techniques:
A surface layer structure should be based on the layer in the use of the required performance and role of the selection of the three layers of the pavement should be selected to use the skeleton structure, should not be selected suspension structure.
B optimum discharge temperature of the mixture, paving temperature, compaction temperature; modified asphalt mixture in the transportation, paving, compaction process of temperature loss law; effective measures to prevent temperature loss in the transportation, paving, rolling process, maximize control of paving, rolling molding process of temperature differences caused by compaction unevenness; mixture of suitable combination of rolling equipment and rolling control.
C for modified asphalt SMA pavement, change the traditional rolling process, using increased compaction work, so that the mixture is molded at high temperature, high compaction, the stone is not crushed, horseshoe grease does not float, the surface structure depth to meet the standard high limit requirements.
(2)Technical indexes
①Standard of engineering quality control during the construction of modified asphalt mixture
(3)Scope of application
Applicable to the paving construction of single-layer and double-layer structure of hot-mixed modified asphalt pavements for high-grade highways, factory and mining roads, airport runways, etc. The paving construction of hot-mixed modified asphalt pavements has been completed in the first half of 2009, which is the first time in the world that the hot-mixed modified asphalt pavement is used in the construction of highway.
(4)Typical projects that have been applied
The technology has been used in Hebei Shi Huang high speed Xin Cang pavement three contracts (SAC structure of the surface layer), Jiangsu Lianxu high speed AB-24 standard, Fen irrigation high speed OPQ23 standard, Fen irrigation high speed OPQ21 standard, Xuju high speed 21 standard (modified asphalt SMA structure), Zhejiang Anti-tai-Qu high speed 8 standard (AK skid resistance structure), Shanxi Dayun High-speed 7 standard, Fujian Ningde high-speed B1 standard (AC structure), the Beijing-Zhuhai high-speed Hubei Second Contract (Superpave12.5 structure) and other projects successfully applied. From 2000 to the end of 2003, the cumulative modified asphalt pavement 267.821km. these projects have been completed, the handover are excellent engineering, put into use, the use of performance recognized by the owners and the community, there is a good social reputation.
Modified asphalt pavement construction technology is researched and developed by the First Highway Engineering Bureau of China Road and Bridge Group, which is a key technology development project funded by China Road and Bridge Group.