Abstract: concrete is currently widely used structural materials. This article mainly from the angle of concrete production analysis of various factors influencing concrete quality, and put forward feasible suggestions and preventive measures to ensure production safety, concrete durability, economic and reasonable.
Key words: concrete raw materials formulation design of transportation maintenance quality risks prevention measures
1 Introduction
Concrete as the most widely used one of the structural materials, it directly related to the quality of engineering quality, service life and people's lives and property safety. Our country is in the infrastructure construction of the peak, if in the production process of quality seriously not quite. Will bring enormous cost. Concrete production and supply is a continuous process, but the concrete is a kind of product cannot immediately be follow-up inspection work completely confirmed whether qualified to immediate pouring of used products. In its production process is often influenced by different factors, will enable the production of concrete quality variation.
Quality of commodity concrete must be qualified strength, good durability, economy of concrete. The three is an organic whole, mutual influence, are indispensable. This will influence the concrete of unfavorable factors of production are analyzed and proposed the preventing and handling measures.
2concrete production in the hidden trouble analysis and Prevention
From the angle of concrete production should be from the raw materials, formulation design, production control, delivery and other aspects of its quality control, ensure the concrete quality fully meet the design requirements. While these aspects are often present factors influencing most place.
2.1concrete because of its raw material quality problems and defects
2.1.1hazard analysis
Concrete construction quality directly affects the whole quality of reinforced concrete structure, and the concrete raw material quality and selecting appropriate also directly influences the quality of concrete engineering. Therefore, to ensure the quality of reinforced concrete structure is one of the important factors are to be from concrete raw materials quality control. Improper selection of raw materials will lead to concrete engineering quality defects or cracks, directly affect the engineering structure quality. Concrete due to improper material selection of quality defects or cracks, supposedly because concrete materials ( including cement and aggregate ) deformation constraint caused by the internal stress is greater than the tensile strength of composites. Material selection of improper common factors are outdated or improper selection of cement variety; condensate condensate soil ratio of cement, aggregate containing excessive adverse; hazardous substances; the heat of hydration of cement admixtures such as improper use of too high. The aggregate containing excessive impurities are most common. Aggregate ( sand, gravel ) accounted for more than 70% of total volume of concrete, concrete quality with the exception of the cement quality but also, and aggregate content of impurities in a close relationship.
2.1.2prevention measures
First of all to the coarse and fine aggregate in use should be performed before testing for impurities from the material, stack sampling part should be distributed evenly, pumping8 roughly equal -15samples. Detection method and basis to see concrete with crushed stone or gravel, sand quality inspection provisions. The second is to control the two pollution problems, should avoid aggregate piles affected by oil, slurry water pollution, is strictly prohibited in the was piling up too lime venues stacked on the gravel aggregate.
The strength of concrete is mainly composed of a water slurry, water slurry and aggregate strength of interfacial adhesion strength, aggregate particle strength. Water, mud will aggregate is firmly bonded into a whole, and the slurry strength depends on the strength grade of cement, the cement quality control in addition to the relevant national, industry standards, regulate and control, we must pay attention to five kinds of cement their characteristics, determines its application environment. According to different engineering conditions, climate condition, choosing appropriate cement variety is a prerequisite for obtaining high quality concrete.
In addition to meet the requirements of concrete strength but also the need for appropriate and easy. Modern concrete workability is largely in the highly effective admixture under reflected, is essentially the admixture of cement with high compatibility issues, both good compatibility, can achieve low water flow and the loss of small effect. Influence of admixture and cement compatibility is the main factor of C3A in cement and mineral composition and content of morphology and other factors. Thus different cement, will affect the water-reducing, enhancement effect, in which the water reducing effect is more obvious. Superplasticizer on cement more selective, different cement water reducing ratio is larger, the mineral composition of cement, admixture, retarder, alkali content, fineness will influence the effect of water reducing agent, such as mixed with anhydrite cement with superplasticizer, for some of the Queensland condensate soil will produce rapid hardening or the initial setting time of concrete greatly shortened, the naphthalene superplasticizer on smaller, molasses class can cause rapid hardening, wood calcium will make the initial setting time. Therefore, the same kind of water-reducing agent in the same dosage, often because of cement with different and obvious using effect is different, or the same kind of water-reducing agent, in different cement in order to achieve the same water-reducing and reinforcement effect of superplasticizer dosage, markedly different. In some cement water reducing agent, some can cause abnormal condensate phenomena. Therefore, when the cement may supply the choice, should choose the water-reducing agent is adapted to improve cement water reducing agent, the use effect. When the water reducing agent for choice, should choose suitable for construction of cement water reducing agent, to make the water reducing agent to exert better effect, before use, should be combined with the project of cement test. Each kind of admixture with appropriate dosage, even for the same kind of admixture, for different purposes have different appropriate dosage. Dosage is too large, not only the economy unreasonable, and may cause quality accident.
2.2concrete formula caused by improper design of quality problem
2.2.1hazard analysis
Concrete mix is the basis for production, directly related to the performance of concrete and the cost of production, is the core part of concrete quality control. The concrete mix design, should according to the structure design of the strength grade of concrete, durability, and engineering structure, transport distance, construction ways so as to determine the variety of raw materials, specifications and mixture slump properties. Concrete mix design is generally based on GB / T55~ 2OOO" code for design of ordinary concrete" described in the Bao Luo formula, as well as the national standard" GB5o 204Queensland concrete structure engineering code for construction and acceptance of", and the combination of test to determine the optimum mix ratio. Modern concrete design has been in the pursuit of durability design, the most economic optimization. The same mixture ratio in the same strength grade, different pouring position and construction method is not suitable, and even the emergence of serious consequences. Such as general pump concrete proportioning, its in order to pump the slurry concrete generally for the rich, but if the mix used in the pile foundation, column or road site, due to plasma volume more easily on the surface of the concrete, forming a paste layer, effect of pouring quality.
2.2.2prevention measures
Therefore, the design of concrete match ratio from the pouring and construction methods for two aspects of needs, according to the maximum gradation density to the design, to meet the construction conditions to minimize the amount of mortar in the concrete viscosity, not enough to affect the construction case, try to reduce the use of water, with superplasticizer adjusting concrete fluidity, such not only can reduce the laitance layer, but also can reduce plastic shrinkage of concrete, which need large number of trial to verify. Mixture ratio in the production and application of also according to raw material variation, weather conditions, construction conditions and make appropriate adjustments.
2.3concrete production metering error caused by quality problems
2.3.1hazard analysis
The production of measuring error can be divided into system error ( dominant error ) and system error ( implicit error ). The systematic error is due to production control software and sensor precision and sensitivity caused by. Generally speaking, the system error through the preparation of appropriate sensors and control software parameters to error less than the specified range. Rather than the system error is mainly in raw materials in the weighing process, sensor outside influences and feedback information exists certain deviation, its embodied in the weighing process, because the mechanical vibration transmission, the weighing device generating a dither, affect the sensor information is correct feedback : while in the powder weighing, generally have a definite pressure ( as for arch breaking or monsoon trough conveyor ), when the gas in the weighing process to accumulate in the call, a form of sensor generates a pressure, when the sensor feedback to the controller, the gas pressure is reduced, the actual dispersed, said material is less; and when the raw materials into the mixer, also can recurring, pressure via a feeding tube symmetry measure produces a top pressure, which then weighing material than the computer read value is on the high side. The impact of these factors in the production process is often difficult to be found, the recessive larger.
2.3.2prevention measures
To overcome such problems have to produce weighing system to maintain focus, solid material called stents, reduced and equipment vibration influence on it, the powder and mixer configuration suitable gas reflux pipe, and unblocked. This measure of production raw material can be performed strictly according to the formula, can be effectively controlled.
2.4concrete transport process to produce quality problem
2.4.1hazard analysis
Concrete transportation, especially for ready-mixed concrete transport, because concrete from ready-mixed completed to pouring site there is a certain distance, and the transit time is often control concrete slump and workability of the same key, which is also a certain risk factors, high temperature weather concrete mixer truck concrete moisture evaporate quickly tail. Easy to give a wrong impression of concrete slump loss of concrete mixing truck; rain weather, the concrete more water, easy to produce segregation. In addition, mixer car drum rotation speed, but also has effect on concrete. Car drum rotates faster, in the transportation process of the concrete mixing aggravate, molecules due to friction heat movement also aggravate, water molecules to increase cement particles, the hydration degree increase, concrete slump loss increases, and easily becomes worse quickly; vehicle drum slowly, or even stop, concrete is easily affected by driving bumps, and produce pulp stone separating, settlement and other undesirable phenomena.
2.4.2prevention measures
The concrete during transportation, vehicle drum remained at about six minutes per turn, and to the site to maintain mixer to rotate at a high speed to five minutes, in order to fully and evenly mixed again before concrete pouring. If the slump loss, can be mixed after certain admixture in order to achieve the desired result.
2.5maintenance of concrete quality problems caused by improper
After pouring concrete delivery of conservation issues, is also affects the quality of concrete pouring material. Concrete from the production, construction, maintenance, hardening is a series of processes.
With the development of concrete technology, concrete construction quality process control is generally accepted, the concrete temperature protection and conservation as concrete pouring process is very important program and link, should also have good design and construction, and every aspect of quality control should be implemented.
Concrete curing measures are mainly spray and water conservation: over the surface to form a layer of mist heat insulation layer, so that the surface of concrete in construction process to reduce direct sunlight intensity, reduce the surface temperature of concrete, reduce the temperature rise of pouring and vibrating process has good effect; surface water conservation can make concrete early maximum temperature decreased1.5 degrees around, but due to casting surface planeness, surface hard all have water, while the adjacent construction period of concrete construction with larger interference, so it has certain difficulty.
The concrete surface protection for surface insulation moisture mainly. Concrete surface crack reason is caused by the shrinkage and temperature stress. Dry shrinkage caused by surface cracks usually only a few centimeters deep, basically rely on maintenance solution. The surface tensile stress caused by temperature factors: temperature change, heat of hydration and the initial temperature difference. Temperature changes are: the sudden drop in temperature, the temperature change and change, especially the concrete in the initial pouring higher internal temperatures when particular attention should be given to the surface protection. On the concrete surface covered by a plastic film or wet linen bags, cling to the concrete surface to a temperature isolation effect, is the most effective measures to prevent the cracks on the surface.
The 3ending
To obtain the high quality concrete, must be in the whole production process to implement a comprehensive quality management ( P, D, C, A loop). P ( plan ) plan configuration quality merchandise concrete measures; D ( DO ) is according to plan implementation; C ( CHECK ) on the production of concrete are examined whether meet the quality requirements; A ( ACTION ) is the conclusion of examination for processing, and to summarize the experience in the practical production. To avoid concrete in the production of various risk factors, need all-around from the selection of raw materials, mixing ratio design, production, quality control, delivery and construction, maintenance and so on should implement a comprehensive quality management.
The original author: Liao Liekui source: China concrete network switched from" Guangdong Forest Survey Design"