Concrete is the basic building material of modern high-rise buildings, in order to meet the different requirements of various forms of construction on the performance of concrete, it is necessary to add a variety of admixtures in concrete mixing plant to change the performance of concrete. In order to ensure the quality of concrete, improve the safety of construction projects and extend the service life, it is necessary to study the selection and addition of admixtures, the reasonable use of admixtures.
Construction industry pouring concrete admixtures as the fifth component of concrete, the use of additives, to improve the overall compactness of concrete, strength, crack resistance, durability, frost resistance, in addition to improving and enhancing the performance of concrete itself can also improve the construction of concrete adaptability, shorten the maintenance time, reduce the labor intensity of staff, improve the mechanization of concrete mixing plant construction, so as to Obtain higher construction efficiency, save construction time and control construction cost. The use of additives effectively compensates for the performance defects of concrete itself, which enables the realization of high strength, high durability and high crack resistance concrete and broadens the scope of application of concrete.
Concrete admixtures are widely used, almost all concrete mixing plant are different degrees of use of concrete admixtures, through the use of different additives to adjust the performance of concrete to meet the requirements of the construction of concrete performance, improve the strength of concrete, or save the amount of cement. Winter concrete construction, concrete surface temperature loss, if the insulation measures are not timely, may lead to the surface of the concrete is a lot of heat, the temperature drops rapidly, the temperature difference between inside and outside and eventually lead to temperature cracks, so you can use early strength agent or early strength water reducing agent, accelerate the concrete solidification, reduce the heat of hydration, so as to control the temperature difference between inside and outside the concrete, weaken the tendency of concrete cracks. Summer concrete slipform construction, large volume concrete construction can use retarding agent, retarding type water reducing agent, delay the release of internal heat of hydration of concrete, extend the time of hydration reaction of concrete, avoid the rapid rise of concrete temperature in a short period of time, the same can play an ideal anti-cracking effect.
Sprayed concrete impermeable protection project, tunnel waterproof concrete structure concrete construction can use rapid setting agent to accelerate the concrete set, so as to form the impermeability faster. Reinforcing steel dense large formwork prestressed reinforced concrete construction in order to facilitate the pouring while controlling the amount of water, reduce the heat of hydration of concrete, you can use high-efficiency water reducing agent to improve the ease of concrete and reduce the amount of water, construction of underwater concrete in order to obtain a higher degree of ease and durability, you can use air-entraining agents and water reducing agents, high grade and ultra-high grade concrete requires the use of high-efficiency water reducing agent to complete the formulation, large In order to compensate for the greater degree of concrete dry shrinkage, the expansion agent can be used to resist the reduction of concrete volume, precast concrete components using admixtures can reduce the preparation and maintenance time, accelerate the production efficiency of concrete components, while improving the adjustment of the vibrating process to improve the quality of concrete components.
Misconceptions of concrete admixture use
Buy low price admixture
A penny for a penny. In the fierce market competition in the construction industry, concrete mixing station in order to ensure the quality of concrete mixing, the need for strict control of the quality of concrete raw materials, the quality of concrete raw materials is the basis of the final quality of concrete, but some concrete mixing station in order to control costs, choose a low price, does not meet the requirements of quality standards and concrete performance requirements of admixtures, or choose the national standard requirements in the The minimum standard, resulting in the provision of admixtures of low quality, performance is difficult to meet the demand.
Admixture quantity control
Some concrete mixing plant are sensitive to the amount of admixture and cement in order to control the cost, and give a clear upper limit of admixture, which brings greater limitations to the concrete mix design work and affects the final concrete performance.
Insufficient quality management of admixture
At this stage, some concrete mixing plant do not pay enough attention to the management of admixture quality, the purchase of admixture is relatively arbitrary, the material admission testing work is not in place, improper storage work, resulting in part of the quality does not meet the standard requirements of the admixture into use, so that the experimental performance of concrete and the initial adaptation effect is not consistent, poor adaptability, leaving a lot of hidden concrete quality problems.
Concrete admixtures common use of misconceptions correction methods
Procurement is the first step in the quality management of concrete admixtures. Concrete mixing plant needs to choose qualified and experienced professional procurement personnel responsible for the procurement of concrete admixtures, compare the quality of suppliers, select reliable and good reputation, should actively build a long-term stable relationship with suppliers to ensure the quality of concrete admixtures. Procurement personnel need to consider the manufacturer’s production scale, transportation costs, technical level and after-sales service capabilities, should not be excessive pursuit of low prices.
After the admission of concrete admixture, first check the quantity, specification and performance of concrete admixture, check the factory technical documents and quality inspection certificate of concrete admixture. After that, the site sampling, in accordance with national standards for the correct collection of samples, sent to professional testing organizations for performance testing, to understand the admixture’s solids, water reduction rate, density, net slurry flow rate and other performance, to confirm that it meets the concrete performance requirements, the quality is not qualified firmly not allowed to enter. The most critical technical performance of concrete admixtures is water reduction rate and concrete water reduction rate, taking into account the need for testing timeliness, generally choose density, cement net flow rate and water reduction rate 3 indicators for testing. If the quality of concrete admixture quality performance does not meet the requirements after admission quality inspection, and exceed the upper and lower limits of the admixture qualification standards, need to return the processing.
Concrete admixture after the admission test to confirm the quality of qualified can be admitted. Subject to changes in environmental conditions and the impact of the concrete admixture itself, the water reduction rate of concrete admixture test results and the final concrete test mix results may have a large difference between, so the material into the warehouse, the need for routine testing, to understand the water reduction rate of concrete admixture, solid content. In the process of routine testing of concrete admixture, if the water reduction rate is found to have a large fluctuation, it is necessary to compare it with the previous admixture qualified samples, analyze the concrete admixture water reduction rate change is its own material performance reasons or other factors, while the routine test results will be reported to the concrete mix design staff in a timely manner, to ensure that the concrete mix design can be based on the concrete raw materials Water content of concrete and the actual situation of concrete admixture water reduction rate timely adjustment, control admixture dose, to avoid the impact on the performance of concrete. In order to ensure the rationality of the concrete mix design, it is required to conduct at least two verification of the common concrete mixes every month. Most of the concrete strength problems and the increase of concrete mix cost are related to the inappropriate verification of the mixes, through the verification of the mixes to understand the rationality of the concrete mixes.
Selection and Use
The selection of suitable concrete additives requires comprehensive consideration of various factors such as concrete mixing plant,cement type, admixture type, coarse and fine aggregate properties, concrete mix ratio, mixing time, and environment. At this stage, China’s construction materials market is mixed, concrete raw materials of various types, numerous models, a wide range of material sources, sand and gravel material quality fluctuations, increasing the difficulty of use and selection. In the specific selection process, concrete admixtures are required to significantly improve one or several properties of concrete, while not bringing serious side effects, but also has good stability and homogeneity, and does not produce erosion of the pre-built reinforcement and metal components in concrete.
Concrete admixture quality inspectors need to strictly enforce the established concrete mix ratio and follow the admixture dosing requirements in concrete to add admixtures correctly. Before the day’s concrete mixing plant construction, quality inspectors need to sample sand, stone and aggregate moisture content, and make appropriate adjustments to the amount of concrete preparation water according to the water content of the concrete raw materials, and correctly handle the gel material as well as the fluctuation of water reduction rate of aggregates and admixtures. If the concrete construction process, the performance of the concrete raw materials has changed, it is necessary to make timely adjustments to the concrete mix ratio, the increase in demand for concrete aggregates, the decline in the water-reducing properties of admixtures will lead to an increase in the amount of water, in this case, the need to properly increase the admixture of concrete admixtures, can not blindly increase the amount of water, to maintain the concrete water-gel ratio, to ensure that the concrete strength to meet performance requirements.
The use of admixtures in concrete can significantly improve the sex, enhance the economic benefits of concrete and technical performance indicators, but if the admixture is not used properly, but may cause adverse effects on the quality of concrete, so in the selection and use of admixtures in the process, the need for strict implementation of the relevant standards, serious concrete mixing plant admixture routine inspection work, according to the test results of the concrete with you to Timely adjustment, to ensure the quality of concrete.