Keywords: reinforced concrete; High efficiency water reducing agent
In the concrete mixed with water reducing agent can improve the workability and strength of concrete,improve the long-term durability of concrete, reduce the shrinkage of hardened concrete, and reducing energy consumption. The application of the superplasticizer, is an important method of the preparation of high performance concrete soil.
Classification and properties of high efficiency water reducing agent, high efficiency water reducing agent is generally divided into synthetic of two kinds of single components and composite components, main control technical indicators are: water reducing rate, air content, the setting time, slumping performance, exudation rate, ratio of compressive strength and durability of relative index, etc., in which water reducing rate as the slump phase at the same time benchmark the difference between the concrete and adding admixtures concrete unit water consumption and the ratio of the base unit water use of concrete, is one of the most important quality index of water reducing agent.
combined forming type high efficiency water-reducing agent :
poly (alkyl aryl sulfonate high efficiency water reducing agent (NS) : according to different raw materials, divided into naphthalene series water reducing agent, methyl naphthalene water reducing agent, anthracene water reducing agent.
The naphthalene series water reducing agent (mainly for the βnaphthalene sulfonate formaldehyde condensation compound) in industrial naphthalene as main synthetic raw materials; The main synthetic materials of naphthalene water reducer are naphthalene methyl or washing oil containing high methyl naphthalene. Anthracene water – reducing agent is mainly composed of anthracene oil.
sulfonated melamine formaldehyde condensate, also known as water-soluble melamine resin system (MS).
oxindene resin sulfonate, also known as gumaron resin series.
aromatic aminosulfonic acid polymers, also known as aminosulfonic acid series.
Polycarboxylic acid (cement good dispersibility, keep the concrete and transgender, liquidity, water reducing rate > 30%), mainly divides into maleic acid polyoxyethylene ester sulfonate and acrylate acrylic ester (including poly carboxylic acid series and terminal sulfonic group multiple polymer).
Effect of the above high efficiency water reducing agent on the newly mixed concrete:
Slump loss:methyl naphthalene>melamine resin series>naphthalene sulfonate formaldehyde>gumaron resin > amino-sulfonic acid series
The amount of air induction in concrete, methyl naphthalene > gumaron resin series > melamine resin series > >naphthalene sulfonate formaldehyde > amino sulfonic acid series.
As for the speed of concrete coagulation, melamine resin series >naphthalene sulfonate formaldehyde > methyl naphthalene > gumaron resin > amino sulfonic acid series
Compound multicomponent high efficiency water reducing agent: it is composed of water reducing agent component and functional component (such as slump preserving component and air conditioning component) in a certain proportion.The main function of the slump preservation component is to reduce the early slump loss of concrete mixture.
classification and characteristics:
calcium lignin sulfonate,sugar calcium and molasses are suitable for short distance transportation. For concrete with strength grade below C40, the slump loss rate can reach more than 50% after more than 1h of newly mixed concrete.
the hydroxy carboxylic acid and its salts (such as citric acid, calcium gluconate, etc.), generally within 1 h control fresh concrete slump loss is small, the disadvantage is that can lead to concrete segregation.
inorganic salts (such as boric acid and various phosphates) have the disadvantages of unstable coagulation with time and temperature change.
reactive polymer (within a molecular chain ester, acid anhydride group), insoluble in water of powder particles in alkaline environment melting, release, in the slurry concentration is relatively constant in the body, thus preventing slump loss, and is released according to the types of reactive polymer, particle size and content.
type of gas component is a hydrophobic surface active agent, stirring and will be attached to mixed with mixture formation of tiny bubbles surface, make the bubbles in the liquid membrane is strong, and stable. The main difference is water reducing agent surface active role mainly in liquid and solid interface, while the air-entraining agent role in the gas and liquid interface. Bleed air components are:
Rosin resins, such as rosin hot polymers and rosin soap;
Alkyl benzene sulfonates, such as alkyl benzene sulfonates, alkyl phenol polyoxyethylene ether, etc.
fatty alcohol sulfonates, such as fatty alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene sodium sulfonate, etc.
Others, such as protein salts, petroleum sulfonates, etc.
Chemical structure characteristics of high efficiency water reducing agent
the polymer contains single ring, multiple ring and heterocyclic ring, that is, it has a large truncation bond (except polycarboxylic acid), so it is easy to generate electrostatic adsorption and form hydrogen bond, which is conducive to solid powder dispersion
the degree of polymerization of the polymer electrolyte should be controlled in appropriate range, relative molecular weight is in commonly 1500 ~ 10000, relatively small molecular weight is advantageous to the orientation of molecules at the gas-liquid interface and falling water table surface tension, and high molecular weight reduce water reducing effect.
harmful groups (such as hydroxymethyl – CH2OH, ether – O -) should be controlled in large molecules.
the molecular chain usually contains the leading functional groups
Leading functional groups in the admixture macromolecules with special performance, and play a leading role in the application. – the primary role of SO3 H for efficient produce high water reducing rate, – COOH leading role for the retarded, slumping, – COOH, SO3 H respectively with one or more of multiple polar groups and groups of polar atoms in the same molecule, and to give a leading role as well as the leading role of some function. With the nature of the leading role of high molecular compound leading performance, can make through compound leading role has the additive property, which can produce synergy with superposition. Such as water reducing rate of FDN and water reducing rate of 20% and 11% with “COOH – SO3 H” double leading functional graft copolymer of polymerization, water reducing rate can be raised by synergy to 30%. Therefore, a high performance water reducing agent for cement concrete can be obtained by molecular design. Introduced in macromolecular chain – COOH, SO3 H leading functional groups of one or several, and consistent with the non-dominant functional group and polar group or groups of atoms and the combination of polarity polarity. Single or double leading functional groups jianshuiji polar monomer in the combination of hydrophilic group and hydrophobic groups to conform to, to appropriate proportion. Double leading functional groups of COOH/SO3 H in the graft copolymer of graft copolymer was the proportion of performance, and should be consistent, appropriate proportion of hate water-based suitable, such as increased (- CH2 CH2 – O -) link , which may lead to bleed air volume too high. In order to make a design product to obtain good performance, in addition to the introduction of polar groups in total polymer, also introduces the activity of reactive groups make some performance is more outstanding, persistent.
Development trend of high efficiency water reducing agent with single component in composite forming
naphthalene series water reducing agent of raw materials substitute. Except naphthalene can use anthracene and anthracene oil, benzene and benzene homologue. With industrial waste water reducing agent or cheap raw materials preparation, cheap, efficient, and eliminate the pollution. For example, using the phenol residue preparation process of water reducing agent are as follows: Residue of phenol – sulfuric acid extraction – sulfuric acid acidification – condensation with formaldehyde – with sodium hydroxide neutralization, concentration, drying, red powder. You also can use sulfonated polystyrene. Its ingredients except with styrene, can also use the alpha 2 methyl vinyl and indene, the preparation of sulfonated polystyrene molecular weight 12000 of polystyrene with concentrated sulfuric acid, fuming sulfuric acid or chlorosulfonic acid sulfonation under the catalyst, the sulfonated polystyrene as the action of naphthalene series water reducing agent to concrete water reducing agent.
modification of lignin sulfonate. In alkaline, Lignin sulfonates with air oxidation to the sugar content of lignin sulfonic acid (in calculating pentose) for m (sugar) : m (lignin sulfonic acid) = 215% ~ 5%, and can effectively reduce slump loss, through the division of ultrafiltration membrane of molecular weight of more than 10000 low molecular area, make the low molecular weight of lignin sulfonic acid solid content less than 20%, adding sulfonic acid formaldehyde condensation product – at the same time, as cement dispersant, which can effectively prevent water mud or concrete fluidity decline. On the basis of further improvement , using polycarbonate or polyolefin thin film materials for ultrafiltration and concentration, the special modified lignin sulfonate was obtained as an essential component of the additive. Another essential ingredients is other cement additives, such as glucose acid salt, melamine sulfonic acid formaldehyde condensation product or its salt, olefin unsaturated and binary carboxylic acid copolymer and polycarboxylic acid, etc. More olefin – unsaturated dicarboxylic of olefin copolymer can be such as ethylene, propylene and butylene b, unsaturated dicarboxylic can be maleic acid and acid etc., its salt alkali metal salt, alkaline earth metal salt or ammonium salt, etc., for example, in maleic anhydride and catalyst azodiisobutyronitrile solution of propylene can be obtained by this kind of dispersant. It can shorten the gel time of delay, improve the liquidity of cement slurry.
other resin-type water-reducing agents, such as composite sulfonated urea-formaldehyde resin. According to the m (sugar) : m (lignin) carbonate = 1: (211-3) charging, hydroxyl methylation reaction, generate 12 methylol urea, press the molar ratio of urea and compound sulfonation agent again for the ratio of 1: (1 ~ 5) in order to join the various components of compound sulfonating agent, to carry on the sulfonation reaction, then under acid condition, in return 1 ~ 4 h, 75 ~ 100 ℃ for condensation reaction, and finally stability under the condition of pH = 715 ~ 810 in molecular rearrangement reaction for a quick (less dosage and water reducing effect is remarkable). To meet the needs of pumping and piping of concrete in high flow continuous production.
polycarboxylic acid has the good property of maintaining slump for a long time.
reactive PRA polymer copolymer, the insoluble reactive polymer copolymerization and concrete under high alkaline alkaline hydrolysis reaction medium, slowly release water soluble hydrolyzate dispersant or retarder at a level to control slump.
carboxylic acid sulfonic group, with the means of molecular design, through a variety of vinyl monomer copolymerization reaction of water soluble cement concrete water reducing agent, leading functional groups are- COOH, SO3 H, polar monomer with combined optimum proportion in the molecular structure appeared on the polymer main chain, and has certain side chain length. The present varieties of water reducing agent with naphthalene series products as the main body, polycarboxylic acid production by the end of 2003 less than 2% of total water reducing agent production, and some countries such as Japan, Europe and the United States has been more widely used polycarboxylic acid high performance water reducing agent, The polycarboxylic acid water reducer will be an important direction for the development of high efficiency water reducer in China.
impurity content and number of polar bases of polymer molecules;
the average molecular weight of the polymer;
the size of molecular weight distribution. Due to the different production process, so the adaptability of cement is also different, the influence of different factory production of the same type of water reducing agent distribution, can make the molecular size and distribution of water reducing agent, to get a more reasonable molecular grading, and thus can achieve good use effect.olycarboxylic acid is new type of water reducing agent. Through a variety of copolymer of vinyl monomer reaction to obtain a water-soluble water reducing agent, must be in macromolecular containing long chain can provide you with the dispersion of cement particles and flow performance of polar monomer (such as carboxyl (-cooh) group, hydroxyl (OH), sulfonic group (- SO3 H) and polyethylene oxide alkyl group – (CH2 CH2O) m – R, etc., and the polar monomer with suitable proportion appeared on the polymer main chain. For example, choose olefin monomer containing carboxylic acid base and carries on the free radical polymerization, olefin monomer containing sulfonic group Binary or ternary copolymer, the synthesis of polymer chain with carboxylic acid and sulfonic acid based on two kinds of anionic surface active groups (the water reducing rate is more than 30% water reducing agent of fresh concrete initial slump basic no loss in the 1 h, 115 h loss l cm).Compared with naphthalene series water reducing agent, polycarboxylic acid dosage of water reducing agent is low, but the water reducing rate,maintain performance, good adaptability to cement, slump and strength increasing obviously, production and no pollution in use process, and many other advantages, therefore has been widely studied.The production proportion of polycarboxylic acid products in Japan has been increasing year by year, while the proportion of naphthalene series has decreased. The general classification of Japanese polycarboxylic acid water reducers is listed as follows:
Development trend of compound multi-component high efficiency water reducing agent: Composite water reducing agent components used in general, complex multicomponent high efficiency water reducing agent of water reducing agent is divided into simple set of water reducing agent, such as single naphthalene series, single melamine, single amino sulfonic acid, but more and more experimental research and engineering application showed that the different kinds of molecular structure of polar group compound use of high efficiency water reducing agent (such as naphthalene series, compound use melamine, naphthalene series with amino sulfonic acid, etc.) when used in combination, can have better than that of single type water reducing agent component price effect. Due to a variety of polar group and a variety of dispersion is a combination of water reducing agent, In under the condition of invariable total dosage, not only makes the water reducing rate of compound high efficiency water reducing agent, and can make the composite cement of high efficiency water reducing agent and adaptability are improved significantly. In addition to different kinds of composite water reducing agent components, different manufacturers of the same high efficiency water reducing agent of composite use, or different manufacturer production of naphthalene series and naphthalene series compound to use, also can obtain very good use effect. In general, the influence factors of water reducing agent and the adaptability of cement with are:
Table 1: ratio of high efficiency water reducing agent production in Japan
Composite use of functional components
In order to improve the workability and durability of concrete, often will compound use a variety of functional components in the compound water reducing agent.It makes concrete has good pumpability and good performance of freezing-thawing resisting, gentle multicomponent compound use. Often will bleed air components with the same type of water reducing agent components can also be mixed use, Such as calcium lignosulfonate and sugar calcium,hydroxy carboxylic acid and its salts and inorganic compound use inorganic salts, etc., because of the great differences between the functional components of concrete performance and the influence of each are not identical, therefore, in the selection of different functional groups of time-sharing should cause enough attention, in meet the concrete work under the premise of performance and durability performance, should as far as possible reduce the composite functional components with different properties, lest cause undesirable consequence.
— SO3H has efficient dispersal effect (high water-reducing effect), and — COOH has efficient retarding effect (significant slump retention value).
through the molecular design, introduced at the same time in the macromolecular chains – COOH and SO3 H group, and to control its proportion, to keep its show the slump of the value, the appropriate ratio of water and gas. Carboxylic acid, sulfonic acid system with strong sex, the molecular design can meet high approaching from the more general to the different requirements of ultra high strength concrete.
composite water reducer components used, can be different types (such as naphthalene series, melamine, amino sulfonic acid, etc.) of the compound use water reducing agent, water reducing agent can also be the same type of different manufacturers, when used in combination can have better effect.
high efficiency water-reducing agent and functional component can meet the working and durability needs of concrete well.
polycarboxylic acid high performance water reducing agent with low dosage, high water reducing rate, and maintain performance, good adaptability to cement, slump and strength increasing obviously, production and no pollution in use process, and many other features, will be an important direction of the development of high efficiency water reducing agent.