A: admixture | polycarboxylate and naphthalene series water reducing agent, what is the difference?
Polycarboxylic admixtures and naphthalene water reducing mechanism of poly carboxylic acid water reducing agent with different, steric repulsion, the latter by electrostatic repulsion, the former in addition to the steric repulsion and strong air isolation" ball" effect and reduce the solid-liquid interfacial energy effect; the latter to electrostatic repulsion effect, basically no other beneficial effects on reduction of water. The former volume is low, the solid content is 0.05% ~ 0.3%, water reducing rate of 25% ~ 35%, up to 40%; the latter volume is 0.3% ~1.5%, the optimum amount of0.5% ~ 1%, the water reducing rate in 15% ~30% between.
Synthesis of poly carboxylic acid water reducing agent, plasticity is strong, can effectively control the slump loss of concrete hardening, but had little effect, enhance the effect is good, and has resistance to shrinkage, PC100polycarboxylate superplasticizer can more effectively improve concrete impermeability, frost resistance, so than other efficient reduction water can be even greater progress of concrete durability.
Two: cement fineness on the impact of poly carboxylic acid water reducing agent
Because of the increasing number of cement enterprises in the cement production process using grinding aids, or to improve the activity of mixed materials with various chemical activator. Cement enterprises merger and reorganization of the different manufacturers in the same brand market, which makes the admixture with cement to bring uncertain factors. .
2.1: from poly carboxylic acid compound made of high performance water-reducing agent in concrete, the water reducing rate and the fluidity of the paste, mortar water reducing rate between relations are not close, so," GB8706- 2008concrete admixture" standard has explicitly the fluidity of the paste and mortar water reducing rate test method to delete.
2.2: two or more than two kinds of poly carboxylic acid water reducing agent, the water reducing rate, setting time, strengthening performance so that the advantages and disadvantages of mutual complementary, can get the performance comprehensive high performance polycarboxylate water reducing agent.
2.3: in the low strength concrete using polycarboxylate superplasticizer, even with a reduced volume, also can compare naphthalene series of high water reducing rate, according to the relationship between the water cement ratio, water reducing cement content, the theory will be greatly reduced. But the concrete slurry total weight reduction will affect the performances of concrete, should be appropriately adjusted for fly ash and other mineral admixture and sand ratio size.
Three: cement mineral components and the influence of chemical composition
Cement cement mineral composition and chemical composition on the adsorption quantity of admixture, the fluidity and strength of growth has a great influence on. Additive adsorption amount less the fluidity of cement paste for larger values.
Four: the influence of cement fineness and particle shape
In order to meet the new standards of cement strength requirements, improve the fineness of cement is the most effective way, but the cement is too small, the increase in surface area, water demand, lower liquid phase residual additive concentration, increase the viscosity of liquids, plasticizing effect becomes worse, concrete slump loss faster; cement or water speed, water heat high, easy to produce cracks.
Five: admixture effect
According to the national standard, allow the cement mixed with a certain amount of admixture, commonly used in admixture with water quenched blast furnace slag, fly ash, zeolite powder, volcano ash, coal stone base, due to admixture of different properties, will also affect the admixture on cement adaptability, volcano ash, coal alkali stone is the worst.
Six: the influence of alkali content
Alkali in concrete mainly comes from the use of raw materials, especially limestone and clay. Alkalinity is lower, the better compatibility, high alkali content will be accelerated cement early hydration rate, leading to water demand increase and accelerate the loss, the plastic effect becomes worse.
Seven: fresh cement storage time and temperature effects
As a result of fresh cement drying degree is high, and the high temperature (80 degrees C and 90 degrees C ), the early hydration fast, hydration heat, so the water demand, but also for the admixture of adsorption of large amount. In the admixture has been available for the construction site condition, through adjusting the dosage of fresh cement and concrete admixtures to solve the incompatible problem, the adjustment as the fresh degree of cement and admixture adaptability and.
Eight : the large dosage of Superplasticizers on fresh concrete stability influence
Research and application of practice shows that: a large quantity of high efficiency water reducing agent in the concrete water cement ratio is very low conditions, can still have greater fluidity, can form dense, production strength and durability of high strength and high performance concrete. Every kind of superplasticizer and cement match between, there is a corresponding saturation concentration. For the majority of high efficiency water reducing agent, the saturated concentration of about0.8% ~ 1.2%. In the mixing of high strength and high performance concrete, special attention should be paid to the superplasticizer suitable dosage, and admixture and mineral admixture use, can achieve the desired effect.
Nine: concrete slump retention and the fluidity of the paste has a sexual relationship is not close.
Adding some pumping agent net fluidity in 1H ~2H can keep very well, but the slump loss of concrete is very rapidly, and some pumping agent in spite of paste in performance is not very good, but it has a good performance in concrete.
Ten: the different manufacturers, different batches of cement, admixture has adaptability problem.
These years, personnel of technology of additive and cement, admixture adaptability problem has conducted in-depth research, has established the following points:
11.1: pure or mixed with lignosulfonate superplasticizer pumping agent met with gypsum, gypsum as retarder in cement, prone to water reducing rate, low slump loss quickly, even flash condensation phenomenon;
11.2: the C3A content in cement clinker, alkali content, species and dosage of admixture, cement fineness, fresh degree on the pumping agent effect influence;
11.3: pumping agent effect is also dependent on the admixture types, surface characters and dosage;
11.4: pumping agent effect and concrete mixture during the preparation of environmental conditions ( temperature, humidity ) also exist certain relationship.
11.5: in the process of cement production is faced with more variable factors, such as grinding aids of the universal application of the pumping agent adaptability problem, city garbage incineration ash, coal gangue and metakaolin as mixed materials brought about by the use of pumping agent adaptability problem, makes a pumping agent to different manufacturers, different batches of cement and admixture is generated between the effect of differ in thousands of ways, has seriously affected the quality of commodity concrete stability.
Twelve: the main factors influence the slump of concrete
(1) the aggregate gradation. Due to the water and cement equivalence volume in the coarse aggregate and the rate of inclusion has the very big difference, in the same water content conditions, fine aggregate concrete slump is far less than the coarse aggregate of concrete slump. Therefore, gradation of aggregate fluctuations, will affect the slump of concrete.
(2) the water content in concrete. Concrete moisture content changes on the concrete slump is obviously. The variation of water content in sand, concrete mixing without considering the change of moisture content in sand, it will affect the slump of concrete.
(3) the temperature of cement. Cement temperature of concrete slump effect is often neglected by the construction personnel. Cement high temperature, not only makes the concrete temperature, and slump due to high temperature of cement, water is larger and smaller.
(4) measurement scale error. Water balance and cement weighing deviation on the slump of concrete influence, if the water balance and cement weighing deviation is not stable, is not easy to control slump.
(5) the quantity of admixture. The amount of additives the number directly to the slump of concrete works. In the production process, admixture dosage should be relatively stable will play a better role.
(6) the cement gypsum dehydration. Cement during the grinding process, due to increase in temperature, easy to cause the cement in the two water gypsum dehydration become hemihydrate gypsum. Half water gypsum in cement concrete mixed with water, quickly reacts with water to form two gypsum, thereby allowing the concrete of mobility decline, affecting the slump of concrete.
(7) additive and cement adaptability. Concrete additive categories and cement variety exists between the adaptability problem, if concrete additive and cement adaptability is not good, will seriously affect the flow of concrete, causing the loss of slump of concrete.
(8) the cement grinding fineness. The fineness of cement will affect the cement standard consistency water requirement. Usually, the cement of the larger specific surface area, water requirement is bigger. Especially with volcano ash mixed material of cement, often large specific surface area, the cement standard consistency water demand is very high, in the concrete water cement ratio under the same conditions, will make the slump of concrete reduce. If the cement fineness fluctuation, it will cause the fluctuation of slump of concrete.
(9) abnormal setting time of cement. In cement clinker burning process, because of some reasons, often resulting in cement clinker some quick setting mineral content changes, so that the cement setting time is not normal, or fluctuating ( fast and slow ), resulting in the loss of slump of concrete greatly changed.
Thirteen: honeycomb pitting surface of concrete formation causes
13.1. Concrete air content is too large, poor quality and air entraining agent.
13.2. Improper concrete mix, concrete is too thick, vibration when the bubble is difficult to discharge.
13.3. Because of poor workability of concrete, segregation and weeping. In order to prevent the concrete, concrete can fully vibrator, a lot of bubbles not line, can also result in hardening the surface of concrete structure surface appearance of honeycomb.
Fourteen: additive and cement not photograph adaptability problems mainly are the main factors:
14.1: the admixture of its reason mainly has following several aspects: (1) different varieties; (2) structure of different functional groups; (3) different polymerization degrees; (4) composite components. The influence of back through different methods will affect the cement adaptability. Different manufacturers produced the admixture can also have many differences, the main reasons are: (1) the production process; (2) factory production process technology; (3) the level of quality management. Therefore, different manufacturers produced products will have difference.
14.2: the mineral composition of cement admixture influence is very big, cement mineral composition mainly aluminum acid three calcium (C3A ), iron and aluminum acid four calcium (C4AF ), three calcium silicate, calcium silicate ( C3S ) two ( C2S ), different mineral composition mainly by the production of cement raw material and production process the decision, the mineral composition of cement admixture effect of element size were C3A > C4AF > C3S > C2S. Hydration reaction of C3A fast, early strength increases quickly, need a large quantity of water, excessively high C3A content ( mass fraction greater than 8% ), C3A adsorbed on the external dosage big, admixture effect loss [2]. The mineral composition of cement and the range of table
14.3: cement production process required to join the final plaster adjusting the setting time, cement manufacturers use regulation set gypsum admixture influencing factors on the order of anhydrite ( anhydrous gypsum hemihydrate gypsum ) > > two gypsum, cement manufacturers to save costs often use industrial anhydrous gypsum, so that does not affect the cement to achieve quality requirements, to the common admixture of concrete and no adverse reaction, but the modern admixture of concrete, the use of anhydrite cement water requirement, adsorbed on the external dosage big, loss of large amount of admixture. Anhydrite on wood calcium effect is more obvious, there may even be a quick set ( a false set ) phenomenon.
14.4: the cement fineness and particle size effect
Cement manufacturers often in order to achieve the new cement standard requirements, improve market competitiveness, enhance the grinding, thereby improving the strength increasing fineness of cement. Cement is meticulous, water demand, the same will be adsorbed on the external dosage is bigger, admixture loss; at the same time fine cement in grinding temperature higher, will also be more hydrated gypsum into anhydrous gypsum, anhydrite content increased, and admixture adaptability will be worse. Cement particle size gradation of cement paste is not good, the bleeding rate for the poor adaptability of cement and additive.
14.5: the alkali content of cement
Alkali content is too high ( alkali content > 0.8%) cement or alkali content is too low ( <0.5% of the alkali content of cement ), is also easy to produce incommensurate admixture. Cement base mainly come from raw materials used, especially limestone and clay. The alkali content of cement is too high or too low, in some varieties of additives are added, will cause the cement gypsum solubility changes, so that the mineral compositions of the cement of C3A hydration rate of speed, water demand increases, work loss became faster. When adding a soluble Na2SO4, can improve its admixture adaptability. Fly ash, slag admixture and cement hydration products of Ca ( OH )2occurred two times in response, reduce the alkality of concrete, so that the additive and cement adaptability improvement [4].
14.6: fly ash and admixture adaptability
Fly ash is too small, will be more dispersed particles of fly ash admixture; fly-ash Burning-loss amount bigger ( i.e. contain more carbon ), water requirement is bigger, more influence of admixture, carbon particle coarse mostly holes, easy absorption, adsorption admixture capability, so that the admixture amount, especially on air-entraining agent effect.
14.7 aggregate effect
The aggregate amount of mud, clay content, a large amount of clay particles will absorb more water, more admixture, the workability of the fresh concrete variation, easy segregation, high slump loss, but also influence the strength of concrete; concrete mix properly, sand rate unreasonable, will also increase the slump loss. Sand ratio is small, easy segregation, climb up the bottom of concrete, slump loss of concrete; sand percentage is too large, too much sand require more water wetting, the slump of concrete decreases, also affected the strength of concrete; aggregate gradation is harmful, especially lacking the intermediate particle size of aggregate, but also easily lead to concrete segregation, climb the bottom, concrete slump loss, effect of concrete quality.
14.8 solution additive and cement is not adapted to the problem, as the case may be, on the basis of experiments, analysis to find the reasons, to adjust the proportioning of concrete, improve the ex-factory slump, to reduce the slump loss.
Can usually be adjusted dosage of fly ash admixture amount, improve, improve the admixture in concrete and the liquid residue,.