外文翻译--矿物掺合料的综合效应与强塑剂混合水泥浆的流动性.doc

中文4300字Combined effect of mineral admixtures with superplasticizers on the fluidity of the blended cement pasteAbstract：The new concrete often incorporates several organic and mineral admixtures which interact with the various constituents of the cements and cause some problems of hardness and workability. In the present study, limestone cement (C1) and pozzolanic cement (C2) were used to make cement paste with two types of superplasticizer; SP1 based on polynaphthalene sulphonate (PNS); and SP2 based on resins melamines (PRM). Marsh cone test was adopted to check the combined effects of the following factors on the fluidity namely the type of cement, the type and the dosage of the superplasticizer, the type and the replacement rate of the mineral admixture and the watercement ratio (W/C). The results of this work show that limestone cement presents a high fluidity with low loss after 1 h relatively to the pozzolanic cement within the saturation proportioning. Superplasticizer SP1 constitutes an incompatibility case when it is mixed with cement containing high C3A or alkali content such as C2 cement. Also, limestone powder is found to be the best mineral admixture when it replaces a part of cement, where more fluidity is exhibited caused by the dilution effect.Keywords：Cement，Limestone powder，Natural pozzolan，Superplasticizer，Fluidity1. IntroductionCurrently, the essential novelty appeared in cement industry is actually the increase use of the mineral admixtures, substituting a part of cement to reduce the carbonic gas emission, to minimize the cement cost and to improve some technical performances.High performances concretes made with low W/C ratio require the use of suitable and compatible superplasticizers with the new cements which can transform a concrete with high consistency into a concrete with high workability. During the use of superplasticizers in concrete, certain cements can sometimes present some problems of incompatibility of cementsuperplasticizer; irregularity of slump and rapid workability loss. The principal approach provided to combat against this difficulty is to select the most efficient couple cementsuperplasticizer, enabling to obtain a maximum water reduction, a better workability and an acceptable rheology during the placement and the finishing concrete.The incorporation of some mineral admixtures such as blast furnace slag, fly ash, silica fume or natural pozzolan can make the interaction between the cementitious materials and superplasticizers more complex, and therefore the selection of the compatible couple requires further consideration.The adsorption of superplasticizer molecules on hydrated phases creates an electrostatically charged germ which participates to the electrostatic repulsion and avoids flocculation.Also, the cement paste characterized by the long needle of ettringite formed at early age usually decreases the paste fluidity .There exists an optimum soluble alkali content with respect to the fluidity and fluidity loss, which was found to be 0.40.5% Na2O equivalent. At this optimum alkali content, the initial fluidity is maximum and fluidity loss is minimum.Neubauer et al.4noted that superplasticizer causes the zeta potential of the cement pastes to become increasingly negative; it suggests that this superplasticizer begins to disperse the cement particles. When new superplasticizers are developed, an interaction problem must be anticipated, cement and superplasticizer will be able to cause sharp variation in fluidity and produce stiffness, depending upon the combination of cement and superplasticizerSwamy et al. works concluded that it is possible to reduce the content of superplasticizer by incorporating slag in the cement; the replacement of the cement by 70% slag reduces 10% of the amount of superplasticizer necessary to get the same workability.The results conducted by Duval and Kadri confirmed that the superplasticizer adsorption depends both on the amount of C3A and the presence of soluble alkali sulphates in the cement. It was proved that the incorporation of fly ash in concrete reduces the need of superplasticizer necessary to obtain a similar slump flow compared with the concrete containing only cement as binder. On the other hand, Sone et al. observed a total loss of fluidity when Portland cement was replaced by blended cement, where superplasticizer content changes from 0.5% to 3%. When the superplasticizer presents a compatibility with a certain mixture composition, it will lose it as soon as the mineral admixture is substituted. Similarly, Bensebti and Houarifound that the fluidity of the cement paste decreases with the introduction of the fillers, this reduction is proportional to their replacement level and type.The investigation of cementsuperplasticizer (CSP) compatibility can be realized by measuring flow time of grout as proposed by several researchers1113. The cement paste fluidity results usually are represented by a curve indicating the flow time CSP system according to superplasticizer dosage at 5 and 60 min age.The type of curve obtained presents three essential points which control the rheological behavior of the cementsuperplasticizer studied and are expressed as follows:Saturation superplasticizer dosage corresponding to a break in the curve when superplasticizer is added over the saturation point; it does not improve any more the fluidity of CSP but only increases the risk of sedimentation and delays the cement setting time. Fluidity level reached for this saturated dosage (flow time); which will be small as much as the paste is fluid. In this text, the fluidity term is the opposite of viscosity. Fluidity loss related to the two curves at 5 and 60 min; it can be expressed by the difference between these two times, which must be very low for compatible couples of cementsuperplasticizer.The objective of this work is to study the interaction cementsuperplasticizer by measuring the fluidity of the cement paste in order to select the compatible superplasticizer with the given cement.The term compatibility characterizes the interaction between the cement and the superplasticizer which offers high fluidity with low saturation dosage and without important fluidity loss. If these performances are not observed, the couple cement and superplasticizer may be marked as incompatible. In addition to this, the effect of increasing the replacement rate of some mineral admixtures on the variation of the cement paste fluidity is examined.2. Experimental methods2.1. MaterialsTwo types of cement are used; the first one is provided from Chlef cement factory (Algeria) CEM II 42.5, named C1 and containing 10% of limestone powder. The second one is provided from Zahana cement factory (Algeria) CEM II 42.5, named C2 and containing 15% of natural pozzolan. The physico-chemical and mineralogical characteristics of these cements are shown inTable 1. Two superplasticizers are used at various dosages to improve the grout fluidity with 40% mass content; SP1 based on polynaphthalene sulphonate (PNS); and SP2 based on resins melamines(PRM). In order to examine the contribution of these mineral admixtures to the fluidity of cement grouts and their compatibility with these superplasticizers, two types of minerals admixtures were used; limestone powder and natural pozzolan which are the raw materials in the manufacture of these two cements. By incorporating various replacement rates of these admixtures, the variation of the grout fluidity was checked at different dosages for the superplasticizer. The characteristics of these mineral admixtures are represented inTable 1.2.2. Mixes productionThe fluidity of the paste is evaluated according to the type of the cement, the superplasticizer and its dosage, the mineral admixture and its replacement rate as well as the W/C ratio.Table 2includes two sets of paste based on cements C1and C2 containing 10% of limestone powder and 15% of natural pozzolan respectively and are considered as control. The fluidity of the paste was assessed for higher replacement rate of these mineral admixtures ranging from 15%, 20% and 25% for limestone powder with cement C1 and 20% and 25% of natural pozzolan with cement C2. The replacement rate of mineral admixture is calculated taking into account the quantity of the mineral admixture in the origin cement (C1 and C2).The binder was mixed with water for various W/C ratio; 0.35, 0.4 and 0.45. Several dosages of each superplasticizer were used in the range of 0.4%, 0.6%, 0.8%, 1.0%,1.2%, 1.5% and 2.0 %Table 1Characteristics of materials used.Table 2Mix proportions for the pastes used in testing.2.3. Test proceduresThe pastes were made in Hobart type mixer with a capacity of 5 l, and using two different speeds (low and high). The procedure used in all test was as follows: a dry cement and mineral admixture were firstly mixed at low speed for 1 min, then 2/3 part of water was added and the paste was mixed for 2 more minutes at low speed; finally, 1/3 part of water and superplasticizer were added and the paste was mixed for 2 more minutes at high speed. To study the rheological behavior of cement with the presence of superplasticizer, cone Marsh test which consists in measuring flow time of a cement grout was used1113. This equipment illustrated in Fig. 1, was used for a long time by oil industry to measure the fluidity of bentonite or cement grouts. For this purpose, this test is adopted to measure the flow time and study therheological properties of cement grouts. The test consists in measuring time that it is necessary to empty a bowl by 1 l of cement paste through an opening of evacuation 5 mm in diameter. This time is 31.5 s for water. The flow time measured enables to evaluate the fluidity of the grout; the longer this time is, the more the grout is viscous and the shorter it is, the more the grout is fluid. The flow time was measured at 5 and 60 min after the contact with water. The saturation dosage is defined as the dosage of superplasticizer beyond which the fluidity of the paste at 5 min does not increase. The difference between the flow time at 60 and 5 min expresses the fluidity loss of the paste.3. ResultsThe results of various cement paste obtained by the combination of the two types of cements with and without adding mineral admixture and the two types of superplasticizer show a clear improvement of the fluidity according to the superplasticizer dosage and the W/C ratio.3.1. Cement type effectBy using the two cements C1 and C2 to make a cement paste with W/C ratio of 0.4 and containing various dosages of superplasticizer SP1 and SP2, the results obtained for the flow time at 5 min and the fluidity loss are illustrated inFigs. 2 and 3. It is to be noted that C1 cement has a better fluidity and low saturation dosage of about 0.8% compared with 1% for that of C2 cement when using SP1. Moreover, C1 cement generates a loss of fluidity less important than that of C2 cement. The later presents an incompatibility with this superplasticizer (SP1) where the flow time at 60 min is largely higher than that at 5 min and remains independent of the superplasticizer dosage with a little effect when it exceeds 1.2%.As shown inFig. 2, C1 cement with limestone powder provides a very fluid mixture with superplasticizer SP1 based on PNS. For W/C ratio of 0.4, the flow time reaches a minimal value of 69 s corresponding to only 0.8% of SP1. Contrary to superplasticizer SP2 based on PRM, the fluidity is deteriorated even for strong dosage and remains higher than 93 s. C2 cement containing natural pozzolan has an opposite behavior compared to C1 cement where its fluidity has a high efficiency with SP2 superplasticizer. This proves that the type of cement has a great control in the superplasticizer adsorption that leads to a judicious choice of the most effective couple CSP to get a concrete with high workability.Fig. 3illustrates the difference between the flow times relative to 5 and 60 min with respect to superplasticizer dosage. This fluidity loss disappears with the increase of superplasticizer dosage especially for C1 cement which has a constant fluidity loss beyond 1.5% for SP2 superplasticizer and slightly less significant for SP1. Similar behavior was observed for C2 cement, where the fluidity loss decreases with the increase of SP2 dosage but remains higher for SP1. Cement with limestone powder (C1) exhibits a less fluidity loss which remains low for moderate dosages of both superplasticizers. On the other hand, cement with natural pozzolan (C2) requires a superplasticizer based on PRM (SP2) or a great dosage of SP1 to preserve its constant fluidity.3.2. Saturation dosageFrom the curves illustrating the variation of flow time according to the dosage of the superplasticizer, the saturation dosage was determined for all couples of cementsuperplasticizer and is presented inTable 3. It can be concluded that the saturation dosage of superplasticizer decreases according to the watercement ratio. Superplasticizer SP2 presents a very good compatibility with the two types of cement, contrary to SP1, which presents an almost total incompatibility. Limestone powder addition with C1 cement contributes to minimize some incompatibility cases with SP1, particularly for a replacement rate higher than 15%. The addition of limestone powder or natural pozzolan to the two types of cement has less sensibility on the saturation dosage with a little increase.3.3. Superplasticizer type effectThe choice of the superplasticizer type has a great importance to obtain the most stable fluidity of the paste. By using two superplasticizers; SP1 and SP2 with C1 cement made with W/C ratio of 0.4.Fig. 4shows that the saturation dosage varies from 0.8 to 1.2% for SP1 and SP2 respectively. Similarly, there was no loss of fluidity observed beyond the saturation dosage for SP2 which justifies its compatibility with this type of cement. On the other hand,the results illustrated in Fig. 5confirm that C2 cement has an acceptable compatibility with superplasticizer SP2 based on PRM,where the fluidity is slightly influenced by the dosage without significant loss beyond 1%. For superplasticizer SP1, the fluidity of the paste made with C2 cement is less important compared with that of C1 cement. It is to be noted that the fluidity obtained is reduced with the increase of the superplasticizer dosage. This indicates that high dosages of some superplasticizers may reduce the paste fluidity, confirming the negative effect of excessive superplasticizer content observed by several works15,16. In the same context,the fluidity loss is considerable for this superplasticizer which proves its incompatibility, particularly with C2 cement.3.4. W/C ratio effectThe cement paste fluidity is very affected by the amount of mixing water, for this reason the fluidity was tested for several W/C ratio. The results presented inTable 3show that superplasticizer SP1 remains incompatible for all W/C ratios, suggesting a notable loss of the fluidity after 1 h from the first contact with water. The fluidity of the mixture made with C1 cement and SP2 superplasticizer clearly improves at 5 min with the increase of W/C ratio as illustrated in Fig. 6. It is noted that for high W/C values, the flow time converges towards a unique value for various dosages of superplasticizer. Also,for a dosage higher than 0.8%, the flow time preserves nearly the same variation according to W/C ratio. From the results represented inFig. 7, the flow time of the mixture made with C2 cement and SP2 superplasticizer decreases with the increase of W/C ratio. When W/C ratio exceeds 0.4, the flow time values are close and remain constant for all superplasticizer dosages.Fig. 6 and 7show that the fluidity of the cement paste made with C1SP2 is more sensitive to the increase of the mixing water than that made with C2SP2, where the fluidity varies only for low W/C ratio.3.5. Mineral admixture effectWhen the replacement rate of the limestone powder increases from 10% to 15%, 20% and 25% in C1 cement, the fluidity of the paste keeps close values for all replacement rates and seems to be more influenced for low W/C ratio. On the other hand, the loss of fluidity appears much influenced by the content of limestone powder present in the cement. This loss increases remarkably for 15% replacement rate and low W/C ratio as it is illustrated in Fig. 8. Furthermore, the limestone powder has a benefic effect on the flow time and does not reveal any loss of fluidity for high W/C ratio.Fig. 9illustrates the effect of the presence of the natural pozzolan on the fluidity of C2 cement. When the replacement rate increases from 15% to 20% and 25%, the fluidity of the paste at 5 min remains constant with a little improvement particularly for low W/C ratio. For 0.35 W/C ratio, the addition of natural pozzolan leads to a considerable loss of fluidity.4. DiscussionThe fluidity of the cement paste is related to the cement hydration and chemical interactions in the cement paste system and can be affected by the combination of cement type and chemical admixture, mineral admixture or watercement ratio. This fluidity depends of the dispersing performances of superplasticizer which is proportional to its adsorption amount on the compound of the cement paste.5.References1 Prince W, Ladnef ME, Aitcin PC. Interaction between ettringite and a polynaphthalene sulfonate superplasticizer in a cementitious paste. Cem Concr Res 2002;32:7985.2 Jiang S, Kim BG, Aitcin PC. Importance of adequate soluble alkali content to ensure cementsuperplasticizer compatibility. Cem Concr Res 1999;29:718.3 Zingg A, Winnedfed F, Holzer L, Pakusch J, Becker S. Interaction of polycarboxylate-based superplasticizers wit