【正文】 lers, this reduction is proportional to their replacement level and type. The investigation of cement–superplasticizer (C–SP) patibility can be realized by measuring flow time of grout as proposed by several researchers[11–13]. The cement paste fluidity results usually are represented by a curve indicating the flow time C–SP 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 cement–superplasticizer studied and are expressed as follows: Saturation superplasticizer dosage corresponding to a break in the curve when superplasticizer is added over the saturation point。 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。 the first one is provided from Chlef cement factory (Algeria) CEM II , named C1 and containing 10% of limestone powder. The second one is provided from Zahana cement factory (Algeria) CEM II , named C2 and containing 15% of natural pozzolan. The physicochemical 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。 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 patibility with these superplasticizers, two types of minerals admixtures were used。 , and . Several dosages of each superplasticizer were used in the range of %, %, %, %,%, % and % Table 1 Characteristics of materials used . Table 2 Mix proportions for the pastes used in testing. . Test procedures The 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。 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. Results The results of various cement paste obtained by the bination 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. . Cement type effect By using the two cements C1 and C2 to make a cement paste with W/C ratio of 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 % pared 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 inpatibility 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 %. 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 , the flow time reaches a minimal value of 69 s corresponding to only % 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 pared 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 C–SP 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 % 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. . Saturation dosage From the curves illustrating the variation of flow time according to the dosage of the superplasticizer, the saturation dosage was determined for all couples of cement–superplasticizer and is presented inTable 3. It can be concluded that the saturation dosage of superplasticizer decreases according to the water–cement ratio. Superplasticizer SP2 presents a very good patibility with the two types of cement, contrary to SP1, which presents an almost total inpatibility. Limestone powder addition with C1 cement contributes to minimize some inpatibility 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 lit