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SP173 In October 1997, the Council for the Orginazation of CANMET/ACI Conferences in association with American Concrete Institute and several cement and concrete organizations in Italy sponsored the fifth conference on the subject in Rome, Italy. This conference was aimed at transferring technology in the fastmoving field of chemical admixtures. A total of more than 60 papers from more than 20 countries were received and reviewed by the ACI review panel and 49 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI special publication SP-173.

Acrylic polymer (AP) performs better than other superplasticizers based on sulfonated-naphthalene-formaldehyde (SNF), sulfonated-melamine formaldehyde (SMF) or modified lignosulfonate (MIS). It is better than the other super-plasticizers in terms of higher initial slump, at equal water-cement ratio (WC), and lower rate of slump loss. AP, however, is a little more expensive than SMF and much more expensive than either NSF or MLS. Therefore, blending of AP with the other polymers could reduce the cost. The purpose of the present work was to study the influence of binary blended admixture (AP on one hand, and SNF, MSF or MLS on the other one) on the performance of superplasticized concretes in terms of slump, slump loss, specific gravity, air content and compressive strength at equal w/c. The data presented in this paper indicates that there is no practical advantage in blending AP with NSF or MSF. Moreover the combination of AP with NSF seems to be unreliable because produces an erratic reduction in the workability of the concrete mixture when about 75% of AP is replaced by NSF. On the other hand, a combination of AP with MLS appears to perform as well as the pure acrylic polymer in terms of workability, slump loss, air content and strength development, provided that the replacement of AP by MLS is not higher than 25%. Therefore, these blended AP-MLS super-plasticizers appear to be very interesting because they are cheaper than the pure acrylic polymer at approximately equal performance.

The ability of tricalcium aluminate hydration products to absorb polynaphthalene sulfonates (PNS) has been studied by reacting a small excess of saturated lime solution, containing various amounts of PNS, with an aqueous solution of sodium aluminate. Using X-ray diffraction, infrared spectroscopy and transmission electron microscopy, it is shown that well defined organomineral intercalation compounds result from the reaction. They can be described as layered double hydroxides where part of the hydroxyl groups have been replaced by the PNS anions. The consequences of the formation of such compounds upon the rheological characteristics in the early hydration period of portland cement is discussed. Emphasis is laid on the fact that the absorptive behavior of calcium aluminate hydrates in the presence of superplasticizers is not at the origin of the occasionally observed abnormal early stiffening. This point is illustrated by the investigation of cases of practical interest, based in particular on the analysis of the pore fluid composition in fresh mortars and pastes.

Calcium nitrate (CN) has been increasingly used as a chloride free set accelerator in later years. Mature cement pastes and concrete have been subjected to microstructure investigations in order to identify possible long term changes when a high dosage of CN was added to the fresh mixes. The following changes were found for 2 year old cement pastes (w/c = 0.50) based on ordinary Portland cement (OPC) and sulphate resistant Portland cement (SRPC) when 5.26 % CN was added: 1) The degree of hydration was only marginally lower. 2) The amount of calcium hydroxide (CH) was significantly lowered (= 10 %) in the case of OPC and unaltered for SRPC. 3) The amount of chemically bound water in both pastes was increased. 4) The average length of the polysilicate anions in the amorphous CSH-gel was prolonged (17% for OPC and 5 % for SRPC). 5) The porosity of the OPC paste was increased (+7%) and inhomogeneously distributed, while it was decreased (-2%) for the SRPC paste. 6) The morphology of calcium hydroxide (CH) in the pastes was changed from being evenly distributed to be gathered in larger (~50um diameter) clusters. This phenomenon may be explained by restricted diffusion due to the high Ca2+ concentration supplied by CN. This latter effect was also observed for a plain concrete (w/c = 0.57) based on high strength Portland cement (HSPC) and 3.86 % CN.

When the historical buildings of the Republic of Venice were erected all the construction materials and the corresponding techniques were always carefully selected. Even at that time architects were aware of the importance of the durability of buildings in a very hostile environment such as that existing in Venice characterized by permanent humid air and capillary rise of salty water from the foundations. In particular cementitious materials were adopted in agreement with the empirical rules of the Romans’ experience and adapted for the particular Venetian environment. The present paper examines two specific cementitious materials which became very popular throughout the world: the stucco plaster and the terrazzo concrete. At the time of the Republic of Venice, chemical admixtures were not available. Therefore, masonry artisans and architects developed a special know-how to manufacture durable materials. This was based on the use of mineral admixtures and natural substances, the invention of innovative binders and the development of special application techniques. After the advent of portland cement and especially of chemical admixtures, modem stucco plaster and terrazzo concrete can be produced with different (not necessarily better) properties and at higher rates of productivity. The present paper examines the microstructural aspect, the composition, the performance, and the manufacturing process of the original and modem materials.