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Seven different polymer latexes, characterised by different resistance to alkaline hydrolysis, were used to produce polymer-modified cement mortars. The following polymers were tested : styrene-butadiene copolymer, vinyl acetate-vinyl versatate copolymer, vinyl acetate-vinyl versatates terpolymer, vinyl acetate-ethylene copolymer, vinyl acetate-vinyl propionate copolymer, vinyl acetate-dibutyl maleate copolymer and vinyl acetate homopolymer. Measurements of compressive strength, dynamic modulus of elasticity, water absorption and bond-strength to a concrete substrate were carried out on the polymer-modified mortars in comparison to a reference mixture without polymers. Infrared and XRD analytical techniques were used to investigate the alkaline hydrolysis of the polymers and cement hydration, respectively. The results indicate that polymers with higher resistance to hydrolysis performed better in terms of higher bond strength to the concrete substrate and lower water absorption of the corresponding mortars.

Recently comb-like macromolecules which have a graft chain made of polyethylene oxide are attracting attention as superplasticizers and put to practical use in the field of flowing and high strength concrete. Comparing ordinary AE water reducing agents, these admktures have a higher water reducing ratio, smaller change of slump with the time and less set retarding property. The properties of solid spheres dispersed in solvent is explained by the magnitude of the inter-particle potential energy. We discuss the total potential energy of alite stabii by adsorbed superplasticizer containing polyethylene oxide graft chains. The interparticle potential energy was mainly controlled by steric hindrance effect of adsorbed macromolecule and van der Waals interaction of .

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.

A consequence of drying shrinkage is intrinsic cracking due to some form of restraint. In thick sections of concrete, drying from the surface causes differential shrinkage and such internal restraint can be responsible for surface cracking because of the induced tensile stress. When thin drying concrete members are restrained externally, a time-dependent failure is likely unless drying shrinkage is minimised. Besides drying shrinkage, the potential for cracking depends on tensile creep and tensile strength or tensile strain capacity and such properties are not normally measured in the laboratory. The possible effects of chemical admixtures on the foregoing properties is also largely unknown. The current research is investigating the role of tensile creep in relieving the tensile stress induced by fully restraining the drying shrinkage of concrete with and without chemical and mineral admixtures. All the relevant properties contributing to the time-dependent strength are being measured using bobbin-shaped specimens previously developed for uniaxial creep determination. The present paper presents the findings for concretes with and without a plasticizer and a new shrinkage reducing admixture. While the plasticizer has little influence on properties, the shrinkage reducing admixture significantly lowers the strength, elastic modulus, free drying shrinkage and creep. When restrained from the age of seven days all the concretes failed between 4 and 13 days, the concrete with the shrinkage reducing admixture failing at the lowest stress but after the longest time.