International Concrete Abstracts Portal

Original Reactive Powder Concrete (RPC) - in form of a superplasticized cement mixture with silica fume, steel fibers and ground fine quartz (150-400 pm) - was studied in comparison with a modified RPC where a graded natural aggregate (max size 8 mm) was used to replace the fine sand and/or part of the cementitious binder. Original and modified RPC were manufactured at a plastic-fluid consistency, cast by vibration and cured at three different conditions: a) room temperature; b) steam-curing at 90°C; c) high pressure steam-curing at 160°C. The addition of the graded aggregate does not reduce the compressive strength provided that the quality of the cement matrix, in terms of its water-cement ratio, is not changed. This result is in contrast with the model proposed to relate the high compressive strength level of RPC (200 MPa) to the absence of coarse aggregate. Both the original and modified RPC (with the coarse aggregate addition) perform better - in terms of higher strength and lower driying shrinkage or creep strain - when they are steam cured rather than cured at room temperature. This improvement was related to a more dense microstructure of the cement matrix, particularly in the RPC specimens steam cured at 16OOC.

The relationships among the amounts of adsorption admixtures to cement particles, the interactive force between cement particles and the zeta potential of cement particle and the fluidity of cement paste prepared at the W/C ratio of 0.3 with lignin sulfonic acid-based admixture (LS), aminobenzene sulfonic acid-based admixture (AS) or melamine sulfonic acid-based admixture (MS) was studied in this paper, aiming at obtaining the basic data for elucidating the effects of the characters of sulfonic acid-based organic admixtures on the fluidity of concrete. The amount of adsorption of the sulfonic acid-based admixture by cement particles are logarithmically related to the molecular weight of the admixtures. The lower the molecular weight, the more the amount adsorbed are. The zeta potential of cement particle in cement paste depends upon the content of sulfonate group in the admixture and the adsorption state of admixture. The interactive force between cement particles are linearly related to the fluidity of cement paste. The steric repulsive force considerably contributes to the dispersion of particles even in the addition of sulfonic acid-based admixture which has been considered so far to disperse the particles mainly by the electrostatic repulsive force. The steric repulsive force is related to the molecular weight of the sulfonic acid-based admixture except AS. The rate of contribution of electrostatic repulsive force to the total repulsive force accounting for the interactive force correlates with the content of sulfonate group in the admixture. The reason why the action of AS is different from those of the other admixtures is probably because the adsorption state of AS is different from those of the others.

The effectiveness of Ca(NO2 )2 and NaN02 as corrosion inhibitors has been confirmed. However, the behavior of NO2 - ion and its stability in the pore solution in concrete containing the inhibitors is a matter of concern for their effective use as a corrosion-inhibiting admixture. Furthermore, it may be important from the viewpoint of the corrosion of reinforcement in concretes contaminated with Cl- ion to examine the behavior of NO2 - ions in relation to Cl-ion concentration in the pore solution in concrete. In this study, the analyses of pore solutions expressed from NaCl containing-mortars with and without the inhibitors were carried out to elucidate effects of the inhibitors on the chloride binding capacity of mortars. Simultaneously, the corrosion rate of steel bars embedded in the mortars was monitored by measurements of the potential and polarization resistance. The N02 - ion concentrations in the pore solutions in NaCl-containing mortars treated with 1% Ca(N02 )2 by mass of cement were lower than those in the corresponding mortars with NaN02 . The addition of NaN02 raised the OH- ion concentration slightly, but the OH- ion concentration was somewhat reduced in the mortars with Ca(NO2 )2 . The combined addition of NaCl and NaNO2 on the other hand, greatly raised the OH- ion concentration. However, the Cl’ /NO2 - ratios in the pore solutions in mortars containing Ca(N02 )2 were slightly lower than in mortars containing NaNO2 because of the dissipation of greater amounts of Cl- ions from the pore solutions in the former than in the latter.

A new family of comb polymers has been developed that have been found to overcome many performance shortcomings typically exhibited by conventional high range water reducing agents, commonly referred to as superplasticizers. This paper discusses some theoretical considerations associated with comb polymer type super-plasticizers, and reports on several key performance advantages such as extended slump life without prolonged set time, minimal variation in slump and air performance as a function of cement brand, and linear dosage response in mortar flow tests.

Heat curing is the most common method used for accelerating the strength development in concrete. Accelerated curing finds large applications i in the precast industry for quick turnaround of forms and casting beds. The increase in the initial strengths is simply a result of increased rate of hydra-ion caused by higher temperature. However, later strengths are often lower than those of the same concrete ured at 20o C. The causes of the strength loss are of physical and chemical nature. The physical cause results in increased porosity and cracking because the concrete constituents have different thermal expansion, (air has the highest). The chemical causes are the differences in the hydration products, microstructure and degree of hydration. Generally, physical causes are the dominating factors for strength loss in heat cured concrete. Results of extensive laboratory and field tests are presented showing that equivalent compressive strengths at 18 hours are obtained with concrete containing the new generation super-plasticizers and heat cured concretes at 60° C. The 28 day strengths of concretes with admixtures are substantially higher. Thus, with the use of these new generation super-plasticizers it’s possible to overcome the negative effects of steam curing such as strength loss, permeability, shrinkage, creep and frost resistence.