International Concrete Abstracts Portal

The scope of this work is to quantify the synergic action of fly ash when mixed with other pozzolans, through the performance of microstructural and durability parameters of HPC. Eleven mixture proportions were tested with fly ash, rice husk ash and silica fume in binary and ternary mixtures, with cement substitution, in mass, from 10 to 50%. The following tests related to HPC durability were made: axial compression strength, elasticity modulus, shrinkage, total chloride content, Cl/OH ionic relationship, water penetration and accelerated carbonation. Some micro structural parameters were determined such as bound water, amount of C-S-H, remaining (C3S+C2S) and C-H. The results were calculated related tot the unitary mass of cement, compared to each other in compressive strength equality of 70 Mpa. Practically all the variables linked to the durability presented better performance in the ternary mixtures, than the arithmetic sums of the respective binary mixtures and this behavior is validated with micro structural evidence. It is suggested that the fly ash have a synergic action in ternary mixtures probably due to the higher dispersion of the cement grains, similar of plasticizing mixture action, resoling in additional nucleation sites and larger amounts of hydration products. A synergic action model of fly ash in ternary mixtures is provided.

The invention of superplasticizers is one of the most important breakthrough that has led to the development of high performance concrete. Superplasticizers can be used for three different purpose, namely (a) to increase workability without changing the mixture composition, (b) to reduce the amount of mixing water in order to reduce the water-cement ratio and then to increase strength and/or improve durability, and © to reduce both water and cement in order to reduce cost in addition to reducing creep, shrinkage and thermal strains caused by heat of cement hydration. Practical examples of these different ways of using superplasticizers are given by referring to the traditional superplasticizers (naphthalene- and melamine-based) and to the recent advances in this area (acrylic polymer-based admixtures). In particular the following topics are examined: composition of superplasticizers, mechanism of action (electrostatic repulsion and steric hindrance), influence of the cement composition (C3A, alkali, SO3) mode of addition of superplasticizer, slump loss, blending of superplasticizers.

The main objective of this paper is to propose a method to estimate the probability of failure of building concrete floor slabs using a probabilistic treatment of the most influencing geometrical, material or environmental variables. The estimation of probability of failure results through an stochastic simulation of the material degradation of the slab with time and the variation of the loads applied. Consequently, the progressive increase of the probability of failure is pictured. This value is the additional information for to decide the appropriate level for the reparation. The presented method treats as random variables these basic ones taking part in the carbonation process, chloride penetration and corrosion. Distribution of degradation, obtain the ultimate response oft the slab at any time and then compare it with the acting loads, which are at their turn obtained through an stochastic treatment. The employment of the first order reliability moment (FORM) is used to estimate the probability of failure either for a part or for the entire slab.

The needs concerning improvement in durability of existing and new bridges in Poland are briefly presented. The requirements to ensure a high durability of new bridge structures constructed on a new network of motorways are especially emphasized. Material possibilities to product high-performance concrete in Poland are presented. Application of high-performance concrete to construct bridge structures with the use of modern erection methods (e.g. incremental launching, cast-in-place canilever balance) is analyzed and exemplified in the light of technical and economical aspects. Especial attention is given to the development of the researches on high-performance concrete in Poland. Some chosen problems are presented in particular, namely: testing an technological problems, hydration and thermal effects and their influence on material properties, bond strength, strength test of structural members subjected to different type of loading. Design problems concerning structural applications of high-performance concrete are also listed requirements in existing design standards or codes is emphasized and a consequence of it for engineering practice is discussed. Concluding remarks summarizing research of high-performance concrete in Poland and its up-to-date and future potential structural applications are formulated.

The goal of this project was to develop self-levelling concrete at lower cost than traditional self-levelling concrete. The concrete of this study was only 20% more expansive than usual concrete utilized for building concrete. Laboratory and on-site data proved that this objective could be reached if the mixture contained: 260kg/m3 normal portland cement,-140kg/m3 powdered limestone,-10kg/m3 chemical admixture composed of a superplasticizer and a viscosity agent. The production of this concrete was followed for one year and the main engineering properties investigated. The 28-day strength was higher than 30MPa and the water-permeability was low, 10-12m/s. 8,000m3 of such concrete were placed within one year and suggested that self-levelling concrete could be an interesting solution to improve the productivity on-site and the quality of buildings.