International Concrete Abstracts Portal

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.

For high strength concrete, the use of superplasticizer and high cement leads to a very low W/C. In this concretes, part of cement used cannot complete its hydration due to the unavailable space to locate the reaction products. In this case, the addition of limestone filter can modify the packing of cement grains and it increases the hydration degree of portland clinker leading to the same strength level. In Europe, a vast experience has been developed with limestone blended cements. However, the use of limestone filler is a recent practice in South American countries. In this paper, the effect of a limestone filler in the production of high strength concrete was studied using 0, 9.3, and 18.1 percent of replacement by mass of clinker. Concretes were design to achieve 50 MPa compressive strength at 28 days (450 kg/m3 of cement content and a water-to-cementitious material ratio of .34). The mechanical properties, including compressive strength, split tensile strength and elasticity modulus were evaluated at 1,3,7,28 and 150 days. The results show that limestone filler increases concrete strength at very early ages due to enhance the clinker grains hydration. It did not affect significantly the mechanical strength of concrete containing 9.3 percent of replacement while for concretes with 18.1 percent of filler, a relative strength reduction was observed after seven days. At all ages, limestone filler replacement improves clinker efficiency but, it decreases with hydration progress.

An investigation was performed to study the estimation of modulus of elasticity at early and later ages, as a function of compressive strength and by the maturity approach. The study includes extensive laboratory work, where compressive strength and modulus of elasticity were measured at different ages for a high performance concrete mixture made with two different types of coarse aggregate, and cured at various curing temperatures. Comparison with provisions to estimate the modulus of elasticity given by ACI 318 and the CEB model code are presented, together with the application of the maturity approach to model the development of the modulus of elasticity. It is concluded that the compressive strength-modulus of elasticity relationships in the international codes may be used to estimate the elastic modulus at later ages if correction factors to account for the type of coarse aggregate are used. These relationships, however, were not able to estimate reliable results at earlier ages. The maturity approach was seen to better estimate the modulus of elasticity at early ages.