International Concrete Abstracts Portal

A model to explain the compressive strength of high-performance concrete was developed using multiple linear regression correlating the compressive strength and variables representing volume ratios of paste materials. The data used to develop and validate the model came from a wide range of binary and ternary silica fume, rice husk ash and fly ash concretes that were made by Isaia with the same set of materials. In such tests, the water-cementitious materials ratio by mass varied from about 0,30 to about 0,50, with rates of cement replacement by pozzolan by mass from 0 to 50 %. The 3, 7, 28, and 91 days compressive strengths of 39 different concrete mixtures were measured. High correlation indices were found in most of studied regressions and the accuracy of the predicted values of compressive strength can be considered very good, specially when obtained from a set of concretes made with the addition of just one kind of pozzolan. In this case, the mean difference the addition of just one kind of pozzolan. In this case, the mean difference between the experimental and the predicted values were 0.4 MPa at the age of 28 days.

Chloride ions penetration can be an important cause of concrete reinforcement depassivation and corrosion, especially in marine environment structures. The influence of ground granulated blast furnace slag replacement in portland cements on chloride ions penetration in cover concrete was investigated. Concretes with W/C of 0.42 and three different Portland cements, containing O%, 27% and 53% of blast furnace slag replacement by mass, were manufactured. The influence of two curing conditions on chloride ions absorption was also investigated: immersion inwater (25OC) for 7 days and steam curing (6O’C) for 2 hours. Concrete samples were submitted to 8 wetting-drying cycles in 5% NaCl solution. Water-soluble chloride ions concentration was monitored in all the 8 cycles, in the cover depth from 0 to 40mm. Concretes produced with slag cements have shown the lowest chloride ions content in both curing methods investigated. Considering 0.4% by cement mass as a maximum value of chloride ion content to prevent reinforcement depassivation, it was observed that blast furnace slag cement concretes have shown results under this limit from the depth of 1Omm when wet-cured and from the depth of 20mm when steam cured.

The application of deterministic models based only on Fick's Laws can show considerable differences compared to the effective chloride profiles in existing marine structures. An important factor to be taken into consideration is the influence of the concrete saturation degree (SD). In the research, a laboratory test method for the influence of the SD on chloride diffusion in hardened cement paste was developed. Test results were applied to an existing marine structure with 22 years old. Results indicate that the concrete SD has a great influence on chloride diffusion and requires further research. It also shows that the SD should be taken into account when estimating the service life of concrete structures and a model is proposed.

Recently the sewage treatment in Porto Alegre, a city with a population of about 1.5 million inhabitants, located in southern Brazil, has increased. With the enlargement of the sewage treatment systems, in the year 2001 about 50% of the city sewage will be treated, which is about 100 tonnes of sludge per day. Sludge resulting from sewage treatment plants creates huge disposal problems. The government and the environmental authorities have been worried about solving this question. Nowadays there is still a lack in definitions for the final disposal and use of these residues. The main problem of this material is its components, because among them there are pathogenic organisms and heavy metals. A joint research between Municipal Prefecture of Porto Alegre and Federal University of Rio Grande do Sul was developed to study the possibility of incineration of the material and the use of the ash in construction. An experimental research program is conducted to determine the engineering properties of the incinerator solid ash. It is necessary to conduct such an investigation in order to evaluate the feasibility of using this ash as a partial substitute for cement in concrete. The initial results indicate that the waste ash may replace 20% by weight of cement in a concrete for normal use.

This paper presents the result of the work performed by the Norwegian Defence Estates Agency on the development of a low cost ultra high performance concrete (UHPC) for protective structures. The aim has been to develop a high strength concrete, about 150 MPa, based on commonly available materials, with workability suitable for traditional construction practice, and produced at a reasonable cost. The documentation program includes studies of the hardened properties of the concrete, in addition to full scale production tests, full scale realistic impact tests and large-scale beam tests. It is verified that concrete with a 2%day compressive cube strength of 150 MPa, based on commonly available high quality materials, may be produced without any major modifications to standard production facilities or procedures. For practical application, the autogenous shrinkage of the concrete may be a critical property whenever the hardening concrete is subject to restraint. The penetration resistance of UHPC is significantly better than normal strength concrete. Increasing the concrete strength from 30 MPa to about 200 MPa the penetration depth will be reduced by a factor of approximately 2.5.