International Concrete Abstracts Portal

This research aims to investigate the pore structures of fly ash concrete and the relation between porosity and compressive strength, and accordingly to establish a strength prediction model. In the study, three water-to-binder ratios (0.35, 0.50, 0.70) and three substitution ratios of cement with fly ash (10%, 20%, 30%) were selected for preparing concrete specimens. These specimens were tested at six ages from 1 day to 91 days for compressive strength and MIP porosity measurement. Test results show that the fly ash concrete consisted of more micro-pores that were larger than 0.05µm at an early age (7 day),but this portion of micro-pores evidently decreased after 28days. It was also found that the capillary pore volume had the closest relation with the strength of fly ash concrete, and the correlation coefficient reaches to 0.954. To establish the strength prediction model, a prediction equation of capillary porosity in fly ash concrete was firstly developed. The proposed prediction model is shown as the following: f'c=a·ln(W/B)+b·ln(R)+c·ln(age)+d·ln(Vc)+e. The calculated results show that the proposed model compared favorably with the other prediction model.

Concrete-polymer materials that include polymer-impregnated concrete (PIC), polymer concrete (PC) and polymer-modified concrete (PMC), have been developed within the past 50 years. PIC, which started out with great promise, has essentially disappeared from the scene. PC has been widely used for repairs, floor and bridge overlays, and precast components, but has not achieved the volume of use that had been projected. PMC has been widely used for overlays and repairs, including spray-on applications. There are many potential applications for the future related to materials processing and applications, which will ensure these materials will continue to be important in the construction field.

The influence of fly ash, ground granulated blast furnace slag, and condensed silica fume on rheological properties of mortars with different cements and different new generation superplasticizers are presented and discussed. Rheological properties of these mortars were studied using Two-point workability test and these mortars can be considered as a model of concrete. The addition of mineral admixtures significantly influences rheological properties of mortars and the nature and range of this influence depend not only on the type, properties and content of mineral admixture but also on the properties of the cement and superplasticizer and interaction of these. The basic influence trends of mineral admixtures on rheology of mortars with polycarboxylate and polyeter superplasticizers are presented. It is concluded that the compatibility of cement and superplasticizer system should be selected taking into account presence and estimated dosage of given mineral admixture. The combined influence of given cement - mineral admixture - superplasticizer system on rheology of fresh concrete should be verified by means of experimentation. Two-point workability test made on mortars enables both selection of optimal cement - mineral admixture - superplasticizer system and collection of data for fresh concrete workability control.

Alkali-activated slag concretes (AASC) are relatively well-known composites. For practical application various different problems must be solved. For example, they are the optimum content of alkaline activator and its nature; the composition of the activator for optimum setting and hardening time; the design of concrete for good workability, for the reaching of the smallest volume exchanges, and for maximum strength and for high durability. These problems are discussed in the present paper. Water glass and/or natrium hydroxide were chosen as the best type of activator and the optimum ratio Na2O and SiO2 were found. Calorimetry, MAS NMR (27Al and 29Si), SEM and other methods were used for the characterisation of the mixes. The concrete mixes are designed as self compacting for easier introduction of these materials into practice. Strengths, volume changes and their time development were measured during the aging of the mixes. Some elements will be produced from the concretes in 2005 and 2006 (elements for cable pipe-lines).

The purpose of the research program was to investigate how the addition of new-generation wastes produced in the coal-fired power plant, fluidized-bed type installations, impact mechanical properties and chemical durability of cements. Tests were made on cements derived from two portland cement clinkers containing widely different amounts of C3A. With addition of the fluidized-bed material from the brown and black coal combustion systems blended portland cements were made. The properties of these blended cements were compared with those of the reference portland cements. The composition of all cements was adjusted to achieve the maximum permissible amount of SO3 i. e. 3.5%. Three different curing procedures were used for mortar specimens: normal temperature and humidity conditions, low pressure steam curing, and autoclaving. Durability to sulfate attack was studied using two methods: one method involved monitoring of linear dimensions of 20 x 20 x 160 mm mortar prisms cured under different conditions and exposed to aqueous solutions of Na2SO4 and MgSO4, with 16±0.5 g/l concentration of SO42- anions. The other method involved investigation of changes of mechanical properties of 25x25x100 mm mortar prisms cured under different conditions and subjected to prolonged sulfate exposure. The strength of samples was measured after different times of exposure in sulfate. Five percent aqueous solutions of Na2SO4 and MgSO4 were used for sulfate immersion test. Compressive and flexural strength tests were measured after 90, 180, 365, and 730 days of exposure. SEM and EDS techniques were used for microstructure studies.