International Concrete Abstracts Portal

Imaging methods for the quantification of cracking in concrete structures caused by alkali-aggregate reaction (AAR) are being employed increasingly due to the development of advanced Non-destructive testing techniques. However, more efficient image interpretation methods need to be developed in order to extract accurate information. This research proposes the application of an enhanced method of texture analysis on concrete imagery using the signal processing technique of Haar’s Wavelet Transform in combination with first-order histogram and second-order Grey Level Co-occurrence Matrix (GLCM) statistical approaches. This wavelet multiscale texture analysis technique provides increased discrimination of deterioration features in concrete images. For the detection and classification of the cracks, an Artificial Neural Network (ANN) method was used; the resulting classifications were used to extract surface information, such as the length and width of the cracks, as well as the total damage. This method was applied on grey scale images of outdoor exposed concrete blocks exhibiting various levels of AAR damage. The resulting levels of damage quantified through the image analysis approach correlate well with damage parameters obtained through in-situ data of the blocks, such as expansion measurements, impact-echo velocities, as well as laboratory data, such as mixture proportions.

In this paper the results of an investigation into the frost salt scaling resistance of cement mortars bearing extra-fine slag (EFS) with Blaine fineness of 500 kg/m2 is reported. The water to cement ratio of the mortar specimens is kept as 0.45. EFS was used as a replacing material for both European CEM III /B blast furnace slag cement and CEM I normal portland cement. Within the framework of this study, the carbonation resistance and pore structure of the cement mortars are also studied. Carbonation resistance is measured by phenolphthalein method after accelerated carbonation test in 3% CO2 chamber. Pore structures of the samples are evaluated by means of mercury intrusion porosimetry. The microstructures of the samples are further characterized by environmental electron microscope. It appears that EFS replacement in CEM III /B and CEM I decreases the frost salt scaling durability of mortars.

Self compacting concrete (SCC) can be placed without any compaction, avoiding some health risks as well as environmental problems. The two essential properties of SCC are a high flowability and a high segregation resistance, obtained by the use of either a large amount of fine particles (P) or a viscosity modifying admixture and a superplasticizer. Already there is a lot of knowledge about composition and workability of SCC, however there are questions regarding long-term durability due to significant difference in the mix proportions of SCC in comparison to traditional concrete. The degradation mechanisms of cementitious materials are greatly influenced by the penetration ability of aggressive fluids, and there is an important relation between the ‘pore structure’ of solids, fluid transport properties and degradation. If the pore structure of SCC turns out to be different from traditional concrete, some changes in durability behaviour might be expected. An experimental program was set up to study the pore structure of self-compacting concrete. Mercury intrusion porosimetry (MIP) was used as a testing method. As MIP can use only small-size specimens, it is customary to study hardened cement paste specimens with similar W/C ratios and curing ages as in actual concrete. In this study tests were performed on samples of hardened cement paste of several ages in order to evaluate the relative influence of various parameters on both traditional and self compacting concrete mixtures.

Water is generally accepted to be one of the main factors affecting Alkali-Silica Reactions (ASR) in concrete. The water content in ASR affected structures is normally expressed as relative humidity (RH). However, the measurement of RH is notoriously very difficult and uncertain, particularly in the field. The degree of capillary saturation (DCS) may be a more suitable parameter to characterize the water content and the progress of damage on structures due to ASR. The relation between the RH in concrete and the DCS varies depending on several factors, where the water/binder-ratio is the most important one. For more than 100 Norwegian concrete structures the DCS has been determined on specimens cut from drilled concrete cores, according to a special procedure. The water content has been determined at depths in the range from about 100 to 400 mm from the surface, depth ranges where it is considered to be rather stable and uninfluenced by seasonal changes in the weather. The results show a good correlation between the presence of ASR in a concrete structure and the DCS. With only a few exceptions the degree of capillary saturation of the concretes with pronounced ASR is higher than 90 %. The extent of damages generally increases with increasing water content above this level.

This paper reports results of a study conducted to assess the effect of chloride concentration on initiation and propagation of reinforcement corrosion. Since it is expected that the tolerable chloride concentration will vary with the type of cement, the combined effect of cement type and the chloride concentration on reinforcement corrosion was evaluated. Concrete specimens were prepared with Type I, Type V, and silica fume blended cements and they were exposed to sodium chloride solutions with varying chloride concentration. Reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. After two years of exposure, the reinforcing steel bars were removed from the concrete specimens and they were examined for the extent of corrosion and the gravimetric weight loss was determined. The electrochemical and gravimetric weight loss measurements indicated a good correlation between the chloride concentration in the exposure solution and the corrosion activity. The time to initiation of reinforcement corrosion and its rate were influenced by the type of cement and the chloride concentration in the exposure solution. Least reinforcement corrosion was noted in the silica fume blended cement concrete specimens followed by Type I and Type V cement concrete specimens.