International Concrete Abstracts Portal

Electrochemical chloride removal was applied to a concrete test area of about 36 m 2 in a reinforced concrete hall which had been used for more than 10 years as a depot for deicing salt, in an attempt to extract the chloride that had penetrated into it. Since the salt had been stored loosely and the interior of the hall was frequently exposed to outside air, the concrete was heavily contaminated by chloride (up to about 15 percent Cl - in cement). Chloride removal was performed with an average current density of 1 A/m 2 for a period of 132 days. The studies were aimed at determining the changes in total chloride content and the Cl - and OH - concentrations of the pore solution at varying concrete depths. It was shown that the efficiency of chloride removal decreased in the concrete cover with increasing depth and that it was least efficient near the reinforcement. The factor that was identified as being responsible for this was the change in OH - concentration of the pore solution that had been caused by reactions at the electrodes. The OH - concentration of the pore solution decreased in the area close to the surface during treatment, while it rose dramatically around the reinforcement (up to approximately 2.5 mol OH -/L). This resulted in an increase of the Chloride Transference Number and, thus, the efficiency of chloride removal close to the concrete surface, as well as a drastic decrease close to the reinforcement. Hence, a reduction of the Cl - to "harmless" levels was not possible in this particular case. However, practice has shown that in many cases such a reduction can be achieved as chloride contamination is normally much less severe; thus, most of the chloride can be extracted from the reinforcement area before the rising Cl -concentration of the pore solution has diminished the efficiency of chloride removal. If, however, chloride has penetrated beyond the reinforcement, it can be removed to a limited extent only.

Pier B in the port of Halifax, NS, Canada, was built in 1930-32 using 18,000 tons of calcium aluminate cement (CAC, Ciment Fondu), sea-dredged sand and aggregates and mixing water pumped from an inland freshwater lake. The climatic conditions at Halifax are extremely severe; it is estimated that exposed concrete is subjected to about 100 freezing and thawing cycles per year. Pier B is over sixty years old and in regular service as a container terminal for ocean-going ships. The main structure is permanently submerged in sea water. A protective layer of facing concrete made of both CAC and normal portland cement, cast over the outside faces in the tidal zone, has needed periodic repair. The CAC concrete displays excellent durability with cylinder compressive strengths of 29 to 49 MPa, modulus of elasticity of about 30 GPa, and a Poisson's ratio typical of normal weight concrete. Records indicate that the CAC concrete was cast with a water-cement ratio of 0.5 to 0.6 and a cement content of about 330 kg/m 3. Volume porosity is of the order of 10 percent. The investigation reported here of cores taken from Pier B in 1993 provides a broad characterization and guide for more detailed examinations in a collaborative program, the results of which will be reported as they become available. A particular focus of interest will be the speculative existence of zones of enhanced impermeability on the exposed faces of the concrete, an effect which has been observed in other old CAC structures.

To improve durability, it is necessary to find remedial solutions to counteract the embrittlement process of natural fiber reinforced composite materials. One solution to alleviate fiber degradation is to reduce the alkalinity of the pore fluid in the cement paste. This can be achieved by replacing a part of the normal portland cement with a highly reactive pozzolanic material. The purpose of this research study was to investigate experimentally the mechanical behavior of sisal pulp-mortar composites containing cement blended with a modified rice husk ash (MRHA). The main variable was the pulp volume fraction. The results of sisal pulp-mortar composites were compared to those using bamboo and pine pulps. The water-cementitious and sand cementitious ratios by weight were kept constant. The dosage of superplasticizer was fixed. The tests on the composites included strengths under direct tension, axial compression, anticlastic, and bending. The material performance tests were conducted for moisture content, water absorption, expansion, drying shrinkage, and impact resistance. he durability of the composites was investigated by simulating aging cycles. The results showed that after being subjected to 48 simulated aging cycles, the sisal pulp- mortar containing five percent pulp volume fraction showed the highest modulus of toughness. Other tests showed that pulp-mortar composites were impervious, durable, possessed high strength and good impact resistance and, therefore, can be considered as suitable substitutes for asbestos-fiber board.

Reports the results of an investigation of the effect of using ground granulated blast furnace slag to prevent alkali-aggregate reaction damage to concrete. The authors discuss the effectiveness of the blast furnace slag on the dilution, stabilization, and fixation of alkali. The relationship between the replacement ratio of blast furnace slag and prevention of the expansion due to the alkali-aggregate reaction in concrete is reported.

Disintegration of many concrete pavements (D-cracking, popouts, etc.) exposed to freezing and thawing is often connected with poor physical quality of aggregates used in the concrete. Inability to differentiate between good and poor quality aggregates is due to the lack of appropriate laboratory techniques for aggregate evaluation. A growing shortage of easily available sources of good quality aggregates highlights the need for aggregate classification. A new rapid laboratory test, called RAO-Method, as well as a new pore size distribution index based on the mercury intrusion porosimetry (MIP) analysis, has been proposed to meet engineers' expectations in the field of aggregate classification. An analysis of some research data of the RAO and MIP tests is presented in this paper to illustrate practical usefulness of the techniques. Results of long-term observations of concrete blocks subjected to outdoor conditions and the results of the new laboratory tests of the aggregates previously used in the blocks were compared. The new tests seem to provide means for more successful evaluation of coarse aggregates for purposes of diagnostics, design, and prediction of service life of concrete.