International Concrete Abstracts Portal

Good adhesion of a repair material to concrete is of vital importance in the application and performance of underwater concrete repair. This paper reviews techniques and results of bond strength test methods: compressive slant-shear test and tensile bond (load-point) test. The objective of this paper is to evaluate the effects of variation in water-to-binder ratio and silica fume and fly ash replacements on bond strength of underwater concrete repairs. The mixtures were proportioned with a Canadian Type 10 cement and two other binders, one with 10% silica fume, and secondly a ternary cement containing 6% silica fume and 20% Class F fly ash replacements. The water-to-binder ratios tested were 0.41 and 0.47. The mixtures were cast in water, on slabs placed in the bottom of forms, in blocks measuring 0.50 x 0.45 x 1 m with the free fall height in water 0.35 m. Cores were obtained from experimental blocks cast in water to evaluate bond strength test between old and new concretes by tensile load-point. The slant-shear adhesion was determined by casting cylinders above water with consolidation, and in water without consolidation. The samples were composed of old concrete cast in air (sawed and smooth surface) with new concrete above. The incorporation of 10% of silica fume, or 20% of fly ash and 6% of silica fume and the reductions of water-to-binder ratio from 0.47 to 0.41 resulted in significant increases in bond strength.

The paper presents the results of the chloride diffusivity of a wide spectrum of concretes with compressive strengths ranging from 30 - 120MPa having GGBS incorporation ranging from 0 - 85%. All these concretes were designed to have specific compressive strengths at the various percentages of replacement through an efficiency concept presented earlier. The chloride diffusivity of these concretes was assessed in accordance with the method suggested by ASTM C 1202 after 90 days of water curing. Tt was observed that a significant improvement in the chloride diffusivity could be achieved even in the lower strength concretes at the higher replacement levels. This clearly shows that it is not always necessary to have high strength to achieve the high chloride impermeability performance in concrete.

The effect of temperature on the acceleration of the pozzolanic reaction rate is well known. In the case of the pozzolanic reaction between MK and calcium hydroxide, the researches have been focused on the hydrated phases and mainly on their stability, taking into account the possible transformation from metastable phases (C2ASH8 and C4AH13) to cubic phase C3ASH6, with the corresponding risk on durability.This paper reports a study to evaluate the influence of temperature on the formation of hydrogarnet (C3ASH6) in metakaolin (MK)/lime matrices subjected to 60°C curing temperature. The MIS and lime were mixed in a ratio of 1 :l by weight, stored and cured at 60°C and up to 123 days of hydration time. The kinetics of the pozzolanic reaction, sequence of appearance of different reaction products, quantities and crystallinity of the hydrogarnet as well as other hydrated phases, has been investigated using thermal (TG and DTA) and diffraction (XRD) analysis. The results showed that under the conditions tested here the hydrogarnet is formed very quickly in the first hours of curing (after 30 hours of hydration). This phase coexists at the same time with C2Ash8 (gehlenite) and C4AH13. The formation and amount of the hydrogarnet was closely related to the calcium hydroxide content in mixtures. There was not any evidence that the hydrogarnet was formed from a transformation reaction, but it was a result of the reaction between MK and lime.

Amorphous silica with high whiteness decomposing the basic mineral olivine, solution of magnesium and ferrous salt washing and filtering or decanting. And (Mg s and surface can be produced by simply Fe)SiO2 in any acid. The result is a silica slurry that can be purified by Such silica has been produced by treating an olivine mineral residue, a by-product of nickel ore recovery, by hydrochloric acid. The free flowing silica residue, after drying at 105C, is proven to have pozzolanic activity (consumption of calcium hydroxide) by thermal analysis (DTA/TG) and by strength measurements of mortars where cement is replaced with silica. The reactivity and strength gain was comparable to conventional silica fume obtained from ferrosilicon plants. The abundant mineral olivine can be a valuable source of amorphous silica for concrete technology, while the waste product lye could be used as a CO2 free magnesium chloride source for magnesium metal production, after purification. The process could also use waste acids, from paper pulp industry.

Different non-aqueous solvents (NAS), such as ethylene glycol, 1,2-propylene glycol and glycerol, were tested in the study of the behavior of NAS/SiOz-rich pozzolans (rice husk ash, RHA, and silica fume, SF). Dissolved SiOa in NAS/pozzolan mixtures was evaluated by several procedures: a) electrical conductivity measurements of the suspension; b) weighing of non-dissolved matter in reflux conditions; and c) titration using barium hydroxide solution. The obtained results were compared to those obtained by the reference method (solubility in boiling KOH solution). A good correlation between data obtained in NAS and the reference method was observed.