International Concrete Abstracts Portal

Plain cement and silica fume cement paste and mortar specimens prepared using Type I cement, 8% silica fume, and potable and treated waters were tested for setting time and compressive strength. Pore solutions extracted from the mortar specimens were analyzed for alkalinity and chloride content. The results showed that the treated water tested in this study qualifies to be used in making concrete on the basis that the chemical composition of treated water and variations in the setting time and compressive strength were within the tolerable limits.

The influence of ground granulated blast-furnace (GGBF) slag on autogenous shrinkage in concrete with a water/cementitious material (w/cm) of 0.3 and 91-day strength in excess of 80 MPa was investigated under tropical conditions. Cement re-placement percentages of 30, 50, 65 and 80% by GGBF slag were examined as well as the finenesses of 4200, 6000 and 7900 cm2/g for the 65% replacement percentage. The GGBF slag increased significantly the cumulative autogenous shrinkage for all replacement percentages and fineness levels tested. The increased autogenous strain occurred within the first 14 days when hydration would have been dominated by the portland cement component, well before significant additional hydration or pore refinement would have been possible due to hydration of the GGBF slag component. This suggests that the driving force for autogenous shrinkage in GGBF slag concrete may differ fundamentally from that for portland cement and silica fume concrete. Possible mechanisms for the increased early autogenous shrinkage in GGBF slag concrete are discussed.

The utilization of waste waters from zeolite production, for the activation of mixtures containing high content of granulated blast-furnace slag with moderate amounts of portland cement clinker and gypsum, was examined. The evaluation of properties of the product, depending on the composition of the starting blend, showed that good compressive strength and satisfactory resistance to carbonation, sulfate attack and freezing and thawing cycling can be obtained with some compositions.

The need to attain the correct assessment of industrial by-products and wastes re-quires an in-depth knowledge of their characteristics. One of the most important characteristics that affects in the aptitude of a thermally calcined product is the calcining conditions like temperature and stay in furnace. This is the aim of the current work which considers the importance of calcining conditions on the pozzolanic properties of a paper sludge as cementing material. The by-product used for this research is a Spanish paper sludge coming from a paper industry which uses 100% of recycled paper as raw materials. Due to the high content of organic material and calcium carbonate and, to the presence of different clayey minerals in sludge like kaolinite and talc, the calcining conditions play an important role on the mineralogy and pozzolanic activity of this sludge. For this reason, different intervals of temperature between 700 and 800°C and, different times of stay in furnace (2.5 and 5h) are studied in order to get the best pozzolanic properties for the paper sludge. The reaction kinetics of pozzolanic reaction cured at 40°C varied with the calcining conditions. The main crystalline phases identified by XRD were hydrocalumite (Ca4Al2O6C121OH2O) and calcium aluminium carbonate hydrate (Ca4Al2O6CO311H2O), stratlingite and hydrogamet.

The rate of chloride ingress in concrete not only depends on the intrinsic proper-ties of concrete but also on the magnitude of applied stresses and the nature of micro-crack propagation under these stresses. Limited information is available on the influence of these factors on the chloride ion penetration into concrete. The significance of applied stresses and the corresponding microcracking behaviour on the transport properties of concrete could provide useful information on the service life prediction of the concrete structure. To date, studies on the chloride ion transport into concrete are primarily based on concrete specimens that are not subjected to any stresses, particularly under sustained uniaxial compression. In the present study, the characteristics of microcracking and chloride diffusion into Grade 20 and 40 concretes are being investigated jointly by UNSW and CSIRO. The concrete specimens were loaded uniaxially in compression and sustained for a maximum duration of 18 months. Chloride ion penetration and micro-crack evaluation of these specimens were monitored periodically. This paper presents some early results on the apparent chloride diffusion coefficient obtained from Grade 20 and 40 concrete specimens that have been subjected simultaneously to sustained compressive stresses and 3% NaCl solution immersion for 90 days. Three levels of sustained compressive stresses at 20%, 35% and 50% of the ultimate strength were investigated. In addition, microcrack evaluation of the companion specimens (subjected to the same stress levels for 90 days) was also carried out. Microscopy technique was used to deter-mine the bond crack length in the concrete after the 90-day sustained period. At 35% sustained stress level, microcracks appear to be stable. However, the apparent chloride diffusion coefficient (Da) was found to decrease when compared with the unloaded control specimen. At 50% sustained stress level, a further reduction in D. was observed even though microcracks appear to have propagated.